Update: 29-Dec-2016


Title:
Collisions in outer space produced an icosahedral phase in the Khatyrka meteorite never observed previously in the laboratory
Authors:
Bindi, L; Lin, C; Ma, C; Steinhardt, PJ Author Full Names: Bindi, Luca; Lin, Chaney; Ma, Chi; Steinhardt, Paul J.
Source:
Scientific Reports, 6 10.1038/srep38117 DEC 8 2016
Abstract:
We report the first occurrence of an icosahedral quasicrystal with composition Al-62.0(8) Cu-31.2(8) Fe-6.8(4), outside the measured equilibrium stability field at standard pressure of the previously reported Al-Cu-Fe quasicrystal (AlxCuyFez, with x between 61 and 64, y between 24 and 26, z between 12 and 13%). The new icosahedral mineral formed naturally and was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite that experienced shock metamorphism, local melting (with conditions exceeding 5 GPa and 1,200 degrees C in some locations), and rapid cooling, all of which likely resulted from impact-induced shock in space. This is the first example of a quasicrystal composition discovered in nature prior to being synthesized in the laboratory. The new composition was found in a grain that has a separate metal assemblage containing icosahedrite (Al63Cu24Fe13), currently the only other known naturally occurring mineral with icosahedral symmetry (though the latter composition had already been observed in the laboratory prior to its discovery in nature). The chemistry of both the icosahedral phases was characterized by electron microprobe, and the rotational symmetry was confirmed by means of electron backscatter diffraction.

Title:
Spin-lattice coupling mediated multiferroicity in (ND4)(2)FeCl5 center dot D2O
Authors:
Tian, W; Cao, H; Wang, J; Ye, F; Matsuda, M; Yan, JQ; Liu, Y; Garlea, VO; Agrawal, HK; Chakoumakos, BC; Sales, BC; Fishman, RS; Fernandez-Baca, JA Author Full Names: Tian, W.; Cao, Huibo; Wang, Jincheng; Ye, Feng; Matsuda, M.; Yan, J. -Q.; Liu, Yaohua; Garlea, V. O.; Agrawal, Harish K.; Chakoumakos, B. C.; Sales, B. C.; Fishman, Randy S.; Fernandez-Baca, J. A.
Source:
PHYSICAL REVIEW B, 94 (21):10.1103/PhysRevB.94.214405 DEC 7 2016
Abstract:
We report a neutron diffraction study of the multiferroic mechanism in (ND4)(2)FeCl5 center dot D2O, a molecular compound that exhibits magnetically induced ferroelectricity. This material exhibits two successive magnetic transitions on cooling: a long-range order transition to an incommensurate (IC) collinear sinusoidal spin state at T-N = 7.3 K, followed by a second transition to an IC cycloidal spin state at T-FE = 6.8 K, the latter of which is accompanied by spontaneous ferroelectric polarization. The cycloid structure is strongly distorted by spin-lattice coupling, as evidenced by the observations of both odd and even higher-order harmonics associated with the cycloid wave vector, and a weak commensurate phase that coexists with the IC phase. The second-order harmonic appears at TFE, thereby providing unambiguous evidence that the onset of the electric polarization is accompanied by a lattice modulation due to spin-lattice interaction. The neutron results, in conjunction with the negative thermal expansion and large magnetostriction observed in Ref. [19], indicate that spin-lattice coupling plays a critical role in the ferroelectric mechanism of (ND4)(2)FeCl5 center dot D2O.

Title:
Hofstadter butterfly of a quasicrystal
Authors:
Fuchs, JN; Vidal, J Author Full Names: Fuchs, Jean-Noel; Vidal, Julien
Source:
PHYSICAL REVIEW B, 94 (20):10.1103/PhysRevB.94.205437 NOV 28 2016
Abstract:
The energy spectrum of a tight-binding Hamiltonian is studied for the two-dimensional quasiperiodic Rauzy tiling in a perpendicular magnetic field. This spectrum known as a Hofstadter butterfly displays a very rich pattern of bulk gaps that are labeled by four integers, instead of two for periodic systems. The role of phason-flip disorder is also investigated in order to extract genuinely quasiperiodic properties. This geometric disorder is found to only preserve main quantum Hall gaps.

Title:
Magnetic field-temperature phase diagrams of multiferroic (Ni0.9Co0.1)(3)V2O8
Authors:
Qureshi, N; Ressouche, E; Mukhin, AA; Ivanov, VY; Barilo, SN; Shiryaev, SV; Skumryev, V Author Full Names: Qureshi, N.; Ressouche, E.; Mukhin, A. A.; Ivanov, V. Yu.; Barilo, S. N.; Shiryaev, S. V.; Skumryev, V.
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174441 NOV 28 2016
Abstract:
We present macroscopic and neutron diffraction data on multiferroic lightly Co doped Ni3V2O8. The magnetic H-T phase diagrams have been derived from magnetization and electric polarization measurements with field directions parallel to the principal crystallographic axes. While the phase diagram for H parallel to b is very similar to that of the parent compound Ni3V2O8 for the commonly involved phases, the zero-field phases in (Ni0.9Co0.1)(3)V2O8 show a stronger instability for applied magnetic fields along the a or c axis. Neutron single-crystal diffraction revealed the magnetic structure of the field-induced phase for H parallel to c with a collinear spin alignment along the a and b axes for the two magnetically inequivalent sites. A pronounced irreversibility has been observed for the transition between the zero-field spin cycloid and the field-induced phase, which is manifested in a propagation vector change from q = (0.322 0 0) to q = (0.306 0 0), with slight modifications of the magnetic structure after reentering the zero-field phase. The reentrant phase is characterized by a significantly larger b component of the cross-tie site spin, therefore showing remanent features of the high-field phase. For H parallel to a the magnetization data reveal anomalies, one of which was proved to reflect a field-induced transition from the cycloidally to the sinusoidally modulated magnetic structure.

Update: 21-Dec-2016


Title:
Enhancement of glass-forming ability and mechanical property of Zr-based Zr-Al-Ni bulk metallic glasses with addition of Pd
Authors:
Hua, NB; Chen, WZ Author Full Names: Hua, Nengbin; Chen, Wenzhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 693 816-824; 10.1016/j.jallcom.2016.09.263 FEB 5 2017
Abstract:
The effects of partial substitution of Ni by Pd in the high-Zr-based Zr65Al10Ni25-xPdx (at.%, x = 0, 5 and 10) alloys on their glass-forming ability (GFA), crystallization kinetics and mechanical property were investigated. The critical diameter for glass formation is increased from 3 mm for Zr65Al10Ni25 alloy to 5 mm for Zr65Al10Ni15Pd10. An icosahedral quasicrystal phase precipitates in the amorphous matrix in the first crystallization step of Zr-Al-Ni-Pd BMGs, implying that strong icosahedral short/medium-range order (IS/MRO) may exist in the Pd-containing alloys. In additional, Pd-bearing Zr-based BMGs present a lower Avrami exponent n indicating the higher stabilization of the supercooled liquid. Moreover, the Zr-Al-Ni-Pd BMGs exhibit larger compressive plasticity, higher notch toughness and Poisson's ratio than those of Zr65Al10Ni25 alloy, which can be correlated with the existence of strong IS/MRO clusters in amorphous phase. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Microstructure evolution and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy subjected to ultrasonic vibration
Authors:
Fang, XG; Wu, SS; Lu, SL; Wang, J; Yang, X Author Full Names: Fang, Xiaogang; Wu, Shusen; Lu, Shulin; Wang, Jing; Yang, Xiong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 679 372-378; 10.1016/j.msea.2016.10.035 JAN 2 2017
Abstract:
Although the icosahedral quasicrystal phase found in Mg-Zn-Y alloys has some outstanding characteristics, the coarse alpha-Mg dendrites and the agglomeration of the secondary phases in as-cast microstructure restrict the improvements in the mechanical properties. In this study, the semisolid slurry of Mg-6Zn-1.4Y alloy was obtained with ultrasonic vibration (UV) treatment and then formed by rheo-squeeze casting (RSC) process. The effects of UV on the microstructure evolution and mechanical properties were systematically investigated. With UV, primary a-Mg grains and the agglomerated Mg-Zn-Y compounds were significantly refined. Notably, a large mass of fine and granular quasicrystal I-phase particles precipitate in the grains at the later stage of solidification. The RSC alloy subjected to 6 W/mL UV exhibited the optimal mechanical properties, with the yield strength of 129 MPa, the ultimate tensile strength of 231 MPa and the elongation of 18.5%. Compared with the samples without UV, they are increased by 18.3%, 14.9% and 55.5%, respectively.

Title:
Intertwined nematic orders in a frustrated ferromagnet
Authors:
Iqbal, Y; Ghosh, P; Narayanan, R; Kumar, B; Reuther, J; Thomale, R Author Full Names: Iqbal, Yasir; Ghosh, Pratyay; Narayanan, Rajesh; Kumar, Brijesh; Reuther, Johannes; Thomale, Ronny
Source:
PHYSICAL REVIEW B, 94 (22):10.1103/PhysRevB.94.224403 DEC 2 2016
Abstract:
We investigate the quantum phases of the frustrated spin-1/2 J(1)-J(2)-J(3) Heisenberg model on the square lattice with ferromagnetic J(1) and antiferromagnetic J(2) and J(3) interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J(1)-J(2)-J(3) Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model.

Title:
Cation distribution in nanocrystalline (Co, Ni)Al2O4 Spinel
Authors:
Agarwal, H; Yadav, TP; Srivastava, ON; Shaz, MA Author Full Names: Agarwal, Harshit; Yadav, T. P.; Srivastava, O. N.; Shaz, M. A.
Source:
CERAMICS INTERNATIONAL, 42 (16):19429-19432; 10.1016/j.ceramint.2016.08.193 DEC 2016
Abstract:
In the present study, the cations Co2+/Ni2+ and Al3+ distribution in nanocrystalline (Co, Ni)Al2O4 spinel have been investigated using X-ray and transmission electron microscopy. The nanocrystalline (Co, Ni) Al2O4 spinet has been synthesized using mechanically activated Al70Co15Ni15 quasicrystalline precursor through annealing at 600 degrees C in controlled oxygen atmosphere. The mechanical activation of single phasic decagonal Al70Co15Ni15 quasicrystal was carried out in a high energy attritor ball mill for 40 h with 40:1 ball to powder ratio using toluene as a process control agent. The high resolution x-ray diffraction data has been refined by the Rietveld method using JANA2006 and subsequently, the corresponding structure has been constructed using Diamond4.0. The structure was also confirmed by analysis of transmission electron microscopy linearized diffraction pattern profile of D-values and corresponding plane. These analyses indicate that the cations Co2+ and Ni2+ distributed in the tetrahedral coordinated sites are the dominant species in the normal spinel phase. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Title:
Commensurate Superstructure of the {Cu(NO3)(H2O)}(HTae)(Bpy) Coordination Polymer: An Example of 2D Hydrogen-Bonding Networks as Magnetic Exchange Pathway
Authors:
de Luis, RF; Larrea, ES; Orive, J; Lezama, L; Arriortua, MI Author Full Names: Fernandez de Luis, Roberto; Larrea, Edurne S.; Orive, Joseba; Lezama, Luis; Arriortua, Maria I.
Source:
INORGANIC CHEMISTRY, 55 (22):11662-11675; 10.1021/acs.inorgchem.6b01199 NOV 21 2016
Abstract:
The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO3)(H2O)}(HTae)(Bpy) (H(2)Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4'-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a twodimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible structure transformation above 100 degrees C. Despite the loss of crystallinity, the spectroscopic studies indicate that the main building blocks of the crystal framework are retained after the transformation. The hydrogen-bonding network not only plays a crucial role stabilizing the crystal structure but also is an important pathway for magnetic exchange transmission. In fact, the magnetic susceptibility curves indicate that after the loss of coordinated water molecules, and hence the collapse of the hydrogen-bonding network, the weak anti-ferromagnetic coupling observed in the initial compound is broken. The electron paramagnetic resonance spectra are the consequence of the average signals from Cu(II) with different orientations, indicating that the magnetic coupling is effective between them. In fact, X- and Q-band data are reflecting different situations; the X-band spectra show the characteristics of an exchange g-tensor, while the Qband signals are coming from both the exchange and the molecular g-tensors.

Title:
The Moment Series Expansion for Quasicrystal with Phason Disorder
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, I.; Strzalka, R.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):833-835; 10.12693/APhysPolA.130.833 OCT 2016
Abstract:
The novel method for structural analysis of quasicrystals with phason flips is presented. The correction for diffraction peaks' intensities can be made within average unit cell approach by modification of the statistical distribution of atomic positions. Characteristic function of the distribution expanded into moment series, involving only even moments, estimates the envelope function and therefore the flip ratio can be evaluated.

Title:
Crystal Structure of the High Temperature Phase of Strontium Barium Niobate
Authors:
Paszkowski, R; Zubko, M; Wokulska, K; Kusz, J; Dec, J Author Full Names: Paszkowski, R.; Zubko, M.; Wokulska, K.; Kusz, J.; Dec, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):856-858; 10.12693/APhysPolA.130.856 OCT 2016
Abstract:
Pure and undoped strontium-barium niobate Sr0.40Ba0.60Nb2O6 (SBN40) single crystals grown by the Czochralski method were investigated by single crystal X-ray diffraction methods. The study below T-C (429 K for SBN40) confirmed the structure with P4bm space group. Above this temperature the structure transforms into the paraelectric, centrosymmetric one with P4/mbm space group. Analysis of the recorded diffraction patterns allowed to observe several signs of crystal structure modulation. On the registered diffraction images satellite reflections were found. A modulation vector q = (delta, +/-delta,), where delta = 0.3075(6) (at room temperature) was found and it was similar to that occurring in the SBN61. In addition, above the phase transition temperature on the (hk) planes with l integer a weak diffuse scattering was observed.

Title:
Solution and Refinement of Magnetic Structures with Jana2006
Authors:
Petricek, V; Henriques, MS; Dusek, M Author Full Names: Petricek, V.; Henriques, M. S.; Dusek, M.
Source:
ACTA PHYSICA POLONICA A, 130 (4):848-851; 10.12693/APhysPolA.130.848 OCT 2016
Abstract:
The program Jana2006 allows the solution and refinement of regular, twinned, modulated, and composite structures against different diffraction data sets. Recently a new option for solving and refining magnetic structures from powder and single crystal neutron diffraction data has been developed.

Title:
Fitting the Long-Range Order of a Decagonal Quasicrystal
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, M.; Kuczera, P.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):845-847; 10.12693/APhysPolA.130.845 OCT 2016
Abstract:
The generalized Penrose tiling is an infinite set of decagonal tilings. It is constructed with the same rhombs (thick and thin) as the conventional Penrose tiling, but its long-range order depends on the so-called shift parameter s is an element of < 0,1). The formula for structure factor, calculated within the average unit cell approach, works in physical space only and is directly dependent on the s parameter. It allows to straightforwardly change the long-range order of the refined structure just by changing the s parameter and keeping the tile decoration unchanged. The possibility and viability of using the shift as one of the refinement parameters during structure refinement was tested for a numerically generated simple binary decagonal quasicrystal.

Title:
Simple Decoration Model of Icosahedral Quasicrystals in Statistical Approach
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, R.; Buganski, I.; Wolny, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):841-844; 10.12693/APhysPolA.130.841 OCT 2016
Abstract:
The statistical approach based on the average unit cell concept was recently successfully applied to structural modelling of icosahedral quasicrystals. The structure factor for arbitrarily decorated icosahedral structure was derived for model Ammann tiling (3D Penrose tiling). It is a fully physical-space model where no higher-dimensional description is needed. In the present paper we show the application of the model to the so-called simple decoration scheme - atomic decoration in the nodes, at mid-edges and along body-diagonal of structural units of 3D Penrose tiling. By analyzing the obtained calculated diffraction patterns we show the correctness of the model and its applicability to binary and ternary icosahedral phases.

Title:
Phononic and Phasonic Debye-Waller Factors for 1D Quasicrystals
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, J.; Buganski, I.; Strzalka, R.
Source:
ACTA PHYSICA POLONICA A, 130 (4):836-840; 10.12693/APhysPolA.130.836 OCT 2016
Abstract:
The main purpose of crystallography is to solve and refine crystal structures based on measured diffraction data. One of important corrections crucial in the refinement process is the Debye-Waller factor correction for phonons in physical, and phasons in perpendicular space. In our paper we show the limitations of the standard approaches to the Debye-Waller correction in case of quasicrystals and propose new approach based on the statistical method. For the model 1D quasicrystal we show that in case of phonons there is no significant objection against classical (exponential) Debye-Waller factor, however using different forms can slightly improve the results of a refinement. In case of phasons the classical formula gives no rise to the efficiency of the refinement and completely new approach is required. We propose a redefinition of the Debye-Waller factor in terms of the statistical approach and show its effectiveness.

Title:
Precession Electron Diffraction Studies of SrxBa1-xNb2O6 and CaxBa1-xNb2O6 Single Crystals
Authors:
Wspaniala-Rak, J; Zubko, M; Stroz, D; Rak, J; Dec, J Author Full Names: Wspaniala-Rak, J.; Zubko, M.; Stroz, D.; Rak, J.; Dec, J.
Source:
ACTA PHYSICA POLONICA A, 130 (4):830-832; 10.12693/APhysPolA.130.830 OCT 2016
Abstract:
Crystal structures of two single crystals SrxBa1-xNb2O6 and CaxBa1-xNb2O6 have been reinvestigated using automated electron diffraction tomography method with beam precession. 3D reciprocal space has been reconstructed based on recorded tilt series. For both samples the crystal structure was refined and the tetragonal symmetry with space group P4bm was confirmed. The three dimensional reciprocal space allowed to observe and to study satellite reflections in both materials.

Title:
FOUR-DIMENSIONAL INCOMMENSURATELY MODULATED STRUCTURE OF THULIUM POLYPHOSPHATE
Authors:
Ma, FX; Zhao, D; Yang, H; Chen, PF; Yang, RJ; Wu, SX Author Full Names: Ma, Fa-Xue; Zhao, Dan; Yang, Hong; Chen, Peng-Fei; Yang, Rui-Juan; Wu, Shan-Xuan
Source:
JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 61 (2):3005-3008; JUN 2016
Abstract:
Single crystal of rare-earth polyphosphate Tm(PO3)(3) has been grown under high temperature molten-salt method and structurally characterized by single crystal X-ray diffraction analysis. Using the four-dimensional superspace formalism for aperiodic structures, we performed the crystal structure refinement of Tm(PO3)(3) as (3+ 1)-dimensional incommensurately modulated structure with monoclinic superspace group C2/c(0, 0.358,0)s0 and a = 14.0620 (12)angstrom, b = 6.6612 (6) angstrom, c = 10.0191 (9) angstrom, beta = 127.6043 (9)degrees, V = 743.51 (11) angstrom(3), Z = 4, M-r = 405.8, D-c = 3.626 g/cm(3), F(000) = 744, mu((MoKa)) = 12.60 mm(-1), R = 0.048 and omega R = 0.050. The structure features infinite chains of corner-sharing PO4 tetrahedra which are affected by positional modulation running along the b-axis. The final structure model was reasonable and did not show any unusual features.

Update: 14-Dec-2016


Title:
Soft-phonon-driven orbital order in CaMn7O12
Authors:
Souliou, SM; Li, Y; Du, X; Le Tacon, M; Bosak, A Author Full Names: Souliou, S. M.; Li, Y.; Du, X.; Le Tacon, M.; Bosak, A.
Source:
PHYSICAL REVIEW B, 94 (18):10.1103/PhysRevB.94.184309 NOV 22 2016
Abstract:
We use variable-temperature x-ray thermal diffuse scattering and inelastic scattering to investigate the lattice dynamics in single crystals of multiferroic CaMn7O12 which undergo a series of orbital and magnetic transitions at low temperatures. Upon approaching the charge and orbital ordering temperature T-o = 250 K from above, we observe intense diffuse scattering features and a pronounced optical phonon softening centered around the superstructure reflections of the incommensurately modulated structure. The phonon anomaly appears well above T-o and continuously increases upon cooling, following a canonical power-law temperature dependence that confirms the transition at T-o to be of second order and related to a soft-phonon lattice instability. Microscopic mechanisms for the incommensurate charge and orbital ordering based on competing interactions and on momentum-dependent electron-phonon coupling could both account for the observed extended momentum width of the phonon softening. Our results highlight the importance of the lattice interactions in the physics of this magnetically induced ferroelectric system.

Title:
High-Pressure Phase Transformations in TiPO4: A Route to Pentacoordinated Phosphorus
Authors:
Bykov, M; Bykova, E; Hanfland, M; Liermann, HP; Kremer, RK; Glaum, R; Dubrovinsky, L; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Hanfland, Michael; Liermann, Hanns-Peter; Kremer, Reinhard K.; Glaum, Robert; Dubrovinsky, Leonid; van Smaalen, Sander
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (48):15053-15057; 10.1002/anie.201608530 NOV 21 2016
Abstract:
Titanium(III) phosphate, TiPO4, is a typical example of an oxyphosphorus compound containing covalent P-O bonds. Single-crystal X-ray diffraction studies of TiPO4 reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high-pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO4-V is the first inorganic phosphorus-containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO4-V coexists with TiPO4-IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO4-II is found to be an incommensurately modulated phase whereas a lock-in transition at about 7 GPa leads to TiPO4-III with a fourfold superstructure compared to the structure of TiPO4-I at ambient conditions. TiPO4-II and TiPO4-III are similar to the corresponding low-temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin-Peierls interactions.

Title:
Influence of elastic strain gradient on the upper limit of flexocoupling strength, spatially modulated phases, and soft phonon dispersion in ferroics
Authors:
Morozovska, AN; Eliseev, EA; Scherbakov, CM; Vysochanskii, YM Author Full Names: Morozovska, Anna N.; Eliseev, Eugene A.; Scherbakov, Christian M.; Vysochanskii, Yulian M.
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174112 NOV 21 2016
Abstract:
Using the Landau-Ginzburg-Devonshire theory, we established the role of the flexoelectric coupling between the gradients of elastic strain and polarization in the stability of spatially modulated phases in ferroics, such as incipient and proper ferroelectrics with commensurate and incommensurate long-range-ordered phases. We included the square of elastic strain gradient in the Landau-Ginzburg-Devonshire functional because this term provides the functional stability for all values of the strain gradient. Analytical expressions for polarization, strain, dielectric susceptibility, and stability threshold were derived for a one-dimensional case. The expressions show that the maximal possible values of the static flexoelectric effect coefficients (upper limits) established by Yudin, Ahluwalia, and Tagantsev without the square of elastic strain gradient and other higher order gradients terms lose their direct meaning. Considering the gradients, the temperature dependent condition for the flexocoupling magnitude exists instead of the upper limits. Also, we established that spatially modulated phases appear and become stable in commensurate ferroelectrics if the flexocoupling constant exceeds a critical value. The critical value depends on the electrostriction and elastic constants, temperature, and gradient coefficients in the Landau-Ginzburg-Devonshire functional. We calculated soft phonon dispersion in commensurate and incommensurate long-range-ordered phases of ferroelectrics with the square of elastic strain gradient, static, and dynamic flexocoupling. It appeared that the dispersion of the optical mode is slightly sensitive to the flexocoupling, and the dispersion of acoustic mode strongly depends on the coupling magnitude. Obtained results demonstrate that nontrivial differences in the dispersion of optical and acoustic modes occur with the change of flexocoupling constant. Therefore, experimental determination of soft phonon dispersion might be very informative to study the influence of strain gradients and flexocoupling on the spatially modulated phase in ferroelectrics with commensurate and incommensurate long-range order.

Title:
MAGNDATA: towards a database of magnetic structures. I. The commensurate case
Authors:
Gallego, SV; Perez-Mato, JM; Elcoro, L; Tasci, ES; Hanson, RM; Momma, K; Aroyo, MI; Madariaga, G Author Full Names: Gallego, Samuel V.; Manuel Perez-Mato, J.; Elcoro, Luis; Tasci, Emre S.; Hanson, Robert M.; Momma, Koichi; Aroyo, Mois I.; Madariaga, Gotzon
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1750-1776; 10.1107/S1600576716012863 5 OCT 2016
Abstract:
A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been developed and is available at the Bilbao Crystallographic Server (http://www. cryst.ehu.es). It includes both commensurate and incommensurate structures. This first article is devoted to explaining the information available on commensurate magnetic structures. Each magnetic structure is described using magnetic symmetry, i.e. a magnetic space group (or Shubnikov group). This ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. A non-standard setting of the magnetic space group is often used in order to keep the origin and unit-cell orientation of the paramagnetic phase, but a description in any desired setting is possible. Domain-related equivalent structures can also be down-loaded. For each structure its magnetic point group is given, and the resulting constraints on any macroscopic tensor property of interest can be consulted. Any entry can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. An online visualization tool using Jmol is available, and the latest versions of VESTA and Jmol support the magCIF format, such that these programs can be used locally for visualization and analysis of any of the entries in the collection. The fact that magnetic structures are often reported without identifying their symmetry and/or with ambiguous information has in many cases forced a reinterpretation and transformation of the published data. Most of the structures in the collection possess a maximal magnetic symmetry within the constraints imposed by the magnetic propagation vector(s). When a lower symmetry is realized, it usually corresponds to an epikernel (isotropy subgroup) of one irreducible representation of the space group of the parent phase. Various examples of the structures present in this collection are discussed.

Title:
Temperature and cooling field dependent exchange coupling in [Cr/Gd](5) multilayers
Authors:
Jiao, ZW; Chen, HJ; Jiang, WD; Wang, JF; Yu, SJ; Hou, YL; Lu, B; Ye, QL Author Full Names: Jiao, Z. W.; Chen, H. J.; Jiang, W. D.; Wang, J. F.; Yu, S. J.; Hou, Y. L.; Lu, B.; Ye, Q. L.
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 213 (9):2531-2536; 10.1002/pssa.201600025 SEP 2016
Abstract:
Exchange coupling has been investigated in the [Cr/Gd](5) multilayers deposited at 25, 200, and 400 degrees C, where the Neel temperature (TN) of antiferromagnetic Cr is slightly higher than the Curie temperature (T-C) of ferromagnetic Gd. It was found that the exchange coupling existed not only at T-C < T < T-N, but also above the temperature (T-N) of antiferromagnetic orderings with incommensurate spin-density wave structures transiting to paramagnetic state. These results can be discussed in terms of the crucial role played by the antiferromagnetic spins of Cr with commensurate spin-density wave structures in the vicinity of the Cr/Gd interfaces. Moreover, the exchange coupling of the multilayers grown at different temperatures exhibited different dependencies on the measuring temperature and the cooling field, respectively. Positive exchange bias was observed in the multilayers grown at 200 and 400 degrees C. The interfacial roughness, grain size, and the antiferromagnetic orderings of Cr may be responsible for the anomalous exchange coupling of the multilayers. In addition, the competition between the exchange coupling at Cr/Gd interfaces and the external field-Cr surface magnetic coupling can explain the appearance of negative or positive exchange bias. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 8-Dec-2016


Title:
Self-assembly of two-dimensional binary quasicrystals: a possible route to a DNA quasicrystal
Authors:
Reinhardt, A; Schreck, JS; Romano, F; Doye, JPK Author Full Names: Reinhardt, Aleks; Schreck, John S.; Romano, Flavio; Doye, Jonathan P. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (1):10.1088/0953-8984/29/1/014006 JAN 11 2017
Abstract:
We use Monte Carlo simulations and free-energy techniques to show that binary solutions of penta-and hexavalent two-dimensional patchy particles can form thermodynamically stable quasicrystals even at very narrow patch widths, provided their patch interactions are chosen in an appropriate way. Such patchy particles can be thought of as a coarse-grained representation of DNA multi-arm 'star' motifs, which can be chosen to bond with one another very specifically by tuning the DNA sequences of the protruding arms. We explore several possible design strategies and conclude that DNA star tiles that are designed to interact with one another in a specific but not overly constrained way could potentially be used to construct soft quasicrystals in experiment. We verify that such star tiles can form stable dodecagonal motifs using oxDNA, a realistic coarse-grained model of DNA.

Title:
Electrochemical and kinetic properties of Ti41.5Zr41.5Ni17 quasicrystal and LiH composite materials
Authors:
Zhai, XJ; Wang, QS; Luo, TH; Zhao, Z; DongyanLiu; Xing, C; Shen, XD; Liu, WQ; LiminWang Author Full Names: Zhai, Xiaojie; Wang, Qingshuang; Luo, Tianhao; Zhao, Zhen; DongyanLiu; Xing, Cheng; Shen, Xiande; Liu, Wanqiang; LiminWang
Source:
MATERIALS RESEARCH BULLETIN, 85 196-201; 10.1016/j.materresbull.2016.09.021 JAN 2017
Abstract:
We report the effect of LiH on the discharge performance of electrodes which are consist of Ti41.5Zr41.5Ni17 quasicrystal in this paper. The Ti41.5Zr41.5Ni17 alloy ribbons are prepared by arc-melting and melt spinning technique subsequently. The final product of Ti41.5Zr41.5Ni17 and LiH composite materials is produced by mechanical alloying (MA) for 20 min, and it is investigated by a three-electrode cell at room temperature. The maximum discharge capacity can achieve 146.6 mAh/g around for Ti41.5Zr41.5Ni17 and LiH composite materials electrode at the first discharge process, which is higher than 96.5 mAh/g of Ti41.5Zr41.5Ni17 quasicrystal at the third discharge process. High-rate dischargeability and cycling stability are improved by adding LiH, which may attribute to the reversible reaction of LiH that enhances the electrochemical reaction activity in the process of electrochemical reaction. The discharge process is also characterized by electrochemical impedance spectroscopy. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Polarization curling and flux closures in multiferroic tunnel junctions
Authors:
Peters, JJP; Apachitei, G; Beanland, R; Alexe, M; Sanchez, AM Author Full Names: Peters, Jonathan J. P.; Apachitei, Geanina; Beanland, Richard; Alexe, Marin; Sanchez, Ana M.
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms13484 NOV 16 2016
Abstract:
Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La, Sr)MnO3 ferroelectric tunnel junctions, the polarization in active PbTiO3 layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient.

Title:
Semiclassical ground-state phase diagram and multi-Q phase of a spin-orbit-coupled model on triangular lattice
Authors:
Liu, CL; Yu, R; Wang, XQ Author Full Names: Liu, Changle; Yu, Rong; Wang, Xiaoqun
Source:
PHYSICAL REVIEW B, 94 (17):10.1103/PhysRevB.94.174424 NOV 15 2016
Abstract:
Motivated by recent experiments on the frustrated quantum magnetic compound YbMgGaO4, we study an effective spin model on triangular lattice taking into account the effects of the spin-orbit coupling. We determine the classical ground-state phase diagram of this model, which includes a 120 degrees Neel and two collinear antiferromagnetic phases. In the vicinity of the phase boundary between the Neel and collinear phases, we identify three intermediate noncollinear antiferromagnetic phases. In each of them the magnetic moments are ordered at multiple incommensurate wave vector Q values. We further study the effects of quantum fluctuations in this model via a linear spin-wave theory. We find that the spin excitation gap of the noncollinear multi-Q antiferromagnetic states is vanishingly small. We also find that multi-Q states are most fragile against quantum fluctuations, and hence most unstable toward spin liquid phases.

Title:
Effect of cooling rate and Mg addition on the structural evaluation of rapidly solidified Al-20wt%Cu-12wt%Fe alloy
Authors:
Karakose, E; Colak, H Author Full Names: Karakose, Ercan; Colak, Hakan
Source:
MATERIALS CHARACTERIZATION, 121 68-75; 10.1016/j.matchar.2016.09.030 NOV 2016
Abstract:
The present work examines the effect of Mg contents and cooling rate on the morphology and mechanical properties of Al20Cu12Fe quasicrystalline alloy. The microstructure of the alloys was analyzed by scanning electron microscopy and the phase composition was identified by X-ray diffractometry. The melting characteristics were studied by differential thermal analysis under an Ar atmosphere. The mechanical features of the melt-spun and conventionally solidified alloys were tested by tensile-strength test and Vickers micro-hardness test. It was found that the final microstructure of the Al20Cu12Fe samples mainly depends on the cooling rate and Mg contents, which suggests that different cooling rates and Mg contents produce different microstructures and properties. The average grain sizes of the melt spun samples were about 100-300 nm at 35 m/s. The nanosize, dispersed, different shaped quasicrystal particles possessed a remarkable effect to the mechanical characteristics of the rapidly solidified ribbons. The microhardness values of the melt spun samples were approximately 18% higher than those of the conventionally counterparts. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Magnetic structure and effect of magnetic field on its domain structure in magnetoelectric Ba1.3Sr0.7CoZnFe11AlO22
Authors:
Ueda, H; Tanaka, Y; Nakajima, H; Mori, S; Ohta, K; Haruki, K; Hirose, S; Wakabayashi, Y; Kimura, T Author Full Names: Ueda, H.; Tanaka, Y.; Nakajima, H.; Mori, S.; Ohta, K.; Haruki, K.; Hirose, S.; Wakabayashi, Y.; Kimura, T.
Source:
APPLIED PHYSICS LETTERS, 109 (18):10.1063/1.4966623 OCT 31 2016
Abstract:
The magnetic structure and the effect of a magnetic field on its domain structure were investigated in a magnetoelectric Y-type hexaferrite, Ba1.3Sr0.7CoZnFe11AlO22, by means of mapping with a micro-focused and circularly polarized X-ray beam in the resonant X-ray diffraction. It was revealed that this hexaferrite exhibits a magnetic order characterized by two distinct antiferromagnetic components: incommensurate helical and commensurate collinear ones, which can be explained as the development of the so-called alternating longitudinal conical structure. A multidomain state due to the handedness of the helical component, i.e., spin-chirality, is transformed into nearly a mono-domain one by using only a magnetic field. Furthermore, the sign of the spin-chirality in the mono-domain state is reversed by reversing the sign of a magnetic field. These results demonstrate that the spin-chirality in this hexaferrite can be manipulated by a magnetic field alone at room temperature. Published by AIP Publishing.

Title:
Structure and Electrical Conductivity of Ag-Doped TiZrNi Quasicrystals
Authors:
Lee, SH; Park, T; Yi, W; Kim, J Author Full Names: Lee, Sang-Hwa; Park, Taehee; Yi, Whikun; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 16 (10):10532-10534; 10.1166/jnn.2016.13189 OCT 2016
Abstract:
To investigate the structure and electrical conductivity of Ag-doped TiZrNi quasicrystals, alloys of (Ti53Zr27Ni20)(100) Ag-x(x) (where, x = 0, 4 and 8) were arc-melted and rapidly quenched in an Ar atmosphere. After optimum quenching, the results of the X-ray diffraction (XRD) measurements revealed that the samples have a pure quasicrystal structure. The quasicrystal structure remained to the maximum 8 at.% of Ag without a significant change in the quasi-lattice constant value, 5.12 angstrom. The specific electrical resistance values of the quasicrystals increased from 4.21 to 5.47x10(-4) Omega. cm with increasing Ag contents from 0 to 8 at.% whereas the coherence lengths decreased from 119 to 93 angstrom accordingly. It is interesting to note that the reduction in the electrical conductivity with the increase in Ag contents is mainly due to the structural incoherence factor, not the atomic conductivity of Ag.

Title:
Direct observation of incommensurate structure in Mo3Si
Authors:
Gulec, A; Yu, XX; Taylor, M; Perepezko, JH; Marks, L Author Full Names: Gulec, Ahmet; Yu, Xiaoxiang; Taylor, Matthew; Perepezko, John H.; Marks, Laurence
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 72 660-666; 10.1107/S2053273316012286 6 OCT 2016
Abstract:
Z-contrast imaging, electron diffraction, atom-probe tomography (APT) and density functional theory calculations were used to study the crystal structure of the Mo3Si phase which was previously reported to have an A15 crystal structure. The results showed that Mo3Si has an incommensurate crystal structure with a non-cubic unit cell. The small off-stoichiometry in composition of the sample which was revealed by APT and atomic resolution Z-contrast imaging suggested that site substitution caused the development of split atomic positions, disorder and vacancies.

Title:
Structure determination of modulated structures by powder X-ray diffraction and electron diffraction
Authors:
Zhou, ZY; Palatinus, L; Sun, JL Author Full Names: Zhou, Zhengyang; Palatinus, Lukas; Sun, Junliang
Source:
INORGANIC CHEMISTRY FRONTIERS, 3 (11):1351-1362; 10.1039/c6qi00219f 2016
Abstract:
Since the first discovery and description of materials, whose structures are not periodic, enormous efforts have been made in studying these aperiodic structures. With these efforts including the development of superspace group theory and structure solution algorithms, numerous incommensurately modulated structures which represent the vast majority of known aperiodic structures have been determined with single crystal X-ray diffraction data. However, the determination of modulated structures remains very difficult for polycrystalline materials. Powder X-ray diffraction and electron microscopy techniques yield remarkable information for polycrystalline materials. By combining these two methods, modulated structures of polycrystalline materials that impede solution by conventional methods can be determined. The power of these methods is illustrated with the examples of the determination of modulated structures of polycrystalline materials.

Update: 23-Nov-2016


Title:
Crystallographic Features and State Stability of the Decagonal Quasicrystal in the Al-Co-Cu Alloy System
Authors:
Nakayama, K; Mizutani, A; Koyama, Y Author Full Names: Nakayama, Kei; Mizutani, Akito; Koyama, Yasumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (11):10.7566/JPSJ.85.114602 NOV 15 2016
Abstract:
In the Al-Co-Cu alloy system, both the decagonal quasicrystal with the space group of P (10) over bar m2 and its approximant Al13Co4 phase with monoclinic Cm symmetry are present around 20 at. % Co-10 at. % Cu. In this study, we examined the crystallographic features of prepared Al-(30 - x) at. % Co-x at. % Cu samples mainly by transmission electron microscopy in order to make clear the crystallographic relation between the decagonal quasicrystal and the monoclinic Al13Co4 structure. The results revealed a coexistence state consisting of decagonal quasicrystal and approximant Al13Co4 regions in Al-20 at. % Co-10 at. % Cu alloy samples. With the help of the coexistence state, the orientation relationship was established between the monoclinic Al13Co4 structure and the decagonal quasicrystal. In the determined relationship, the crystallographic axis in the quasicrystal was found to be parallel to the normal direction of the (010) m plane in the Al13Co4 structure, where the subscript m denotes the monoclinic system. Based on data obtained experimentally, the state stability of the decagonal quasicrystal was also examined in terms of the Hume-Rothery (HR) mechanism on the basis of the nearly-free-electron approximation. It was found that a model based on the HR mechanism could explain the crystallographic features such as electron diffraction patterns and atomic arrangements found in the decagonal quasicrystal. In other words, the HR mechanism is most likely appropriate for the stability of the decagonal quasicrystal in the Al-Co-Cu alloy system.

Title:
Prediction of entropy stabilized incommensurate phases in the system MoS2-MoTe2
Authors:
Burton, BP; Singh, AK Author Full Names: Burton, B. P.; Singh, A. K.
Source:
JOURNAL OF APPLIED PHYSICS, 120 (15):10.1063/1.4964868 OCT 21 2016
Abstract:
A first principles phase diagram calculation, that included van der Waals interactions, was performed for the 3D bulk system (1 X).MoS2 (X) . MoTe2. Surprisingly, the predicted phase diagram has at least two ordered phases, at X approximate to 0: 46, even though all calculated formation energies are positive; in a ground-state analysis that examined all configurations with 16 or fewer anion sites. The lower-temperature I-phase is predicted to transform to a higher-temperature I'-phase at T approximate to 500 K, and I0 disorders at T approximate to 730 K. Both these transitions are predicted to be first-order, and there are broad two-phase fields on both sides of the ordered regions. Both the I-and I'-phases are predicted to be incommensurate, i. e., aperiodic: I-phase in three dimensions; and I'-phase in two dimensions.

Title:
Structural transformations in highly oriented seven modulated martensite Ni-Mn-Ga thin films on an Al2O3 (11(2)over-bar0) substrate
Authors:
Sharma, A; Mohan, S; Suwas, S Author Full Names: Sharma, Amit; Mohan, Sangeneni; Suwas, Satyam
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (19):3016-3026; 10.1557/jmr.2016.317 OCT 2016
Abstract:
Highly oriented Ni-Mn-Ga thin film with multiple variants and room temperature orthorhombic martensite structure were prepared on a single crystalline Al2O3 (11 (2) over bar0) substrate by DC magnetron sputtering. X-ray diffraction and rocking curve measurements reveal the film as (202)(7M) oriented with an excellent crystal quality ( = 1.8 degrees). Spot-like pole figures indicate that the Ni-Mn-Ga film grows with a strong in-plane preferred orientation. An in-depth analysis of the measured pole figure reveals the presence of a retained austenite phase in the film. Two phase transformations, M-S approximate to 345 K and T-C approximate to 385 K, are observed and are attributed to first order structural transformation from cubic to orthorhombic, and second order phase transformation from ferromagnetic to paramagnetic, respectively. In situ high temperature x-ray diffraction measurements provide a clear indication of a thermally-induced martensite austenite reversible structural phase transformation in the film. The presence of martensite plates with seven modulated orthorhombic structure and adaptive nano-twins are some of the important microscopic features observed in the film with transmission electron microscopy investigations.

Update: 16-Nov-2016


Title:
A guide to lifting aperiodic structures
Authors:
Baake, M; Ecija, D; Grimm, U Author Full Names: Baake, Michael; Ecija, David; Grimm, Uwe
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (9):507-515; 10.1515/zkri-2016-1982 SEP 2016
Abstract:
The embedding of a given point set with non-crystallographic symmetry into higher-dimensional space is reviewed, with special emphasis on the Minkowski embedding known from number theory. This is a natural choice that does not require an a priori construction of a lattice in relation to a given symmetry group. Instead, some elementary properties of the point set in physical space are used, and explicit methods are described. This approach works particularly well for the standard symmetries encountered in the practical study of quasicrystalline phases. We also demonstrate this with a recent experimental example, taken from a sample with square-triangle tiling structure and (approximate) 12-fold symmetry.

Title:
Effect of Pt addition to Ag-Au bimetallic nanoclusters: A molecular dynamics study of Ag-Au-Pt ternary system
Authors:
Akbarzadeh, H; Shamkhali, AN; Abbaspour, M; Salemi, S; Hajizadeh, Z Author Full Names: Akbarzadeh, Hamed; Shamkhali, Amir Nasser; Abbaspour, Mohsen; Salemi, Sirous; Hajizadeh, Zohreh
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 692 647-657; 10.1016/j.jallcom.2016.09.066 JAN 25 2017
Abstract:
In this work addition of Pt atoms to Ag0.5Au0.5 nanoclusters and formation of Ag0.5-chi Au0.5-chi Pt2 chi (with chi - 0.1, 0.17, 0.2, 0.25, 0.3, and 0.4) and total number of atoms equal to 1415 and 2057 ternary nanoclusters is studied by molecular dynamics simulation. The results indicated that at low concentrations of Pt, nanoclusters exhibit a local-ordered structure in such a way that (Pt-Ag-n-Au-2n) cores are surrounded by extra Ag atoms. By increase of Pt concentration total order of the nanocluster also increases. For nanoclusters with 0.0 < chi(Pt) < 0.4 total order of the system is decreased due to lower concentration of Ag-Pt and Au-Pt interactions. For chi(Pt) - 0.4 system, total order of the nanocluster again increases considerably which represents a Pt-rich nanocluster with some Ag and Au impurity. Also, all nanoclusters with chi(Pt) > 0.0 exhibit an icosahedral-fcc phase transition before melting and temperature of this phase transition is decreased by increase of Pt concentration. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Controlling Magnetic Ordering in Ca1-xEuxCo2As2 by Chemical Compression
Authors:
Tan, XY; Yaroslavtsev, AA; Cao, HB; Geondzhian, AY; Menushenkov, AP; Chernikov, RV; Nataf, L; Garlea, VO; Shatruk, M Author Full Names: Tan, Xiaoyan; Yaroslavtsev, Alexander A.; Cao, Huibo; Geondzhian, Andrey Y.; Menushenkov, Alexey P.; Chernikov, Roman V.; Nataf, Lucie; Garlea, V. Ovidiu; Shatruk, Michael
Source:
CHEMISTRY OF MATERIALS, 28 (20):7459-7469; 10.1021/acs.chemmater.6b03184 OCT 25 2016
Abstract:
To investigate the interplay between electronic structure and itinerant magnetism, Ca1-xEuxCo2As2 solid solutions (x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7, 0.9, 1.0) were prepared by reactions between constituent elements in molten Bi. All of the samples crystallize in the ThCr2Si2 structure type. The crystal structure refinement revealed the formation of Co vacancies, the concentration of which decreases as the Eu content increases. The Eu site exhibits mixed valence in all samples. X-ray absorption near-edge structure spectroscopy revealed that the average Eu oxidation state decreases from +2.17 at 0 < x <= 0.6 to +2.14 at x >= 0.65. The same borderline behavior is observed in magnetic properties. The substitution of Eu for Ca causes the transition from the antiferromagnetic (AFM) ordering of Co moments in CaCo2As2 to ferromagnetic (FM) ordering of Co moments in Ca1-xEuxCo2As2 with 0.1 <= x <= 0.6. At higher Eu content, AFM ordering of Eu moments is observed, whereas the Co sublattice exhibits only paramagnetic behavior. Single-crystal neutron diffraction studies revealed that both Co and Eu sublattices order FM in Ca0.5Eu0.5Co2As2 with the magnetic moments aligned along the tetragonal c axis. In the AFM phases with x >= 0.65, only Eu moments are ordered in a helical spin structure defined by an incommensurate propagation vector k = [00q], with the moment lying in the ab plane. The changes in magnetic behavior are well-justified by the analysis of the electronic density of states and crystal orbital Hamilton population.

Title:
Role of Structure- and Defect Chemistry in High-Performance Thermoelectric Bismuth Strontium Cobalt Oxides
Authors:
Baran, JD; Kepaptsoglou, D; Molinari, M; Kulwongwit, N; Azough, F; Freer, R; Ramasse, QM; Parker, SC Author Full Names: Baran, Jakub D.; Kepaptsoglou, Demie; Molinari, Marco; Kulwongwit, Nuth; Azough, Feridoon; Freer, Robert; Ramasse, Quentin M.; Parker, Stephen C.
Source:
CHEMISTRY OF MATERIALS, 28 (20):7470-7478; 10.1021/acs.chemmater.6b03200 OCT 25 2016
Abstract:
[Bi0.87SrO2](2)[CoO2](1.82) (BSCO) is one of the best p-type thermoelectric oxides but its structural and electronic properties are still poorly understood. BSCO is a misfit-layered compound consisting of an incommensurate stacking of hexagonal CoO2 and double rock-salt BiSrO2 layers. Here we combine experimental and computational approaches to investigate its crystallographic and electronic structure as well as thermoelectric transport properties. Considering different approximations for the subsystems stacking, we present a structural model that agrees well with both bulk and atomic-scale experimental data. This model, which suggests a level of Bi deficiency in the rock-salt layers, is then used to discuss the material's electronic, magnetic, and transport properties. We show that Bi deficiency leads to a band gap opening and increases p-type electronic conductivity due to the formation of Co4+ species that serve as itinerant holes within the predominantly Co3+ framework of the CoO2 layer. We validate these predictions using electron energy loss spectroscopy in the scanning transmission electron microscope. The relationship between the hole-doping mechanism and the changes of the local structure (in particular the level of Bi deficiency) is evaluated. The reliability of the simulations is supported by the calculated temperature dependence of the Seebeck coefficient, in good agreement with experimental measurements.

Title:
Weak coupling of pseudoacoustic phonons and magnon dynamics in the incommensurate spin-ladder compound Sr14Cu24O41
Authors:
Chen, X; Bansal, D; Sullivan, S; Abernathy, DL; Aczel, AA; Zhou, JS; Delaire, O; Shi, L Author Full Names: Chen, Xi; Bansal, Dipanshu; Sullivan, Sean; Abernathy, Douglas L.; Aczel, Adam A.; Zhou, Jianshi; Delaire, Olivier; Shi, Li
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134309 OCT 21 2016
Abstract:
Intriguing lattice dynamics have been predicted for aperiodic crystals that contain incommensurate substructures. Here we report inelastic neutron scattering measurements of phonon and magnon dispersions in Sr14Cu24O41, which contains incommensurate one-dimensional (1D) chain and two-dimensional (2D) ladder substructures. Two distinct pseudoacoustic phonon modes, corresponding to the sliding motion of one sublattice against the other, are observed for atomic motions polarized along the incommensurate axis. In the long wavelength limit, it is found that the sliding mode shows a remarkably small energy gap of 1.7-1.9 meV, indicating very weak interactions between the two incommensurate sublattices. The measurements also reveal a gapped and steep linear magnon dispersion of the ladder sublattice. The high group velocity of this magnon branch and weak coupling with acoustic and pseudoacoustic phonons can explain the large magnon thermal conductivity in Sr14Cu24O41 crystals. In addition, the magnon specific heat is determined from the measured total specific heat and phonon density of states and exhibits a Schottky anomaly due to gapped magnon modes of the spin chains. These findings offer new insights into the phonon and magnon dynamics and thermal transport properties of incommensurate magnetic crystals that contain low-dimensional substructures.

Title:
Helicity-dependent photocurrent in a Bi2Se3 thin film probed by terahertz emission spectroscopy
Authors:
Hamh, SY; Park, SH; Jerng, SK; Jeon, JH; Chun, SH; Lee, JS Author Full Names: Hamh, Sun Young; Park, Soon-Hee; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Chun, Seung-Hyun; Lee, Jong Seok
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.161405 OCT 20 2016
Abstract:
We investigate photocarrier dynamics in a Bi2Se3 thin film via terahertz (THz) emission spectroscopy. We report amplitude and phase modulations of the emitted THz wave under the variations in a polarization of an input laser beam and sample azimuth. Photon-helicity-dependent responses are manifested in both time and frequency domains, and azimuth dependence of such circular anisotropy exhibits a clear threefold periodicity. We analyze these results based on the symmetry of the bulk and the surface of Bi2Se3 and demonstrate that the observed helicity-dependent photocurrent originates from the circular photon drag effect, namely, linear and angular momentum transfers from photons to photocarriers.

Title:
Crystallographic computing system Jana2006: solution and refinement of twinned structures
Authors:
Petricek, V; Dusek, M; Plasil, J Author Full Names: Petricek, Vaclav; Dusek, Michal; Plasil, Jakub
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (10):583-599; SI 10.1515/zkri-2016-1956 OCT 2016
Abstract:
Twinning is a phenomenon complicating structure analysis of single crystals of standard as well as modulated structures. Jana2006 as a software for advanced structure analysis contains tools for recognition and refinement of twins including most complicated cases of modulated and magnetic structures. In order to efficiently use the tools of Jana2006 related to twinning, we explain the basic terminology and the underlying theory, especially the symmetry of the diffraction patterns affected by twinning. We present typical diffraction patterns of twins and show how twinning can be recognized or detected by various tools and described with twinning matrices. Data processing of twins and ways of how they can be imported to Jana2006 are also discussed. Two examples demonstrate the solution of typical twins: twinning by metric merohedry and twinning by reticular merohedry, followed by the third example demonstrating twinning in a commensurately *modulated structure*. The relationship between the dimensionality of the structure and twinning is discussed, too.

Update: 10-Nov-2016


Title:
Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2
Authors:
May, AF; Calder, S; Parker, DS; Sales, BC; McGuire, MA Author Full Names: May, Andrew F.; Calder, Stuart; Parker, David S.; Sales, Brian C.; McGuire, Michael A.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep35325 OCT 14 2016
Abstract:
Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFe2Ge2 has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K. Powder neutron diffraction confirms antiferromagnetic ordering below T-N approximate to 175 K, and an incommensurate spin density wave is observed below approximate to 125 K. Coupled with the small refined moments (0.5-1 mu B/Fe), this provides a picture of itinerant magnetism in CuFe2Ge2. The neutron diffraction data also reveal a coexistence of two magnetic phases that further highlights the near-degeneracy of various magnetic states. These results demonstrate that the ground state in CuFe2Ge2 can be easily manipulated by external forces, making it of particular interest for doping, pressure, and further theoretical studies.

Title:
Charge density wave modulation and gap measurements in CeTe3
Authors:
Ralevic, U; Lazarevic, N; Baum, A; Eiter, HM; Hackl, R; Giraldo-Gallo, P; Fisher, IR; Petrovic, C; Gajic, R; Popovic, ZV Author Full Names: Ralevic, U.; Lazarevic, N.; Baum, A.; Eiter, H. -M.; Hackl, R.; Giraldo-Gallo, P.; Fisher, I. R.; Petrovic, C.; Gajic, R.; Popovic, Z. V.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165132 OCT 14 2016
Abstract:
We present a study of charge density wave (CDW) ordering in CeTe3 at room temperature using a scanning tunneling microscope and Raman spectroscopy. Two characteristic CDW ordering wave vectors obtained from the Fourier analysis are assessed to be |c* - q| = 4.19 nm(-1) and |q| = 10.26 nm(-1) where |c*| = 2 Pi/c is the reciprocal lattice vector. The scanning tunneling spectroscopy measurements, along with inelastic light ( Raman) scattering measurements, show a CDWgap Delta(max) of approximately 0.37 eV. In addition to the CDW modulation, we observe an organization of the Te sheet atoms in an array of alternating V- and N-shaped groups along the CDW modulation, as predicted in the literature.

Title:
Remarkable Stability of Charge Density Wave Order in La1.875Ba0.125CuO4
Authors:
Chen, XM; Thampy, V; Mazzoli, C; Barbour, AM; Miao, H; Gu, GD; Cao, Y; Tranquada, JM; Dean, MPM; Wilkins, SB Author Full Names: Chen, X. M.; Thampy, V.; Mazzoli, C.; Barbour, A. M.; Miao, H.; Gu, G. D.; Cao, Y.; Tranquada, J. M.; Dean, M. P. M.; Wilkins, S. B.
Source:
PHYSICAL REVIEW LETTERS, 117 (16):10.1103/PhysRevLett.117.167001 OCT 11 2016
Abstract:
The occurrence of charge-density-wave (CDW) order in underdoped cuprates is now well established, although the precise nature of the CDW and its relationship with superconductivity is not. Theoretical proposals include contrasting ideas such as that pairing may be driven by CDW fluctuations or that static CDWs may intertwine with a spatially modulated superconducting wave function. We test the dynamics of CDW order in La1.825Ba0.125CuO4 by using x-ray photon correlation spectroscopy at the CDW wave vector, detected resonantly at the Cu L-3 edge. We find that the CDW domains are strikingly static, with no evidence of significant fluctuations up to 2 (3)/(4) h. We discuss the implications of these results for some of the competing theories.

Title:
Structure of the Al13Co4(100) surface: Combination of surface x-ray diffraction and ab initio calculations
Authors:
Gaudry, E; Chatelier, C; McGuirk, GM; Loli, LNS; de Weerd, MC; Ledieu, J; Fournee, V; Felici, R; Drnec, J; Beutier, G; de Boissieu, M Author Full Names: Gaudry, E.; Chatelier, C.; McGuirk, G. M.; Serkovic Loli, L. N.; de Weerd, M. -C.; Ledieu, J.; Fournee, V.; Felici, R.; Drnec, J.; Beutier, G.; de Boissieu, M.
Source:
PHYSICAL REVIEW B, 94 (16):10.1103/PhysRevB.94.165406 OCT 10 2016
Abstract:
The structure of the quasicrystalline approximant Al13Co4(100) has been determined by surface x-ray diffraction (SXRD) and complementary density-functional-theory (DFT) calculations. Thanks to the use of a two-dimensional pixel detector, which speeds up the data acquisition enormously, an exceptionally large set of experimental data, consisting of 124 crystal truncation rods, has been collected and used to refine this complex structure of large unit cell and low symmetry. Various models were considered for the SXRD analysis. The best fit is consistent with a surface termination at the puckered type of planes but with a depletion of the protruding Co atoms. The surface energy of the determined surface model was calculated using DFT, and it takes a rather low value of 1.09 J/m(2). The results for the atomic relaxation of surface planes found by SXRD or DFT were in excellent agreement. This work opens up additional perspectives for the comprehension of related quasicrystalline surfaces.

Title:
Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase
Authors:
Fredrickson, RT; Fredrickson, DC Author Full Names: Fredrickson, Rie T.; Fredrickson, Daniel C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 787-801; 10.1107/S2052520616010350 5 OCT 2016
Abstract:
Despite being one of the most common minerals in the earth's crust the crystal structure of intermediate e-plagioclase remains only partially understood, due in a large part to its complex diffraction patterns including satellite reflections. In this article we present a detailed analysis of the structure of e-plagioclase (An44) using single-crystal X-ray diffraction measured at ambient and low temperature (T = 100 K), in which the full modulated structure is successfully refined. As in earlier studies, the diffraction pattern exhibits strong main a-reflections and weak e-satellite reflections. The average structure could be solved in terms of an albite-like basic cell with the triclinic centrosymmetric and non-centrosymmetric space groups P (1) over bar and P1 (treated in its C (1) over bar and C1 setting, respectively, to follow conventions in the literature), while the incommensurately modulated structure was modeled in (3 + 1) D superspace, employing both the centro-and noncentrosymmetric superspace groups X (1) over bar(alpha beta gamma)0 and X1(alpha beta gamma) 0, where X refers to a special (3 + 1) D lattice centering with centering vectors (0 0 1/2 1/2), (1/2 1/2 0 1/2), and (1/2 1/2 1/2 0). Individual positional and occupational modulations for Ca/Na were refined with deeper insights being revealed in the non-centrosymmetric structure model. Through the structural details emerging from this model, the origin of the modulation can be traced to the communication between Ca/Na site positions through their bridging aluminosilicate (Si/Al) O-4 tetrahedra.

Title:
Charge and spin coupling in magnetoresistive oxygen-vacancy strontium ferrate SrFeO3-delta
Authors:
Lee, SH; Frawley, TW; Yao, CH; Lai, YC; Du, CH; Hatton, PD; Wang, MJ; Chou, FC; Huang, DJ Author Full Names: Lee, S. H.; Frawley, T. W.; Yao, C. H.; Lai, Y. C.; Du, Chao-Hung; Hatton, P. D.; Wang, M. J.; Chou, F. C.; Huang, D. J.
Source:
NEW JOURNAL OF PHYSICS, 18 10.1088/1367-2630/18/9/093033 SEP 20 2016
Abstract:
Using magnetization, conductivity and x-ray scattering measurements, we demonstrate that the giant magnetoresistance of the oxygen-deficient ferrite SrFeO2.875+0.02 is a consequence of the coupling between the charge and spin order parameters and the tetragonal to monoclinic structural distortion. Upon cooling the sample at T similar or equal to 120 K we find a shoulder in both field-cool and zero field cool magnetization data and the simultaneous appearance of incommensurate structural satellites observed using x-ray diffraction. These satellites are shown to be due to incommensurate charge ordering with the high temperature delocalized Fe3.5+ ions becoming localized with a charge disproportion forming an incommensurate charge-ordered phase. Strong resonant enhancement of these satellites at the Fe L-III absorption edge confirms that this charge ordering is occurring at the Fe(2) sites. Further cooling increases the charge order correlation until T similar or equal to 62Kwhere there is a full structural transition from the tetragonal phase to a mononclinic phase. This causes a jump in the charge order wavevector from an incommensurate value of 0.610 to a commensurate ground state position of 5/8. This first-order structural transition displays considerable hysteresis as well as dramatic reductions in the magnetization, resistivity and magnetoresistance. The transition also causes an antiferromagnetic spin-ordering with a doubled unit cell along the c-axis. Well as observing new commensurate magnetic reflections at the Fe-III edge we also observed resonant enhancement at the oxygen K-edge showing considerable hybridization between the Fe 3d and oxygen 2p states at low temperatures. Our results show that the formation of a magnetic long-rage ordered ground state drives the charge ordering from an incommensurate ordering to a commensurate ground state. This is evidence of a strong coupling between the magnetic and charge order parameters which is the basis for the unusual magnetoresistive effects observed at the transition.

Update: 3-Nov-2016


Title:
Ab-initio, Mossbauer spectroscopy, and magnetic study of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 689 726-732; 10.1016/j.jallcom.2016.08.021 DEC 25 2016
Abstract:
We report the results of ab-initio electronic structure and electric field gradient calculations and of X-ray diffraction, Fe-57 Mossbauer spectroscopy, and magnetic studies of the approximant Al72Ni9Fe19 to a decagonal Al-Ni-Fe quasicrystal. The approximant crystallizes in the hexagonal space group P63/mmc with the lattice parameters a = 7.6989(2) A ($) over circle and c = 7.6724(2) A ($) over circle. A pseudogap in the density of states, centered at similar to 0.30 eV above the Fermi level and with a width of similar to 0.35 eV, is found. Evidence for the covalent nature of the chemical bonding and good metallicity of Al72Ni9Fe19 is provided. The Mossbauer spectra and a 1/T-like dependence of the magnetic susceptibility indicate that Al72Ni9Fe19 is a paramagnet down to 2.0 K. The shape of the Mossbauer spectra is accounted for by a superposition of two quadrupole doublets corresponding to Fe atoms located at two inequivalent crystallographic sites. A sudden change of the quadrupole splittings of the two doublets at similar to 200 K indicates a possible structural phase transition. Excellent agreement between the calculated and measured quadrupole splittings is observed. The Debye temperature of Al72Ni9Fe19 is found to be 431 (3) K. (C) 2016 Elsevier B. V. All rights reserved.

Title:
High temperature phases with wurtzite-derived structure in Zn2LiGaO4-ZnO alloy system
Authors:
Kita, M; Fukada, T; Yamaguchi, S; Omata, T Author Full Names: Kita, Masao; Fukada, Tomoaki; Yamaguchi, Shu; Omata, Takahisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 69-76; 10.1016/j.jallcom.2016.06.249 A DEC 15 2016
Abstract:
We investigated the structural phase transformations of Zn2LiGaO4, which is a quaternary oxide semiconductor with a wide band gap of 4.0 eV, and its alloys with ZnO by using in-situ high-temperature X-ray diffraction (XRD), room-temperature XRD and selected-area electron diffraction of samples quenched from high temperatures of >873 K. Three types of phases with the wurtzite-derived structure were found in the y(Zn2LiGaO4)(1/4)-(1-y)ZnO alloy system. First is the low-temperature phase, phase I, in which constituent cations are ordered similarly to those in a Cd2AgGaS4-type structure. Phase I has an incommensurate modulation vector of 1.04b* and is stable at <1070 K and compositions of 0.96 <= y <= 1 and is stable at room temperature for y = 0.92. The second phase, phase II, appears at intermediate temperatures of 773-1373 K at 0.96 <= y <= 1, and its incommensurate modulation vector is 1.08b*. *Phase* III, which has no long-range cation ordering but still has short-range cation ordering, is stable for 0.92 <= y < 1 at high temperatures and for 0.2 < y < 0.92 from room temperature to high temperatures. We discuss the driving force of the transformations among the three phases in terms of their crystal structure and the mismatch in thermal expansion between -Zn-O-Zn-O- and -Li-O-Ga-O- linkages. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Anisotropy of the electric transport properties of decagonal Al-Cu-Co(Fe) quasicrystals
Authors:
Shulyatev, DA; Klyueva, MV; Devaradjan, U Author Full Names: Shulyatev, D. A.; Klyueva, M. V.; Devaradjan, U.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (9):883-888; 10.1134/S0031918X16070152 SEP 2016
Abstract:
The method of growth from a melt solution was used to obtain iron-alloyed (0.08 at %) Al-Cu-Co single crystals with a decagonal symmetry. The temperature dependences of the electrical resistivity in magnetic fields of 0-18 T were measured using samples oriented in the periodic direction (rho (p) (T)) and in the quasi-periodic plane (rho (q) (T)). A strong anisotropy of the resistivity was observed; the rho (p) (T) curve is linear, whereas the rho (q) (T) curve is approximated well by a second-order polynomial. A strong anisotropy of the magnetoresistance was also observed; a positive magnetoresistance Delta rho/rho similar to 10(-3) for the current flowing in the quasiperiodic plane; and a weak (close to zero) negative magnetoresistance for the current flowing along the periodic direction.

Update: 27-Oct-2016


Title:
Application of electron backscatter diffraction (EBSD) to quasicrystal-containing microstructures in the Mg-Cd-Yb system
Authors:
Tanaka, R; Ohhashi, S; Fujita, N; Demura, M; Yamamoto, A; Kato, A; Tsai, AP Author Full Names: Tanaka, R.; Ohhashi, S.; Fujita, N.; Demura, M.; Yamamoto, A.; Kato, A.; Tsai, A. P.
Source:
ACTA MATERIALIA, 119 193-202; 10.1016/j.actamat.2016.08.011 OCT 15 2016
Abstract:
We develop a new analysis system for identifying orientation of an icosahedral quasicrystal (iQc) in a SEM installed with an electron backscatter diffraction (EBSD) instrument. The system is successfully applied to determine the orientation of any given iQc grain by reading and assigning the Kikuchi bands obtained with the EBSD. This enables us to analyze relative orientations of iQc and alpha Mg grains in a eutectic structure obtained through a unidirectional solidification process for the Mg-Cd-Yb system. According to EBSD analysis, growth direction of the eutectic structure is shown to be clearly parallel to a two-fold axis of the iQc and {10-10} of alpha Mg, and a unique orientation relationship in iQc and alpha Mg grains is verified in all iQc-alpha Mg coexisting regions. The similarity between primary inter-planar spacings of the iQc and alpha Mg phases is a key factor for stabilizing the interface of two phases and favoring the formation of eutectic structure. This stabilization mechanism is supported by a simple argument on the energetics of a quasiperiodic/periodic lattice interface. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Two-Level Electron Excitations and Distinctive Physical Properties of Al-Cu-Fe Quasicrystals
Authors:
Prekul, A; Shchegolikhina, N Author Full Names: Prekul, Alexandre; Shchegolikhina, Natalya
Source:
CRYSTALS, 6 (9):10.3390/cryst6090119 SEP 2016
Abstract:
This article is not a review in the conventional sense. Rather, it is a monographic study of the implications of detection in Al-Cu-Fe quasicrystals of the electronic heat capacity contributions associated with the two-level electron excitations. Our aim was to reveal correlations between these contributions, on the one hand, and specific features of electron transport, magnetic susceptibility, Hall-effect, tunnelling and optical spectra, on the other hand. It is shown that the full range of these features can be understood in the framework of the unified conceptual scheme based on two-level electron excitations.

Title:
Statistical Approach to Diffraction of Periodic and Non-Periodic Crystals-Review
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
CRYSTALS, 6 (9):10.3390/cryst6090104 SEP 2016
Abstract:
In this paper, we show the fundamentals of statistical method of structure analysis. Basic concept of a method is the average unit cell, which is a probability distribution of atomic positions with respect to some reference lattices. The distribution carries complete structural information required for structure determination via diffraction experiment regardless of the inner symmetry of diffracting medium. The shape of envelope function that connects all diffraction maxima can be derived as the Fourier transform of a distribution function. Moreover, distributions are sensitive to any disorder introduced to ideal structure-phonons and phasons. The latter are particularly important in case of quasicrystals. The statistical method deals very well with phason flips and may be used to redefine phasonic Debye-Waller correction factor. The statistical approach can be also successfully applied to the peak's profile interpretation. It will be shown that the average unit cell can be equally well applied to a description of Bragg peaks as well as other components of diffraction pattern, namely continuous and singular continuous components. Calculations performed within statistical method are equivalent to the ones from multidimensional analysis. The atomic surface, also called occupation domain, which is the basic concept behind multidimensional models, acquires physical interpretation if compared to average unit cell. The statistical method applied to diffraction analysis is now a complete theory, which deals equally well with periodic and non-periodic crystals, including quasicrystals. The method easily meets also any structural disorder.

Title:
A Review of Transmission Electron Microscopy of Quasicrystals-How Are Atoms Arranged?
Authors:
Li, RT; Li, Z; Dong, ZL; Khor, KA Author Full Names: Li, Ruitao; Li, Zhong; Dong, Zhili; Khor, Khiam Aik
Source:
CRYSTALS, 6 (9):10.3390/cryst6090105 SEP 2016
Abstract:
Quasicrystals (QCs) possess rotational symmetries forbidden in the conventional crystallography and lack translational symmetries. Their atoms are arranged in an ordered but non-periodic way. Transmission electron microscopy (TEM) was the right tool to discover such exotic materials and has always been a main technique in their studies since then. It provides the morphological and crystallographic information and images of real atomic arrangements of QCs. In this review, we summarized the achievements of the study of QCs using TEM, providing intriguing structural details of QCs unveiled by TEM analyses. The main findings on the symmetry, local atomic arrangement and chemical order of QCs are illustrated.

Title:
Elastodynamic Analysis of a Hollow Cylinder with Decagonal Quasicrystal Properties: Meshless Implementation of Local Integral Equations
Authors:
Hosseini, SM; Sladek, J; Sladek, V Author Full Names: Hosseini, Seyed Mahmoud; Sladek, Jan; Sladek, Vladimir
Source:
CRYSTALS, 6 (8):10.3390/cryst6080094 AUG 2016
Abstract:
A meshless approximation and local integral equation (LIE) formulation are proposed for elastodynamic analysis of a hollow cylinder made of quasicrystal materials with decagonal quasicrystal properties. The cylinder is assumed to be under shock loading. Therefore, the general transient elastodynamic problem is considered for coupled phonon and phason displacements and stresses. The equations of motion in the theory of compatible elastodynamics of wave type for phonons and wave-telegraph type for phasons are employed and can be easily modified to the elasto-hydro dynamic equations for quasicrystals (QCs). The angular dependence of the tensor of phonon-phason coupling coefficients handicaps utilization of polar coordinates, when the governing equations would be given by partial differential equations with variable coefficients. Despite the symmetry of the geometrical shape, the local weak formulation and meshless approximation are developed in the Cartesian coordinate system. The response of the cylinder in terms of both phonon and phason stress fields is obtained and studied in detail.

Title:
A ZrNiAl related high-pressure modification of CeRuSn
Authors:
Niehaus, O; Heymann, G; Huppertz, H; Rodewald, UC; Chevalier, B; Matar, SF; Hoffmann, RD; Pottgen, R Author Full Names: Niehaus, Oliver; Heymann, Gunter; Huppertz, Hubert; Rodewald, Ute Ch.; Chevalier, Bernard; Matar, Samir F.; Hoffmann, Rolf-Dieter; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 45 (36):14216-14229; 10.1039/c6dt02294d 2016
Abstract:
Monoclinic CeRuSn with its own structure type transforms to a high-pressure modification at 11.5 GPa and 1470 K (1000 t press, Walker type module). The structure of the high-pressure phase was refined from X-ray single crystal diffractometer data at room temperature. The HP-CeRuSn subcell structure adopts the ZrNiAl type: P (6) over bar 2m, a = 751.4(3) and c = 394.6(2) pm, wR2 = 0.0787, 310 F-2 values and 15 variables. The Ru2 atoms within the Sn-6 trigonal prisms show a strongly enhanced U-33 parameter. Weak satellite reflections indicate a commensurate modulation: (3 + 1)D superspace group P31m(1/3,1/3,gamma)000, a = 751.4(3) and c = 394.6(2) pm, gamma = -1/3, wR2 = 0.0786, 1584 F-2 values, 32 variables for the main reflections and wR2 = 0.3757 for the satellites of 1st order. A description of this new superstructure variant of the ZrNiAl type is possible in a transformed 3D supercell with the space group R3m and Z = 9. The driving force for formation of the modulation is strengthening of Ru-Sn bonding within the comparatively large Ru@Sn-6 trigonal prisms. Electronic structure calculations point to an almost depleted Ce 4f shell. This is substantiated by temperature-dependent magnetic susceptibility data. Fitting of the data within the inter-configuration fluctuation model (ICF) resulted in cerium valences of 3.41 at 10 K and 3.31 at 350 K. Temperature dependent specific heat data underline the absence of magnetic ordering.

Update: 20-Oct-2016


Title:
Complex magnetic ordering in Tm3Cu4Si4
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 577-584; 10.1016/j.jallcom.2016.07.241 B DEC 15 2016
Abstract:
Tm3Cu4Si4 crystalizes in the orthorhombic Gd3Cu4Ge4-type crystal structure with trivalent Tm atoms occupying 2(d) and 4(e) Wyckoff sites. Neutron diffraction data shows that at 1.7 K the Tm magnetic moments form a commensurate magnetic structure defined by the propagation vectors (k) over right arrow (2d) = [0,1/2,0] and (k) over right arrow (4e) = [1/4,0,1/2] for the 2(d) and 4(e) sites, respectively. With increasing temperature, the magnetic order in the 4(e) sublattice undergoes near 2.5 K an order-order transition into an incommensurate magnetic structure and then disappears at 2.9 K. Similar changes in the magnetic structure occur in the 2(d) sublattice at 3.3 and 3.8 K, respectively. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Al-rich region of Al-Cu-Mn
Authors:
Grushko, B; Mi, SB Author Full Names: Grushko, B.; Mi, S. B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 957-963; 10.1016/j.jallcom.2016.07.075 B DEC 15 2016
Abstract:
The Al-Cu-Mn alloy system was studied above 45 at.% Al between 550 and 910 degrees C by scanning electron microscopy, powder X-ray diffraction and differential thermal analysis. A wide ternary region of the so-called beta-phase extending along similar to 50 at.% Al was confirmed. It has a CsCl-type structure with a approximate to 0.292-0.298 nm. The total gamma(1)/gamma(2)-region extends from Al-Mn up to similar to 17 at.% Cu and the high-temperature T-Al3Mn phase (Pnma, a approximate to 1.48, b approximate to 1.24, c approximate to 1.25 nm) extends up to similar to 15 at.% Cu. The so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found to exist in a compositional region of Al74-80Cu5-12.5Mn12.5-18. The ternary phase earlier reported at Al57.9Cu26.3Mn15.8 was confirmed. It exists below 697 degrees C in a compositional region of Al55-58Cu29-Mn-37(7.5-14). The decagonal D-3-phase was concluded to be stable in a compositional region of Al61.5-68.5Cu19-29.5Mn9-16. Below 631 degrees C an fcc phase (a = 0.5814 nm) was revealed around similar to Al60Cu36.5Mn3.5. Partial isothermal sections at 550, 600, 650, 750, 850 and 910 degrees C were constructed. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Microstructural characteristics and mechanical properties of Mg-Zn-Y alloy containing icosahedral quasicrystals phase treated by pulsed magnetic field
Authors:
Zhang, L; Zhou, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Zhou, W.; Hu, P. H.; Zhou, Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 688 868-874; 10.1016/j.jallcom.2016.07.280 B DEC 15 2016
Abstract:
Pulsed magnetic field (PMF) has been imposed during solidification of Mg-Zn-Y alloy containing icosahedral quasicrystals phase (I-phase) in this work. The effects of vibration power on the solidification microstructure and mechanical properties of Mg93Zn6Y alloy were studied. The results show that the solidification microstructure of the Mg93Zn6Y alloy was further refined with increasing vibration power. The primary alpha-Mg in the alloy treated by PMF was changed from dendrites with the average grain size more than 1 mm untreated by PMF to rosette-like and polyhedral morphology with the average grain size of 122 mm. Moreover, the I-phase was changed from continuous thick skeletal to discontinuous fine reticular and particle-like morphology. The fraction of I-phase in the alloy treated by PMF was also reduced due to the increase of concentrations of Zn and Y elements inside grains. The mechanical properties of Mg93Zn6Y alloy treated by PMF were also improved significantly. The yield strength, ultimate tensile strength and elongation of the alloy treated by PMF at a vibration power of 350 Wat room temperature were 162 MPa, 221 MPa and 1.99%, which were increased by 65%, 66% and 124% respectively, compared to those of the alloy untreated by PMF. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Laser-Induced Charge-Density-Wave Transient Depinning in Chromium
Authors:
Jacques, VLR; Laulhe, C; Moisan, N; Ravy, S; Le Bolloc'h, D Author Full Names: Jacques, V. L. R.; Laulhe, C.; Moisan, N.; Ravy, S.; Le Bolloc'h, D.
Source:
PHYSICAL REVIEW LETTERS, 117 (15):10.1103/PhysRevLett.117.156401 OCT 3 2016
Abstract:
We report on time-resolved x-ray diffraction measurements following femtosecond laser excitation in pure bulk chromium. Comparing the evolution of incommensurate charge-density-wave (CDW) and atomic lattice reflections, we show that, a few nanoseconds after laser excitation, the CDW undergoes different structural changes than the atomic lattice. We give evidence for a transient CDW shear strain that breaks the lattice point symmetry. This strain is characteristic of sliding CDWs, as observed in other incommensurate CDW systems, suggesting the laser-induced CDW sliding capability in 3D systems. This first evidence opens perspectives for unconventional laser-assisted transport of correlated charges.

Title:
Phase transition of solid bismuth under high pressure
Authors:
Chen, HY; Xiang, SK; Yan, XZ; Zheng, LR; Zhang, Y; Liu, SG; Bi, Y Author Full Names: Chen, Hai-Yan; Xiang, Shi-Kai; Yan, Xiao-Zhen; Zheng, Li-Rong; Zhang, Yi; Liu, Sheng-Gang; Bi, Yan
Source:
CHINESE PHYSICS B, 25 (10):10.1088/1674-1056/25/10/108103 OCT 2016
Abstract:
As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III, and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction (XRD) technology. Using x-ray absorption fine structure (XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.

Title:
Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
Authors:
Hong, F; Yue, BB; Wang, JL; Studer, A; Fang, CS; Wang, XL; Dou, SX; Cheng, ZX Author Full Names: Hong, Fang; Yue, Binbin; Wang, Jianli; Studer, Andrew; Fang, Chunsheng; Wang, Xiaolin; Dou, Shixue; Cheng, Zhenxiang
Source:
APPLIED PHYSICS LETTERS, 109 (10):113-117; 10.1063/1.4962465 SEP 5 2016
Abstract:
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35K from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well. Published by AIP Publishing.

Update: 13-Oct-2016


Title:
Crystallization behavior and mechanical properties of (Al90Fe5Ce5)(100-x)Ti-x amorphous alloys
Authors:
Singh, D; Singh, D; Mandal, RK; Srivastava, ON; Tiwari, RS Author Full Names: Singh, Dharmendra; Singh, Devinder; Mandal, R. K.; Srivastava, O. N.; Tiwari, R. S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 687 990-998; 10.1016/j.jallcom.2016.06.272 DEC 5 2016
Abstract:
The crystallization behavior and mechanical properties of melt-spun (Al90Fe5Ge5)(100-x)Ti-x (x = 0, 4, 8 and 12 at.%) alloys have been investigated. The amorphous phase seems to be stable up to x = 8. The crystallization products for the amorphous alloys with x = 0-8 mainly composed of fcc-Al and icosahedral phases in the glassy matrix. The load dependent hardness behavior of amorphous alloys with and without Ti addition has been studied. The hardness value of the amorphous alloys has been found to be 3.72 and 3.07 GPa for x = 0 and 8 at 100 g load respectively. The annealed ribbons have higher hardness and strength as compared to that of as-synthesized ribbons. The enhanced values of hardness of the (Al90Fe5Ce5)(100-x)Ti-x (x = 0, 4 and 8) alloys are attributed to the combined effects of icosahedral nano particles and Al nanoparticles in amorphous matrix. The absence of cracks around the indentation area up to 500 g of load for amorphous alloys suggests better capability to resist crack propagation in comparison to the annealed alloys. The formation of shear bands around the indentation periphery has been observed. The number of visible shear bands for the as-synthesized ribbons is higher in comparison to those of annealed ribbons. The values of yield strength and Meyer exponent of these alloys are also compared. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Spatially modulated spin structure (SMSS) in BiFeO3-30 years later
Authors:
Sosnowska, IM Author Full Names: Sosnowska, I. M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (42):10.1088/0953-8984/28/42/421002 OCT 26 2016

Title:
Martensitic transition, structure and magnetic anisotropy of martensite in Ni-Mn-Sn single crystal
Authors:
Czaja, P; Szczerba, MJ; Chulist, R; Balanda, M; Przewoznik, J; Chumlyakov, YI; Schell, N; Kapusta, C; Maziarz, W Author Full Names: Czaja, P.; Szczerba, M. J.; Chulist, R.; Balanda, M.; Przewoznik, J.; Chumlyakov, Y. I.; Schell, N.; Kapusta, Cz.; Maziarz, W.
Source:
ACTA MATERIALIA, 118 213-220; 10.1016/j.actamat.2016.07.059 OCT 1 2016
Abstract:
The structural and magnetic properties of Ni50Mn37.5Sn12.5 single crystal were investigated. The alloy undergoes martensitic transformation at 308 K from the austenite phase to the structurally modulated tetragonal 4M martensite phase with lattice parameters a(4M) = 6.177 angstrom, c(4M) = 5.669 angstrom. The alloy shows 7.9% pre-strain upon uniaxial compression along the (001) direction, which is near the theoretical 8.2% maximum twinning strain. Magnetization measurements reveal that the magnetic anisotropy of the martensite phase is uniaxial with the easy magnetization axis corresponding to the shortest c axis of the tetragonally distorted unit cell, while its a axis is the hard magnetization direction. The magnetic anisotropy constant K-u saturates at low temperature around 7 x 10(4) j/m(3) and then gradually decreases with increasing temperature as the system approaches the Curie temperature of martensite at 215 K. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Er1.33Pt3Ga8: A modulated variant of the Er4Pt9Al24-structure type
Authors:
Oswald, IWH; Gourdon, O; Bekins, A; Evans, J; Treadwell, LJ; Chan, JY; Macaluso, RT Author Full Names: Oswald, Iain W. H.; Gourdon, Olivier; Bekins, Amy; Evans, Jess; Treadwell, LaRico J.; Chan, Julia Y.; Macaluso, Robin T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 242 161-167; SI 10.1016/j.jssc.2016.04.009 2 OCT 2016
Abstract:
Single crystals of Er1.33Pt3Ga8 were synthesized in a molten Ga flux. Er1.33Pt3Ga8 can be considered to be a modulated variant of the Er4Pt9Al24-structure type, where the partial occupancies are ordered. Indeed, the presence of weak satellite reflections indicates a complex organization and distribution of the Er and Ga atoms within the [ErGa] slabs. The structure has been solved based on single crystal X-ray diffraction data in the monoclinic superspace group X2/m(0 beta 0)00 with a commensurate modulated vector q=1/3b*. Precession images also indicate diffusion in the perpendicular direction indicating a partial disorder of this arrangement from layer to layer. In addition, Er1.33Pt3Ga8 shows antiferromagnetic ordering at T-N similar to 5 K. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Strong magnetoelastic coupling at the transition from harmonic to anharmonic order in NaFe(WO4)(2) with 3d(5) configuration
Authors:
Holbein, S; Ackermann, M; Chapon, L; Steffens, P; Gukasov, A; Sazonov, A; Breunig, O; Sanders, Y; Becker, P; Bohaty, L; Lorenz, T; Braden, M Author Full Names: Holbein, S.; Ackermann, M.; Chapon, L.; Steffens, P.; Gukasov, A.; Sazonov, A.; Breunig, O.; Sanders, Y.; Becker, P.; Bohaty, L.; Lorenz, T.; Braden, M.
Source:
PHYSICAL REVIEW B, 94 (10):10.1103/PhysRevB.94.104423 SEP 21 2016
Abstract:
The crystal structure of the double tungstate NaFe(WO4)(2) arises from that of the spin-driven multiferroic MnWO4 by inserting nonmagnetic Na layers. NaFe(WO4)(2) exhibits a three-dimensional incommensurate spin-spiral structure at low temperature and zero magnetic field, which, however, competes with commensurate order induced by magnetic field. The incommensurate zero-field phase corresponds to the condensation of a single irreducible representation but it does not imply ferroelectric polarization because spirals with opposite chirality coexist. Sizable anharmonic modulations emerge in this incommensurate structure, which are accompanied by large magnetoelastic anomalies, while the onset of the harmonic order is invisible in the thermal-expansion coefficient. In magnetic fields applied along the monoclinic axis, we observe a first-order transition to a commensurate structure that again is accompanied by large magnetoelastic effects. The large magnetoelastic coupling, a reduction of the b lattice parameter, is thus associated only with the commensurate order. Upon releasing the field at low temperature, the magnetic order transforms to another commensurate structure that considerably differs from the incommensurate low-temperature phase emerging upon zero-field cooling. The latter phase, which exhibits a reduced ordered moment, seems to be metastable.

Title:
Unusual Relaxor Ferroelectric Behavior in Stairlike Aurivillius Phases
Authors:
Steciuk, G; Boullay, P; Pautrat, A; Barrier, N; Caignaert, V; Palatinus, L Author Full Names: Steciuk, Gwladys; Boullay, Philippe; Pautrat, Alain; Barrier, Nicolas; Caignaert, Vincent; Palatinus, Lukas
Source:
INORGANIC CHEMISTRY, 55 (17):8881-8891; 10.1021/acs.inorgchem.6b01373 SEP 5 2016
Abstract:
New ferroelectric layered materials were found in the pseudobinary system Bi5Nb3O15-ABi(2)Nb(2)O(9) (A= Ba, Sr and Pb). Preliminary observations made by transmission electron microscopy indicate that these compounds exhibit a complex incommensurately modulated structure. A (3 + 1)D structural model is obtained using ab initio phasing by charge flipping based on the analysis of precession electron diffraction tomography data. The (3 + 1)D structure is further validated by a refinement against neutron powder diffraction. These materials possess a layered structure with discontinuous [Bi2O2] slabs and perovskite blocks. While these structural units are characteristics of Aurivillius phases, the existence of periodic crystallographic shear planes offers strong similarities with collapsed or stairlike structures known in high-Tc superconductors and related compounds. Using dielectric spectroscopy, we study the phase transitions of these new layered materials. For A = Ba and Sr, a Vogel-Fulcher-like behavior characteristic of the so-called relaxor ferroelectrics is observed and compared to "canonical" relaxors. For A = Sr, the absence of a Bums temperature separated from the freezing temperature appears as a rather unusual behavior.

Title:
An exceptional series of phase transitions in hydrophobic amino acids with linear side chains
Authors:
Gorbitz, CH; Karen, P; Dusek, M; Petricek, V Author Full Names: Gorbitz, Carl Henrik; Karen, Pavel; Dusek, Michal; Petricek, Vaclav
Source:
IUCRJ, 3 341-353; 10.1107/S2052252516010472 5 SEP 2016
Abstract:
The solid-state phase transitions and intermediate structures of S-2-aminobutanoic acid (L-2-aminobutyric acid), S-2-aminopentanoic acid (L-norvaline), S-2-aminohexanoic acid (L-norleucine) and L-methionine between 100 and 470 K, identified by differential scanning calorimetry, have been characterized in a comprehensive single-crystal X-ray diffraction investigation. Unlike other enantiomeric amino acids investigated until now, this group featuring linear side chains displays up to five distinct phases. The multiple transitions between them involve a number of different processes: alteration of the hydrogen-bond pattern, to our knowledge the first example of this observed for an amino acid, sliding of molecular bilayers, seen previously only for racemates and quasiracemates, concerted side-chain rearrangements and abrupt as well as gradual modifications of the side-chain disorder. Ordering of L-norleucine upon cooling even proceeds via an incommensurately modulated structure. L-Methionine has previously been described as being fully ordered at room temperature. An accurate refinement now reveals extensive disorder for both molecules in the asymmetric unit, while two previously unknown phases occur above room temperature.

Title:
Heuristic Description of Magnetoelectricity of Cu2OSeO3
Authors:
Milde, P; Neuber, E; Bauer, A; Pfleiderer, C; Berger, H; Eng, LM Author Full Names: Milde, Peter; Neuber, Erik; Bauer, Andreas; Pfleiderer, Christian; Berger, Helmuth; Eng, Lukas M.
Source:
NANO LETTERS, 16 (9):5612-5618; 10.1021/acs.nanolett.6b02167 SEP 2016
Abstract:
CuO2SeO3 is an insulating material that hosts topologically nontrivial spin whirls, so-called skyrmions, and exhibits magnetoelectric coupling allowing to manipulate these skyrmions by means of electric fields. We report magnetic force microscopy imaging of the real-space spin structure on the surface of a.. bulk single crystal of CuO2SeO3. Based on measurements of the electric polarization using Kelvin-probe force microscopy, we develop a heuristic description of the magnetoelectric properties in CuO2SeO3. The model successfully describes the dependency of the electric polarization on the magnetization in all magnetically modulated phases.

Update: 6-Oct-2016


Title:
Multi-phase quasicrystalline alloys for superior wear resistance
Authors:
Lee, K; Hsu, JL; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Hsu, Jialin; Naugle, Donald; Liang, Hong
Source:
MATERIALS & DESIGN, 108 440-447; 10.1016/j.matdes.2016.06.113 OCT 15 2016
Abstract:
Highly wear-resistant alloys are important in many engineering and biomedical applications. In this research, a multi-phase quasicrystal-based alloy was developed using a rapid arc-melting technique. The alloy contains three characteristic phases, hard lambda-Al13Fe4, quasicrystal icosahedral (i-phase), and ductile tau-AlCu. The Vickers micro hardness of each was 828, 795, and 552, respectively, with an overall hardness of 334 (HR15T). Due to the co-existence of these three phases, this alloy exhibits both hardness and ductility. As such, the new material has favorable wear and crack resistance. The approaches used in this study are beneficial for the future design and development of this class of quasicrystalline alloys. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Quantization of states and strain-induced transformation of charge-density waves in the quasi-one-dimensional conductor TaS3
Authors:
Zybtsev, SG; Pokrovskii, VY Author Full Names: Zybtsev, S. G.; Pokrovskii, V. Ya.
Source:
PHYSICAL REVIEW B, 94 (11):10.1103/PhysRevB.94.115140 SEP 16 2016
Abstract:
We report studies of low-field conductivity, sigma, of nanosized samples of orthorhombic TaS3 as a function of strain, epsilon. The sigma(epsilon) curves show steplike changes associated with the "quantization" of the wave vector, q, of the charge-density wave. Based on the effect we have revealed the change of the q-vector with strain: its in-chain component (normalized by the reciprocal lattice constant) is found to increase with sample stretch. A similar q(epsilon) dependence results from the analysis of the sigma(epsilon) hysteresis for macroscopic samples. This means that the strain-induced anomalies cannot be explained by the transition of the CDW to fourfold commensurability with the pristine lattice (lock-in transition), as it was supposed earlier. We also discuss the metastable length states and the elastic anomalies in TaS3 in light of the observed q(epsilon) dependence.

Title:
Thermoelastic analysis of a two-dimensional decagonal quasicrystal with a conductive elliptic hole
Authors:
Guo, JH; Yu, J; Xing, YM; Pan, EN; Li, LH Author Full Names: Guo, Junhong; Yu, Jing; Xing, Yongming; Pan, Ernian; Li, Lianhe
Source:
ACTA MECHANICA, 227 (9):2595-2607; 10.1007/s00707-016-1657-7 SEP 2016
Abstract:
A general solution in terms of the Stroh-type formalism for quasicrystals is developed for two-dimensional thermoelastic deformation. The solution is then applied to analyze the deformation of a conductive elliptic hole embedded in the decagonal quasicrystal plane which is under a remotely uniform heat flow. The hoop stresses around the elliptic hole are derived in an exact closed form. When the thermal conductivity inside the hole is neglected, the present results are reduced to the existing solutions in the literature. Some numerical examples are provided to show the effects of the geometrical shape of the hole and the thermal conductivity inside the hole on the hoop stresses. The results show that along the hole the variations of the hoop stress of the phonon field are completely different from those of the phason field. Compared to the corresponding insulated case, consideration of a conductive elliptic hole would lead to very different and interesting thermoelastic behaviors.

Title:
Microstructural changes in an extruded Mg-Zn-Y alloy reinforced by quasicrystalline I-phase by small additions of calcium, manganese and cerium-rich mischmetal
Authors:
Medina, J; Perez, P; Garces, G; Tolnai, D; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Tolnai, D.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS CHARACTERIZATION, 118 186-198; 10.1016/j.matchar.2016.05.019 AUG 2016
Abstract:
The effects of calcium, manganese and cerium-rich mischmetal additions on the microstructure and texture of the extruded Mg-6Zn-1Y (wt.%) alloy have been investigated. The microstructure of the alloys consisted of a magnesium matrix embedding second phase particles aligned along the extrusion direction. The nature and volume fraction of the second phases depended on the alloying element. Thus, Ce-rich mischmetal promoted the formation of T-phase while calcium additions resulted in the formation of a ternary Mg-Zn-Ca compound. Only, manganese additions did not affect the existence of the I-phase present in the ternary alloy. The texture was measured and it was found that calcium addition has a significant effect weakening the extrusion texture. (C) 2016 Elsevier Inc. All rights reserved.

Title:
First Step Towards a Devil's Staircase in Spin-Crossover Materials
Authors:
Trzop, E; Zhang, DP; Pineiro-Lopez, L; Valverde-Munoz, FJ; Munoz, MC; Palatinus, L; Guerin, L; Cailleau, H; Real, JA; Collet, E Author Full Names: Trzop, Elzbieta; Zhang, Daopeng; Pineiro-Lopez, Lucia; Valverde-Munoz, Francisco J.; Carmen Munoz, M.; Palatinus, Lukas; Guerin, Laurent; Cailleau, Herve; Antonio Real, Jose; Collet, Eric
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 55 (30):8675-8679; 10.1002/anie.201602441 JUL 18 2016
Abstract:
The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)(3))(2)](4,4'-bipy)(2)}(n) exhibits a thermal high-spin (HS)<-> low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction gamma(HS). Between the fully HS (gamma(HS)= 1) and LS (gamma(HS)= 0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the gamma(HS). 0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the gamma(HS) approximate to 0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of "Devil's staircase"-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case.

Title:
Atomic-scale mapping of twins and relevant defective structures in Al20Cu2Mn3 decagonal approximant
Authors:
Wang, J; Zhang, B; He, ZB; Wu, B; Ma, XL Author Full Names: Wang, J.; Zhang, B.; He, Z. B.; Wu, B.; Ma, X. L.
Source:
PHILOSOPHICAL MAGAZINE, 96 (23):2457-2467; 10.1080/14786435.2016.1205229 2016
Abstract:
Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

Update: 29-Sep-2016


Title:
Structure and mechanical properties in a powder-processed icosahedral-phase-strengthened aluminum alloy
Authors:
Watson, TJ; Gordillo, MA; Cernatescu, I; Aindow, M Author Full Names: Watson, Thomas J.; Gordillo, Mauricio A.; Cernatescu, Iuliana; Aindow, Mark
Source:
SCRIPTA MATERIALIA, 123 51-54; 10.1016/j.scriptamat.2016.05.037 OCT 2016
Abstract:
Nanocomposite powder particles of aluminum with dispersed icosahedral quasicrystals were produced by gas atomization from an Al-Cr-Mn-Co-Zr alloy. Bulk dispersion -strengthened material was obtained from the powder by blind-die compaction and forging. The material exhibited an attractive combination of room temperature mechanical properties with a dynamic elastic modulus of 90.5 GPa, a tensile yield strength of 690 MPa with 6% elongation to failure, and a high cycle fatigue life of 109 cycles at 207 MPa applied stress. The material also exhibited significant potential for elevated temperature applications with a modulus of 75 GPa and yield strength of 400 MPa at 300 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Strengthening mechanisms in an Al-Fe-Cr-Ti nano-quasicrystalline alloy and composites
Authors:
Pedrazzini, S; Galano, M; Audebert, F; Collins, DM; Hofmann, F; Abbey, B; Korsunsky, AM; Lieblich, M; Escorial, AG; Smith, GDW Author Full Names: Pedrazzini, S.; Galano, M.; Audebert, F.; Collins, D. M.; Hofmann, F.; Abbey, B.; Korsunsky, A. M.; Lieblich, M.; Garcia Escorial, A.; Smith, G. D. W.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 672 175-183; 10.1016/j.msea.2016.07.007 AUG 30 2016
Abstract:
We report a study of the structure-processing-property relationships in a high strength Al93Fe3Cr2Ti2 nano-quasicrystalline alloy and composites containing 10 and 20 vol% ductilising pure Al fibres. The superimposed contributions of several different strengthening mechanisms have been modelled analytically using data obtained from systematic characterisation of the monolithic alloy bar. An observed yield strength of 544 MPa has been substantiated from a combination of solid solution strengthening, work hardening, precipitation hardening and Hall-Petch grain size dependent effects. These materials have been shown by other authors in previous published work to be highly sensitive to the size distribution of particles in the powder from which they are made, and the subsequent thermomechanical processing conditions. The processing condition employed in this study provided micron-sized grains with a strong [111] preferential orientation along the extrusion direction and a bimodal size distribution of the icosahedral nano-quasicrystalline precipitates. Both were deemed to be a significant contributor to the high yield strength observed. The addition of pure Al fibres was found to decrease the yield strength linearly with increasing Al content, and to auginent the ductility of the composites. (C) 2016 The Authors. Published by Elsevier B.V.

Title:
Observation and Structure Determination of an Oxide Quasicrystal Approximant
Authors:
Forster, S; Trautmann, M; Roy, S; Adeagbo, WA; Zollner, EM; Hammer, R; Schumann, FO; Meinel, K; Nayak, SK; Mohseni, K; Hergert, W; Meyerheim, HL; Widdra, W Author Full Names: Foerster, S.; Trautmann, M.; Roy, S.; Adeagbo, W. A.; Zollner, E. M.; Hammer, R.; Schumann, F. O.; Meinel, K.; Nayak, S. K.; Mohseni, K.; Hergert, W.; Meyerheim, H. L.; Widdra, W.
Source:
PHYSICAL REVIEW LETTERS, 117 (9):10.1103/PhysRevLett.117.095501 AUG 24 2016
Abstract:
We report on the first observation of an approximant structure to the recently discovered two-dimensional oxide quasicrystal. Using scanning tunneling microscopy, low-energy electron diffraction, and surface x-ray diffraction in combination with ab initio calculations, the atomic structure and the bonding scheme are determined. The oxide approximant follows a 3(2.)4.3.4 Archimedean tiling. Ti atoms reside at the corners of each tiling element and are threefold coordinated to oxygen atoms. Ba atoms separate the TiO3 clusters, leading to a fundamental edge length of the tiling 6.7 angstrom.

Title:
Polymorphism in Zintl Phases ACd(4)Pn(3): Modulated Structures of NaCd(4)Pn(3) with Pn = P, As
Authors:
Grotz, C; Baumgartner, M; Freitag, KM; Baumer, F; Nilges, T Author Full Names: Grotz, Carolin; Baumgartner, Maximilian; Freitag, Katharina M.; Baumer, Franziska; Nilges, Tom
Source:
INORGANIC CHEMISTRY, 55 (15):7764-7776; 10.1021/acs.inorgchem.6b01233 AUG 1 2016
Abstract:
NaCd4P3 and NaCd4As3 were synthesized via short-way transport using the corresponding elements and CdI2 as mineralizer. At room temperature, the two beta-polymorphs adopt the RbCd4As3 structure type which has been recently reported for alkali metal (A)-d(10) transition metal (T)-pnictides (Pn). The title compounds crystallize rhombohedrally in space group R (3) over barm at room temperature and show reversible phase transitions to incommensurately modulated alpha-polymorphs at lower temperatures. The low-temperature phases are monoclinic and can be described in space group Cm(alpha 0 gamma)s with q vectors of q = (-0.04,0,0.34) for alpha-NaCd4P3 and q(1) = (-0.02,0,0.34) for alpha-NaCd4As3. Thermal properties, Raman spectroscopy, and electronic structures have been determined. Both compounds are Zintl phases with band gaps of 1.05 eV for beta-NaCd4P3 and similar to 0.4 eV for beta-NaCd4As3.

Title:
Crystal structure of modulated martensite and crystallographic correlations between martensite variants of Ni50Mn38Sn12 alloy
Authors:
Lin, CQ; Yan, HL; Zhang, YD; Esling, C; Zhao, X; Zuo, L Author Full Names: Lin, Chunqing; Yan, Haile; Zhang, Yudong; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 1276-1283; 10.1107/S1600576716010372 4 AUG 2016
Abstract:
A comprehensive study on the crystal structure, the microstructure and the crystallographic features of the martensite in an Ni50Mn38Sn12 alloy has been conducted in the present work. The results show that the martensite possesses a 4O modulated structure. The martensite is organized into broad plates in the original austenite grain. The plates contain irregularly shaped colonies with two characteristic microstructural patterns: a classical lamellar pattern and a herringbone pattern. Crystallographic analyses by scanning electron microscopy/electron backscatter diffraction demonstrate that in each colony there are four orientation variants (A, B, C and D) and they form three types of twins (type I, type II and compound twin). The interfaces between corresponding variants are coincident with their twinning plane K1. The interface planes of the compound twin pairs A&D and B&C can have one or two different orientations, which leads to the two microstructural patterns. The corresponding variants in neighboring colonies within one broad plate (intra-plate colonies) possess close orientations, but the type I and the type II twin relationships are interchanged. The variants in neighboring colonies situated in adjacent plates (inter-plate colonies) are type I or type II twin related but with some angular deviations. The plate interface is defined by the {221} plane of the variant pair with largest thickness. The results of the present work provide comprehensive microstructural and crystallographic information on modulated martensite in NiMnSn alloys that is useful for the understanding of their specific functionalities and helpful for further investigation on property optimization of these materials.

Title:
Superior room-temperature ductility of typically brittle quasicrystals at small sizes
Authors:
Zou, Y; Kuczera, P; Sologubenko, A; Sumigawa, T; Kitamura, T; Steurer, W; Spolenak, R Author Full Names: Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph
Source:
NATURE COMMUNICATIONS, 7 10.1038/ncomms12261 AUG 2016
Abstract:
The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of similar to 4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals-dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices.

Title:
Magnetism and superconductivity in a quasi-2D anisotropic system doped with charge carriers
Authors:
Palistrant, ME Author Full Names: Palistrant, M. E.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 123 (1):86-97; 10.1134/S1063776116050198 JUL 2016
Abstract:
The theory of multiband superconducting systems with variable density of charge carriers is analyzed. The possibility of emergence of nonphonon high-temperature superconductivity due to the predominance of electron-electron interband interactions over intraband interactions, as well as due to the fact that the thermodynamic and magnetic properties of multiband systems in the superconducting phase differ qualitatively from those of single-band systems, is indicated. Phase transitions in a quasi-2D anisotropic medium upon a change in the carrier concentration, i.e., a transition from the commensurate to the incommensurate state of the spin density wave, are analyzed. Such a transition is observed when the Umklapp processes in the lattice structure are taken into account. These processes facilitate a deviation of wavevector Q of the spin density wave from 2k (F) , as well as a displacement of the bandgap relative to the Fermi surface. This leads to the generation of free charge carriers and the possibility of superconductivity. It is shown that superconductivity accompanies the magnetism. The conditions for the coexistence of these two phenomena are determined.

Title:
Direct imaging of incommensurate wave pockets in the charge-density-wave state of LaTe2
Authors:
Yang, HX; Cai, Y; Ma, C; Li, J; Long, YJ; Chen, GF; Tian, HF; Wei, LL; Li, JQ Author Full Names: Yang, H. X.; Cai, Y.; Ma, C.; Li, J.; Long, Y. J.; Chen, G. F.; Tian, H. F.; Wei, L. L.; Li, J. Q.
Source:
EPL, 114 (6):10.1209/0295-5075/114/67002 JUN 2016
Abstract:
We herein report the study of the atomic structure for a fully incommensurate CDW in LaTe2 using Cs-corrected scanning transmission electron microscopy (STEM). It is directly revealed for the first time that the atomic displacements adopt an incommensurate wave-pocket structure along each Te chain. This pocket structure has a long periodicity determined by the CDW incommensurability. We can use the sinusoidal waves as the first-order approximation to characterize the atomic motions within the pocket pattern, which can yield atomic displacements in good agreement with the theoretical model commonly used for studying CDW. These facts demonstrate that the incommensurate pocket patterns should be an essential structural nature in the CDW states and play a critical role for developing the mechanism of the CDW transitions. Copyright (C) EPLA, 2016

Update: 22-Sep-2016


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

Update: 15-Sep-2016


Title:
Fatigue properties and microstructure of quasicrystalline AlFeCrTi alloy
Authors:
Chlupova, A; Chlup, Z; Kruml, T Author Full Names: Chlupova, Alice; Chlup, Zdenek; Kruml, Tomas
Source:
INTERNATIONAL JOURNAL OF FATIGUE, 91 251-256; 10.1016/j.ijfatigue.2016.06.007 1 OCT 2016
Abstract:
Aluminium based material having chemical composition of Al93Fe3Ti2Cr2 (at.%) was prepared by hot extrusion of gas atomised powder. Microstructure consisting of aluminium matrix and icosahedral quasicrystalline particles was investigated by scanning and transmission electron microscopy a X-ray spectroscopy. Size, distribution and inner structure of quasicrystalline particles were determined. When quasicrystalline particles having submicron size were present in the microstructure together with fine-grained aluminium matrix, it resulted in enhancement of mechanical properties. Fatigue experiments were performed in load controlled regime with positive mean stress and fatigue life data for this quasicrystalline material were compared with similar results for commercially available aluminium alloys. Longer fatigue life together with higher fatigue strength reaching value of 350 MPa was observed. It is approx. 100 MPa higher than for commercially produced coarse-grained aluminium alloys. Fractographic observations revealed presence of fish eye fracture patterns and validity of weakest link fracture mechanism acting in this type of material under investigation. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Quasi-ordered C-60 molecular films grown on the pseudo-ten-fold (100) surface of the Al13Co4 quasicrystalline approximant
Authors:
Fournee, V; Gaudry, E; Ledieu, J; de Weerd, MC; Diehl, RD Author Full Names: Fournee, V.; Gaudry, E.; Ledieu, J.; de Weerd, M-C; Diehl, R. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (35):10.1088/0953-8984/28/35/355001 SEP 7 2016
Abstract:
The growth of C-60 films on the pseudo-ten-fold (1 0 0) surface of the orthorhombic Al13Co4 quasicrystalline approximant was studied experimentally by scanning tunneling microscopy, low-energy electron diffraction and photoemission spectroscopy. The (1 0 0) surface terminates at bulk-planes presenting local atomic configurations with five-fold symmetry-similar to quasicrystalline surfaces. While the films deposited at room temperature were found disordered, high-temperature growth (up to 693 K) led to quasi-ordered molecular films templated on the substrate rectangular unit mesh. The most probable adsorption sites and geometries were investigated by density functional theory (DFT) calculations. A large range of adsorption energies was determined, influenced by both symmetry and size matching at the molecule-substrate interface. The quasi-ordered structure of the film can be explained by C-60 adsorption at the strongest adsorption sites which are too far apart compared to the distance minimizing the intermolecular interactions, resulting in some disorder in the film structure at a local scale. Valence band photoemission indicates a broadening of the molecular orbitals resulting from hybridization between the substrate and overlayer electronic states. Dosing the film at temperature above 693 K led to molecular damage and formation of carbide thin films possessing no azimuthal order with respect to the substrate.

Title:
Exchange anisotropy as mechanism for spin-stripe formation in frustrated spin chains
Authors:
Pregelj, M; Zaharko, O; Herak, M; Gomilsek, M; Zorko, A; Chapon, LC; Bourdarot, F; Berger, H; Arcon, D Author Full Names: Pregelj, M.; Zaharko, O.; Herak, M.; Gomilsek, M.; Zorko, A.; Chapon, L. C.; Bourdarot, F.; Berger, H.; Arcon, D.
Source:
PHYSICAL REVIEW B, 94 (8):10.1103/PhysRevB.94.081114 AUG 29 2016
Abstract:
We investigate the spin-stripe mechanism responsible for the peculiar nanometer modulation of the incommensurate magnetic order that emerges between the vector-chiral and the spin-density-wave phase in the frustrated zigzag spin-1/2 chain compound beta-TeVO4. A combination of magnetic-torque, neutron-diffraction, and spherical-neutron-polarimetry measurements is employed to determine the complex magnetic structures of all three ordered phases. Based on these results, we develop a simple phenomenological model, which exposes the exchange anisotropy as the key ingredient for the spin-stripe formation in frustrated spin systems.

Title:
Electronic structure and magneto-optical Kerr effect spectra of ferromagnetic shape-memory Ni-Mn-Ga alloys: Experiment and density functional theory calculations
Authors:
Uba, S; Bonda, A; Uba, L; Bekenov, LV; Antonov, VN Author Full Names: Uba, S.; Bonda, A.; Uba, L.; Bekenov, L. V.; Antonov, V. N.
Source:
PHYSICAL REVIEW B, 94 (5):10.1103/PhysRevB.94.054427 AUG 25 2016
Abstract:
In this joint experimental and ab initio study, we focused on the influence of the chemical composition and martensite phase transition on the electronic, magnetic, optical, and magneto-optical properties of the ferromagnetic shape-memory Ni-Mn-Ga alloys. The polar magneto-optical Kerr effect (MOKE) spectra for the polycrystalline sample of the Ni-Mn-Ga alloy of Ni60Mn13Ga27 composition were measured by means of the polarization modulation method over the photon energy range 0.8 <= hv <= 5.8 eV in magnetic field up to 1.5 T. The optical properties (refractive index n and extinction coefficient k) were measured directly by spectroscopic ellipsometry using the rotating analyzer method. To complement experiments, extensive first-principles calculations were made with two different first-principles approaches combining the advantages of a multiple scattering Green function method and a spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic, and MO properties of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases in the stoichiometric and off-stoichiometric compositions. The optical and MOKE properties of Ni-Mn-Ga systems are very sensitive to the deviation from the stoichiometry. It was shown that the ab initio calculations reproduce well experimental spectra and allow us to explain the microscopic origin of the Ni2MnGa optical and magneto-optical response in terms of interband transitions. The band-by-band decomposition of the Ni2MnGa MOKE spectra is presented and the interband transitions responsible for the prominent structures in the spectra are identified.

Title:
Reflection quasilattices and the maximal quasilattice
Authors:
Boyle, L; Steinhardt, PJ Author Full Names: Boyle, Latham; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064107 AUG 25 2016
Abstract:
We introduce the concept of a reflection quasilattice, the quasiperiodic generalization of a Bravais lattice with irreducible reflection symmetry. Among their applications, reflection quasilattices are the reciprocal (i.e., Bragg diffraction) lattices for quasicrystals and quasicrystal tilings, such as Penrose tilings, with irreducible reflection symmetry and discrete scale invariance. In a follow-up paper, we will show that reflection quasilattices can be used to generate tilings in real space with properties analogous to those in Penrose tilings, but with different symmetries and in various dimensions. Here we explain that reflection quasilattices only exist in dimensions two, three, and four, and we prove that there is a unique reflection quasilattice in dimension four: the "maximal reflection quasilattice" in terms of dimensionality and symmetry. Unlike crystallographic Bravais lattices, all reflection quasilattices are invariant under rescaling by certain discrete scale factors. We tabulate the complete set of scale factors for all reflection quasilattices in dimension d > 2, and for all those with quadratic irrational scale factors in d = 2.

Title:
Atomic structure of the i-R-Cd quasicrystals and consequences for magnetism
Authors:
Yamada, T; Takakura, H; Kong, T; Das, P; Jayasekara, WT; Kreyssig, A; Beutier, G; Canfield, PC; de Boissieu, M; Goldman, AI Author Full Names: Yamada, T.; Takakura, H.; Kong, T.; Das, P.; Jayasekara, W. T.; Kreyssig, A.; Beutier, G.; Canfield, P. C.; de Boissieu, M.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.060103 AUG 15 2016
Abstract:
We report on the six-dimensional (6D) structural refinement of three members of the i-R-Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R-Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1-xYxCd6 1/1 approximants that the dilution of themagnetic R ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.

Title:
Three-Dimensional Icosahedral Phase Field Quasicrystal
Authors:
Subramanian, P; Archer, AJ; Knobloch, E; Rucklidge, AM Author Full Names: Subramanian, P.; Archer, A. J.; Knobloch, E.; Rucklidge, A. M.
Source:
PHYSICAL REVIEW LETTERS, 117 (7):10.1103/PhysRevLett.117.075501 AUG 8 2016
Abstract:
We investigate the formation and stability of icosahedral quasicrystalline structures using a dynamic phase field crystal model. Nonlinear interactions between density waves at two length scales stabilize three-dimensional quasicrystals. We determine the phase diagram and parameter values required for the quasicrystal to be the global minimum free energy state. We demonstrate that traits that promote the formation of two-dimensional quasicrystals are extant in three dimensions, and highlight the characteristics required for three-dimensional soft matter quasicrystal formation.

Title:
Modulated crystal structure of InMo4O6
Authors:
Schultz, P; Simon, A; Oeckler, O Author Full Names: Schultz, Peter; Simon, Arndt; Oeckler, Oliver
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 642-649; SI 10.1107/S205252061600874X 4 AUG 2016
Abstract:
The (3 + 1)-dimensional modulated crystal structure of the metal-rich cluster compound InMo4O6 was solved and refined from single-crystal data in the superspace group P4/mbm(00 gamma)00ss [q = 0, 0, 0.1536 (4); a = 9.6664 (9), c = 2.8645 (3) angstrom; R1(all) = 0.046, wR(all) = 0.076]. The crystal structure is closely related to the NaMo4O6 structure type. It is built from rods of Mo-6 clusters condensed via trans edges. These form channels parallel to [001], in which In-6 and In-7 oligomers alternate. Weak diffuse planes parallel to (001)* interconnect the *satellite* *reflections*; they occur due to two-dimensional rod disorder of the In oligomer chains.

Title:
Magnetic anisotropy in the frustrated spin-chain compound beta-TeVO4
Authors:
Weickert, F; Harrison, N; Scott, BL; Jaime, M; Leitmae, A; Heinmaa, I; Stern, R; Janson, O; Berger, H; Rosner, H; Tsirlin, AA Author Full Names: Weickert, F.; Harrison, N.; Scott, B. L.; Jaime, M.; Leitmae, A.; Heinmaa, I.; Stern, R.; Janson, O.; Berger, H.; Rosner, H.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (6):10.1103/PhysRevB.94.064403 AUG 1 2016
Abstract:
Isotropic and anisotropic magnetic behavior of the frustrated spin-chain compound beta-TeVO4 is reported. Three magnetic transitions observed in zero magnetic field are tracked in fields applied along different crystallographic directions using magnetization, heat capacity, and magnetostriction measurements. Qualitatively different temperature-field diagrams are obtained below 10 T for the field applied along a or b and along c, respectively. In contrast, a nearly isotropic high-field phase emerges above 18 T and persists up to the saturation that occurs around 22.5 T. Upon cooling in low fields, the transitions at T-N1 and T-N2 toward the spin-density-wave and stripe phases are of the second order, whereas the transition at T-N3 toward the helical state is of the first order and entails a lattice component. Our microscopic analysis identifies frustrated J(1)-J(2) spin chains with a sizable antiferromagnetic interchain coupling in the bc plane and ferromagnetic couplings along the a direction. The competition between these ferromagnetic interchain couplings and the helical order within the chain underlies the incommensurate order along the a direction, as observed experimentally. While a helical state is triggered by the competition between J(1) and J(2) within the chain, the plane of the helix is not uniquely defined because of competing magnetic anisotropies. Using high-resolution synchrotron diffraction and Te-125 nuclear magnetic resonance, we also demonstrate that the crystal structure of beta-TeVO4 does not change down to 10 K, and the orbital state of V4+ is preserved.

Title:
Internal field emission nature of the fine structure of tunnel spectra in icosahedral quasicrystals
Authors:
Prekul, AF; Schegolikhina, NI Author Full Names: Prekul, A. F.; Schegolikhina, N. I.
Source:
JETP LETTERS, 103 (9):603-606; 10.1134/S0021364016090071 MAY 2016
Abstract:
Calorimetric and tunnel data for the icosahedral phases of the Al-Cu-Fe system have been jointly analyzed. It has been found that the field-dependent part of the tunnel conductance can be represented as the sum of elementary terms similar in nature to thermal Schottky anomalies. As a result, the features of the fine structure of tunnel spectra in the form of zero-bias anomalies, peaks, and humps can be due to the internal field emission and can indicate a wide distribution of two-level electron traps in the electronic structure of quasicrystals. It was previously assumed that these features constitute a direct image of the density of single-electron states of the conduction band.

Update: 9-Sep-2016


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

Update: 1-Sep-2016


Title:
Electron diffraction study of cobalt-rich Hf-Co
Authors:
Li, XZ; Jin, YL; Wang, MY; Shield, JE; Skomski, R; Sellmyer, DJ Author Full Names: Li, X. -Z.; Jin, Y. -L.; Wang, M. -Y.; Shield, J. E.; Skomski, R.; Sellmyer, D. J.
Source:
INTERMETALLICS, 75 54-61; 10.1016/j.intermet.2016.06.002 AUG 2016
Abstract:
Intermetallic compounds having compositions from HfCo4 to HfCo8 were investigated by transmission electron microscopy, selected-area electron diffraction, and energy-dispersive x-ray spectroscopy. A major crystalline phase, closely related to the orthorhombic Zr2Co11 phase in structure, has been observed in the samples with the composition ranges from HfCo6 to HfCo8. The phase, referred to as either Hf2Co11 or HfCo7 phase in the literature, is actually one common phase, having a broad composition range and referred to as mu-phase in the present paper. In addition to the mu-phase, we have found coexisted fcc-Co phase and a minor Hf2Co7 phase. The Hf6Co23 phase has been identified in the HfCo4 and HfCo5 samples. Tilt-series electron diffraction revealed that the mu-phase is a one-dimensional incommensurate structure, which can be described approximately as B-centered orthorhombic with a = 0.47 nm, b = 0.82 nm, and c = 3.86 nm. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy
Authors:
Liu, BB; Ye, F Author Full Names: Liu, Binbin; Ye, Feng
Source:
INTERMETALLICS, 75 31-35; 10.1016/j.intermet.2016.05.010 AUG 2016
Abstract:
Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti40Zr25Cu12Ni3Be20 alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti40Zr25Cu12Ni3Be20 BMG. The glassy state has higher state density at Fermi level than its quasi crystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I -phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasi crystalline state is quite similar to glassy state but far from crystalline state. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
2D materials and van der Waals heterostructures
Authors:
Novoselov, KS; Mishchenko, A; Carvalho, A; Neto, AHC Author Full Names: Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H.
Source:
SCIENCE, 353 (6298):461-+; 10.1126/science.aac9439 JUL 29 2016
Abstract:
The physics of two-dimensional ( 2D) materials and heterostructures based on such crystals has been developing extremely fast. With these new materials, truly 2D physics has begun to appear ( for instance, the absence of long-range order, 2D excitons, commensurate-incommensurate transition, etc.). Novel heterostructure devices-such as tunneling transistors, resonant tunneling diodes, and light-emitting diodes-are also starting to emerge. Composed from individual 2D crystals, such devices use the properties of those materials to create functionalities that are not accessible in other heterostructures. Here we review the properties of novel 2D crystals and examine how their properties are used in new heterostructure devices.

Update: 25-Aug-2016


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

Update: 18-Aug-2016


Title:
Influence of icosahedral short range order on diffusion in liquids: A study on Al-Zn-Cr alloys
Authors:
Kurtuldu, G; Jarry, P; Rappaz, M Author Full Names: Kurtuldu, Guven; Jarry, Philippe; Rappaz, Michel
Source:
ACTA MATERIALIA, 115 423-433; 10.1016/j.actamat.2016.05.051 AUG 15 2016
Abstract:
It has been shown recently that minute additions of Cr in Al-Zn alloys refine the solidified grain structure and induce multiply-twinned grains which can only be explained if the icosahedral symmetry is considered (Kurtuldu et al., 2013). It has been suggested that Cr addition to Al-Zn alloys promotes the formation of icosahedral short-range order (ISRO) in the liquid, leading to the formation of icosahedral quasicrystals (iQC) acting then as a template for the nucleation of the fcc Al-phase. If ISRO exists in liquid Al-Zn-Cr alloys, this should influence diffusion of solute elements in the liquid. The present study focuses on the effect of Cr addition on Zn diffusion in liquid Al-Zn-Cr alloys. The solute diffusion coefficients of Zn and Cr in the liquid were deduced from the solute profiles in the quenched liquid ahead of a planar solid liquid interface. By comparison with the same measurement in Al-Zn alloys, it is shown that Cr indeed slows down the diffusion (and mobility) of Zn atoms, an effect which reinforces the hypothesis of ISRO in Al-Zn liquid induced by Cr. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Structure and microstructure of Ni-Mn-Ga single crystal exhibiting magnetic shape memory effect analysed by high resolution X-ray diffraction
Authors:
Heczko, O; Cejpek, P; Drahokoupil, J; Holy, V Author Full Names: Heczko, Oleg; Cejpek, Petr; Drahokoupil, Jan; Holy, Vaclav
Source:
ACTA MATERIALIA, 115 250-258; 10.1016/j.actamat.2016.05.047 AUG 15 2016
Abstract:
Subtle changes of (micro-) structure can have far-reaching consequences for magnetic shape memory (MSM) effect, also called magnetic induced reorientation (MIR). Detailed X-ray structure analysis using reciprocal mapping of Ni-Mn-Ga single crystals exhibiting MIR at room temperature and prepared in single macrotwin orientation revealed 10M modulated structure. It indicated that the modulation was harmonic, i.e. commensurate, but it also showed that the difference when compared to non commensurate mode or even to adaptive model was very small. The distinction between commensurate and non-commensurate modulation could not be reliably resolved due to large broadening of diffraction peaks. The broadening was caused by small size (less than 100 nm) of structurally coherent L2(1) ordered domains. The small size of these coherent domains is a result of large concentration of antiphase boundaries. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
The 7 x 1 Fermi Surface Reconstruction in a Two-dimensional f-electron Charge Density Wave System: PrTe3
Authors:
Lee, E; Kim, DH; Kim, HW; Denlinger, JD; Kim, H; Kim, J; Kim, K; Min, BI; Min, BH; Kwon, YS; Kang, JS Author Full Names: Lee, Eunsook; Kim, D. H.; Kim, Hyun Woo; Denlinger, J. D.; Kim, Heejung; Kim, Junwon; Kim, Kyoo; Min, B. I.; Min, B. H.; Kwon, Y. S.; Kang, J. -S.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep30318 JUL 25 2016
Abstract:
The electronic structure of a charge density wave (CDW) system PrTe3 and its modulated structure in the CDW phase have been investigated by employing ARPES, XAS, Pr 4 f RPES, and first-principles band structure calculation. Pr ions are found to be nearly trivalent, supporting the CDW instability in the metallic Te sheets through partial filling. Finite Pr 4 f spectral weight is observed near the Fermi level, suggesting the non-negligible Pr 4 f contribution to the CDW formation through the Pr 4 f-Te 5p hybridization. The two-fold symmetric features in the measured Fermi surface (FS) of PrTe3 are explained by the calculated FS for the assumed 7 x 1 CDW supercell formation in Te sheets. The shadow bands and the corresponding very weak FSs are observed, which originate from both the band folding due to the 3D interaction of Te sheets with neighboring Pr-Te layers and that due to the CDW-induced FS reconstruction. The straight vertical FSs are observed along k(z), demonstrating the nearly 2D character for the near-E-F states. The observed linear dichroism reveals the in-plane orbital character of the near-E-F Te 5p states.

Update: 11-Aug-2016


Title:
Structure and multiferroic properties of multi-doped Bi1-xErxFe0.96Mn0.02Co0.02O3 thin films
Authors:
Zheng, YJ; Tan, GQ; Xia, A; Ren, HJ Author Full Names: Zheng, Yujuan; Tan, Guoqiang; Xia, Ao; Ren, Huijun
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 684 438-444; 10.1016/j.jallcom.2016.05.193 NOV 5 2016
Abstract:
Multiferroic Bi1-xErxFe0.96Mn0.02Co0.02O3 (BExFMCO, x = 0.08-0.12) thin films have been successfully prepared on fluorine doped tin oxide (FTO) substrates by the chemical solution deposition method. The structural characteristics of the thin films were investigated by X-ray diffraction (XRD), Rietveld refinement and Raman spectra, indicating a structural transition from typical rhombohedral-R3c:H (BFO) to two-phase coexistence of triclinic-P1 and orthorhombic-Pbmn (BE0.12FMCO). XPS analyses suggest there is the coexistence of Fe2+ and Fe3+ ions in all the thin films. The multi-doping exhibits small effects on oxygen vacancies due to the complex effects of doping ions. Intensive super exchange between Fe2+ and Fe3+ and the decreased leakage current densities are observed in BE0.1FMCO thin films. Multi-doped thin films show the superior ferroelectric properties with a giant remanent polarization (the BE0.1FMCO thin film with P-r similar to 104.43 mu C/cm(2)). The enhanced ferroelectric properties of BExFMCO thin films can be mainly attributed to the structural transition via doping. The highest magnetization values of M-s similar to 9.78 emu/cm(3) and M-r similar to 2.1 emu/cm(3) are obtained in the BE0.1FMCO thin films, which can be attributed to the super exchange between Fe2+ and Fe3+ ions and the altered space modulated spin structure due to structural transition. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Chemical Pressure-Driven Incommensurability in CaPd5: Clues to High-Pressure Chemistry Offered by Complex Intermetallics
Authors:
Kilduff, BJ; Fredrickson, DC Author Full Names: Kilduff, Brandon J.; Fredrickson, Daniel C.
Source:
INORGANIC CHEMISTRY, 55 (13):6781-6793; 10.1021/acs.inorgchem.6b01124 JUL 4 2016
Abstract:
While composition and pressure are generally considered orthogonal parameters in the synthesis and optimization of solid state materials, their distinctness is blurred by the concept of chemical pressure (CP): microscopic pressure arising from lattice constraints rather than an externally applied force. In this article, we describe the first cycle of an iterative theoretical/experimental investigation into this connection. We begin by theoretically probing the ability of physical pressure to promote structural transitions in CaCu5-type phases that are driven by CP in other systems. Our results point to the instability of the reported CaCu5-type CaPd5 phase to such a transition even at ambient pressure, suggesting that new structural chemistry should arise at only modest pressures. We thus attempted to synthesize CaPd5 as a starting material for high-pressure experiments. However, rather than obtaining the expected CaCu5-type phase, we encountered crystals of an incommensurately modulated variant CaCu5+q/2, whose composition is related to its satellite spacing, q = qb(basic)* with q approximate to 0.44. Its structure was solved and refined in the (3 + 1)D superspace group Cmcm(0 beta 0)s00, revealing CaCu5-type slabs separated by distorted Pd hexagonal nets with an incommensurate periodicity. DFT-CP analysis on a commensurate model for CaPd5+q/2 indicates that the new Pd nets serve to relieve intense negative CPs that the Ca atoms would experience in a CaCu5-type CaPd5 phase but suffer from a desire to contract relative to the rest of the structure. In this way, both the Pd layer substitution and incommensurability in CaPd5+q/2 are anticipated by the CP schemes of simpler model systems, with CP quadrupoles tracing the paths of the favorable atomic motions. This picture offers predictions for how elemental substitution and physical pressure should affect these structural motifs, which could be applicable to the magnetic phase Zr2Co11 whose previously proposed structures show close parallels to CaPd5+q/2.

Update: 4-Aug-2016


Title:
Distributed Hybridization Model for Quantum Critical Behavior in Magnetic Quasicrystals
Authors:
Otsuki, J; Kusunose, H Author Full Names: Otsuki, Junya; Kusunose, Hiroaki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073712 JUL 15 2016
Abstract:
A quantum critical behavior of the magnetic susceptibility was observed in a quasicrystal containing ytterbium. At the same time, a mixed-valence feature of Yb ions was reported, which appears to be incompatible with the magnetic instability. We derive the magnetic susceptibility by expressing the quasiperiodicity as the distributed hybridization strength between Yb 4f and conduction electrons. Assuming a wide distribution of the hybridization strength, the most f electrons behave as renormalized paramagnetic states in the Kondo or mixed-valence regime, but a small number of f moments remain unscreened. As a result, the bulk magnetic susceptibility exhibits a nontrivial power-law-like behavior, while the average f-electron occupation is that of mixed-valence systems. This model thus resolves two contradictory properties of Yb quasicrystals.

Title:
Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2
Authors:
Makino, K; Okuyama, D; Avdeev, M; Sato, TJ Author Full Names: Makino, Koya; Okuyama, Daisuke; Avdeev, Maxim; Sato, Taku J.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (7):10.7566/JPSJ.85.073705 JUL 15 2016
Abstract:
Magnetic susceptibility and neutron powder diffraction experiments have been performed on the noncentrosymmetric ternary compound Pr5Ru3Al2. The previously reported ferromagnetic transition at 24K was not detected in our improved-quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at T-c similar or equal to 3.8 K. The neutron powder diffraction experiment further indicates that an incommensurate magnetic structure is established below T-c with the magnetic modulation vector q similar or equal to (0.066, 0.066, 0.066) (r.l.u.). A candidate for the magnetic structure is proposed using representation analysis.

Title:
Local growth of icosahedral quasicrystalline tilings
Authors:
Hann, CT; Socolar, JES; Steinhardt, PJ Author Full Names: Hann, Connor T.; Socolar, Joshua E. S.; Steinhardt, Paul J.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014113 JUL 14 2016
Abstract:
Icosahedral quasicrystals (IQCs) with extremely high degrees of translational order have been produced in the laboratory and found in naturally occurring minerals, yet questions remain about how IQCs form. In particular, the fundamental question of how locally determined additions to a growing cluster can lead to the intricate long-range correlations in IQCs remains open. In answer to this question, we have developed an algorithm that is capable of producing a perfectly ordered IQC yet relies exclusively on local rules for sequential, face-to-face addition of tiles to a cluster. When the algorithm is seeded with a special type of cluster containing a defect, we find that growth is forced to infinity with high probability and that the resultant IQC has a vanishing density of defects. The geometric features underlying this algorithm can inform analyses of experimental systems and numerical models that generate highly ordered quasicrystals.

Title:
Unique magnetic structure of YbCo2Si2
Authors:
Mufti, N; Kaneko, K; Hoser, A; Gutmann, M; Geibel, C; Krellner, C; Stockert, O Author Full Names: Mufti, N.; Kaneko, K.; Hoser, A.; Gutmann, M.; Geibel, C.; Krellner, C.; Stockert, O.
Source:
PHYSICAL REVIEW B, 94 (4):10.1103/PhysRevB.94.045116 JUL 14 2016
Abstract:
We report on the results of powder and single-crystal neutron diffraction to investigate the magnetic order in YbCo2Si2 below the Neel temperature T-N = 1.7 K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector k(1) = (0.25 0.25 1) is found, while the intermediate phase (T > 0.9 K) is characterized by an incommensurate magnetic structure with k(2) = (0.25 0.086 1). The magnetic structure in YbCo2Si2 is in marked contrast to all other known RCo2Si2 compounds (R = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.

Title:
Reinterpretation of the zero-temperature conductivity in icosahedral AlPdRe
Authors:
Rapp, O Author Full Names: Rapp, O.
Source:
PHYSICAL REVIEW B, 94 (2):10.1103/PhysRevB.94.024202 JUL 13 2016
Abstract:
The zero-temperature conductivity sigma(0) of icosahedral (i)-AlPdRe has been found to be simply related to the resistance ratio R = rho(4.2 K)/rho(295 K) by a power law, sigma(0) similar to R (1.74), over four orders of magnitude in sigma(0). This relation includes metallic single grain samples, and polygrain samples of different morphologies which are metallic for small R values, and insulatinglike at large R. Electronic transport properties of single grain i-AlPdRe samples are thus found to be on common ground with polygrain i-AlPdRe. The relation between R and sigma(0) can be qualitatively understood from published band-structure calculations on quasicrystalline approximants.

Title:
Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8
Authors:
Ranjith, KM; Nath, R; Majumder, M; Kasinathan, D; Skoulatos, M; Keller, L; Skourski, Y; Baenitz, M; Tsirlin, AA Author Full Names: Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014415 JUL 13 2016
Abstract:
We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at T-N1 similar or equal to 18 K and T-N2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below T-N2. The ordered moment of 1.8 mu(B) at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between T-N2 and T-N1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01 (1) over bar] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+.

Title:
Static magnetic order on the metallic triangular lattice in CrSe2 detected by mu+SR
Authors:
Sugiyama, J; Nozaki, H; Umegaki, I; Uyama, T; Miwa, K; Brewer, JH; Kobayashi, S; Michioka, C; Ueda, H; Yoshimura, K Author Full Names: Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Uyama, Takeshi; Miwa, Kazutoshi; Brewer, Jess H.; Kobayashi, Shintaro; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi
Source:
PHYSICAL REVIEW B, 94 (1):10.1103/PhysRevB.94.014408 JUL 7 2016
Abstract:
The magnetic nature of a metallic two-dimensional triangular compound, CrSe2, has been investigated by muon spin rotation and relaxation (mu+SR) measurements using both powder and single crystal samples. It is found that CrSe2 enters into a static antiferromagnetic (AF) ordered state below 157 K (=T-N). Furthermore, the AF state is slightly changed below around 20 K (=T-N2). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical 120 degrees AF are clearly eliminated for the ground state of CrSe2. The most probable one is an incommensurate spin density wave order.

Title:
Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal
Authors:
Yamada, T; Takakura, H; Euchner, H; Gomez, CP; Bosak, A; Fertey, P; de Boissieu, M Author Full Names: Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Gomez, Cesar Pay; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc
Source:
IUCRJ, 3 247-258; 10.1107/S2052252516007041 4 JUL 2016
Abstract:
The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.

Title:
Mysteries of icosahedral quasicrystals: how are the atoms arranged?
Authors:
Ishimasa, T Author Full Names: Ishimasa, Tsutomu
Source:
IUCRJ, 3 230-231; 10.1107/S2052252516009842 4 JUL 2016

Update: 28-Jul-2016


Title:
Defects forming the optical absorption edge in TlGaSe2 layered crystal
Authors:
Seyidov, MY; Suleymanov, RA; Sale, Y Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Sale, Yasin
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 96-97 17-21; 10.1016/j.jpcs.2016.04.009 SEP-OCT 2016
Abstract:
In this work, we present the results of optical experiments designed to investigate the changes in optical absorption spectra of TlGaSe2 ferroelectric-semiconductor with incommensurate (INC) phase in experimental conditions where crystal is kept several hours within the INC-phase (the regime of so called "memory" effect). The fundamental absorption of TlGaSe2, experimentally investigated by optical transmission measurements performed in the temperature range 15-300 K. An extraordinary modification of the optical absorption edge in the range of Urbach's tail is discovered as a result of the annealing within the INC-phase. The role of native defects forming the band edge in the observed phenomena in TlGaSe2 is discussed. (C) 2016 Elsevier Ltd. All rights reserved.

Title:
Phase transitions and magnetic structures in MnW1-xMoxO4 compounds (x <= 0.2)
Authors:
Hardy, V; Payen, C; Damay, F; Meddar, L; Josse, M; Andre, G Author Full Names: Hardy, Vincent; Payen, Christophe; Damay, Francoise; Meddar, Lynda; Josse, Michael; Andre, Gilles
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (33):10.1088/0953-8984/28/33/336003 AUG 24 2016
Abstract:
Temperature-dependent specific heat, magnetization and neutron diffraction data have been collected in zero magnetic field for polycrystalline samples of MnW1-xMoxO4 (x <= 0.2) solid solution whose end-member MnWO4 exhibits a magnetoelectric multiferroic phase (AF2 phase) between T-1 approximate to 8 K and T-2 = 12.5 K. In MnW1-xMoxO4, diamagnetic W6+ are replaced with diamagnetic Mo6+ cations and magnetic couplings among Mn2+ (3d(5), S = 5/2) ions are modified due the doping-induced tuning of the orbital hybridization between Mn 3d and O 2p states. It was observed that magnetic phase transition temperatures which are associated with the second-order AF3-to-paramagnetic (T-N) and AF2-to-AF3 (T-2) transitions in pure MnWO4 slightly increase with the Mo content x. Magnetic specific heat data also indicate that the first-order AF1-to-AF2 phase transition at T-1 survives a weak doping x <= 0.05. This latter phase transition becomes invisible above the base temperature 2 K for higher level of doping x >= 0.10. Neutron powder diffraction datasets collected above 1.5 K for a sample of MnW0.8Mo0.2O4 were analyzed using the Rietveld method. The magnetic structure below approximate to 14 K is a helical incommensurate spin order with a temperature-independent propagation vector k = (-0.217(6), 0.5, 0.466(4)). This cycloidal magnetic structure is similar to the polar AF2 structure observed in MnWO4. The AF1 up-up-down-down collinear spin arrangement observed in MnWO4 is absent in our MnW0.8Mo0.2O4 sample.

Title:
Shock synthesis of quasicrystals with implications for their origin in asteroid collisions
Authors:
Asimow, PD; Lin, C; Bindi, L; Ma, C; Tschauner, O; Hollister, LS; Steinhardt, PJ Author Full Names: Asimow, Paul D.; Lin, Chaney; Bindi, Luca; Ma, Chi; Tschauner, Oliver; Hollister, Lincoln S.; Steinhardt, Paul J.
Source:
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 113 (26):7077-7081; 10.1073/pnas.1600321113 JUN 28 2016
Abstract:
We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe0.252+)(2)SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. The compositional range of the icosahedral phase is Al68-73Fe11-16Cu10-12Cr1-4Ni1-2 and extends toward higher Al/(Cu+Fe) and Fe/Cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the Al-Cu-Fe system. The shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors.

Title:
Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals
Authors:
Liang, XG; Hamid, I; Duan, HM Author Full Names: Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming
Source:
AIP ADVANCES, 6 (6):10.1063/1.4954741 JUN 2016
Abstract:
The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. Thedifferences of the sequences can be explained by analyzing the parameters of the Gupta-type manybody inter-atomic potentials. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Update: 22-Jul-2016


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

Update: 14-Jul-2016


Title:
Microstructural control and hardening response of Mg-6Zn-0.5Er-0.5Ca alloy
Authors:
Zheng, XB; Liu, K; Wang, ZH; Li, SB; Du, WB Author Full Names: Zheng, Xiao-Bing; Liu, Ke; Wang, Zhao-Hui; Li, Shu-Bo; Du, Wen-Bo
Source:
RARE METALS, 35 (7):526-531; 10.1007/s12598-015-0462-0 JUL 2016
Abstract:
The effects of heat treatment on microstructures and hardening response of Mg-6Zn-0.5Er-0.5Ca (wt%) alloy were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM) in this paper. The results show that the Mg-6Zn-0.5Er-0.5Ca alloy contains Mg3Zn6Er1 quasicrystalline phase (I-phase) and Ca2Mg6Zn3 phase under as-cast condition. Most of the Ca2Mg6Zn3 phases and I-phases dissolve into matrix during heat treatment at 475 degrees C for 5 h. After the as-solution alloy was aged at 175 degrees C for 36 h, a large amount of MgZn2 precipitate with several nanometers precipitate. It is suggested that the trace addition of Ca results in refining the size of the precipitate, and the presence of the nanoscale MgZn2 phase is the main factor to improve the peak-aged hardness greatly to 87 HV, which increases about 40 % compared with that of as-cast alloy.

Title:
Atomistic simulation of frictional anisotropy on quasicrystal approximant surfaces
Authors:
Ye, ZJ; Martini, A; Thiel, P; Lovelady, HH; McLaughlin, K; Rabson, DA Author Full Names: Ye, Zhijiang; Martini, Ashlie; Thiel, Patricia; Lovelady, Heather H.; McLaughlin, Keith; Rabson, David A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235438 JUN 23 2016
Abstract:
J. Y. Park et al. [Science 309, 1354 (2005)] have reported eight times greater atomic-scale friction in the periodic than in the quasiperiodic direction on the twofold face of a decagonal Al-Ni-Co quasicrystal. We present results of molecular-dynamics simulations intended to elucidate mechanisms behind this giant frictional anisotropy. Simulations of a bare atomic-force-microscope tip on several model substrates and under a variety of conditions failed to reproduce experimental results. On the other hand, including the experimental passivation of the tip with chains of hexadecane thiol, we reproduce qualitatively the experimental anisotropy in friction, finding evidence for entrainment of the organic chains in surface furrows parallel to the periodic direction.

Title:
Magnetic correlations in a periodic Anderson model with nonuniform conduction electron coordination
Authors:
Hartman, N; Chiu, WT; Scalettar, RT Author Full Names: Hartman, N.; Chiu, W. -T.; Scalettar, R. T.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235143 JUN 21 2016
Abstract:
The periodic Anderson model is widely studied to understand strong correlation physics and especially the competition of antiferromagnetism and singlet formation. In this paper we extend quantum Monte Carlo work on lattices with uniform numbers of neighbors to geometries in which the conduction electron sites can have variable coordination z. This situation is relevant both to recently discovered magnetic quasicrystals and also to magnetism in doped heavy fermion systems. Our key results are the presence of antiferromagnetic order at weak interorbital hybridization Vfd, and a delay in singlet formation to larger values of Vfd on sites with larger z. The staggered magnetization tends to be larger on sites with higher z, providing insight into the behavior to be expected in crown, dice, and CaVO lattices.

Title:
Weak crystallization theory of metallic alloys
Authors:
Martin, I; Gopalakrishnan, S; Demler, EA Author Full Names: Martin, Ivar; Gopalakrishnan, Sarang; Demler, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (23):10.1103/PhysRevB.93.235140 JUN 20 2016
Abstract:
Crystallization is one of the most familiar, but hardest to analyze, phase transitions. The principal reason is that crystallization typically occurs via a strongly first-order phase transition, and thus rigorous treatment would require comparing energies of an infinite number of possible crystalline states with the energy of liquid. A great simplification occurs when crystallization transition happens to be weakly first order. In this case, weak crystallization theory, based on unbiased Ginzburg-Landau expansion, can be applied. Even beyond its strict range of validity, it has been a useful qualitative tool for understanding crystallization. In its standard form, however, weak crystallization theory cannot explain the existence of a majority of observed crystalline and quasicrystalline states. Here we extend the weak crystallization theory to the case of metallic alloys. We identify a singular effect of itinerant electrons on the form of weak crystallization free energy. It is geometric in nature, generating strong dependence of free energy on the angles between ordering wave vectors of ionic density. That leads to stabilization of fcc, rhombohedral, and icosahedral quasicrystalline (iQC) phases, which are absent in the generic theory with only local interactions. As an application, we find the condition for stability of iQC that is consistent with the Hume-Rothery rules known empirically for the majority of stable iQC; namely, the length of the primary Bragg-peak wave vector is approximately equal to the diameter of the Fermi sphere.

Title:
Effect of MWNTs-addition on cathodic performance of Ti-V-Ni composites for Ni-MH batteries
Authors:
Lin, J; Sun, LS; Liang, F; Wu, YM; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Sun, Lianshan; Liang, Fei; Wu, Yaoming; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (22):9471-9475; 10.1016/j.ijhydene.2016.03.211 JUN 15 2016
Abstract:
Composites of Ti1.4V0.6Ni alloy and various amounts of multiwalled carbon nanotubes (MWNTs) have been synthesized by high energy mechanical ball-milling method. The composites mainly contain icosahedral quasicrystal and TiNi-type phases. In contrast to Ti1.4V0.6Ni, all milled composites have excellent activation properties activated at the first charge/discharge cycle, together with excellent rate discharge abilities. The composites are able to deliver outstanding maximum discharge capacities of 295.5 mAh g(-1) enhanced by 68.2 mAh g(-1) in comparison to Ti1.4V0.6Ni alloy, and good cycling stabilities with capacity retention of more than 40% after 100 charge/discharge cycles higher than Ti1.4V0.6Ni alloy. Experimental and theoretical investigations suggest that the unusual electrochemical performance of this composite is depended on the copacetic electrocatalytic activity of MWNTs addition and the enhancement of hydrogen diffusion progress. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Fundamental solutions and analysis of three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Fan, CY; Li, Y; Xu, GT; Zhao, MH Author Full Names: Fan, CuiYing; Li, Yuan; Xu, GuangTao; Zhao, MingHao
Source:
MECHANICS RESEARCH COMMUNICATIONS, 74 39-44; 10.1016/j.mechrescom.2016.03.009 JUN 2016
Abstract:
In this study, three-dimensional cracks in one-dimensional hexagonal piezoelectric quasicrystals are investigated. Based on the general solutions and Hankel transform, the fundamental solutions for unit point extended displacement discontinuities (including the phonon and phason displacement discontinuities and the electric potential discontinuity) are derived. The extended displacement discontinuity boundary integral equations for a planar crack of arbitrary shape in the periodic plane of one-dimensional hexagonal piezoelectric quasicrystals are established in terms of the extended displacement discontinuities. Using the boundary integral equation method, the singularities of near-crack border fields are obtained and the stress and electric displacement intensity factors are derived. (C) 2016 Elsevier Ltd. All rights reserved.

Update: 7-Jul-2016


Title:
Characterization of SrBiMn2-xTixO6 perovskites: Local ordering influence on the dielectric and magnetic response
Authors:
Alonso-Dominguez, D; Alvarez-Serrano, I; Lopez, ML; Cuello, GJ; Asensio, E; Garcia-Hernandez, M; Veiga, ML; Pico, C Author Full Names: Alonso-Dominguez, D.; Alvarez-Serrano, I.; Lopez, M. L.; Cuello, Gabriel J.; Asensio, Eloy; Garcia-Hernandez, Mar; Veiga, M. L.; Pico, C.
Source:
CERAMICS INTERNATIONAL, 42 (10):11889-11900; 10.1016/j.ceramint.2016.04.111 AUG 1 2016
Abstract:
Two new phases in the (SrTiO3)-(BiMnO3) perovskite type system were studied. These SrBiMn2-xTixO6 (x=0.5 and 0.75) ceramics were prepared by the liquid-mix method as polycrystalline powders. They were characterized by neutron diffraction (ND), electrical and magnetic measurements and these results were analysed in connection with the x=0.25 phase, previously described by us. Their crystal structures were fitted in the tetragonal 14/mcm space group, with additional superstructure reflections suggesting local ordering. Electron microscopy results revealed these ordering effects are actually present concerning both perovskite sublattices. The electrical response pointed to a mechanism consisting in variable range hopping of polarons. A relaxor ferroelectric behaviour dependent on the pellets thickness was found with T-m in the 140-240 K range. The magnetic structures imply an incommensurable modulation of the magnetic moments along the c or a directions, depending on the substitution degree x. A cluster picture in terms of chemically different nanoregions responsible of the macroscopic response is discussed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Title:
Quasicrystallinity expressed in two-dimensional coordination networks
Authors:
Urgel, JI; Ecija, D; Lyu, GQ; Zhang, R; Palma, CA; Auwarter, W; Lin, NA; Barth, JV Author Full Names: Urgel, Jose I.; Ecija, David; Lyu, Guoqing; Zhang, Ran; Palma, Carlos-Andres; Auwaerter, Willi; Lin, Nian; Barth, Johannes V.
Source:
NATURE CHEMISTRY, 8 (7):657-662; 10.1038/nchem.2507 JUL 2016
Abstract:
The recognition of quasicrystals, which exhibit long-range order but lack translational symmetry, represented both the introduction of a new class of materials and a transformative breakthrough in crystallography. Concomitant with the exploration of quasicrystallinity, metal-organic architectures emerged as promising and versatile systems with significant application potential. Their building principles have been studied extensively and become manifest in a multitude of intricate amorphous and crystalline phases. To date, however, indications for quasicrystalline order have been elusive in metal-organic coordination networks (MOCNs). Here we employ rare-earth-directed assembly to construct a two-dimensional tiling with quasicrystalline characteristics at a well-defined gold substrate. By careful stoichiometry control over europium centres and functional linkers, we produced a porous network, including the simultaneous expression of four-fold, five-fold and six-fold vertices. The pertaining features were directly inspected by scanning tunnelling microscopy, and the molecule-europium reticulation was recognized as square-triangle tessellation with dodecagonal symmetry. Our findings introduce quasicrystallinity in surface-confined MOCNs with a nanoporous structure and anticipate functionalities that arise from quasicrystalline ordering of the coordinative spheres.

Title:
Microstructure and mechanical properties of aluminium matrix composites reinforced by Al62Cu25.5Fe12.5 melt spun ribbon
Authors:
Litynska-Dobrzynska, L; Mitka, M; Goral, A; Stan-Glowinska, K; Dutkiewicz, J Author Full Names: Litynska-Dobrzynska, Lidia; Mitka, Mikolaj; Goral, Anna; Stan-Glowinska, Katarzyna; Dutkiewicz, Jan
Source:
MATERIALS CHARACTERIZATION, 117 127-133; 10.1016/j.matchar.2016.04.025 JUL 2016
Abstract:
Aluminium matrix composites containing 15, 30 and 50 vol.% of pulverized Al62Cu25.5Fe12.5 (in at.%) melt spun ribbons have been prepared by a vacuum hot pressing (T = 673 K, P = 600 MPa). The microstructure of the initial ribbon and the composites was investigated using X-ray, scanning and transmission electron microscopy. In the as-spun ribbon the quasicrystalline icosahedral phase (i-phase) coexisted with the cubic copper rich beta-Al(Cu, Fe) intermetallic compound. The phase composition of Al-Cu-Fe particles changed after consolidation process and the i-phase transformed partially to the omega-Al70Cu20Fe10 phase. Additionally, the Theta-Al2Cu phase formed at the alpha(Al)/Al-Cu-Fe particle interfaces. With an increase in volume fraction of the reinforcement the hardness of the composites increased up to HV = 180 for the highest amount of added particles. The ultimate compression strength of the same sample reached the value of 545 MPa. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Exploring metamagnetism of single crystalline EuNiGe3 by neutron scattering
Authors:
Fabreges, X; Gukasov, A; Bonville, P; Maurya, A; Thamizhavel, A; Dhar, SK Author Full Names: Fabreges, X.; Gukasov, A.; Bonville, P.; Maurya, A.; Thamizhavel, A.; Dhar, S. K.
Source:
PHYSICAL REVIEW B, 93 (21):10.1103/PhysRevB.93.214414 JUN 15 2016
Abstract:
We present here a neutron diffraction study, both in zero field and as a function of magnetic field, of the magnetic structure of the tetragonal intermetallic EuNiGe3 on a single crystalline sample. This material is known to undergo a cascade of transitions, first at 13.2 K towards an incommensurate modulated magnetic structure, then at 10.5 K to an antiferromagnetic structure. We show here that the low-temperature phase presents a spiral moment arrangement with wave vector k = (1/4, delta, 0). For a magnetic field applied along the tetragonal c axis, the square root of the scattering intensity of the (1 0 1) reflection matches very well the complex metamagnetic behavior of the magnetization along c measured previously. For the magnetic field applied along the b axis, two magnetic transitions are observed below the transition to a fully polarized state.

Title:
Commensurate and incommensurate spin-density waves in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
AIP ADVANCES, 6 (5):10.1063/1.4942549 MAY 2016
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point (QCP) is obtained as the Neel temperature tends to zero. The transfer of pairs of electrons between the pockets can lead to a superconducting dome above the QCP (if Q is commensurate with the lattice, i.e. equal to G/2). If the vector Q is not commensurate with the lattice there are eight possible phases: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with modulated order parameter of the FFLO type. The renormalization group equations are studied and numerically integrated. A re-entrant SDW phase (either commensurate or incommensurate) is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Update: 30-Jun-2016


Title:
The Z '=12 superstructure of A-cobalt(III) sepulchrate trinitrate governed by C-H center dot center dot center dot O hydrogen bonds
Authors:
Dey, S; Schonleber, A; Mondal, S; Prathapa, SJ; van Smaalen, S; Larsen, FK Author Full Names: Dey, Somnath; Schoenleber, Andreas; Mondal, Swastik; Prathapa, Siriyara Jagannatha; van Smaalen, Sander; Larsen, Finn Krebs
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 372-380; 10.1107/S2052520616005503 3 JUN 2016
Abstract:
A-Cobalt(III) sepulchrate trinitrate crystallizes in P6(3)22 with Z = 2 (Z' = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groups A and B. Coordinated by six sepulchrate molecules, highly disordered nitrate groups C are accommodated between the slabs. Here we report the fully ordered, low temperature crystal structure of Co(sep)(NO3)(3). It is found to be a high-Z' structure with Z' = 12 of the 12-fold 6a(h) x root 3b(h) x c(h) superstructure with monoclinic symmetry P2(1) (c unique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate group C, the latter assuming different orientations for each of the Z' = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groups A and B vary less than the orientations of the nitrate group C do. Molecular packing in the superstructure is found to be determined by short C-H center dot center dot center dot H-C contacts, with H center dot center dot center dot H distances of 2.2-2.3 angstrom, and by short C H center dot center dot center dot O contacts, with H center dot center dot center dot O distances down to 2.2 angstrom. These contacts presumably represent weak C-H center dot center dot center dot O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N-H center dot center dot center dot O hydrogen bonds with observed H center dot center dot center dot O distances of 2.4-2.6 angstrom.

Title:
New insight on bismuth cuprates with incommensurate modulated structures
Authors:
Mironov, AV; Petricek, V; Khasanova, NR; Antipov, EV Author Full Names: Mironov, Andrei V.; Petricek, Vaclav; Khasanova, Nellie R.; Antipov, Evgeny V.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 395-403; 10.1107/S2052520616005643 3 JUN 2016
Abstract:
The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6+delta (2201) phase [a = 5.3874 (5), b = 5.3869 (4), c = 24.579 (3) angstrom; beta = 90.01 (1)degrees, q = 0.2105 (3)a* + 0.538 (4)c*, Z = 4, the (3 + 1) -dimensional monoclinic A2/a(alpha 0 gamma) group] has been refined with R = 0.041, wR = 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite with a(2) = 2.437, b(2) = 5.387, c(2) = 24.614, beta(2) = 93.06, q(2) = 0.4524a(2)* -0.243c(2)* and the (3 + 1)-dimensional A2/m(alpha 0 gamma)0s group for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra 0 atom is determined in the bridging position shifted similar to 0.6 angstrom from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuth U-11 atomic displacement parameter in similar to 20% of the unit cells (t = -0.05-0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18 (1) corresponds to the results of chemical analysis.

Update: 23-Jun-2016


Title:
Thermo-mechanical study of bulk glass forming Zr-Cu-Ni-Al alloys
Authors:
Spassov, T; Gyurov, S; Stefanov, G; Rangelov, A; Drenchev, L; Russew, K Author Full Names: Spassov, Tony; Gyurov, Stoyko; Stefanov, Georgi; Rangelov, Antoan; Drenchev, Lyudmil; Russew, Krassimir
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 443 103-107; 10.1016/j.jnoncrysol.2016.04.006 JUL 1 2016
Abstract:
The thermal stability and viscous flow behavior of bulk glass forming Zr(68)Cu(13)Ni(11.5)A(17.5) and Zr69Cu12.5Ni11Al7.5 alloys are studied. The viscosity experimental results are interpreted based on the free volume model (FVM). The values of the obtained model parameters are used to estimate the glass forming ability (GFA) in terms of Angell parameter, and the fracture strength of the alloys based on its correlation with the glass transition temperature (T-g). The viscosity data are compared with DSC measurements. The two glasses, having similar composition, revealed comparable T-g, but one of them (Zr68Cu13Ni11.5Al7.5) showed substantially lower crystallization temperature due to quasicrystals formation. Higher GFA was obtained for Zr69Cu12.5Ni11Al7.5 alloy. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Origin of Quantum Criticality in Yb-Al-Au Approximant Crystal and Quasicrystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063703 JUN 15 2016
Abstract:
To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb15Al34Au51, the approximant crystal Yb14Al35Au51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits chi similar to T-0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size.

Title:
Pressure-Driven Quantum Criticality and T/H Scaling in the Icosahedral Au-Al-Yb Approximant
Authors:
Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.063706 JUN 15 2016
Abstract:
We report on ac magnetic susceptibility measurements under pressure of the Au-Al-Yb alloy, a crystalline approximant to the icosahedral quasicrystal that shows unconventional quantum criticality. In describing the susceptibility as chi(T)(-1) - chi(0)(-1) alpha T-gamma, we find that chi(0)(-1) decreases with increasing pressure and vanishes to zero at the critical pressure P-c similar or equal to 2 GPa, with gamma (similar or equal to 0.5) unchanged. We suggest that this quantum criticality emerges owing to critical valence fluctuations. Above P-c, the approximant undergoes a magnetic transition at T similar or equal to 100 mK. These results are contrasted with the fact that, in the quasicrystal, the quantum criticality is robust against the application of pressure. The applicability of the so-called T/H scaling to the approximant is also discussed.

Title:
d-Density Wave Scenario Description of the New Hidden Charge Order in Cuprates
Authors:
Makhfudz, I Author Full Names: Makhfudz, Imam
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (6):10.7566/JPSJ.85.064701 JUN 15 2016
Abstract:
In this paper, we show that the theory of high T-c superconductivity based on a microscopic model with d-density wave (DDW) scenario in the pseudogap phase is able to reproduce some of the most important features of the recent experimentally discovered hidden charge order in several families of Cuprates. In particular, by computing and comparing energies of charge orders of different modulation directions derived from a full microscopic theory with d-density wave scenario, the axial charge order phi(X(Y)) with wavevector Q = (Q(0), 0)((0, Q(0))) is shown to be unambiguously energetically more favorable over the diagonal charge order phi(X+Y) with wavevector Q = (Q(0), +/- Q(0)) at least in commensurate limit, to be expected also to hold even to more general incommensurate case, in agreement with experiment. The two types of axial charge order phi(X) and phi(Y) are degenerate by symmetry. We find that within the superconducting background, biaxial (checkerboard) charge order is energetically more favorable than uniaxial (stripe) charge order, and therefore checkerboard axial charge order should be the one observed in experiments, assuming a single domain of charge ordered state on each CuO2 plane.

Title:
Superlubricity in quasicrystalline twisted bilayer graphene
Authors:
Koren, E; Duerig, U Author Full Names: Koren, Elad; Duerig, Urs
Source:
PHYSICAL REVIEW B, 93 (20):10.1103/PhysRevB.93.201404 MAY 31 2016
Abstract:
The unique atomic positions in quasicrystals lead to peculiar self-similarity and fractal-like structural morphology. Accordingly, many of the material properties are supposed to manifest exceptional characteristics. In this Rapid Communication, we explain through numerical simulations the fundamental and peculiar aspects of quasicrystals wearless friction manifested in a 30 degrees twisted bilayer graphene system. In particular, the sliding force exhibits a fractal structure with distinct area correlations due to the natural mixture between both periodic and aperiodic lateral modulations. In addition, zero power scaling of the sliding force with respect to the contact area is demonstrated for a geometric sequence of dodecagonal elements.

Title:
Temperature dependences of the electric polarization and wave number of incommensurate structures in multiferroics
Authors:
Pikin, SA Author Full Names: Pikin, S. A.
Source:
CRYSTALLOGRAPHY REPORTS, 61 (3):449-455; 10.1134/S1063774516030214 MAY 2016
Abstract:
It is shown that the electric polarization and wave number of incommensurate modulations, proportional to each other, increase according to the Landau law in spin multiferroic cycloids near the N,el temperature. In this case, the constant magnetization component (including the one for a conical spiral) is oriented perpendicular to the spin incommensurability wave vector. A similar temperature behavior should manifest itself for spin helicoids, the axes of which are oriented parallel to the polarization vector but their spin rotation planes are oriented perpendicular to the antiferromagnetic order plane. When the directions of axes of the magnetization helicoid and polarization vector coincide, the latter is quadratic with respect to magnetization and linearly depends on temperature, whereas the incommensurate-modulation wave number barely depends on temperature. Structural distortions of unit cells for multiferroics of different types determine their axial behavior.

Update: 20-Jun-2016


Title:
Determination of shapes and preferred growth directions of icosahedral quasicrystals from the 2D-sections
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, Franc; Boncina, Tonica
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 681 532-540; 10.1016/j.allcom.2016.04.255 OCT 5 2016
Abstract:
The icosahedral quasicrystalline phases have been present in many alloys either as nearly regular polyhedra or dendrites. This work provides a systematic approach for the determination of shapes of polyhedra with icosahedral symmetry, and the determination of preferred growth directions of icosahedral dendrites from their 2D-sections; i.e. from the surface of polished samples. The possible shapes of polyhedra and dendrites by differently oriented intersecting planes are presented within the icosahedral stereographic triangle. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycomb alpha-Li2IrO3
Authors:
Williams, SC; Johnson, RD; Freund, F; Choi, S; Jesche, A; Kimchi, I; Manni, S; Bombardi, A; Manuel, P; Gegenwart, P; Coldea, R Author Full Names: Williams, S. C.; Johnson, R. D.; Freund, F.; Choi, Sungkyun; Jesche, A.; Kimchi, I.; Manni, S.; Bombardi, A.; Manuel, P.; Gegenwart, P.; Coldea, R.
Source:
PHYSICAL REVIEW B, 93 (19):10.1103/PhysRevB.93.195158 MAY 26 2016
Abstract:
The layered honeycomb magnet alpha-Li2IrO3 has been theoretically proposed as a candidate to display unconventional magnetic behaviour associated with Kitaev interactions between spin-orbit entangled j(eff) = 1/2 magnetic moments on a honeycomb lattice. Here we report single crystal magnetic resonant x-ray diffraction combined with powder magnetic neutron diffraction to reveal an incommensurate magnetic order in the honeycomb layers with Ir magnetic moments counterrotating on nearest-neighbor sites. This unexpected type of magnetic structure for a honeycomb magnet cannot be explained by a spin Hamiltonian with dominant isotropic (Heisenberg) couplings. The magnetic structure shares many key features with the magnetic order in the structural polytypes beta- and gamma-Li2IrO3, understood theoretically to be stabilized by dominant Kitaev interactions between Ir moments located on the vertices of three-dimensional hyperhoneycomb and stripyhoneycomb lattices, respectively. Based on this analogy and a theoretical soft-spin analysis of magnetic ground states for candidate spin Hamiltonians, we propose that Kitaev interactions also dominate in alpha-Li2IrO3, indicative of universal Kitaev physics across all three members of the harmonic honeycomb family of Li2IrO3 polytypes.

Title:
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS2 and 2H-TaSe2
Authors:
Freitas, DC; Rodiere, P; Osorio, MR; Navarro-Moratalla, E; Nemes, NM; Tissen, VG; Cario, L; Coronado, E; Garcia-Hernandez, M; Vieira, S; Nunez-Regueiro, M; Suderow, H Author Full Names: Freitas, D. C.; Rodiere, P.; Osorio, M. R.; Navarro-Moratalla, E.; Nemes, N. M.; Tissen, V. G.; Cario, L.; Coronado, E.; Garcia-Hernandez, M.; Vieira, S.; Nunez-Regueiro, M.; Suderow, H.
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184512 MAY 24 2016
Abstract:
We present measurements of the superconducting and charge-density-wave (CDW) critical temperatures (T-c and T-CDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that T-c increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of T-CDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases, coexisting with superconductivity within our full pressure range.

Title:
Self-lubricating, low-friction, wear-resistant Al-based quasicrystalline coatings
Authors:
de Lima, BASG; Gomes, RM; de Lima, SJG; Dragoe, D; Barthes-Labrousse, MG; Kouitat-Njiwa, R; Dubois, JM Author Full Names: Silva Guedes de Lima, Bruno Alessandro; Gomes, Rodinei Medeiros; Guedes de Lima, Severino Jackson; Dragoe, Diana; Barthes-Labrousse, Marie-Genevieve; Kouitat-Njiwa, Richard; Dubois, Jean-Marie
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 17 (1):71-79; 10.1080/14686996.2016.1152563 2016
Abstract:
After gas atomization, a quasicrystalline powder based on aluminium was used to prepare a thick coating by high-velocity oxygen-fuel flame torch spraying. This layer was deposited on top of a bond-coat layer on a steel plate. A post-spraying annealing treatment turned the two layers to their stable state, a.-brass crystal and an icosahedral quasicrystal, respectively. The projection parameters were selected in such a way that the coating behaved like a self-lubricating material, which offered very good wear resistance (duration of pin-on-disk tests superior to 5 km with negligible material loss) and low friction (mu <= 6% against sintered tungsten carbide), in contrast to the state of the art. This property was achieved thanks to, on the one hand, excellent bonding to the substrate via the bound coat, and on the other hand, presence at the boundaries between quasicrystalline flakes of a mixture of both threefold and fourfold coordinated carbon originating from spray processing. Application to hard materials used in mechanical devices is appealing, especially because soft, lubricating additives may not be needed, thus considerably increasing the lifetime of the devices and reducing waste of materials.

Update: 8-Jun-2016


Title:
Evolution of the magnetic structure of TbRu2Al10 in applied field
Authors:
White, R; Hutchison, WD; Mizushima, T; Studer, AJ Author Full Names: White, R.; Hutchison, W. D.; Mizushima, T.; Studer, A. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 679 169-176; 10.1016/j.jallcom.2016.04.039 SEP 15 2016
Abstract:
TbRu2Al10 is found to undergo two magnetic phase transitions as a function of temperature and three as a function of applied field at low temperature. The Tb3+ magnetic moments order antiferromagnetically along the c-axis at 15.0(3) K, with an incommensurate sinusoidally modulated structure with a propagation vector of k = (0, 0.759(1), 0). At 6.5(3) K the structure switches to square wave order. Analysis of single crystal TbRu2Al10 has revealed that this square wave structure is altered to a 'pulse wave' on application of a 1.30 T magnetic field along the c-axis, with two in fifty of the magnetic moments across the structure changing direction to be aligned parallel with the direction of the field. At 1.85 T a further three moments flip, leading to a duty cycle of 60% and resulting in a total change of one in ten moments from the starting square wave structure. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Two iridates, two models, and two approaches: A comparative study on magnetism in three-dimensional honeycomb materials
Authors:
Lee, EKH; Rau, JG; Kim, YB Author Full Names: Lee, Eric Kin-Ho; Rau, Jeffrey G.; Kim, Yong Baek
Source:
PHYSICAL REVIEW B, 93 (18):10.1103/PhysRevB.93.184420 MAY 17 2016
Abstract:
Two recent theoretical works studied the role of Kitaev interactions in the newly observed incommensurate magnetic order in the hyper-honeycomb (beta-Li2IrO3) and stripy-honeycomb (gamma-Li2IrO3) iridates. Each of these works analyzed a different model (JK Gamma versus coupled zigzag chain model) using a contrasting method (classical versus soft-spin analysis). The lack of commonality between these works precludes meaningful comparisons and a proper understanding of these unusual orderings. In this study, we complete the unfinished picture initiated by these two works by solving both models with both approaches for both three-dimensional (3D) honeycomb iridates. Through comparisons between all combinations of models, techniques, and materials, we find that the bond-isotropic JK Gamma model consistently predicts the experimental phase of beta-Li2IrO3 regardless of the method used, while the experimental phase of gamma-Li2IrO3 can be generated by the soft-spin approach with eigenmode mixing irrespective of the model used. To gain further insights, we solve a one-dimensional (1D) quantum spin-chain model related to both 3D models using the density matrix renormalization group method to form a benchmark. We discover that in the 1D model, incommensurate correlations in the classical and soft-spin analysis survive in the quantum limit only in the presence of the symmetric-off-diagonal exchange Gamma found in the JK Gamma model. The relevance of these results to the real materials is also discussed.

Update: 1-Jun-2016


Title:
Ternary phases forming adjacent to Al3Mn-Al4Mn in Al-Mn-TM (TM = Fe, Co, Ni, Cu, Zn, Pd)
Authors:
Grushko, B; Pavlyuchkov, D; Mi, SB; Balanetskyy, S Author Full Names: Grushko, B.; Pavlyuchkov, D.; Mi, S. B.; Balanetskyy, S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 677 148-162; 10.1016/j.jallcom.2016.03.220 AUG 25 2016
Abstract:
The Al-Mn alloy system contains complex intermetallics in its Al-rich part, and this was the first system where quasiperiodic structures were recognized. In the present work, the solubility of TMs (TM = Fe, Co, Ni, Cu, Zn and Pd) in the stable binaries, the stabilization effect of these elements on the metastable binaries and the formation of ternary compounds are specified and compared. While the solubility of all these TMs in hexagonal mu-Al4Mn and lambda-Al4Mn is low, the high-temperature orthorhombic T-Al3Mn dissolves up to at least 14.5, 12, 16 and 7.5 at.% Fe, Cu, Zn and Pd, respectively. The metastable hexagonal phi-Al10Mn3 is stabilized by Fe, Co and Ni in wide ternary compositional regions, and in Al-Co-Mn such a region propagates up to Al5Co2. In alloys with Fe, Co and Ni, a ternary hexagonal phase isostructural to the Al-Cr-Ni zeta-phase (P6(3)/m, a approximate to 1.76, c approximate to 1.25 nm) is formed along similar to 80 at.% Al, while in alloys with Cu and Pd the orthorhombic so-called R-phase (Bbmm, a approximate to 2.41, b approximate to 1.25, c approximate to 0.76 nm) was found at similar compositions. This structure is also known in Al-Zn-Mn but at much lower-Al Al68Zn14.5Mn17.5, while in the range of 75-80 at.% Al a monoclinic phase isostructural to eta-Al11Cr2 (C2/c, a approximate to 1.76, b approximate to 3.04, c approximate to 1.76 nm, beta approximate to 90 degrees) is formed. In addition to the stable decagonal D-3-phase in Al-Fe-Mn and Al-Pd-Mn reported earlier, the stabilization of binary Al-Mn D-3-phase was revealed around Al64Cu20Mn16. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Medium-range structure and glass forming ability in Zr-Cu-Al bulk metallic glasses
Authors:
Zhang, P; Maldonis, JJ; Besser, MF; Kramer, MJ; Voyles, PM Author Full Names: Zhang, Pei; Maldonis, Jason J.; Besser, M. F.; Kramer, M. J.; Voyles, Paul M.
Source:
ACTA MATERIALIA, 109 103-114; 10.1016/j.actamat.2016.02.006 MAY 1 2016
Abstract:
Fluctuation electron microscopy experiments combined with hybrid reverse Monte Carlo modeling show a correlation between medium-range structure at the nanometer scale and glass forming ability in two Zr-Cu-Al bulk metallic glass (BMG) alloys. Both Zr50Cu35Al15 and Zr50Cu45Al5 exhibit two nanoscale structure types, one icosahedral and the other more crystal-like. In Zr50Cu35Al15, the poorer glass former, the crystal-like structure is more stable under annealing below the glass transition temperature, T-g, than in Zr50Cu45Al5. Variable resolution fluctuation microscopy of the MRO clusters show that in Zr50Cu35Al15 on sub-T-g annealing, the crystal-like clusters shrink even as they grow more ordered, while icosahedral-like clusters grow. Overall, the results suggest that achieving better glass forming ability in this alloy system may depend more on destabilizing crystal-like structures than enhancing non-crystalline structures. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Influence of pre-strain on the aging hardening effect of the Mg-9.02Zn-1.68Y alloy
Authors:
Ye, J; Lin, XP; Zhao, TB; Liu, NN; Xie, HB; Niu, Y; Teng, F Author Full Names: Ye, Jie; Lin, Xiao-ping; Zhao, Tian-bo; Liu, Ning-ning; Xie, Hong-bin; Niu, Yi; Teng, Fei
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 663 49-55; 10.1016/j.msea.2016.03.115 APR 29 2016
Abstract:
The solid-solution state Mg-7.68Zn-1.68Y alloy was pre-compressed before the isothermal aging treatment at 200 degrees C, then the pre-induced twinning and its influence on the aging microstructure and aging hardening effect were investigated using EBSD, TEM and SEM. Results showed that: about 15% (area fraction) lenticular (1012) tensile twinning were induced into the matrix when the alloy was compressed by 3% pre-strain; and when the amount of pre-strain increased, area fraction of twinning would increase, average size of twinning would decrease, morphology and structure of twinning would change: when the pre-strain reached 15%, about 28% (area fraction) of narrow double twinning (10 (1) over bar1)-(10 (1) over bar2)would be induced, while the anamorphosis of double twinning were mostly inter-crossing. In addition, twinning could become an effective substrate for nucleation. And different from precipitates in the matrix, which is rod-shaped beta'(1)1-MgZn2 growing along a certain direction, precipitates in the twin boundaries were granular icosahedral quasi -crystal phase with 5 -times rotational symmetric diffraction pattern. And when the pre-strain was in the range of 3-15%, aging hardening effect increased with pre-strain; when pre-strain were 10-15%, the peak hardness arrived 110HV, 28% improved compared to that of the not pre-deformed one (86HV); when the pre-strain exceeded 20%, the aging hardening effect would decrease. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Determination of the zero-field magnetic structure of the helimagnet MnSi at low temperature
Authors:
de Reotier, PD; Maisuradze, A; Yaouanc, A; Roessli, B; Amato, A; Andreica, D; Lapertot, G Author Full Names: de Reotier, P. Dalmas; Maisuradze, A.; Yaouanc, A.; Roessli, B.; Amato, A.; Andreica, D.; Lapertot, G.
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144419 APR 22 2016
Abstract:
Below a temperature of approximately 29 K the manganese magnetic moments of the cubic binary compound MnSi order to a long-range incommensurate helical magnetic structure. Here we quantitatively analyze a high-statistic zero-field muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi by exploiting the result of representation theory as applied to the determination of magnetic structures. Instead of a gradual rotation of the magnetic moments when moving along a (111) axis, we find that the angle of rotation between the moments of certain subsequent planes is essentially quenched. It is the magnetization of pairs of planes which rotates when moving along a (111) axis, thus preserving the overall helical structure.

Title:
Incommensurate-commensurate transitions in the monoaxial chiral helimagnet driven by the magnetic field
Authors:
Laliena, V; Campo, J; Kishine, JI; Ovchinnikov, AS; Togawa, Y; Kousaka, Y; Inoue, K Author Full Names: Laliena, Victor; Campo, Javier; Kishine, Jun-Ichiro; Ovchinnikov, Alexander S.; Togawa, Yoshihiko; Kousaka, Yusuke; Inoue, Katsuya
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134424 APR 20 2016
Abstract:
The zero-temperature phase diagram of the monoaxial chiral helimagnet in the magnetic-field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behavior. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For high anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions and the tricritical behavior. It is shown that for high anisotropy, as in CrNb3S6, the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6.

Title:
Low-Temperature Oxidation of Fine UO2 Powders: A Process of Nanosized Domain Development
Authors:
Leinders, G; Pakarinen, J; Delville, R; Cardinaels, T; Binnemans, K; Verwerft, M Author Full Names: Leinders, Gregory; Pakarinen, Janne; Delville, Remi; Cardinaels, Thomas; Binnemans, Koen; Verwerft, Marc
Source:
INORGANIC CHEMISTRY, 55 (8):3915-3927; 10.1021/acs.inorgchem.6b00127 APR 18 2016
Abstract:
The nanostructure and phase evolution in low-temperature oxidized (40-250 degrees C), fine UO2 powders (<200 nm) have been investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The extent of oxidation was also measured via in situ thermogravimetric analysis. The oxidation of fine powders was found to, proceed differently as compared to oxidation of coarse grained UO2. No discrete surface oxide layer was observed and no U3O8 was formed, despite the high degree of oxidation (up to O/U = 2.45). Instead, nanosized (5-15 nm) amorphous nuclei (interpreted as amorphous UO3), unmodulated and modulated U4O9, and a continuous range of U3O7-z phases with varying tetragonal distortion (c/a > 1) were observed. Oxidation involves formation of higher uranium oxides in nanodomains near the grain surface which, initially, have a disordered defect structure ("disordered U4O9"). As oxidation progresses, domain growth increases and the long period modulated structure of U4O9 develops ("ordered U4O9"). A similar mechanism is understood to happen also in U3O7-z.

Title:
Disorder-promoted C-4-symmetric magnetic order in iron-based superconductors
Authors:
Hoyer, M; Fernandes, RM; Levchenko, A; Schmalian, J Author Full Names: Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Joerg
Source:
PHYSICAL REVIEW B, 93 (14):10.1103/PhysRevB.93.144414 APR 18 2016
Abstract:
In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C-4) to orthorhombic (C-2). However, recently, a regime of C-4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M-1 and M-2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mossbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C-2 to C-4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.

Title:
Low-temperature magnetic phase transitions in the multiferroic Nd0.9Dy0.1Fe3(BO3)(4). Part 1. Transitions induced by magnetic fields directed along the trigonal symmetry axis. Spontaneous transitions with temperature changes
Authors:
Zvyagina, GA; Zhekov, KR; Bilych, IV; Kolodyazhnaya, MP; Zvyagin, AA; Bludov, AN; Pashchenko, VA; Gudim, IA Author Full Names: Zvyagina, G. A.; Zhekov, K. R.; Bilych, I. V.; Kolodyazhnaya, M. P.; Zvyagin, A. A.; Bludov, A. N.; Pashchenko, V. A.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 42 (4):273-279; 10.1063/1.4947480 APR 2016
Abstract:
The elastic and magnetic characteristics of single-crystal Nd0.9Dy0.1Fe3(BO3)(4) are studied at low temperatures in zero magnetic field and in external fields H vertical bar vertical bar C-3. The temperature dependences of the acoustic mode velocities and the magnetic susceptibility manifest a transition of the magnetic subsystem into a magnetically ordered state and two successive, spontaneous spin-reorientation phase transitions. The possibility of a spontaneous transition into an incommensurate (spiral) magnetic phase in the crystal is discussed. It is shown that an external magnetic field directed along the trigonal axis of the crystal induces a sequence of spin-reorientation phase transitions. An H-T phase diagram (H vertical bar vertical bar C-3) is constructed for this compound. Published by AIP Publishing.

Title:
3D Morphology and Formation Process of the Icosahedral Quasicrystalline Phase in Rapidly Solidified Al-Mn Alloy
Authors:
Kang, HJ; Hu, ZL; Gao, XX; Chen, ZN; Lu, YP; Jie, JC; Guo, JJ Author Full Names: Kang, Hui-Jun; Hu, Zhong-Lue; Gao, Xiao-Xia; Chen, Zong-Ning; Lu, Yi-Ping; Jie, Jin-Chuan; Guo, Jing-Jie
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 29 (1):28-31; 10.1007/s40195-015-0357-y JAN 2016
Abstract:
Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al-18Mn alloy (in wt%). Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons. 3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching. A model has been proposed to describe the formation process of the icosahedral phase and alpha-Al during the rapid solidification. The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles, and subsequently engulfed by the alpha-Al which propagates in a planar morphology.

Title:
Diffraction pattern of modulated structures described by Bessel functions
Authors:
Wolny, J; Buganski, I; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw
Source:
PHILOSOPHICAL MAGAZINE, 96 (13):1344-1359; 10.1080/14786435.2016.1161859 2016
Abstract:
We performed detailed analysis of 1D modulated structure (MS) with harmonic modulation within the statistical approach. By applying two-mode Fourier transform, we were able to derive analytically the structure factor for MS with single harmonic modulation component. We confirmed in a very smooth way that ordinary Bessel functions of the first kind define envelopes tuning the intensities of the diffraction peaks. This applies not only to main reflections of the diffraction pattern but also to all satellites. In the second part, we discussed in details the similarities between harmonically modulated structures with multiple modulations and 1D model quasicrystal. The Fourier expansion of the nodes' positions in the Fibonacci chain gives direct numerical definition of the atomic arrangement in MS. In that sense, we can define 1D quasicrystal as a MS with infinite number of harmonic modulations. We prove that characteristic measures (like v(u) relation typical for statistical approach and diffraction pattern) calculated for MS asymptotically approach their counterparts for 1D quasicrystal as large enough number of modulation terms is taken into account.

Title:
The Effect of the Drop Tube Process for the Quasicrystal Fine Particles Formation
Authors:
Takeda, Y; Kawamura, T; Nagayama, K Author Full Names: Takeda, Yuya; Kawamura, Tadaharu; Nagayama, Katsuhisa
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 80 (4):273-279; 10.2320/jinstmet.JBW201506 2016
Abstract:
In general, quasicrystalline structures are produced by liquid quenching using a single roll, Bridgman and Czochralski method, which is typical for the production of single crystals. However, there are few reports of the quasicrystal formation using a containerless process; therefore, the effect of such a process is unclear. In this study, we have investigated the production of quasicrystalline fine particles and the formation ability of Al63Cu25Fe12, Al65Cu20Fe15, and Al70Ni15Co15 ternary alloys using a drop tube apparatus with a free fall length of 2.5 m. In addition, we have aimed to examine the effectiveness of the drop tube process for quasicrystal formation. The formation of dodecahedron crystals, which are considered a quasicrystalline phase, was observed in Al63Cu25Fe12 ternary fine particle samples prepared using the drop tube process under a He atmosphere (1 atm). Based on the heat flux, the calculated results suggested that the icosahedral phase was formed at high cooling rates of similar to 10(5) K/s. In the Al70Ni15Co15 ternary fine particle sample, aggregation of prismatic crystals was observed in the fine particle samples prepared using the drop tube process under an atmosphere of He (1 atm) and Ar (1 atm). Furthermore, formation of prismatic crystals was observed on the surface of fine particle samples prepared under a low-pressure Ar atmosphere (0.5 atm), under which the formation ability of quasicrystals was observed to be the highest. From these results, the formation ability of the Al-Ni-Co-based decagonal phase is suggested to increase with decreasing cooling rates. This result is different from that of the Al-Cu-Fe-based icosahedral quasicrystals.

Update: 27-May-2016


Title:
Self-consistent theory of nanodomain formation on nonpolar surfaces of ferroelectrics
Authors:
Morozovska, AN; Ievlev, AV; Obukhovskii, VV; Fomichov, Y; Varenyk, OV; Shur, VY; Kalinin, SV; Eliseev, EA Author Full Names: Morozovska, Anna N.; Ievlev, Anton V.; Obukhovskii, Vyacheslav V.; Fomichov, Yevhen; Varenyk, Oleksandr V.; Shur, Vladimir Ya.; Kalinin, Sergei V.; Eliseev, Eugene A.
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165439 APR 28 2016
Abstract:
We propose a self-consistent theoretical approach capable of describing the features of the anisotropic nanodomain formation induced by a strongly inhomogeneous electric field of a charged scanning probe microscopy tip on nonpolar cuts of ferroelectrics. We obtained that a threshold field, previously regarded as an isotropic parameter, is an anisotropic function that is specified from the polar properties and lattice pinning anisotropy of a given ferroelectric in a self-consistent way. The proposed method for the calculation of the anisotropic threshold field is not material specific, thus the field should be anisotropic in all ferroelectrics with the spontaneous polarization anisotropy along the main crystallographic directions. The most evident examples are uniaxial ferroelectrics, layered ferroelectric perovskites, and low-symmetry incommensurate ferroelectrics. Obtained results quantitatively describe the differences at several times in the nanodomain length experimentally observed on X and Y cuts of LiNbO3 and can give insight into the anisotropic dynamics of nanoscale polarization reversal in strongly inhomogeneous electric fields.

Title:
Incommensurate spin correlations in highly oxidized cobaltates La2-xSrxCoO4
Authors:
Li, ZW; Drees, Y; Kuo, CY; Guo, H; Ricci, A; Lamago, D; Sobolev, O; Rutt, U; Gutowski, O; Pi, TW; Piovano, A; Schmidt, W; Mogare, K; Hu, Z; Tjeng, LH; Komarek, AC Author Full Names: Li, Z. W.; Drees, Y.; Kuo, C. Y.; Guo, H.; Ricci, A.; Lamago, D.; Sobolev, O.; Ruett, U.; Gutowski, O.; Pi, T. W.; Piovano, A.; Schmidt, W.; Mogare, K.; Hu, Z.; Tjeng, L. H.; Komarek, A. C.
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep25117 APR 27 2016
Abstract:
We observe quasi-static incommensurate magnetic peaks in neutron scattering experiments on layered cobalt oxides La2-xSrxCoO4 with high Co oxidation states that have been reported to be paramagnetic. This enables us to measure the magnetic excitations in this highly hole-doped incommensurate regime and compare our results with those found in the low-doped incommensurate regime that exhibit hourglass magnetic spectra. The hourglass shape of magnetic excitations completely disappears given a high Sr doping. Moreover, broad low-energy excitations are found, which are not centered at the incommensurate magnetic peak positions but around the quarter-integer values that are typically exhibited by excitations in the checkerboard charge ordered phase. Our findings suggest that the strong inter-site exchange interactions in the undoped islands are critical for the emergence of hourglass spectra in the incommensurate magnetic phases of La2-xSrxCoO4.

Title:
Electronic nature of the lock-in magnetic transition in CeXAl4Si2
Authors:
Gunasekera, J; Harriger, L; Dahal, A; Maurya, A; Heitmann, T; Disseler, SM; Thamizhavel, A; Dhar, S; Singh, DJ; Singh, DK Author Full Names: Gunasekera, J.; Harriger, L.; Dahal, A.; Maurya, A.; Heitmann, T.; Disseler, S. M.; Thamizhavel, A.; Dhar, S.; Singh, D. J.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 93 (15):10.1103/PhysRevB.93.155151 APR 25 2016
Abstract:
We have investigated the underlying magnetism in newly discovered single crystal Kondo lattices CeXAl4Si2, where X = Rh, Ir. We show that the compound undergoes an incommensurate-to-commensurate magnetic transition at T-c = 9.19 K (10.75 K in Ir). The spin correlation in the incommensurate phase is described by a spin density wave configuration of Ce ions, which locks in to the long-range antiferromagnetic order at T = T-c. The analysis of the experimental data, combined with the calculation of the electronic properties, suggests the role of the Fermi surface nesting as the primary mechanism behind this phenomenon.

Title:
Direct imaging of coexisting ordered and frustrated sublattices in artificial ferromagnetic quasicrystals
Authors:
Farmer, B; Bhat, VS; Balk, A; Teipel, E; Smith, N; Unguris, J; Keavney, DJ; Hastings, JT; De Long, LE Author Full Names: Farmer, B.; Bhat, V. S.; Balk, A.; Teipel, E.; Smith, N.; Unguris, J.; Keavney, D. J.; Hastings, J. T.; De Long, L. E.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134428 APR 25 2016
Abstract:
We have used scanning electron microscopy with polarization analysis and photoemission electron microscopy to image the two-dimensional magnetization of permalloy films patterned into Penrose P2 tilings (P2T). The interplay of exchange interactions in asymmetrically coordinated vertices and short-range dipole interactions among connected film segments stabilize magnetically ordered, spatially distinct sublattices that coexist with frustrated sublattices at room temperature. Numerical simulations that include long-range dipole interactions between sublattices agree with images of as-grown P2T samples and predict a magnetically ordered ground state for a two-dimensional quasicrystal lattice of classical Ising spins.

Title:
Confinement transition to density wave order in metallic doped spin liquids
Authors:
Patel, AA; Chowdhury, D; Allais, A; Sachdev, S Author Full Names: Patel, Aavishkar A.; Chowdhury, Debanjan; Allais, Andrea; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165139 APR 25 2016
Abstract:
Insulating quantum spin liquids can undergo a confinement transition to a valence bond solid via the condensation of topological excitations of the associated gauge theory. We extend the theory of such transitions to fractionalized Fermi liquids (FL*): These are metallic doped spin liquids in which the Fermi surfaces only have gauge neutral quasiparticles. Using insights from a duality transform on a doped quantum dimer model for the U(1)-FL* state, we show that projective symmetry group of the theory of the topological excitations remains unmodified, but the Fermi surfaces can lead to additional frustrating interactions. We propose a theory for the confinement transition of Z2-FL* states via the condensation of visons. A variety of confining, incommensurate density wave states are possible, including some that are similar to the incommensurate d-form factor density wave order observed in several recent experiments on the cuprate superconductors.

Title:
Two Kinds of Contact Problems in Dodecagonal Quasicrystals of Point Group 12 mm
Authors:
Zhao, XF; Li, X; Ding, SH Author Full Names: Zhao, Xuefen; Li, Xing; Ding, Shenghu
Source:
ACTA MECHANICA SOLIDA SINICA, 29 (2):167-177; APR 2016
Abstract:
In this paper, two kinds of contact problems in 2-D dodecagonal quasicrystals were discussed using the complex variable function method: one is the finite frictional contact problem, the other is the adhesive contact problem. The analytic expressions of contact stresses in the phonon and phason fields were obtained for a flat rigid punch, which showed that: (1) for the finite frictional contact problem, the contact stress exhibited power-type singularities at the edge of the contact zone; (2) for the adhesive contact problem, the contact stress exhibited oscillatory singularities at the edge of the contact zone. The distribution regulation of contact stress under punch was illustrated; and the low friction property of quasicrystals was verified graphically.

Title:
Structure modulation, band structure, density of states and luminescent properties of columbite-type ZnNb2O6
Authors:
Zhao, D; Ma, FX; Zhang, RJ; Li, FF; Zhang, L; Yang, J; Fan, YC; Xin, X Author Full Names: Zhao, Dan; Ma, Fa-Xue; Zhang, Rui-Juan; Li, Fei-Fei; Zhang, Lei; Yang, Juan; Fan, Yun-Chang; Xin, Xia
Source:
CRYSTENGCOMM, 18 (16):2929-2936; 10.1039/c5ce01828e 2016
Abstract:
Zinc niobate ZnNb2O6, with a columbite-type structure, is a promising dielectric, photocatalytic and luminescent material, but the crystal structure has not been studied in detail. For the first time, we redetermined the crystal structure using single crystal X-ray diffraction and established the commensurately modulated structure model through high-dimensional formalism. The structure features a (3 + 1)-dimensional superspace group Pbcn(alpha 00)00s with the modulation vector q = 1/3a*. At the same time, calculations of the band structure and the density of states were performed using density functional theory to reveal the electronic origins of the optical transitions. In addition, the photoluminescent properties of ZnNb2O6 were studied, showing that a broad emission band at approximately 470 nm can achieve a high quantum efficiency of up to 64% with an optimal sintered temperature of 950 degrees C.

Update: 18-May-2016


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

Update: 12-May-2016


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

Update: 5-May-2016


Title:
Long-period modulated structure and electric-field-induced structural transformation in Na0.5Bi0.5TiO3-based lead-free piezoelectrics
Authors:
Khatua, DK; Senyshyn, A; Ranjan, R Author Full Names: Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134106 APR 14 2016
Abstract:
Na0.5Bi0.5TiO3- based lead-free piezoelectrics exhibiting giant piezostrain are technologically interesting materials for actuator applications. The lack of clarity with regard to the structure of the nonpolar phase of this system has hindered the understanding of the structural mechanism associated with the giant piezostrain and other related phenomena. In this paper, we have investigated the structure and field-induced phase transformation behavior of a model system (0.94 - x) Na0.5Bi0.5TiO3-0.06BaTiO(3)-xK(0.5)Na(0.5)NbO(3) (0.0 <= x <= 0.025). A detailed structural analysis using neutron powder diffraction revealed that the nonpolar phase is neither cubic nor a mixture of rhombohedral (R3c) and tetragonal (P4bm) phases as commonly reported in literature but exhibits a long-period modulated structure, which is most probably of the type root 2 x root 2 x n with n = 16. Our results suggest that the giant piezoelectric strain is associated with a field-induced phase transformation of the long-period modulated structure to rhombohedral R3c structure above a critical field. We also demonstrate that the giant piezostrain is lost if the system retains a fraction of the field-induced R3c phase. A possible correlation among depolarization temperature, giant piezostrain, and its electrical fatigue behavior has also been indicated.

Title:
Temperature-dependent Fermi surface of the misfit cobaltite [Bi2Sr2O4](0.51)CoO2: A comparison with [Bi2Ba2O4](0.50)CoO2
Authors:
Takakura, S; Yamamoto, I; Koga, E; Ichikawa, F; Azuma, J; Maki, M Author Full Names: Takakura, Sho-ichi; Yamamoto, Isamu; Koga, Emi; Ichikawa, Fusao; Azuma, Junpei; Maki, Makoto
Source:
PHYSICAL REVIEW B, 93 (16):10.1103/PhysRevB.93.165118 APR 14 2016
Abstract:
Angle-resolved photoemission spectroscopy has been performed to investigate the Fermi surface (FS) and the electronic structure of misfit cobaltites, by comparing [Bi2Sr2O4](p)CoO2 with [Bi2Ba2O4](0.50)CoO2. In [Bi2Sr2O4](0.51)CoO2, we observed a suppression of spectral weight near the Fermi energy. Nevertheless, the FS can be mapped out by measuring the photoelectron intensity distribution. The FS size changes with temperature. Additionally, results show that the electronic band structure at a higher binding energy was changed by changing the sample temperature. Our results provide insight into the characteristics of the pseudogap state in the misfit-layered cobaltites. The unusual properties are probably related to the local deformations of the incommensurate structure.

Title:
Structure modulations in nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si)
Authors:
Zhou, ZY; Xu, X; Fei, R; Mao, JG; Sun, JL Author Full Names: Zhou, Zhengyang; Xu, Xiang; Fei, Rao; Mao, Jianggao; Sun, Junliang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 194-200; 10.1107/S2052520615019733 2 APR 2016
Abstract:
Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs2TB4O9 (T = Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace group I2(alpha beta 0)0. The refinement results strongly suggest that the main structure modulation feature of Cs2TB4O9 is the ordering of the O atoms. With these modulated structure models, the unreasonable B-O distances in the average structures were explained as the ordering of BO4 and BO3.

Title:
Melilite-like modulation and temperature-dependent evolution in the framework structure of K2Sc[Si2O6]F
Authors:
Hejny, C; Kahlenberg, V; Eberhard, T; Kruger, H Author Full Names: Hejny, Clivia; Kahlenberg, Volker; Eberhard, Tim; Krueger, Hannes
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 209-222; 10.1107/S2052520615024865 2 APR 2016
Abstract:
The crystal structure of synthetic K2Sc[Si2O6] F has been solved and refined as an incommensurately modulated structure in (3 + 2)-dimensional superspace. This paper describes the tetragonal structure in the superspace group P4(2)/mnm(alpha, alpha,0) 000s(-alpha, alpha,0) 0000 [a = 8.9878 (1), c = 8.2694 (2) angstrom, V = 668.01 (2) angstrom(3)] with modulation wavevectors q(1) = 0.2982 (4)(a* + b*) and q(2) = 0.2982 (4)(-a* + b*). Structure refinement taking into account the modulation of positional and ADP parameters for all atoms from 3074 observed main hkl00 and satellite reflections hklmn of first order with single, m.n = 0, and mixed, m.n = +/- 1, indices converged to a final R value of 0.0514. The structure is a mixed octahedral-tetrahedral framework composed of [ScO4F2] octahedra, [Si4O12] rings and K in variable coordination. Due to the modulation the O atoms move into and out of the first coordination sphere of K leading to a minimum of five and a maximum of 10 interatomic K-O distances up to 3.1 angstrom Although this feature is comparable to observations in modulated fresnoite and melilite group compounds, these structures differ from K2Sc[Si2O6] F with respect to their topology. On temperature increase the intensity of the satellite reflections decreases until they disappear just above 443 K. The high-temperature normal structure, in space group P4(2)/mnm, is identical to the room-temperature average structure of K2Sc[Si2O6]F.

Update: 29-Apr-2016


Title:
Metastable phase formation in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 675 149-157; 10.1016/j.jallcom.2016.03.106 AUG 5 2016
Abstract:
Two metastable phases have been identified in as-cast Mg-rich Mg-Gd-Zn alloys by TEM characterization. The I-phase was found to have a composition close to Gd11Mg29Zn60 with an icosahedral structure (a(R) = 0.524 nm). The H2-phase, with a composition close to Gd16Mg14Zn70, was identified to have a hexagonal structure (a = 0.937 nm and c = 0.977 nm). An extension of the thermodynamic description of the ternary Mg-Gd-Zn phase diagram to incorporate the formation of these metastable phases has been modelled. Thermodynamic simulation of metastable phase formation has been conducted by suppressing the formation of more stable phases in a constrained Scheil solidification simulation to form I and H2 phases. The results of these solidification simulations are compared with reported as-cast alloy structures. Limiting values for the Gd/Zn atomic ratio, similar to< 0.55 and similar to> 1.4, are found to be crucial for phase selection. An application to Mg-Zn-Gd-Y alloys is discussed briefly. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Phenomenological Magnetic Model in Tsai-Type Approximants
Authors:
Sugimoto, T; Tohyama, T; Hiroto, T; Tamura, R Author Full Names: Sugimoto, Takanori; Tohyama, Takami; Hiroto, Takanobu; Tamura, Ryuji
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (5):10.7566/JPSJ.85.053701 MAY 15 2016
Abstract:
Motivated by the recent discovery of canted ferromagnetism in the Tsai-type approximants Au-Si-REs (RE = Tb, Dy, and Ho), we propose a phenomenological magnetic model reproducing their magnetic structure and thermodynamic quantities. In the model, the cubic symmetry (m (3) over bar) of the approximately regular icosahedra plays a key role in the peculiar magnetic structure determined by a neutron diffraction experiment. Our magnetic model does not only explain magnetic behaviors in the quasicrystal approximants, but also provides a good starting point for the possibility of the coexistence between the magnetic long-range order and the aperiodicity in quasicrystals.

Title:
Low temperature magneto-structural transitions in Mn3Ni20P6
Authors:
Cedervall, J; Beran, P; Vennstrom, M; Danielsson, T; Ronneteg, S; Hoglin, V; Lindell, D; Eriksson, O; Andre, G; Andersson, Y; Nordblad, P; Sahlberg, M Author Full Names: Cedervall, Johan; Beran, Premysl; Vennstrom, Marie; Danielsson, Therese; Ronneteg, Sabina; Hoglin, Viktor; Lindell, David; Eriksson, Olle; Andre, Gilles; Andersson, Yvonne; Nordblad, Per; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 237 343-348; 10.1016/j.jssc.2016.02.028 MAY 2016
Abstract:
X-ray and neutron powder diffraction has been used to determine the crystal and magnetic structure of Mn3Ni20P6. The crystal structure can be described as cubic with space group Fm (3) over barm (225) without any nuclear phase transformation within studied temperature interval from room temperature down to 4 K. The magnetic structure of Mn3Ni20P6 is complex with two independent magnetic positions for the Mn atoms and the compound passes three successive magnetic phase transitions during cooling. At 30 K the spins of the Mn atoms on the Wyckoff 4a site (Mn1) order to form a primitive cubic anti ferromagnetic structure with propagation vector k=(0 0 1). Between 29 and 26 K the Mn atoms on the Wyckoff 8c site (Mn2) order independently on already ordered Mn1 magnetic structure forming a commensurate antiferromagnetic structure with propagation vector k= (0 0 1/2) and below 26 K, both Mn positions order to form an incommensurate helical structure with propagation vector k=(0 0 similar to 0.45). Magnetization vs. temperature curve of Mn3Ni20P6 shows a steep increase indicating some magnetic ordering below 230 K and a sharp field dependent anomaly in a narrow temperature range around 30 K. (C) 2016 Elsevier Inc. All rights reserved.

Title:
Europium and manganese magnetic ordering in EuMn2Ge2
Authors:
Ryan, DH; Rejali, R; Cadogan, JM; Flacau, R; Boyer, CD Author Full Names: Ryan, D. H.; Rejali, Rasa; Cadogan, J. M.; Flacau, R.; Boyer, C. D.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (16):10.1088/0953-8984/28/16/166003 APR 27 2016
Abstract:
The antiferromagnetic structures of both the manganese and europium sublattices in EuMn2Ge2 have been determined using thermal neutron diffraction. T-N(Mn) = 714(5) K with the 3.35(5) mu(B) (at 285 K) Mn moments ordering according to the I4 '/m ' m ' m space group. The Eu order is incommensurate with the 6.1(2) mu(B) (at 3.6 K) Eu moments oriented parallel to the c-axis with a propagation vector of k = [0.153(2) 0 0]. Both neutron diffraction and Eu-151 Mossbauer spectroscopy reveal evidence of magnetic short-range ordering of the Eu sublattice around and above T-N(Eu) similar to 10 K. The ordering temperature of the Eu sublattice is strongly affected by the sample's thermal history and rapid quenching from the melting point may lead to a complete suppression of that ordering.

Title:
Quantum diffusion of electrons in quasiperiodic and periodic approximant lattices in the rare earth-cadmium system
Authors:
Armstrong, NMR; Mortimer, KD; Kong, T; Bud'ko, SL; Canfield, PC; Basov, DN; Timusk, T Author Full Names: Armstrong, N. M. R.; Mortimer, K. D.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.; Basov, D. N.; Timusk, T.
Source:
PHILOSOPHICAL MAGAZINE, 96 (11):1122-1130; 10.1080/14786435.2016.1150612 APR 12 2016
Abstract:
Icosahedral quasicrystals are characterised by the absence of a distinct Drude peak in their low-frequency optical conductivity and the same is true of their crystalline approximants. We have measured the optical conductivity of i-GdCd [GRAPHICS] , an icosahedral quasicrystal, and two approximants, GdCd [GRAPHICS] and YCd [GRAPHICS] . We find that there is a significant difference in the optical properties of these compounds. The approximants have a zero frequency peak, characteristic of a metal, whereas the quasicrystal has a striking minimum. This is the first example where the transport properties of a quasicrystal and its approximant differ in such a fundamental way. Using a generalised Drude model introduced by Mayou, we find that our data are well described by this model. It implies that the quantum diffusion of electron wave packets through the periodic and quasiperiodic lattices is responsible for these dramatic differences: in the approximants, the transport is superdiffusive, whereas the quasicrystals show subdiffusive motion of the electrons.

Title:
Electromagnons, magnons, and phonons in Eu1-xHoxMnO3
Authors:
Chen, ZY; Schmidt, M; Wang, Z; Mayr, F; Deisenhofer, J; Mukhin, AA; Balbashov, AM; Loidl, A Author Full Names: Chen, Zhenyu; Schmidt, M.; Wang, Zhe; Mayr, F.; Deisenhofer, J.; Mukhin, A. A.; Balbashov, A. M.; Loidl, A.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134406 APR 6 2016
Abstract:
Here we present a detailed study of the terahertz and far-infrared response of the mixed perovskite manganite system Eu1-xHoxMnO3 for holmium concentrations x = 0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P parallel to a to P parallel to c. Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange-striction mechanism may not be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find an excitation close to 40 cm(-1). A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P parallel to c all the spectral weight of the electromagnons comes from the lowest-phonon mode. However, for the phase with the polarization P parallel to a additional spectral weight must be transferred from higher frequencies.

Title:
Effect of platinum substitution on the structural and magnetic properties of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Singh, S; D'Souza, SW; Nayak, J; Caron, L; Suard, E; Chadov, S; Felser, C Author Full Names: Singh, Sanjay; D'Souza, S. W.; Nayak, J.; Caron, L.; Suard, E.; Chadov, S.; Felser, C.
Source:
PHYSICAL REVIEW B, 93 (13):10.1103/PhysRevB.93.134102 APR 6 2016
Abstract:
Ni2MnGa exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work, the crystal structure, phase transitions, and the magnetic properties of quaternary Ni2-x Pt-x MnGa(0 <= x <= 1) shape memory alloys were studied experimentally by x-ray diffraction, magnetization measurements, and neutron diffraction and compared to ab initio calculations. Compositions within 0 <= x <= 0.25 exhibit the cubic austenite phase at room temperature. The x approximate to 0.3 composition exhibits a seven-layer modulated monoclinic martensite structure. Within 0.4 <= x <= 1, the system stabilizes in the nonmodulated tetragonal structure. The martensite transition has very narrow thermal hysteresis 0 <= x <= 0.3, which is a typical characteristic of a shape memory alloy. By increasing x, the temperature of the martensite transition increases, while that of the magnetic transition decreases. The x = 1 composition (NiPtMnGa) in the martensite phase undergoes a para-to-ferrimagnetic transition. The saturation magnetization exhibits a nontrivial behavior with increasing up to x approximate to 0.25, above which, it suddenly decreases. Powder neutron diffraction reveals the presence of antisite disorder, with about 17% of the original Ga sites being occupied by Mn. Computations suggest that the antisite disorder triggers an antiferromagnetic coupling between two Mn atoms in different crystallographic positions, resulting into a sudden drop of the saturation magnetization for higher x.

Title:
Comparative study of the field-induced and spontaneous AF2 ' multiferroic phases in MnWO4 and Mn0.90Co0.10WO4 within the magnetic symmetry framework
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Ressouche, E; Mukhin, AA; Skumryev, V Author Full Names: Urcelay-Olabarria, Irene; Luis Garcia-Munoz, Jose; Ressouche, Eric; Mukhin, Alexander A.; Skumryev, Vassil
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 520-527; 10.1107/S1600576716000881 2 APR 2016
Abstract:
(Mn,Co)WO4 compounds are regarded as reference spin-induced multiferroics. A comparative study is presented here, within the magnetic symmetry framework, of the incommensurate magnetic orders responsible for the ferroelectric phases of (i) MnWO4 under a magnetic field (H vertical bar vertical bar b) and (ii) Mn0.90Co0.10WO4 in the absence of an external field. On the one hand, although these two ferroelectric phases are stabilized under different external physical conditions, both present the same Xc1'(alpha 0 gamma)ss magnetic symmetry and practically the same modulation vector. The magnetic ordering in both phases is an elliptical helix with the magnetic moments (as the polarization vector, P) perpendicular to the b axis, although in most of the ferroelectric compositions of the (Mn,Co)WO4 family the spins rotate in planes containing b (and have P vertical bar vertical bar b). On the other hand, the anisotropy of the resulting magnetic modulations is extraordinarily different in the two phases. This is described and explained in the light of the different anisotropies of Co and Mn ions.

Title:
Structure determination of a pseudo-decagonal quasicrystal approximant by the strong-reflections approach and rotation electron diffraction
Authors:
Singh, D; Yun, YF; Wan, W; Grushko, B; Zou, XD; Hovmoller, S Author Full Names: Singh, Devinder; Yun, Yifeng; Wan, Wei; Grushko, Benjamin; Zou, Xiaodong; Hovmoller, Sven
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 433-441; 10.1107/S1600576716000042 2 APR 2016
Abstract:
The structure of a complicated pseudo-decagonal (PD) quasicrystal approximant in the Al-Co-Ni alloy system, denoted as PD1, was solved by the strong-reflections approach on three-dimensional rotation electron diffraction (RED) data, using the phases from the known PD2 structure. RED shows that the PD1 crystal is primitive and orthorhombic, with a = 37.3, b = 38.8, c = 8.2 angstrom. However, as with other approximants in the PD series, the superstructure reflections (corresponding to c = 8.2 angstrom) are much weaker than those of the main reflections (corresponding to c = 4.1 angstrom), so it was decided to solve the PD1 structure in the smaller primitive unit cell first, i.e. with unit-cell parameters a = 37.3, b = 38.8, c = 4.1 angstrom and space group Pnam. A density map of PD1 was calculated from only the 15 strongest unique reflections. It contained all 31 Co/Ni atoms and many weaker peaks corresponding to Al atoms. The structure obtained from the strong-reflections approach was confirmed by applying direct methods to the complete RED data set. Successive refinement using the RED data set resulted in 108 unique atoms (31 Co/Ni and 77 Al). This is one of the most complicated approximant structures ever solved by electron diffraction. As with other approximants in the PD series, PD1 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. The simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.

Title:
Jacques Friedel and the physics of metals and alloys
Authors:
Villain, J; Lavagna, M; Bruno, P Author Full Names: Villain, Jacques; Lavagna, Mireille; Bruno, Patrick
Source:
COMPTES RENDUS PHYSIQUE, 17 (3-4):276-290; 10.1016/j.crhy.2015.12.010 MAR-APR 2016
Abstract:
This is an introduction to the theoretical physics of metals for students and physicists from other specialities. Certain simple consequences of the Fermi statistics in pure metals are first addressed, namely the Peierls distortion, Kohn anomalies and the Labbe-Friedel distortion. Then the physics of dilute alloys is discussed. The analogy with nuclear collisions was a fruitful starting point, which suggested one should analyze the effects of impurities in terms of a scattering problem with the introduction of phase shifts. Starting from these concepts, Friedel derived a theory of the resistivity of alloys, and a celebrated sum rule relating the phase shifts at the Fermi level to the number of electrons in the impurity, which turned out to play a prominent role later in the context of correlated impurities, as for instance in the Kondo effect. Friedel oscillations are also an important result, related to incommensurate magnetic structures. It is shown how they can be derived in various ways: from collision theory, perturbation theory, self-consistent approximations and Green's function methods. While collision theory does not permit to take the crystal structure into account, which is responsible for electronic bands, those effects can be included in other descriptions, using for instance the tight binding approximation. (C) 2015 The Authors. Published by Elsevier Masson SAS on behalf of Academie des sciences.

Update: 22-Apr-2016


Title:
X-ray study of the anomalous thermal hystereses of the modulation wavevectors in Cs2HgCl4
Authors:
Bagautdinov, B; Shaw, Z; Orlov, A; Aliev, MA Author Full Names: Bagautdinov, Bagautdin; Shaw, Zachery; Orlov, Andrii; Aliev, Marat A.
Source:
PHASE TRANSITIONS, 89 (5):471-479; 10.1080/01411594.2015.1080258 MAY 3 2016
Abstract:
A rich sequence of structural modulations in Cs2HgCl4 as a function of temperature was studied by means of X-ray diffraction. Accurate satellite-position measurements on the cooling and heating paths of the crystal revealed abnormal thermal hystereses for incommensurate phases and coexistences of neighboring commensurate phases. A well-defined X-ray picture of the a-axis modulated phases in the range of 221-184K were observed on the heating path, while the c-axis modulated phases existing below 184K were definitely detected on the cooling path. The proper conditions for a precise phase diagram of Cs2HgCl4 can be correlated with relatively defect-free transformations of a-axis modulations at heating and of c-axis modulations at cooling. The peculiarity of Cs2HgCl4 to switch modulation direction among the a- and c-axes at 184K allows us deliberately accumulate and thus control a majority of mobile defects on the mutually perpendicular (100) or (001) planes by possessing crystal within temperature domain of a- or c-axes modulations, respectively.

Title:
Phase transformation behavior of Cu-10Ni-3Al-0.8Si alloy
Authors:
Shen, LN; Li, Z; Zhao, YY; Wang, Y; Dong, QY; Wang, MY Author Full Names: Shen, Leinuo; Li, Zhou; Zhao, Yuyuan; Wang, Yang; Dong, Qiyi; Wang, Mengying
Source:
MATERIALS CHEMISTRY AND PHYSICS, 173 421-428; 10.1016/j.matchemphys.2016.02.033 APR 15 2016
Abstract:
Microstructure evolution of solution treated Cu-10Ni-3Al-0.8Si alloy aged at different temperatures was investigated and different transformation products were observed: modulated structure resulting from spinodal decomposition, L1(2) ordering of matrix, continuous Ni3Al precipitates, continuous delta-Ni2Si precipitates and discontinuous precipitates. Modulated structure, L1(2) ordering of matrix and micro-twins formed initially at 450 degrees C, while continuous Ni3Al and delta-Ni2Si particles precipitated soon. Increasing temperature led to the formation of discontinuous precipitates, dissolution of Ni3Al and cellular decomposition. The alloy showed excellent over-aging resistance at 450 degrees C because the Ni3Al and delta-Ni2Si precipitates grew very slowly and the addition of silicon hindered the precipitation of the coarsening NiAl phase. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Interplay of charge density wave and multiband superconductivity in 2H-PdxTaSe2
Authors:
Bhoi, D; Khim, S; Nam, W; Lee, BS; Kim, C; Jeon, BG; Min, BH; Park, S; Kim, KH Author Full Names: Bhoi, D.; Khim, S.; Nam, W.; Lee, B. S.; Kim, Chanhee; Jeon, B. -G.; Min, B. H.; Park, S.; Kim, Kee Hoon
Source:
SCIENTIFIC REPORTS, 6 10.1038/srep24068 APR 5 2016
Abstract:
2H-TaSe2 has been one of unique transition metal dichalcogenides exhibiting several phase transitions due to a delicate balance among competing electronic ground states. An unusual metallic state at high-T is sequentially followed by an incommensurate charge density wave (ICDW) state at approximate to 122 K and a commensurate charge density wave (CCDW) state at approximate to 90 K, and superconductivity at T-C similar to 0.14 K. Upon systematic intercalation of Pd ions into TaSe2, we find that CCDW order is destabilized more rapidly than ICDW to indicate a hidden quantum phase transition point at x similar to 0.09-0.10. Moreover, T-C shows a dramatic enhancement up to 3.3 K at x = 0.08, similar to 24 times of T-C in 2H-TaSe2, in proportional to the density of states N(E-F). Investigations of upper critical fields H-C2 in single crystals reveal evidences of multiband superconductivity as temperature-dependent anisotropy factor gamma(H) = H-C2(ab)/HHC2C, quasi-linear increase of H-C2(C) (T), and an upward, positive-curvature in H-C2(ab) (T) near T-C. Furthermore, analysis of temperature-dependent electronic specific heat corroborates the presence of multiple superconducting gaps. Based on above findings and electronic phase diagram vs x, we propose that the increase of N(E-F) and effective electron-phonon coupling in the vicinity of CDW quantum phase transition should be a key to the large enhancement of T-C in PdxTaSe2.

Title:
Synthesis and anisotropic properties of single crystalline Ln(2)Ru(3)Al(15+x) (Ln=Gd, Tb)
Authors:
Morrison, G; Prestigiacomo, J; Haldolaarachchige, N; Rai, BK; Young, DP; Stadler, S; Morosan, E; Chan, JY Author Full Names: Morrison, Gregory; Prestigiacomo, Joseph; Haldolaarachchige, Neel; Rai, Binod K.; Young, David P.; Stadler, Shane; Morosan, Emilia; Chan, Julia Y.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 186-194; SI 10.1016/j.jssc.2015.08.009 APR 2016
Abstract:
Single crystals of Ln(2)Ru(3)Al(15+x)(Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd2Ru3Al15.08 orders antiferromagnetically at 17.5 K. Tb2Ru3Al15.05 enters an antiferromagnetic state at 16.6 K followed by a likely incommensurate-to-commensurate transition at 14.9 K for crystals oriented with HI lab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb2Ru3Al15.05 display a stepwise behavior and indicate strong crystalline electric field effects. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Crystal growth of incommensurate members of 2H-hexagonal perovskite related oxides: Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt)
Authors:
Ferreira, T; Morrison, G; Yeon, J; zur Loye, HC Author Full Names: Ferreira, Timothy; Morrison, Gregory; Yeon, Jeongho; zur Loye, Hans-Conrad
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 236 2-9; SI 10.1016/j.jssc.2015.10.040 APR 2016
Abstract:
Millimeter sized crystals of six oxides of approximate composition Ba4MzPt3-zO9 (M=Co, Ni, Cu, Zn, Mg, Pt) were grown from molten K2CO3 fluxes and found to crystallize in a 2H hexagonal perovskite-related structure type. The compositions of these incommensurate structures, which belong to the A(3n+3m)A'(n) B3m+nO9m+6n family of 2H hexagonal perovskite related oxides, were characterized by X-ray diffraction, energy dispersive spectroscopy, and magnetic susceptibility measurements. The specific synthetic considerations, crystal growth conditions, and magnetic susceptibility measurements are discussed. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Interplay between multiple charge-density waves and the relationship with superconductivity in PdxHoTe3
Authors:
Lou, R; Cai, YP; Liu, ZH; Qian, T; Zhao, LX; Li, Y; Liu, K; Han, ZQ; Zhang, DD; He, JB; Chen, GF; Ding, H; Wang, SC Author Full Names: Lou, Rui; Cai, Yipeng; Liu, Zhonghao; Qian, Tian; Zhao, Lingxiao; Li, Yu; Liu, Kai; Han, Zhiqing; Zhang, Dandan; He, Junbao; Chen, Genfu; Ding, Hong; Wang, Shancai
Source:
PHYSICAL REVIEW B, 93 (11):10.1103/PhysRevB.93.115133 MAR 21 2016
Abstract:
HoTe3, a member of the rare-earth tritelluride (RTe3) family, and its Pd-intercalated compounds, PdxHoTe3, where superconductivity (SC) sets in as the charge-density wave (CDW) transition is suppressed by the intercalation of a small amount of Pd, are investigated using angle-resolved photoemission spectroscopy (ARPES) and electrical resistivity. Two incommensurate CDWs with perpendicular nesting vectors are observed in HoTe3 at low temperatures. With a slight Pd intercalation (x = 0.01), the large CDW gap decreases and the small one increases. The momentum dependence of the gaps along the inner Fermi surface (FS) evolves from orthorhombicity to near tetragonality, manifesting the competition between two CDW orders. At x = 0.02, both CDW gaps decrease with the emergence of SC. Further increasing the content of Pd for x = 0.04 will completely suppress the CDW instabilities and give rise to the maximal SC order. The evolution of the electronic structures and electron-phonon couplings (EPCs) of the multiple CDWs upon Pd intercalation are carefully scrutinized. We discuss the interplay between multiple CDW orders, and the competition between CDW and SC in detail.

Update: 15-Apr-2016


Title:
Cycloid spirals and cycloid cone transition in the HoMn6-xCrxGe6 (T, x) magnetic phase diagramm by neutron diffraction
Authors:
Schobinger-Papamantellos, P; Rodriguez-Carvajal, J; Buschow, KHJ Author Full Names: Schobinger-Papamantellos, P.; Rodriguez-Carvajal, J.; Buschow, K. H. J.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 408 233-243; 10.1016/j.jmmm.2016.02.018 JUN 15 2016
Abstract:
The structures and magnetic properties of the antiferromagnetic hexagonal pseudo ternary compounds HoMn6-xCrxGe6 (x=1, 1.5 and 2) are studied by neutron diffraction in the temperature range 1.5-300 K. The substitution of nonmagnetic Cr for Mn greatly affects the magnetic properties of HoMn6Ge6 by reducing the ordering temperature from 466 K to 278 K, 205 K and 130 K for (x=0, 1, 1.5 and 2) respectively, increasing the c/a ratio, suppressing the high temperature (HT) commensurate phase with q(2)=(0, 0, 1/2) and changing the high temperature (LT) q(1)=(0, 0, q(1z)) skew spiral rotation plane. HoMn5CrGe6 and HoMn4Cr2Ge6 display in the entire magnetically ordered regime cycloid spiral structures with the wave vector: q=(0, 0, q(z)), q(z) approximate to 0.18(3) r.l.u. and q(z) approximate to 64.8 degrees turn angle. The Ho and Mn/ Cr (001) layers have ferromagnetic arrangements coupled antiferromagnetically. The Ho moments in the z=0 layer are oriented in a direction opposite to the line bisecting the angle 2 phi(Mn) approximate to 2 x 28 degrees of the Mn layers at z = +/-similar to 0.25. This triple unit changes orientation collectively in the direction of q within the (b, c) plane containing the wave vector. Above 50 K, the wave vector length increases linearly from 0.24 to 0.28 (1) r.l.u. below T-N. The HT HoMn4.5Cr1.5Ge6 cycloid spiral, is stable in the range T-t < T < T-N (q(1)=(0,0,q(1z)), q(1z)=0.1711(3) r. I.u., Phi(s), =61.6 degrees at 40 K). At variance to the other compounds, crossing Try 36 K from above, it undergoes a first order magnetoelastic transition from a cycloid HT q(1) to a LT longitudinal cone structure: q(2)=(0, 0, q2z), q2z=0.149 r.l.u., Phi(s)=53.6 degrees and cone angle Phi(c)=47 degrees. The q(1) and q(2) phases coexist in the LT range down to 1.5 K <= T <= T-t in varying amounts with T. This transition is directly manifested by the splitting of the HT magnetic satellites and the increase of characteristic nuclear intensities. The results are summarised in a (T, x) magnetic phase diagram. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductor La2-x(Sr, Ba)(x)CuO4
Authors:
Wagman, JJ; Carlo, JP; Gaudet, J; Van Gastel, G; Abernathy, DL; Stone, MB; Granroth, GE; Kolesnikov, AI; Savici, AT; Kim, YJ; Zhang, H; Ellis, D; Zhao, Y; Clark, L; Kallin, AB; Mazurek, E; Dabkowska, HA; Gaulin, BD Author Full Names: Wagman, J. J.; Carlo, J. P.; Gaudet, J.; Van Gastel, G.; Abernathy, D. L.; Stone, M. B.; Granroth, G. E.; Kolesnikov, A. I.; Savici, A. T.; Kim, Y. J.; Zhang, H.; Ellis, D.; Zhao, Y.; Clark, L.; Kallin, A. B.; Mazurek, E.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 93 (9):10.1103/PhysRevB.93.094416 MAR 14 2016
Abstract:
We present time-of-flight neutron scattering measurements on single crystals of La2-xBaxCuO4 (LBCO) with 0 <= x <= 0.095 and La2-xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high-temperature cuprate superconductivity, ranging from insulating, three-dimensional commensurate long-range antiferromagnetic order, for x <= 0.02, to two-dimensional (2D) incommensurate antiferromagnetism coexisting with superconductivity for x >= 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear enhancement of the inelastic scattering coincident with the low-energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore, we show that the low-temperature, low-energy magnetic spectral weight is substantially larger for samples with nonsuperconducting ground states relative to any of the samples with superconducting ground states. Spin gaps, suppression of low-energy magnetic spectral weight as a function of decreasing temperature, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO.

Update: 7-Apr-2016


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

Update: 1-Apr-2016


Title:
Evidence of multiferroicity in NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Damay, F; Gukasov, A; Moshopoulou, E; Auban-Senzier, P; Pasquier, C; Andre, G; Porcher, F; Elkaim, E; Doubrovsky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Damay, F.; Gukasov, A.; Moshopoulou, E.; Auban-Senzier, P.; Pasquier, C.; Andre, G.; Porcher, F.; Elkaim, E.; Doubrovsky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICAL REVIEW B, 93 (10):10.1103/PhysRevB.93.104406 MAR 8 2016
Abstract:
Recently, RMn2O5 (R = rare earth, Bi, Y) type multiferroics have drawn considerable attention, because of magnetically induced ferroelectricity along with an extremely large magnetoelectric coupling. Here, we present a detailed study on NdMn2O5 which is a crucial composition between the nonferroelectric PrMn2O5 and ferroelectric SmMn2O5. We report the results of heat capacity, magnetization, dielectric permittivity, and electric polarization measurements along with an accurate description of the structural and microscopic magnetic properties obtained from high resolution x-ray and neutron diffraction studies. We show that NdMn2O5 is ferroelectric, although the magnitude of polarization is much weaker than that of the other multiferroic members. The direction of the polarization is along the crystallographic b axis and its magnitude can be tuned with the application of a magnetic field. Moreover, unlike the other multiferroic members of this series, ferroelectricity in NdMn2O5 emerges in an incommensurate magnetic state. The present study also provides evidence in support of the influence of the rare-earth size on the magnetoelectric phase diagram.

Title:
Thermally and Electrochemically Driven Topotactical Transformations in Sodium Layered Oxides NaxVO2
Authors:
Didier, C; Guignard, M; Suchomel, MR; Carlier, D; Darriet, J; Delmas, C Author Full Names: Didier, Christophe; Guignard, Marie; Suchomel, Matthew R.; Carlier, Dany; Darriet, Jacques; Delmas, Claude
Source:
CHEMISTRY OF MATERIALS, 28 (5):1462-1471; 10.1021/acs.chemmater.5b04882 MAR 8 2016
Abstract:
Phase diagrams and structural transformations in the complex NaxVO2 system have been studied using electrochemical (de)intercalation and in situ and operando high resolution synchrotron powder diffraction. Starting from O'3-Na1/2VO2 obtained by sodium electrochemical deintercalation of O'3-NaVO2, the structural details of irreversible and reversible thermally driven transformations to P'3 and P3 type structures are presented. Subsequently, these P'3-NaxVO(2) phases provide a platform for operando studies exploring the NaxVO2 phase diagram as a function of sodium electrochemical (de) intercalation. In this system, three single phase domains have been found: a line phase P'3-Na1/2VO2, one solid solution for 0.53 <= x <= 0.55 characterized by an incommensurate modulated structure, and a second solid solution for 0.63 <= x <= 0.65 with a defective structure resulting from a random stack of O'3 and P'3 layers. With further sodium intercalation (x > 0.65), the structure irreversibly transforms to the starting parent phase O3-NaVO2. This work reveals new details about the diverse structural polymorphs found in sodium layered oxides used as electrode battery materials and the transitional pathways between them as a function of temperature and composition.

Title:
Tailoring Magnetic Behavior in the Tb-Au-Si Quasicrystal Approximant System
Authors:
Gebresenbut, GH; Andersson, MS; Nordblad, P; Sahlberg, M; Gomez, CP Author Full Names: Gebresenbut, Girma H.; Andersson, Mikael S.; Nordblad, Per; Sahlberg, Martin; Gomez, Cesar Pay
Source:
INORGANIC CHEMISTRY, 55 (5):2001-2008; 10.1021/acs.inorgchem.5b02286 MAR 7 2016
Abstract:
A novel synthesis method, "arc-melting-self-flux", has been developed and a series of five Tsai-type 1/1 approximant crystals in the Tb-Au-Si system have been synthesized. The synthesis method, by employing a temperature program which oscillates near the melting and nucleation points of the approximants, has provided high-quality and large single crystals in comparison to those obtained from the standard arc-melting-annealing and self-flux methods. The atomic structures of the approximants have been determined from single-crystal X-ray diffraction data and described using concentric atomic clusters with icosahedral symmetry. The compounds are nearly isostructural with subtle variations; two types of atomic clusters which mainly vary at their cluster centers are observed. One type contains a Tb site at the center, and the other contains a disordered tetrahedron decorated with Au/Si mixed sites. Both cluster types can be found coexisting in the approximants. The compounds have different average weighted ratios of central Tb to disordered tetrahedron in the bulk material. Furthermore, a strategy for chemically tuning magnetic behavior is presented. Magnetic property measurements on the approximants revealed that the magnetic transition temperature (T-c) decreases as the occupancy of the central Tb site increases. T-c decreased from 11.5 K for 0% occupancy of the central Tb to 8 K for 100% occupancy. Enhanced magneto crystalline anisotropy is observed for the approximants with higher central Tb occupancy in comparison to their low central Tb occupancy counterparts. Hence, the previously reported "ferrimagnetic-like" magnetic structure model remains valid.

Title:
Athermal and deformation-induced omega-phase transformations in biomedical beta-type alloy Ti-9Cr-0.20
Authors:
Liu, HH; Niinomi, M; Nakai, M; Cho, K Author Full Names: Liu, Huihong; Niinomi, Mitsuo; Nakai, Masaaki; Cho, Ken
Source:
ACTA MATERIALIA, 106 162-170; 10.1016/j.actamat.2016.01.008 MAR 2016
Abstract:
The alloy Ti-9Cr-0.20 has been developed as a potential material for implant rods used in spinal fixation applications, since it exhibits good mechanical properties and a remarkably "changeable Young's modulus", which is achieved by suppressing the athermal omega-phase formed upon quenching and enhancing the deformation-induced omega-phase transformation. In this study, athermal and deformation induced omega-phase transformations in Ti-9Cr-0.20 were investigated systematically by transmission electron microscopy. This was done in order to understand the nature of these omega-phase transformations, as well as the specific functionality the "changeable Young's modulus" resulting from them. In solution-treated alloy samples, in addition to ideal omega-structures, structures considered as initial omega-structures associated with incommensurate omega-phase were observed. This might be attributed to the composition heterogeneity, heterogeneity of oxygen distribution, and/or the inhomogeneous distribution of defects such as vacancies and locally strained areas. Following cold rolling, some of the selected area electron diffraction patterns of the alloy showed that the reflections of one omega-variant had increased significantly in intensity while those of the other omega-variant had decreased sharply. This vanishing of one type of variant omega-structures is attributable to two possible mechanisms: (i) a reversal mechanism, under which the particular <111> partial dislocations transform the corresponding omega-variants back into beta-phase or (ii) a re-orientation mechanism, according to which the omega-variants unfavorable with regard to the loading direction re-orient and turn into the preferred omega-variants. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
SrPt2Al2 - A(3+2)D-incommensurately modulated variant of the CaBe2Ge2 type structure
Authors:
Hoffmann, RD; Stegemann, F; Janka, O Author Full Names: Hoffmann, Rolf-Dieter; Stegemann, Frank; Janka, Oliver
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):127-142; 10.1515/zkri-2015-1891 MAR 2016
Abstract:
The first ternary compound in the Sr-Pt-Al system, SrPt2Al2, was synthesized by melting of the elements in a sealed niobium tube in a high frequency furnace. The structure of SrPt2Al2 was determined by single-crystal X-ray diffraction on the basis of data sets recorded at 90, 150, 210, 270 and 300 K. The compound crystallizes in an incommensurately modulated (3+2)D structure being related to the tetragonal primitive CaBe2Ge2 type structure. The structure was refined in the orthorhombic superspace group Pmmn(alpha, 0,0) 0s0(0,beta,0) s00 (alpha = 0.222(1) a*, beta = 0.224(1) b*, a = b = 436.89(5), c = 1010.16(13) pm at 90 K) with R-M = 0.0403, R-S,R-1 = 0.0597 and R-S,R-2 = 0.2046. The structural relation with CaBe2Ge2 along with a refinement in the tetragonal superspace group P4/nmm(alpha, 0,0)-0000(0,alpha,0)00s0 is discussed with respect to the temperature dependence of the q-vectors and by group-subgroup relations. The modulation, from the standpoint of the crystal chemistry, is mainly caused by the distortion of the Pt arrangements within the pseudo-tetragonal ab plane.

Title:
The modulated structure of intermediate-valent CeCoGa
Authors:
Niehaus, O; Hoffmann, RD; Chevalier, B; Pottgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (3):143-153; 10.1515/zkri-2015-1882 MAR 2016
Abstract:
CeCoGa was synthesized by melting of the elements in an arc-melting furnace as well as in a sealed niobium tube in an induction furnace. A further annealing step improves the purity and crystallinity of the samples significantly. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Already at room temperature CeCoGa crystallizes in a superstructure of the HT-CeCoAl type. This superstructure can be described in the (3 + 1)D superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 1/3 with a temperature independent q-vector (Z = 4). For the 300 K data (also for 90 K) the commensurate *modulated structure* could be refined with 1336 F-2 values, 56 variables and residuals of wR = 0.0348 for the main and wR = 0.0605 for the satellites of 1st order [a = 1101.7(1), b = 436.0(1) and c = 482.4(1) pm, beta = 103.2(1)degrees]. Furthermore a description in a transformed 3D supercell with the space group C2/m and Z = 12 is possible. For the 90 K data this 3D supercell was refined with 1289 F-2 values, 56 variables and a residual of wR = 0.0409 [a = 1618.8(1), b = 435.3(1) and c = 1094.1(1) pm, beta = 119.3(1)degrees]. The relation of the HT-CeCoAl type structure, the (3 + 1)D modulated and the 3D supercell structure are discussed on the basis of a group-subgroup relation. By thermal analysis and magnetic measurements the phase transition temperature to the HT-CeCoAl type structure is stated slightly above 475 K. Furthermore intermediate cerium valence was identified by the magnetic susceptibility.

Title:
The estimation of phason flips in 1D quasicrystal from the diffraction pattern
Authors:
Buganski, I; Strzalka, R; Wolny, J Author Full Names: Buganski, Ireneusz; Strzalka, Radoslaw; Wolny, Janusz
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 253 (3):450-457; 10.1002/pssb.201552426 MAR 2016
Abstract:
The statistical approach based on the average unit-cell concept and the envelop functions for the diffraction pattern were used to estimate the number of phason flips in the model 1D quasicrystal (Fibonacci chain). The characteristic function of a statistical distribution expanded to a power series with distribution moments as coefficients can be used to retrieve phases of diffraction peaks. In addition, the number of flips in the structure can be designated in two ways: with the value of the second moment's value and directly from the shape of a probability density function retrieved from the diffraction pattern. In this paper, all calculations are performed for a nondecorated Fibonacci chain. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Title:
Schottky effect in the i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant
Authors:
Jazbec, S; Kashimoto, S; Kozelj, P; Vrtnik, S; Jagodic, M; Jaglicic, Z; Dolinsek, J Author Full Names: Jazbec, S.; Kashimoto, S.; Kozelj, P.; Vrtnik, S.; Jagodic, M.; Jaglicic, Z.; Dolinsek, J.
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054208 FEB 23 2016
Abstract:
The analysis of low-temperature specific heat of rare-earth (RE)-containing quasicrystals and periodic approximants and consequent interpretation of their electronic properties in the T -> 0 limit is frequently hampered by the Schottky effect, where crystalline electric fields lift the degeneracy of the RE-ion Hund's rule ground state and introduce additional contribution to the specific heat. In this paper we study the low-temperature specific heat of a thulium-containing i-Zn-Ag-Sc-Tm icosahedral quasicrystal and its 1/1 Zn-Sc-Tm approximant, both being classified as "Schottky" systems. We have derived the crystal-field Hamiltonian for pentagonal symmetry of the crystalline electric field, pertinent to the class of Tsai-type icosahedral quasicrystals and their approximants, where the RE ions are located on fivefold axes of the icosahedral atomic cluster. Using the leading term of this Hamiltonian, we have calculated analytically the Schottky specific heat in the presence of an external magnetic field and made comparison to the experimental specific heat of the investigated quasicrystal and approximant. When the low-temperature specific heat C is analyzed in a C/T versus T-2 scale (as it is customarily done for metallic specimens), the Schottky specific heat yields an upturn in the T -> 0 limit that cannot be easily distinguished from a similar upturn produced by the electron-electron interactions in exchange-enhanced systems and strongly correlated systems. Our results show that extraction of the electronic properties of RE-containing quasicrystals from their low-temperature specific heat may be uncertain in the presence of the Schottky effect.

Title:
Mechanical and tribological properties of AlCuFe quasicrystal and Al(Si)CuFe approximant thin films
Authors:
Olsson, S; Broitman, E; Garbrecht, M; Birch, J; Hultman, L; Eriksson, F Author Full Names: Olsson, Simon; Broitman, Esteban; Garbrecht, Magnus; Birch, Jens; Hultman, Lars; Eriksson, Fredrik
Source:
JOURNAL OF MATERIALS RESEARCH, 31 (2):232-240; 10.1557/jmr.2015.384 JAN 28 2016
Abstract:
Multilayered thin films of Al/Cu/Fe have been prepared by magnetron sputtering and annealed into quasicrystalline and approximant phases on Al2O3 and Si substrates, respectively. The nanomechanical and nanotribological properties, such as hardness, elastic modulus, friction, and toughness, have been measured using a triboindenter and analytical methods. The approximant phase was proved to be slightly harder than the quasicrystalline phase with a hardness of about 15.6 GPa, and with a similar elastic modulus of about 258 GPa. These values however decreased rapidly with an increasing amount of Si in the approximant. The indentation toughness of the approximant, <0.1 MPa/m(1/2), was however inferior to that of the quasicrystals with 1.5 MPa/m(1/2). Friction coefficients were measured in a range of 0.10-0.14 for both the quasicrystalline and approximant thin films.

Update: 24-Mar-2016


Title:
Design and Synthesis of a Geopolymer-Enhanced Quasi-Crystalline Composite for Resisting Wear and Corrosion
Authors:
Ozaydin, MF; Liang, H Author Full Names: Ozaydin, M. Fevzi; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 138 (2):10.1115/1.4031400 APR 2016
Abstract:
Multiphase composites are attractive for improved mechanical performance and corrosion resistance. In this research, a new composite consisting quasi-crystalline Al75Mn14Si7Fe4 alloy of icosahedral, cubic alpha-AlMnSiFe, monoclinic Al13Fe4 phases, and ferro-silico-aluminate geopolymer was synthesized using rapid solidification and thermal treatment methods. The concentration of icosahedral phase (i-phase) was controlled and the formation of geopolymer was obtained through heat treatment. Characterization showed that the microhardness and wear resistance were increased with the amount of i-phase. The corrosion resistance, on the other hand, was improved with the existence of the geopolymer. This research demonstrates an effective approach in processing a multi-phase composite that has desired properties and performance through multiphase design and composition.

Title:
Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model
Authors:
Yamase, H; Eberlein, A; Metzner, W Author Full Names: Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter
Source:
PHYSICAL REVIEW LETTERS, 116 (9):10.1103/PhysRevLett.116.096402 MAR 4 2016
Abstract:
We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Neel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.

Title:
Evolution of the charge density wave superstructure in ZrTe3 under pressure
Authors:
Hoesch, M; Garbarino, G; Battaglia, C; Aebi, P; Berger, H Author Full Names: Hoesch, Moritz; Garbarino, Gaston; Battaglia, Corsin; Aebi, Philipp; Berger, Helmuth
Source:
PHYSICAL REVIEW B, 93 (12):10.1103/PhysRevB.93.125102 MAR 1 2016
Abstract:
The material ZrTe3 is a well-known example of an incommensurate periodic lattice distortion (PLD) at low temperatures due to a charge density wave (CDW). Previous studies have found a sharp boundary as a function of pressure between CDW below 5 GPa and bulk superconductivity above this value. We present a study of low-temperature-high-pressure single crystal x-ray diffraction along with ab initio density functional theory calculations. The modulation vector q(CDW) is found to change smoothly with pressure until the PLD is lost. Fermi surface calculations reproduce these changes, but neither these nor the experimental crystal lattice structure show a particular step change at 5 GPa, thus leading to the conclusion that the CDW is lost accidentally by tipping the balance of CDW formation in the Fermi surface nesting that stabilizes it.

Title:
Incommensurate spin-density-wave antiferromagnetism in CeRu2Al2B
Authors:
Bhattacharyya, A; Khalyavin, DD; Kruger, F; Adroja, DT; Strydom, AM; Kockelmann, WA; Hillier, AD Author Full Names: Bhattacharyya, A.; Khalyavin, D. D.; Krueger, F.; Adroja, D. T.; Strydom, A. M.; Kockelmann, W. A.; Hillier, A. D.
Source:
PHYSICAL REVIEW B, 93 (6):10.1103/PhysRevB.93.060410 FEB 29 2016
Abstract:
The newly discovered Ising-type ferromagnet CeRu2Al2B exhibits an additional phase transition at T-N = 14.2 K before entering the ferromagnetic ground state at T-C = 12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of T-C < T < T-N. The propagation vector q similar to (0,0,0.148) is nearly temperature independent in this region and discontinuously locks into q = 0 at T-C. Mean-field calculations of an effective Ising model indicate that the modulated SDW phase is stabilized by a strong competition between ferromagnetic and antiferromagnetic exchange interactions. This makes CeRu2Al2B a particularly attractive model system to study the global phase diagram of ferromagnetic heavy-fermion metals under the influence of magnetic frustration.

Update: 17-Mar-2016


Title:
The modulated structures of La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6)
Authors:
Peschke, S; Johrendt, D Author Full Names: Peschke, Simon; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 231 (2):89-95; 10.1515/zkri-2015-1883 FEB 2016
Abstract:
The solid solutions La2-xPrxO2MnSe2 (0 <= x <= 1) and La2-xNdxO2MnSe2 (0 <= x <= 0.6) were synthesized in a NaI/KI flux between 800 and 900 degrees C. The selenide oxides adopt a ZrCuSiAs-related structure with modulated [MnSe2](2)(-)- layers which consist of a mixture of edge- and corner-sharing MnSe4/2-tetrahedra. The crystal structures are described with a (3+1)D model in superspace group Cmme(alpha 01/2)0s0. The modulation vector q can be-controlled by partial substitution of La3+ for Pr3+ and Nd3+ via the unit cell volume leading to, amongst others, (La0.55Pr0.45)(2)O2MnSe2 with alpha = 1/6, which allows the projection onto 3D space by using a simple sixfold a axis.

Title:
M2PO3N (M = Ca, Sr): ortho-Oxonitridophosphates with beta-K2SO4 Structure Type
Authors:
Marchuk, A; Schultz, P; Hoch, C; Oeckler, O; Schnick, W Author Full Names: Marchuk, Alexey; Schultz, Peter; Hoch, Constantin; Oeckler, Oliver; Schnick, Wolfgang
Source:
INORGANIC CHEMISTRY, 55 (2):974-982; 10.1021/acs.inorgchem.5b02647 JAN 18 2016
Abstract:
Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 degrees C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 degrees C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) angstrom, b = 5.5778(3) angstrom, c = 9.8132(7) angstrom, R1 = 0.020, wR2 = 0.047] crystallizes in the beta-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(a00)0ss [Z = 4, a = 6.7942(7) angstrom, b = 5.4392(6) angstrom, c = 9.4158(11) angstrom, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu2+, Ca2PO3N exhibits luminescence in the green range (lambda(em) = 525 nm) of the visible spectrum if excited by near-UV light (lambda(exc) = 400 nm).

Update: 11-Mar-2016


Title:
Incommensurate crystal supercell and polarization flop observed in the magnetoelectric ilmenite MnTiO3
Authors:
Silverstein, HJ; Skoropata, E; Sarte, PM; Mauws, C; Aczel, AA; Choi, ES; van Lierop, J; Wiebe, CR; Zhou, HD Author Full Names: Silverstein, Harlyn J.; Skoropata, Elizabeth; Sarte, Paul M.; Mauws, Cole; Aczel, Adam A.; Choi, Eun Sang; van Lierop, Johan; Wiebe, Christopher R.; Zhou, Haidong
Source:
PHYSICAL REVIEW B, 93 (5):10.1103/PhysRevB.93.054416 FEB 19 2016
Abstract:
MnTiO3 has been studied for many decades, but it was only in the last few years that its magnetoelectric behavior had been observed. Here, we use neutron scattering on two separately grown single crystals and two powder samples to show the presence of a supercell that breaks R (3) over bar symmetry. We also present the temperature and field dependence of the dielectric constant and pyroelectric current and show evidence of nonzero off-diagonal magnetoelectric tensor elements (forbidden by R (3) over bar symmetry) followed by a polarization flop accompanying the spin flop transition at mu H-0(SF) = 6.5T. Mossbauer spectroscopy on MnTiO3 gently doped with Fe-57 was used to help shed light on the impact of the supercell on the observed behavior. Although the full supercell structure could not be solved at this time due to a lack of visible reflections, the full scope of the results presented here suggest that the role of local spin-lattice coupling in the magnetoelectric properties of MnTiO3 is likely more important than previously thought.

Title:
Magnetic ordering in pressure-induced phases with giant spin-driven ferroelectricity in multiferroic TbMnO3
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Osakabe, T; Kikkawa, A; Kitazawa, H Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Osakabe, Toyotaka; Kikkawa, Akiko; Kitazawa, Hideaki
Source:
PHYSICAL REVIEW B, 93 (8):10.1103/PhysRevB.93.081104 FEB 16 2016
Abstract:
In order to clarify the mechanism associated with pressure/magnetic-field-induced giant ferroelectric polarization in TbMnO3, this work investigated changes in magnetic ordering brought about by variations in temperature, magnetic field, and pressure. This was accomplished by means of neutron diffraction analyses under high pressures and high magnetic fields, employing a single crystal. The incommensurate magnetic ordering of a cycloid structure was found to be stable below the reported critical pressure of 4.5 GPa. In contrast, a commensurate E-type spin ordering of Mn spins and a noncollinear configuration of Tb spins with k = (0, 1/2,0) appeared above 4.5 GPa. The application of a magnetic field along the a axis (H-parallel to a) under pressure induces a k = (0,0,0) antiferromagnetic structure in the case of Tb spins above H-parallel to a, enhancing the ferroelectric polarization, while the E-type ordering of Mn spins is stable even above the critical field. From the present experimental findings, we conclude that the E-type ordering of Mn spins induces giant ferroelectric polarization through an exchange striction mechanism. The H-parallel to a-induced polarization enhancement can be understood by considering that the polarization, reduced by the polar ordering of Tb moments in a zero field, can be recovered through a field-induced change to nonpolar k = (0,0,0) ordering at H-parallel to a similar to 2 T.

Title:
Alumina nanowire growth by water decomposition and the peritectic reaction of decagonal Al65Cu15Co20 quasicrystals
Authors:
Tellez-Vazquez, JO; Patino-Carachure, C; Rosas, G Author Full Names: Tellez-Vazquez, J. O.; Patino-Carachure, C.; Rosas, G.
Source:
MATERIALS CHARACTERIZATION, 112 155-159; 10.1016/j.matchar.2015.12.023 FEB 2016
Abstract:
In this paper, the results of the Al2O3 nanowires' growth through a chemical reaction between Al and water vapor at 1050 degrees C are presented. Our approach is based on two primary considerations. First, at room temperature, the Al65Cu15Co20 alloy is affected by the following mechanism: 2AI (s) + 3H(2)O (g) -> Al2O3 (s) + H-2 (g). In this reaction, the released hydrogen induces cleavage fracture of the material to form small particles. Second, the Al65Cu15Co20 quasicrystalline phase is transformed on heating to liquid + Al (Cu, Co) cubic phase through a peritectic reaction at 1050 degrees C. The Al-rich liquid then reacts with water vapor, forming Al2O3 nanowires. X-ray diffraction (XRD) analysis shows that the formed nanowires have a hexagonal structure, and infrared analysis further confirms the presence of alpha-Al2O3 phase in the final products. Transmission electron microscopy observations show that nanoparticles are present at the end of nanowires, suggesting the VLS growth mechanism. Elemental analysis by energy dispersive spectroscopy (EDS) indicates that the particles at the tip of the nanowires are mainly formed by Co and Cu alloying elements and small amounts of Al. Electron microscopy observations showed nanowires with diameters ranging from 20 to 70 nm; the average diameter was 37 nm and the nanowire lengths were up to several micrometers. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Structure and reactivity with oxygen of Pr2NiO4+delta: an in situ synchrotron X-ray powder diffraction study
Authors:
Broux, T; Prestipino, C; Bahout, M; Paofai, S; Elkaim, E; Vibhu, V; Grenier, JC; Rougier, A; Bassat, JM; Hernandez, O Author Full Names: Broux, Thibault; Prestipino, Carmelo; Bahout, Mona; Paofai, Serge; Elkaim, Erik; Vibhu, Vaibhav; Grenier, Jean-Claude; Rougier, Aline; Bassat, Jean-Marc; Hernandez, Olivier
Source:
DALTON TRANSACTIONS, 45 (7):3024-3033; 10.1039/c5dt03482e 2016
Abstract:
The promising SOFC cathode material Pr2NiO4.22 has been studied in situ under a pure oxygen atmosphere from 25 to 950 degrees C by high resolution synchrotron X-ray powder diffraction. At room temperature (RT) delta = 0.22(1), the average crystal structure turns out to be monoclinic. The subtle monoclinic distortion (gamma = 90.066(1)degrees at RT), retained up to 460 degrees C, is interpreted in terms of specific tilt schemes of the NiO6 octahedra. It is also shown that Pr2NiO4.22 is incommensurately structurally modulated already at room temperature, in the same manner as the homologous cobaltate La2CoO4.14. The phase transition to the High Temperature Tetragonal (HTT) phase was completed at 480 degrees C without any evidence for the Low Temperature Orthorhombic (LTO) phase allowing clarifying the phase diagram of this K2NiF4-type ternary oxide. Moreover, it turns out that above 800 degrees C, the HTT phase transforms reversibly into two coexisting isomorphous tetragonal phases. The incommensurate modulation subsists up to 950 degrees C, although modified concomitantly with the two abovementioned phase transformations. In addition, the role of kinetics on the decomposition process is highlighted through thermo-gravimetric analyses.

Update: 3-Mar-2016


Title:
Analysis of modulated Ho2PdSi3 crystal structure at Pd K and Ho L absorption edges using resonant elastic X-scattering
Authors:
Nentwich, M; Zschornak, M; Richter, C; Novikov, D; Meyer, DC Author Full Names: Nentwich, Melanie; Zschornak, Matthias; Richter, Carsten; Novikov, Dmitri; Meyer, Dirk C.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (6):10.1088/0953-8984/28/6/066002 FEB 17 2016
Abstract:
Replacing Si atoms with a transition metal in rare earth disilicides results in a family of intermetallic compounds with a variety of complex magnetic phase transitions. In particular, the family R2PdSi3 shows interesting magnetic behavior arising from the electronic interaction of the R element with the transition metal in the Si network, inducing the specific structure of the related phase. Within this series, the highest degree of superstructural order was reported for the investigated representative Ho2PdSi3, although several competing superstructures have been proposed in literature. The diffraction anomalous fine structure (DAFS) method is highly sensitive to the local structure of chosen atoms at specific positions within the unit cell of a crystalline phase. In combination with x-ray absorption fine structure (XAFS), this sophisticated synchrotron method has been applied in the present work to several selected reflections, i.a. a satellite reflection. Extensive electronic modeling was used to test the most relevant structure proposals. The 2 x 2 x 8 superstructure has been strongly confirmed, although a small amount of disorder in the modulation is very probable.

Title:
Effect of LiH on electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal
Authors:
Liu, DY; Zhao, Z; Luo, TH; Xing, C; Fei, L; Lin, J; Hou, JH; Jiang, DY; Liu, WQ; Wang, LM Author Full Names: Liu, Dongyan; Zhao, Zhen; Luo, Tianhao; Xing, Cheng; Fei, Liang; Lin, Jing; Hou, Jianhua; Jiang, Dayong; Liu, Wanqiang; Wang, Limin
Source:
SOLID STATE SCIENCES, 52 19-22; 10.1016/j.solidstatesciences.2015.12.002 FEB 2016
Abstract:
The electrochemical hydrogen storage properties and mechanisms of the Ti55V10Ni35 quasicrystal + xLiH(x = 3, 6 and 9 wt.%) system are investigated and discussed in this paper. A composite material in the Ti55V10Ni35 quasicrystal and system has been synthesized moderately by means of mechanical milling under an argon atmosphere, which can avoid reaction of releasing of hydrogen during the process of milling. The results indicate that the addition of LiH significantly improves the electrochemical characteristics of composite material. The maximum discharge capacity increases from 220.1 mAh/g to 292.3 mAh/g on Ti55V10Ni35 + 6 wt.% LiH, and the cycling stability is also enhanced too. In addition, the high rate dischargeability (HRD) is ameliorated remarkably, and the value of HRD value at 240 mA/g rises by 78.1%-87.8% for Ti55V10Ni35 + 6 wt.% LiH alloy electrodes. The improvement of characteristics of the electrochemical hydrogen storage characteristics may be attributed to LiH, which has excellent electrochemical activity. (C) 2015 Elsevier Masson SAS. All rights reserved.

Title:
Synthesis, structure, and magnetic characterization of Cr4US8
Authors:
Ward, MD; Chan, IY; Malliakas, CD; Lee, M; Choi, ES; Ibers, JA Author Full Names: Ward, Matthew D.; Chan, Ian Y.; Malliakas, Christos D.; Lee, Minseong; Choi, Eun Sang; Ibers, James A.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 233 67-74; 10.1016/j.jssc.2015.10.009 JAN 2016
Abstract:
The compound Cr4US8 has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2(1)/c (0 alpha gamma)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS6 octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr4US8 is complex. At temperatures above similar to 120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and chi(T) decreases monotonously with temperature, which is reminiscent of the Curie-Weiss law. At lower temperatures, the temperature dependence of chi(T) is complex and strongly dependent on the magnetic field strength. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Electronic transport in polycrystalline samples of icosahedral phases
Authors:
Vekilov, YK; Chernikov, MA; Dolinichek, Y Author Full Names: Vekilov, Yu. Kh.; Chernikov, M. A.; Dolinichek, Ya.
Source:
PHYSICS OF METALS AND METALLOGRAPHY, 117 (1):16-21; 10.1134/S0031918X15110113 JAN 2016
Abstract:
The low-temperature electronic transport in polycrystals of quasicrystalline phases with an icosahedral structure has been analyzed within the model of the granular electronic system. In this model, the grains (drops) of a metallic icosahedral phase are surrounded by extended defects and grain boundaries, which create an insulating environment. The electron transport in this model is determined by the size quantization of electronic states inside metallic grains, by intergranular tunneling, and by electrostatic barriers. Depending on the temperature and structural state of the system, the hopping conductivity with variable lengths of jumps in the Efros-Shklovskii or Mott regime is observed with predominantly elastic cotunneling. In the case of strong intergranular coupling, the system passes into the metallic regime with the exponential temperature dependence of the electrical conductivity.

Update: 25-Feb-2016


Title:
From an electron micrograph to a postage stamp
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 27 (1):5-7; SI 10.1007/s11224-015-0629-1 FEB 2016
Abstract:
Soon following Dan Shechtman's discovery of quasicrystals, Agnes Csanady and her associates started producing beautiful quasicrystals of flowerlike morphology. The image of one of their specimen appeared on the Israeli postage stamp honoring Shechtman's discovery, his Nobel Prize, and the International Year of Crystallography.

Title:
Ultrafast resonant soft x-ray diffraction dynamics of the charge density wave in TbTe3
Authors:
Moore, RG; Lee, WS; Kirchman, PS; Chuang, YD; Kemper, AF; Trigo, M; Patthey, L; Lu, DH; Krupin, O; Yi, M; Reis, DA; Doering, D; Denes, P; Schlotter, WF; Turner, JJ; Hays, G; Hering, P; Benson, T; Chu, JH; Devereaux, TP; Fisher, IR; Hussain, Z; Shen, ZX Author Full Names: Moore, R. G.; Lee, W. S.; Kirchman, P. S.; Chuang, Y. D.; Kemper, A. F.; Trigo, M.; Patthey, L.; Lu, D. H.; Krupin, O.; Yi, M.; Reis, D. A.; Doering, D.; Denes, P.; Schlotter, W. F.; Turner, J. J.; Hays, G.; Hering, P.; Benson, T.; Chu, J. -H.; Devereaux, T. P.; Fisher, I. R.; Hussain, Z.; Shen, Z. -X.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024304 JAN 25 2016
Abstract:
Understanding the emergence of collective behavior in correlated electron systems remains at the forefront of modern condensed matter physics. Disentangling the degrees of freedom responsible for collective behavior can lead to insights into the microscopic origins of emergent properties and phase transitions. Utilizing an optical pump, resonant soft x-ray diffraction probe we are able to track, in real time, the dynamics of the charge density wave (CDW) in TbTe3, a model system that violates traditional views of a Fermi surface nested CDW. We observe coherent oscillations corresponding to the CDW amplitude mode at 2.4 THz and a coherent optical phonon mode at similar to 1.7 THz. We show how such observations reveal the anisotropic energy optimization between in-plane Te charge density modulations and the three-dimensional lattice coupling.

Title:
Ti-V-Ni with graphene-mixing icosahedral quasicrystalline composites: Preparation, structure and its application in Ni-MH rechargeable batteries
Authors:
Lin, J; Lu, C; Sun, LS; Liang, F; Cao, ZY; Wang, LM Author Full Names: Lin, Jing; Lu, Chong; Sun, Lianshan; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 41 (2):1098-1103; 10.1016/j.ijhydene.2015.11.067 JAN 12 2016
Abstract:
The Ti-V-Niquasicrystalline was prepared by arc-melting and subsequent melt-spinning technique, and the Ti1.4V0.6Ni + x graphene (x = 3, 5, 7, 10 and 13, wt%) composites were obtained by mechanical ball-milling method. The structures and electrochemical hydrogen storage properties of the composites were investigated. The results showed that, the structures of the composites contained icosahedral quasicrystal, Ti2Ni-type, NiTi and graphene phases. The electrochemical hydrogen storage properties of the composites were improved with graphene addition. The cycling stabilities after 50 charging/discharging cycles of Ti1.4V0.6Ni + x graphene composites were improved obviously, especially the Ti1.4V0.6Ni + 10 graphene composite showed the best cycling stability of 70.3%, increased by 6.5%, compared with the Ti1.4V0.6Ni electrode. The high-rate discharge abilities of the composites were also increased appreciably. The improvement in the hydrogen storage characteristics should own to the proper graphene addition and that could cause copacetic electrocatalytic activity and anti-corrosion ability. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Orientation Relations and Conversion Matrix Between M3 Supercell and Pseudohexagonal Subcell in Tricalcium Silicate Solid Solution
Authors:
Min, HH; Xu, F; Lu, YN; Yang, J; Ding, LF; Su, F; Zhu, JM Author Full Names: Min Hui-Hua; Xu Feng; Lu Yi-Nong; Yang Jing; Ding Lin-Fei; Su Fan; Zhu Jian-Min
Source:
CHINESE JOURNAL OF INORGANIC CHEMISTRY, 32 (1):145-152; JAN 10 2016
Abstract:
A M3 modification of tricalcium silicate (C3S) solid solution was investigated using transmission electron microscope (TEM). Selected area electron diffraction (SAED) patterns and high resolution transmission electron microscopy (HRTEM) images were analyzed based on a pseudohexagonal subcell (Space group R3m; a=0.705 9 nm, b=0.705 5 nm, c=2.492 4 nm, alpha=89.79 degrees,beta=90.04 degrees, gamma=120.14 degrees). Reflections caused by the superstructure were proven to occur along the modulation wave vector [(1) over bar .17](H)(*) with one-dimensional type and could be expressed as ha+kb+lc*+m/[6(-a+b+7C*)], where m=+/- 1,+/- 2 and +/- 3. SAED patterns and HRTEM images based on the M3 supercell (Space group Cm; a=3.310 8 nm, b=0.703 6 nm, c=1.852 1 nm, beta=94.137 degrees) were simulated and finally the orientation relations between M3 supercell and pseudohexagonal subcell were established as follows: (600)(M3), (020)(M3) and (006)(M3) were equivalent to ((1) over bar1 (2) over bar)(H), ((1) over bar(1) over bar0)(H) and ((1) over bar 17)(H)* respectively, and [100](M3)//[(7) over bar7 (2) over bar](H), [010](M3)// [(1) over bar(1) over bar0](H), and [001](M3)//[(1) over bar 11](H): Furthermore, the conversion matrix between M3 supercell and pseudohexagonal subcell was established.

Title:
Soft spherical nanostructures with a dodecagonal quasicrystal-like order
Authors:
Rochal, SB; Konevtsova, OV; Shevchenko, IA; Lorman, VL Author Full Names: Rochal, S. B.; Konevtsova, O. V.; Shevchenko, I. A.; Lorman, V. L.
Source:
SOFT MATTER, 12 (4):1238-1247; 10.1039/c5sm02265g 2016
Abstract:
We develop a theory which predicts curvature-related structural peculiarities of soft spherical nanostructures with a dodecagonal local arrangement of subunits. Spherical templates coated with a thin film of a soft quasicrystal (QC)-forming material constitute the most promising direction to realize these nanostructures. Disordered and perfect spherical nanostructures are simulated using two approaches. The first of them models a random QC-like spherical nanostructure with extended curvature-induced topological defects similar to scars in colloidal spherical crystals. The second approach is inspired by the physics of viral capsids. It deals with the most regular spherical nanostructures with a local QC-like order derived from three well-known planar dodecagonal tilings. We explain how the additional QC-like degrees of freedom assist the nanostructure stabilization and determine the point defect number and location without extended scar formation. Unusual for nanoassemblies snub cube geometry is shown to be the most energetically favorable global organization of these spherical QC nanostructures.

Title:
Thermal conductivity of solid thiophene in an incommensurate orientational state
Authors:
Korolyuk, OA; Krivchikov, AI; Vdovichenko, GA; Romantsova, OO; Horbatenko, YV Author Full Names: Korolyuk, O. A.; Krivchikov, A. I.; Vdovichenko, G. A.; Romantsova, O. O.; Horbatenko, Yu. V.
Source:
LOW TEMPERATURE PHYSICS, 42 (1):68-73; 10.1063/1.4940993 JAN 2016
Abstract:
The thermal conductivity of solid thiophene at equilibrium vapor pressure between 2K < T < 170K, has been measured in a sequence of incommensurate metastable orientationally disordered phases II, II1, II2, and II2g with different degrees of orientational ordering of the molecules. It is found that in phase states II, II1 and II2 with dynamic orientational disorder of the molecules, the thermal conductivity does not depend on the temperature. It is shown that the temperature dependence of the thermal conductivity kappa(T) of orientational glass V-g and II2g (incommensurate) does not have any of the anomalies that are typical for amorphous materials and glasses. The temperature dependence kappa(T) of the incommensurate state of orientational glass II2g is bell-shaped, which is typical for the thermal conductivity of crystals with long-range orientational order. In the II2g state, as temperature drops from T-g to almost 10K, the thermal conductivity increases according to kappa(T) = A/T + B, where the first term describes the input of the propagating phonons, wherein the average length of their mean free path is greater than half of the phonon wavelength. The B term is associated with the input of localized short-wave, or "diffuse" vibrational modes. At low temperatures T <= 7K, kappa(T) proportional to T-3 is observed with increasing temperatures, which corresponds to the boundary scattering of phonons. (C) 2016 AIP Publishing LLC.

Title:
Synthesis of quasi-crystalline phases in the Al-Cu-Fe-Cr system
Authors:
Chugunov, DB; Meshkov, LL; Kalmykov, KB; Osipov, AK Author Full Names: Chugunov, D. B.; Meshkov, L. L.; Kalmykov, K. B.; Osipov, A. K.
Source:
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY, 61 (1):11-17; 10.1134/S003602361601006X JAN 2016
Abstract:
Phase equilibria in the Al-Cu-Fe system alloyed with 5% Cr were studied. Based on the data of X-ray powder diffraction analysis, electron microscopy, and differential thermal analysis, the effect of temperature on i a double dagger" d phase transitions in alloys Al65Cu25Fe5Cr5 and Al70Cu20Fe5Cr5. In the Al-Cu-Fe-Cr system, multiphase structures were detected; these structures are mixtures of quasi-crystalline and approximant phases, the contents and morphologies of which depend on the composition of the initial mixture and the crystallization rate.

Title:
STRUCTURE AND MECHANICAL PROPERTIES OF QUASICRYSTALLINE AND APPROXIMANT PHASES OBTAINED FROM TITANIUM-BASED QUINARY ALLOY
Authors:
Firstov, SA; Gorban', VF; Karpets, MV; Krapivka, NA; Danilenko, NI; Pechkovskii, EP; Rokitskaya, EA Author Full Names: Firstov, S. A.; Gorban', V. F.; Karpets, M. V.; Krapivka, N. A.; Danilenko, N. I.; Pechkovskii, E. P.; Rokitskaya, E. A.
Source:
STRENGTH OF MATERIALS, 47 (6):781-788; 10.1007/s11223-015-9714-3 NOV 2015
Abstract:
The paper presents the investigation of influence of cooling rate and conditions of melt crystallization on the change in phase composition and physical and mechanical properties of alloy Ti60Cr30Al3Si2(SiO2)(5). The influence of thermal treatment on the stability and properties of quasicrystalline and approximant phases is studied. Using the method of high-temperature indentation it is found that the diffusive mechanism of plastic strain of the alloy is strongly observed at 800 degrees C (0.68T(m)).

Update: 18-Feb-2016


Title:
Structural and electrocaloric properties of multiferroic-BiFeO3 doped 0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3) solid solutions
Authors:
Zheng, GP; Uddin, S; Zheng, XC; Yang, JH Author Full Names: Zheng, Guang-Ping; Uddin, Sarir; Zheng, Xiucheng; Yang, Junhe
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 663 249-255; 10.1016/j.jallcom.2015.12.056 APR 5 2016
Abstract:
Single-phase (1-x)(0.94Bi(0.5)Na(0.5)TiO(3)-0.06BaTiO(3))-xBiFeO(3) (BNT-BT-xBF, x = 0.05, 0.1 and 0.15) solid solutions are fabricated using a modified citrate method. The structural, ferroelectric and electrocaloric properties are significantly affected by the multiferroic BiFe03 doping, which is found to favor the antiferroelectric (AFE) state of the solid solutions. The dynamic mechanical analysis suggests that the BiFeO3 induced ordering of oxygen octahedrons plays a dominant role in the formation of AFE incommensurate phases and leads to the enhanced negative electrocaloric effect (ECE). A maximum ECE temperature change of 1.65 degrees C under an applied field of 70 kV/cm is observed. It is suggested that the magnetoelectric coupling is effective in enhancing the negative ECE in BNT-BT-xBF. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Indirect assessment of the surface energy of the Al-Cu-Fe quasicrystal
Authors:
de Lima, DCG; Dos Passos, TA; de Weerd, MC; Kenzari, S; Medeiros, RG; de Lima, SJG; Dubois, JM Author Full Names: Guedes de Lima, Danielle Cavalcante; Dos Passos, Tiberio Andrade; de Weerd, Marie-Cecile; Kenzari, Samuel; Medeiros, Rodinei Gomes; Guedes de Lima, Severino Jackson; Dubois, Jean-Marie
Source:
JOURNAL OF MATERIALS SCIENCE, 51 (8):4070-4078; 10.1007/s10853-016-9728-7 APR 2016
Abstract:
This work summarizes an attempt to estimate the surface energy of the stable, icosahedral Al-Cu-Fe quasicrystal (i-ACF hereafter). To this end, samples of i-ACF were prepared by sintering a powder produced by ball milling and heat treating a master ingot of composition Al59Cu25.5Fe12.5B3 (at.%), icosahedral lattice structure, and containing negligibly small amounts of contaminating crystalline phases. This powder was then sintered in the shape of a cylinder appropriate for pin-on-disk tests in ambient air. Variable amounts of either Sn or Bi were added to the powder prior to sintering. These elements do not dissolve in the quasicrystal and form small pockets of pure Sn or Bi that are either isolated or percolating, depending on the added volume of metal. Analysis of pin-on-disk data deduced from tests performed at room temperature allows us to conclude that the surface energy of the quasicrystal itself falls between the respective surface energies of the pure metals: gamma(Bi) a parts per thousand currency sign gamma(QC) a parts per thousand currency sign gamma(Sn) or 0.5 a parts per thousand currency sign gamma(i-ACF) a parts per thousand currency sign 0.8 J/m(2).

Title:
Flexoelectricity, incommensurate phases and the Lifshitz point
Authors:
Pottker, H; Salje, EKH Author Full Names: Poettker, Henning; Salje, Ekhard K. H.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/075902 FEB 24 2016
Abstract:
The solutions for the minimizers of the energy density f(q, p) = Aq(2) + Bq(4) + p(2) + g(A,B) + beta(q'p-p'q) + vertical bar q'vertical bar(2) + k vertical bar p'vertical bar(2) describe the flexoelectric effect with a flexoelectric coupling coefficient beta. The order parameters q and p can be visualized as strain and polarisation, respectively. The parameter k denotes the ratio of intrinsic length scales for q and p. We show that the structural ground-states include 3 phases, namely the paraelastic state q = p = 0, the ferroelastic state where polarization exists inside and near twin boundaries, and the incommensurate (modulated) phases with a very rich array of structural modulations ranging from nearly pure sine waves to kink arrays and ripple states. The phases coincide in the multicritical Lifshitz point. Linear flexoelectricity p similar to q' is encountered only approximately inside the ferroelastic phase and near the phase boundary between the paraelastic phase and the incommensurate phase. The relationship between the polarisation and the strain gradient is highly non-linear in all other states. The spatial profiles and energy distributions are discussed in detail.

Title:
Muon-spin relaxation study of the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In)
Authors:
Williams, RC; Xiao, F; Thomas, IO; Clark, SJ; Lancaster, T; Cornish, GA; Blundell, SJ; Hayes, W; Paul, AK; Felser, C; Jansen, M Author Full Names: Williams, R. C.; Xiao, F.; Thomas, I. O.; Clark, S. J.; Lancaster, T.; Cornish, G. A.; Blundell, S. J.; Hayes, W.; Paul, A. K.; Felser, C.; Jansen, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 28 (7):10.1088/0953-8984/28/7/076001 FEB 24 2016
Abstract:
We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2BOsO6 (B = Fe, Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below T-N = 135 +/- 2 K. Upon cooling below T-2 approximate to 67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below T-N = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.

Title:
B-cation effect on relaxor behavior and electric properties in Sr2NaNb5-xSbxO15 tungsten bronze ceramics
Authors:
Fan, JY; Yang, B; Wei, LL; Wang, ZM Author Full Names: Fan, Jianyong; Yang, Bian; Wei, Lingling; Wang, Zhongming
Source:
CERAMICS INTERNATIONAL, 42 (3):4054-4062; 10.1016/j.ceramint.2015.11.077 FEB 15 2016
Abstract:
Sr2NaNb5-xSbxO15 ceramics (SNNS, x=0.0, 0.3, 0.5, 1.0) with 'filled' tungsten bronze structure were prepared by the conventional solid-state reaction method. Effects of introducing Sb concentration in B-sites on the microstructure, dielectric and ferroelectric properties were investigated in detail. With increasing of Sb concentration, the crystal structure of SNNS ceramics distorted slightly from the TB orthorhombic Ccm2 phase to tetragonal P4bm phase, and then to paraelectric P4/mbm phase at room temperature. The smaller ionic radius of Sb5+ (0.60 angstrom) compared with that of Nb5+ (0.64 angstrom) contributed to the shrinkage of crystal structure. It was found that accompanying with the introduction of Sb, some unique dielectric and ferroelectric behavior emerged for SNNS ceramics. Only the samples with x < 0.5 showed additional dielectric anomaly in low temperature range, which was attributed to the incommensurate superstructure ICS-associated dielectric dispersion process caused by local structural fluctuation. With increasing of Sb concentration, T-c shifted to lower temperatures, and the diffuse phase transition and relaxor behavior appeared to be exceptionally induced around T-c at higher Sb concentration. The underlying mechanisms of relaxor behavior induced by different Sb concentration in B-sites for SNNS ceramics were clarified in detail. Moreover, the ferroelectric properties deteriorated and even disappeared at higher Sb concentration, because the ceramics showed P4/mbm phase structure as a result of decreasing of T-c to lower than room temperature. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Title:
Glass-like Lattice Thermal Conductivity and Thermoelectric Properties of Incommensurate Chimney-Ladder Compound FeGe gamma
Authors:
Sato, N; Ouchi, H; Takagiwa, Y; Kimura, K Author Full Names: Sato, Naoki; Ouchi, Hideyasu; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
CHEMISTRY OF MATERIALS, 28 (2):529-533; 10.1021/acs.chemmater.5b03952 JAN 26 2016
Abstract:
We have characterized the thermoelectric properties of FeGe gamma which is one of the promising Nowotny chimney-ladder compounds. A glass-like low lattice thermal conductivity below 1.0 W m(-1) K-1 is observed around 373 K because of its complex structural nature, i.e., incommensurate structure. A first-principles band structure calculation implies that a narrow band gap of similar to 0.2 eV is formed near the Fermi level for a hypothetical composition of Fe2Ge3 with a Ru2Sn3-type structure, leading to a large power factor of 1.90 mW m(-1) K-2 near 600 K. The maximum dimensionless figure-of-merit of 0.57 is attractive as a starting point; calculation using the Boltzmann transport equation under a constant relaxation time approximation predicts that a further enhancement of ZT exceeding unity at 600-700 K can be achieved by optimizing the valence electron count per transition metal and further reduction of the lattice thermal conductivity.

Title:
Modulated structures and associated microstructures in the ferroelectric phase of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0
Authors:
Tsukasaki, H; Ishii, Y; Tanaka, E; Kurushima, K; Mori, S Author Full Names: Tsukasaki, Hirofumi; Ishii, Yui; Tanaka, Eri; Kurushima, Kosuke; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 55 (1):10.7567/JJAP.55.011502 JAN 2016
Abstract:
In order to understand the ferroelectric and ferroelastic phases in Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0, we have investigated the crystal structures and their associated microstructures of the ferroelectric and ferroelastic phases mainly by transmission electron microscopy (TEM) and scanning transmission electron microscopy-high-angle angular dark-field (STEM-HAADF) experiments, combined with powder X-ray diffraction experiments. Electron diffraction experiments showed that the ferroelectric and ferroelastic phases of Ba1-xSrxAl2O4 for 0.7 <= x <= 1.0 should be characterized as a modulated structure with the modulation vector of q = 0, 1/2, 0, whose space group should be monoclinic P2(1). High-resolution TEM experiments revealed that the microstructures in the monoclinic phase can be characterized as twin structures and nanometer-sized planar defects due to the monoclinic structure with the modulated structures, which are responsible for anomalous elastic behaviors and mechanoelectro-optical properties. In addition, subatomic-resolution STEM-HAADF images clearly indicated that the displacement of Al3+ ions involved in the AlO4 tetrahedra should play a crucial role in the formation of the modulated structures and twin structures. (C) 2016 The Japan Society of Applied Physics

Title:
Influence of high energy milling on the microstructure and magnetic properties of the AlCu-Fe phases: the case of the i-Al64Cu23Fe13 quasicrystalline and the omega-Al70Cu20Fe10 crystalline phases
Authors:
Quispe, MP; Landauro, CV; Vergara, MZP; Quispe-Marcatoma, J; Rojas-Ayala, C; Pena-Rodriguez, VA; Baggio-Saitovitch, E Author Full Names: Pillaca Quispe, Mirtha; Landauro, Carlos V.; Pinto Vergara, Milida Z.; Quispe-Marcatoma, Justiniano; Rojas-Ayala, Chachi; Pena-Rodriguez, Victor A.; Baggio-Saitovitch, Elisa
Source:
RSC ADVANCES, 6 (7):5367-5376; 10.1039/c5ra21093c 2016
Abstract:
The effect of mechanical milling in i-Al64Cu23Fe13 quasicrystalline and omega-Al70Cu20Fe10 crystalline phases is systematically investigated in the present work. The Al-Cu-Fe samples were obtained by arc furnace technique and then nanostructured by means of mechanical milling. The results indicate that the solid samples present a weak ferromagnetic behavior at 300 K, showing a saturation magnetization of 0.124 emu g(-1) for the icosahedral phase (i-phase) and 0.449 emu g(-1) for the tetragonal phase (omega phase). These small values could be an indication that only a few percentage of Fe atoms carry magnetic moment. The magnetic response in the nanostructured u-phase increases up to 3.5 times higher than its corresponding solid counterpart. Whereas for the i-phase this increment is about 16 times higher. Moreover, the speed of the variation of the studied physical parameters after reducing the average grain size has been obtained from the exponent (alpha) of a power law fit of the experimental data. The values of a, corresponding to the magnetic response, are slightly different in each phase, which should be related to the different chemical composition and/or the type of long range order. Additionally, we also search for a critical grain size. However, this critical value has not been observed in the studied samples.

Update: 10-Feb-2016


Title:
Magnetic structures in TmPdIn and TmAgSn
Authors:
Baran, S; Szytula, A; Kaczorowski, D; Damay, F Author Full Names: Baran, S.; Szytula, A.; Kaczorowski, D.; Damay, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 11-15; 10.1016/j.jallcom.2015.11.200 MAR 25 2016
Abstract:
Low temperature antiferromagnetic structures of TmPdIn and TmAgSn have been derived from powder neutron diffraction data. The magnetic structure of TmPdIn is a commensurate one and related to a propagation vector (k) over right arrow = [1/3, 1/3, 1/2] while the incommensurate sine-modulated structure of TmAgSn is connected with (k) over right arrow = [k(x), -k(x), 0] where k(x) = 0.1314(2). The thulium magnetic moments are constrained within the basal plane and show 'triangular' arrangement. Validity of obtained magnetic structures is discussed on the basis of symmetry analysis. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Mossbauer spectroscopy, magnetic, and ab-initio study of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal
Authors:
Nejadsattari, F; Stadnik, ZM; Przewoznik, J; Grushko, B Author Full Names: Nejadsattari, Farshad; Stadnik, Zbigniew M.; Przewoznik, Janusz; Grushko, Benjamin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 662 612-620; 10.1016/j.jallcom.2015.12.115 MAR 25 2016
Abstract:
The structural, magnetic, and Mossbauer spectral properties of the approximant Al76Ni9Fe15 to a decagonal Al-Ni-Fe quasicrystal, complemented by ab-initio electronic structure and the hyperfine-interaction parameters calculations, are reported. The approximant studied crystallizes in the monoclinic space group C2/m with the lattice parameters a = 15.3898(3) angstrom, b = 8.0840(2) angstrom, c = 12.4169(2) angstrom, and beta = 107.870(2)degrees. The existence of a pseudogap in the calculated electronic density of states slightly above the Fermi level suggests electronic stabilization according to the Hume-Rothery-type mechanism. High metallicity of Al76Ni9Fe15 is predicted. Both the Mossbauer spectra and magnetic susceptibility data indicate that Al76Ni9Fe15 is a paramagnet down to 2.0 K. The presence of the distribution of the electric quadrupole splitting in the Mossbauer spectra measured in the temperature range 4.5-296.1 K is observed. The increase of the average quadrupole splitting with decreasing temperature is well described by a T-3/2 power-law relation. The Debye temperature of Al76Ni9Fe15 is found to be 431(3) K. (C) 2015 Elsevier B.V. All rights reserved.

Title:
The Use and Abuse of Transcranial Magnetic Stimulation to Modulate Corticospinal Excitability in Humans (vol 10, e0144151, 2015)
Authors:
Heroux, ME; Taylor, JL; Gandevia, SC Author Full Names: Heroux, Martin E.; Taylor, Janet L.; Gandevia, Simon C.
Source:
PLOS ONE, 11 (1):10.1371/journal.pone.0147890 JAN 21 2016

Title:
Composition-driven spin glass to ferromagnetic transition in the quasicrystal approximant Au-Al-Gd
Authors:
Ishikawa, A; Hiroto, T; Tokiwa, K; Fujii, T; Tamura, R Author Full Names: Ishikawa, A.; Hiroto, T.; Tokiwa, K.; Fujii, T.; Tamura, R.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024416 JAN 21 2016
Abstract:
We investigated the composition dependence of the magnetic susceptibility of the quasicrystal approximant Au-Al-Gd. A composition-driven ferromagnetic transition is observed in a quasicrystal approximant, which is attributed to the Ruderman-Kittel-Kasuya-Yosida (RKKY) oscillation via a variation in the Fermi wave vector. The ferromagnetic transition is most simply understood as a result of the close matching of the nearest and second-nearest spin distances with the maximum positions of the RKKY potential. The present work provides an idea that allows us to tailor the magnetic order via the electron concentration in quasicrystal approximants as well as in quasicrystals.

Title:
Complex phase diagram of Ba1-xNaxFe2As2: A multitude of phases striving for the electronic entropy
Authors:
Wang, L; Hardy, F; Bohmer, AE; Wolf, T; Schweiss, P; Meingast, C Author Full Names: Wang, L.; Hardy, F.; Boehmer, A. E.; Wolf, T.; Schweiss, P.; Meingast, C.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014514 JAN 19 2016
Abstract:
The low-temperature electronic phase diagram of Ba1-xNaxFe2As2, obtained using high-resolution thermal-expansion and specific-heat measurements, is shown to be considerably more complex than previously reported, containing nine different phases. Besides the magnetic C-2 and reentrant C-4 phases, we find evidence for an additional, presumably magnetic, phase below the usual spin-density-wave transition, as well as a possible incommensurate magnetic phase. All these phases coexist and compete with superconductivity, which is particularly strongly suppressed by the C-4-magnetic phase due to a strong reduction of the electronic entropy available for pairing in this phase.

Title:
Use of frit-disc crucibles for routine and exploratory solution growth of single crystalline samples
Authors:
Canfield, PC; Kong, T; Kaluarachchi, US; Jo, NH Author Full Names: Canfield, Paul C.; Kong, Tai; Kaluarachchi, Udhara S.; Jo, Na Hyun
Source:
PHILOSOPHICAL MAGAZINE, 96 (1):84-92; 10.1080/14786435.2015.1122248 JAN 2 2016
Abstract:
Solution growth of single crystals from high temperature solutions often involves the separation of residual solution from the grown crystals. For many growths of intermetallic compounds, this separation has historically been achieved with the use of plugs of silica wool. Whereas this is generally efficient in a mechanical sense, it leads to a significant contamination of the decanted liquid with silica fibres. In this paper, we present a simple design for frit-disc alumina crucible sets that has made their use in the growth single crystals from high temperature solutions both simple and affordable. An alumina frit-disc allows for the clean separation of the residual liquid from the solid phase. This allows for the reuse of the decanted liquid, either for further growth of the same phase, or for subsequent growth of other, related phases. In this paper, we provide examples of the growth of isotopically substituted TbCd6 and icosahedral i-RCd quasicrystals, as well as the separation of (i) the closely related Bi2Rh3S2 and Bi2Rh3.5S2 phases and (ii) PrZn11 and Pr2Zn17.

Title:
Mn3TeO6 - a new multiferroic material with two magnetic substructures
Authors:
Zhao, L; Hu, ZW; Kuo, CY; Pi, TW; Wu, MK; Tjeng, LH; Komarek, AC Author Full Names: Zhao, Li; Hu, Zhiwei; Kuo, Chang-Yang; Pi, Tun-Wen; Wu, Maw-Kuen; Tjeng, Liu Hao; Komarek, Alexander C.
Source:
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 9 (12):730-734; 10.1002/pssr.201510347 DEC 2015
Abstract:
From magnetic susceptibility, dielectric permittivity, electric polarization and specific heat measurements we discover spin-induced ferroelectricity and magnetoelectric coupling in Mn3TeO6 and observe two successive magnetic transitions at low temperatures. A non-ferroelectric intermediate magnetic state occurs below 23 K and a multiferroic ground state emerges below 21 K. Moreover, Mn3TeO6 is a candidate for a multiferroic material where two types of incommensurate spin structures, cycloidal and helical, coexist. Theoretically, both spin substructures may contribute to the macro electric polarization via different mechanisms. This could open new ways of manipulating the ferroelectric polarization in a multiferroic material. (c) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Update: 4-Feb-2016


Title:
Highly modulated structure and upconversion photoluminescence properties of PbGd2(MoO4)(4):Er3+/Yb3+ phosphors
Authors:
Lim, CS Author Full Names: Lim, Chang Sung
Source:
MATERIALS RESEARCH BULLETIN, 75 211-216; 10.1016/j.materresbull.2015.11.058 MAR 2016
Abstract:
Double molybdate of PbGd2-x(MoO4)(4):Er3+/Yb3+ phosphors with the correct doping concentrations of Er3+ and Yb3+ (x= Er3+ + Yb3+, Er3+ = 0.05, 0.1, 0.2 and Yb3+ = 0.2, 0.45) were successfully synthesized by microwave sol-gel process. The highly modulated structure and the upconversion photoluminescence properties were investigated in detail. The synthesized particles, formed after heat-treatment at 900 degrees C for 16 h, showed a well ctystallized morphology with particle sizes of 2-5 mu m. Under excitation at 980 nm, the PbGd1.7(MoO4)(4):Er(0.1)Ybo(0.2) and PbGd1.5(MoO4)(4):Er0.05Yb0.45 particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, and a very weak 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the disordered structures of PbGd2-x(MoO4)(4) by the incorporation of the Er3+ and Yb3+ ions into the crystal lattice, which resulted in the highly modulated structure as well as a concentration quenching effect of Er3+ ions. (C) 2015 Published by Elsevier Ltd.

Title:
Gabor frames for quasicrystals, K-theory, and twisted gap labeling
Authors:
Kreisel, M Author Full Names: Kreisel, Michael
Source:
JOURNAL OF FUNCTIONAL ANALYSIS, 270 (3):1001-1030; 10.1016/j.jfa.2015.11.011 FEB 1 2016
Abstract:
We study the connection between Gabor frames for quasicrystals, the topology of the hull of a quasicrystal A, and the K-theory of an associated twisted groupoid algebra. In particular, we construct a finitely generated projective module over this algebra, and any multiwindow Gabor frame for A can be used to construct an idempotent representing this module in K-theory. For lattice subsets in dimension two, this allows us to prove a twisted version of Bellissard's gap labeling theorem. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Observation of nonequilibrium behavior near the Lifshitz point in ferroelectrics with incommensurate phase
Authors:
Rushchanskii, KZ; Molnar, A; Bilanych, R; Yevych, R; Kohutych, A; Vysochanskii, YM; Samulionis, V; Banys, J Author Full Names: Rushchanskii, K. Z.; Molnar, A.; Bilanych, R.; Yevych, R.; Kohutych, A.; Vysochanskii, Yu. M.; Samulionis, V.; Banys, J.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014101 JAN 14 2016
Abstract:
We have investigated nonequilibrium properties of proper uniaxial Sn2P2(SexS1-x)(6) ferroelectrics with the type II incommensurate phase above Lifshitz point x(LP) similar to 0.28. We performed measurements of dielectric susceptibility in cooling and heating regimes with the rate ranging 0.002-0.1 K/min, as well as high-resolution ultrasound investigation and hypersound Brillouin scattering experiments. For samples with x >= 0.28 clear anomalies are observed at incommensurate second-order transition (T-i) and at first-order lock-in transition (T-c) in the regime of very slow cooling rate, whereas the intermediate incommensurate phase is not observed when the rate is faster than 0.1 K/min. In general, increasing the cooling rate leads to smearing of the anomaly at T-c. We relate this effect to cooling rate dependence of domain-wall concentration and their size: domain width decreases when cooling rate increases. At certain conditions, the size of domain is comparable to the incommensurate phase modulation period, which is in the micrometer range in the vicinity of Lifshitz point and leads to pinning of the modulation period by domain walls.

Title:
Spatial spin-modulated structure and hyperfine interactions of Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x=0, 0.05)
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gapochka, AM; Kiseleva, TY; Komarov, AE; Shatokhin, MS; Makarova, AO Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gapochka, A. M.; Kiseleva, T. Yu.; Komarov, A. E.; Shatokhin, M. S.; Makarova, A. O.
Source:
PHYSICS OF THE SOLID STATE, 58 (1):102-107; 10.1134/S1063783416010261 JAN 2016
Abstract:
The results of the Mossbauer studies on Fe-57 nuclei in multiferroics BiFe1-x T (x) O-3 (T = Sc, Mn; x = 0, 0.05) in the temperature range of 5.2-300 K have been presented. The Mossbauer spectra have been analyzed in terms of the model of an incommensurate spatial spin-*modulated structure* of cycloid type. Information has been obtained about the effect of the substitution of Sc and Mn atoms for Fe atoms on the hyperfine parameters of the spectrum: the shift and the quadrupole shift of the Mossbauer line, the isotropic and anisotropic contributions to the hyperfine magnetic field, and also the parameter of anharmonicity of the spatial spin-modulated structure.

Title:
Multilayered sandwich-like architecture containing large-scale faceted Al-Cu-Fe quasicrystal grains
Authors:
Wei, DX; He, ZB Author Full Names: Wei, Dongxia; He, Zhanbing
Source:
MATERIALS CHARACTERIZATION, 111 154-161; 10.1016/j.matchar.2015.11.027 JAN 2016
Abstract:
Faceted quasicrystals are structurally special compared with traditional crystals. Although the application of faceted quasicrystals has been expected, wide-scale application has not occurred owing to the limited exposure of the facets. Using a facile method of heat treatment, we synthesize a multilayered sandwich-like structure with each layer composed of large-scale pentagonal-dodecahedra of Al-Cu-Fe quasicrystals. Moreover, there are channels between the adjacent Al-Cu-Fe layers that serve to increase the exposure of the facets of quasicrystals. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction are used to characterize the multilayered architecture, and the generation mechanisms of this special structure are also discussed. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Effect of applied pressure on microstructure and mechanical properties of Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites prepared by squeeze casting
Authors:
Yang, L; Hou, H; Zhao, YH; Yang, XM Author Full Names: Yang, Ling; Hou, Hua; Zhao, Yu-hong; Yang, Xiao-min
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (12):3936-3943; 10.1016/S1003-6326(15)64041-9 DEC 2015
Abstract:
The Mg-Zn-Y quasicrystal-reinforced AZ91D magnesium matrix composites were prepared by squeeze casting process. The effects of applied pressure on microstructure and mechanical properties of the composites were investigated. The results show that squeeze casting process is an effective method to refine the grain. The composites are mainly composed of alpha-Mg, beta-Mg17Al12 and Mg3Zn6Y icosahedral quasicrystal phase (I-phase). With the increase of applied pressure, the contents of beta-Mg17Al12 phase and Mg3Zn6Y quasicrystal particles increase, further matrix grain refinement occurs and coarse dendritic alpha-Mg transforms into equiaxed grain structure. The composite exhibits the maximum ultimate tensile strength and elongation of 194.3 MPa and 9.2% respectively when the applied pressure is 100 MPa, and a lot of dimples appear on the tensile fractography. Strengthening mechanisms of quasicrystal-reinforced AZ91D magnesium matrix composites are chiefly fine-grain strengthening and quasicrystal particles strengthening.

Update: 28-Jan-2016


Title:
Controlling many-body states by the electric-field effect in a two-dimensional material
Authors:
Li, LJ; O'Farrell, ECT; Loh, KP; Eda, G; Ozyilmaz, B; Neto, AHC Author Full Names: Li, L. J.; O'Farrell, E. C. T.; Loh, K. P.; Eda, G.; Ozyilmaz, B.; Neto, A. H. Castro
Source:
NATURE, 529 (7585):185-U129; 10.1038/nature16175 JAN 14 2016
Abstract:
To understand the complex physics of a system with strong electron-electron interactions, the ideal is to control and monitor its properties while tuning an external electric field applied to the system (the electric-field effect). Indeed, complete electric-field control of many-body states in strongly correlated electron systems is fundamental to the next generation of condensed matter research and devices(1-3). However, the material must be thin enough to avoid shielding of the electric field in the bulk material. Two-dimensional materials do not experience electrical screening, and their charge-carrier density can be controlled by gating. Octahedral titanium diselenide (1T-TiSe2) is a prototypical two-dimensional material that reveals a charge-density wave (CDW) and superconductivity in its phase diagram(4), presenting several similarities with other layered systems such as copper oxides(5), iron pnictides(6), and crystals of rare-earth elements and actinide atoms(7). By studying 1T-TiSe2 single crystals with thicknesses of 10 nanometres or less, encapsulated in two-dimensional layers of hexagonal boron nitride, we achieve unprecedented control over the CDW transition temperature (tuned from 170 kelvin to 40 kelvin), and over the superconductivity transition temperature (tuned from a quantum critical point at 0 kelvin up to 3 kelvin). Electrically driving TiSe2 over different ordered electronic phases allows us to study the details of the phase transitions between many-body states. Observations of periodic oscillations of magnetoresistance induced by the Little-Parks effect show that the appearance of superconductivity is directly correlated with the spatial texturing of the amplitude and phase of the superconductivity order parameter, corresponding to a two-dimensional matrix of superconductivity. We infer that this superconductivity matrix is supported by a matrix of incommensurate CDW states embedded in the commensurate CDW states. Our results show that spatially modulated electronic states are fundamental to the appearance of two-dimensional superconductivity.

Title:
Structure of periodic crystals and quasicrystals in ultrathin films of Ba-Ti-O
Authors:
Cockayne, E; Mihalkovic, M; Henley, CL Author Full Names: Cockayne, Eric; Mihalkovic, Marek; Henley, Christopher L.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.020101 JAN 7 2016
Abstract:
We model the remarkable thin-film Ba-Ti-O structures formed by heat treatment of an initial perovskite BaTiO3 thin film on a Pt(111) surface. All structures contain a rumpled Ti-O network with all Ti threefold coordinated with O and with Ba occupying the larger. mainly Ti7O7, pores. The quasicrystal structure is a simple decoration of three types of tiles: square, triangle, and 30 degrees. rhombus, with edge lengths 6.85 angstrom, joined edge-to-edge in a quasicrystalline pattern; observed periodic crystals in ultrathin film Ba-Ti-O are built from these and other tiles. Simulated STM images reproduce the patterns seen experimentally and identify the bright protrusions as Ba atoms. The models are consistent with all experimental observations.

Title:
Ultrafast Metamorphosis of a Complex Charge-Density Wave
Authors:
Haupt, K; Eichberger, M; Erasmus, N; Rohwer, A; Demsar, J; Rossnagel, K; Schwoerer, H Author Full Names: Haupt, Kerstin; Eichberger, Maximilian; Erasmus, Nicolas; Rohwer, Andrea; Demsar, Jure; Rossnagel, Kai; Schwoerer, Heinrich
Source:
PHYSICAL REVIEW LETTERS, 116 (1):10.1103/PhysRevLett.116.016402 JAN 6 2016
Abstract:
Modulated phases, commensurate or incommensurate with the host crystal lattice, are ubiquitous in solids. The transition between such phases involves formation and rearrangement of domain walls and is generally slow. Using ultrafast electron diffraction, we directly record the photoinduced transformation between a nearly commensurate and an incommensurate charge-density-wave phase in 1T-TaS2. The transformation takes place on the picosecond time scale, orders of magnitude faster than previously observed for commensurate-to-incommensurate transitions. The transition speed and mechanism can be linked to the peculiar nanoscale structure of the photoexcited nearly commensurate phase.

Title:
Phase diagram of the Kondo lattice model on the kagome lattice
Authors:
Ghosh, S; Brien, PO; Henley, CL; Lawler, MJ Author Full Names: Ghosh, Shivam; Brien, Patrick O'; Henley, Christopher L.; Lawler, Michael J.
Source:
PHYSICAL REVIEW B, 93 (2):10.1103/PhysRevB.93.024401 JAN 4 2016
Abstract:
We consider the potential for novel forms of magnetism arising from the subtle interplay between electrons and spins in the underscreened kagome Kondo lattice model. At weak coupling, we show that incommensurate noncoplanar multiwave vector magnetic orders arise at nearly all fillings and that this results from Fermi surface effects that introduce competing interactions between the spins. At strong coupling, we find that such a complex order survives near half filling despite the presence of ferromagnetism at all other fillings. We show this arises due to state selection among a massive degeneracy of states at infinite coupling. Finally, we show that at intermediate filling only commensurate orders seem to survive, but these orders still include noncoplanar magnetism. So, the mere presence of both local moments and itinerant electrons enables complex orders to form unlike any currently observed in kagome materials.

Title:
Incommensurate to commensurate antiferromagnetism in CeRhAl4Si2: An Al-27 NMR study
Authors:
Sakai, H; Hattori, T; Tokunaga, Y; Kambe, S; Ghimire, NJ; Ronning, F; Bauer, ED; Thompson, JD Author Full Names: Sakai, H.; Hattori, T.; Tokunaga, Y.; Kambe, S.; Ghimire, N. J.; Ronning, F.; Bauer, E. D.; Thompson, J. D.
Source:
PHYSICAL REVIEW B, 93 (1):10.1103/PhysRevB.93.014402 JAN 4 2016
Abstract:
Al-27 nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAl4Si2, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of T-N1 = 14 K and T-N2 = 9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below T-N2, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between T-N1 and T-N2. The spin-lattice relaxation rate suggests that the 4 f electrons behave as local moments at temperatures above T-N1.

Title:
Trapping of Oxygen Vacancies at Crystallographic Shear Planes in Acceptor-Doped Pb-Based Ferroelectrics
Authors:
Batuk, D; Batuk, M; Tsirlin, AA; Hadermann, J; Abakumov, AM Author Full Names: Batuk, Dmitry; Batuk, Maria; Tsirlin, Alexander A.; Hadermann, Joke; Abakumov, Artem M.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 54 (49):14787-14790; 10.1002/anie.201507729 DEC 1 2015
Abstract:
The defect chemistry of the ferroelectric material PbTiO3 after doping with Fe-III acceptor ions is reported. Using advanced transmission electron microscopy and powder X-ray and neutron diffraction, we demonstrate that even at concentrations as low as circa 1.7% (material composition approximately ABO(2.95)), the oxygen vacancies are trapped into extended planar defects, specifically crystallographic shear planes. We investigate the evolution of these defects upon doping and unravel their detailed atomic structure using the formalism of superspace crystallography, thus unveiling their role in nonstoichiometry in the Pb-based perovskites.

Update: 14-Jan-2016


Title:
Dislocations in icosahedral quasicrystalline phase embedded in hot-deformed Mg alloys
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 658 483-487; 10.1016/j.jallcom.2015.10.284 FEB 15 2016
Abstract:
We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg-3.5Zn-0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Microstructures and phase transformations in as-aged Mn2.04NiGa Heusler alloy
Authors:
Du, ZW; Han, XL; Li, T; Liu, EK; Ma, XD; Xiong, JC; Wu, GH Author Full Names: Du, Z. W.; Han, X. L.; Li, T.; Liu, E. K.; Ma, X. D.; Xiong, J. C.; Wu, G. H.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 657 443-449; 10.1016/j.jallcom.2015.10.111 FEB 5 2016
Abstract:
The room-temperature microstructures and phase transformation of Mn2.04NiGa alloy were investigated by transmission electron microscopy (TEM), electron backscattered diffraction (EBSD) and high-angle annular dark field scanning-TEM (HAADF-STEM). The Mn2.04NiGa alloy annealed at 1073 K for 72 h is mainly austenite phase with Hg2CuTi-type structure. After 623 K/72 h ageing, nano-scaled MnNiGa precipitates considered as Ni2In-type hexagonal structure were found by TEM. A crystalline orientation relationship between precipitates and austensite can be described by ((22) over bar4)(A)//(0 (1) over bar 10)(H), [1 (1) over bar0](A)//[2 (11) over bar0](H). These precipitates are accompanying with Mn-rich martensite lamellae. Both non-modulated and nearly 16-layered modulated structures are generally in coexistence in one martensite lath. A crystalline orientation relationship between the ageing-induced martensite and austenite is (111)(A)//(110)(M), [011](A)//[1 (1) over bar2]M. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Origin of modulated phases and magnetic hysteresis in TmB4
Authors:
Wierschem, K; Sunku, SS; Kong, T; Ito, T; Canfield, PC; Panagopoulos, C; Sengupta, P Author Full Names: Wierschem, Keola; Sunku, Sai Swaroop; Kong, Tai; Ito, Toshimitsu; Canfield, Paul C.; Panagopoulos, Christos; Sengupta, Pinaki
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214433 DEC 23 2015
Abstract:
We investigate the low-temperature magnetic phases in TmB4, a metallic quantum magnet on the geometrically frustrated Shastry-Sutherland lattice, using coordinated experimental and theoretical studies. Our results provide an explanation for the appearance of the intriguing fractional plateau in TmB4 and accompanying magnetic hysteresis. Together with observation of the bump in the half plateau, our results support the picture that the magnetization plateau structure in TmB4 is strongly influenced by the zero-field modulated phases. We present a phenomenological model to explain the appearance of the modulated phases and a microscopic Hamiltonian that captures the complete magnetic behavior of TmB4.

Update: 7-Jan-2016


Title:
Magnetic properties and complex magnetic phase diagram in non-centrosymmetric EuRhGe3 and EuIrGe3 single crystals
Authors:
Maurya, A; Bonville, P; Kulkarni, R; Thamizhavel, A; Dhar, SK Author Full Names: Maurya, Arvind; Bonville, P.; Kulkarni, R.; Thamizhavel, A.; Dhar, S. K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 401 823-831; 10.1016/j.jmmm.2015.10.134 MAR 1 2016
Abstract:
We report the magnetic properties of two Eu based compounds, single crystalline EuIrGe3 and EuRhGe3, inferred from magnetisation, electrical transport, heat capacity and Eu-151 Mossbauer spectroscopy. These previously known compounds crystallise in the non-centrosymmetric, tetragonal, I4 mm, BaNiSn3-type structure. Single crystals of EuIrGe3 and EuRhGe3 were grown using a high temperature solution growth method using In as flux. EuIrGe3 exhibits two magnetic transition temperatures T-N1 = 12.4 K, and T(N)2 = 7.3 K, whereas EuRhGe3 presents a single one at T-N = 12K. Eu-151 Mossbauer spectra show evidence for a cascade of transitions from paramagnetic to incommensurate amplitude modulated followed by an equal moment phase at lower temperature in EuIrGe3. This latter phase alone occurs in EuRhGe3. In both compounds, the magnetisation measured up to 14 T suggests that the equal moment magnetic phase has a spiral spin arrangement. The field induced reorientations are also well documented in the magnetotransport data. A superzone gap is observed for the current density J vertical bar vertical bar [001], which is enhanced by a transverse magnetic field. The magnetic phase diagram constructed from all the data is complex, revealing the presence of many phases in the H - T space. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Structural and magnetic phase transitions in CeCu6-xT(x) (T = Ag, Pd)
Authors:
Poudel, L; de la Cruz, C; Payzant, EA; May, AF; Koehler, M; Garlea, VO; Taylor, AE; Parker, DS; Cao, HB; McGuire, MA; Tian, W; Matsuda, M; Jeen, H; Lee, HN; Hong, T; Calder, S; Zhou, HD; Lumsden, MD; Keppens, V; Mandrus, D; Christianson, AD Author Full Names: Poudel, L.; de la Cruz, C.; Payzant, E. A.; May, A. F.; Koehler, M.; Garlea, V. O.; Taylor, A. E.; Parker, D. S.; Cao, H. B.; McGuire, M. A.; Tian, W.; Matsuda, M.; Jeen, H.; Lee, H. N.; Hong, T.; Calder, S.; Zhou, H. D.; Lumsden, M. D.; Keppens, V.; Mandrus, D.; Christianson, A. D.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214421 DEC 15 2015
Abstract:
The structural and the magnetic properties of CeCu6-xAgx(0 <= x <= 0.85) and CeCu6-xPdx (0 <= x <= 0.4) have been studied using neutron diffraction, resonant ultrasound spectroscopy (RUS), x-ray diffraction measurements, and first principles calculations. The structural and magnetic phase diagrams of CeCu6-xAgx and CeCu6-xPdx as a function of Ag/Pd composition are reported. The end member, CeCu6, undergoes a structural phase transition from an orthorhombic (Pnma) to a monoclinic (P2(1)/c) phase at 240 K. In CeCu6-xAgx, the structural phase transition temperature (T-s) decreases linearly with Ag concentration and extrapolates to zero at x(S) approximate to 0.1. The structural transition in CeCu6-xPd (x) remains unperturbed with Pd substitution within the range of our study. The lattice constant b slightly decreases with Ag/Pd doping, whereas a and c increase with an overall increase in the unit cell volume. Both systems, CeCu6-xAgx and CeCu6-xPdx, exhibit a magnetic quantum critical point (QCP), at x approximate to 0.2 and x approximate to 0.05, respectively. Near the QCP, long range antiferromagnetic ordering takes place at an incommensurate wave vector (delta(1) 0 delta(2)), where delta(1) similar to 0.62, delta 2 similar to 0.25, x = 0.125 for CeCu6-xPdx and delta(1) similar to 0.64, delta(2) similar to 0.3, x = 0.3 for CeCu6-xAgx. The magnetic structure consists of an amplitude modulation of the Ce moments which are aligned along the c axis of the orthorhombic unit cell.

Title:
Overcoming magnetic frustration and promoting half-metallicity in spinel CoCr2O4 by doping with Fe
Authors:
Ganguly, S; Chimata, R; Sanyal, B Author Full Names: Ganguly, Shreemoyee; Chimata, Raghuveer; Sanyal, Biplab
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224417 DEC 14 2015
Abstract:
In this paper, we present a systematic study of the effects of Fe doping on the electronic and magnetic structures of spinel CoCr2O4 by ab initio density functional theory and atomistic spin dynamics calculations. Our calculated magnetic structure for pristine CoCr2O4 correctly reproduces the experimental one with a q-vector of (0.67, 0.67,0.0), establishing the accuracy of the calculated interatomic exchange interactions. We show that the noncollinear spin structure with a nonzero q-vector in the spinel structure is driven towards collinearity by Fe doping by a complex interplay between interatomic exchange interactions. In the inverse spinel structure with 100% Fe doping, a collinear antiferromagnetic order develops along with a half-metallic electronic structure, which evolves due to the chemical disorder between Fe and Co in the B sites described by the coherent potential approximation. This is a comprehensive theoretical study to understand the evolution of magnetic and electronic properties of multiferroic CoCr2O4 doped with Fe.

Update: 31-Dec-2015


Title:
Decoupling of the antiferromagnetic and insulating states in Tb-doped Sr2IrO4
Authors:
Wang, JC; Aswartham, S; Ye, F; Terzic, J; Zheng, H; Haskel, D; Chikara, S; Choi, Y; Schlottmann, P; Custelcean, R; Yuan, SJ; Cao, G Author Full Names: Wang, J. C.; Aswartham, S.; Ye, Feng; Terzic, J.; Zheng, H.; Haskel, Daniel; Chikara, Shalinee; Choi, Yong; Schlottmann, P.; Custelcean, Radu; Yuan, S. J.; Cao, G.
Source:
PHYSICAL REVIEW B, 92 (21):10.1103/PhysRevB.92.214411 DEC 8 2015
Abstract:
Sr2IrO4 is a spin-orbit-coupled insulator with an antiferromagnetic (AFM) transition at T-N = 240 K. We report results of a comprehensive study of single-crystal Sr2Ir1-xTbxO4 (0 <= x <= 0.03). This study found that a mere 3% (x = 0.03) of tetravalent Tb4+ (4f(7)) substituting for Ir4+ (rather than Sr2+) completely suppresses the long-range collinear AFM transition but retains the insulating state, leading to a phase diagram featuring a decoupling of the magnetic interactions and charge gap. The insulating state at x = 0.03 is characterized by an unusually large specific heat at low temperatures and an incommensurate magnetic state having magnetic peaks at (0.95,0,0) and (0,0.95,0) in the neutron diffraction, suggesting a spiral or spin-density-wave order. It is apparent that Tb doping effectively changes the relative strength of the spin-orbit interaction (SOI) and the tetragonal crystal electric field and enhances the Hund's rule coupling that competes with the SOI, and destabilizes the AFM state. However, the disappearance of the AFM is accompanied by no metallic state chiefly because an energy level mismatch for the Ir and Tb sites weakens charge carrier hopping and causes a persistent insulating state. This work highlights an unconventional correlation between the AFM and insulating states in which the magnetic transition plays no critical role in the formation of the charge gap in the iridate.

Title:
Long-range magnetic order in models for rare-earth quasicrystals
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224409 DEC 7 2015
Abstract:
We take a two-step theoretical approach to study magnetism of rare-earth quasicrystals by considering Ising spins on quasiperiodic tilings, coupled via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First, we compute RKKY interactions from a tight-binding Hamiltonian defined on the two-dimensional quasiperiodic tilings. We find that the magnetic interactions are frustrated and strongly dependent on the local environment. This results in the formation of clusters with strong bonds at certain patterns of the tilings that repeat quasiperiodically. Second, we examine the statistical mechanics of Ising spins with these RKKY interactions, using extensive Monte Carlo simulations. Although models that have frustrated interactions and lack translational invariance might be expected to display spin-glass behavior, we show that the spin system has a phase transition to low-temperature states with long-range quasiperiodic magnetic order. Additionally, we find that in some of the systems spin clusters can fluctuate much below the ordering temperature.

Title:
One-Dimensional Quasicrystals from Incommensurate Charge Order
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, Felix; van Wezel, Jasper
Source:
PHYSICAL REVIEW LETTERS, 115 (23):10.1103/PhysRevLett.115.236401 DEC 3 2015
Abstract:
Artificial quasicrystals are nowadays routinely manufactured, yet only two naturally occurring examples are known. We present a class of systems with the potential to be realized both artificially and in nature, in which the lowest energy state is a one-dimensional quasicrystal. These systems are based on incommensurately charge-ordered materials, in which the quasicrystalline phase competes with the formation of a regular array of discommensurations as a way of interpolating between incommensurate charge order at high temperatures and commensurate order at low temperatures. The nonlocal correlations characteristic of the quasicrystalline state emerge from a free-energy contribution localized in reciprocal space. We present a theoretical phase diagram showing that the required material properties for the appearance of such a ground state allow for one-dimensional quasicrystals to form in real materials. The result is a potentially wide class of one-dimensional quasicrystals.

Title:
Disorder in the composite crystal structure of the manganese 'disilicide' MnSi1.73 from powder X-ray diffraction data
Authors:
Akselrud, L; Gil, RC; Wagner-Reetz, M; Grin, Y Author Full Names: Akselrud, L.; Gil, R. Cardoso; Wagner-Reetz, M.; Grin, Yu.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):707-712; SI 10.1107/S2052520615019757 DEC 2015
Abstract:
The crystal structure of the higher manganese silicide MnSi1.7 (known in the literature as HMS) is investigated in samples with different compositions obtained by different techniques at temperatures not higher than 1273 K. Powder X-ray diffraction was applied. The crystal structure is described as incommensurate composite. In addition to the ordered model already known in the literature, the partial disorder in the silicon substructure was detected and described introducing an additional atomic site with a different modulation function.

Title:
Type II Bi-1 (-) xWxO1.5 (+) (1.5x): a (3+3)-dimensional commensurate modulation that stabilizes the fast-ion conducting delta phase of bismuth oxide
Authors:
Wind, J; Auckett, JE; Withers, RL; Piltz, RO; Maljuk, A; Ling, CD Author Full Names: Wind, Julia; Auckett, Josie E.; Withers, Ray L.; Piltz, Ross O.; Maljuk, Andrey; Ling, Chris D.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 (6):679-687; SI 10.1107/S2052520615018351 DEC 2015
Abstract:
The Type II phase in the Bi1 - xWxO1.5 (+) (1.5x) system is shown to have a (3 + 3)-dimensional modulated delta-Bi2O3-related structure, in which the modulation vector epsilon 'locks in' to a commensurate value of 1/3. The structure was refined in a 3 x 3 x 3 supercell against single-crystal Laue neutron diffraction data. Ab initio calculations were used to test and optimize the local structure of the oxygen sublattice around a single mixed Bi/W site. The underlying crystal chemistry was shown to be essentially the same as for the recently refined (3 + 3)-dimensional modulated structure of Type II Bi-1 (-) xNbxO1.5 (+) (x) (Ling et al., 2013), based on a transition from fluorite-type to pyrochlore-type via the appearance of W4O18 'tetrahedra of octahedra' and chains of corner-sharing WO6 octahedra along < 110 >(F) directions. The full range of occupancies on this mixed Bi/W site give a hypothetical solid-solution range bounded by Bi23W4O46.5 (x = 0.148) and Bi22W5O48 (x = 0.185), consistent with previous reports and with our own synthetic and analytical results.

Title:
Determination of the incommensurate modulated structure of Bi2Sr1.6La0.4CuO6+delta by aberration-corrected transmission electron microscopy
Authors:
Ge, BH; Wang, YM; Luo, HQ; Wen, HH; Yu, R; Cheng, ZY; Zhu, J Author Full Names: Ge, Binghui; Wang, Yumei; Luo, Huiqian; Wen, Haihu; Yu, Rong; Cheng, Zhiying; Zhu, Jing
Source:
ULTRAMICROSCOPY, 159 67-72; 10.1016/j.ultramic.2015.08.004 1 DEC 2015
Abstract:
The incommensurate modulated structure (IMS) of Bi2Sr1.6La0.4Cu6+delta (BSLCO) has been studied by aberration-corrected transmission electron microscopy in combination with a high-dimensional (HD) space description. Two images are deconvoluted in the negative Cs imaging (NCSI) and positive Cs imaging (PCSI) modes. Similar results for the IMS have been obtained from two corresponding projected potential maps (PPMs), and the size of the dots representing atoms in the NCSI PPM is found to be smaller than that in the PCSI PPM. Considering that the object size is one of the factors that influence the precision of the structural determination, modulation functions for all unoverlapped atoms in BSLCO were determined on the basis of the NCSI PPM in combination with the HD space description. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Crystal Structure and Thermoelectric Properties of Chimney-Ladder Higher Manganese Silicides
Authors:
Miyazaki, Y Author Full Names: Miyazaki, Yuzuru
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (11):530-537; SI 10.2320/jinstmet.JA201508 2015
Abstract:
Crystal structure, electronic structure and thermoelectric (TE) properties of Nowotny chimney-ladder (NCL) higher manganese silicides (HMSs) are reviewed. According to a (3+1). dimensional superspace approach, HMSs are revealed to belong to incommensurate composite crystals, wherein [Mn] and [Si] subsystems possess an irrational c-axis ratio gamma=c(Mn)/c(Si). The gamma parameter, also represents a stoichiometry of the HMSs as MnSi gamma, dictates the electronic structure, directly relating to a valence electron counting number, VEC. The p-type TE performance can be enhanced by a partial substitution of V, Cr, etc., while n-type HMSs can be obtained by heavily substituting Mn with Fe, etc., to realize VEC > 14. A unique thermal expansion has been discovered at T similar to 800 K, which would deteriorate TE performance and hence to be avoided from a practical application point of view.

Title:
Electronic vs. structural ordering in a manganese(III) spin crossover complex
Authors:
Fitzpatrick, AJ; Trzop, E; Muller-Bunz, H; Dirtu, MM; Garcia, Y; Collet, E; Morgan, GG Author Full Names: Fitzpatrick, Anthony J.; Trzop, Eliza; Mueller-Bunz, Helge; Dirtu, Marinela M.; Garcia, Yann; Collet, Eric; Morgan, Grace G.
Source:
CHEMICAL COMMUNICATIONS, 51 (99):17540-17543; 10.1039/c5cc05129k 2015
Abstract:
A symmetry breaking spin transition in a Mn(III) complex is reported with three structural phases, a high symmetry high temperature S = 2 phase, an intermediate S = 1/S = 2 ordered phase and an aperiodic low temperature phase with S = 1 cations. The aperiodicity is interpreted as resulting from long-range ordering of the NTf2- anions.

Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, S; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79 (12):664-671; 10.2320/jinstmet.J2015012 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt. spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a quenched alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 min indicate the presence of a modulated structure (lambda= 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt. spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5 degrees)C/s).

Update: 24-Dec-2015


Title:
Single-Crystal Neutron Diffraction Study of the Heavy-Electron Superconductor CeNiGe3
Authors:
Ikeda, Y; Ueta, D; Yoshizawa, H; Nakao, A; Munakata, K; Ohhara, T Author Full Names: Ikeda, Yoichi; Ueta, Daichi; Yoshizawa, Hideki; Nakao, Akiko; Munakata, Koji; Ohhara, Takashi
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.123701 DEC 15 2015
Abstract:
A single-crystal neutron diffraction study was performed on anomalous antiferromagnetic ordering in the heavyelectron superconductor CeNiGe3. We observed incommensurate magnetic Bragg reflections characterized by the incommensurate propagation vector k(2) = (0, 0.41, 1/2) below the Neel temperature of 5K, but no significant magnetic reflection with the commensurate propagation vector k(1) = (1, 0, 0), at which another magnetic reflection was observed in a previous neutron diffraction study with a polycrystalline sample. From the single-crystal study, we suggest that the magnetic phase of CeNiGe3 at ambient pressure is characterized only by the incommensurate propagation vector k(2).

Title:
Electronic Properties of Incommensurate Atomic Layers
Authors:
Koshino, M; Moon, P Author Full Names: Koshino, Mikito; Moon, Pilkyung
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (12):10.7566/JPSJ.84.121001 DEC 15 2015
Abstract:
We present a brief theoretical overview of electronic properties of incommensurate multilayer systems, i.e., a pair of two-dimensional atomic layers stacked in an arbitrary orientation. We introduce the general theoretical scheme to describe the interlayer interaction between incommensurate crystal structures, and apply the formula to two specific examples, the twisted bilayer graphene and graphene-hBN composite bilayer. In each case, we calculate the electronic band structure and demonstrate that the low-energy electronic properties are significantly modified by the interlayer interaction, particularly when the two lattice structures are close to each other. We also study the energy spectrum and the quantum Hall effect in magnetic fields, where we see that the spectral structure exhibits a fractal nature, as known as the Hofstadter butterfly. We argue about the optical absorption properties of the twisted bilayer graphene and show that the interlayer interaction gives rise to the characteristic spectroscopic features in zero magnetic field and also in strong magnetic field.

Title:
Amorphous hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Takasaki, A.; Hoser, A.
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (45):15534-15539; 10.1016/j.ijhydene.2015.09.136 DEC 7 2015
Abstract:
The Ti-Zr-Ni alloys can be synthesized in crystalline, amorphous and quasicrystalline phases. They are produced by mechanical alloying or melt-spinning and they are good candidate materials for hydrogen storage applications. In this communication we modified the Ti45Zr38Ni17 compounds by substituting 3d metals (cobalt) for Ni to obtain amorphous phase. The cobalt atoms are located at the same positions as nickel. We describe a series of phase transitions associated with a hydrogen uptake in the amorphous Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The investigated alloys exhibited a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. It has been found, that the amorphous powders were decomposed into simple hydrides being exposed to H-2 at temperatures above 200 degrees C. In order to overcome that problem, a processing route to obtain the amorphous hydrides was established. The heated amorphous hydrides underwent an unusual and fascinating transformation into the glassy quasicrystal phase with no hydrogen loss. A further temperature increase triggered another structural transformation into the cubic phase, which was associated with hydrogen release from the structure. The crystal structure evolution was characterized by the variety of diffraction techniques. Thermodynamic properties were studied by differential scanning calorimetry and thermal desorption spectroscopy. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Static and quasielastic properties of the spiral magnet Ba2CuGe2O7 studied by neutron resonance spin echo spectroscopy and neutron Larmor labeling
Authors:
Muhlbauer, S; Kindervater, J; Hassler, W Author Full Names: Muehlbauer, S.; Kindervater, J.; Haessler, W.
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224406 DEC 4 2015
Abstract:
We provide a route to use elastic and quasielastic neutron spin echo spectroscopy (Larmor labeling) for a unified approach to study both the static and dynamic properties of incommensurate magnetic structures with small propagation vectors. The archetypal noncentrosymmetric spiral magnet Ba2CuGe2O7 serves as a model system for our study. We show how Larmor labeling can efficiently decouple instrumental wavelength resolution and effective-(Q) over right arrow resolution and give high-precision access to the structural properties of the incommensurate domains of Ba2CuGe2O7.

Title:
Two types of nematicity in the phase diagram of the cuprate superconductor YBa2Cu3Oy
Authors:
Cyr-Choiniere, O; Grissonnanche, G; Badoux, S; Day, J; Bonn, DA; Hardy, WN; Liang, R; Doiron-Leyraud, N; Taillefer, L Author Full Names: Cyr-Choiniere, O.; Grissonnanche, G.; Badoux, S.; Day, J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Doiron-Leyraud, N.; Taillefer, Louis
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224502 DEC 2 2015
Abstract:
Nematicity has emerged as a key feature of cuprate superconductors, but its link to other fundamental properties such as superconductivity, charge order, and the pseudogap remains unclear. Here we use measurements of transport anisotropy in YBa2Cu3Oy to distinguish two types of nematicity. The first is associated with short-range charge-density-wave modulations in a doping region near p = 0.12. It is detected in the Nernst coefficient, but not in the resistivity. The second type prevails at lower doping, where there are spin modulations but no charge modulations. In this case, the onset of in-plane anisotropy-detected in both the Nernst coefficient and the resistivity-follows a line in the temperature-doping phase diagram that tracks the pseudogap energy. We discuss two possible scenarios for the latter nematicity.

Title:
Direct observation of an optically induced charge density wave transition in 1T-TaSe2
Authors:
Sun, SS; Wei, LL; Li, ZW; Cao, GL; Liu, Y; Lu, WJ; Sun, YP; Tian, HF; Yang, HX; Li, JQ Author Full Names: Sun, Shuaishuai; Wei, Linlin; Li, Zhongwen; Cao, Gaolong; Liu, Y.; Lu, W. J.; Sun, Y. P.; Tian, Huanfang; Yang, Huaixin; Li, Jianqi
Source:
PHYSICAL REVIEW B, 92 (22):10.1103/PhysRevB.92.224303 DEC 2 2015
Abstract:
Four-dimensional ultrafast transmission electron microscopy measurements reveal a rich variety of structural dynamic phenomena at a phase transition in the charge density wave (CDW) of 1T-TaSe2. Under photoexcitation, remarkable changes in both the CDW intensity and orientation are clearly observed, associated with the transformation from a commensurate (C) phase into an incommensurate (IC) phase in a time scale of picoseconds. Moreover, the transient states reveal a notable "structural isosbestic point" at a wave vector of q(iso) where the C and IC phases yield their diffracting efficiencies in equal ratio. This observation reveals that the crystal planes parallel to q(iso) adopt a common dynamic feature in the CDW phases throughout whole nonequilibrium transition. The second-order characteristics observed in this nonequilibrium phase transition have also been analyzed based on time-resolved structural data.

Title:
Ancient Metal Mirror Alloy Revisited: Quasicrystalline Nanoparticles Observed
Authors:
Sekhar, JA; Mantri, AS; Yamjala, S; Saha, S; Balamuralikrishnan, R; Rao, PR Author Full Names: Sekhar, J. A.; Mantri, A. S.; Yamjala, S.; Saha, Sabyasachi; Balamuralikrishnan, R.; Rao, P. Rama
Source:
JOM, 67 (12):2976-2983; 10.1007/s11837-015-1524-3 DEC 2015
Abstract:
This article presents, for the first time, evidence of nanocrystalline structure, through direct transmission electron microscopy (TEM) observations, in a Cu-32 wt.% Sn alloy that has been made by an age-old, uniquely crafted casting process. This alloy has been used as a metal mirror for centuries. The TEM images also reveal five-sided projections of nano-particles. The convergent beam nano-diffraction patterns obtained from the nano-particles point to the nano-phase being quasicrystalline, a feature that has never before been reported for a copper alloy, although there have been reports of the presence of icosahedral 'clusters' within large unit cell intermetallic phases. This observation has been substantiated by x-ray diffraction, wherein the observed peaks could be indexed to an icosahedral quasi-crystalline phase. The mirror alloy casting has been valued for its high hardness and high reflectance properties, both of which result from its unique internal microstructure that include nano-grains as well as quasi-crystallinity. We further postulate that this microstructure is a consequence of the raw materials used and the manufacturing process, including the choice of mold material. While the alloy consists primarily of copper and tin, impurity elements such as zinc, iron, sulfur, aluminum and nickel are also present, in individual amounts not exceeding one wt.%. It is believed that these trace impurities could have influenced the microstructure and, consequently, the properties of the metal mirror alloy.

Title:
Mathematical crystallography in the 21st century
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (12):691-698; SI 10.1515/zkri-2015-1870 DEC 2015
Abstract:
As crystallography merges with materials science and engineering, mathematical crystallography is growing in new directions, including: Characterizing new materials with unusual properties; Imaging, including but not limited to diffraction; Exploring and exploiting superspaces; Mapping the aperiodic landscape, from chaos to classical periodicity and beyond; Re-modeling the structures of real crystals, both periodic and aperiodic; Modeling self-assembly and self-reorganization on the nanoscale. In short, it's not (just) about space groups and tilings anymore.

Title:
Incommensurate charge density wave modulated by period of Hubbard superlattices
Authors:
Zhang, LL; Huang, J; Duan, CB; Wang, WZ Author Full Names: Zhang, Liang-Liang; Huang, Jin; Duan, Cheng-Bo; Wang, Wei-Zhong
Source:
MODERN PHYSICS LETTERS B, 29 (32):10.1142/S0217984915502085 NOV 30 2015
Abstract:
The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and L-0 free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of evenodd L-0 disparity. For even L-0, we always observe a commensurate charge density wave (CDW). For odd L-0, we observe a commensurateincommensurate CDW transition at a critical on-site repulsion around the particlehole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.

Title:
Incommensurate-commensurate magnetic phase transition in SmRu2Al10
Authors:
Takai, S; Matsumura, T; Tanida, H; Sera, M Author Full Names: Takai, Shun; Matsumura, Takeshi; Tanida, Hiroshi; Sera, Masafumi
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174427 NOV 30 2015
Abstract:
Magnetic properties of single crystalline SmRu2Al10 have been investigated by electrical resistivity, magnetic susceptibility, and specific heat. We have confirmed the successive magnetic phase transitions at T-N = 12.3 K and T-M = 5.6 K. Resonant x-ray diffraction has also been performed to study the magnetic structures. Below TN, the Sm3+ moments order in an incommensurate structure with q(1) = (0,0.759,0). The magnetic moments are oriented along the orthorhombic b axis, which coincides with the magnetization easy axis in the paramagnetic phase. A very weak third harmonic peak is also observed at q(3) = (0,0.278,0). The transition at T-M is a lock-in transition to the commensurate structure described by q(1) = (0,0.75,0). A well-developed third harmonic peak is observed at q(3) = (0,0.25,0). From the discussion of the magnetic structure, we propose that the long-range RKKY interaction plays an important role, in addition to the strong nearest-neighbor antiferromagnetic interaction.

Title:
Microstructure and High Damping Properties of Mg-Zn-Y Alloys Containing LPSO Phase and I Phase
Authors:
Wan, DQ; Li, JJ; Yu, T Author Full Names: Wan Diqing; Li Junjie; Yu Tian
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (11):2651-2655; NOV 2015
Abstract:
A high damping Mg-Zn-Y alloy containing LPSO phase and I phase was investigated. The microstructure of a high damping Mg80Y4Zn16 (at%) alloy was examined by optical microscopy (OM) and SEM. Furthermore, the differential thermal analysis (DTA) was used to analyze its phase transformation. Microstructure evolution and damping properties under the conditions of the different solid solution time (3, 6, 9 h) were studied. The results show that the main phase component of the Mg80Y4Zn16 alloy is alpha-Mg, Mg12ZnY (X phase), Mg3Zn6Y (I phase) and Mg10ZnY2 phase (LPSO phase), in which I phase and LPSO phase coexistence is firstly reported. The average damping value of the alloy is 0.03, indicating that it is a high damping alloy. The damping is strain amplitude dependent. The high damping mechanism was also discussed.

Update: 17-Dec-2015


Title:
On the adaptability of 1/1 cubic approximant structure in the Mg-Al-Zn system with the particular example of Mg32Al12Zn37
Authors:
Montagne, P; Tillard, M Author Full Names: Montagne, Pierre; Tillard, Monique
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 159-165; 10.1016/j.jallcom.2015.09.201 JAN 25 2016
Abstract:
Intermetallic Mg alloys are of interest in the development of light materials with specific properties and some of them are crystalline approximants of quasicrystalline materials. Mg32Al12Zn37 single crystal structure, cubic, Im (3) over bar, a = 14.1845(1) angstrom, is disordered and belongs to the well known 1/1 approximant structural type commonly called Mg-32(Al1-xZnx)(49) or T-phase. In this family, Mg32Al12Zn37 is a new member remarkable for its very special composition nearby intersection of the 2/1 and 1/1 lines that mark composition domains of cubic 2/1 and 1/1 approximants. Structural features are discussed comparatively with literature data to emphasize the great adaptability through atom disorder of the 1/1 structure. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Icosahedral hydrides of the Ti45Zr38Ni17-xCox nano-powders
Authors:
Zywczak, A; Rusinek, D; Czub, J; Sikora, M; Stepien, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A Author Full Names: Zywczak, A.; Rusinek, D.; Czub, J.; Sikora, M.; Stepien, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 656 702-706; 10.1016/j.jallcom.2015.09.278 JAN 25 2016
Abstract:
In this communication we report the phase transitions associated with a hydrogen uptake in the quasicrystalline Ti45Zr38Ni17-xCox alloys that were prepared by mechanical alloying. The crystal structure evolution of the alloys was characterized by means of the variety of diffraction techniques (X-ray, neutron, and electron) as well as extended X-ray absorption fine structure spectroscopy (EXAFS). That analysis was supported by the results of the thermodynamic measurements, namely differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17-xCox phases into the quasicrystalline state starts at the temperature of 475 degrees C. At 525 degrees C the icosahedral phase (the i-phase) is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). The investigated icosahedral nano-powders exhibit a high capacity for gaseous H-2 reaching 2.2 wt.% at elevated temperatures. After a hydrogen uptake, a complex phase constitution including the simple hydrides is evidenced. Although the i-phases form again after hydrogen desorption, they are accompanied by the additional Zr3Co phase. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Thermal diffusivity and 3D-XY critical behavior of ferroelectric semiconductors (PbxSn1-x)(2)P2Se6
Authors:
Shvalya, V; Oleaga, A; Salazar, A; Kohutych, AA; Vysochanskii, YM Author Full Names: Shvalya, V.; Oleaga, A.; Salazar, A.; Kohutych, A. A.; Vysochanskii, Yu. M.
Source:
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 88 78-84; 10.1016/j.jpcs.2015.10.004 JAN 2016
Abstract:
An ac photopyroelectric calorimeter has been used to study the thermal diffusivity of the ferroelectric semiconductors family (PbxSn1 (-) (x))(2)P2Se6 (x=0-1) from 30 K to room temperature. Phase transitions have been found for x=0, 0.05, 0.2, 0.47 but not for x=1 in the full temperature range. A continuous phase transition has been found for x=0, 0.05, 0.2 and 0.47 which corresponds to the paraelectric commensurate to incommensurate phase. It has been possible to study the critical behavior of this transition for x=0, 0.05 and the critical parameters obtained have been alpha=-0.019, A(+)/A(-)=1.00 and alpha=-0.026, A(+)/A(-) A(-)=1.03, respectively, having fitted at the same time both the low and high temperature branches of the transition as rigorous critical theory indicates; these results agree with the theoretical prediction from renormalization group theory that this kind of transition complies with the 3D-XY universality class (alpha(theor)=-0.014, A(+)/A(-)=1.06), which has been experimentally confirmed only in a few materials. A first order incommensurate to ferroelectric phase transition has been characterized in x=0, 0.05 at lower temperature. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Planar lattices with tailorable coefficient of thermal expansion and high stiffness based on dual-material triangle unit
Authors:
Wei, K; Chen, HS; Pei, YM; Fang, DN Author Full Names: Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining
Source:
JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, 86 173-191; 10.1016/j.jmps.2015.10.004 JAN 2016
Abstract:
The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CIEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Magnetic structures of R5Ni2In4 and R11Ni4In9 (R = Tb and Ho): strong hierarchy in the temperature dependence of the magnetic ordering in the multiple rare-earth sublattices
Authors:
Ritter, C; Provino, A; Manfrinetti, P; Pecharsky, VK; Gschneidner, KA; Dhar, SK Author Full Names: Ritter, C.; Provino, A.; Manfrinetti, P.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Dhar, S. K.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (47):10.1088/0953-8984/27/47/476001 DEC 2 2015
Abstract:
The magnetic properties and magnetic structures of the R5Ni2In4 and the microfibrous R11Ni4In9 compounds with R = Tb and Ho have been examined using magnetization, heat capacity, and neutron diffraction data. Rare earth atoms occupy three and five symmetrically inequivalent rare earth sites in R5Ni2In4 and R11Ni4In9 compounds, respectively. As a result of the intra-and inter-magnetic sublattice interactions, the magnetic exchange interactions are different for various rare earth sites; this leads to a cascade of magnetic transitions with a strong hierarchy in the temperature dependence of the magnetic orderings. A transition at T-C = 125 K in Tb5Ni2In4 [kappa(1) = (0, 0, 0)] leads to a ferro/ferrimagnetic order where the magnetic ordering in one of the three R-sublattices leads to the ordering of another one; the third sublattice stays non-magnetic. New magnetic Bragg peaks appearing below T-N = 20 K can be indexed with the incommensurate magnetic propagation vector kappa(2) = (0, 0.636, 1/2); at T-N = 20 K a cycloidal spin order, which acts mostly upon the third R-sublattice, occurs. Ho5Ni2In4 establishes first antiferromagnetism [kappa = (0, 0, 0)] at T-N = 31 K on two R-sublattices; then the system becomes ferro/ferrimagnetic at T-C = 25 K with the third sublattice ordering as well. Tb11Ni4In9 has three magnetic transitions at T-C = 135 K, T-N1 = 35 K and at T-N2 = 20 K; they are respectively coupled to the appearance of different propagation vectors [kappa(1) = (0, 0, 0), kappa(2) = (0, 0, 1/2), kappa(3) = (0, 1, 1/2)], which themselves are operating differently on the five different R-sublattices. Two sublattices remain mostly ferromagnetic down to lowest temperature while the three others are predominantly coupled antiferromagnetically. In Ho11Ni4In9 a purely antiferromagnetic order, described by four different magnetic propagation vectors [kappa(1) = (0, 0.62, 0), kappa(2) = (0, 1, 0), kappa(3) = (0, 0, 1/2), kappa(4) = (0, 1, 1/2)], succeedingly includes all five different sublattices on cooling through transitions at T-N1 = 22 K, T-N2 = 12 K, T-N3 = 8 K and T-N4 = 7 K. The strength of the magnetic interactions of the different sublattices can be linked to structural details for both R5Ni2In4 and R11Ni4In9 compounds.

Title:
Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (44):10.1088/0953-8984/27/44/446002 NOV 11 2015
Abstract:
The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.

Title:
Quasicrystals at extreme conditions: The role of pressure in stabilizing icosahedral A(163)Cu(24)Fe(13) at high temperature
Authors:
Stagno, V; Bindi, L; Park, CY; Tkachev, S; Prakapenka, VB; Mao, HK; Hemley, RJ; Steinhardt, PJ; Fei, YW Author Full Names: Stagno, Vincenzo; Bindi, Luca; Park, Changyong; Tkachev, Sergey; Prakapenka, Vitali B.; Mao, H. -K.; Hemley, Russell J.; Steinhardt, Paul J.; Fei, Yingwei
Source:
AMERICAN MINERALOGIST, 100 (11-12):2412-2418; 10.2138/am-2015-5412 NOV-DEC 2015
Abstract:
Icosahedrite, the first natural quasicrystal with composition Al63Cu24Fe13, was discovered in several grains of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The presence of icosahedrite associated with high-pressure phases like ahrensite and stishovite indicates formation at high pressures and temperatures due to an impact-induced shock. Previous experimental studies on the stability of synthetic icosahedral AlCuFe have either been limited to ambient pressure, for which they indicate incongruent melting at similar to 1123 K, or limited to room-temperature, for which they indicate structural stability up to about 35 GPa. These data are insufficient to experimentally constrain the formation and stability of icosahedrite under the conditions of high pressure and temperature that formed the Khatyrka meteorite. Here we present the results of room-temperature, high-pressure diamond-anvil cells measurements of the compressional behavior of synthetic icosahedrite up to 50 GPa. High P-T experiments were also carried out using both laser-heated diamond-anvil cells combined with in situ synchrotron X-ray diffraction (at 42 GPa) and multi-anvil apparatus (at 21 GPa) to investigate the structural evolution and crystallization of possible coexisting phases. The results demonstrate that the quasiperiodic order of icosahedrite is retained over the P-T range explored. We find that pressure acts to stabilize the icosahedral symmetry at temperatures much higher than previously reported. Direct solidification of AlCuFe quasicrystals from an unusual Al-Cu-rich melt is possible but it is limited to a narrow temperature range. Alternatively, quasicrystals may form after crystallization through solid-solid reactions of Al-rich phases. In either case, our results show that quasicrystals can preserve their structure even after hypervelocity impacts spanning a broad range of pressures and temperatures.

Title:
New horizon in quasicrystals
Authors:
Samavat, F; Kiani, M Author Full Names: Samavat, F.; Kiani, M.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):935-938; 10.1134/S1063774515060280 NOV 2015
Abstract:
Quasicrystals (QCs) are aperiodic intermetallic alloys that possess a long range positional order. They often exhibit crystallographically forbidden symmetries, most commonly fivefold and tenfold. The forbidden symmetry is related to the fact that the atoms are arranged quasiperiodically. Quasiperiodic translational order has physical consequences. For example, since electrons and phonons in quasicrystals do not encounter a periodic potential, quasicrystals have unusual resistive and elastic properties, and these have been exploited in several applications. The purpose of this introduction is to present certain properties that are relevant to the surface science of quasicrystals, as a launching point for the other articles in this special issue of progress in surface science.

Title:
Penrose tilings as model sets
Authors:
Shutov, AV; Maleev, AV Author Full Names: Shutov, A. V.; Maleev, A. V.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):797-804; 10.1134/S1063774515060322 NOV 2015
Abstract:
The Baake construction, based on generating a set of vertices of Penrose tilings as a model set, is refined. An algorithm and a corresponding computer program for constructing an uncountable set of locally indistinguishable Penrose tilings are developed proceeding from this refined construction. Based on an analysis of the parameters of tiling vertices, 62 versions of rhomb combinations at the tiling center are determined. The combinatorial structure of Penrose tiling worms is established. A concept of flip transformations of tilings is introduced that makes it possible to construct Penrose tilings that cannot be implemented in the Baake construction.

Title:
Birefringence of mechanically stressed Rb2ZnCl4 crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, VB; Kohut, ZO Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V. B.; Kohut, Z. O.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (6):929-934; 10.1134/S1063774515060164 NOV 2015
Abstract:
The spectral and temperature dependences of the birefringence of mechanically free and uniaxially stressed Rb2ZnCl4 crystals have been investigated. It is shown that annealing a crystal leads to step changes in the birefringence at the phase transition from the incommensurate to commensurate phase, whereas the birefringence of as-prepared crystals changes continuously. It is established that the birefringence of Rb2ZnCl4 crystal is sensitive to uniaxial pressure; however, uniaxial stress does not change the character of its dispersion and temperature dependences. A new "pseudoisotropic" state of this crystal and a baric shift of the points of paraelectric phase-incommensurate phase-commensurate phase transitions to different temperature regions are found.

Title:
Refinement of Thermodynamic Parameters of the Mg24Y5, W and H Phases in the Mg-Zn-Y System
Authors:
Minamoto, S; Horiuchi, T; Miura, S Author Full Names: Minamoto, Satoshi; Horiuchi, Toshiaki; Miura, Seiji
Source:
MATERIALS TRANSACTIONS, 56 (10):60-64; 10.2320/matertrans.MH201418 OCT 2015
Abstract:
The Mg-Zn-Y alloy shows excellent mechanical properties which can be achieved by combining LPSO phase (known as X phase) and an icosahedral quasicrystal phase (land Z phases) in Mg solid solution (a phase). Thermodynamic data for the binary/ternary compounds Mg24Y5, X, Wand H have to be critically assessed to obtain accurate information of three-phase equilibrium in order to understand equilibria among these phases. In this research, we focused on developing CALPHAD (CALculation of PHAse Diagrams) thermodynamic database to evaluate phase diagrams for the Mg-Zn-Y system. Especially thermodynamic models for the Mg24Y5, W and H phases have been determined based on crystallographic data. Then thermodynamic parameters have been assessed to yield experimental data from EPMA/WDS, SEM, TEM and X-Ray diffraction.

Title:
Dielectric Properties and Phase Diagram of (Sr1-xBax)(2)Nb2O7 Single Crystals
Authors:
Akishige, Y; Kamata, M; Tsukada, S Author Full Names: Akishige, Yukikuni; Kamata, Misako; Tsukada, Shinya
Source:
FERROELECTRICS, 485 (1):73-79; SI 10.1080/00150193.2015.1060832 AUG 26 2015
Abstract:
Dielectric constants, epsilon(b) and epsilon(c) along the crystallographic b and c axes respectively, were measured in a temperature range of 10 - 700K on Ba-substituted Sr2Nb2O7 single crystals with different Ba concentrations up to x = 0.32. When x = 0, two dielectric anomalies were observed at T-I = 489K and at T-L = 100K, owing to the incommensurate phase transition and the low-temperature ferroelectric phase transition, respectively. Both T-I and T-L decrease with Ba-content x at initial slopes of ca. -19 and -37K/mol%, respectively, and become broad at x = 0.04 and almost disappear at x = 0.08. Furthermore, Ba-substitution induces a weak and broad dielectric maximum in epsilon(b)' vs. T curve at approximately T-m = 465K for x > 0.2. Phase diagram of this system was proposed.

Update: 10-Dec-2015


Title:
Smearing-type wear behavior of Al62Cu25.5Fe12.5 quasicrystal abrasive on soft metals
Authors:
Chen, YJ; Qiang, JB; Dong, C Author Full Names: Chen, Yongjun; Qiang, Jianbin; Dong, Chuang
Source:
INTERMETALLICS, 68 23-30; 10.1016/j.intermet.2015.09.001 JAN 2016
Abstract:
The abrasive polishing behavior of Al62Cu25.5Fe12.5 quasicrystal on Cu, Al and austenite stainless steel alloys were investigated, to compare with commonly used hard abrasives such as diamond, alumina and silica. The quasicrystal abrasive showed a dominating smearing-type wear mechanism, in sharp contrast to all the other three abrasives, as reflected by large indent size shrinking with respect to surface removal depth. The quasicrystal abrasive polishing, producing a flattened surface with minor depth removal, may open new application fields where low-wearing and fine surface finishing are demanded. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
X-ray diffraction study of the icosahedral AlCuFe quasicrystal at megabar pressures
Authors:
Takagi, S; Kyono, A; Mitani, S; Sugano, N; Nakamoto, Y; Hirao, N Author Full Names: Takagi, Sota; Kyono, Atsushi; Mitani, Saki; Sugano, Neo; Nakamoto, Yuki; Hirao, Naohisa
Source:
MATERIALS LETTERS, 161 13-16; 10.1016/j.matlet.2015.08.057 DEC 15 2015
Abstract:
We report in-situ synchrotron X-ray diffraction study of icosahedral (i)-AlCuFe quasicrystal (QC) at high pressure up to 104 GPa under ambient temperature using the diamond anvil technique. With compression, there is no obvious change of the diffraction pattern within the measured pressure range. Five characteristic peaks from the i-AlCuFe QC maintain up to 104 GPa. The unit cell volume of the i-AlCuFe QC decreases monotonously until 72 GPa. The experimental P-V compression curve below 72 GPa was fitted to the Birch-Murnaghan equation of state with V-0=2023(19) angstrom(3), K-0=131(7) GPa, K'=4.0 (fixed). The resulting EoS parameters are approximately consistent with those observed in previous study. A discontinuous volume change is observed between 72 and 75 GPa. These observed results indicate a phase transition from i-AlCuFe QC to an approximant crystal (AC) which has a similar local atomic arrangement as the QC. This study suggests that i-AlCuFe QC maintains its structure at least up to 72 GPa and then transforms to AC with small displacement of atoms. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Ni coated Ti1.4V0.6Ni composite as the negative electrode in Ni-MH battery
Authors:
Sun, LS; Lin, J; Liang, F; Cao, ZY; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Liang, Fei; Cao, Zhanyi; Wang, Limin
Source:
MATERIALS LETTERS, 161 686-689; 10.1016/j.matlet.2015.09.081 DEC 15 2015
Abstract:
Ti1.4V0.6Ni composite is synthesized by arc-melting and subsequent melt-spinning techniques. An improved electrochemical stability of Ti14V0.6Ni composite is obtained by chemical plating Ni. The phase structures of the composite contain icosahedral quasicrystal phase (i-phase) and TiNi-type phase. Different amount of Ni is coated on the surface of the composite particles. When Ti14V0.6Ni is plated with 19 wt% Ni, the discharge capacity retention ratio is promoted. Ni coating layer inhibits the dissolution of V from the composite and also promotes the high rate discharge property. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Antiphase Boundaries in the Turbostratically Disordered Misfit Compound (BiSe)(1+delta)NbSe2
Authors:
Mitchson, G; Falmbigl, M; Ditto, J; Johnson, DC Author Full Names: Mitchson, Gavin; Falmbigl, Matthias; Ditto, Jeffrey; Johnson, David C.
Source:
INORGANIC CHEMISTRY, 54 (21):10309-10315; 10.1021/acs.inorgchem.5b01648 NOV 2 2015
Abstract:
(BiSe)(1+delta)NbSe2 ferecrystals were synthesized in order to determine whether structural modulation in BiSe layers, characterized by periodic antiphase boundaries and Bi-Bi bonding, occurs. Specular X-ray diffraction revealed the formation of the desired compound with a c-axis lattice parameter of 1.21 nm from precursors with a range of initial compositions and initial periodicities. In-plane X-ray diffraction scans could be indexed as hk0 reflections of the constituents, with a rectangular basal BiSe lattice and a trigonal basal NbSe2 lattice. Electron micrographs showed extensive turbostratic disorder in the samples and the presence of periodic antiphase boundaries (approximately 1.5 nm periodicity) in BiSe layers oriented with the [110] direction parallel to the zone axis of the microscope. This indicates that the structural modulation in the BiSe layers is not due to coherency strain resulting from commensurate in-plane lattices. Electrical transport measurements indicate that holes are the dominant charge carrying species, that there is a weak decrease in resistivity as temperature decreases, and that minimal charge transfer occurs from the BiSe to NbSe2 layers. This is consistent with the lack of charge transfer from the BiX to the TX2 layers reported in misfit layer compounds where antiphase boundaries were observed. This suggests that electronic considerations, i.e., localization of electrons in the Bi-Bi pairs at the antiphase boundaries, play a dominant role in stabilizing the structural modulation.

Title:
Unravelling structural ambiguities in lithium- and manganese-rich transition metal oxides
Authors:
Shukla, AK; Ramasse, QM; Ophus, C; Duncan, H; Hage, F; Chen, GY Author Full Names: Shukla, Alpesh Khushalchand; Ramasse, Quentin M.; Ophus, Colin; Duncan, Hugues; Hage, Fredrik; Chen, Guoying
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9711 OCT 2015
Abstract:
Although Li- and Mn-rich transition metal oxides have been extensively studied as high-capacity cathode materials for Li-ion batteries, the crystal structure of these materials in their pristine state is not yet fully understood. Here we apply complementary electron microscopy and spectroscopy techniques at multi-length scale on well-formed Li-1.2(Ni0.13Mn0.54Co0.13)O-2 crystals with two different morphologies as well as two commercially available materials with similar compositions, and unambiguously describe the structural make-up of these samples. Systematically observing the entire primary particles along multiple zone axes reveals that they are consistently made up of a single phase, save for rare localized defects and a thin surface layer on certain crystallographic facets. More specifically, we show the bulk of the oxides can be described as an aperiodic crystal consisting of randomly stacked domains that correspond to three variants of monoclinic structure, while the surface is composed of a Co- and/or Ni-rich spinel with antisite defects.

Title:
Fermi states and anisotropy of Brillouin zone scattering in the decagonal Al-Ni-Co quasicrystal
Authors:
Rogalev, VA; Groning, O; Widmer, R; Dil, JH; Bisti, F; Lev, LL; Schmitt, T; Strocov, VN Author Full Names: Rogalev, V. A.; Groening, O.; Widmer, R.; Dil, J. H.; Bisti, F.; Lev, L. L.; Schmitt, T.; Strocov, V. N.
Source:
NATURE COMMUNICATIONS, 6 10.1038/ncomms9607 OCT 2015
Abstract:
Quasicrystals (QCs) are intermetallic alloys that have excellent long-range order but lack translational symmetry in at least one dimension. The valence band electronic structure near the Fermi energy E-F in such materials is of special interest since it has a direct relation to their unusual physical properties. However, the Fermi surface (FS) topology as well as the mechanism of QC structure stabilization are still under debate. Here we report the first observation of the three-dimensional FS and valence band dispersions near E-F in decagonal Al70Ni20Co10 (d-AlNiCo) QCs using soft X-ray angle-resolved photoemission spectroscopy. We show that the FS, formed by dispersive Al sp-states, has a multicomponent character due to a large contribution from high-order bands. Moreover, we discover that the magnitude of the gap at the FS related to the interaction with Brillouin zone boundary (Hume-Rothery gap) critically differs for the periodic and quasiperiodic directions.

Update: 3-Dec-2015


Title:
Microstructure and mechanical properties of laser beam welded Al-Li alloy 2060 with Al-Mg filler wire
Authors:
Zhang, XY; Yang, WX; Xiao, RS Author Full Names: Zhang, Xinyi; Yang, Wuxiong; Xiao, Rongshi
Source:
MATERIALS & DESIGN, 88 446-450; 10.1016/j.matdes.2015.08.144 DEC 25 2015
Abstract:
Alloy 2060-T8 is a newly developed high-strength Al-Li alloy for applications in aircraft industry. Crack-free welds were obtained in laser beam welding with 5087 filler wire under optimized welding conditions. In this paper, fusion zone microstructure and joint mechanical properties were investigated. Microstructure typical for the weld metal consists of alpha-Al matrix with a few nanoscale precipitates inside and a coarse icosahedral quasi-crystalline T-2 phase at the dendritic and grain boundaries. The quasicrystalline occurred normally in Al-Li-Cu alloys with higher Li contents. Our investigations show that the icosahedral quasicrystalline phase T-2 phase forms in the laser-welded Al-Li alloy 2060 with lower Li content as a result of segregation and replacement of Mg element. The joint tensile strength in as-welded condition is around 317 MPa, about 63% of that of the base metal, and fracture occurs within the fusion zone. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Explosively welded multilayer Ni-Al composites
Authors:
Bataev, IA; Ogneva, TS; Bataev, AA; Mali, VI; Esikov, MA; Lazurenko, DV; Guo, Y; Jorge, AM Author Full Names: Bataev, I. A.; Ogneva, T. S.; Bataev, A. A.; Mali, V. I.; Esikov, M. A.; Lazurenko, D. V.; Guo, Y.; Jorge Junior, A. M.
Source:
MATERIALS & DESIGN, 88 1082-1087; 10.1016/j.matdes.2015.09.103 DEC 25 2015
Abstract:
In this study, the structure of explosively welded Ni-Al multilayer composites was investigated. In particular, the interface between Ni and Al plates was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). Continuous interlayers of mixed Al and Ni were found at the interface. The Al and Ni in these zones were heated above their melting temperatures, non-uniformly mixed, and rapidly solidified. Several intermetallic phases, including the decagonal phase and metastable Al9Ni2, were observed in these zones using electron diffraction. A cellular dislocation structure formed in the Ni plates and a polygonized dislocation structure formed in the Al plates due to the extremely high strain rate deformation and heating. Subsequent heat treatment at 620 degrees C led to the rapid formation of stable intermetallic layers at the interfaces. The growth of the intermetallic layers was considerably faster in the explosively welded composite than in the reference sample. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Effect of icosahedral phase on the crystallographic texture and mechanical anisotropy of duplex structured Mg-Li alloys
Authors:
Xu, DK; Li, CQ; Wang, BJ; Han, EH Author Full Names: Xu, D. K.; Li, C. Q.; Wang, B. J.; Han, E. H.
Source:
MATERIALS & DESIGN, 88 88-97; 10.1016/j.matdes.2015.08.123 DEC 25 2015
Abstract:
Through comparing the microstructure and mechanical properties of Mg-6%Li and Mg-6%Li-6%Zn-1.2%Y alloys, the difference in their mechanical anisotropy have been deeply investigated. Due to the formation of I-phase (Mg3Zn6Y, icosohedral structure), the volume fraction of beta-Li phases formed in Mg-6%Li-6%Zn-1.2%Y alloy was two times higher than that in Mg-6%Li alloy even these two alloys having the same Li content. Texture analysis demonstrated that I-phase particle stimulated nucleation of recrystallization (PSN) and the formation of higher volume fraction of beta-Li phases can remarkably weaken the basal texture of alpha-Mg phases, resulting in a very weak mechanical anisotropy. On the contrary, the basal texture of the alpha-Mg phases in Mg-6%Li alloy was quite strong and obvious mechanical anisotropy between differently oriented samples can be observed. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Phase Formation in the Rapidly Solidified Al70-xGaxPd13Mn17 Alloys
Authors:
Yadav, TP; Shaz, MA; Mukhopadhyay, NK; Tiwari, RS; Srivastava, ON Author Full Names: Yadav, T. P.; Shaz, M. A.; Mukhopadhyay, N. K.; Tiwari, R. S.; Srivastava, O. N.
Source:
TRANSACTIONS OF THE INDIAN INSTITUTE OF METALS, 68 (6):1145-1149; 10.1007/s12666-015-0660-3 DEC 2015
Abstract:
In the present investigation, the effect of Ga substitution at Al site on the phase formation and stabilization of decagonal quasicrystalline phase in the rapidly solidified Al70-xGaxPd13Mn17 alloys have been studied by employing X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive x-ray analysis. The as-cast and rapidly solidified alloys with x = 0, 2.5 and 5 have been investigated. The melt-spinning technique has been used for rapid solidification of the as-cast alloys. The alloys up to 5 at.% Ga exhibit the formation of small amount of icosahedral quasicrystalline phases along with major amount of decagonal phase in the rapidly solidied ribbons. The energy dispersive X-ray analysis investigations suggest the homogeneous presence of Ga in the quasicrystalline alloys.

Title:
Three-dimensional charge density wave order in YBa2Cu3O6.67 at high magnetic fields
Authors:
Gerber, S; Jang, H; Nojiri, H; Matsuzawa, S; Yasumura, H; Bonn, DA; Liang, R; Hardy, WN; Islam, Z; Mehta, A; Song, S; Sikorski, M; Stefanescu, D; Feng, Y; Kivelson, SA; Devereaux, TP; Shen, ZX; Kao, CC; Lee, WS; Zhu, D; Lee, JS Author Full Names: Gerber, S.; Jang, H.; Nojiri, H.; Matsuzawa, S.; Yasumura, H.; Bonn, D. A.; Liang, R.; Hardy, W. N.; Islam, Z.; Mehta, A.; Song, S.; Sikorski, M.; Stefanescu, D.; Feng, Y.; Kivelson, S. A.; Devereaux, T. P.; Shen, Z. -X.; Kao, C. -C.; Lee, W. -S.; Zhu, D.; Lee, J. -S.
Source:
SCIENCE, 350 (6263):949-952; 10.1126/science.aac6257 NOV 20 2015
Abstract:
Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured with x-ray scattering at zero and low fields. We combined a pulsed magnet with an x-ray free-electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields of up to 28 tesla. While the zero-field CDW order, which develops at temperatures below similar to 150 kelvin, is essentially two dimensional, at lower temperature and beyond 15 tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW appears around the zero-field superconducting transition temperature; in contrast, the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.

Title:
Tuning of magnetic ordering by Y substitution onto Tb site in the nanocrystalline TbMnO3
Authors:
Chakraborty, KR; Shukla, R; Kaushik, SD; Mukadam, MD; Siruguri, V; Tyagi, AK; Yusuf, SM Author Full Names: Chakraborty, Keka R.; Shukla, Rakesh; Kaushik, S. D.; Mukadam, M. D.; Siruguri, V.; Tyagi, A. K.; Yusuf, S. M.
Source:
JOURNAL OF APPLIED PHYSICS, 118 (16):10.1063/1.4934251 OCT 28 2015
Abstract:
We report the magnetic properties, of nano-crystalline powders Tb1-xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4), as perceived by neutron diffraction, and elucidate the effect of Tb site substitution on the magnetic structure of TbMnO3. All samples crystallized in the orthorhombic structure conforming to space group Pnma, and exhibited an incommensurate collinear antiferromagnetic ordering of the Mn ions below similar to 40 K. Furthermore, at T <= 20 K, all these samples showed a change in magnetic structure (of Mn moments) to a spiral ordering down to 2K, the lowest measured temperature. For the samples with x = 0, 0.1, and 0.2, a short-ranged two dimensional (2D) ordering of Tb moments was also observed at 2K. However, for the other samples (x-0.3 and 0.4), no magnetic ordering of Tb moments was found down to 2K. So with Y substitution, a crossover from 2D ordering to a disordering of Tb moments was observed. The moments at the Mn site were found to be lower than the full Mn3+(4 mu B) moment for all the samples below 40 K. The magnetic properties of all the samples studied by us in nano form are more pronounced than those of the reported single crystals of same compositions [V. Yu. Ivanov et al., JETP Lett. 91, 392-397 (2010)]. (C) 2015 AIP Publishing LLC.

Title:
Exchange integrals of commensurate and incommensurate structures of MFe4Al8 (M = U, Sc)
Authors:
Recko, K Author Full Names: Recko, K.
Source:
JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17 (9-10):1403-1409; SEP-OCT 2015
Abstract:
The appearance of the commensurability of UFe4Al8 alloy considering incommensurability of ScFe4Al8 compound is analysed on the basis of Heisenberg Hamiltonian. The influence of Dzyaloshinskii - Moriya and Ruderman-Kittel-Kasuya-Yoshida as well as the dipolar interactions as the main reasons of the noncollinearity and incommensurability of the alloys belonging to ThMn12 family is investigated. The values and directions of the spin ordering found by magnetic diffraction are compared to that one's deriving from grand state configurations obtained by a simulated annealing algorithm. The lock-in magnetic modulations due to substitution of scandium by uranium atoms is discussed based on an appropriate exchange constants ratios.

Title:
The Incommensurate Phase Transformation in TlInS2 Ferroelectric
Authors:
Salnik, A; Gololobov, YP; Borovoy, NA Author Full Names: Salnik, A.; Gololobov, Yu. P.; Borovoy, N. A.
Source:
FERROELECTRICS, 484 (1):62-68; SI 10.1080/00150193.2015.1059716 AUG 5 2015
Abstract:
The features of the crystal structure of c and 2c TlInS2 polytypes have been studied by single-crystal X-ray diffraction method in the temperature range 180 K-300 K. In the c polytype the appearance of the incommensurate phase with modulation vector q. d; 0; 0: 25/. dD0: 04/was observed at the temperature of 238 K (on cooling). The active phase formation occurred between 213 K and 217 K. The incommensurability parameter d decreases monotonically to the zero as the temperature approaches 195 K. For the 2c polytype the modulation satellites for both incommensurate and commensurate phases were not observed in the temperature range 180 K-300 K.

Update: 26-Nov-2015


Title:
Superconductivity in the orthorhombic phase of thermoelectric CsPbxBi4-xTe6 with 0.3 <= x <= 1.0
Authors:
Zhang, RX; Yang, HX; Tian, HF; Chen, GF; Wu, SL; Wei, LL; Li, JQ Author Full Names: Zhang, R. X.; Yang, H. X.; Tian, H. F.; Chen, G. F.; Wu, S. L.; Wei, L. L.; Li, J. Q.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 232 50-55; 10.1016/j.jssc.2015.08.050 DEC 2015
Abstract:
Experimental measurements clearly reveal the presence of bulk superconductivity in the CsPbxBi4-xTe6 (0.3 <= x <= 1.0) materials, i.e. the first member of the thermoelectric series of Cs[PbmBi3Te5+m], these materials have the layered orthorhombic structure containing infinite anionic [PbBi3Te6]- slabs separated with Cs+ cations. Temperature dependences of electrical resistivity, magnetic susceptibility, and specific heat have consistently demonstrated that the superconducting transition in Cs0.96Pb0.25Bi3.75Te6.04 occurs at T-c=3.1 K, with a superconducting volume fraction close to 100% at 1.8 K. Structural study using aberration-corrected STEM/TEM reveals a rich variety of microstructural phenomena in correlation with the Pb-ordering and chemical inhomogeneity. The superconducting material CS0.96Pb0.25Bi3.75Te6.04 with the highest T-c shows a clear ordered structure with a modulation wave vector of q approximate to a*/2+c*/1.35 on the a-c plane. Our study evidently demonstrates that superconductivity deriving upon doping of narrow-gap semiconductor is a viable approach for exploration of novel superconductors. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Phason space analysis and structure modelling of 100 angstrom-scale dodecagonal quasicrystal in Mn-based alloy
Authors:
Ishimasa, T; Iwami, S; Sakaguchi, N; Oota, R; Mihalkovic, M Author Full Names: Ishimasa, Tsutomu; Iwami, Shuhei; Sakaguchi, Norihito; Oota, Ryo; Mihalkovic, Marek
Source:
PHILOSOPHICAL MAGAZINE, 95 (33):3745-3767; 10.1080/14786435.2015.1095365 NOV 22 2015
Abstract:
The dodecagonal quasicrystal classified into the five-dimensional space group P12(6)/mmc, recently discovered in a Mn-Cr-Ni-Si alloy, has been analysed using atomic-resolution spherical aberration-corrected electron microscopy, i.e. high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and conventional transmission electron microscopy. By observing along the 12-fold axis, non-periodic tiling consisting of an equilateral triangle and a square has been revealed, of which common edge length is a=4.560 angstrom. These tiles tend to form a network of dodecagons of which size is (2+root 3)a approximate to 17 angstrom in diameter. The tiling was interpreted as an aggregate of 100 angstrom-scale oriented domains of high- and low-quality quasicrystals with small crystallites appearing at their boundaries. The quasicrystal domains exhibited a densely filled circular acceptance region in the phason space. This is the first observation of the acceptance region in an actual dodecagonal quasicrystal. Atomic structure model consistent with the electron microscopy images is a standard Frank-Kasper decoration of the triangle and square tiles that can be inferred from the crystal structures of Zr4Al3 and Cr3Si. Four kinds of layers located at z = 0, +/- 1/4 and 1/2 are stacked periodically along the 12-fold axis, and the atoms at z = 0 and 1/2 form hexagonal anti-prisms consistently with the 12(6)-screw axis. The validity of this structure model was examined by means of powder X-ray diffraction.

Title:
Effect of Ca and CaO on the microstructure and hot compressive deformation behavior of Mg-9.5Zn-2.0Y alloy
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 648 146-156; 10.1016/j.msea.2015.09.014 NOV 11 2015
Abstract:
In this study, the effect of adding 0.3 wt% Ca to a Mg-9.5Zn-2.0Y alloy with icosahedral (I) phase (Mg3Zn6Y) was examined. The Ca alloying was done by two different routes, either through a master alloy produced with Mg and CaO (which is convenient from the points of view of safety and cost) or by direct addition of powdered Ca to the molten alloy. The small addition of Ca (CaO) effectively increased the ignition temperature of the alloys (by about 90 K), which is promising for fire suppression and safe handling with the molten alloys, but it led to the formation of Ca2Mg5Zn13 phase at grain boundaries or interdendritic interfaces, causing partial melting and intergranular cracking during compressive deformation near similar to 615 K. As a result, the upper limit of hot workability temperature decreased to 598 K, which is lower than that of the Mg-9.5Zn-2.0Y alloy by 125 K. The cast Mg-9.5Zn-2.0Y-03Ca alloys prepared using the two different routes exhibited high similarity in ignition temperature, chemical composition, microstructure, hot compressive behaviors and processing maps, indicating that the use of CaO is as effective as the use of Ca in producing the same quality of Ca containing Mg alloys. The flow stresses during hot compressive deformation and the activation energy for plastic flow remained unaffected by the Ca (CaO) alloying, but decreased the strain rate sensitivity at high strain rates over 10(-3) s(-1) due to the initiation of either power-law breakdown or partial melting by adiabatic heating. Because of this, the Ca containing alloy lost hot workability at high strain rates by comparison to the Ca-free alloy. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Incommensurateness in nanotwinning models of modulated martensites
Authors:
Benesova, B; Frost, M; Kampschulte, M; Melcher, C; Sedlak, P; Seiner, H Author Full Names: Benesova, Barbora; Frost, Miroslav; Kampschulte, Malte; Melcher, Christof; Sedlak, Petr; Seiner, Hanus
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180101 NOV 6 2015
Abstract:
We study the formation of modulated martensites in ferromagnetic shape memory alloys by a mathematical model originating from the nanotwinning concept. The results show that the incommensurateness, systematically observed in experiments for the modulated phases, may be understood as a precursor effect of the intermartensitic transitions, and its appearance does not contradict the nanotwinning concept itself. The model sufficiently explains the different levels of incommensurateness reported from different experimental observations for the 14-layered and 10-layered martensites of the Ni-Mn-Ga alloy and outlines the mechanism of formation of faults in the stacking sequences of these materials.

Title:
Quantum phase transitions and decoupling of magnetic sublattices in the quasi-two-dimensional Ising magnet Co3V2O8 in a transverse magnetic field
Authors:
Fritsch, K; Ehlers, G; Rule, KC; Habicht, K; Ramazanoglu, M; Dabkowska, HA; Gaulin, BD Author Full Names: Fritsch, K.; Ehlers, G.; Rule, K. C.; Habicht, K.; Ramazanoglu, M.; Dabkowska, H. A.; Gaulin, B. D.
Source:
PHYSICAL REVIEW B, 92 (18):10.1103/PhysRevB.92.180404 NOV 5 2015
Abstract:
The application of a magnetic field transverse to the easy axis, Ising direction in the quasi-two-dimensional kagome staircase magnet, Co3V2O8, induces three quantum phase transitions at low temperatures, ultimately producing a novel high field polarized state, with two distinct sublattices. New time-of-flight neutron scattering techniques, accompanied by large angular access, high magnetic field infrastructure allow the mapping of a sequence of ferromagnetic and incommensurate phases and their accompanying spin excitations. At least one of the transitions to incommensurate phases at mu H-0(c1) similar to 6.25 T and mu H-0(c2) similar to 7 T is discontinuous, while the final quantum critical point at mu H-0(c3) similar to 13 T is continuous.

Title:
Fluctuating orders and quenched randomness in the cuprates
Authors:
Nie, LM; Sierens, LEH; Melko, RG; Sachdev, S; Kivelson, SA Author Full Names: Nie, Laimei; Sierens, Lauren E. Hayward; Melko, Roger G.; Sachdev, Subir; Kivelson, Steven A.
Source:
PHYSICAL REVIEW B, 92 (17):10.1103/PhysRevB.92.174505 NOV 4 2015
Abstract:
We study a quasi-two-dimensional classical Landau-Ginzburg-Wilson effective field theory in the presence of quenched disorder in which incommensurate charge-density wave and superconducting orders are intertwined. The disorder precludes long-range charge-density wave order, but not superconducting or nematic order. We select three representative sets of input parameters and compute the corresponding charge-density wave structure factors using both large-N techniques and classical Monte Carlo simulations. Where nematicity and superconductivity coexist at low temperature, the peak height of the charge-density wave structure factor decreases monotonically as a function of increasing temperature, unlike what is seen in x-ray experiments on YBa2Cu3O6+x. Conversely, where the thermal evolution of the charge-density wave structure factor qualitatively agrees with experiments, the nematic correlation length, computed to one-loop order, is shorter than the charge-density wave correlation length.

Title:
Symmetries and color symmetries of a family of tilings with a singular point
Authors:
Evidente, IF; Felix, RP; Loquias, MJC Author Full Names: Evidente, Imogene F.; Felix, Rene P.; Loquias, Manuel Joseph C.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 583-591; 10.1107/S2053273315016137 6 NOV 2015
Abstract:
Tilings with a singular point are obtained by applying conformal maps on regular tilings of the Euclidean plane and their symmetries are determined. The resulting tilings are then symmetrically colored by applying the same conformal maps on colorings of regular tilings arising from sublattice colorings of the centers of the tiles. In addition, conditions are determined in order that the coloring of a tiling with singularity that is obtained in this manner is perfect.

Title:
Unusual Strong Incommensurate Modulation in a Tungsten-Bronze-Type Relaxor PbBiNb5O15
Authors:
Lin, K; Zhou, ZY; Liu, LJ; Ma, HQ; Chen, J; Deng, JX; Sun, JL; You, L; Kasai, H; Kato, K; Takata, M; Xing, XR Author Full Names: Lin, Kun; Zhou, Zhengyang; Liu, Laijun; Ma, Hongqiang; Chen, Jun; Deng, Jinxia; Sun, Junliang; You, Li; Kasai, Hidetaka; Kato, Kenichi; Takata, Masaki; Xing, Xianran
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (42):13468-13471; 10.1021/jacs.5b08230 OCT 28 2015
Abstract:
Pb- or Bi-based perovskite oxides have been widely studied and used because of their large ferroelectric polarization features induced by stereochemically active 6s(2) lone pair electrons. It is intriguing whether this effect could exist in other related systems. Herein, we designed and synthesized a mixed Pb and Bi A site polar compound, PbBiNb5O15, with the TTB framework. The as-synthesized material turns out to be a relaxor with weak macroscopic ferroelectricity but adopts strong local polarizations. What's more, unusual five orders of incommensurate satellite reflections with strong intensities were observed under the electron diffraction, suggesting that the modulation is highly developed with large amplitudes. The structural modulation was solved with a (3 + 1)D superspace group using high-resolution synchrotron radiation combined with anomalous dispersion X-ray diffraction technique to distinguish Pb from Bi. We show that the strong modulation mainly originates from lone-pair driven Pb2+-Bi3+ ordering in the large pentagonal caves, which can suppress the local polarization in x-y plane in long ranges. Moreover, the as-synthesized ceramics display strong relaxor ferroelectric feature with transition temperature near room temperature and moderate dielectric properties, which could be functionalized to be electromechanical device materials.

Title:
On the stability of a quasicrystal and its crystalline approximant in a system of hard disks with a soft corona
Authors:
Pattabhiraman, H; Gantapara, AP; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Gantapara, Anjan P.; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 143 (16):10.1063/1.4934499 OCT 28 2015
Abstract:
Using computer simulations, we study the phase behavior of a model system of colloidal hard disks with a diameter sigma and a soft corona of width 1.4 sigma. The particles interact with a hard core and a repulsive square-shoulder potential. We calculate the free energy of the random-tiling quasicrystal and its crystalline approximants using the Frenkel-Ladd method. We explicitly account for the configurational entropy associated with the number of distinct configurations of the random-tiling quasicrystal. We map out the phase diagram and find that the random tiling dodecagonal quasicrystal is stabilised by entropy at finite temperatures with respect to the crystalline approximants that we considered, and its stability region seems to extend to zero temperature as the energies of the defect-free quasicrystal and the crystalline approximants are equal within our statistical accuracy. (C) 2015 AIP Publishing LLC.

Title:
Corrosion Behavior of Psi and beta Quasicrystalline Al-Cu-Fe Alloy
Authors:
Torres, A; Serna, S; Patino, C; Rosas, G Author Full Names: Torres, Alvaro; Serna, Sergio; Patino, Cristobal; Rosas, Gerardo
Source:
ACTA METALLURGICA SINICA-ENGLISH LETTERS, 28 (9):1117-1122; 10.1007/s40195-015-0302-0 SEP 2015
Abstract:
Two nanostructured Al-Cu-Fe alloys, Al64Cu24Fe12 and Al62.5Cu25.2Fe12.3, have been studied. Icosahedral quasicrystalline (psi) Al64Cu24Fe12 and crystalline cubic (beta) Al62.5Cu25.2Fe12.3 cylindrical ingots were first produced using normal casting techniques. High-energy mechanical milling was then conducted to obtain psi icosahedral and beta intermetallic nanostructured powders. Electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization were used to investigate the electrochemical corrosion characteristics of the powders in solutions with different pH values. Current density (i(corr)), polarization resistance (R-p), and impedance modulus (vertical bar Z vertical bar) were determined. The results showed that regardless of pH value, increasing the solution temperature enhanced the corrosion resistance of the both phases. However, the electrochemical behavior of the psi phase indicated that its stability depends on the submerged exposure time in neutral and alkaline environments. This behavior was related to the type of corrosion products present on the surfaces of the particles along with the diffusion and charge-transfer mechanisms of the corrosion process.

Update: 19-Nov-2015


Title:
Large coincidence lattice on Au/Fe3O4 incommensurate structure for spintronic applications
Authors:
Munoz-Noval, A; Rubio-Zuazo, J; Salas-Colera, E; Serrano, A; Rubio-Marcos, F; Castro, GR Author Full Names: Munoz-Noval, Alvaro; Rubio-Zuazo, Juan; Salas-Colera, Eduardo; Serrano, Aida; Rubio-Marcos, Fernando; Castro, German R.
Source:
APPLIED SURFACE SCIENCE, 355 698-701; 10.1016/j.apsusc.2015.07.158 NOV 15 2015
Abstract:
The design of metallic hybrid systems for spintronics has been widely studied during the past decade, motivated by the promising technological applications of these materials. Nevertheless, the importance of preserving the native structure and properties of the interfaces is often ignored. Here, we present the fabrication of nanocrystalline Au(001) onto a single oriented Fe3O4 (0 0 1) thin film as a promising hybrid system to develop spintronic devices by growing Au over the Fe3O4 by using a simple one-pot Pulsed Laser Deposition (PLD) approach. The structural coupling between Au nanocrystals and Fe3O4 layer results in the development of an incommensurate structure based on a coincidence lattice of order 35, which preserves the intrinsic properties of the Au nanocrystals, the Fe3O4 matrix and the interface between them. The general strategy described in the present work preserves the structure and main intrinsic properties of the constituting materials, being a fundamental issue for the future development of spintronic devices. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Unoccupied electronic structure of Ni2MnGa ferromagnetic shape memory alloy
Authors:
Maniraj, M; D'Souza, SW; Rai, A; Schlagel, DL; Lograsso, TA; Chakrabarti, A; Barman, SR Author Full Names: Maniraj, M.; D'Souza, S. W.; Rai, Abhishek; Schlagel, D. L.; Lograsso, T. A.; Chakrabarti, Aparna; Barman, S. R.
Source:
SOLID STATE COMMUNICATIONS, 222 1-4; 10.1016/j.ssc.2015.08.003 NOV 2015
Abstract:
Momentum resolved inverse photoemission spectroscopy measurements show that the dispersion of the unoccupied bands of Ni(2)MaGa is significant in the austenite phase. In the martensite phase, it is markedly reduced, which is possibly related to the structural transition to an incommensurate modulated state in the martensite phase. Based on the first principle calculations of the electronic structure of Ni-Mn-Ga, we show that the modification of the spectral shape with surface composition is related to change in the hybridization between the Mn 3d and Ni 3d-like states that dominate the unoccupied conduction band. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Local cluster symmetry of a highly ordered quasicrystalline Al58Cu26Ir16 extracted through multivariate analysis of STEM images
Authors:
Seki, T; Abe, E Author Full Names: Seki, Takehito; Abe, Eiji
Source:
MICROSCOPY, 64 (5):341-349; 10.1093/jmicro/dfv035 OCT 2015
Abstract:
The structure of a highly ordered Al58Cu26Ir16 decagonal quasicrystal (d-QC), which is constructed by a periodic stack of quasiperiodic atomic planes, was investigated using aberration-corrected scanning transmission electron microscopy. The entire quasiperiodic structure can be well described based on the pentagonal Penrose lattice decorated with a decagonal columnar cluster 2 nm across, and the individual clusters apparently showed up with localized atomic disorder to various degree that blurs the underlying cluster symmetry. Multivariate analysis of the cluster images with principal component analysis has successfully extracted two fundamental clusters, which are with definite mirror and 10-fold-rotation symmetries; this is the first solid example of the d-QC composed of multiple fundamental clusters with different symmetry. Consequently, it is found that all the observed variations can be reasonably interpreted by a linear combination between these two fundamental clusters of mirror and 10-fold symmetries, indicating that the possible atomic disorder is strongly restricted by these particular symmetries. Characteristic distributions of the mirror/10-fold clusters on the pentagonal Penrose lattice are also described.

Update: 12-Nov-2015


Title:
Magnetic anisotropy in FeSb studied by Fe-57 Mossbauer spectroscopy
Authors:
Komedera, K; Jasek, AK; Blachowski, A; Ruebenbauer, K; Krzton-Maziopa, A Author Full Names: Komedera, K.; Jasek, A. K.; Blachowski, A.; Ruebenbauer, K.; Krzton-Maziopa, A.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 399 221-227; 10.1016/j.jmmm.2015.09.076 FEB 1 2016
Abstract:
The Fe1+xSb compound has been synthesized close to stoichiometry with x=0.023(8). The compound was investigated by Fe-57 Mossbauer spectroscopy in the temperature range 4.2-300 K. The anti-ferromagnetic ordering temperature was found as 232 K i.e. much higher than for the less stoichiometric material. Regular iron was found to occupy two different positions in proportion 2:1. They differ by the electric quadrupole coupling constants and both of them exhibit extremely anisotropic electric field gradient tensor (EFG) with the asymmetry parameter eta approximate to 1. The negative component of both EFGs is aligned with the c-axis of the hexagonal unit cell, while the positive component is aligned with the (120) direction. Hence, a model describing deviation from the NiAs P6(3)/mmc symmetry group within Fe-planes has been proposed. Spectra in the magnetically ordered state could be explained by introduction of the incommensurate spin spirals propagating through the iron atoms in the direction of the c-axis with a complex pattern of the hyperfine magnetic fields distributed within a-b plane. Hyperfine magnetic field pattern of spirals due to major regular iron is smoothed by the spin polarized itinerant electrons, while the minor regular iron exhibits hyperfine field pattern characteristic of the highly covalent bonds to the adjacent antimony atoms. The excess interstitial iron orders magnetically at the same temperature as the regular iron, and magnetic moments of these atoms are likely to form two-dimensional spin glass with moments lying in the a-b plane. The upturn of the hyperfine field for minor regular iron and interstitial iron is observed below 80 K. Magneto-elastic effects are smaller than for FeAs, however the recoilless fraction increases significantly upon transition to the magnetically ordered state. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Flat and conical incommensurate magnetic structures in the two-subsystem partially frustrated Heisenberg ferrimagnet
Authors:
Martynov, SN Author Full Names: Martynov, S. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 398 121-126; 10.1016/j.jmmm.2015.09.046 JAN 15 2016
Abstract:
The phase transitions into flat and conical incommensurate magnetic structures are considered for a ferrimagnet with the dominant nonfrustrated exchange between the spins in one crystallographic position, competing exchanges between the spins in another position and frustrated exchange between the spins in different positions. The appearance conditions and the temperatures of the second order phase transitions are analytically obtained in the mean field approximation. The first order phase transition between these states is studied and the phase diagrams of temperature vs frustrated exchanges are calculated by the numerical minimization of free energy. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Temperature dependence of the propagation vector in Ni3-xCoxV2O8 with x=0.1 and 0.5
Authors:
Lee, S; Lee, H; Choi, YN; Semkin, MA; Teplykh, AE; Skryabin, YN; Li, WH; Pirogov, AN Author Full Names: Lee, Seongsu; Lee, Heeju; Choi, Yong Nam; Semkin, M. A.; Teplykh, A. E.; Skryabin, Yu. N.; Li, Wen-Hsien; Pirogov, A. N.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 397 225-229; 10.1016/j.jmmm.2015.08.106 JAN 1 2016
Abstract:
We present the susceptibility and neutron diffraction data on multiferroic Ni3-xCoxV2O8 with x=0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order-disorder transition occurs at T-HTI=8.5 K in both samples. Below T-HTI, the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x=0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x=0.5 exhibits a definite temperature dependence, which differs from the case of the undopal sample (x=0)., (C) 2015 Elsevier By. All rights reserved.

Title:
Microstructure of mechanically alloyed and annealed Al62Cu25.5Fe12.5 powder
Authors:
Mitka, M; Goral, A; Rogal, L; Litynska-Dobrzynska, L Author Full Names: Mitka, Mikolaj; Goral, Anna; Rogal, Lukasz; Litynska-Dobrzynska, Lidia
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 653 47-53; 10.1016/j.jallcom.2015.08.250 DEC 25 2015
Abstract:
The influence of mechanical alloying (MA) of Al62Cu25.5Fe12.5 (at.%) powder obtained with different milling speeds and milling time and subsequent annealing on its microstructure and phase composition was investigated by means X-ray diffraction, scanning and transmission electron microscopy (SEM and TEM) methods. The power was milled in a high energy planetary ball mill at the rotation speed 250, 300 and 350 rpm for 3, 6, 10 and 20 h using WC milling media. The annealing of milled powders was performed at 800 degrees C for 4 h. Nano-quasicrystalline icosahedral phase (i-phase) was obtained in the as-milled powder at a speed 350 rpm, while the lower milling speed resulted in the formation of cubic beta-Al(Cu, Fe) phase. In all annealed powders the i-phase coexisting with the ordered lambda-Al(Cu, Fe) phase and small amount of the l-Al13Fe4 phase has been observed. The highest volume fraction of i-phase was found in the annealed powder milled at 250 rpm. After annealing the grain size increases compared to the as-milled powder. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Fabrication and properties of Ti-Zr-Ni quasicrystal and bulk composite materials by high pressure sintering
Authors:
Han, QG; Zhong, JL; Zhang, Q; Liu, B; Wang, LM Author Full Names: Han, Qi-Gang; Zhong, Ji-Lun; Zhang, Qiang; Liu, Biao; Wang, Li-Min
Source:
JOURNAL OF NON-CRYSTALLINE SOLIDS, 428 62-67; 10.1016/j.jnoncrysol.2015.08.008 NOV 15 2015
Abstract:
The overall composition of Ti40.83Zr40.83Ni18.34 quasicrystal powders that consist of the stable icosahedral phase (I-phase) was prepared by mechanical alloying and the subsequent heat treatment in a vacuum furnace. Then, bulk composite materials (BCMs) with the composition of Ti40.83Zr40.83Ni18.34 I-phase quasicrystal powders and carbonyl nickel powders as metal bonding agent (20 wt.%), have been fabricated by high pressure sintering. The Vickers hardness, compressive strength, deformation at fracture, Young's modulus, and wear resistance of the BCMs have been studied in detail, after being sintered at different pressure and temperature. It indicates that high pressure sintering enables us to produce the BCMs (about 10 mm in diameter and 3 mm in height) with a short sintered time of 10 mm and high pressure of 3.0 GPa. In addition, the optimum sintered condition is 3.0 GPa-600 degrees C, which is beneficial of the improvement of the performances of BCM, such as the Vickers hardness of 389, the compressive strength of 430 MPa, the deformation at fracture of 2.20%, the Young's modulus of 19 GPa, the lowest value of friction coefficient at 0.45 +/- 0.13, and wear mass losses of 024 mm(3). This work shows a promise in practical fabrication of BCM that consist of the stable Ti-Zr-Ni icosahedral quasicrystalline phase may be developed. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Nanosized helical magnetic domains in strongly frustrated Fe3PO4O3
Authors:
Ross, KA; Bordelon, MM; Terho, G; Neilson, JR Author Full Names: Ross, K. A.; Bordelon, M. M.; Terho, G.; Neilson, J. R.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134419 OCT 26 2015
Abstract:
Fe3PO4O3 forms a noncentrosymmetric lattice structure (space group R3m) comprising triangular motifs of Fe3+ coupled by strong antiferromagnetic interactions (vertical bar circle dot(CW)vertical bar > 900 K). Neutron diffraction from polycrystalline samples shows that strong frustration eventually gives way to an ordered helical incommensurate structure below T-N = 163 K, with the helical axis in the hexagonal ab plane and a modulation length to similar to 86 angstrom. The magnetic structure consists of an unusual needlelike correlation volume that extends past 900 angstrom along the hexagonal c axis but is limited to similar to 70 angstrom in the ab plane, despite the three-dimensional nature of the magnetic sublattice topology. The small in-plane correlation length, which persists to at least T = T-N/40, indicates a robust blocking of long-range order of the helical magnetic structure, and therefore stable domain walls, or other defect spin textures, must be abundant in Fe3PO4O3. Temperature-dependent neutron powder diffraction reveals small negative thermal expansion below T-N. No change in lattice symmetry is observed on cooling through TN, as revealed by high-resolution synchrotron x-ray diffraction. The previously reported reduced moment of the Fe3+ ions (S = 5/2), mu similar to 4.2 mu(B), is confirmed here through magnetization studies of a magnetically diluted solid solution series of compounds, Fe(3-x)GaxPO4O3, and is consistent with the refined magnetic moment from neutron diffraction 4.14(2) mu(B). We attribute the reduced moment to a modified spin density distribution arising from ligand charge transfer in this insulating oxide.

Title:
Solitonic Spin-Liquid State Due to the Violation of the Lifshitz Condition in Fe1+yTe
Authors:
Materne, P; Koz, C; Rossler, UK; Doerr, M; Goltz, T; Klauss, HH; Schwarz, U; Wirth, S; Rossler, S Author Full Names: Materne, Ph.; Koz, C.; Roessler, U. K.; Doerr, M.; Goltz, T.; Klauss, H. H.; Schwarz, U.; Wirth, S.; Roessler, S.
Source:
PHYSICAL REVIEW LETTERS, 115 (17):10.1103/PhysRevLett.115.177203 OCT 21 2015
Abstract:
A combination of phenomenological analysis and Mossbauer spectroscopy experiments on the tetragonal Fe1+yTe system indicates that the magnetic ordering transition in compounds with higher Fe excess, y >= 0.11, is unconventional. Experimentally, a liquidlike magnetic precursor with quasistatic spin order is found from significantly broadened Mossbauer spectra at temperatures above the antiferromagnetic transition. The incommensurate spin-density wave order in Fe1+yTe is described by a magnetic free energy that violates the weak Lifshitz condition in the Landau theory of second-order transitions. The presence of multiple Lifshitz invariants provides the mechanism to create multidimensional, twisted, and modulated solitonic phases.

Title:
Rare earth ferrites LuFe2O4 +/- x polymorphism, polytypism and metastable phases
Authors:
Hervieu, M; Damay, F; Maignan, A; Martin, C Author Full Names: Hervieu, M.; Damay, F.; Maignan, A.; Martin, C.
Source:
SOLID STATE SCIENCES, 48 A1-A16; 10.1016/j.solidstatesciences.2015.07.013 OCT 2015
Abstract:
This work is a compendium of the structural properties of layered LnFe(2)O(4 +/- x) ferrites, focussed on recently discovered polymorphs and their transitions through five complex commensurate and incommensurate modulated structures. These phases are obtained varying the oxygen content (reversibly from O-4.0 to O-4.5) or applying high pressure (up to 15 GPa). The relationships between the different structures are discussed and models are proposed. These ferrites, which contain magnetic cations and exhibit remarkable 3D flexibility, open the road for magnetic, electric, catalytic or energy materials. (C) 2015 Elsevier Masson SAS. All rights reserved.

Title:
Low temperature oxygen diffusion mechanisms in Nd2NiO4+delta and Pr2NiO4+delta via large anharmonic displacements, explored by single crystal neutron diffraction
Authors:
Ceretti, M; Wahyudi, O; Cousson, A; Villesuzanne, A; Meven, M; Pedersen, B; Bassat, JM; Paulus, W Author Full Names: Ceretti, M.; Wahyudi, O.; Cousson, A.; Villesuzanne, A.; Meven, M.; Pedersen, B.; Bassat, J. M.; Paulus, W.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (42):21140-21148; 10.1039/c5ta05767a 2015
Abstract:
We investigated the structure of Nd2NiO4+delta and Pr2NiO4+delta by single crystal neutron diffraction studies. While the real structure of both compounds is incommensurate, the scattering density of the respective average structures was explored using the Maximum Entropy Method. Unusually high displacement factors were found for the equatorial and apical oxygen atoms showing respectively large displacement amplitudes towards [001] and [110] with respect to the F-symmetry cell. The shifts of the apical oxygen atoms reach up to 1 angstrom from their average position, corresponding to a 25 degrees tilt of the NiO6 octahedra. At 400 degrees C, i.e. slightly above the orthorhombic-tetragonal phase transition, the anharmonic apical oxygen displacements towards [110] in the commensurate tetragonal parent structure are strongly enhanced, showing a double-well potential and pointing towards the interstitial vacancy sites, creating a quasi continuous shallow energy diffusion pathway between apical and interstitial oxygen sites. These large displacement amplitudes are considered to be - at least partially - of dynamical origin, which is consistent with a phonon assisted diffusion mechanism, already activated at very moderate temperatures.

Update: 5-Nov-2015


Title:
Effects of cyclic extrusion and compression parameters on microstructure and mechanical properties of Mg-1.50Zn-0.25Gd alloy
Authors:
Huang, H; Tang, ZB; Tian, Y; Jia, GZ; Niu, JL; Zhang, H; Pei, J; Yuan, GY; Ding, WJ Author Full Names: Huang, Hua; Tang, Zibo; Tian, Yuan; Jia, Gaozhi; Niu, Jialin; Zhang, Hua; Pei, Jia; Yuan, Guangyin; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 86 788-796; 10.1016/j.matdes.2015.07.155 DEC 5 2015
Abstract:
Mg-1.50Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and then subjected to cyclic extrusion and compression (CEC) at 250, 300, 350 and 400 degrees C, respectively. The effects of CEC parameters including passes and temperatures on microstructure evolution and room temperature tensile mechanical properties were characterized and discussed. The results show that more passes are beneficial for secondary phase precipitation, grain refinement and basal texture weakening; while moderate temperature is beneficial for secondary phase precipitation and basal texture weakening by particle stimulated recrystallization nucleation (PSN), and lower temperature is beneficial for grain refinement. The alloy has the highest yield strength after CEC at 250 degrees C because of grain refinement and basal texture strengthening, while it has the highest elongation after being processed with 8 passes of CEC due to grain refinement and basal texture weakening. The processing passes have more important effects on microstructure evolution and mechanical properties than that of temperature during CEC. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Evolution of the dense packings of spherotetrahedral particles: from ideal tetrahedra to spheres
Authors:
Jin, WW; Lu, P; Li, SX Author Full Names: Jin, Weiwei; Lu, Peng; Li, Shuixiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep15640 OCT 22 2015
Abstract:
Particle shape plays a crucial role in determining packing characteristics. Real particles in nature usually have rounded corners. In this work, we systematically investigate the rounded corner effect on the dense packings of spherotetrahedral particles. The evolution of dense packing structure as the particle shape continuously deforms from a regular tetrahedron to a sphere is investigated, starting both from the regular tetrahedron and the sphere packings. The dimer crystal and the quasicrystal approximant are used as initial configurations, as well as the two densest sphere packing structures. We characterize the evolution of spherotetrahedron packings from the ideal tetrahedron (s = 0) to the sphere (s = 1) via a single roundness parameter s. The evolution can be partitioned into seven regions according to the shape variation of the packing unit cell. Interestingly, a peak of the packing density Phi is first observed at s approximate to 0.16 in the Phi-s curves where the tetrahedra have small rounded corners. The maximum density of the deformed quasicrystal approximant family (Phi approximate to 0.8763) is slightly larger than that of the deformed dimer crystal family (Phi approximate to 0.8704), and both of them exceed the densest known packing of ideal tetrahedra (Phi approximate to 0.8563).

Title:
Neutron diffraction investigation of the H - T phase diagram above the longitudinal incommensurate phase of BaCo2V2O8
Authors:
Grenier, B; Simonet, V; Canals, B; Lejay, P; Klanjsek, M; Horvatic, M; Berthier, C Author Full Names: Grenier, B.; Simonet, V.; Canals, B.; Lejay, P.; Klanjsek, M.; Horvatic, M.; Berthier, C.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134416 OCT 20 2015
Abstract:
The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has been shown to be describable by the Tomonaga-Luttinger liquid theory in its gapless phase induced by a magnetic field applied along the Ising axis. Above 3.9 T, this leads to an exotic field-induced low-temperature magnetic order, made of a longitudinal incommensurate spin-density wave, stabilized by weak interchain interactions. By single-crystal neutron diffraction we explore the destabilization of this phase at a higher magnetic field. We evidence a transition at around 8.5 T towards a more conventional magnetic structure with antiferromagnetic components in the plane perpendicular to the magnetic field. The phase diagram boundaries and the nature of this second field-induced phase are discussed with respect to previous results obtained by means of nuclear magnetic resonance and electron spin resonance, and in the framework of the simple model based on the Tomonaga-Luttinger liquid theory, which obviously has to be refined in this complex system.

Title:
Microscopic adjustment of misfit strain and charge segregation in [Bi2Sr2O4](0.51)CoO2
Authors:
Maki, M; Takakura, S; Nishizaki, T; Ichikawa, F Author Full Names: Maki, Makoto; Takakura, Sho-ichi; Nishizaki, Terukazu; Ichikawa, Fusao
Source:
PHYSICAL REVIEW B, 92 (16):10.1103/PhysRevB.92.165117 OCT 16 2015
Abstract:
From scanning tunneling microscopy of the misfit-layered cobaltate [Bi2Sr2O4](0.51)CoO2 single crystals, we observed structural short corrugations oriented in the direction inclined with respect to the incommensurate axis. Results show that the spatial distribution of the electronic charge density is also modified in relation to the atomic displacement. Our data strongly suggest that the rocksalt structure flexibly mounted on the CoO2 layer affects the electronic properties of this system.

Title:
Phase Diagram of Modulated Structures in Ferroelectric Crystals Based on Quantum Ising Model with Third-Neighbor Interactions
Authors:
Mashiyama, H Author Full Names: Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (10):10.7566/JPSJ.84.104712 OCT 15 2015
Abstract:
Incommensurate commensurate phase transitions are analyzed using a model derived from the normal coordinate Hamiltonian for a crystal lattice. The Hamiltonian consists of a local self-potential and effective third-neighbor interactions. Free energies of various modulated phases are calculated with a mean-field approximation under the condition that two quantum states within the local potential are important at low temperature. It is demonstrated that the quantum effect works to stabilize the incommensurate phase rather than the commensurate phase. Even at zero temperature, the incommensurate phase can occupy a finite region in the phase diagram. This situation is similar to quantum paraelectricity in some ferroelectrics, and can be expected as a general feature of modulated structures of dielectric crystals. The phase diagram for ferroic first- and third-neighbor interactions but antiferroic second-neighbor interactions is constructed theoretically and is discussed in detail to explain qualitatively the low-temperature behavior of some ferroelectric crystals.

Title:
Competing magnetic and structural states in multiferroic YMn2O5 at high pressure
Authors:
Kozlenko, DP; Dang, NT; Kichanov, SE; Lukin, EV; Pashayev, AM; Mammadov, AI; Jabarov, SH; Dubrovinsky, LS; Liermann, HP; Morgenroth, W; Mehdiyeva, RZ; Smotrakov, VG; Savenko, BN Author Full Names: Kozlenko, D. P.; Dang, N. T.; Kichanov, S. E.; Lukin, E. V.; Pashayev, A. M.; Mammadov, A. I.; Jabarov, S. H.; Dubrovinsky, L. S.; Liermann, H. -P.; Morgenroth, W.; Mehdiyeva, R. Z.; Smotrakov, V. G.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 92 (13):10.1103/PhysRevB.92.134409 OCT 12 2015
Abstract:
The magnetic, structural, and vibrational properties of YMn2O5 multiferroic have been studied by means of neutron, x-ray powder diffraction, and Raman spectroscopy at pressures up to 6 and 30 GPa, respectively. Application of high pressure, P > 1 GPa, leads to a gradual suppression of the commensurate and incommensurate antiferromagnetic (AFM) phases with a propagation vector q = (1/2,0, q(z) similar to 1/4) and appearance of the commensurate AFM phase with q = (1/2,0,1/2). This observation is sharply contrasting to general trend towards stabilization of commensurate AFM phase with q = (1/2,0,1/4) found in other RMn2O5 compounds upon lattice compression. At P similar to 16 GPa a structural phase transformation accompanied by anomalies in lattice compression and pressure behavior of vibrational modes was observed. The comparative analysis of high-pressure and R-cation radius variation effects clarified a role of particular magnetic interactions in the formation of the magnetic states of RMn2O5 compounds.

Update: 29-Oct-2015


Title:
First-order commensurate-incommensurate magnetic phase transition in the coupled FM spin-1/2 two-leg ladders
Authors:
Jahangiri, J; Hadipour, H; Mandavifar, S; Shayesteh, SF Author Full Names: Jahangiri, J.; Hadipour, H.; Mandavifar, S.; Shayesteh, S. Farjami
Source:
PHYSICA B-CONDENSED MATTER, 476 24-28; 10.1016/j.physb.2015.07.012 NOV 1 2015
Abstract:
We consider the spin-1/2 two-leg ladders with ferromagnetic (FM) interactions along legs and rungs. Using the stochastic series expansion QMC method, we study the low-temperature magnetic behavior of the system. An isolated spin-1/2 FM two-leg ladder is in the gapped saturated FM phase at zero temperature. As soon as the spin-1/2 FM two-leg ladders are connected with antiferromagnetic (AFM) inter-ladder interaction, a first-order commensurate-incommensurate quantum phase transition occurs in the ground state magnetic phase diagram. In fact a jump in the magnetization curve is observed. We found that, coupled spin-1/2 FM two-leg ladders are in a nonmagnetic phase at zero temperature. Applying a magnetic field, the ground state of coupled spin-1/2 FM two-leg ladders remains in the nonmagnetic phase up to a quantum saturate critical field. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Predicting complex mineral structures using genetic algorithms
Authors:
Mohn, CE; Kob, W Author Full Names: Mohn, Chris E.; Kob, Walter
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (42):10.1088/0953-8984/27/42/425201 OCT 28 2015
Abstract:
We show that symmetry-adapted genetic algorithms are capable of finding the ground state of a range of complex crystalline phases including layered- and incommensurate superstructures. This opens the way for the atomistic prediction of complex crystal structures of functional materials and mineral phases.

Title:
Incommensurate modulation and thermal expansion of Sr3B2 (+) Si-x(1) (-) O-x(8) (-) (x/2) solid solutions
Authors:
Volkov, S; Bubnova, R; Bolotina, N; Krzhizhanovskaya, M; Belousova, O; Filatov, S Author Full Names: Volkov, Sergey; Bubnova, Rimma; Bolotina, Nadezhda; Krzhizhanovskaya, Maria; Belousova, Olga; Filatov, Stanislav
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 489-497; 10.1107/S2052520615011713 5 OCT 2015
Abstract:
Crystal structures of Sr3B2 (+) Si-x(1) (-) O-x(8) (- x/2) solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0 beta gamma)000(0 beta gamma)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P2(1)/n(0 beta gamma). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.

Title:
Decagonite, Al71Ni24Fe5, a quasicrystal with decagonal symmetry from the Khatyrka CV3 carbonaceous chondrite
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
AMERICAN MINERALOGIST, 100 (10):2340-2343; 10.2138/am-2015-5423 OCT 2015
Abstract:
Decagonite is the second natural quasicrystal, after icosahedrite (Al63Cu24Fe13), and the first to exhibit the crystallographically forbidden decagonal symmetry. It was found as rare fragments up to similar to 60 mu m across in one of the grains (labeled number 126) of the Khatyrka meteorite, a CV3 carbonaceous chondrite. The meteoritic grain contains evidence of a heterogeneous distribution of pressures and temperatures that occurred during impact shock, in which some portions of the meteorite reached at least 5 GPa and 1200 degrees C. Decagonite is associated with Al-bearing trevorite, diopside, forsterite, ahrensite, clinoenstatite, nepheline, coesite, pentlandite, Cu-bearing troilite, icosahedrite, khatyrkite, taenite, Al-bearing taenite, and steinhardtite. Given the exceedingly small size of decagonite, it was not possible to determine most of the physical properties for the mineral. A mean of seven electron microprobe analyses (obtained from three different fragments) gave the formula Al70.2(3)Ni24.5(4)Fe5.3(2), on the basis of 100 atoms. A combined TEM and single-crystal X-ray diffraction study revealed the unmistakable signature of a decagonal quasicrystal: a pattern of sharp peaks arranged in straight lines with 10-fold symmetry together with periodic patterns taken perpendicular to the 10-fold direction. For quasicrystals, by definition, the structure is not reducible to a single three-dimensional unit cell, so neither cell parameters nor Z can be given. The likely space group is P10(5)/mine, as is the case for synthetic A(17)Ni(24)Fe(5). The five strongest powder-diffraction lines [d in angstrom (I/I-0)] are: 2.024 (100), 3.765 (50), 2.051 (45), 3.405 (40), 1.9799 (40). The new mineral has been approved by the IMA-NMNC Commission (IMA2015-017) and named decagonite for the 10-fold symmetry of its structure. The finding of a second natural quasicrystal informs the longstanding debate about the stability and robustness of quasicrystals among condensed matter physicists and demonstrates that mineralogy can continue to surprise us and have a strong impact on other disciplines.

Title:
Secondary phases in quasicrystal-reinforced Mg-3.5Zn-0.6Gd Mg alloy
Authors:
Huang, H; Tian, Y; Yuan, GY; Chen, CL; Wang, ZC; Ding, WJ; Inoue, A Author Full Names: Huang, Hua; Tian, Yuan; Yuan, Guangyin; Chen, Chunlin; Wang, Zhongchang; Ding, Wenjiang; Inoue, Akihisa
Source:
MATERIALS CHARACTERIZATION, 108 132-136; 10.1016/j.matchar.2015.09.005 OCT 2015
Abstract:
The secondary phases in quasicrystal-reinforced Mg-Zn-Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [1 1 (2) over bar 0](Mg)parallel to[2-fold](I-phase) and (0001)(Mg)parallel to(5-fold)(I-phase). We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [(1) over bar 101](Mg)parallel to[mirror 2-fold](I-phase) and (0 (1) over bar 1 1)(Mg)parallel to(5-fold)(I-phase) are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Strain induced incommensurate structures in vicinity of reconstructive phase transitions
Authors:
Korzhenevskii, AL; Dmitriev, V Author Full Names: Korzhenevskii, A. L.; Dmitriev, V.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (37):10.1088/0953-8984/27/37/375401 SEP 23 2015
Abstract:
General conditions controlling the formation of incommensurate phases in crystals undergoing reconstructive phase transitions are analyzed in the framework of a model-free phenomenological approach. A universal trend to stabilizing such intermediate phases in the vicinity of reconstructive phase transitions stems from the fact that certain high-order improper Lifshitz invariants reduce at such transformations to ones bi-linearly coupling critical displacement gradients and strains or even to the proper Lifshitz invariant. The approach developed here introduces a universal mechanism for the formation both of premartensite incommensurate phases and complex structures with giant unit cells, as found in some elemental crystals at high pressure.

Title:
Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys
Authors:
Cakir, A; Acet, M; Righi, L; Albertini, F; Farle, M Author Full Names: Cakir, A.; Acet, M.; Righi, L.; Albertini, F.; Farle, M.
Source:
AIP ADVANCES, 5 (9):10.1063/1.4932233 SEP 2015
Abstract:
The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q approximate to 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature. (C) 2015 Author(s).

Update: 22-Oct-2015


Title:
Thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K; Sawama, K; Hiroto, T; Nishio, K; Tamura, R Author Full Names: Takagiwa, Y.; Kimura, K.; Sawama, K.; Hiroto, T.; Nishio, K.; Tamura, R.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 652 139-144; 10.1016/j.jallcom.2015.08.081 DEC 15 2015
Abstract:
The thermoelectric properties of Tsai-type Au-Al-RE (RE: Yb, Tm, Gd) icosahedral quasicrystals (QCs) and their approximant crystals (ACs) have been investigated from 373 K to 873 K. Comparison of their thermoelectric properties above room temperature is of great interest since resonant states are likely to be present in the electronic density of states near the Fermi level for the Au-Al-Yb QC, which should influence the thermoelectric properties and, hence, the dimensionless figure of merit. The electrical conductivity of Au-Al-Yb ACs varies significantly, i.e. from 3000 Omega(-1) cm(-1) to 5200 Omega(-1) cm(-1), with changing the Au/Al composition whereas the other compounds have conductivities of similar to 3000 Omega(-1) cm(-1). Such an anomalous behavior of the Au-Al-Yb ACs is understood to be due to the existence of a resonant peak originating from hybridization of Yb f-states and Au/Al sp-states. A maximum power factor of 230 mu Wm(-1) K-2 at 873 K is obtained in 1/1-Au48Al37Yb15 AC, which is significantly higher than those of Al-based icosahedral phases at the same temperature. On the other hand, the room-temperature thermal conductivities for Au-Al-RE compounds range from 3 to 4 W m(-1) K-1, reflecting their complex crystal structures with a large unit cell and mixed and/or partially occupied sites. Consequently, both 1/1-Au50Al35Yb15 and Au48Al37Yb15 ACs have similar maximum figures of merit of 0.014 at 873 K. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Deformation mechanism of Ni54Mn25Ga20.9Gd0.1 high-temperature shape memory alloy
Authors:
Zhang, X; Sui, JH; Cai, W; Liu, QS; Liu, AL Author Full Names: Zhang, Xin; Sui, Jiehe; Cai, Wei; Liu, Qingsuo; Liu, Ailian
Source:
INTERMETALLICS, 67 52-55; 10.1016/j.intermet.2015.07.017 DEC 2015
Abstract:
Ni54Mn25Ga20.9Gd0.1 Polycrystalline high-temperature shape memory alloy displayed high compressive fracture strain of 24.6% and large shape memory effect of 7.5%. However, its deformation mechanism was still unknown. In this paper, the structure revolution characterized by XRD and TEM indicated a new deformation mechanism different before was found. The deformation process of Ni54Mn25Ga20.9Gd0.1 alloy could be divided into four stages, including elastic deformation of non-modulated tetragonal martensite (T), stress-induced T to seven-layered modulated martensite (7 M) transformation, variants reorientation of 7 M, and elastic plastic deformation of reoriented 7 M. The 7 M formed by compression deformation disappeared completely after heating to the temperature above A(f). (C) 2015 Elsevier Ltd. All rights reserved.

Title:
From crystal morphology to molecular and scale crystallography
Authors:
Janner, A; Janssen, T Author Full Names: Janner, A.; Janssen, T.
Source:
PHYSICA SCRIPTA, 90 (8):10.1088/0031-8949/90/8/088007 AUG 2015
Abstract:
A number of topics, ranging from morphology of aperiodic crystals to indexed enclosing forms of axial-symmetric proteins, nucleic acids and viruses, have been selected among those investigated by the authors in 50 years of research. The basic symmetries involved in fields like superspace, molecular and scale crystallography, are considered from a personal point of view in their time evolution. A number of specific subjects follow, chosen among a few highlights and presented according to the experience of the authors: snow crystals, calaverite AuTe2, the incommensurately modulated crystals Rb2ZnBr4, [N(CH3)(4)](2)ZnCl4 and the mitochondrial ferritin.

Title:
Atomic structure of icosahedral quasicrystals: stacking multiple quasi-unit cells
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (97):79279-79297; 10.1039/c5ra13874d 2015
Abstract:
An effective tiling approach is proposed for the structural description of icosahedral quasicrystals based on the original substitution algorithm. The atomic structure of icosahedral quasicrystals may by derived by using the iterative and recursive inflation/deflation procedure with subsequent decoration of quasi-unit cells. The quasi-unit cells are stacked in three-dimensional space face-to-face without any gaps between them producing the whole infinite icosahedral structure in the same manner as the usual periodic crystals are generated by multiplication of their unit cells containing one or more atoms in a specific spatial arrangement. A variety of examples illustrating the efficiency of the general algorithm is presented. Stacking of quasi-unit cells along the five-fold axis, as well as the arrangement of cells normal to the five-fold, three-fold, and two-fold axes are presented. The possible atomic structure of an icosahedral single-component quasicrystal is derived. Three types of inequivalent sites with exact icosahedral symmetry may simultaneously exist in the quasicrystalline structure. The structure of characteristic clusters enforced by the compatibility with the quasicrystalline type of ordering is discussed.

Update: 15-Oct-2015


Title:
Solid-state formation of icosahedral quasicrystals at Zn3Mg3Y2/Mg interfaces in a Mg-Zn-Y alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 65-69; 10.1016/j.jallcom.2015.07.254 NOV 25 2015
Abstract:
Solid-state formation of Zn6Mg3Y icosahedral quasicrystals was observed at interfaces between Mg and W-Zn3Mg3Y2 crystals in a Mg-Zn-Y alloy by in situ transmission electron microscopy investigations. The quasicrystals were formed at about 593 K which is about 130 K below the peritectic temperature. Thermally driven interdiffusion of atoms across the W/Mg interface firstly produces local regions with Zn:Mg:Y close to 6:3:1 at the surface of W phase particles, where the cuboctahedral packing of atoms in W phase transforms to icosahedral packing through slight rearrangement of atoms, leading to the nucleation and growth of icosahedral clusters. The icosahedral clusters act as nuclei for the growth of icosahedral quasicrystals. Both valence electron concentration and the densest packing of atoms play important roles in the formation of Zn6Mg3Y quasicrystals. Solid-state formation of icosahedral quasicrystals at W/Mg interfaces provide a feasible way to modify the weakly bonded W/Mg interfaces, which is thus believed to be able to improve the magnesium alloy's mechanical properties. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Properties of Ti40.83Zr40.83Ni18.34 quasicrystalline alloys sintered by Spark Plasma Sintering
Authors:
Han, QG; Chen, ML; Zhang, Q; Sun, LS; Lin, J; Wang, LM Author Full Names: Han, Qi-Gang; Chen, Meng-Lu; Zhang, Qiang; Sun, Lian-Shan; Lin, Jing; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 154-158; 10.1016/j.jallcom.2015.07.297 NOV 25 2015
Abstract:
The quasicrystalline alloy powders with the composition of Ti40.83Zr40.83Ni18.34 are prepared by mechanical alloying (MA) techniques, and the bulk part is obtained by Spark Plasma Sintering (SPS) method. The structure, mechanical properties, friction and wear properties of the bulk part are investigated. The results showed that the structure of the bulk part is pure icosahedral quasicrystalline phase (I-phase). The Vickers Hardness of the bulk part is 7.03 GPa. The maximum compression strength, the elastic deformation and Young modulus is (662 +/- 50) MPa, 2.7 +/- 0.1% and (30 +/- 3) GPa, respectively. The lowest value of friction coefficient is 0.40 at a normal load of 100 N, a sliding velocity of 10 mm/s, a sliding time of 10 min and an ambient temperature of 293.15 K. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni alloy comprising quasicrystal coating with Cu
Authors:
Sun, LS; Lin, J; Cao, ZY; Liang, F; Wang, LM Author Full Names: Sun, Lianshan; Lin, Jing; Cao, Zhanyi; Liang, Fei; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 15-21; 10.1016/j.jallcom.2015.07.252 NOV 25 2015
Abstract:
The Ti1.4V0.6Ni alloy ribbons are prepared by arc-melting and subsequently melt spinning technique. Different percentage compositions of x Cu (x = 1, 3, 5 and 10 wt%) are covered on the surface of the alloy particles utilizing electro-less plating method. The phase structures of the Ti1.4V0.6Ni alloy contain icosahedral quasicrystal phase (I-phase), fcc-Ti2Ni-type phase and bcc-V-based solid solution phase. With increasing x value, the maximum electrochemical hydrogen storage capacity reaches 260 mAh g(-1) when x = 10. After 100 cycles, 23% capacity retention rate is promoted by covering 10 wt% Cu on the alloy than the bare Ti1.4V0.6Ni. Cu offers well electrical conductivity and corrosion resistance, especially it also inhibits the dissolution of V from the alloys. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Investigation on incommensurate modulation structure and T-c in Ca-doped Bi-2201 system
Authors:
Sun, BZ; Zhang, M; Wang, RY; Jiang, YL; Wang, H; Qi, Y Author Full Names: Sun, B. Z.; Zhang, M.; Wang, R. Y.; Jiang, Y. L.; Wang, H.; Qi, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 650 430-435; 10.1016/j.jallcom.2015.08.015 NOV 25 2015
Abstract:
A series of samples with the nominal composition of Bi2Sr2-xCaxCuO6+delta (x = 0.2, 0.4, 0.6, 0.8, 1.0) ceramics are synthesized by sol-gel growth. The microstructure and the incommensurate modulation structure (IMS) were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The superconductivity and the onset temperature of superconducting transition (T-c,T-onset) were analysed. In the whole Ca-doping range, an IMS in b-c planes can be identified and the values of T-c,T-onset are all exceed 80 K. With an increase of chi, the b-component of modulation vector q*, the basic *structural* parameters b and c of Bi-2201 phase have a trend of fall first then rise, whereas the c-component of modulation vector, the angle theta between q* and b* vectors and the values of T-c,T-onset are reversely varied. It can be verified that Ca concentration x = 0.6 is an extreme value, at which the distortion of the CuO2 layers makes the concentration of mobile carriers and the value of T-c,(onset) optimizing. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Approximants of Al-Cr-Fe-Si decagonal quasicrystals described by single structural block
Authors:
He, ZB; Wei, DX; Shen, X; Chen, Y; Ma, HK; Wang, LL; Du, K; Yao, Y; Yu, RC Author Full Names: He, Zhanbing; Wei, Dongxia; Shen, Xi; Chen, Yuan; Ma, Haikun; Wang, Leilei; Du, Kui; Yao, Yuan; Yu, Richeng
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 647 797-801; 10.1016/j.jallcom.2015.06.165 OCT 25 2015
Abstract:
The orthorhombic (3/2, 2/1) approximant with a = 3.06 nm, b = 1.23 nm, c = 2.24 nm, and the coexisting (2/1, 3/2) approximant of decagonal quasicrystals with a = 1.90 nm, c = 3.64 nm, and beta congruent to 90 degrees are found in Al-Cr-Fe-Si alloys by aberration-corrected transmission electron microscope. The structural relationships of these two approximants are analyzed and discussed based on the high-angle annular dark-field scanning transmission electron microscopy images at atomic resolution. We find that both of their structural tiling along the [010] direction can be described by one shield-like tile, with the superiority over the previous HBS tiling model due to the clarity. Combining the shield-like tile and HBS tiling model, the domains of approximants are clearly demonstrated. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Incommensurate antiferromagnetism induced by a charge density wave in the cubic phase of TbGe2.85
Authors:
Tsvyashchenko, AV; Salamatin, DA; Sidorov, VA; Petrova, AE; Fomicheva, LN; Kichanov, SE; Salamatin, AV; Velichkov, A; Kozlenko, DR; Nikolaev, AV; Ryasny, GK; Makarova, OL; Menzel, D; Budzynski, M Author Full Names: Tsvyashchenko, A. V.; Salamatin, D. A.; Sidorov, V. A.; Petrova, A. E.; Fomicheva, L. N.; Kichanov, S. E.; Salamatin, A. V.; Velichkov, A.; Kozlenko, D. R.; Nikolaev, A. V.; Ryasny, G. K.; Makarova, O. L.; Menzel, D.; Budzynski, M.
Source:
PHYSICAL REVIEW B, 92 (10):10.1103/PhysRevB.92.104426 SEP 23 2015
Abstract:
Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of TbGe2.85 (the AuCu3 structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with Cd-111 probes inserted in the TbGe2.85 lattice suggest that the charge density wave is incommensurate in the temperature region 19-145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in TbGe2.85 and TbPd3.

Title:
Direct evidence of an incommensurate phase in NaNbO3 and its implication in NaNbO3-based lead-free antiferroelectrics
Authors:
Guo, HZ; Shimizu, H; Randall, CA Author Full Names: Guo, Hanzheng; Shimizu, Hiroyuki; Randall, Clive A.
Source:
APPLIED PHYSICS LETTERS, 107 (11):10.1063/1.4930067 SEP 14 2015
Abstract:
Hot-stage in situ transmission electron microscopy was employed to investigate the temperature-induced complex sequence of phase transitions in NaNbO3 polycrystalline. In addition to the commonly recognized P (Pbma) -> R (Pmnm) -> S (Pnmm) phase transitions, incommensurate phases were observed to exist in P and R phase regions. The former (in the P -> R transition region) is coincident with a diffused dielectric peak appearing at similar to 170 degrees C, and the latter (in the R -> S transition region) serves as an intermediate structure to bridge the two sub-phases in the R phase region. The incommensurate phase in the P phase region can be inferred from the polarization current density and differential dielectric permittivity anomalies, and it provides the bridge structure during the electric field-induced polarization reversal and antiferroelectric-to-ferroelectric transition in NaNbO3 solid solutions. (C) 2015 AIP Publishing LLC.

Title:
Structure and electrical properties of tetragonal tungsten bronze Ba2CeFeNb4O15
Authors:
Ma, HQ; Lin, K; Liu, LJ; Yang, BL; Rong, YC; Chen, J; Deng, JX; Kawaguchi, S; Kato, K; Xing, XR Author Full Names: Ma, Hongqiang; Lin, Kun; Liu, Laijun; Yang, Baoling; Rong, Yangchun; Chen, Jun; Deng, Jinxia; Kawaguchi, Shogo; Kato, Kenichi; Xing, Xianran
Source:
RSC ADVANCES, 5 (94):76957-76962; 10.1039/c5ra16115k 2015
Abstract:
The crystal structure and electrical microstructure of a tetragonal tungsten bronze (TTB) ceramic, BaCeFeNb4O15 (BCFN), were investigated by high-resolution synchrotron X-ray powder diffraction (SPD), selected area electron diffraction (SAED), and AC impedance spectroscopy. SPD and SAED reveal that the BCFN has a tetragonal structure with space group P4/mbm, and includes an incommensurate modulated behavior. Impedance and AC conductivity tests in the range of 200-360 degrees C suggest thermally activated electrical behavior which originates from both the bulk and the grain boundary elements of the ceramics. The dielectric relaxation in the grain boundaries is due to the trap-controlled ac conduction around doubly ionized oxygen vacancies while the relaxation of the bulk may be associated with the localized electron hopping between the transition-metal ions. These results could be helpful in understanding the electrical conduction and relaxation processes in Fe-containing TTB-type oxides.

Update: 8-Oct-2015


Title:
Oxygen vacancy ordering and its mobility in YMnO3
Authors:
Zhang, QH; Shen, X; Yao, Y; Wang, YG; Jin, CQ; Yu, RC Author Full Names: Zhang, Q. H.; Shen, X.; Yao, Y.; Wang, Y. G.; Jin, C. Q.; Yu, R. C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 648 253-257; 10.1016/j.jallcom.2015.07.032 NOV 5 2015
Abstract:
Oxygen vacancy (V-O) ordering and its mobility in YMnO3 have been studied via electron-beam irradiation. By controlling the beam intensity, three commensurate (A, B and C-type) and one incommensurate V-O-orderings can be formed. The transformation from the A-type to the C-type ordering has also been revealed, which could be attributed to the migration of V-O from the apical V-O site to the planar V-O site. Further, intense irradiation can introduce more V(O)s and make a breakdown of the ferroelectric displacements of Y ions. These results suggest that the V(O)s in YMnO3 system are highly active in several ordered ways and also have a high mobility. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Evolution of atomic distribution during devitrification of bulk metallic glass investigated by atom probe microscopy
Authors:
Mridha, S; Jaeger, DL; Arora, HS; Banerjee, R; Mukherjee, S Author Full Names: Mridha, Sanghita; Jaeger, David L.; Arora, Harpreet Singh; Banerjee, Rajarshi; Mukherjee, Sundeep
Source:
MATERIALS LETTERS, 158 99-103; 10.1016/j.matlet.2015.05.034 NOV 1 2015
Abstract:
Evolution of atomic distribution during devitrification of a zirconium-based bulk metallic glass, Zr41.2Ti13.8Cu12.5Ni10.0Be22.5, was investigated using three-dimensional atom probe microscopy. Atom probe analysis showed uniform distribution of constituent elements for the as-cast alloy, with no phase separation. The metallic glass was annealed at different temperatures to study the crystallization pathways and the length scale, distribution, and morphology of the phases formed. Devitrification was found to proceed via the formation of a metastable icosahedral phase. The devitrification pathway is explained based on "strong-liquid" behavior of this alloy. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Conduction mechanisms and enhanced multiferroic properties of Sr doped Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films
Authors:
Yan, X; Tan, GQ; Ye, W; Ren, HJ; Xia, A Author Full Names: Yan, Xia; Tan, Guoqiang; Ye, Wei; Ren, Huijun; Xia, Ao
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (10):7407-7414; 10.1007/s10854-015-3371-y OCT 2015
Abstract:
Pure BiFeO3 (BFO) and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 (BPSxFMO, x = 0.02-0.05) thin films were deposited on fluorine-doped SnO2 (FTO/glass) substrates by a sol-gel method. The systematic studies of crystalline structure, surface morphologies, leakage conduction mechanisms, ferroelectric and magnetic properties of pure BiFeO3 and Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were investigated. X-ray diffraction patterns, Rietveld analysis and Raman scattering spectra reveal that the (Pr, Sr and Mn) co-doped BiFeO3 thin films give rise to a trigonal (R3m: R) structure transition with respect to the original rhombohedral structure of pure BiFeO3 film. Fowler-Nordheim tunneling conduction mechanism dominates the leakage current of all the films in the relatively high electric field. The significantly enhanced ferroelectric properties of the Bi0.85-xPr0.15SrxFe0.97Mn0.03O3 thin films were observed in comparison with pure BiFeO3 film. In addition, the BPS2FMO film shows the enhanced ferromagnetism with the saturation magnetization (M (s) similar to 1.97 emu cm(-3)), which is almost three times larger than that of pure BFO film (M (s) similar to 0.67 emu cm(-3)), as a result of the small grain size effect and the collapse of space modulated spin structure by the structure transition.

Title:
Crystalline and Spin Chiralities in Multiferroics with Langasite-type Structure and Fe1-xCoxSi Crystals
Authors:
Pikin, SA; Lyubutin, IS; Dudka, AP Author Full Names: Pikin, S. A.; Lyubutin, I. S.; Dudka, A. P.
Source:
CRYSTALLOGRAPHY REPORTS, 60 (5):729-736; 10.1134/S1063774515050077 SEP 2015
Abstract:
It is shown that, when magnetic ordering occurs in layered iron-containing langasites (sp. gr. P321), one of the reasons for spin chiralities of different signs is the presence of structural chirality (the existence of inversion twins), which, in turn, is due to the nonsymmetricity of these crystals. Spin helicoids arise in these multiferroics at split sites of Fe3+ ions below the N,el point. The direction of electric polarization vectors coincides with the direction of the magnetic helicoid axes because of the piezoelectric properties of these materials. Due to the magnetostriction effects, structural chirality wave vector k (z) exceeds the magnetic helicoid wave vector by a factor of 2: k (z) = 2q (z). The temperatures of transitions to the chiral structural and chiral magnetic states may differ. In particular, if the structural transition initial temperature exceeds the magnetic transition temperature (T-U > T-M ), structural displacements may arise in the absence of magnetism at T-M < T < T-U. In noncentrosymmetric Fe1-xCoxSi crystals (sp. gr. P2(1)3), which are not multiferroics, magnetic chirality is due to the Dzyaloshinski-Moriya interaction. The dependence of the moduli of incommensurate wave number of the corresponding helicoid on the atomic composition of the crystals under consideration is nonmonotonic.

Update: 1-Oct-2015


Title:
Strongly anisotropic and complex magnetic behavior in EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, Oleksandr; Kaczorowski, Dariusz
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 291-297; 10.1016/j.jallcom.2015.06.125 OCT 15 2015
Abstract:
Single crystals of EuRhGe3 were studied by means of magnetic susceptibility, magnetization, heat capacity, resistivity and magnetoresistance measurements, performed in wide ranges of temperature and magnetic field strength. The compound was characterized as a Curie-Weiss paramagnet, due to divalent Eu ions, that orders antiferromagnetically at T-N = 11.3 K. In the ordered state, EuRhGe3 exhibits strong magnetic anisotropy. The magnetic moments are probably nearly confined within the ab plane of the tetragonal crystallographic unit cell, and the magnetic propagation vector is likely perpendicular to this plane. The bulk thermodynamic and transport data concordantly suggest that in zero magnetic field the magnetic structure of EuRhGe3 is incommensurate with the chemical one and bears an amplitude-modulated character. In external magnetic field applied within the easy magnetization plane, two other magnetic structures were detected, each of them having an antiferromagnetic nature. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Electrochemical synthesis of Co7Ni3 and Co6Ni4 nanorods with controlled crystalline phase. Application to methanol electro-oxidation
Authors:
Vilana, J; Escalera-Lopez, D; Gomez, E; Valles, E Author Full Names: Vilana, Joan; Escalera-Lopez, Daniel; Gomez, Elvira; Valles, Elisa
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 669-674; 10.1016/j.jallcom.2015.06.134 OCT 15 2015
Abstract:
CoNi nanorods with modulated crystalline phase have been synthesised by means of a potentiostatic deposition method, using a single electrolytic bath, by only varying the electrodeposition potential. The growth of the nanorods in the interior on the nanochannels of the membrane is mainly controlled by the limited transport of the Co(II) and Ni(II) ions to the growth front. Two types of CoNi nanorods of several microns long, with similar composition but different crystalline phases depending on the applied potential, have been obtained. The potentials for the electrosynthesis of the nanorods have been selected to induce different deposition rates and, as a consequence, different crystalline phases, hcp for the lower deposition rates and fcc (+hcp) for the highest ones. For each selected potential, the nanorods present the same composition and crystalline phase along the rods. The test of the two types of nanorods for the methanol electro-oxidation demonstrated both the specific electrocatalytic behaviour of each one and the promising behaviour of the nanorods as electrocatalysts in direct methanol fuel cells in basic medium, due to their higher surface/volume ratio than that of thin films and the superior stability than that of nanoparticles. The influence of the crystalline phase in the methanol electro-oxidation has been also corroborated from pure-hcp and pure-fcc CoNi films. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Structural phase transitions in the Ti45Zr38Ni17-xFex nano-alloys and their deuterides
Authors:
Rusinek, D; Czub, J; Niewolski, J; Gondek, L; Gajewska, M; Takasaki, A; Hoser, A; Zywczak, A Author Full Names: Rusinek, D.; Czub, J.; Niewolski, J.; Gondek, L.; Gajewska, M.; Takasaki, A.; Hoser, A.; Zywczak, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 646 90-95; 10.1016/j.jallcom.2015.06.023 OCT 15 2015
Abstract:
The mechanically alloyed Ti-Zr-Ni materials are extensively studied due to their promising properties concerning biomedical, electronic or hydrogen related applications (for example the gaseous hydrogen storage and the MNiH batteries). In this paper we address the very crucial issue of the structural properties and transformations of the amorphous and quasicrystalline Ti45Zr38Ni17-xFex (x = 0, 4, 8) and their hydrides. According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17 phase into the icosahedral quasicrystalline state (the i-phase) is quasi-continuous and starts at the relatively low temperature of 300 degrees C. At 500 degrees C the i-phase is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase). Interestingly, the deuterided i-phase exhibits completely different thermal evolution. Namely, this phase decomposes into the simple intermetallic compounds above 625 degrees C. What is worth-mentioning is that the release of deuterium is strictly related to that structural decomposition. The possibility of hydrogenation of the amorphous Ti45Zr38Ni17-xFe (x) phases with maintaining the amorphous nature of the alloys is the other extremely important field of our interest. We established a processing route to meet our goal. Finally, we show that introducing deuterium triggers an exciting phase transition from the deuterided amorphous phase into the unknown before, partially disordered, quasicrystallinelike phase (the glassy quasicrystal) without releasing of deuterium. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Reassessment of the effects of Ce on quasicrystal formation and microstructural evolution in rapidly solidified Al-Mn alloys
Authors:
Coury, FG; Botta, WJ; Bolfarini, C; Kiminami, CS; Kaufman, MJ Author Full Names: Coury, F. G.; Botta, W. J.; Bolfarini, C.; Kiminami, C. S.; Kaufman, M. J.
Source:
ACTA MATERIALIA, 98 221-228; 10.1016/j.actamat.2015.07.046 OCT 1 2015
Abstract:
Rapidly solidified Al-Mn-Ce alloys have been reported to exhibit desirable properties due to the uniform distribution of quasicrystalline (QC) particles in an Al matrix. In this study, several ternary alloy compositions that encompassed the alloys reported in the previous reports, namely Al-6Mn-2Ce, Al-6Mn-4Ce, AI-8Mn-4Ce, Al-12Mn-2Ce and Al-10Mn-5Ce, were prepared by melt spinning and their microstructures were characterized by electron microscopy and X-ray diffraction. The results are in direct contrast with the previous reports available in the literature in that the formation of QCs was only observed in the Al-12Mn-2Ce alloy; in the others, the dispersed phase was not the QC; rather, the structural and compositional information presented in this paper together with data recently published in the literature enabled a reinterpretation of the effect of Ce on rapidly solidified Al-Mn alloys. The main conclusion is that Ce favors the formation of a ternary metastable phase with approximate stoichiometry Al20Mn2Ce. This phase forms in a wide portion of the Al-rich region of the ternary phase diagram and can even coexist with the QC phase in alloys containing low amounts of Ce; in this case, the QC contains no detectable Ce by TEM/EDS, consistent with the conclusion that Ce does not favor QC formation in contrast to the previous reports. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Discovery of a Sodium-Ordered Form of Na3V2(PO4)(3) below Ambient Temperature
Authors:
Chotard, JN; Rousse, G; David, R; Mentre, O; Courty, M; Masquelier, C Author Full Names: Chotard, Jean-Noel; Rousse, Gwenaelle; David, Renald; Mentre, Olivier; Courty, Matthieu; Masquelier, Christian
Source:
CHEMISTRY OF MATERIALS, 27 (17):5982-5987; 10.1021/acs.chemmater.5b02092 SEP 8 2015
Abstract:
The crystal structure of the NASICON Na3V2(PO4)(3) phase (NVP) has been investigated as a function of temperature. Combining laboratory and synchrotron X-ray powder diffraction with single crystal X-ray diffraction, we demonstrate the presence of four polymorphs of NVP from 30 to 225 degrees C. While the high temperature gamma-NVP crystallizes in the classical rhombohedral cell (S.G. R (3) over barc, a = 8.73382(4) angstrom, c = 21.91438(17) angstrom), the low temperature alpha-NVP undergoes a monoclinic distortion (S.G. C2/c, a = 15.1244(6) angstrom, b = 8.7287(3) angstrom, c = 21.6143(8) angstrom, beta = 90.163(2)degrees) together with an ordering of the Na atoms. In the middle temperature range, two incommensurate modulated structures (beta- and beta '-NVP) are also reported for the first time.

Title:
Intermediate-valent CeCoAl - a commensurate modulated structure with short Ce-Co distances
Authors:
Niehaus, O; Hoffmann, RD; Tence, S; Chevalier, B; Poettgen, R Author Full Names: Niehaus, Oliver; Hoffmann, Rolf-Dieter; Tence, Sophie; Chevalier, Bernard; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 230 (9-10):579-591; 10.1515/zkri-2015-1856 SEP 2015
Abstract:
CeCoAl was synthesized by melting of the elements in a sealed niobium tube in an induction furnace. Annealing of the sample gave access to a single phase sample. Its structure was refined on the basis of single-crystal X-ray diffractometer data at different temperatures. Above 271 K CeCoAl crystallizes in its own structure type in the space group C2/m [a = 1107.4(2), b = 440.6(1) and c = 479.6(1) pm, beta = 104.6(1)degrees]. Data obtained at 300 K lead to 511 F-2 values with 20 variables and a residual of [I >= 3 sigma(I)] wR = 0.0539. Below 271 K satellites give rise to the superspace group C2/m(alpha 0 gamma) 00; alpha = 2/3, gamma = 2/5 with a temperature independent q-vector. For the 90 K data (also for 180 and 220 K) the commensurate modulated structure could be refined with 4817 F-2 values, 129 variables and residuals of wR = 0.0347 (main), wR = 0.1927 (satellites 1st order), wR = 0.1541 (satellites 2nd order) and wR = 0.1768 (satellites 3rd order) [a = 1107.5(1), b = 440.3(1) and c = 479.0(1) pm, beta = 104.7(1)degrees]. For the three temperatures only minor variations of the modulation amplitudes are observed. The relation of the low temperature (3+1)D 3a x 5c approximant and the room temperature 3D structure is discussed on the basis of a group-subgroup relation. By investigation of the heat capacity, the phase transition could be identified as a second order one with a transition temperature of 271 K. Magnetic measurements clearly prove the intermediate cerium valence which is in line with the short Ce-Co distances.

Title:
The birth of time-of-flight (TOF) neutron powder diffraction at pulsed neutron source (invited)
Authors:
Sosnowska, IM Author Full Names: Sosnowska, Izabela M.
Source:
CRYSTAL RESEARCH AND TECHNOLOGY, 50 (9-10):705-715; 10.1002/crat.201400439 SEP 2015
Abstract:
Behind every improvement there is a story. The early history of the TOF neutron powder diffraction technique is presented. Successes and problems in the application of this technique in material science are reported. Powder diffraction technique is very useful when materials, in a single crystal form, reveal complicated electric and magnetic domain structures. Finding and describing the magnetic structure of multiferroics is the great success of ultra-high resolution TOF neutron diffraction. This unique role of the TOF method in discovery of the modulated magnetic structure of BiFeO3 is presented. To date, the TOF powder neutron diffraction technique gives the richest information on the long period modulated magnetic structure of BiFeO3 and its solid solutions. Determination of magnetic moment direction in a crystal lattice is the unique area of application of the TOF technique. The current status and perspectives of the application of the TOF neutron powder diffraction technique in material science are presented in the review.

Update: 24-Sep-2015


Title:
HREM observation and high-pressure composition isotherm measurement of Ti45Zr38Ni17 quasicrystal powders synthesized by mechanical alloying
Authors:
Tominaga, T; Takasaki, A; Shibato, T; Swierczek, K Author Full Names: Tominaga, Tomoki; Takasaki, Akito; Shibato, Tsuyoshi; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S292-S294; 1 10.1016/j.jallcom.2014.12.200 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti45Zr38Ni17 were mechanical alloyed and annealed subsequently, and the microstructures were characterized by high-resolution electron microscopy (HREM) and an X-ray diffractometry, and hydrogen absorption and desorption pressure-composition (PC) isotherms were measured at 523 K, 573 K and 623 K by a Sieverts type apparatus. The annealing after mechanical alloying (MA) caused formation of an icosahedral quasicrystal with a Ti2Ni type crystal phases. 5 or 10-fold rotational symmetry, which is prohibited to normal crystals, was observed by HREM in a digital diffractogram and an simulated atomic arrangement derived from the digital diffractogram. The hydrogen storage capacity (hydrogen to metal atom ratio: H/M) at 523 K was about 1.3, which decreased with increasing hydrogenation temperatures. All the PC isotherms were steep, and no plateau pressure was observed. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Hydrogen storage properties for Mg-Zn-Y quasicrystal and ternary alloys
Authors:
Luo, XL; Grant, DM; Walker, GS Author Full Names: Luo, Xuanli; Grant, David M.; Walker, Gavin S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S23-S26; 1 10.1016/j.jallcom.2015.01.266 OCT 5 2015
Abstract:
Three Zn-Mg-Y alloys with nominal compositions of Zn50Mg42Y8 and Zn60Mg30Y10 were prepared by induction melting or gas atomisation. XRD and SEM analysis shows samples ZMY-1 and ZMY-2 consisted of multiple phases including icosahedral quasicrystal (QC) i-phase, hexagonal H-phase and Mg7Zn3, whilst ZMY-3 contained QC only. The hydrogen storage properties of the Zn-Mg-Y quasicrystal and ternary alloys were investigated for the first time. The quasicrystal sample ZMY-3 hydrogenated at 300 degrees C had 0.3 wt.% capacity and the DSC decomposition peak temperature was 503 degrees C. Amongst the three samples, the highest hydrogen storage capacity (0.9 wt.%) and the lowest decomposition peak temperature (445 degrees C) was achieved by sample ZMY-1. The pressure-composition-isotherm (PCI) curve of ZMY-1 sample showed a flat plateau gave a plateau pressure of 3.5 bar at 300 degrees C, which indicates a lower dehydrogenation enthalpy than MgH2. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Electrochemical properties of Ti49Zr26Ni25-xPdx (x=0-6) quasicrystal electrodes produced by mechanical alloying
Authors:
Ariga, Y; Takasaki, A; Kimijima, T; Swierczek, K Author Full Names: Ariga, Youhei; Takasaki, Akito; Kimijima, Tsubasa; Swierczek, Konrad
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 645 S152-S154; 1 10.1016/j.jallcom.2015.01.114 OCT 5 2015
Abstract:
Elemental powders consisted of chemical composition of Ti49Zr26Ni25 Pd-x(x) (x = 0, 1, 3, 6) were mechanically alloyed and annealed subsequently, and the discharge performance of the electrodes was measured by a three-electrode cell at room temperature. The annealing after mechanical alloying caused a formation of the icosahedral quasicrystal phase with a Ti2Ni type crystal, C14 Laves and alpha-Ti/Zr phases. The quasilattice constant increased with increasing amount of Pd substituted for Ni up to 3 at.% due to difference in atomic radius between Pd and Ni. The maximum discharge capacity achieved was about 220 mA h/g from a (Ti49Zr26Ni22Pd3) electrode at the first discharge process. (C) 2015 Elsevier B.V. All rights reserved.

Title:
TEM study of the (SbS)(1+delta)(NbS2)(n), (n=1, 2, 3; delta similar to 1.14, 1.20) misfit layer phases
Authors:
Gomez-Herrero, A; Landa-Canovas, AR; Otero-Diaz, LC Author Full Names: Gomez-Herrero, A.; Landa-Canovas, A. R.; Otero-Diaz, L. C.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 230 357-368; 10.1016/j.jssc.2015.07.029 OCT 2015
Abstract:
In the Sb-Nb-S system four new misfit layer phases have been found and carefully investigated via Transmission Electron Microscopy (TEM). Their structures are of composite modulated structure type with stoichiometries that can be formulated as (SbS)(1+delta)(NbS2)(n); for n=1, delta similar to 1.14 and 1.19; for n=2, delta similar to 1.18 and for n=3, delta similar to 1.19. Selected Area Electron Diffraction (SAED) patterns show an almost commensurate fit between the pseudo-tetragonal (SbS) and the pseudo-orthohexagonal (NbS2)(n) subcells along the misfit direction a, with 3(SbS) approximate to 5(NbS2), being b the same for both sub-lattices and c the stacking direction. For n=1, a commensurate phase with 4a(SbS)=7a(NbS2) has also been observed. In addition to the characteristic misfit and associated modulation of the two sub-structures, a second modulation is also present which appears to be primarily associated with the (SbS) sub-structure of both the n=1 and n=2 phases. High Resolution Transmission Electron Microscopy (HRTEM) images show ordered stacking sequences between the (SbS) and (NbS2)(n) lamellae for each of the four phases, however, disordered intergrowths were also occasionally found. Most of the crystals showed different kinds of twinning defects on quite a fine scale. Many crystals showed curled up edges. In some cases the lamellar crystals were entirely folded giving rise to similar diffraction patterns as found for cylindrical crystals. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Enhancement of superconductivity at the onset of charge-density-wave order in a metal
Authors:
Wang, YX; Chubukov, AV Author Full Names: Wang, Yuxuan; Chubukov, Andrey V.
Source:
PHYSICAL REVIEW B, 92 (12):10.1103/PhysRevB.92.125108 SEP 4 2015
Abstract:
We analyze superconductivity in the cuprates near the onset of an incommensurate charge-density-wave (CDW) order with momentum Q = (Q, 0)/(0, Q), as observed in experiments. We first consider a semiphenomenological charge-fermion model in which hot fermions, separated by Q, attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near the CDW transition, T-c = A (g) over bar (c), where (g) over bar (c) is charge-fermion coupling and Ais the prefactor, which we explicitly compute. We then consider the particular microscopic scenario in which the CDW order parameter emerges as a composite field made of primary spin-density-wave fields. We show that charge-fermion coupling (g) over bar (c) is of the order of spin-fermion coupling (g) over bar (s). As a consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally, we analyze the effect of an external magnetic field H. We show that, as H increases, the optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with experiments.

Title:
Quasiperiodicity and 2D topology in 1D charge-ordered materials
Authors:
Flicker, F; van Wezel, J Author Full Names: Flicker, F.; van Wezel, Jasper
Source:
EPL, 111 (3):10.1209/0295-5075/111/37008 AUG 2015
Abstract:
The mathematical description of 1D quasicrystals has recently been linked to that of 2D quantum Hall states. The topological classification of 1D quasicrystals and the corresponding interpretation of their observed charge transport have been widely discussed. We demonstrate the equivalence of both 1D quasicrystals and 2D quantum Hall states to a mean-field treatment of charge order. Using the fractal nature of the spectrum of charge-ordered states we consider incommensurate order as a limit of commensurate. The topological properties of both are identical, arising from a 2D parameter space of phase and wave vector, and fit into class A of the Tenfold Way. The topological nature of all the systems can be tested by measuring a quantized particle transport upon dragging the charge order. Copyright (C) EPLA, 2015

Update: 17-Sep-2015


Title:
Low temperature superplasticity of ultrafine grained Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline phase
Authors:
Kim, WJ; Yoo, YJ Author Full Names: Kim, W. J.; Yoo, Y. J.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 643 47-50; 10.1016/j.msea.2015.07.022 SEP 3 2015
Abstract:
The ultrafine grained Mg-9.25Zn-1.66Y alloy sheet with I-phase prepared by directly applying high-ratio differential speed rolling to the as-cast microstructure exhibited excellent low-temperature super-plasticity (386-888% at 443-473 K) at a moderately high strain rate of 10(-3) s(-1). A criterion for achieving low temperature superplasticity was proposed. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Premartensite to martensite transition and its implications for the origin of modulation in Ni2MnGa ferromagnetic shape-memory alloy
Authors:
Singh, S; Bednarcik, J; Barman, SR; Felser, C; Pandey, D Author Full Names: Singh, Sanjay; Bednarcik, J.; Barman, S. R.; Felser, C.; Pandey, Dhananjai
Source:
PHYSICAL REVIEW B, 92 (5):10.1103/PhysRevB.92.054112 AUG 28 2015
Abstract:
We present results of a temperature-dependent high-resolution synchrotron x-ray powder diffraction study of sequence of phase transitions in Ni2MnGa. Our results show that the incommensurate martensite phase results from the incommensurate premartensite phase and not from the austenite phase assumed in the adaptive phase model. The premartensite phase transforms to the martensite phase through a first order phase transition with coexistence of the two phases in a broad temperature interval (similar to 40 K), discontinuous change in the unit cell volume as also in the modulation wave vector across the transition temperature, and considerable thermal hysteresis in the characteristic transition temperatures. The temperature variation of the modulation wave vector q shows smooth analytic behavior with no evidence for any devilish plateau corresponding to an intermediate or ground state commensurate lock-in phase. The existence of the incommensurate 7M-like modulated structure down to 5 K suggests that the incommensurate 7M-like modulation is the ground state of Ni2MnGa and not the Bain distorted tetragonal L1(0) phase or any other lock-in phase with a commensurate modulation. These findings can be explained within the framework of the soft phonon model.

Title:
KEu(MoO4)(2): Polymorphism, Structures, and Luminescent Properties
Authors:
Morozov, VA; Arakcheeva, AV; Pattison, P; Meert, KW; Smet, PF; Poelman, D; Gauquelin, N; Verbeeck, J; Abakumov, AM; Hadermann, J Author Full Names: Morozov, Vladimir A.; Arakcheeva, Alla V.; Pattison, Philip; Meert, Katrien W.; Smet, Philippe F.; Poelman, Dirk; Gauquelin, Nicolas; Verbeeck, Johan; Abakumov, Artem M.; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 27 (16):5519-5530; 10.1021/acs.chemmater.5b01622 AUG 25 2015
Abstract:
In this paper, with the example of two different polymorphs of KEu(MoO4)(2), the influence of the ordering of the A-cations on the luminescent properties in scheelite related compounds (A',A '') [(B',B '')O-4](m) is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923-1203 K and ambient pressure: a low temperature anorthic alpha-phase and a monoclinic high temperature beta-phase with an incommensurately *modulated structure*. The *structures* of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic beta-KEu(MoO4)(2) has a (3+1)-dimensional incommensurately modulated structure (superspace group I2/b(alpha beta 0)00, a = 5.52645(4) angstrom, b = 5.28277(4) angstrom, c = 11.73797(8) angstrom, gamma = 91.2189(4)degrees, q = 0.56821(2)a*-0.12388(3)b*), whereas the anorthic alpha-phase is (3+1)-dimensional commensurately modulated (superspace group I (1) over bar(alpha beta gamma)0, a = 5.58727(22) angstrom, b = 5.29188(18)angstrom, c = 11.7120(4) angstrom, alpha = 90.485(3)degrees, beta = 88.074(3)degrees, gamma = 91.0270(23)degrees, q = 1/2a* + 1/2c*). In both cases the modulation arises due to Eu/K cation ordering at the A site: the formation of a 2-dimensional Eu3+ network is characteristic for the alpha-phase, while a 3-dimensional Eu3+-framework is observed for the beta-phase structure. The luminescent properties of KEu(MoO4)(2) samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed.

Title:
Precipitates in a quasicrystal-strengthened Al-Mn-Be-Cu alloy
Authors:
Zupanic, F; Wang, D; Gspan, C; Boncina, T Author Full Names: Zupanic, Franc; Wang, Di; Gspan, Cristian; Boncina, Tonica
Source:
MATERIALS CHARACTERIZATION, 106 93-99; 10.1016/j.matchar.2015.05.013 AUG 2015
Abstract:
In this work, an Al-Mn-Be-Cu alloy was studied containing a primary and eutectic icosahedral quasicrystalline phase in the as-cast microstructure. Special attention was given to a transmission electron microscopy investigation of precipitates formed within the aluminium solid solution (Al-ss) at different temperatures. At 200 degrees C, only binary Al-Cu precipitates (theta') were formed. At 300 degrees C, icosahedral quasicrystalline (IQC) precipitates prevailed with a crystallographic orientation relationship with the Al-ss. The rods of the T-phase (Al20Mn3Cu2) which were precipitated above 400 degrees C, also had a specific orientation relationship with the Al-ss. The primary and eutectic IQC microstructural constituent started to transform rapidly to the T-phase and Be4Al(Mn,Cu) at 500 degrees C. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Self-assembly of the decagonal quasicrystalline order in simple three-dimensional systems
Authors:
Ryltsev, R; Klumov, B; Chtchelkatchev, N Author Full Names: Ryltsev, Roman; Klumov, Boris; Chtchelkatchev, Nikolay
Source:
SOFT MATTER, 11 (35):6991-6998; 10.1039/c5sm01397f 2015
Abstract:
Using molecular dynamics simulations we show that a one-component system can be driven to a three-dimensional decagonal (10-fold) quasicrystalline state just by purely repulsive, isotropic and monotonic interaction pair potential with two characteristic length scales; no attraction is needed. We found that self-assembly of a decagonal quasicrystal from a fluid can be predicted by two dimensionless effective parameters describing the fluid structure. We demonstrate stability of the results under changes of the potential by obtaining the decagonal order for three particle systems with different interaction potentials, both purely repulsive and attractive, but with the same values of the effective parameters. Our results suggest that soft matter quasicrystals with decagonal symmetry can be experimentally observed for the same systems demonstrating the dodecagonal order for an appropriate tuning of the effective parameters.

Update: 10-Sep-2015


Title:
The Effect of Icosahedral Phase on Dynamic Recrystallization Evolution and Hot Workability of Mg-2.0Zn-0.3Zr-0.2Y Alloy
Authors:
Lv, BJ; Peng, J; Chu, Z Author Full Names: Lv, Bin-Jiang; Peng, Jian; Chu, Zhong
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (9):3502-3512; 10.1007/s11665-015-1604-0 SEP 2015
Abstract:
The effect of Icosahedral phase (I-phase) on hot deformation behavior, dynamic recrystallization (DRX) evolution, and hot workability of Mg-2.0Zn-0.3Zr-0.2Y alloy has been investigated in the temperature range of 300-500 A degrees C and strain rate range of 0.001-1 s(-1) using Gleeble 3500D thermo-mechanical simulator. Based on regression analysis for Arrhenius-type equation of flow behavior, the average activation energy of deformation was determined as Q = 277.8 kJ/mol. The model of DRX evolution is . The DRX model agreed well with the microstructure evolution of the alloy at all deformation conditions. At lower strain rates (0.001-0.01 s(-1)), continuous DRX (CDRX) is the main DRX mechanism that occurred near the original grain boundaries. Twin-dynamic recrystallization (TDRX) began to occur at lower deformation temperatures and higher strain rates (0.1-1 s(-1)). At a deformation temperature range of 250 to 350 A degrees C and a strain rate of 1 s(-1), the main DRX mechanism is TDRX, and the density of twins decreased, and CDRX began to occur near the original grain boundaries. When the deformation temperature increased to 400 A degrees C, TDRX disappeared and CDRX occurred near original grain boundaries and I-phase particles. According to the flow stress behavior and DRX model, the processing maps have exhibited the optimum deformation conditions to be 450 A degrees C and the strain rate range of 0.01-0.001 s(-1).

Title:
Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules
Authors:
Lumpi, D; Kautny, P; Stoger, B; Frohlich, J Author Full Names: Lumpi, Daniel; Kautny, Paul; Stoeger, Berthold; Froehlich, Johannes
Source:
IUCRJ, 2 584-600; 10.1107/S2052252515011665 5 SEP 2015
Abstract:
The crystallization behavior of methylthio-or methylsulfonyl-containing spacer extended Z, Z-bis-ene-yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized with C2/c symmetry and can be considered as merotypes. Increasing the steric bulk of the core by introduction of ethylenedioxythiophene (EDOT) gave a structure incommensurately modulated in the [010] direction. Further increase of steric demand in the case of a dimethoxythiophene restored periodicity along [010] but resulted in a doubling of the c vector. Two different polytypes were observed, which feature geometrically different layer interfaces (non-OD, order-disorder, polytypes), one with a high stacking fault probability. Oxidation of the methylthio groups of the benzene-based molecule to methylsulfonyl groups led to three polymorphs (two temperature-dependent), which were analyzed by Hirshfeld surface d(e)/d(i) fingerprint plots. The analogously oxidized EDOT-based molecule crystallized as systematic twins owing to its OD polytypism. Shortening of the backbone by removal of the aryl core resulted in an enantiomorphic structure and a further shortening by removal of a methylthio-ene fragment again in a systematically twinned OD polytype.

Title:
Good reproductive preparation method of Li-intercalated hexagonal boron nitride and transmission electron microscopy - Electron energy loss spectroscopy analysis
Authors:
Sumiyoshi, A; Hyodo, H; Sato, Y; Terauchi, M; Kimura, K Author Full Names: Sumiyoshi, A.; Hyodo, H.; Sato, Y.; Terauchi, M.; Kimura, K.
Source:
SOLID STATE SCIENCES, 47 68-72; 10.1016/j.solidstatesciences.2015.04.011 SEP 2015
Abstract:
A Li-intercalated hexagonal boron nitride (Li-h-BNIC) phase was synthesized using a highly reproducible method that involves annealing an Li3N and h-BN mixture at 1220 K. Powder X-ray diffraction, electrical conductivity measurements, transmission electron microscopy (TEM) and electron energy loss spectroscopy were performed. The stacking of BN atomic layers in the Li-h-BNIC phase is not the same as the two-layer stacking periodicity of h-BN. TEM observation suggests the existence of incommensurate periodicity along the intralayer direction. From the low-loss and core-loss spectra, the Li-h-BNIC phase is not metal as predicted by the first-principle calculations. Satellite peaks of 1 s to pi* transition in the B K-edge core-loss spectrum indicate the presence of N atom vacancies modified by O atoms in the h-BN atomic layer. (C) 2015 Elsevier Masson SAS. All rights reserved.

Title:
Cluster-Based Solidification and Growth Algorithm for Decagonal Quasicrystals
Authors:
Kuczera, P; Steurer, W Author Full Names: Kuczera, P.; Steurer, W.
Source:
PHYSICAL REVIEW LETTERS, 115 (8):10.1103/PhysRevLett.115.085502 AUG 21 2015
Abstract:
A novel approach is used for the simulation of decagonal quasicrystal (DQC) solidification and growth. It is based on the observation that in well-ordered DQCs the atoms are largely arranged along quasiperiodically spaced planes parallel to the tenfold axis, running throughout the whole structure in five different directions. The structures themselves can be described as quasiperiodic arrangements of decagonal columnar clusters (cluster covering) that partially overlap in a systematic way. Based on these findings, we define a cluster interaction model within the mean field approximation, with effectively asymmetric interactions ranging beyond the nearest neighbors. In our Monte Carlo simulations, this leads to a long-range ordered quasiperiodic ground state. Indications of two finite-temperature unlocking phase transitions are observed, and are related to the two fundamental length scales that are characteristic for the system.

Title:
Complex variable method for an anti-plane elliptical cavity of one-dimensional hexagonal piezoelectric quasicrystals
Authors:
Yu, J; Guo, JH; Xing, YM Author Full Names: Yu Jing; Guo Junhong; Xing Yongming
Source:
CHINESE JOURNAL OF AERONAUTICS, 28 (4):1287-1295; 10.1016/j.cja.2015.04.013 AUG 2015
Abstract:
Based on the fundamental equations of piezoelasticity of quasicrystal media, using the symmetry operations of point groups, the linear piezoelasticity behavior of one-dimensional (1D) hexagonal quasicrystals is investigated and the piezoelasticity problem of 1D hexagonal quasicrystals is decomposed into two uncoupled problems, i.e., the classical plane elasticity problem of conventional hexagonal crystals and the phonon-phason-electric coupling elasticity problem of 1D hexagonal quasicrystals. The final governing equations are derived for the phonon-phason-electric coupling anti-plane elasticity of 1D hexagonal quasicrystals. The complex variable method for an anti-plane elliptical cavity in 1D hexagonal piezoelectric quasicrystals is proposed and the exact solutions of complex potential functions, the stresses and displacements of the phonon and the phason fields, the electric displacements and the electric potential are obtained explicitly. Reducing the cavity into a crack, the explicit solutions in closed forms of electro-elastic fields, the field intensity factors and the energy release rate near the crack tip are derived. (C) 2015 The Authors.

Update: 27-Aug-2015


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

Update: 20-Aug-2015


Title:
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Authors:
Stone, MB; Lumsden, MD; Garlea, VO; Grenier, B; Ressouche, E; Samulon, EC; Fisher, IR Author Full Names: Stone, M. B.; Lumsden, M. D.; Garlea, V. O.; Grenier, B.; Ressouche, E.; Samulon, E. C.; Fisher, I. R.
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.020415 JUL 28 2015
Abstract:
We determine the low-field ordered magnetic phases of the S = 1 dimerized antiferromagnet Ba3Mn2O8 using single-crystal neutron diffraction. We find that for magnetic fields between mu H-0 = 8.80 T and 10.56 T applied along the [1 (1) over bar0] direction the system exhibits spin density wave order with incommensurate wave vectors of type (eta,eta,epsilon). For mu H-0 > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field-induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. The nature of these two transitions is fundamentally different: the low-field transition is a second-order transition to a spin density wave ground state, while the one at higher field, toward the spiral phase, is of first order.

Title:
Symmetry-Based Computational Tools for Magnetic Crystallography
Authors:
Perez-Mato, JM; Gallego, SV; Tasci, ES; Elcoro, L; de la Flor, G; Aroyo, MI Author Full Names: Perez-Mato, J. M.; Gallego, S. V.; Tasci, E. S.; Elcoro, L.; de la Flor, G.; Aroyo, M. I. Edited by: Clarke DR
Source:
ANNUAL REVIEW OF MATERIALS RESEARCH, VOL 45, 45 217-248; 10.1146/annurev-matsci-070214-021008 2015 Book Series: Annual Review of Materials Research
Abstract:
In recent years, two important advances have opened new doors for the characterization and determination of magnetic structures. Firstly, researchers have produced computer-readable listings of the magnetic or Shubnikov space groups. Secondly, they have extended and applied the superspace formalism, which is presently the standard approach for the description of nonmagnetic incommensurate structures and their symmetry, to magnetic structures. These breakthroughs have been the basis for the subsequent development of a series of computer tools that allow a more efficient and comprehensive application of magnetic symmetry, both commensurate and incommensurate. Here we briefly review the capabilities of these computation instruments and present the fundamental concepts on which they are based, providing various examples. We show how these tools facilitate the use of symmetry arguments expressed as either a magnetic space group or a magnetic superspace group and allow the exploration of the possible magnetic orderings associated with one or more propagation vectors in a form that complements and goes beyond the traditional representation method. Special focus is placed on the programs available online at the Bilbao Crystallographic Server (http://www. cryst.ehu.es).

Update: 13-Aug-2015


Title:
Thermodynamic Aspects of Homogeneous Nucleation Enhanced by Icosahedral Short Range Order in Liquid Fcc-Type Alloys
Authors:
Rappaz, M; Kurtuldu, G Author Full Names: Rappaz, Michel; Kurtuldu, Gueven
Source:
JOM, 67 (8):1812-1820; 10.1007/s11837-015-1328-5 AUG 2015
Abstract:
We have recently shown that minute solute element additions to liquid metallic alloys can strongly influence the nucleation of the fcc phase and act as a grain refinement method. Electron back-scattered diffraction observations revealed a concomitant increase in the percentage of nearest neighbor (nn) grains that are in a twin relationship. Furthermore, multiple-twinned (MT) nn grain configurations with a fivefold symmetry around a common < 110 > direction have been identified, an occurrence that can be explained when the symmetry of the icosahedron is accounted for. It was then conjectured that a new nucleation mechanism occurs in two steps: first, the formation of small icosahedral quasicrystals in the melt, followed by heteroepitaxy of the fcc phase on facets of these quasicrystals. In the present contribution, based on thermodynamics arguments, it is proposed that the first step occurs by spinodal decomposition of the liquid, in a manner similar to Guinier-Preston zones formation in solid state precipitation, while the second step is a transformation of these quasicrystal precursors into MT-fcc nanocrystals once the driving force for this transformation is sufficient to overcome the fcc-liquid interfacial energy and the elastic strains associated with MT-fcc nanoparticles. This explanation sets up guidelines for finding solute elements and composition ranges that favor this grain refinement mechanism.

Title:
Symmetry of icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 26 (4):923-942; 10.1007/s11224-014-0559-3 AUG 2015
Abstract:
The concept of infinitely fragmented fractal tiling is proposed for the description of the structure and symmetry of quasicrystals. Fractal tilings may serve as unique "parent" structures for the corresponding local isomorphism class. The generating symmetry elements and some special features of the resulting symmetry groups of the fractal tilings are analyzed. Simple inflation/deflation rules for icosahedral quasicrystals are proposed, and natural local matching rules are derived.

Title:
Incommensurate spin density wave at a ferromagnetic quantum critical point in a three-dimensional parabolic semimetal
Authors:
Murray, JM; Vafek, O; Balents, L Author Full Names: Murray, James M.; Vafek, Oskar; Balents, Leon
Source:
PHYSICAL REVIEW B, 92 (3):10.1103/PhysRevB.92.035137 JUL 21 2015
Abstract:
We explore the ferromagnetic quantum critical point in a three-dimensional semimetallic system with upwardand downward-dispersing bands touching at the Fermi level. Evaluating the static spin susceptibility to leading order in the coupling between the fermions and the fluctuating ferromagnetic order parameter, we find that the ferromagnetic quantum critical point is masked by an incommensurate, longitudinal spin density wave phase. We first analyze an idealized model that, despite having strong spin-orbit coupling, still possesses O(3) rotational symmetry generated by the total angular momentum operator. In this case, the direction of the incommensurate spin density wave propagation can point anywhere, while the magnetic moment is aligned along the direction of propagation. Including symmetry-allowed anisotropies in the fermion dispersion and the coupling to the order parameter field, however, we find that the ordering wavevector instead breaks a discrete symmetry and aligns along either the [111] or [100] direction, depending on the signs and magnitudes of these two types of anisotropy.

Title:
Spin- and Pair-Density-Wave Glasses
Authors:
Mross, DF; Senthil, T Author Full Names: Mross, David F.; Senthil, T.
Source:
PHYSICAL REVIEW X, 5 (3):10.1103/PhysRevX.5.031008 JUL 20 2015
Abstract:
Spontaneous breaking of translational symmetry, known as density-wave order, is common in nature. However, such states are strongly sensitive to impurities or other forms of frozen disorder leading to fascinating glassy phenomena. We analyze impurity effects on a particularly ubiquitous form of broken translation symmetry in solids: a spin-density wave (SDW) with spatially modulated magnetic order. Related phenomena occur in pair-density-wave (PDW) superconductors where the superconducting order is spatially modulated. For weak disorder, we find that the SDW or PDW order can generically give way to a SDWor PDW glass-new phases of matter with a number of striking properties, which we introduce and characterize here. In particular, they exhibit an interesting combination of conventional (symmetry-breaking) and spin-glass (Edwards-Anderson) order. This is reflected in the dynamic response of such a system, which-as expected for a glass-is extremely slow in certain variables, but, surprisingly, is fast in others. Our results apply to all uniaxial metallic SDW systems where the ordering vector is incommensurate with the crystalline lattice. In addition, the possibility of a PDW glass has important consequences for some recent theoretical and experimental work on La2-xBaxCu2O4.

Title:
A magnetocaloric effect arising from a ferromagnetic transition in the martensitic state in Heusler alloy of Ni50Mn36Sb8Ga6
Authors:
Tian, FH; Zeng, YY; Xu, MW; Yang, S; Lu, T; Wang, JQ; Chang, TY; Adil, M; Zhang, Y; Zhou, C; Song, XP Author Full Names: Tian, Fanghua; Zeng, Yuyang; Xu, Minwei; Yang, Sen; Lu, Tao; Wang, Jieqiong; Chang, Tieyan; Adil, Murtaza; Zhang, Yin; Zhou, Chao; Song, Xiaoping
Source:
APPLIED PHYSICS LETTERS, 107 (1):10.1063/1.4926411 JUL 6 2015
Abstract:
We report a magnetocaloric effect with nearly zero thermal hysteresis in Heusler alloy of Ni50Mn36Sb8Ga6 around room temperature due to a ferromagnetic transition in martensitic state (FTMS). The refrigerant capacity value of this ferromagnetic transition in the vicinity of onset temperature T-M(C) can arrive at 163.8 J/kg, much higher than that of first-order magnetically martensitic transition in the same alloy. Such a magnetocaloric effect in FTMS is attributed to a second-order (or a weak first-order) transition from an antiferromagnetic phase with modulated 7M orthorhombic structure to a ferromagnetic phase with modulated 4O orthorhombic structure. (C) 2015 AIP Publishing LLC.

Update: 6-Aug-2015


Title:
Microstructural transformation of quasicrystalline AlFeCrTi extruded bars upon long thermal treatments
Authors:
Garcia-Escorial, A; Natale, E; Cremaschi, VJ; Todd, I; Lieblich, M Author Full Names: Garcia-Escorial, A.; Natale, E.; Cremaschi, V. J.; Todd, I.; Lieblich, M.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S199-S203; 1 10.1016/j.jallcom.2014.12.164 SEP 15 2015
Abstract:
Bulk Al93Fe3Cr2Ti2 bars extruded from gas atomised powder particles present a microstructure of an aluminium matrix reinforced with a spherical nanoquasicrystalline phase. In this work the evolution of the microstructure of Al93Fe3Cr2Ti2 extruded bars upon heating at 400 degrees C for up to 1000 h is investigated by means of X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. According to our observations we propose that the quasicrystalline alloy evolves in two steps: a first step consists in the decomposition of the supersaturated solid solution of the matrix and the quasicrystals, and a second step in the transformation of the quasicrystals into the equilibrium phases. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Characterization of aluminium matrix composites reinforced by Al-Cu-Fe quasicrystalline particles
Authors:
Litynska-Dobrzynska, L; Dutkiewicz, J; Stan-Glowinska, K; Wajda, W; Dembinski, L; Langlade, C; Coddet, C Author Full Names: Litynska-Dobrzynska, L.; Dutkiewicz, J.; Stan-Glowinska, K.; Wajda, W.; Dembinski, L.; Langlade, C.; Coddet, C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 643 S114-S118; 1 10.1016/j.jallcom.2014.11.125 SEP 15 2015
Abstract:
Aluminium matrix composites were consolidated from elemental Al powder and atomised Al65Cu20Fe15 particles by vacuum hot pressing technique. The spherical Al65Cu20Fe15 particles consisted of icosahedral quasicrystalline dendrites or cells and cubic tau-AlCu(Fe) phase located in interdendritic areas. The composites with different content of the reinforcement particles (20, 40 and 60 wt%) were prepared. All composites showed density about 99% and a good bonding between the Al65Cu20Fe15 particles and the matrix. It was shown that the phase composition of the atomised particles did not change after consolidation for the composite containing 20% and 40% added particles while Al2Cu precipitates formed at the Al/Al65Cu20Fe15 interfaces and inside the matrix in the composite with 60% of Al65Cu20Fe15 particles. With the increase of the volume fraction of the reinforcement in the composite the hardness as well as compressive strength increased reaching the value of 173 HV0.5 and 370 MPa, respectively for 60% of Al65Cu20Fe15 particles. The friction coefficient slightly varied in the range 0.5-0.7 depending on the composition. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Formation of Complex Intermetallics in the Al-Rich Part of Al-Pt-Ru
Authors:
Kapush, D; Samuha, S; Meshi, L; Velikanova, TY; Grushko, B Author Full Names: Kapush, D.; Samuha, S.; Meshi, L.; Velikanova, T. Ya.; Grushko, B.
Source:
JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 36 (4):327-332; 10.1007/s11669-015-0385-3 AUG 2015
Abstract:
The study confirmed the stability of the previously reported ternary C-phase (, a = 0.77353(3) nm for Al73.5Pt10Ru16.5), whose composition was found to range between Al73Pt6Ru21 and Al73.5Pt14.5Ru12. The thermodynamically stable decagonal phase was revealed for the first time at 700-900 A degrees C in a small compositional region around Al78Pt6Ru16. It belongs to the D-4 structural type (1.65 nm periodicity in the specific direction). The metastable Al-Pt chi-phase (P31c) is stabilized by the addition of only similar to 1.5 at.% Ru and extends up to similar to 12 at.% Ru. The lattice parameters for Al76Pt18.6Ru5.4 are a = 1.2256(4) and c = 2.7331(4) nm.

Title:
Periodic almost-Schrodinger equation for quasicrystals
Authors:
Blinov, IV Author Full Names: Blinov, Igor V.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep11492 JUL 24 2015
Abstract:
A new method for finding electronic structure and wavefunctions of electrons in quasiperiodic potential is introduced. To obtain results it uses slightly modified Schrodinger equation in spaces of dimensionality higher than physical space. It enables to get exact results for quasicrystals without expensive non-exact calculations.

Title:
Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce-2 RuZn4
Authors:
Hartwig, S; Prokes, K; Hansen, T; Ritter, C; Gerke, B; Pottgen, R; Mydosh, JA; Forster, T Author Full Names: Hartwig, Steffen; Prokes, Karel; Hansen, Thomas; Ritter, Clemens; Gerke, Birgit; Poettgen, Rainer; Mydosh, J. A.; Foerster, Tobias
Source:
PHYSICAL REVIEW B, 92 (2):10.1103/PhysRevB.92.024420 JUL 17 2015
Abstract:
Neutron powder diffraction experiments were performed on the intermediate-valence Ce-2 RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites is magnetically active. Ce-2 RuZn4 orders antiferromagnetically at T-N = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector q(m) = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) mu(B).

Title:
Commensurate and incommensurate spin-density waves and the superconductivity dome in heavy electron systems
Authors:
Schlottmann, P Author Full Names: Schlottmann, P.
Source:
PHYSICAL REVIEW B, 92 (4):10.1103/PhysRevB.92.045115 JUL 16 2015
Abstract:
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as the Neel temperature tends to zero. If the vector Q is commensurate with the lattice (umklapp with Q = G/2), pairs of electrons can be transferred between the pockets and a superconducting dome above the quantum critical point may arise. If the vector Q is not commensurate with the lattice, there are eight phases that need to be considered: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with a modulated order parameter of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type. The renormalization group equations are studied and numerically integrated. The phase diagram is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of vertical bar Q - G/2 vertical bar.

Title:
Non-Fermi-Liquid Behavior in Metallic Quasicrystals with Local Magnetic Moments
Authors:
Andrade, EC; Jagannathan, A; Miranda, E; Vojta, M; Dobrosavljevic, V Author Full Names: Andrade, Eric C.; Jagannathan, Anuradha; Miranda, Eduardo; Vojta, Matthias; Dobrosavljevic, Vladimir
Source:
PHYSICAL REVIEW LETTERS, 115 (3):10.1103/PhysRevLett.115.036403 JUL 14 2015
Abstract:
Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures T, leading to a power-law distribution of Kondo temperatures P(T-K) similar to T-K(alpha-1), with a nonuniversal exponent alpha, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. For alpha < 1, the resulting singular P(T-K) induces non-Fermi-liquid behavior with diverging thermodynamic responses as T -> 0.

Update: 30-Jul-2015


Title:
Effect of Ti addition on the glass forming ability, crystallization, and plasticity of (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses
Authors:
Shi, B; Xu, YL; Ma, WL; Li, C; Estefania, CV; Li, JG Author Full Names: Shi, Bo; Xu, Yuanli; Ma, Wenli; Li, Chao; Estefania, Carmen Verge; Li, Jiangong
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 639 345-349; 10.1016/j.msea.2015.04.100 JUL 15 2015
Abstract:
A series of (Zr(64.13)Cu(15.7)sNi(10.12)Al(10))(100-x)Ti-x (x=0-7) bulk metallic glasses were prepared by water-cooled copper mold casting method. The glass forming ability, crystallization behavior, and plasticity of the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x alloys with different Ti contents were studied. The reduced glass transition temperature increases with Ti addition and a maximum value of 0.562 is achieved at x=5, indicating that the glass forming ability increases with Ti addition. Compared with that of one crystallization step for the sample without Ti addition, the Ti (x >= 2) containing alloys exhibit a two-step crystallization behavior. In addition, the initial crystallization temperature decreases from 744 to 684 K as x increases from 0 to 7. Icosahedral quasicrystal phase was found to precipitate in the amorphous matrix in the first crystallization step, implying that strong icosahedral short-range order may exist in the Ti (x >= 2) containing alloys. moreover, the (Zr64.13Cu15.75Ni10.12Al10)(100-x)Ti-x bulk metallic glasses exhibit excellent plasticity, i.e., a plastic engineering strain in compression larger than 80% for x <= 6. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Effects of Al-Cr-Fe Quasicrystal Content on Tribological Properties of Cold-Sprayed Titanium Composite Coatings
Authors:
Khun, NW; Li, RT; Loke, K; Khor, KA Author Full Names: Khun, N. W.; Li, R. T.; Loke, K.; Khor, K. A.
Source:
TRIBOLOGY TRANSACTIONS, 58 (4):616-624; 10.1080/10402004.2014.991860 2015
Abstract:
Titanium (Ti) composite coatings were prepared on commercially available Ti substrates via a cold-spray process. Quasicrystalline Al-Cr-Fe particles were incorporated in the cold-sprayed Ti matrices at different contents to form a new type of wear-resistant Ti composite coating. The tribological properties of the Ti composite coatings were systematically investigated using steel ball-on-disc microtribological testing. The incorporation of 10 wt% Al-Cr-Fe particles gave rise to the higher wear resistance of the Ti composite coating than that of the Ti coating due to the higher wear resistance of the Al-Cr-Fe particles than that of the Ti matrix. As a result, an increase in the Al-Cr-Fe particle content to 20 wt% increased the wear resistance of the Ti composite coating. However, the wear resistance of the Ti composite coating decreased with a further increase in the Al-Cr-Fe particle content to 30 wt% due to the significantly increased volume of micropores in the composite coating. It could be concluded that the Ti composite coating with 20 wt% Al-Cr-Fe particles had the highest wear resistance among the cold-sprayed coatings used in this study.

Title:
Complex physical properties of EuMgSi - a complementary study by neutron powder diffraction and Eu-151 Mossbauer spectroscopy
Authors:
Niehaus, O; Ryan, DH; Flacau, R; Lemoine, P; Chernyshov, D; Svitlyk, V; Cuervo-Reyes, E; Slabon, A; Nesper, R; Schellenberg, I; Pottgen, R Author Full Names: Niehaus, O.; Ryan, D. H.; Flacau, R.; Lemoine, P.; Chernyshov, D.; Svitlyk, V.; Cuervo-Reyes, E.; Slabon, A.; Nesper, R.; Schellenberg, I.; Poettgen, R.
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 3 (27):7203-7215; 10.1039/c5tc01017a 2015
Abstract:
X-ray pure samples of EuMgSi were synthesized by reactions of the elements in sealed niobium tubes using a high frequency and subsequently a resistance furnace. The structure was investigated by single crystal X-ray diffraction: TiNiSi-type, Pnma, a = 769.5(2), b = 455.0(1), c = 836.9(2) pm, wR(2) = 0.033 [I > 2 sigma(I)], and 705 F-2 values with 20 variables. Powder synchrotron radiation diffraction experiments did not reveal any structural changes down to 4.3 K. Magnetic susceptibility data and Eu-151 Mossbauer spectra clearly indicate a stable Eu2+ configuration. Two distinct magnetic anomalies around 12 and 14 K can be observed for different samples with dc- and ac-susceptibility, heat capacity and resistivity measurements. Fitting of hyperfine field splitting as a function of temperature (Eu-151 Mossbauer spectroscopy data) with a Brillouin function also leads to a magnetic ordering around 14 K. Electronic structure calculations in coincidence with the resistivity measurement prove narrow (or nearly zero) gap-semiconducting behaviour. The calculated band gap energy of 0.03 eV should be considered with precautions due to the accuracy of this method. An incommensurate magnetic structure with the propagation vector k = [q(x) approximate to 0.37, 0, 0] was determined using neutron diffraction data at 5.5 K. In consensus of dc- and ac-susceptibility and neutron powder diffraction a complex combination of antiferromagnetic and ferromagnetic interactions, most likely by super-exchange, is confirmed. These cause two magnetic ordering temperatures, though only one independent crystallographic Eu site in terms of the crystal structure is present in EuMgSi.

Update: 23-Jul-2015


Title:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments
Authors:
Liu, SJ; Yang, GY; Luo, SF; Jie, WQ Author Full Names: Liu, S. J.; Yang, G. Y.; Luo, S. F.; Jie, W. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 846-853; 10.1016/j.jallcom.2015.05.062 SEP 25 2015
Abstract:
Microstructure and mechanical properties of sand mold cast Mg-4.58Zn-2.6Gd-0.18Zr magnesium alloy after different heat treatments were investigated. As-cast alloy was composed of alpha(Mg) matrix, interdendritic alpha(Mg) + W(Mg3Zn3Gd2) eutectic, icosahedral quasicrystalline I(Mg3Zn6Gd) phase and Mg3Gd particles within alpha(Mg) matrix. After solution treatment at 505 degrees C for 16 h, most of alpha(Mg) + W(Mg3Zn3Gd2) eutectic dissolved into alpha(Mg) matrix, but a new phase, Zn2Zr3, precipitated within alpha(Mg) matrix. The appropriate aging treatment was done at 220 degrees C for 16 h, after which some dispersive fine eutectics re-precipitated along the grain boundary. Furthermore, rod-like beta(1)' and plate-like beta(2)' formed within alpha(Mg) matrix. The ultimate tensile strength, yield strength and elongation of the experimental alloy in the T6 state at room temperature were 280 MPa, 175 MPa and 7.5%, respectively. According to strengthening contribution calculation, it is revealed that both the second phase strengthening and the solid solution strengthening played important roles in improving the mechanical properties after T6 treatment. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Hot compression characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with icosahedral quasicrystalline phase
Authors:
Kwak, TY; Lim, HK; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Kim, W. J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 644 645-653; 10.1016/j.jallcom.2015.04.158 SEP 25 2015
Abstract:
Hot compressive characteristics and processing maps of a cast Mg-9.5Zn-2.0Y alloy with I-phase (ZW92) were studied in the temperature range between 523 and 723 K and in the strain rate range between 10(-3) and 10 s(-1). According to the analysis of deformation behavior, the rate-controlling mechanism governing deformation during entire compression process was lattice diffusion controlled dislocation climb creep and power-law breakdown. Comparison of the processing maps of ZW92 with those of the cast Mg-Zn-Y alloys with different types of intermetallic compounds (W- and long period stacking ordered phases) and the cast Mg-Al-Zn alloy (AZ80) alloy with beta-Mg17Al12 phase in terms of eta values and the domain sizes of the unstable regime indicated that ZW92 exhibited a better hot workability at high strain rates above 1 s-1. This result was attributed to the suppression of power law breakdown in ZW92 due to occurrence of extensive dynamic recrystallization at high strain rates, which was facilitated by the effective fragmentation and dispersion of I-phase during deformation at high strain rates. A fully recrystallized microstructure composed of defect-free fine grains (9.34 mu m) with high fraction of high angle grain boundaries (0.81) was obtained at 623 K - 10 s(-1). (C) 2015 Elsevier B.V. All rights reserved.

Update: 16-Jul-2015


Title:
Structural crossover from nonmodulated to long-period modulated tetragonal phase and anomalous change in ferroelectric properties in the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3
Authors:
Rao, BN; Khatua, DK; Garg, R; Senyshyn, A; Ranjan, R Author Full Names: Rao, Badari Narayana; Khatua, Dipak Kumar; Garg, Rohini; Senyshyn, Anatoliy; Ranjan, Rajeev
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214116 JUN 29 2015
Abstract:
The highly complex structure-property interrelationship in the lead-free piezoelectric (x) Na1/2Bi1/2TiO3 - (1 - x) BaTiO3 is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticality in this system at x = 0.80, i.e., well within the conventional tetragonal phase field. This criticality manifests as a nonmonotonic variation of the tetragonality and coercivity and is shown to be associated with a crossover from a nonmodulated tetragonal phase (for x < 0.8) to a long-period modulated tetragonal phase (for x > 0.80). It is shown that the stabilization of long-period modulation introduces a characteristic depolarization temperature in the system. While differing qualitatively from the two-phase model often suggested for the critical compositions of this system, our results support the view with regard to the tendency in perovskites to stabilize long-period modulated structures as a result of complex interplay of antiferrodistortive modes [Bellaiche and Iniguez, Phys. Rev. B 88, 014104 ( 2013); Prosandeev, Wang, Ren, Iniguez, ands Bellaiche, Adv. Funct. Mater. 23, 234 (2013)].

Title:
Crystal structure, incommensurate magnetic order, and ferroelectricity in Mn1-xCuxWO4 (0 <= x <= 0.19)
Authors:
Kumar, CMN; Xiao, Y; Lunkenheimer, P; Loidl, A; Ohl, M Author Full Names: Kumar, C. M. N.; Xiao, Y.; Lunkenheimer, P.; Loidl, A.; Ohl, M.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235149 JUN 29 2015
Abstract:
We have carried out a systematic study on the effect of Cu doping on nuclear, magnetic, and dielectric properties in Mn1-xCuxWO4 for 0 <= x <= 0.19 by a synergic use of different techniques, viz, heat capacity, magnetization, dielectric, and neutron powder diffraction measurements. Via heat capacity and magnetization measurements we show that with increasing Cu concentration magnetic frustration decreases, which leads to the stabilization of commensurate magnetic ordering. This was further verified by temperature-dependent unit cell volume changes derived from neutron diffraction measurements which was modeled by the Gruneisen approximation. Dielectric measurements show a low temperature phase transition below about 9-10 K. Furthermore, magnetic refinements reveal no changes below this transition indicating a possible spin-flop transition which is unique to the Cu doped system. From these combined studies we have constructed a magnetoelectric phase diagram of this compound.

Title:
Interplay between magnetic order at Mn and Tm sites alongside the structural distortion in multiferroic films of o-TmMnO3
Authors:
Windsor, YW; Ramakrishnan, M; Rettig, L; Alberca, A; Bothschafter, EM; Staub, U; Shimamoto, K; Hu, Y; Lippert, T; Schneider, CW Author Full Names: Windsor, Y. W.; Ramakrishnan, M.; Rettig, L.; Alberca, A.; Bothschafter, E. M.; Staub, U.; Shimamoto, K.; Hu, Y.; Lippert, T.; Schneider, C. W.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235144 JUN 26 2015
Abstract:
We employ resonant soft x-ray diffraction to individually study the magnetic ordering of the Mn and the Tm sublattices in single-crystalline films of orthorhombic (o-)TmMnO3. The same magnetic ordering wave vector of (0 q 0) with q approximate to 0.46 is found for both ionic species, suggesting that the familiar antiferromagnetic order of the Mn ions induces a magnetic order on the Tm unpaired 4f electrons. Indeed, intensity variations of magnetic reflections with temperature corroborate this scenario. Calculated magnetic fields at the Tm sites are used as a model magnetic structure for the Tm, which correctly predicts intensity variations at the Tm resonance upon azimuthal rotation of the sample. The model allows ruling out a bc-cycloid modulation of the Mn ions as the cause for the incommensurate ordering, as found in TbMnO3. The structural distortion, which occurs in the ferroelectric phase below T-C, was followed through nonresonant diffraction of structural reflections forbidden by the high-temperature crystal symmetry. The (0 q 0) magnetic reflection appears at the Mn resonance well above T-C, indicating that this reflection is sensitive also to the intermediate sinusoidal magnetic phase. The model presented suggests that the Tm 4f electrons are polarized well above the ferroelectric transition and are possibly not affected by the transition at T-C. The successful description of the induced order observed at the Tm resonance is a promising example for future element-selective studies in which "spectator" ions may allow access to previously unobtainable information about other constituent ions.

Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, CB; Abakumov, AM Author Full Names: Pinheiro, Carlos Basilio; Abakumov, Artem M.
Source:
IUCRJ, 2 137-154; 10.1107/S2052252514023550 1 JAN 2015
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.

Title:
A CENTURY OF X-RAY CRYSTALLOGRAPHY AND 2014 INTERNATIONAL YEAR OF X-RAY CRYSTALLOGRAPHY
Authors:
Kojic-Prodic, B Author Full Names: Kojic-Prodic, Biserka
Source:
MACEDONIAN JOURNAL OF CHEMISTRY AND CHEMICAL ENGINEERING, 34 (1):19-32; 2015
Abstract:
The 100(th) anniversary of the Nobel prize awarded to Max von Laue in 1914 for his discovery of diffraction of X-rays on a crystal marked the beginning of a new branch of science - X-ray crystallography. The experimental evidence of von Laue's discovery was provided by physicists W. Friedrich and P. Knipping in 1912. In the same year, W. L. Bragg described the analogy between X-rays and visible light and formulated the Bragg's law, a fundamental relation that connected the wave nature of X-rays and fine structure of a crystal at atomic level. In 1913 the first simple diffractometer was constructed and structure determination started by the Braggs, father and son. In 1915 their discoveries were acknowledged by a Nobel Prize in physics. Since then, X-ray diffraction has been the basic method for determination of three-dimensional structures of synthetic and natural compounds. The three-dimensional structure of a substances defines its physical, chemical, and biological properties. Over the past century the significance of X-ray crystallography has been recognized by about forty Nobel prizes. X-ray structure analysis of simple crystals of rock salt, diamond and graphite, and later of complex biomolecules such as B12-vitamin, penicillin, haemoglobin/myoglobin, DNA, and biomolecular complexes such as viruses, chromatin, ribozyme, and other molecular machines have illustrated the development of the method. Among these big discoveries the double helix DNA structure was an epochal achievement of the 20(th) century. These discoveries, together with many others of the X-ray crystallography, have completely changed our views and helped to develop other new fields of science such as molecular genetics, biophysics, structural molecular biology, material science, and many others. During the last decade, the implementation of free electron X-ray lasers, a new experimental tool, has opened up femtosecond dynamic crystallography. This highly advanced methodology enables to solve the structures and dynamics of the most complex biological assemblies involved in a cell metabolism. The advancements of science and technology over the 20th and 21(st) centuries are of great influence on our views in almost all human activities. The importance of Xray crystallography for science and technology advocates for its high impact on a wide area of research and declares it as a highly interdisciplinary science. In short, crystallography has defined the shape of the modern world. Focusing on single crystal diffraction, this essay tackles only one field of crystallography; the comprehensive review on X-ray crystallography can hardly be fitted into a single article. The aim with this review was to highlight the most striking examples illustrating some of the milestones over the past century.

Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R Author Full Names: Withers, Ray
Source:
IUCRJ, 2 74-84; 10.1107/S2052252514022556 1 JAN 2015
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered 'disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.

Update: 9-Jul-2015


Title:
Microwave sol-gel synthesis and upconversion photoluminescence properties of CaGd2(WO4)(4):Er3+/Yb3+ phosphors with incommensurately modulated structure
Authors:
Lim, CS; Aleksandrovsky, A; Molokeev, M; Oreshonkov, A; Atuchin, V Author Full Names: Lim, Chang Sung; Aleksandrovsky, Aleksandr; Molokeev, Maxim; Oreshonkov, Aleksandr; Atuchin, Victor
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 228 160-166; 10.1016/j.jssc.2015.04.032 AUG 2015
Abstract:
CaGd2-x(WO4)(4):Er3+/Yb3+ phosphors with the doping concentrations of Er3+ and Yb3+ (x=Er3++Yb3+, Er3+=0.05, 0.1, 0.2 and Yb3+=0.2, 0.45) have been successfully synthesized by the microwave sol-gel method. The crystal structure of CaGd2-x(WO4)(4):Er3+/Yb3+ tungstates have been refined, and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after the heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. Under the excitation at 980 nm, CaGd2(WO4)(4):Er3+/Yb3+ particles exhibited a strong 525-nm and a weak 550-nm emission bands in the green region and a very weak 655-nm emission band in the red region. The Raman spectrum of undoped CaGd2(WO4)(4) revealed about 12 narrow lines. The strongest band observed at 903 cm(-1) was assigned to the v(1) symmetric stretching vibration of WO4 tetrahedrons. The spectra of the samples doped with Er and Yb obtained under the 514.5 nm excitation were dominated by Er3+ luminescence preventing the recording of these samples Raman spectra. Concentration quenching of the erbium luminescence at H-2(11/2)-> I-4(15/2) transition is weak in the range of erbium doping level x(Er)=0.05-0.2, while, for transition S-4(3/2)-> 4I(15/2), the signs of concentration quenching become pronounced at x(Er)=0.2. (C) 2015 Elsevier Inc. All rights reserved.

Title:
Direct evidence for stress-induced transformation between coexisting multiple martensites in a Ni-Mn-Ga multifunctional alloy
Authors:
Huang, L; Cong, DY; Wang, ZL; Nie, ZH; Dong, YH; Zhang, Y; Ren, Y; Wang, YD Author Full Names: Huang, L.; Cong, D. Y.; Wang, Z. L.; Nie, Z. H.; Dong, Y. H.; Zhang, Y.; Ren, Y.; Wang, Y. D.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 48 (26):10.1088/0022-3727/48/26/265304 JUL 8 2015
Abstract:
The structural response of coexisting multiple martensites to stress field in a Ni-Mn-Ga multifunctional alloy was investigated by the in situ high-energy x-ray diffraction technique. Stress-induced transformation between coexisting multiple martensites was observed at 110 K, at which five-layered modulated (5M), seven-layered modulated (7M) and non-modulated (NM) martensites coexist. We found that a tiny stress of as low as 0.5 MPa could trigger the transformation from 5M and 7M martensites to NM martensite and this transformation is partly reversible. Besides the transformation between coexisting multiple martensites, rearrangement of martensite variants also occurs during loading, at least at high stress levels. The present study is instructive for designing advanced multifunctional alloys with easy actuation.

Title:
Quasicrystal dissolution and performance of isothermally heat-treated Mg-Zn-Y alloy
Authors:
Wan, DQ; Luo, X; Liu, YJ; Yu, T Author Full Names: Wan, Di-Qing; Luo, Xian; Liu, Ya-Juan; Yu, Tian
Source:
RARE METALS, 34 (7):452-456; 10.1007/s12598-013-0119-9 JUL 2015
Abstract:
Conventional casting method was employed to prepare Mg-Zn-Y alloy only with alpha-Mg+I-phase; however, the grain size of quasicrystal is quite large in the as-cast state. Therefore, isothermal treatment was applied to refine the quasicrystal phase. The result shows that after the Mg-Zn-Y alloy was isothermally treated at 500 degrees C for several hours, the coarse quasicrystal can be gradually dissolved and thus refined. Generally, the dissolving processes of quasicrystal are slow first and then accelerate; after isothermally treated with 8 h at 500 degrees C, the quasicrystal is almost completely dissolved into the matrix only with 1-5 mu m tiny quasicrystals remained. Refinement of quasicrystal can markedly reduce the wear resistance, but increase the corrosion resistance.

Title:
How important is the {103} plane of stable Ge2Sb2Te5 for phase-change memory?
Authors:
Zhang, W; Zheng, WT; Kim, JG; Cui, XQ; Li, L; Qi, JG; Kim, YJ; Song, SA Author Full Names: Zhang, W.; Zheng, W. T.; Kim, J. -G.; Cui, X. Q.; Li, L.; Qi, J. G.; Kim, Y. -J.; Song, S. A.
Source:
JOURNAL OF MICROSCOPY, 259 (1):10-15; 10.1111/jmi.12242 JUL 2015
Abstract:
Closely correlating with {200} plane of cubic phase, {103} plane of hexagonal phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. The behaviors of {103} plane of hexagonal phase render the phase-change memory process as a nanoscale shape memory. Lay description Exploring the phase-change mechanism, structures and properties of chalcogenides has been currently one of the hot topics. Ge-Sb-Te chalcogenides are of tremendous technological importance ranging from optical data storage to PRAM. Exhibiting the best performance for DVD-RAM in terms of speed and stability, Ge2Sb2Te5 is currently the most important phase-change alloy. There exist three solid phases in Ge2Sb2Te5: amorphous, metastable rocksalt (FCC) and stable hexagonal (Hex) phases. The whole switching operation in optical data storage and electronic memories is based on the following rapid cycling processes by either laser or electric heating: amorphousFCC (Erase/SET process)Hexliquidamorphous (Write/RESET process). The stable Hex is an indispensable concern to bridge the aforementioned whole cycling framework. In this work, structural correlations between the two crystalline phases were analyzed and the rich structural phenomena were unraveled. Closely correlated with {200} plane of FCC phase, {103} plane of Hex phase of Ge2Sb2Te5 plays a crucial role in achieving fast phase change process as well as formation of modulation structures, dislocations and twins in Ge2Sb2Te5. We propose that from a point view of maintaining the ultra-high transition speed, (103) of Hex phase can effectively facilitate phase-change memory. This leads to a novel concept that phase-change process can be treated as a nanoscale shape-memory, towards essential understanding of the relevant structural features of Ge-Sb-Te chalcogenides.

Title:
Antiferromagnetic Dichroism in a Complex Multisublattice Magnetoelectric CuB2O4
Authors:
Boldyrev, KN; Pisarev, RV; Bezmaternykh, LN; Popova, MN Author Full Names: Boldyrev, K. N.; Pisarev, R. V.; Bezmaternykh, L. N.; Popova, M. N.
Source:
PHYSICAL REVIEW LETTERS, 114 (24):10.1103/PhysRevLett.114.247210 JUN 19 2015
Abstract:
Magnetic control of the crystal chirality was announced by Saito et al. [Phys. Rev. Lett. 101, 117402 (2008)] on the ground of experiments in CuB2O4. This claim has raised a sharp dispute in the literature because it seemed to contradict the fundamental symmetry principles. We settle this dispute on the basis of a high-resolution optical spectroscopy study of excitonic transitions in CuB2O4. We find that a large sublattice-sensitive antiferromagnetic linear dichroism (LD) emerges at the Neel temperature T-N = 21 K and show how it could simulate a "magnetic-field control of the crystal chirality." We prove that the discovered LD is related microscopically to the magnetic Davydov splitting. This LD is highly sensitive to subtle changes in the spin subsystems, which allowed us to observe a splitting of the phase transition into an incommensurate magnetic phase into two transitions (T-1* = 8.5 and T-2* = 7.9 K) and to suggest elliptical spiral structures below T-1*, instead of a simple circular helix proposed earlier.

Title:
Lattice vibrations in the Frenkel-Kontorova model. I. Phonon dispersion, number density, and energy
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224305 JUN 17 2015
Abstract:
We studied the lattice vibrations of two interpenetrating atomic sublattices via the Frenkel-Kontorova (FK) model of a linear chain of harmonically interacting atoms subjected to an on-site potential using the technique of thermodynamic Green's functions based on quantum field-theoretical methods. General expressions were deduced for the phonon frequency-wave-vector dispersion relations, number density, and energy of the FK model system. As the application of the theory, we investigated in detail cases of linear chains with various periods of the on-site potential of the FK model. Some unusual but interesting features for different amplitudes of the on-site potential of the FK model are discussed. In the commensurate structure, the phonon spectrum always starts at a finite frequency, and the gaps of the spectrum are true ones with a zero density of modes. In the incommensurate structure, the phonon spectrum starts from zero frequency, but at a nonzero wave vector; there are some modes inside these gap regions, but their density is very low. In our approximation, the energy of a higher-order commensurate state of the one-dimensional system at a finite temperature may become indefinitely close to the energy of an incommensurate state. This finding implies that the higher-order incommensurate-commensurate transitions are continuous ones and that the phase transition may exhibit a "devil's staircase" behavior at a finite temperature.

Title:
Lattice vibrations in the Frenkel-Kontorova Model. II. Thermal conductivity
Authors:
Meng, QP; Wu, LJ; Welch, DO; Zhu, YM Author Full Names: Meng, Qingping; Wu, Lijun; Welch, David O.; Zhu, Yimei
Source:
PHYSICAL REVIEW B, 91 (22):10.1103/PhysRevB.91.224306 JUN 17 2015
Abstract:
We applied the formulas for the phonon spectral-density function that we presented in the previous paper of this series to analyze the thermal conductivity of the lattice in the framework of the Frenkel-Kontorova (FK) model. We found that two extra mechanisms of phonon scattering (different from the point impurities, three-phonon processes, and boundary scattering typical of all crystals), viz., resonance, and anharmonic scattering, that mainly influences the thermal conductivity of the lattice. The frequencies of resonance scattering are discrete, and their number increases from a finite number to infinity with their transition from the commensurate to the incommensurate state. Changing the amplitude and period of the FK model changes the frequencies and the frequency number of resonance scattering and the intensity of anharmonic scattering. We analyze these changes in detail. Our theory can explain all existing numerical results on this problem and suggest strategies to reduce the thermal conductivity of the lattice of layered materials.

Title:
Characterization of deep level defects and thermally stimulated depolarization phenomena in La-doped TlInS2 layered semiconductor
Authors:
Seyidov, MY; Suleymanov, RA; Mikailzade, FA; Kargin, EO; Odrinsky, AP Author Full Names: Seyidov, MirHasan Yu.; Suleymanov, Rauf A.; Mikailzade, Faik A.; Kargin, Elif Orhan; Odrinsky, Andrei P.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (22):10.1063/1.4922347 JUN 14 2015
Abstract:
Lanthanum-doped high quality TlInS2 (TlInS2: La) ferroelectric-semiconductor was characterized by photo-induced current transient spectroscopy (PICTS). Different impurity centers are resolved and identified. Analyses of the experimental data were performed in order to determine the characteristic parameters of the extrinsic and intrinsic defects. The energies and capturing cross section of deep traps were obtained by using the heating rate method. The observed changes in the Thermally Stimulated Depolarization Currents (TSDC) near the phase transition points in TlInS2: La ferroelectric-semiconductor are interpreted as a result of self-polarization of the crystal due to the internal electric field caused by charged defects. The TSDC spectra show the depolarization peaks, which are attributed to defects of dipolar origin. These peaks provide important information on the defect structure and localized energy states in TlInS2: La. Thermal treatments of TlInS2: La under an external electric field, which was applied at different temperatures, allowed us to identify a peak in TSDC which was originated from La-dopant. It was established that deep energy level trap BTE43, which are active at low temperature (T <= 156 K) and have activation energy 0.29 eV and the capture cross section 2.2 x 10(-14) cm(2), corresponds to the La dopant. According to the PICTS results, the deep level trap center B5 is activated in the temperature region of incommensurate (IC) phases of TlInS2: La, having the giant static dielectric constant due to the structural disorders. From the PICTS simulation results for B5, native deep level trap having an activation energy of 0.3 eV and the capture cross section of 1.8 x 10(-16) cm(2) were established. A substantial amount of residual space charges is trapped by the deep level localized energy states of B5 in IC-phase. While the external electric field is applied, permanent dipoles, which are originated from the charged B5 deep level defects, are aligned in the direction of the applied electric field and the equilibrium polarization can be reached in a relatively short time. When the polarization field is maintained, while cooling the temperature of sample to a sufficiently low degrees, the relaxation times of the aligned dipoles drastically increases. Practically, frozen internal electric field or electrets states remain inside the TlInS2: La when the applied bias field is switched off. The influence of deep level defects on TSDC spectra of TlInS2: La has been revealed for the first time. (C) 2015 AIP Publishing LLC.

Title:
Coexistence of the spin and electron-hole quantum liquids in frustrated manganites La1-y Sm (y) MnO3+delta
Authors:
Bukhanko, FN; Bukhanko, AF Author Full Names: Bukhanko, F. N.; Bukhanko, A. F.
Source:
PHYSICS OF THE SOLID STATE, 57 (6):1114-1127; 10.1134/S1063783415060062 JUN 2015
Abstract:
The structural, electronic, and magnetic phase transformations induced in the temperature range of 4.2-300 K by the isovalent substitution of the rare-earth Sm3+ ion for the La3+ ion with a larger radius have been investigated in the system of self-doped manganites La1-y Sm (y) MnO3+delta (delta similar to 0.1, 0 a parts per thousand currency sign y a parts per thousand currency sign 1). It has been found using the X-ray diffraction analysis that the substitution La -> Sm is accompanied by a significant increase of the GdFeO3-type and Jahn-Teller-type lattice distortions. At a temperature of 300 K, an increase in the Sm concentration y leads to a concentration phase transition from the pseudocubic O* phase to the orthorhombic O phase, as well as to the appearance of an s-shaped anomaly of the lattice parameter a at concentrations y a parts per thousand yen 0.4 and an anomalous peak in the concentration dependence of the electrical resistance R(y) near y a parts per thousand 0.85. The magnetic T-y-aOE (c) r (A) phase diagrams of the La1-y Sm (y) MnO3+delta system in the temperature range of 4.2-250 K have been constructed according to the results of measurements of the temperature dependences of the direct-current (dc) magnetization M(T). It has been revealed that the samples with y a parts per thousand yen 0.8 exhibit signs of the melting of the A- and CE-type modulated antiferromagnetic (AFM) structures in the form of an anomalous decrease both in the critical temperature of the transition to a frustrated AFM state and in the magnetization of the samples with an increase in the concentration y. The anomalies observed in the temperature dependences of the alternating-current (ac) dielectric permittivity of the La1-y Sm (y) MnO3+delta samples have been explained within the existing concepts of the Bose-Einstein condensation of an electron-hole liquid in the form of metallic droplets in an excitonic insulator.

Update: 2-Jul-2015


Title:
Ni- and Cu-free Ti-based metallic glasses with potential biomedical application
Authors:
Guo, Y; Bataev, I; Georgarakis, K; Jorge, AM; Nogueira, RP; Pons, M; Yavari, AR Author Full Names: Guo, Y.; Bataev, I.; Georgarakis, K.; Jorge, A. M., Jr.; Nogueira, R. P.; Pons, M.; Yavari, A. R.
Source:
INTERMETALLICS, 63 86-96; 10.1016/j.intermet.2015.04.004 AUG 2015
Abstract:
In the present work Ti-Fe-Si and Ti-Fe-Si-X (X = Zr, Pd, Ge) glassy alloys are discussed as potential biomedical materials. Depending on composition and experimental conditions these alloys possess glassy, quasicrystalline or crystalline structure. The glassy state and crystallization behavior of the melt spun ribbons were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Hank's solution was used as simulated body fluid for corrosion tests. Ternary Ti-Fe-Si alloys near the Ti65Fe30Si5 eutectic point were prone to form quasicrystals if the cooling rate was not high enough to retain amorphous structure. The compositions on the steeper side of the eutectic point could be vitrified. The results indicate that small additions of Zr can have a positive effect on glass formation, while additions of Ge, Pd may have a detrimental effect by promoting crystallization. Ti Fe Si and Ti Fe Si Zr alloys exhibited high corrosion properties, superior to that of pure Ti and most of Ti-based glassy alloys reported in the literature. Being free of Ni and Cu this group of alloys may be considered for possible biomedical application. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Amorphous-i phase-big cube-amorphous cyclic phase transformation of mechanically alloyed Zr75Ni20Al5 system
Authors:
El-Eskandarany, MS Author Full Names: El-Eskandarany, M. Sherif
Source:
INTERMETALLICS, 63 27-36; 10.1016/j.intermet.2015.01.010 AUG 2015
Abstract:
Cyclic glassy-metastable-glassy phase transformations were investigated during mechanical alloying of Zr75Ni20Al5 powders, using high-energy ball milling technique. After 20 h of continuous milling, a single glassy phase was obtained. The synthesized glassy powder, which is homogeneous in structure and composition, showed a glass transition temperature lied at 510 degrees C and a large supercooled liquid region extended to 86.5 degrees C. This glassy phase, which crystallized through a single sharp exothermic peak at 596.5 degrees C, tended to transformed into icosahedral (i-phase) nano-quasicrystalline grains upon further milling to 30 h. This i-phase showed serious instability against the mechanical deformations generated by the milling tools, and hence transformed into big cube phase with increasing the milling time to 45 h. In a cyclic phase transformation the obtained big cube phase subsequently transformed into the same glassy phase after 60 h of milling. This observed cyclic phase transformation was observed twice upon further milling to 90 h without serious compositional changes. The iron contamination contents in the ball-milled powders had constant values of about 0.16 wt.% and did not change with changing the structure of the powders. The present work shows that this phenomenon does not have any obvious analogues with the periodic redox reactions or with diffusive-reactive phenomena known in chemistry. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the milling time. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09816 JUN 12 2015
Abstract:
Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn6Mg3Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn6Mg3Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn3MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn3MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn: Mg: Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn3MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials.

Title:
Bulk electronic structure of Zn-Mg-Y and Zn-Mg-Dy icosahedral quasicrystals
Authors:
Nayak, J; Maniraj, M; Gloskovskii, A; Krajci, M; Sebastian, S; Fisher, IR; Horn, K; Barman, SR Author Full Names: Nayak, J.; Maniraj, M.; Gloskovskii, A.; Krajci, M.; Sebastian, S.; Fisher, I. R.; Horn, K.; Barman, S. R.
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235116 JUN 11 2015
Abstract:
We use bulk sensitive hard x-ray photoelectron spectroscopy to provide unambiguous evidence for a pseudogap in the density of states around the Fermi level in icosahedral Zn-Mg-Y and Zn-Mg-Dy quasicrystals, in agreement with our density functional theory calculations. The pseudogap in these Zn-based quasicrystals is less pronounced compared to the Al-based ones such as Al-Pd-Mn and Al-Cu-Fe [J. Nayak et al., Phys. Rev. Lett. 109, 216403 ( 2012)]. This observation is in agreement with transport studies that indicate a larger charge carrier concentration in the Zn-based quasicrystals. Compared to Zn-Mg-Dy, the pseudogap is somewhat deeper in Zn-Mg-Y. The larger width of the Mg 1s and Zn 2p core-level spectra in Zn-Mg-Y is explained by different configurations of the local atomic surrounding compared to Zn-Mg-Dy.

Title:
Synthesis, structures and magnetic properties of the dimorphic Mn2CrSbO6 oxide
Authors:
Dos Santos-Garcia, AJ; Solana-Madruga, E; Ritter, C; Avila-Brande, D; Fabelo, O; Saez-Puche, R Author Full Names: Dos Santos-Garcia, Antonio J.; Solana-Madruga, Elena; Ritter, Clemens; Avila-Brande, David; Fabelo, Oscar; Saez-Puche, Regino
Source:
DALTON TRANSACTIONS, 44 (23):10665-10672; 10.1039/c4dt03849e 2015
Abstract:
The perovskite polymorph of Mn2CrSbO6 compound has been synthesized at 8 GPa and 1473 K. It crystallizes in the monoclinic P2(1)/n space group with cell parameters a = 5.2180 (2) angstrom, b = 5.3710(2) angstrom, c = 7.5874(1) angstrom and alpha = 90.36(1)degrees. Magnetic susceptibility and magnetization measurements show the simultaneous antiferromagnetic ordering of Mn2+ and Cr3+ sublattices below T-N = 55 K with a small canting. Low temperature powder neutron diffraction reveals a commensurate magnetic structure with spins confined to the ac-plane and a propagation vector kappa = [1/2 0 1/2]. The thermal treatment of this compound induces an irreversible phase transition to the ilmenite polymorph, which has been isolated at 973 K and crystallizes in R (3) over bar space group with cell parameters a = 5.2084 (4) angstrom and c = 14.4000 (11) angstrom. Magnetic susceptibility, magnetization and powder neutron diffraction data confirm the antiferromagnetic helical ordering of spins in an incommensurate magnetic structure with kappa = [00 0.46] below 60 K, and the temperature dependence of the propagation vector up to kappa = [00 0.54] at about 10 K.

Title:
Ordering effects in the crystal structure and electrochemical properties of the Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite
Authors:
Munoz-Gil, D; Avila-Brande, D; Urones-Garrote, E; Garcia-Martin, S Author Full Names: Munoz-Gil, Daniel; Avila-Brande, David; Urones-Garrote, Esteban; Garcia-Martin, Susana
Source:
DALTON TRANSACTIONS, 44 (23):10867-10874; 10.1039/c4dt03873h 2015
Abstract:
Layered-type ordering and oxygen vacancies ordering are revealed in GdBaMnFeO6-delta perovskite. Selected area electron diffraction and high-resolution transmission electron microscopy results indicate a modulation of the crystal structure. Ba and Gd ordering in (001)(p) layers is confirmed by high angle annular dark field scanning transmission electron microscopy and electron energy-loss spectroscopy. These techniques also revealed formation of layer-stacking defects in the crystals. Direct imaging of the oxygen sublattice is obtained by phase image reconstruction. Location of the oxygen vacancies in the (GdO)(x) layers is achieved by analysis of the intensity of the averaged phase image. Physical properties of the GdBaMnFeO6-delta perovskite, are likely to be strongly affected by its ordering effects and crystal microstructure. In this sense, layered-type GdBaMnFeO6-delta perovskite show better electrochemical properties as cathodes in SOFCs than ion disordered Gd0.5Ba0.5Mn0.5Fe0.5O3-delta perovskite.

Update: 25-Jun-2015


Title:
Symplectic approach for the plane elasticity problem of quasicrystals with point group 10 mm
Authors:
Wang, H; Li, LH; Huang, JJ; Chen, A Author Full Names: Wang, Hua; Li, Lianhe; Huang, Junjie; Chen, Alatancang
Source:
APPLIED MATHEMATICAL MODELLING, 39 (12):3306-3316; 10.1016/j.apm.2014.10.060 JUN 15 2015
Abstract:
The symplectic approach is introduced into the plane elasticity problem of quasicrystals with point group 10 mm. The basic equations of the problem are equivalently written as the Hamiltonian dual equations. It is shown that the generalized eigenvector system of the corresponding Hamiltonian operator matrix is complete in the Cauchy Principal Value (CPV) sense. The analytical solution and related numerical results of the problem are then given. (C) 2014 Elsevier Inc. All rights reserved.

Title:
Magnetic structure and multiferroic coupling in pyroxene NaFeSi2O6
Authors:
Baum, M; Komarek, AC; Holbein, S; Fernandez-Diaz, MT; Andre, G; Hiess, A; Sidis, Y; Steffens, P; Becker, P; Bohaty, L; Braden, M Author Full Names: Baum, M.; Komarek, A. C.; Holbein, S.; Fernandez-Diaz, M. T.; Andre, G.; Hiess, A.; Sidis, Y.; Steffens, P.; Becker, P.; Bohaty, L.; Braden, M.
Source:
PHYSICAL REVIEW B, 91 (21):10.1103/PhysRevB.91.214415 JUN 9 2015
Abstract:
By comprehensive neutron diffraction measurements we have studied the magnetic structure of aegirine (NaFeSi2O6) in and above its multiferroic phase. Natural aegirine exhibits two magnetic transitions into incommensurate magnetic order with a propagation vector of (k) over right arrow (inc) = (0, similar to 0.78,0). Between 9 and 6 K, we find a transverse spin-density wave with moments pointing near the c direction. Below 6 K, magnetic order becomes helical and spins rotate in the ac plane. The same irreducible representation is involved in the two successive transitions. In addition, the ferroelectric polarization (P) over right arrow appearing along the b direction cannot be described by the most common multiferroic mechanism but follows (P) over right arrow proportional to ($) over right arrow (i) x (S) over right arrow (j). Synthetic NaFeSi2O6 does not exhibit the pure incommensurate helical order but shows coexistence of this order with a commensurate magnetic structure. By applying moderate pressure to natural aegirine, we find that the incommensurate magnetic ordering partially transforms to the commensurate one, underlining the nearly degenerate character of the two types of order in NaFeSi2O6.

Title:
Matrix product state approach to a frustrated spin chain with long-range interactions
Authors:
Li, ZH; Wang, AM Author Full Names: Li, Zhi-Hua; Wang, An-Min
Source:
PHYSICAL REVIEW B, 91 (23):10.1103/PhysRevB.91.235110 JUN 8 2015
Abstract:
We make extensive simulations over a spin chain model that combines the frustrated J(1) - J(2) spin chain and the long-range nonfrustrated (-1)((r-1))r(-alpha) decay interactions through the variational matrix product state method for both finite and infinite lengths. We study both the ground-state entanglement and phase diagram. We find that it is most entangled in the rotation invariant long-range ordered antiferromagnetic phase, where the entanglement scales approximately logarithmically. We determine the development of the Majudar-Ghosh point to a disorder line from entanglement. And we approximately determine the transition from the dimerized and incommensurate phase of the J(1) - J(2) model to a decoupled phase by studying spin correlation and the dimerization order parameter. Some implications for entanglement in systems with long-range interactions are stated.

Title:
Influence of Ti doping on the incommensurate charge density wave in 1T-TaS2
Authors:
Chen, XM; Miller, AJ; Nugroho, C; de la Pena, GA; Joe, YI; Kogar, A; Brock, JD; Geck, J; MacDougall, GJ; Cooper, SL; Fradkin, E; Van Harlingen, DJ; Abbamonte, P Author Full Names: Chen, X. M.; Miller, A. J.; Nugroho, C.; de la Pena, G. A.; Joe, Y. I.; Kogar, A.; Brock, J. D.; Geck, J.; MacDougall, G. J.; Cooper, S. L.; Fradkin, E.; Van Harlingen, D. J.; Abbamonte, P.
Source:
PHYSICAL REVIEW B, 91 (24):10.1103/PhysRevB.91.245113 JUN 8 2015
Abstract:
We report temperature-dependent transport and x-ray diffraction measurements of the influence of Ti hole doping on the charge density wave (CDW) in 1T-Ta1-xTixS2. Confirming past studies, we find that even trace impurities eliminate the low-temperature commensurate (C) phase in this system. Surprisingly, the magnitude of the in-plane component of the CDW wave vector in the nearly commensurate (NC) phase does not change significantly with Ti concentration, as might be expected from a changing Fermi surface volume. Instead, the angle of the CDWin the basal plane rotates, from 11.9 degrees at x = 0 to 16.4 degrees at x = 0.12. Ti substitution also leads to an extended region of coexistence between incommensurate (IC) and NC phases, indicating heterogeneous nucleation near the transition. Finally, we explain a resistive anomaly originally observed by Di Salvo [F. J. Di Salvo et al., Phys. Rev. B 12, 2220 (1975)] as arising from pinning of the CDW on the crystal lattice. Our study highlights the importance of commensuration effects in the NC phase, particularly at x similar to 0.08.

Title:
Dispersionless Spin Waves and Underlying Field-Induced Magnetic Order in Gadolinium Gallium Garnet
Authors:
d'Ambrumenil, N; Petrenko, OA; Mutka, H; Deen, PP Author Full Names: d'Ambrumenil, N.; Petrenko, O. A.; Mutka, H.; Deen, P. P.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227203 JUN 2 2015
Abstract:
We report the results of neutron diffraction and inelastic neutron scattering on a powder sample of Gd3Ga5O12 at high magnetic fields. Analysis of the diffraction data shows that in high fields (B greater than or similar to 1.8 T) the spins are not fully aligned, but are canted slightly as a result of the dipolar interaction. The magnetic phase for fields less than or similar to 1.8 T is characterized by antiferromagnetic peaks at (210) and an incommensurate wave vector. The dominant contribution to inelastic scattering at large momentum transfers is from a band of almost dispersionless excitations. We show that these correspond to the spin waves localized on ten site rings, expected on the basis of nearest neighbor exchange interaction, and that the spectrum at high fields B greater than or similar to 1.8 T is well described by a spin wave theory.

Title:
Aperiodic crystals and beyond
Authors:
Grimm, U Author Full Names: Grimm, Uwe
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 258-274; 10.1107/S2052520615008409 3 JUN 2015
Abstract:
Crystals are paradigms of ordered structures. While order was once seen as synonymous with lattice periodic arrangements, the discoveries of incommensurate crystals and quasicrystals led to a more general perception of crystalline order, encompassing both periodic and aperiodic crystals. The current definition of crystals rests on their essentially point-like diffraction. Considering a number of recently investigated toy systems, with particular emphasis on non-crystalline ordered structures, the limits of the current definition are explored.

Title:
Structures beyond superspace
Authors:
Senechal, M Author Full Names: Senechal, Marjorie
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 250-251; 10.1107/S2052520615009907 3 JUN 2015

Title:
The modulated average structure of mullite
Authors:
Birkenstock, J; Petricek, V; Pedersen, B; Schneider, H; Fischer, RX Author Full Names: Birkenstock, Johannes; Petricek, Vaclav; Pedersen, Bjoern; Schneider, Hartmut; Fischer, Reinhard X.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 358-368; 10.1107/S205252061500757X 3 JUN 2015
Abstract:
Homogeneous and inclusion-free single crystals of 2: 1 mullite (Al4.8Si1.2O9.6) grown by the Czochralski technique were examined by X-ray and neutron diffraction methods. The observed diffuse scattering together with the pattern of satellite reflections confirm previously published data and are thus inherent features of the mullite structure. The ideal composition was closely met as confirmed by microprobe analysis (Al-4.82 (3) Si-1.18 (1) O-9.59 (5)) and by average structure refinements. 8 (5) to 20 (13)% of the available Si was found in the T* position of the tetrahedra triclusters. The strong tendencey for disorder in mullite may be understood from considerations of hypothetical superstructures which would have to be n-fivefold with respect to the three-dimensional average unit cell of 2: 1 mullite and n-fourfold in case of 3: 2 mullite. In any of these the possible arrangements of the vacancies and of the tetrahedral units would inevitably be unfavorable. Three directions of incommensurate modulations were determined: q(1) = [0.3137 (2) 0 1/2], q(2) = [0 0.4021 (5) 0.1834 (2)] and q(3) = [0 0.4009 (5) -0.1834 (2)]. The one-dimensional incommensurately modulated crystal structure associated with q1 was refined for the first time using the superspace approach. The modulation is dominated by harmonic occupational modulations of the atoms in the di- and the triclusters of the tetrahedral units in mullite. The modulation amplitudes are small and the harmonic character implies that the modulated structure still represents an average structure in the overall disordered arrangement of the vacancies and of the tetrahedral structural units. In other words, when projecting the local assemblies at the scale of a few tens of average mullite cells into cells determined by either one of the modulation vectors q(1), q(2) or q(3) a weak average modulation results with slightly varying average occupation factors for the tetrahedral units. As a result, the real structure of mullite is locally ordered (as previously known), but on the long-range its average is not completely disordered, the modulated structure of mullite may be denoted the true 'average structure of mullite'.

Title:
Neutron Laue and X-ray diffraction study of a new crystallographic superspace phase in n-nonadecane-urea
Authors:
Zerdane, S; Mariette, C; McIntyre, GJ; Lemee-Cailleau, MH; Rabiller, P; Guerin, L; Ameline, JC; Toudic, B Author Full Names: Zerdane, S.; Mariette, C.; McIntyre, G. J.; Lemee-Cailleau, M. -H.; Rabiller, P.; Guerin, L.; Ameline, J. C.; Toudic, B.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 293-299; 10.1107/S2052520615005442 3 JUN 2015
Abstract:
Aperiodic composite crystals present long-range order without translational symmetry. These materials may be described as the intersection in three dimensions of a crystal which is periodic in a higher-dimensional space. In such materials, symmetry breaking must be described as structural changes within these crystallographic superspaces. The increase in the number of superspace groups with the increase in the dimension of the superspace allows many more structural solutions. This is illustrated in n-nonadecane-urea, revealing a fifth higher-dimensional phase at low temperature.

Title:
One-Third Magnetization Plateau with a Preceding Novel Phase in Volborthite
Authors:
Ishikawa, H; Yoshida, M; Nawa, K; Jeong, M; Kramer, S; Horvatic, M; Berthier, C; Takigawa, M; Akaki, M; Miyake, A; Tokunaga, M; Kindo, K; Yamaura, J; Okamoto, Y; Hiroi, Z Author Full Names: Ishikawa, H.; Yoshida, M.; Nawa, K.; Jeong, M.; Kraemer, S.; Horvatic, M.; Berthier, C.; Takigawa, M.; Akaki, M.; Miyake, A.; Tokunaga, M.; Kindo, K.; Yamaura, J.; Okamoto, Y.; Hiroi, Z.
Source:
PHYSICAL REVIEW LETTERS, 114 (22):10.1103/PhysRevLett.114.227202 JUN 1 2015
Abstract:
We have synthesized high-quality single crystals of volborthite, a seemingly distorted kagome antiferromagnet, and carried out high-field magnetization measurements up to 74 T and V-51 NMR measurements up to 30 T. An extremely wide 1/3 magnetization plateau appears above 28 T and continues over 74 T at 1.4 K, which has not been observed in previous studies using polycrystalline samples. NMR spectra reveal an incommensurate order (most likely a spin-density wave order) below 22 T and a simple spin structure in the plateau phase. Moreover, a novel intermediate phase is found between 23 and 26 T, where the magnetization varies linearly with magnetic field and the NMR spectra indicate an inhomogeneous distribution of the internal magnetic field. This sequence of phases in volborthite bears a striking similarity to those of frustrated spin chains with a ferromagnetic nearest-neighbor coupling J(1) competing with an antiferromagnetic next-nearest-neighbor coupling J(2)

Title:
Pressure-induced normal-incommensurate and incommensurate-commensurate phase transitions in CrOCl
Authors:
Bykov, M; Bykova, E; Dubrovinsky, L; Hanfland, M; Liermann, HP; van Smaalen, S Author Full Names: Bykov, Maxim; Bykova, Elena; Dubrovinsky, Leonid; Hanfland, Michael; Liermann, Hanns-Peter; van Smaalen, Sander
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09647 MAY 21 2015
Abstract:
The high-pressure behavior of layered CrOCl is shown to be governed by non-bonded interactions between chlorine atoms in relation to a rigid framework composed of Cr and O atoms. The competition between optimizing intra-and interlayer Cl-Cl distances and the general trend towards denser packing defines a novel mechanism for high-pressure phase transitions of inorganic materials. CrOCl possesses an incommensurate phase for 16-51 GPa. Single-crystal x-ray diffraction in a diamond anvil cell provides an accurate description of the evolution of the incommensurate wave with pressure. It thus demonstrates a continuous increase of the amplitude up to 30 GPa, followed by a decrease of the wavelength until a lock-in transition occurs at 51 GPa.

Title:
Magnetism in rare-earth quasicrystals: RKKY interactions and ordering
Authors:
Thiem, S; Chalker, JT Author Full Names: Thiem, Stefanie; Chalker, J. T.
Source:
EPL, 110 (1):10.1209/0295-5075/110/17002 APR 2015
Abstract:
We study magnetism in simple models for rare-earth quasicrystals, by considering Ising spins on a quasiperiodic tiling, coupled via RKKY interactions. Computing these interactions from a tight-binding model on the tiling, we find that they are frustrated and strongly dependent on the local environment. Although such features are often associated with spin glass behaviour, we show using Monte Carlo simulations that the spin system has a phase transition to a low-temperature state with long-range quasiperiodic magnetic order. Copyright (C) EPLA, 2015

Title:
Synthesis and structure of the new pentanary uranium (VI) silicate, K4CaUSi4O14, a member of a structural family related to fresnoite
Authors:
Morrison, G; Smith, MD; Tran, TT; Halasyamani, PS; Loye, HCZ Author Full Names: Morrison, Gregory; Smith, Mark D.; Tran, T. Thao; Halasyamani, P. Shiv; Loye, Hans-Conrad Zur
Source:
CRYSTENGCOMM, 17 (22):4218-4224; 10.1039/c5ce00504c 2015
Abstract:
Single crystals of K4CaUSi4O14 have been grown from a eutectic CaF2-KF flux. K4CaUSi4O14 crystallizes in a new structure which exhibits a 49-fold superstructure believed to be due to a modulation of the uranium and silicon polyhedra. We report the sub-cell of the structure which adopts the tetragonal space group P (4) over bar n2 with lattice parameters a = 9.2862(2) angstrom c = 8.3796(4) angstrom, and V = 722.60(5)angstrom(3). K4CaUSi4O14 is a member of a structural family related to the mineral fresnoite which we describe here. Finally, we report UV-vis absorbance and SHG measurements on the compound, which is non-centrosymmetric.

Title:
The symmetry of the thermoelastic properties of quasicrystals
Authors:
Sokolova, MY; Khristich, DV Author Full Names: Sokolova, M. Yu.; Khristich, D. V.
Source:
PMM JOURNAL OF APPLIED MATHEMATICS AND MECHANICS, 78 (5):524-528; 10.1016/j.jappmathmech.2015.03.012 2014
Abstract:
The thermoelastic properties of quasicrystals, possessing 5-th, 8-th, 10-th and 12-th order rotational axes, not characteristic of crystalline bodies, are considered. Using group analysis, canonical representations of the second and fourth rank tensors, characterizing the properties of quasicrystals, are constructed. The fact that orthogonal, decagonal and dodecagonal quasicrystals belong to the class of transversely isotropic materials and the isotropy of icosahedric quasicrystals and fullerenes are proved. (C) 2015 Elsevier Ltd. All rights reserved.

Update: 18-Jun-2015


Title:
Magnetostructural transitions in Mn-rich Heusler Mn-Ni-In melt-spun ribbons with enhanced magnetocaloric effect
Authors:
Li, HW; Feng, ST; Ren, J; Zhai, QJ; Fu, JX; Luo, ZP; Zheng, HX Author Full Names: Li, Hongwei; Feng, Shutong; Ren, Jian; Zhai, Qijie; Fu, Jianxun; Luo, Zhiping; Zheng, Hongxing
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 391 17-21; 10.1016/j.jmmm.2015.04.098 OCT 1 2015
Abstract:
The magnetostructural transition behavior and magnetocaloric effect of Mn-rich Heusler Mn-Ni-In melt spun ribbons have been investigated in the present study. Experimental results showed that the martensitic transition temperatures decreased by substituting small amounts of Ni with Mn in Mn49+xNi42-xIn9 (x=0,1,2). Within a temperature range from 100 K to 380 K, the Mn(49)Ni(41)ln(9) underwent a martensitic transformation from a paramagnetic L2(1)-type cubic austenite to a ferromagnetic modulated fourteen layered monoclinic (14M) martensite, followed with a ferromagnetic -> weak-magnetic transition in martensite upon cooling. While for both Mn50Ni41In9 and Mn51Ni40In9, the paramagnetic -> ferromagnetic transition in austenite occurred prior to the martensitic transformation upon cooling. Under a magnetic field change of 30 kOe, the maximum magnetic entropy changes of the Mn50Ni41In9 melt spun ribbons were found to be 5.7 J/kg K and -2.3 J/kg K in the vicinity of martensitic transformation and magnetic transition of austenite, respectively. An enhanced total effective refrigeration capacity as high as 184.2 J/kg was obtained in the Mn50Ni41In9 melt spun ribbons. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Microstructure and phase transformation of forged Mg-3.7Zn-0.3Y-0.3Gd quasicrystal alloy
Authors:
Yang, Y; Zhang, K; Ma, ML; Li, XG Author Full Names: Yang, Yang; Zhang, Kui; Ma, Minglong; Li, Xinggang
Source:
JOURNAL OF MATERIALS RESEARCH, 30 (10):1693-1700; 10.1557/jmr.2015.97 MAY 28 2015
Abstract:
An alloy with the composition of Mg-3.7Zn-0.3Y-0.3Gd (in at.%) which contains quasicrystal phase was studied by multiple means. The as-cast alloy has dendritic structure and consists of -Mg, I-phase, W-phase, and Mg-Zn precipitations. The alloy was forged one pass and annealed at 440 degrees C for 4 h, then followed by two passes of compressions. Eutectics were crushed and partially dissolved after deformation and annealing. The tensile strength increased after each forge pass. Submicron scale particles precipitated all around the grains during the deformations, and the amount of precipitations was proportional to the amount of deformations. These precipitated particles were observed by high resolution transmission electron microscopy (TEM). The existence of rhomboid W'-phase with face center cubic (FCC) structure and globular I-phase was confirmed. A quasi-periodicity lamellar phase combined with I-phase was founded, which was considered to be the transient phase between I-phase and I-phase.

Title:
Effect of substrate and orientation on charge ordering behaviors in epitaxial Pr0.5Ca0.35Sr0.15MnO3 films
Authors:
Yang, HW; Wang, C; Cai, RS; Hu, FX; Wang, YQ; Sun, JR Author Full Names: Yang, H. W.; Wang, C.; Cai, R. S.; Hu, F. X.; Wang, Y. Q.; Sun, J. R.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4913731 MAY 7 2015
Abstract:
The charge ordering (CO) behaviors of Pr0.5Ca0.35Sr0.15MnO3 films grown on STO(100), STO(110) and LAO(100) are systematically investigated by transport measurements and transmission electron microscopy (TEM) examinations. From the transport measurements, the CO transition temperatures of all the three films are much higher than those of the bulk materials, showing that the film strain could enhance the CO transition. From TEM observations, many superlattice spots appear in the electron diffraction patterns taken from the films, indicating the appearance of the CO modulation structures at room temperature. The modulation vectors are determined to be (1/2, 0, 0) for STO (100), (1/2, 1/2, 1/2) for STO (110), and both (0, 1/2, 0) and (1/2, 1/2, 0) for LAO (100). It is shown that both the substrate orientation and the film strain have a great effect on the CO modulation structures. The CO state is much easier to appear in the compressive strain direction which is due to the Mn-O-Mn angle tilting. (C) 2015 AIP Publishing LLC.

Title:
Spin reorientation in multiferroic spinel Co0.5Fe0.5Cr2O4 with Mossbauer spectroscopy
Authors:
Myoung, BR; Kim, CS Author Full Names: Myoung, Bo Ra; Kim, Chul Sung
Source:
JOURNAL OF APPLIED PHYSICS, 117 (17):10.1063/1.4918968 MAY 7 2015
Abstract:
We studied the magnetic properties of multiferroic spinel Co0.5Fe0.5Cr2O4, especially focusing on the spin-ordering, spin-reorientation, and charge re-distribution effects. From the Rietveld refinement analysis, the crystal structure was identified to be a normal cubic spinel of Fd-3m. Based on the temperature-dependent measurements of the magnetization and magnetic hyperfine field (H-hf), Curie temperature (T-C) of Co0.5Fe0.5Cr2O4 was determined to be around 86K where H-hf (sic) 0. From the change of slope in the M-T curve, the conical-spiral magnetic ordering temperature was determined to be 20 K, which coincides with H-hf measurement. Also, we have observed the decrease in the slope of the electric quadrupole splitting (Delta E-Q) curve above 20K, suggesting that the change in Delta E-Q around T-S is originated from charge redistribution due to the spin-relocation associated with the distortion of each tetrahedral site around Fe2+ ion above T-S. This indicates that Co0.5Fe0.5Cr2O4 has the noncollinear conical-spiral spin ordering with incommensurate spin structure below T-S, while above T-S, it has ferrimagnetic spin ordering with commensuration in the collinear state. In addition, the Jahn-teller distortion temperature is measured to be around 155K, since both Delta E-Q and Delta(1) of T-5(2g) band decrease rapidly with increasing temperature and disappear around 155 K. (C) 2015 AIP Publishing LLC.

Title:
Zone-Folded Phonons and the Commensurate-Incommensurate Charge-Density-Wave Transition in 1T-TaSe2 Thin Films
Authors:
Samnakay, R; Wickramaratne, D; Pope, TR; Lake, RK; Salguero, TT; Balandin, AA Author Full Names: Samnakay, R.; Wickramaratne, D.; Pope, T. R.; Lake, R. K.; Salguero, T. T.; Balandin, A. A.
Source:
NANO LETTERS, 15 (5):2965-2973; 10.1021/nl504811s MAY 2015
Abstract:
Bulk 1T-TaSe2 exhibits unusually high charge density wave (CDW) transition temperatures of 600 and 473 K below which the material exists in the incommensurate (I-CDW) and the commensurate (C-CDW) charge-density-wave phases, respectively. The (13)(1/2) x (13)(1/2), C-CDW reconstruction of the lattice coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to Gamma. The C-CDW transition temperatures as a function of film thickness are determined from the evolution of these new Raman peaks, and they are found to decrease from 473 to 413 K as the film thicknesses decrease from 150 to 35 nm. A comparison of the Raman data with ab initio calculations of both the normal and C-CDW phases gives a consistent picture of the zone-folding of the phonon modes following lattice reconstruction, The Raman peak at similar to 154 cm(-1) originates from the zone-folded phonons in the C-CDW phase. In the I-CDW phase, the loss of translational symmetry coincides with a strong suppression and broadening of the Raman peaks. The observed,change: in the C-CDW transition temperature is consistent with total energy calculations of bulk and monolayer 1T-TaSe2.

Title:
Temperature-Pressure Phase Diagram for Rb2ZnCl4 Crystals
Authors:
Kurlyak, VY; Stadnyk, VY; Stakhura, V Author Full Names: Kurlyak, V. Yu.; Stadnyk, V. Yo.; Stakhura, V.
Source:
JOURNAL OF APPLIED SPECTROSCOPY, 82 (2):228-233; 10.1007/s10812-015-0090-3 MAY 2015
Abstract:
We have studied the effect of uniaxial stress along the principal crystallophysical directions on the temperature variations in the birefringence Delta n (i) and the refractive indices ni for Rb2ZnCl4 crystals in the region of phase transitions from the paraelectric phase to the incommensurate phase and then to the commensurate ferroelectric phase. We have established that Delta n (i) and n (i) are rather sensitive to the action of uniaxial stresses. We have observed a significant pressure-induced shift of the paraelectric - incommensurate - ferroelectric phase transition points in different temperature regions, depending on the direction of the uniaxial compression.

Update: 11-Jun-2015


Title:
Effect of Li on electrochemical properties of Ti1.4V0.6Ni quasicrystal alloy produced by rapid quenching
Authors:
Ouyang, ZT; Liu, K; Shang, JM; Xing, C; Liu, WQ; Wang, LM Author Full Names: Ouyang, Zhongtao; Liu, Kun; Shang, Jinming; Xing, Cheng; Liu, Wanqiang; Wang, Limin
Source:
INTERMETALLICS, 62 50-55; 10.1016/j.intermet.2015.03.010 JUL 2015
Abstract:
The effect of Li on the electrochemical performance of electrodes consisting of Ti1.4V0.6Ni quasicrystal was investigated at room temperature in three-electrode cell set-up. The quasicrystal sample was initially synthesized by arc melting, followed by melt-spinning, and then infiltrated with Li atoms by electroosmosis. According to X-ray diffraction, all ribbon samples were determined to be icosahedral quasicrystal phase (I-phase), V-based solid solution phase with BCC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some Li atoms into the Ti1.4V0.6Ni quasicrystal lattice under the condition of an electroosmosis current of 0.6 A, we could observe the appearance of Li diffraction peaks. Importantly, the slight shift to the left observed in the diffraction peaks indicated that lattice expansion was caused by the infiltration of Li. The discharge capacity of Ti1.4V0.6Ni-Li material was higher than that of Ti1.4V0.6Ni.The maximum discharge capacity of 307.1 mAh/g was recorded for Ti1.4V0.6Ni Li at a current density of 30 mAh/g. Both high-rate dischargeability and cycling stability were enhanced as a result of infiltrating Li. The lithium could get into the lattice, which resulted in the formation of microspores on surface of alloy, thus improving electrochemical activity of the alloy electrode. At the same time, the electrochemical reaction kinetics of alloy electrodes was also researched. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Synthesis and Characterization of Bulk Al-Cu-Fe Based Quasicrystals and Composites by Spray Forming
Authors:
Mukhopadhyay, NK; Uhlenwinkel, V; Srivastava, VC Author Full Names: Mukhopadhyay, N. K.; Uhlenwinkel, V.; Srivastava, V. C.
Source:
JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, 24 (6):2172-2178; SI 10.1007/s11665-015-1442-0 JUN 2015
Abstract:
The bulk quasicrystalline (QC) materials and their composites have attracted considerable interest due to their promising mechanical properties. In the present investigation, spray forming has been used to synthesize bulk single-phase icosahedral quasicrystals and composites in Al62.5Cu25Fe12.5 system as well as in quaternary system containing 10% Sn. The elemental materials were induction melted under nitrogen cover and a billet of 250 mm in diameter and 350 mm in height was spray formed. The phase constitution of the spray-formed materials showed a bulk single-phase icosahedral quasicrystal as a major phase along with other crystalline phases. A large number of annealing twins were observed in the microstructure in ternary AlCuFe alloys. It is interesting to note that due to addition of Sn, the volume fraction of beta-Al(CuFe) phase was found to increase and annealing twins were almost absent. The hardness of the single-phase AlCuFe alloy and Sn-containing composites was found to be 8.6 and 6.0 GPa, respectively, at a load of 300 g. In general, the hardness decreases with heat treatment at high temperatures. However, in case of Sn-ontaining alloy, hardness increases with low-temperature heat treatment. Long and hair-like cracks (Palmqvist type) are observed to form from the corner of the indentations of the ternary alloys, whereas in Sn-containing composites, the cracks are not sharp and long suggesting the enhancement of fracture toughness in the composites. Attempts have been made to understand the effect of Sn on the evolution of icosahedral phase, other crystalline phases and their composite effects on the mechanical properties.

Title:
Superconductivity and the electronic phase diagram of LaPt2-xGe2+x
Authors:
Maeda, S; Matano, K; Yatagai, R; Oguchi, T; Zheng, GQ Author Full Names: Maeda, S.; Matano, K.; Yatagai, R.; Oguchi, T.; Zheng, Guo-qing
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174516 MAY 22 2015
Abstract:
In many cases, unconventional superconductivity are realized by suppressing another order parameter, such as charge density wave (CDW) or spin density wave (SDW). This suggests that the fluctuations of these order parameters play an important role in producing superconductivity. LaPt2Ge2 undergoes a tetragonal-to-monoclinic structural phase transition (SPT) at T-s = 394 K, accompanying a double period modulation in the a-axis direction, and superconducts at T-c = 0.41 K. We performed band calculations and found 2D (two dimensional)-like Fermi surfaces with partial nesting. A reduction in the density of states in the monoclinic phase was found in the calculation and confirmed by Pt-195-NMR. We suggest a CDW as a possible cause for the SPT. By changing the stoichiometry between Pt and Ge, we succeeded in suppressing T-s and increasing T-c in LaPt2-xGe2+x. Comparison of La-139- and Pt-195-NMR data reveals moderate fluctuations associated with SPT. From La-139-NQR measurements at zero field, we found that an isotropic superconducting gap is realized in LaPt2-xGe2+x (x = 0.20). We discuss the relationship between superconductivity and the SPT order/fluctuations.

Title:
Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi1-xCaxFe1-xMnxO3 ceramics
Authors:
Kumar, P; Shankhwar, N; Srinivasan, A; Kar, M Author Full Names: Kumar, Pawan; Shankhwar, Nisha; Srinivasan, A.; Kar, Manoranjan
Source:
JOURNAL OF APPLIED PHYSICS, 117 (19):10.1063/1.4921433 MAY 21 2015
Abstract:
The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO3 lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO3 at room temperature is observed to be similar to 13.8 degrees. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO3. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO3 measured using UV-Vis spectra was supported by the resonance Raman spectra. (C) 2015 AIP Publishing LLC.

Title:
Coexistence of Charge-Density-Wave and Pair-Density-Wave Orders in Underdoped Cuprates
Authors:
Wang, YX; Agterberg, DF; Chubukov, A Author Full Names: Wang, Yuxuan; Agterberg, Daniel F.; Chubukov, Andrey
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.197001 MAY 15 2015
Abstract:
We analyze incommensurate charge-density-wave (CDW) and pair-density-wave (PDW) orders with transferred momenta (+/- Q, 0)/(0, +/- Q) in underdoped cuprates within the spin-fermion model. Both orders appear due to an exchange of spin fluctuations before magnetic order develops. We argue that the ordered state with the lowest energy has nonzero CDW and PDW components with the same momentum. Such a state breaks C-4 lattice rotational symmetry, time-reversal symmetry, and mirror symmetries. We argue that the feedback from CDW/PDW order on fermionic dispersion is consistent with ARPES data. We discuss the interplay between the CDW/PDWorder and d(x2-y2) superconductivity and make specific predictions for experiments.

Title:
Incommensurate Systems as Model Compounds for Disorder Revealing Low-Temperature Glasslike Behavior
Authors:
Remenyi, G; Sahling, S; Biljakovic, K; Staresinic, D; Lasjaunias, JC; Lorenzo, JE; Monceau, P; Cano, A Author Full Names: Remenyi, G.; Sahling, S.; Biljakovic, K.; Staresinic, D.; Lasjaunias, J. -C.; Lorenzo, J. E.; Monceau, P.; Cano, A.
Source:
PHYSICAL REVIEW LETTERS, 114 (19):10.1103/PhysRevLett.114.195502 MAY 14 2015
Abstract:
We show that the specific heat of incommensurately modulated crystals with broken translational periodicity presents similar features at low temperatures to those of amorphous and glass materials. Here we demonstrate that the excess to the constant C-p(T)/T-3 law (or Debye limit) is made up of an upturn below 1 K and of a broad bump at T approximate to 10 K that directly originates from the gapped phase and amplitude modes of the incommensurate structure. We argue that the low-energy dynamics of incommensurate systems constitute a plausible simplification of the landscape of interactions present in glasses, giving rise to their low-temperature anomalies.

Title:
A Crystal-Chemical Framework for Relaxor versus Normal Ferroelectric Behavior in Tetragonal Tungsten Bronzes
Authors:
Zhu, X; Fu, M; Stennett, MC; Vilarinho, PM; Levin, I; Randall, CA; Gardner, J; Morrison, FD; Reaney, IM Author Full Names: Zhu, X.; Fu, M.; Stennett, M. C.; Vilarinho, P. M.; Levin, I.; Randall, C. A.; Gardner, J.; Morrison, F. D.; Reaney, I. M.
Source:
CHEMISTRY OF MATERIALS, 27 (9):3250-3261; 10.1021/acs.chemmater.5b00072 MAY 12 2015
Abstract:
Tetragonal tungsten bronzes (TTBs), an important class of oxides known to exhibit ferroelectricity, undergo complex distortions, including rotations of,oxygen octahedra, which give rise to either incommensurately or commensurately modulated superstructures. Many TTBs display broad, frequency-dependent relaxor dieletric behavior rather than sharper frequency-independent normal ferroelectric anomalies, but the exact reasons that favor a particular type of dielectric response for a given composition remain unclear. In this contribution the influence of incommensurate/commensurate dispiacive modulations on the onset of relaxor/ferroelectric behavior in TTBs is assessed in the context of basic crystal-chemical factors, such as positional disorder, ionic radii and polarizabilities, and point defects. We present a predictive crystal-chemical model that rationalizes composition structure properties relations for a broad range of TTB systems.

Title:
Structural transformation in quasicrystal-forming Al-Cu-Fe alloys
Authors:
Boularas, H; Debili, MY; Alleg, S Author Full Names: Boularas, H.; Debili, M. Y.; Alleg, S.
Source:
METALLURGICAL RESEARCH & TECHNOLOGY, 112 (2):10.1051/metal/2015008 2015
Abstract:
Three Al-Cu-Fe alloys with various iron contents (6 at.%, 12 at.% and 15 at.%), were synthesized by fusion under high-frequency magnetic induction and characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry(DSC). The microstructure evolution was carried out both in the as-quenched state as well after heat treatment at 500 degrees C in relation to iron composition. Particular attention was been paid to the alloy containing 15%, and we were been able to determine by DSC that a massive transformation from crystal (beta) to quasicrystal i-psi (Al6Fe2Cu) occurs for this composition.

Title:
Formation of an Icosahedral Quasicrystal and Its Approximant in Au-Al-Sc System
Authors:
So, YG; Kimoto, K; Edagawa, K Author Full Names: So, Yeong-Gi; Kimoto, Koji; Edagawa, Keiichi
Source:
MATERIALS TRANSACTIONS, 56 (4):495-499; 10.2320/matertrans.M2014421 2015
Abstract:
The formation of the icosahedral (i-) and 1/1-approximant (1/1-) phases in the Au-Al-Sc system has been investigated. A primitive-type i-phase was found to form in an Au45Al40Sc15 alloy. This i-phase was shown to be thermodynamically stable at 973 K. A stable 1/1-phase was found to form at 1173K for compositions of Au44+xAl41-xSc15 (x = 0, 1, 2, 3). High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that the 1/1-phase consists of Tsai-type icosahedral clusters. Similar local structures were observed in the HAADF-STEM image for the i-phase, indicating that the i-phase consists of Tsai-type clusters identical to the clusters in the 1/1-phase. The composition of the Au-Al-Sc i-phase is consistent with the formation conditions, including those in the valence electrons per atom ratio and in the atomic size factor, which has been shown previously for other Tsai-type i-phases. This fact demonstrates the importance of these conditions for stabilization of Tsai-type i-phases.

Update: 3-Jun-2015


Title:
The study of Al-3(Mn, Pd) crystal and Al-Mn-Pd decagonal quasicrystal by spherical aberration-corrected scanning transmission microscopy and atomic-resolution energy dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1511-1523; 10.1080/14786435.2015.1039623 MAY 13 2015
Abstract:
An Al3Mn-type Al-3(Mn, Pd) crystal and an Al-Mn-Pd decagonal quasicrystal (DQC) in an Al70Mn20Pd10 alloy are studied using a spherical aberration (Cs)-corrected scanning transmission electron microscope (STEM) with high-angle annular dark-field (HAADF) and annular bright-field (ABF) techniques, together with atomic-resolution energy dispersive X-ray spectroscopy (EDS). Mn and Pd atomic positions in the Al-3(Mn, Pd) structure projected along the b-axis (pseudo-tenfold rotational axis) are represented by separate bright dots in observed HAADF-STEM images. Besides, Al as well as Mn and Pd atomic positions are represented as dark dots in ABF-STEM images. Most Mn and Pd atomic positions in the Al-3(Mn, Pd) structure can be observed on atomic-resolution EDS maps. On the basis of the good correlation between the STEM images and the EDS maps, and also considering the structure of the Al-3(Mn, Pd) crystal, which was determined by X-ray diffraction using a single crystal, observed HAADF and ABF-STEM images of the Al-Mn-Pd DQC have been interpreted. Pd and Mn atomic positions in the Al-Mn-Pd DQC can be detected on the observed EDS maps. It can be seen that Pd is enriched around the centre of the columnar clusters, having a decagonal section with 2nm in diameter. It can therefore be concluded that Pd plays an important role in the stabilization of the decagonal clusters, which form the Al-Mn-Pd DQC structure.

Title:
The structure of an Al-Rh-Cu decagonal quasicrystal studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy
Authors:
Hiraga, K; Yasuhara, A; Yamamoto, K; Yubuta, K Author Full Names: Hiraga, Kenji; Yasuhara, Akira; Yamamoto, Kazuki; Yubuta, Kunio
Source:
PHILOSOPHICAL MAGAZINE, 95 (14):1524-1535; 10.1080/14786435.2015.1039624 MAY 13 2015
Abstract:
The structure of an Al-Rh-Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al63Rh18.5Cu18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in tau(2)(tau: golden ratio)-inflated pentagonal tiling with a bond-length of 2nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed.

Update: 28-May-2015


Title:
Refinement of the icosahedral quasicrystalline phase and the grain size of Mg-9.25Zn-1.66Y alloy by high-ratio differential speed rolling
Authors:
Kwak, TY; Lim, HK; Han, SH; Kim, WJ Author Full Names: Kwak, T. Y.; Lim, H. K.; Han, S. H.; Kim, W. J.
Source:
SCRIPTA MATERIALIA, 103 49-52; 10.1016/j.scriptamat.2015.03.004 JUL 1 2015
Abstract:
Differential speed rolling was applied to a Mg-9.25Zn-1.66Y alloy with an icosahedral quasicrystalline (I) phase to refine its cast microstructure by severe plastic deformation. The grain size was reduced to gm. A higher speed ratio, which produces a higher shear strain, was more effective in breaking up the eutectic I phase structure and dispersing the broken particles into the matrix. The processed alloy exhibited a high yield stress of 337 MPa and a good elongation of 10.7%. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Evidence for magneto-electric and spin-lattice coupling in PbFe0.5Nb0.5O3 through structural and magneto-electric studies
Authors:
Matteppanavar, S; Rayaprol, S; Singh, K; Reddy, VR; Angadi, B Author Full Names: Matteppanavar, Shidaling; Rayaprol, Sudhindra; Singh, Kiran; Reddy, V. Raghavendra; Angadi, Basavaraj
Source:
JOURNAL OF MATERIALS SCIENCE, 50 (14):4980-4993; 10.1007/s10853-015-9046-5 JUL 2015
Abstract:
Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb(Fe0.5Nb0.5)O-3 (PFN) in the temperature range of 290-2 K to understand the structural and magnetic properties as a function of temperature. ND data were refined using the Rietveld refinement method for both crystallographic and magnetic structures. The structure at room temperature was found to be monoclinic, in Cm space group. No structural transition was observed till 2 K. At low temperatures (i.e., from T < T (N); T (N) = 155 K), an additional peak appears at scattering vector, Q = 1.35 (-1), indicating the onset of antiferromagnetic ordering. The magnetic structure was found to be commensurate with the crystallographic structure and could be refined using the propagation vector, k = [0.125, 0.5, and 0.5]. Magnetization, ferroelectric P-E loops, and dielectric measurements on PFN reveal a strong anomaly at the antiferromagnetic transition temperature (T (N)) indicating the magneto-electric coupling. The refined temperature-dependent structural parameters such as unit cell volume and monoclinic distortion angle (beta) reveal pronounced anomalies at the magnetic ordering temperature (T (N)), which indicates strong spin-lattice coupling. An anomaly in lattice volume was observed with a small negative thermal expansion below and a large thermal expansion above the T (N), respectively. It shows the occurrence of isostructural phase transition accompanying the magnetic ordering below T (N) 155 K, leading to significant change in ionic polarization, octahedral tilt angle, and lattice strain around T (N). We have used refined atomic positional coordinates from the nuclear and magnetic structures, to obtain ionic polarization. These detailed studies confirm the magneto-electric and spin-lattice coupling in PFN across T-N.

Title:
Pressure-induced successive magnetic and structural phase transitions in Fe1.087Te
Authors:
Jorgensen, JE; Hansen, TC Author Full Names: Jorgensen, Jens-Erik; Hansen, Thomas Christian
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (5):10.1140/epjb/e2015-50713-6 MAY 11 2015
Abstract:
The crystal and magnetic structures of Fe1.087Te have been studied by neutron powder diffraction in the temperature range from 5 to 170 K at pressures in the range from approximate to 0.8 to approximate to 7 GPa. The p, T-phase diagram contains three phases with monoclinic, orthorhombic and tetragonal symmetry. The monoclinic and orthorhombic phases are both antiferromagnetically ordered and stable at temperatures below approximate to 69 K while the non-magnetic tetragonal phase is stable above this temperature. The monoclinic phase is stable for p less than or similar to 1.2 GPa while the orthorhombic phase is stable for 1.2 less than or similar to p less than or similar to 1.7 GPa and the tetragonal phase becomes stable at higher pressures at the lowest measured temperatures. The magnetic ordering is antiferromagnetic bicollinear and commensurate in the monoclinic phase but incommensurate and pressure dependent in the orthorhombic phase. The pressure-induced collapse of magnetic order at approximate to 1.7 GPa is accompanied by abrupt changes in volume and compressibility, suggestive of a spin state change of the Fe2+ ions in the FeTe layers.

Title:
Amount of valence charge of Al- and Zn-based quasicrystals and related approximant crystals evaluated by chemical shift observations and Bader analysis
Authors:
Koshiya, S; Terauchi, M Author Full Names: Koshiya, S.; Terauchi, M.
Source:
PHILOSOPHICAL MAGAZINE, 95 (13):1462-1470; 10.1080/14786435.2015.1033486 MAY 3 2015
Abstract:
The amounts of decreased charge at Al sites of Al-based (Al-Pd-Cr-Fe, Al-Si-Mn, and Al-Re-Si) and at Zn sites of Zn-based (Zn-Mg-Zr) quasicrystals and approximant crystals were estimated. The evaluation was done by comparisons between chemical shifts experimentally observed by soft-X-ray emission spectroscopy and the amount of valence charge obtained by Bader analysis for first principle calculations of reference materials (Al, alpha-Al2O3, Zn, and ZnO). Decreased charges at Al sites of Al-based quasicrystals and at Zn sites of Zn-based quasicrystals were evaluated to be 1.0-2.5 e(-)/atom and 1.1-1.2 e(-)/atom, respectively. A covalent bonding nature alloy of Al-Re-Si also showed a decrease in valence charge at Al sites.

Title:
Infinitely Adaptive Transition Metal Oxychalcogenides: The Modulated Structures of Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2
Authors:
Wang, CH; Ainsworth, CM; Gui, DY; McCabe, EE; Tucker, MG; Evans, IR; Evans, JSO Author Full Names: Wang, Chun-Hai; Ainsworth, Chris M.; Gui, Dong-Yun; McCabe, Emma E.; Tucker, Matthew G.; Evans, Ivana R.; Evans, John S. O.
Source:
CHEMISTRY OF MATERIALS, 27 (8):3121-3134; 10.1021/acs.chemmaer.5b00666 APR 28 2015
Abstract:
This article reports the syntheses, structures, and physical properties of the oxychalcogenides (Ce1-xLax)(2)O2MnSe2 with x = 0-0.7. These materials have a layered structure related to that of the LaOFeAs-derived superconductors but with the transition metal sites 50% occupied. Ce2O2MnSe2 contains alternating layers of composition: [Ce2O2](2+) and [MnSe2](2-). The size mismatch between the layers leads to an incommensurate structure with a modulation vector of q = ae+ Ob*+0.5c* with a = 0.158(1), which can be described with a (3 + 1)D superspace structural model in superspace group Cmme(a,0,(1) / OM [67.12]. There is a strong modulation of Mn site occupancies, leading to a mixture of corner- and edge-sharing MnSe4/2 tetrahedra in the [MnSe2](2-) layers. The modulation vector can be controlled by partial substitution of Ce3+ for larger La3+, and a simple commensurate (Ce0.78La0.22)(2)O2MnSe2 with a = 1/6. The materials respond to the change in relative size of the oxide and chalcogenide blocks by varying the ratio of corner- to edge-sharing tetrahedra. The superspace model lets us unify the structural description of the five different ordering patterns reported to date for different Ln(2)O(2)MSe(2) (Ln = lanthanide) materials. Mn moments in Ce2O2MnSe2 and (Ce0.78La0.22)(2)O2MnSe2 order antiferromagnetically below TN = 150 K, and Ce moments order below similar to 70 K. The magnetic structures of both materials have been determined using neutron diffraction. Both materials are semiconductors; Ce2O2MnSe2 has a = 9 x 10(-6) Omega(-1) cm(-1) at room temperature and an activation energy for charge carrier mobility from RT to 170 degrees C of -,0.4 eV.

Title:
Effect of Pd Substitution on Phase Formation and Stability in Ti-Zr-Ni Quasicrystalline Alloys
Authors:
Huang, HG; Chen, L; Xu, QY Author Full Names: Huang Huogen; Chen Liang; Xu Qinying
Source:
RARE METAL MATERIALS AND ENGINEERING, 44 (4):821-825; APR 2015
Abstract:
Pd can be used as an adding element to improve hydrogenation properties of Ti-Zr-Ni quasicrystalline alloys. However, the action mechanism of Pd addition is unclear yet. The effects of Pd substituting Ti and Zr in Ti45Zr38Ni17 and Ti40Zr40Ni20 alloys were studied by means of XRD, TEM and DSC examination. The results show that icosahedral quasicrystal can be formed purely through 4%similar to 6% Pd substitution for Ti or 4% for Zr in the Ti45Zr38Ni17 alloy, as well as 3%similar to 4% for Ti or possibly below 3% for Zr in the Ti40Zr40Ni20 alloy. This indicates a higher substitution limit for Ti in order for the heritance of the quasicrystal phase. Two derived quasicrystals Ti39Zr38Ni17Pd6 and Ti36Zr40Ni20Pd4 can be transformed into crystalline phases after annealing at 400 degrees C, demonstrating their lower thermo-stabilities in comparison to such Ti-Zr-Ni alloys being stable at about 700 degrees C. Both the replacement tendency and the decrease of the thermostability of quasicrystal phase might be ascribed to appropriate atomic size of Pd.

Title:
X-ray induced lock-in transition of cycloidal magnetic order in a multiferroic perovskite manganite
Authors:
Yamasaki, Y; Nakao, H; Murakami, Y; Nakajima, T; Sampietro, AL; Ohsumi, H; Takata, M; Arima, T; Tokura, Y Author Full Names: Yamasaki, Y.; Nakao, H.; Murakami, Y.; Nakajima, T.; Sampietro, A. Lafuente; Ohsumi, H.; Takata, M.; Arima, T.; Tokura, Y.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.100403 MAR 24 2015
Abstract:
We report the x-ray photoexcitation effects on cycloidal magnetic order in a multiferroic perovskite-type manganite Gd0.5Tb0.5MnO3. The material exhibits a competition between the P (electric polarization)parallel to a ferroelectric state with the commensurate (C) ab-plane cycloidal and the P parallel to c ferroelectric state with the incommensurate (IC) bc-plane cycloidal spin structure. The phase transition between these two phases can be induced by an application of a magnetic field. We found that the x-ray irradiation can induce the bidirectional and persistent phase transition between IC and C phases. The nonresonant x-ray magnetic diffraction revealed that both the initial and the x-ray induced phases have the bc-plane cycloidal magnetic structure, whereas the magnetic wave number varies between IC and C. The x-ray induced bc-plane cycloidal C phase is thus the hidden multiferroic phase in the Gd1-xTbxMnO3 system, which does not show up with the application of any static field.

Update: 20-May-2015


Title:
High-resolution Brillouin scattering studies of phase transitions in Ca2MgSi2O7 and Ca2ZnSi2O7 silicates
Authors:
Maczka, M; Hanuza, J; Kaminskii, A; Kojima, S Author Full Names: Maczka, Miroslaw; Hanuza, Jerzy; Kaminskii, Alexander; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 638 34-37; 10.1016/j.jallcom.2015.03.055 JUL 25 2015
Abstract:
Temperature-dependent Micro-Brillouin scattering studies of Ca2MgSi2O7 and Ca2ZnSi2O7 single crystals were performed. Step-like decrease of Brillouin shifts and strong broadening of Brillouin bands corresponding to the c(33) elastic constant were observed at 351 K for Ca2MgSi2O7 and 407 K for Ca2ZnSi2O7. This behavior was attributed to coupling of strain to the square of the order parameter due to structural transitions into incommensurate phases. Analysis of the observed acoustic anomalies showed critical slowing down behavior of the relaxation time characterizing interaction between the order parameter and acoustic phonon. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Investigation of multiferroic behaviour of TbMnO3 nanoplates
Authors:
Acharya, SA; Khule, SM; Gaikwad, VM Author Full Names: Acharya, S. A.; Khule, S. M.; Gaikwad, V. M.
Source:
MATERIALS RESEARCH BULLETIN, 67 111-117; 10.1016/j.materresbull.2015.03.013 JUL 2015
Abstract:
In the present study, hydrothermally prepared TbMnO3 in plates-like morphology at nanoscale are investigated in multiferroic view point. X-ray diffraction study confirms the orthorhombic phase of as-synthesized TbMnO3. Microstructural features studied by Scanning Electron Microscopy and Transmission Electron Microscopy show the plates-like morphology of as-synthesized TbMnO3 at nanoscale. Local distortions investigated by FT-Raman exhibits redshift in T mode by about 20 cm(-1) as compared to that of the single crystal. The redshift in T mode is mainly due to defect by tilting of octahedra and respective changes in bond angle of Mn-O(1)-Mn. This is assigned to the size-morphology induced defects. The temperature dependent zero-field-cooled and field-cooled magnetization are measured at H=50 Oe and in the temperature range 2-300 K. The anomalies in magnetization are obtained at 8 and 42 K. Bifurcation of the ZFC and FC curves are observed very close to magnetic transition temperature 42 K. The 42 K anomaly is related to the sine wave ordering of Mn3+ moment; and 8K anomaly is associated with magnetic ordering of the Tb3+-sublattice propagation vector. The anomalies in the electric properties, epsilon' (T), tan delta (T), which are noticed within the 28K range, coincide with the temperature of incommensurate-commensurate (or lock-in) magnetic transition of TbMnO3. This study confirms that multiferroic behavior is retained in TbMnO3 nanoplates. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Spatial decay of the phason field in quasicrystal linear elasticity
Authors:
Mariano, PM; Salvatori, L Author Full Names: Mariano, Paolo Maria; Salvatori, Luca
Source:
MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, 23 (4):10.1088/0965-0393/23/4/045004 JUN 2015
Abstract:
We present numerical simulations showing that a conservative phason self-action, i.e. the stationary part of the phason diffusion, promotes in quasicrystal linear elasticity the phason spatial decay. The proof of the possible existence of such a phason self-action is based on the invariance requirements of the external power of all actions over a quasicrystal, with respect to isometry-based changes in observers in the physical and phason spaces. The numerical result confirms a 2011 theoretical prevision by Colli and Mariano.

Title:
Phase equilibria and transformations in ternary Mg-Gd-Zn alloys
Authors:
Grobner, J; Kozlov, A; Fang, XY; Zhu, SM; Nie, JF; Gibson, MA; Schmid-Fetzer, R Author Full Names: Groebner, Joachim; Kozlov, Artem; Fang, Xi-Ya; Zhu, Suming; Nie, Jian-Feng; Gibson, Mark A.; Schmid-Fetzer, Rainer
Source:
ACTA MATERIALIA, 90 400-416; 10.1016/j.actamat.2015.02.044 MAY 15 2015
Abstract:
Phase equilibria and transformations in ternary Mg-Gd-Zn alloys were studied experimentally by investigating 22 samples with up to 40 at.% Gd and 60 at.% Zn. These results, combined with a critical review of literature data, were used to develop thermodynamic descriptions of the Gd Zn and the Mg-Gd-Zn systems and to calculate the Mg-Gd-Zn phase diagram in the entire composition range. In the ternary system the hexagonal long-period stacking ordered structure 14H, the hexagonal phase H1, Gd11Mg24Zn64, and five solid solution phases with ternary compositions, GdMg5, GdMg3, GdMg2, Gd(Mg,Zn), and W are found to be stable, whereas the icosahedral phase I, GdMg3Zn6, and other hexagonal phases are metastable. In addition, a new stable phase Gd20Mg19Zn81 with a face-centered cubic structure is identified in the Mg Gd Zn system. Based on the thermodynamic description obtained in this work, the microstructures and phase transformations previously observed in the as-cast, solution heat treated and aged conditions are discussed. It is shown that the current thermodynamic predictions are in good accord with the experimental findings, suggesting the viability of such an approach for the microstructure design of Mg-Gd-Zn alloys. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Spectroscopic study of metallic magnetism in single-crystalline Nb1-yFe2+y
Authors:
Rauch, D; Kraken, M; Litterst, FJ; Sullow, S; Luetkens, H; Brando, M; Forster, T; Sichelschmidt, J; Neubauer, A; Pfleiderer, C; Duncan, WJ; Grosche, FM Author Full Names: Rauch, D.; Kraken, M.; Litterst, F. J.; Suellow, S.; Luetkens, H.; Brando, M.; Foerster, T.; Sichelschmidt, J.; Neubauer, A.; Pfleiderer, C.; Duncan, W. J.; Grosche, F. M.
Source:
PHYSICAL REVIEW B, 91 (17):10.1103/PhysRevB.91.174404 MAY 6 2015
Abstract:
We have investigated single crystals and polycrystals from the series Nb1-yFe2+y, -0.004 <= y <= 0.018, by electron spin resonance, muon spin relaxation, and Mossbauer spectroscopy. Our data establish that at lowest temperatures all samples exhibit bulk magnetic order. Slight Fe excess induces low-moment ferromagnetism, consistent with bulk magnetometry, while Nb-rich and stoichiometric NbFe2 display spin density wave order with small magnetic moment amplitudes of order similar to 0.001-0.01 mu(B)/Fe. This provides microscopic evidence for a modulated magnetic state on the border of ferromagnetism in NbFe2.

Title:
Long-range modulation of a composite crystal in a five-dimensional superspace
Authors:
Guerin, L; Mariette, C; Rabiller, P; Huard, M; Ravy, S; Fertey, P; Nichols, SM; Wang, B; Mannsfeld, SCB; Weber, T; Hollingsworth, MD; Toudic, B Author Full Names: Guerin, Laurent; Mariette, Celine; Rabiller, Philippe; Huard, Michael; Ravy, Sylvain; Fertey, Pierre; Nichols, Shane M.; Wang, Bo; Mannsfeld, Stefan C. B.; Weber, Thomas; Hollingsworth, Mark D.; Toudic, Bertrand
Source:
PHYSICAL REVIEW B, 91 (18):10.1103/PhysRevB.91.184101 MAY 5 2015
Abstract:
The intergrowth crystal of n-tetracosane/urea presents a misfit parameter, defined by the ratio gamma = c(h)/c(g) (c(host)/c(guest)), that is very close to a commensurate value (gamma congruent to 1/3). High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of gamma = 0.3369, which is found to be constant at all temperatures studied. A complex sequence of structural phases is reported. The high temperature phase (phase I) exists in the four-dimensional superspace group P6(1)22(00 gamma). At T-c1 = 179(1) K, a ferroelastic phase transition increases the dimension of the crystallographic superspace. This orthorhombic phase (phase II) is characterized by the five-dimensional (5D) superspace group C222(1)(00 gamma)(10 delta) with a modulation vector a(o)* + c(m)* = a(o)* + delta . c(h)*, in which the supplementary misfit parameter is delta = 0.025(1) in host reciprocal units. This corresponds to the appearance of a modulation of very long period (about 440 +/- 16 angstrom). At T-c2 = 163.0(5) K, a 5D to 5D phase transition leads to the crystallographic superspace group P2(1)2(1)2(1)(00 gamma)(00 delta) with a very similar value of delta. This phase transition reveals a significant hysteresis effect.

Title:
X-ray investigation of lateral hetero-structures of inversion domains in LiNbO3, KTiOPO4 and KTiOAsO4
Authors:
Lyford, TS; Collins, SP; Fewster, PF; Thomas, PA Author Full Names: Lyford, Thomas S.; Collins, Stephen P.; Fewster, Paul F.; Thomas, Pamela A.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 255-267; 10.1107/S2053273315001503 3 MAY 2015
Abstract:
In this paper periodically domain-inverted (PDI) ferroelectric crystals are studied using high-resolution X-ray diffraction. Rocking curves and reciprocal-space maps of the principal symmetric Bragg reflections in LiNbO3 (LN) (Lambda = 5 mu m), KTiOPO4 (KTP) (Lambda = 9 mu m) and KTiOAsO4 (KTA) (Lambda = 39 mu m) are presented. For all the samples strong satellite reflections were observed as a consequence of the PDI structure. Analysis of the satellites showed that they were caused by a combination of coherent and incoherent scattering between the adjacent domains. Whilst the satellites contained phase information regarding the structure of the domain wall, this information could not be rigorously extracted without a priori knowledge of the twinning mechanism. Analysis of the profiles reveals strain distributions of Delta d/d = 1.6 x 10(-4) and 2.0 x 10(-4) perpendicular to domain walls in KTP and LN samples, respectively, and lateral correlation lengths of 63 mu m (KTP), 194 mu m (KTA) and 10 mu m (LN). The decay of crystal truncation rods in LN and KTP was found to support the occurrence of surface corrugations.

Title:
Structure factor for an icosahedral quasicrystal within a statistical approach
Authors:
Strzalka, R; Buganski, I; Wolny, J Author Full Names: Strzalka, Radoslaw; Buganski, Ireneusz; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 279-290; 10.1107/S2053273315001473 3 MAY 2015
Abstract:
This paper describes a detailed derivation of a structural model for an icosahedral quasicrystal based on a primitive icosahedral tiling (three-dimensional Penrose tiling) within a statistical approach. The average unit cell concept, where all calculations are performed in three-dimensional physical space, is used as an alternative to higher-dimensional analysis. Comprehensive analytical derivation of the structure factor for a primitive icosahedral lattice with monoatomic decoration (atoms placed in the nodes of the lattice only) presents in detail the idea of the statistical approach to icosahedral quasicrystal structure modelling and confirms its full agreement with the higher-dimensional description. The arbitrary decoration scheme is also discussed. The complete structure-factor formula for arbitrarily decorated icosahedral tiling is derived and its correctness is proved. This paper shows in detail the concept of a statistical approach applied to the problem of icosahedral quasicrystal modelling.

Title:
Path-independent integral in fracture mechanics of quasicrystals
Authors:
Sladek, J; Sladek, V; Atluri, SN Author Full Names: Sladek, J.; Sladek, V.; Atluri, S. N.
Source:
ENGINEERING FRACTURE MECHANICS, 140 61-71; 10.1016/j.engfracmech.2015.03.039 MAY 2015
Abstract:
Path-independent integrals are successfully utilized for accurate evaluation of fracture parameters in crystalic materials, where atomic arrangement is periodic. In quasicrystals (QC) the atomic arrangement is quasiperiodic in one-, two-or three-directions. The 2-d elastic problem for quasicrystal is described by coupled governing equations for phonon and phason displacements. Conservation laws for quasicrystals are utilized to derive path-independent integrals for cracks. The relation between the energy release and stress intensity factor for a crack under the mode I is given for decagonal QCs. The path-independent integral formulation is valid also for cracks in QCs with continuously varying material properties. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
Density functional theory calculations of the turbostratically disordered compound [(SnSe)(1+y)](m)(VSe2)(n)
Authors:
Rudin, SP; Johnson, DC Author Full Names: Rudin, Sven P.; Johnson, David C.
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144203 APR 30 2015
Abstract:
Among composite materials that layer constituent substances of nanoscale thicknesses, [(SnSe)(1+y)](m)(VSe2)(n) emerges as an example where the constituents retain incommensurate lattice structures. Perpendicular to the stacking direction, the system exhibits random translations and random rotations on average, i.e., turbostratic disorder, with local regions showing twelvefold diffraction patterns. Earlier theoretical work on these structures showed that combining density functional theory with an empirical treatment of the van der Waals interaction gave structural parameters in good agreement with experiment, but no attempt was made to examine the relative orientations. Here we approximate the extended system with one extended constituent and one finite constituent, which allows the treatment of all relative orientations on equal footing. The calculations show how the twelvefold periodicity follows from how the ions of the SnSe layer lock in with favored positions relative to the VSe2 layer, and the associated energy scale supports arguments for the overall turbostratic disorder. The success of this approximation in describing the structural parameters of the extended [(SnSe)(1+y)](m)(VSe2)(n) system encourages its use for other properties and for other similar systems with other chemistries.

Title:
Linear spin wave theory for single-Q incommensurate magnetic structures
Authors:
Toth, S; Lake, B Author Full Names: Toth, S.; Lake, B.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (16):10.1088/0953-8984/27/16/166002 APR 29 2015
Abstract:
Linear spin wave theory provides the leading term in the calculation of the excitation spectra of long-range ordered magnetic systems as a function of 1/root S. This term is acquired using the Holstein-Primakoff approximation of the spin operator and valid for small dS fluctuations of the ordered moment. We propose an algorithm that allows magnetic ground states with general moment directions and single-Q incommensurate ordering wave vector using a local coordinate transformation for every spin and a rotating coordinate transformation for the incommensurability. Finally we show, how our model can determine the spin wave spectrum of the magnetic C-site langasites with incommensurate order.

Title:
Soft chemical control of the crystal and magnetic structure of a layered mixed valent manganite oxide sulfide
Authors:
Blandy, JN; Abakumov, AM; Christensen, KE; Hadermann, J; Adamson, P; Cassidy, SJ; Ramos, S; Free, DG; Cohen, H; Woodruff, DN; Thompson, AL; Clarke, SJ Author Full Names: Blandy, Jack N.; Abakumov, Artem M.; Christensen, Kirsten E.; Hadermann, Joke; Adamson, Paul; Cassidy, Simon J.; Ramos, Silvia; Free, David G.; Cohen, Harry; Woodruff, Daniel N.; Thompson, Amber L.; Clarke, Simon J.
Source:
APL MATERIALS, 3 (4):10.1063/1.4918973 APR 2015
Abstract:
Oxidative deintercalation of copper ions from the sulfide layers of the layered mixed-valent manganite oxide sulfide Sr2MnO2Cu1.5S2 results in control of the copper-vacancy modulated superstructure and the ordered arrangement of magnetic moments carried by the manganese ions. This soft chemistry enables control of the structures and properties of these complex materials which complement mixed-valent perovskite and perovskite-related transition metal oxides. (C) 2015 Author(s).

Title:
Periodic and incommensurately modulated phases in a (2-methylimidazolium) tetraiodobismuthate(III) thermochromic organic-inorganic hybrid
Authors:
Gagor, A; Weclawik, M; Bondzior, B; Jakubas, R Author Full Names: Gagor, A.; Weclawik, M.; Bondzior, B.; Jakubas, R.
Source:
CRYSTENGCOMM, 17 (17):3286-3296; 10.1039/c5ce00046g 2015
Abstract:
A(2-methylimidazolium) tetraiodobismuthate(III) (abbreviated as (2-MIm)BiI4) hybrid undergoes structural phase transition to an incommensurately modulated phase at 308 K. The relative coordinates of the modulation q-vector do not change down to 150 K indicating the stability of the incommensurate crystal packing that may be modeled by the sinusoidal waves of displacements. The transformation is triggered by the deformation of [BiI4-](n) chains which entails ordering of 2-MIm(+) counterions that couple to the anionic substructure via weak hydrogen bond interactions. Differential scanning calorimetry (DSC) and dielectric spectroscopy methods confirm the phase transition at 308 K (phase I -> phase II). Two dielectric relaxation processes that may be assigned to the dynamics of the polar 2-MIm(+) cations are present: a low frequency relaxator close to T-c and a high frequency one in a wide temperature region over phase II. The compound shows significant thermochromism characteristics for direct gap semiconductors. DOS calculations, together with the asymmetric local environment of bismuth ions, imply the presence of the stereo-chemically active bismuth lone pair 6s(2) electrons in both phases.

Update: 14-May-2015


Title:
Magnetic anisotropy in the incommensurate ScFe4Al8 system
Authors:
Recko, K; Dobrzynski, L; Waliszewski, J; Szymanski, K Author Full Names: Recko, K.; Dobrzynski, L.; Waliszewski, J.; Szymanski, K.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 388 82-89; 10.1016/j.jmmm.2015.03.096 AUG 15 2015
Abstract:
Neutron scattering and magnetization data are used for estimation of the spin ordering in ScFe4Al8. Results of experimental measurements are compared with the ground state configurations obtained by simulated annealing algorithms. The origins of the magnetocrystalline anisotropy of the scandium intermetallic alloy and the conditions of the coexistence of two different magnetic modulations as a function of the exchange integrals are discussed. The influence of the dipolar interactions for the noncollinearity and incommensurability in ScFe4Al8 was determined. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Thermal expansion of a Au - Al - Yb intermediate valence quasicrystal
Authors:
Watanuki, T; Kashimoto, S; Ishimasa, T; Machida, A; Yamamoto, S; Tanaka, Y; Mizumaki, M; Kawamura, N; Watanabe, S Author Full Names: Watanuki, T.; Kashimoto, S.; Ishimasa, T.; Machida, A.; Yamamoto, S.; Tanaka, Y.; Mizumaki, M.; Kawamura, N.; Watanabe, S.
Source:
SOLID STATE COMMUNICATIONS, 211 19-22; 10.1016/1.ssc2015.03.008 JUN 2015
Abstract:
The thermal expansion of a Au - Al - Yb intermediate-valence quasicrystal has been studied. X-ray diffraction measurements showed zero thermal expansion below 50 K. By comparison with an isostructural Au - Al - Tm quasicrystal, the contribution of the Yb valence variation was extracted, and it was shown that its negative thermal expansion component compensated for the positive thermal expansion of the original lattice. On cooling, the Yb contribution grew steeply below approximately 155 K down to the lowest experimental temperature of 5 K, due to enlargement of the Yb atomic radius, which was caused by the valence shift toward the divalent state. Additionally, a larger Yb contribution to the thermal expansion was demonstrated in a crystalline approximant to this quasicrystal. The magnitude of this contribution was approximately 1.4 Limes larger than in the case of the quasicrystal itself, resulting in a slight negative thermal expansion below 50 K. A heterogeneous valence model for the quasicrystal that we proposed previously accounts for this magnitude difference. (C) 2015 Elsevier Ltd. All rights reserved.

Title:
The unusual normal state and charge-density-wave order in 2H-NbSe2
Authors:
Koley, S; Mohanta, N; Taraphder, A Author Full Names: Koley, S.; Mohanta, N.; Taraphder, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (18):10.1088/0953-8984/27/18/185601 MAY 13 2015
Abstract:
Competition between collective states like charge-density-wave and superconductivity, unencumbered by the spin degrees of freedom, is played out in some of the transition metal dichalcogenides. Although 2H-NbSe2 has received much less attention than some of the other members of the family (such as 1T-TiSe2 and 2H-TaSe2) of late, it shows superconductivity at 7.2 K and incommensurate charge ordering at 33 K. Recent experiments, notably angle resolved photoemission spectroscopy, have cast serious doubts on the theories based on Fermi surface nesting and electron-phonon interaction. The normal state has been found to be a poor, incoherent metal and remarkably, the coherence increases in the broken symmetry state. From a preformed excitonic liquid scenario, we show that there exists a natural understanding of the experimental data on 2H-NbSe2, based on electron-electron interaction. The collective instabilities, in this scenario, are viewed as a condensation of an incoherent excitonic liquid already present at high temperature.

Title:
Muon spin rotation and neutron scattering study of the noncentrosymmetric tetragonal compound CeAuAl3
Authors:
Adroja, DT; de la Fuente, C; Fraile, A; Hillier, AD; Daoud-Aladine, A; Kockelmann, W; Taylor, JW; Koza, MM; Burzuri, E; Luis, F; Arnaudas, JI; del Moral, A Author Full Names: Adroja, D. T.; de la Fuente, C.; Fraile, A.; Hillier, A. D.; Daoud-Aladine, A.; Kockelmann, W.; Taylor, J. W.; Koza, M. M.; Burzuri, E.; Luis, F.; Arnaudas, J. I.; del Moral, A.
Source:
PHYSICAL REVIEW B, 91 (13):10.1103/PhysRevB.91.134425 APR 24 2015
Abstract:
We have investigated the noncentrosymmetric tetragonal heavy fermion compound CeAuAl3 using muon spin rotation (mu SR), neutron diffraction (ND), and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport, and thermal properties. Themagnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with, possibly, another magnetic transition near 0.18 K. The heat capacity shows a sharp lambda-type anomaly at 1.1 K in zero field, which broadens and moves to a higher temperature in an applied magnetic field. Our zero-field mu SR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further, the ND study reveals an incommensurate magnetic order with a magnetic propagation vector k = (0,0,0.52(1)) and a spiral structure of Ce moments coupled ferromagnetically within the ab plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 and 24.6 meV in the paramagnetic phase of CeAuAl3 that can be explained on the basis of the CEF theory and the Kramer's theorem for a Ce ion having a 4f(1) electronic state. Furthermore, low energy quasielastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuations below 30 K. We have estimated a Kondo temperature of T-K = 3.5 K from the quasielastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl3 The CEF parameters, energy level scheme, and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl3.

Title:
One-dimensional chain melting in incommensurate potassium
Authors:
McBride, EE; Munro, KA; Stinton, GW; Husband, RJ; Briggs, R; Liermann, HP; McMahon, MI Author Full Names: McBride, E. E.; Munro, K. A.; Stinton, G. W.; Husband, R. J.; Briggs, R.; Liermann, H. -P.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144111 APR 22 2015
Abstract:
Between 19 and 54 GPa, potassium has a complex composite incommensurate host-guest structure which undergoes two intraphase transitions over this pressure range. The temperature dependence of these host-guest phases is further complicated by the onset of an order-disorder transition in their guest chains. Here, we report single-crystal, quasi-single-crystal, and powder synchrotron x-ray diffraction measurements of this order-disorder phenomenon in incommensurate potassium to 47 GPa and 750 K. The so-called chain melting transition is clearly visible over a 22 GPa pressure range, and there are significant changes in the slope of the phase boundary which divides the ordered and disordered phases, one of which results from the intraphase transitions in the guest structure.

Title:
Structures of spherical viral capsids as quasicrystalline tilings
Authors:
Konevtsova, OV; Lorman, VL; Rochal, SB Author Full Names: Konevtsova, O. V.; Lorman, V. L.; Rochal, S. B.
Source:
PHYSICS OF THE SOLID STATE, 57 (4):810-814; 10.1134/S1063783415040125 APR 2015
Abstract:
Spherical viral shells with icosahedral symmetry have been considered as quasicrystalline tilings. Similarly to known Caspar-Klug quasi-equivalence theory, the presented approach also minimizes the number of conformations necessary for the protein molecule bonding with its neighbors in the shell, but is based on different geometrical principles. It is assumed that protein molecule centers are located at vertices of tiles with identical edges, and the number of different tile types is minimal. Idealized coordinates of nonequivalent by symmetry protein positions in six various capsid types are obtained. The approach describes in a uniform way both the structures satisfying the well-known Caspar-Klug geometrical model and the structures contradicting this model.

Update: 7-May-2015


Title:
The question of intrinsic origin of the metal-insulator transition in i-AlPdRe quasicrystal
Authors:
Delallaye, J; Berger, C Author Full Names: Delallaye, Julien; Berger, Claire
Source:
EUROPEAN PHYSICAL JOURNAL B, 88 (4):10.1140/epjb/e2015-50720-7 APR 15 2015
Abstract:
The icosahedral (i-) AlPdRe is the most resistive quasicrystalline alloy discovered so far. Resistivities (rho) of 1 Omega cm at 4 K and correlated resistance ratios (RRR = rho(4) kappa/rho(300) K) of more than 200 are observed in polycrystalline samples. These values are two orders of magnitude larger than for the isomorphous i-AlPdMn phase. We discuss here the controversial microscopic origin of the i-AlPdRe alloy electrical specificity. It has been proposed that the high resistivity values are due to extrinsic parameters, such as secondary phases or oxygen contamination. From comprehensive measurements and data from the literature including electronic transport correlated with micro structural and micro chemical analysis, we show that on the contrary there is mounting evidence in support of an origin intrinsic to the i-phase. Similarly to the other quasicrystalline alloys, the electrical resistivity of the i-AlPdRe samples depends critically on minute changes in the structural quality and chemical composition. The low resistivity in i-AlPdRe single-grains compared to polycrystaline samples can be explained by difference in chemical composition, heterogeneity and thermal treatment.

Title:
Beyond Entropy: Magnetic Forces Induce Formation of Quasicrystalline Structure in Binary Nanocrystal Superlattices
Authors:
Yang, ZJ; Wei, JJ; Bonville, P; Pileni, MP Author Full Names: Yang, Zhijie; Wei, Jingjing; Bonville, Pierre; Pileni, Marie-Paule
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (13):4487-4493; 10.1021/jacs.5b00332 APR 8 2015
Abstract:
Here, it is shown that binary superlattices of Co/Ag nanocrystals with the same size, surface coating, differing by their type of crystallinity are governed by Co-Co magnetic interactions. By using 9 nm amorphous-phase Co nanocrystals and 4 nm polycrystalline Ag nanocrystals at 25 degrees C, triangle-shaped NaCl-type binary nanocrystal superlattices are produced driven by the entropic force, maximizing the packing density. By contrast, using ferromagnetic 9 nm single domain (hcp) Co nanocrystals instead of amorphous-phase Co, dodecagonal quasicrystalline order is obtained, together with less-packed phases such as the CoAg13 (NaZn13-type), CoAg (AuCu-type), and CoAg3 (AuCu3-type) structures. On increasing temperature to 65 degrees C, 9 nm hcp Co nanocrystals become superparamagnetic, and the system yields the CoAg3 (AuCu3-type) and CoAg2 (AlB2-type) structures, as observed with 9 nm amorphous Co nanocrystals. Furthermore, by decreasing the Co nanocrystal size from 9 to 7 nm, stable AlB2-type binary nanocrystal superlattices are produced, which remain independent of the crystallinity of Co nanocrystals with the superparamagnetic state.

Title:
Incommensurate and commensurate modulations of Ba5RTi3Nb7O30 (R = La, Nd) tungsten bronzes and the ferroelectric domain structures
Authors:
Mao, MM; Li, K; Zhu, XL; Chen, XM Author Full Names: Mao, Min Min; Li, Kun; Zhu, Xiao Li; Chen, Xiang Ming
Source:
JOURNAL OF APPLIED PHYSICS, 117 (13):10.1063/1.4916723 APR 7 2015
Abstract:
Incommensurate and commensurate structural modulations of Ba5RTi3Nb7O30 (R=La, Nd) tungsten bronze ceramics were investigated by using a cooling holder equipped transmission electron microscopy in the temperature range from 100 K to 363 K. The incommensurate modulation was observed in both Ba5LaTi3Nb7O30 and Ba5NdTi3Nb7O30 at room temperature, while there was a transition from incommensurate tilted structure to commensurate superstructure for Ba5NdTi3Nb O-7(30) with decreasing temperature. The incommensurate and commensurate modulations were determined by the A-site occupancy of Ba and R cations. The A-site disorder resulted in larger incommensurability parameter delta and the diffusion of the *satellite reflection* spots. The effect of A-site disorder on the coupling between long-range dipolar order and the commensurate modulation was also discussed. The obvious ferroelectric 180 degrees domains with spike-like shape parallel to c axis were observed for Ba5NdTi3Nb7O30, while no macro ferroelectric domain was determined for Ba5LaTi3Nb7O30. (C) 2015 AIP Publishing LLC.

Title:
Periodically distributed objects with quasicrystalline diffraction pattern
Authors:
Wolny, J; Kuczera, P; Strzalka, R Author Full Names: Wolny, Janusz; Kuczera, Pawel; Strzalka, Radoslaw
Source:
APPLIED PHYSICS LETTERS, 106 (13):10.1063/1.4916830 MAR 30 2015
Abstract:
It is possible to construct fully periodically distributed objects with a diffraction pattern identical to the one obtained for quasicrystals. These objects are probability distributions of distances obtained in the statistical approach to aperiodic structures distributed periodically. The diffraction patterns have been derived by using a two-mode Fourier transform-a very powerful method not used in classical crystallography. It is shown that if scaling is present in the structure, this two-mode Fourier transform can be reduced to a regular Fourier transform with appropriately rescaled scattering vectors and added phases. Detailed case studies for model sets 1D Fibonacci chain and 2D Penrose tiling are discussed. Finally, it is shown that crystalline, quasicrystalline, and approximant structures can be treated in the same way. (C) 2015 AIP Publishing LLC.

Update: 30-Apr-2015


Title:
Correlation effects and non-collinear magnetism in the doped Hubbard model
Authors:
Igoshev, PA; Timirgazin, MA; Gilmutdinov, VF; Arzhnikov, AK; Irkhin, VY Author Full Names: Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 383 2-7; 10.1016/j.jmmm.2014.10.031 JUN 1 2015
Abstract:
The ground-state magnetic phase diagram is investigated for the two- and three-dimensional t-t' Hubbard model. We take into account commensurate ferro-, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often missed in previous investigations. We trace the influence of correlation effects on the stability of both spiral and collinear magnetic order by comparing the results of employing both the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave boson approach by Kotliar and Ruckenstein with correlation effects included. We found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistic large Hubbard U, if the correlation effects are taken into account. The electronic phase separation plays an important role in the formation of magnetic states and corresponding regions are wide, especially in the vicinity of half-filling. The details of magnetic ordering for different cubic lattices are discussed. (C) 2014 Elsevier B.V. All rights reserved

Title:
Structural, vibrational, and dielectric properties of Ruddlesden-Popper Ba2ZrO4 from first principles
Authors:
Louis, L; Nakhmanson, SM Author Full Names: Louis, Lydie; Nakhmanson, Serge M.
Source:
PHYSICAL REVIEW B, 91 (13):10.1103/PhysRevB.91.134103 APR 13 2015
Abstract:
Using first-principles computational techniques, we have investigated the structural, vibrational, and dielectric properties of a Ruddlesden-Popper-type layered oxide Ba2ZrO4 subjected to a wide range of biaxial strains emulating epitaxial thin-film environment. Under compressive strains, this compound experiences an incommensurate distortion characterized by planar displacements of individual perovskite slabs away from their high symmetry positions. On the other hand, under increasing epitaxial tension, the original centrosymmetric structure becomes unstable-first, with respect to antiferrodistortive oxygen cage rotations and then also with respect to in-plane polar distortions. Both the incommensurate-to-commensurate and the nonpolar-to-polar phase transformations are accompanied by anomalies of the static dielectric response, however, only in the latter case a divergence of the in-plane dielectric constant is observed. Remarkably, even after the transition into the ferroelectric state (with polarization of up to 0.12 C/m(2) at 3.5% tension) dielectric permittivity of Ba2ZrO4 remains unusually high, which is explained by an emergence of a Goldstone-like excitation in the system manifested through an in-plane libration of the polarization vector. Since Ba2ZrO4 displays a yet poorly understood tendency to absorb small molecules, such as water and CO2, acquiring better insights into the physical underpinnings of its behavior can produce more efficient functional materials for applications in advanced technologies for carbon sequestration.

Title:
Charge-Density Wave in Ca-Intercalated Bilayer Graphene Induced by Commensurate Lattice Matching
Authors:
Shimizu, R; Sugawara, K; Kanetani, K; Iwaya, K; Sato, T; Takahashi, T; Hitosugi, T Author Full Names: Shimizu, Ryota; Sugawara, Katsuaki; Kanetani, Kohei; Iwaya, Katsuya; Sato, Takafumi; Takahashi, Takashi; Hitosugi, Taro
Source:
PHYSICAL REVIEW LETTERS, 114 (14):10.1103/PhysRevLett.114.146103 APR 7 2015
Abstract:
We report the emergence of a charge-density wave (CDW) in Ca-intercalated bilayer graphene (C6CaC6), the thinnest limit of superconducting C6Ca, observed by low-temperature, high-magneticfield scanning tunneling microscopy or spectroscopy, and angle-resolved photoemission spectroscopy. While the possible superconductivity was not observed in epitaxially grown C6CaC6 on a SiC substrate, a CDW order different from that observed on the surface of bulk C6Ca was observed. It is inferred that the CDW state is induced by the potential modulation due to the commensurate lattice matching between the C6CaC6 film and the SiC substrate.

Title:
Microstructure and phase transformation of as-cast and annealed Mg-4Zn-1Y alloy containing quasi-crystal phase
Authors:
Yang, Y; Zhang, K; Li, XG; Li, YJ; Ma, ML; Shi, GL; Yuan, JW Author Full Names: Yang, Yang; Zhang, Kui; Li, Xing-Gang; Li, Yong-Jun; Ma, Ming-Long; Shi, Guo-Liang; Yuan, Jia-Wei
Source:
RARE METALS, 34 (4):239-244; 10.1007/s12598-014-0443-8 APR 2015
Abstract:
By means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses, the microstructures of as-cast and heat-treated Mg-4Zn-1Y (wt%) alloy containing quasi-crystal phase were studied. The microstructure of the as-cast alloy consists of alpha-Mg solid solution grains, intermetallic particles and eutectic phases (W-phase and I-phase), and huge grains with serious dendritic segregation are clearly observed. After heat treatment, phase transformation and dissolution occur in the alloy and many phases remain. When the alloy was treated above 410 A degrees C, the eutectic phases transform into spherical shape as the I-phase turns to W-phase. After heat treatment for long time, the alloy is over burnt and the W-phase decomposes to Mg-Y binary phase.

Title:
Microstructural changes in quasicrystalline Al - Mn - Be - Cu alloy after various heat treatments
Authors:
Strekelj, N; Naglic, I; Klancnik, G; Nagode, A; Markoli, B Author Full Names: Strekelj, Neva; Naglic, Iztok; Klancnik, Grega; Nagode, Ales; Markoli, Bostjan
Source:
INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, 106 (4):342-351; 10.3139/146.111195 APR 2015
Abstract:
In this study we investigated the microstructural changes after a variety of heat treatments of the quasicrystalline Al - Mn - Be - Cu alloy. In addition, we report on Vickers microhardness measurements and tensile-test results for the same materials. The samples were produced in a conventional manner, i.e., melting in an electrical resistance furnace in air and a gravitational casting process using a round copper die, which was in the form of a tensile-test specimen with a diameter of 5 mm. After the casting, some of the samples were just solution treated (annealed) and then quenched in water, while others were additionally aged (artificially - T6, or naturally - T4) or directly aged after the casting. In comparison to the as-cast state, the Vickers microhardness values of the aluminum-based matrix and the tensile properties of the samples decreased when just the solution treatment, T4 or T6 treatment was performed. The tensile properties also decreased after the heat treatments. A microstructural inspection revealed that the microstructural changes occurred already during the solution treatment, i.e., the formation of the phases Be4Al(Mn,Cu) and tau(1)-Al29Mn6Cu4 on the approximant H-Al4Mn and quasicrystalline i-phase particles' edges and the occurrence of precipitates in the alpha(Al) matrix. The precipitates that would additionally contribute to the hardening of the alloy did not form. The directly aged samples showed little or no increase in microhardness values in comparison to the as-cast samples, but possibilities of theta '' precipitates being formed from the already saturated matrix after the casting could not be excluded. After all the heat treatments the quasicrystalline i-phase, as a primary and eutectic phase, was preserved.

Title:
Influence of I-phase and W-phase on microstructure and mechanical properties of Mg-8Li-3Zn alloy
Authors:
Wei, GB; Peng, XD; Zhang, B; Hadadzadeh, A; Xu, TC; Xie, WD Author Full Names: Wei, Guo-bing; Peng, Xiao-dong; Zhang, Bao; Hadadzadeh, Amir; Xu, Tian-cai; Xie, Wei-dong
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 25 (3):713-720; 10.1016/S1003-6326(15)63656-1 MAR 2015
Abstract:
Microstructures and mechanical properties of LZ83-xY alloys containing I-phase and W-phase were investigated by XRD, OM, SEM and EDS. The experimental results show that the content of I-phase and W-phase changes by varying Zn/Y mass ratio in the LZ83-xY alloys. The cohesion of I-phase/alpha-Mg eutectic pockets can enhance the strength in the as-cast LZ83-0.5Y and LZ83-1.0Y alloys, while the W-phase has no obvious strengthening effect on the LZ83-1.5Y alloy. In the extruded alloys, the I-phase and W-phase were extruded into the particles with nanoscale size in the beta-Li matrix phase. The dispersion strengthening of W-phase was more obvious because of the higher volume fraction. The ultimate tensile strength of extruded LZ83-1.5Y alloy is up to 238 MPa while the elongation is up to 20%.

Title:
Topological Hofstadter insulators in a two-dimensional quasicrystal
Authors:
Tran, DT; Dauphin, A; Goldman, N; Gaspard, P Author Full Names: Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085125 FEB 27 2015
Abstract:
We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.

Title:
The refined theory of 2D quasicrystal deep beams based on elasticity of quasicrystals
Authors:
Gao, Y; Yu, LY; Yang, LZ; Zhang, LL Author Full Names: Gao, Yang; Yu, Lian-Ying; Yang, Lian-Zhi; Zhang, Liang-Liang
Source:
STRUCTURAL ENGINEERING AND MECHANICS, 53 (3):411-427; FEB 10 2015
Abstract:
Based on linear elastic theory of quasicrystals, various equations and solutions for quasicrystal beams are deduced systematically and directly from plane problem of two-dimensional quasicrystals. Without employing ad hoc stress or deformation assumptions, the refined theory of beams is explicitly established from the general solution of quasicrystals and the Lur'e symbolic method. In the case of homogeneous boundary conditions, the exact equations and exact solutions for beams are derived, which consist of the fourth-order part and transcendental part. In the case of non-homogeneous boundary conditions, the exact governing differential equations and solutions under normal loadings only and shear loadings only are derived directly from the refined beam theory, respectively. In two illustrative examples of quasicrystal beams, it is shown that the exact or accurate analytical solutions can be obtained in use of the refined theory.

Title:
Low-Temperature Physical Properties of Single-Crystalline EuCoGe3 and EuRhGe3
Authors:
Bednarchuk, O; Kaczorowski, D Author Full Names: Bednarchuk, O.; Kaczorowski, D.
Source:
ACTA PHYSICA POLONICA A, 127 (2):418-420; FEB 2015
Abstract:
Since a few years europium-based intermetallics have been attracting more and more attention due to their intriguing physical properties with anomalous behaviours in magnetically ordered states. Here, we report on the formation and the bulk physical properties of two tetragonal compounds EuCoGe3 and EuRhGe3, studied on high-quality single-crystalline specimens. In both materials, the Eu ions are in their divalent state, which gives rise to an antiferromagnetic ordering below T-N = 15.4 K and T-N = 11.3 K, respectively. In addition, EuCoGe3 exhibits a successive antiferromagnetic phase transition at T-2 = 13.4 K. Based on some characteristic features in the temperature variations of the magnetic susceptibility, specific heat and electrical resistivity, we suggest that in both germanides an amplitude modulated magnetic structure develops below the respective T-N, with the Eu magnetic moments directed along the crystallographic [001] axis in EuCoGe3 and perpendicular to this direction in EuRhGe3.

Title:
The J(1)-J(2) Model on the Anisotropic Triangular and the Square Lattice: Similarities and Differences
Authors:
Schmidt, B; Thalmeier, P Author Full Names: Schmidt, B.; Thalmeier, P.
Source:
ACTA PHYSICA POLONICA A, 127 (2):324-326; FEB 2015
Abstract:
The Heisenberg model on a triangular lattice is a prime example for a geometrically frustrated spin system. However most experimentally accessible compounds have spatially anisotropic exchange interactions. As a function of this anisotropy, ground states with different magnetic properties can be realized. On the other hand, the J(1)-J(2) model on the square lattice is a well-known example for frustration induced by competing exchange. The classical phase diagrams of the two models are related in a broad range of the control parameter phi - tan(-1)(J(2)/J(1)). In both cases three different types of ground states are realized, each model having a ferromagnetic and an antiferromagnetic region in the phase diagram, and a third phase with columnar magnetic order for the square lattice and an in general incommensurate spiral structure for the triangular lattice. Quantum effects lift degeneracies in the non-FM phases and lead to additional nonmagnetic regions in the phase diagrams. The contribution of zero point fluctuations to ground state energy, wave vector, and ordered moment is discussed.

Title:
Reconstruction of the Exchange Integrals Map of ScFe4Al8 Magnetic Structure
Authors:
Recko, K; Dobrzynski, L; Waliszewski, J; Szymanski, K Author Full Names: Recko, K.; Dobrzynski, L.; Waliszewski, J.; Szymanski, K.
Source:
ACTA PHYSICA POLONICA A, 127 (2):424-426; FEB 2015
Abstract:
The influence of the dipolar as well as crystal field interaction as the main reasons of the noncollineaxity and incommensurability of the 3d-3d-3p alloy belonging to ThMn12 family is investigated. Available data on the single crystal neutron scattering experiments for ScFe4Al8 compound are discussed. The values and directions of the spin ordering found by magnetic diffraction are compared to that one derived from ground state configurations obtained by a simulated annealing algorithm.

Update: 23-Apr-2015


Title:
Crystal structure determination of incommensurate modulated martensite in Ni-Mn-In Hensler alloys
Authors:
Yan, HL; Zhang, YD; Xu, N; Senyshyn, A; Brokmeier, HG; Esling, C; Zhao, X; Zuo, L Author Full Names: Yan, Haile; Zhang, Yudong; Xu, Nan; Senyshyn, Anatoliy; Brokmeier, Heinz-Guenter; Esling, Claude; Zhao, Xiang; Zuo, Liang
Source:
ACTA MATERIALIA, 88 375-388; 10.1016/j.actamat.2015.01.025 APR 15 2015
Abstract:
The crystal structure of modulated martensite in Mn-rich off-stoichiometric Ni2Mn1.44In0.56 alloy was determined with high-resolution powder neutron diffraction and synchrotron X-ray diffraction in the frame of (3 + 1)-dimensional superspace theory. The average crystal structure and the modulation wave vector were firstly derived by analyzing the reflection separations induced by the martensitic transformation on the basis of the transformation orientation inheritance. This treatment could be applied to predetermine the modulated structures of materials with displacive structural transformation. The crystal structure of modulated martensite was finally refined by the Rietveld method. Results show that the martensite possesses an incommensurate 6M modulated structure of superspace group I2/m(alpha 0 gamma)00, with lattice parameters a= 4.3919(4) angstrom, b = 5.6202(1) angstrom, c = 4.3315(7) angstrom, and beta = 93.044(1)degrees, and the modulation wave vector q = 0.343(7) c.* The detailed site occupations for extra-Mn atoms with respect to the stoichiometric case were investigated by ab initio calculations. The extra-Mn atoms have a preference to be uniformly dispersed. A threefold layered superstructure in the 3-dimensional space was proposed to approximately describe the incommensurate modulated structure. This 6M superstructure model is considered to be representative for off-stoichiometric Ni-(Co)-Mn-In modulated martensite with martensitic transformation around room temperature. The present study is expected to offer an important basis for reliable crystallographic and microstructural characterizations on Ni-Mn-In alloys, so as to understand the underlying mechanisms of their multifunctional magneto-responsive properties. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Magnetic structures in the magnetic phase diagram of Ho2RhIn8
Authors:
Cermak, P; Prokes, K; Ouladdiaf, B; Boehm, M; Kratochvilova, M; Javorsky, P Author Full Names: Cermak, Petr; Prokes, Karel; Ouladdiaf, Bachir; Boehm, Martin; Kratochvilova, Marie; Javorsky, Pavel
Source:
PHYSICAL REVIEW B, 91 (14):10.1103/PhysRevB.91.144404 APR 7 2015
Abstract:
The magnetic phase diagram of the tetragonal Ho2RhIn8 compound has similar features to many related systems, revealing a zero magnetic field AF1 and a field-induced AF2 phases. Details of the magnetic order in the AF2 phase were not reported yet for any of the related compounds. In addition, only the Ho2RhIn8 phase diagram contains a small region of the incommensurate zero-field AF3 phase. We have performed a number of neutron diffraction experiments on single crystals of Ho2RhIn8 using several diffractometers including experiments in both horizontal and vertical magnetic fields up to 4 T. We present details of the magnetic structures in all magnetic phases of the rich phase diagram of Ho2RhIn8. The Ho magnetic moments point along the tetragonal c axis in every phase. The ground-state AF1 phase is characterized by propagation vector k = (1/2,0,0). The more complex ferrimagnetic AF2 phase is described by four propagation vectors k(0) = ( 0,0,0), k(1) = (1/2,0,0), k(2) = ( 0,1/ 2,1/2), k(3) = (1/2,1/2,1/2). The magnetic structure in the AF3 phase is incommensurate with k(AF3) = ( 0.5, delta, 0). Our results are consistent with theoretical calculations based on crystal field theory.

Title:
Taking a closer look for a broader view: combining powder diffraction with electron crystallography for a better understanding of modulated structures
Authors:
Palatinus, L Author Full Names: Palatinus, Lukas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 125-126; 10.1107/S2052520615005910 2 APR 2015

Title:
Resonance-stabilized partial proton transfer in hydrogen bonds of incommensurate phenazine-chloranilic acid
Authors:
Noohinejad, L; Mondal, S; Ali, SI; Dey, S; van Smaalen, S; Schonleber, A Author Full Names: Noohinejad, Leila; Mondal, Swastik; Ali, Sk Imran; Dey, Somnath; van Smaalen, Sander; Schoenleber, Andreas
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 228-234; 10.1107/S2052520615004084 2 APR 2015
Abstract:
The co-crystal of phenazine (Phz) and chloranilic acid (H(2)ca) becomes ferroelectric upon cooling through the loss of inversion symmetry. Further cooling results in the development of an incommensurate ferroelectric phase, followed by a lock-in transition towards a twofold superstructure. Here we present the incommensurately modulated crystal structure of Phz-H(2)ca at T = 139 K with a symmetry given by the superspace group P2(1)(1/2 sigma(2) 1/2)0 and sigma(2) = 0.5139. The modulation mainly affects the positions of the protons within half of the intermolecular hydrogen bonds that are responsible for the spontaneous polarization in all three low-temperature phases. Evidence for proton transfer in part of the hydrogen bonds is obtained from the correlated dependence on the phase of the modulation of the lengths of bonds involved in resonance stabilization of the acidic anion, and much smaller variations of bond lengths of atoms not involved in the resonance mechanism. Incommensurability is explained as competition between proton transfer favored for single hydrogen bonds on the basis of pK(a) values and avoiding unfavorable Coulomb repulsion within the lattice of the resulting ionic molecules.

Title:
Synergy between transmission electron microscopy and powder diffraction: application to modulated structures
Authors:
Batuk, D; Batuk, M; Abakumov, AM; Hadermann, J Author Full Names: Batuk, Dmitry; Batuk, Maria; Abakumov, Artem M.; Hadermann, Joke
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 71 127-143; 10.1107/S2052520615005466 2 APR 2015
Abstract:
The crystal structure solution of modulated compounds is often very challenging, even using the well established methodology of single-crystal Xray crystallography. This task becomes even more difficult for materials that cannot be prepared in a single-crystal form, so that only polycrystalline powders are available. This paper illustrates that the combined application of transmission electron microscopy (TEM) and powder diffraction is a possible solution to the problem. Using examples of anion-deficient perovskites modulated by periodic crystallographic shear planes, it is demonstrated what kind of local structural information can be obtained using various TEM techniques and how this information can be implemented in the crystal structure refinement against the powder diffraction data. The following TEM methods are discussed: electron diffraction (selected area electron diffraction, precession electron diffraction), imaging (conventional high-resolution TEM imaging, high-angle annular dark-field and annular bright-field scanning transmission electron microscopy) and state-of-the-art spectroscopic techniques (atomic resolution mapping using energy-dispersive X-ray analysis and electron energy loss spectroscopy).

Title:
Magnetic ordering and ferroelectricity in multiferroic 2H-AgFeO2: Comparison between hexagonal and rhombohedral polytypes
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Tsujimoto, Y; Belik, AA Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Tsujimoto, Yoshihiro; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 91 (9):10.1103/PhysRevB.91.094434 MAR 30 2015
Abstract:
Magnetic and dielectric properties of the hexagonal triangular lattice antiferromagnet 2H-AgFeO2 have been studied by neutron diffraction, magnetic susceptibility, specific heat, pyroelectric current, and dielectric constant measurements. The ferroelectric polarization, P similar or equal to 5 mu C/m(2), has been found to appear below 11 K due to a polar nature of the magnetic ground state of the system. In the temperature range of 11 K <= T <= 18 K, an incommensurate spin density wave (ICM1) with the nonpolar magnetic point group mmm1' and the k(1) = (0, q(b)(1),0; q(b)(1) = 0.390-0.405) propagation vector takes place. Below 14 K, a proper screw ordering (ICM2) and k(2) = (0, q(b)(2),0; q(b)(2) = 0.385-0.396) appears as a minor phase which coexists with ICM1 and the ground state down to the lowest measured temperature 5.5 K. No ferroelectric polarization associated with the ICM2 phase was observed in agreement with its nonpolar point group 2221'. Finally, a spiral order with cycloid and proper screw components (ICM3), and k(3) = (q(a)(3), q(b)(3),0; q(a)(3) = 0.0467, q(b)(3) = 0.349) emerges below 11 K as the ground state of the system. Based on the deduced magnetic point group 21', we conclude that the ferroelectric polarization in ICM3 is parallel to the c axis and is caused by the inverse Dzyloshinskii-Moriya effect with p(1) proportional to r(ij) x (S-i x S-j). Unlike the rhombohedral 3R-AgFeO2 polytype, the additional contribution to the macroscopic polarization p(2) proportional to S-i x S-j is not allowed in the present case due to the symmetry constraints imposed by the hexagonal lattice of 2H-AgFeO2.

Title:
Field effects with H vertical bar vertical bar b on the incommensurate magnetic structures of multiferroic MnWO4 studied within the superspace formalism
Authors:
Urcelay-Olabarria, I; Garcia-Munoz, JL; Mukhin, AA Author Full Names: Urcelay-Olabarria, I.; Garcia-Munoz, J. L.; Mukhin, A. A.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.104429 MAR 30 2015
Abstract:
We investigate the magnetic-field-induced (H vertical bar vertical bar b) transition in the reference improper multiferroic MnWO4 using superspace formalism. The distinct superspace group symmetries are determined from single-crystal neutron diffraction. The study of the full magnetic symmetry of the incommensurate magnetic phases under field provides the keys for understanding its magnetic and ferroelectric behavior up to 12 T. At moderate fields, below the transition, the magnetic modulations of the two Mn sites in the simple cell are independent. At the field-induced transition between multiferroic phases, the electric polarization undergoes a flip from the monoclinic b axis to the ac plane. An additional component in the polarization is predicted along the c axis, due to a point symmetry change from 2(y) 1' to m(y)1'. In contrast with the low-field phase, above the transition the influence of the magnetic field results in the coupling between the magnetic modulations of the two Mn sites of the original monoclinic cell.

Title:
Updating the phase diagram of the archetypal frustrated magnet Gd3Ga5O12
Authors:
Deen, PP; Florea, O; Lhotel, E; Jacobsen, H Author Full Names: Deen, P. P.; Florea, O.; Lhotel, E.; Jacobsen, H.
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014419 JAN 15 2015
Abstract:
The applied magnetic field and temperature phase diagram of the archetypal frustrated magnet, Gd3Ga5O12, has been reinvestigated using single-crystal magnetometry and polarized neutron diffraction. The updated phase diagram is substantially more complicated than previously reported and can be understood in terms of competing interactions with loops of spins, trimers, and decagons, in addition to competition and interplay between antiferromagnetic, incommensurate, and ferromagnetic order. Several additional distinct phase boundaries are presented. The phase diagram centers around a multiphase convergence to a single point at 0.9 T and similar to 0.35 K, below which, in temperature, a very narrow magnetically disordered region exists. These data illustrate the richness and diversity that arise from frustrated exchange on the three-dimensional hyperkagome lattice.

Title:
Chemical ordering of Co and Ni in a W-(AlCoNi) crystalline approximant related to Al-Co-Ni decagonal quasicrystals studied by atomic resolution energy-dispersive X-ray spectroscopy
Authors:
Yasuhara, A; Hiraga, K Author Full Names: Yasuhara, Akira; Hiraga, Kenji
Source:
PHILOSOPHICAL MAGAZINE LETTERS, 95 (1):52-57; 10.1080/09500839.2015.1006705 JAN 2 2015
Abstract:
A W-(AlCoNi) crystalline approximant, which is closely related to Al-Co-Ni decagonal quasicrystals, in an Al72.5Co20Ni7.5 alloy has been studied by atomic resolution energy-dispersive X-ray spectroscopy (EDS), in an instrument attached to a spherical aberration (Cs)-corrected scanning transmission electron microscope. On high-resolution EDS maps of Co and Ni elements, obtained by integrating many sets of EDS data taken from undamaged areas, chemical ordering of Co and Ni is clearly detected. In the structure of the W-(AlCoNi) phase, consisting of arrangements of transition-metal (TM) atoms located at vertices of pentagonal tilings and pentagonal arrangements of mixed sites (MSs) of TM and Al atoms, Co atoms occupy the TM atom positions with the pentagonal tiling and Ni is enriched in part of the pentagonal arrangements of MSs.

Update: 16-Apr-2015


Title:
Nematic fluctuations and their wave vector in two-dimensional metals
Authors:
Punk, M Author Full Names: Punk, Matthias
Source:
PHYSICAL REVIEW B, 91 (11):10.1103/PhysRevB.91.115131 MAR 17 2015
Abstract:
We revisit the problem of electrons on a square lattice below half-filling close to an Ising-nematic quantum critical point. For Fermi surfaces with sufficiently strong antinodal nesting, the static nematic susceptibility is maximal at the antinodal nesting wave vector within a simple random phase approximation calculation. We present a detailed analysis of the nematic susceptibility within Eliashberg theory and show that the strong interaction between fermions in the antinodal regions shifts the maximum of the nematic susceptibility to slightly larger wave vectors. The corresponding order is akin to the incommensurate charge-density wave with d-wave form factor found recently in some underdoped cuprate materials. At sufficiently high temperatures around T/t similar to 0.1, nematic fluctuations are strongest at zero wave vector.

Title:
Ferroelectricity induced by ferriaxial crystal rotation and spin helicity in a B-site-ordered double-perovskite multiferroic In2NiMnO6
Authors:
Terada, N; Khalyavin, DD; Manuel, P; Yi, W; Suzuki, HS; Tsujii, N; Imanaka, Y; Belik, AA Author Full Names: Terada, Noriki; Khalyavin, Dmitry D.; Manuel, Pascal; Yi, Wei; Suzuki, Hiroyuki S.; Tsujii, Naohito; Imanaka, Yasutaka; Belik, Alexei A.
Source:
PHYSICAL REVIEW B, 91 (10):10.1103/PhysRevB.91.104413 MAR 17 2015
Abstract:
We have performed dielectric measurements and neutron diffraction experiments on the double perovskite In2NiMnO6. A ferroelectric polarization, P similar or equal to 30 mu C/m(2), is observed in a polycrystalline sample below T-N = 26 K where a magnetic phase transition occurs. The neutron diffraction experiment demonstrates that a complex noncollinear magnetic structure with " cycloidal" and " proper screw" components appears below T-N, which has the incommensurate propagation vector k = (k(a),0, k(c); k(a) similar or equal to 0.274, k(c) similar or equal to - 0.0893). The established magnetic point group 21' implies that the macroscopic ferroelectric polarization is along the monoclinic b axis. Recent theories based on the inverse Dzyaloshinskii- Moriya effect allow us to specify two distinct contributions to the polarization of In2NiMnO6. One of them is associated with the cycloidal component, p(1) proportional to r(ij) x (S-i x S-j)(perpendicular to), and the other with the proper screw component, p(2) proportional to [r(ij) center dot ( S-i x S-j)(parallel to)] A. The latter is explained by coupling between spin helicity and " ferriaxial" crystal rotation with macroscopic ferroaxial vector A, characteristic of the B- site ordered perovskite systems with out- of- plane octahedral tilting.

Title:
X-ray standing wave study of Si clusters on a decagonal Al-Co-Ni quasicrystal surface
Authors:
Woodruff, DP; Ledieu, J; Lovelock, KRJ; Jones, RG; Deyko, A; Wearing, LH; McGrath, R; Chaudhuri, A; Li, HI; Su, SY; Mayer, A; Stanisha, NA; Diehl, RD Author Full Names: Woodruff, D. P.; Ledieu, J.; Lovelock, K. R. J.; Jones, Robert G.; Deyko, A.; Wearing, L. H.; McGrath, R.; Chaudhuri, A.; Li, H. I.; Su, S. Y.; Mayer, A.; Stanisha, N. A.; Diehl, R. D.
Source:
PHYSICAL REVIEW B, 91 (11):10.1103/PhysRevB.91.115418 MAR 12 2015
Abstract:
Quantitative adsorption structure determinations on quasicrystals are scarce because most techniques for measuring surface structures are not well suited to the complex and infinite unit cells of quasicrystals. The normal incidence standing x-ray wave field technique presents a solution to these problems because it can be made inherently surface sensitive and does not involve extensive computational effort. We describe a method for applying this technique to adsorbates on quasicrystals, with specific application to a submonolayer of Si atoms on a decagonal Al-Co-Ni surface. We demonstrate the sensitivity of the technique to both adsorption site and geometry, leading to the conclusion that the Si atoms, which form six-atom pentagonal clusters, have an average height of 1.77 +/- 0.05 angstrom above pentagonal hollow sites, with a significant height variation among the Si atoms in the cluster. In particular, the central Si atom sits more deeply than the five surrounding Si atoms, which are, on average, 2.7 angstrom away from the central Si atom. Although this study was performed on a decagonal quasicrystal that is periodic perpendicular to the surface, we describe how the technique can be applied to cases with no periodicity.

Title:
Effect of pointlike impurities on d(x2-y2) charge-density waves in cuprate superconductors
Authors:
Atkinson, WA; Kampf, AP Author Full Names: Atkinson, W. A.; Kampf, A. P.
Source:
PHYSICAL REVIEW B, 91 (10):MAR 12 2015
Abstract:
Many cuprate superconductors possess an unusual charge- ordered phase that is characterized by an approximate dx2 - y2 intraunit cell form factor and a finite modulation wave vector q*. We study the effects of impurities on this charge- ordered phase via a single- band model in which bond order is the analog of charge order in the cuprates. Impurities are assumed to be pointlike and are treated within the self- consistent t- matrix approximation. We show that suppression of bond order by impurities occurs through the local disruption of the dx2 - y2 form factor near individual impurities. Unlike d- wave superconductors, where the sensitivity of Tc to impurities can be traced to a vanishing average of the dx2 - y2 order parameter over the Fermi surface, the response of bond order to impurities is dictated by a few Fermi surface " hotspots." The bond order transition temperature Tbo thus follows a different universal dependence on impurity concentration ni than does the superconducting Tc. In particular, Tbo decreases more rapidly than Tc with increasing ni when there is a nonzero Fermi surface curvature at the hotspots. Based on experimental evidence that the pseudogap is insensitive to Zn doping, we conclude that a direct connection between charge order and the pseudogap is unlikely. Furthermore, the enhancement of stripe correlations in the La- based cuprates by Zn doping is evidence that this charge order is also distinct from stripes.

Title:
Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal
Authors:
Lowe, M; Yadav, TP; Fournee, V; Ledieu, J; McGrath, R; Sharma, HR Author Full Names: Lowe, M.; Yadav, T. P.; Fournee, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.
Source:
JOURNAL OF CHEMICAL PHYSICS, 142 (9):10.1063/1.4913567 MAR 7 2015
Abstract:
The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol. (C) 2015 AIP Publishing LLC.

Title:
Flux Synthesis, Modulated Crystal Structures, and Physical Properties of REMn0.5SeO (RE = La, Ce)
Authors:
Peschke, S; Nitsche, F; Johrendt, D Author Full Names: Peschke, Simon; Nitsche, Fabian; Johrendt, Dirk
Source:
ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE, 641 (3-4):529-536; 10.1002/zaac.201400603 MAR 2015
Abstract:
The selenide oxides REMn0.5SeO (RE = La, Ce) were synthesized by heating RE2O3, RE, Mn, and Se in a NaI/KI flux at 800 degrees C, and their modulated crystal structures determined by X-ray single crystal and powder diffraction {P 1 1 2/n(1/2)0s, Z = 2, LaMn0.5SeO: a = 405.7(1), b = 405.7(1), c = 915.2(1) pm, = 90 degrees, q = [1/10, -1/10, 1/2]; CeMn0.5SeO: a = 402.0(1), b = 401.8(1), c = 910.7(1) pm, = 90.000(4)degrees, q = [0.0789(2), -0.0783(2), 1/2]}. The structures are related to the ZrCuSiAs-type structure with ordered vacancies at the manganese sites. The resulting modulations of the checkerboard pattern in the [Mn0.5Se] layers can be approximated by 10ax10bx2c and 51ax51bx2c supercells in LaMn0.5SeO and CeMn0.5SeO, respectively. Both compounds are insulators. The optical bandgap of LaMn0.5SeO was determined to 2.13 eV from the Kubelka-Munk function. Magnetic measurements indicate antiferromagnetic ordering of the Mn2+ moments with Neel points well above room temperature, as known from related manganese compounds.

Title:
Microstructure and phase compositions of as-cast Mg-3.9Zn-0.6RE (Gd, Y) alloy with different Gd/Y ratios
Authors:
Yang, Y; Zhang, K; Ma, ML; Yuan, JW Author Full Names: Yang, Yang; Zhang, Kui; Ma, Ming-Long; Yuan, Jia-Wei
Source:
RARE METALS, 34 (3):160-163; 10.1007/s12598-014-0444-7 MAR 2015
Abstract:
Mg-Zn-RE (Gd, Y) alloys with different Gd/Y atomic ratios were prepared by conventional casting, and the microstructure of the alloys was studied by multiple means. Icosahedral quasicrystal phases are observed in all alloys. The different Gd/Y atomic ratios affect the microstructures of the alloys irregularly. The alloy with more Gd has large dendritic structure and more complicated phase composition which are composed of I-phase lamellar eutectic, W-phase divorced eutectic, Mg-RE cuboid particles and Mg-Zn binary phases. Other two alloys show similar microstructures and phase compositions with very thin lamellar eutectics which distribute along the interdendritic region, and the lamellar eutectics are formed by I-phase and Mg. The element contents of the I-phases and Mg-RE phases are partially controlled by the Gd/Y atomic ratio.

Title:
Coupling between an incommensurate antiferromagnetic structure and a soft ferromagnet in the archetype multiferroic BiFeO3/cobalt system (vol 91, 014402, 2015)
Authors:
Elzo, M; Moubah, R; Blouzon, C; Sacchi, M; Grenier, S; Belkhou, R; Dhesi, S; Colson, D; Torres, F; Kiwi, M; Viret, M; Jaouen, N Author Full Names: Elzo, Marta; Moubah, Reda; Blouzon, Camille; Sacchi, Maurizio; Grenier, Stephane; Belkhou, Rachid; Dhesi, Sarnjeet; Colson, Dorothee; Torres, Felipe; Kiwi, Miguel; Viret, Michel; Jaouen, Nicolas
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.019903 JAN 30 2015

Update: 9-Apr-2015


Title:
Synthesis and structural analysis of C-60-C-70 two-component fullerene nanowhiskers
Authors:
Konno, T; Wakahara, T; Miyazawa, K Author Full Names: Konno, Toshio; Wakahara, Takatsugu; Miyazawa, Kun'ichi
Source:
JOURNAL OF CRYSTAL GROWTH, 416 41-46; 10.1016/j.jcrysgro.2014.12.016 APR 15 2015
Abstract:
C-60-C-70 two-component fullerene nanowhiskers (C-60-C(70)NWs) were synthesized by liquid-liquid interfacial precipitation (LLIP) using various ratios of C-70 to C-60 and then analyzed using a focused ion beam processing apparatus (FIB-SEM), scanning electron microscopy (SEM). Raman spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD) and high-performance liquid chromatography (HPLC). Both C-60 and C-70 were saturated in the supernatant solutions with fullerene compositions in the mother solutions ranging from 124 mass% C-70 to 73.4 mass% C-70. C-60-C(70)NWs contained a small amount of rhombohedral phase, indicating polymerization of C-60. The solid solubility limit of C-70 in the C-60 matrix was found to be 13.7 mass%. In addition to fine C-60-C(70)NWs, thick C-60-C-70 needle-like crystals were formed. The thick C-60-C-70 needle-like crystals were fractured using a molybdenum probe in the FIB. The fractured surfaces of the C-60-C-70 needle-like crystals showed modulated structures with chemical compositions characteristic of spinodal decomposition. The activation energy of diffusion was determined to be 37.1 kJ/mol. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Broken translational and rotational symmetry via charge stripe order in underdoped YBa2Cu3O6+y
Authors:
Comin, R; Sutarto, R; Neto, EHDS; Chauviere, L; Liang, R; Hardy, WN; Bonn, DA; He, F; Sawatzky, GA; Damascelli, A Author Full Names: Comin, R.; Sutarto, R.; Neto, E. H. da Silva; Chauviere, L.; Liang, R.; Hardy, W. N.; Bonn, D. A.; He, F.; Sawatzky, G. A.; Damascelli, A.
Source:
SCIENCE, 347 (6228):1335-1339; 10.1126/science.1258399 MAR 20 2015
Abstract:
After the discovery of stripelike order in lanthanum-based copper oxide superconductors, charge-ordering instabilities were observed in all cuprate families. However, it has proven difficult to distinguish between unidirectional (stripes) and bidirectional (checkerboard) charge order in yttrium-and bismuth-based materials. We used resonant x-ray scattering to measure the two-dimensional structure factor in the superconductor YBa2Cu3O6+y in reciprocal space. Our data reveal the presence of charge stripe order (i.e., locally unidirectional density waves), which may represent the true microscopic nature of charge modulation in cuprates. At the same time, we find that the well-established competition between charge order and superconductivity is stronger for charge correlations across the stripes than along them, which provides additional evidence for the intrinsic unidirectional nature of the charge order.

Title:
Synchronized collapse and formation of long-period stacking and chemical orders in Mg85Zn6Y9
Authors:
Matsushita, M; Bednarcik, J; Sakata, Y; Akamatsu, S; Nishiyama, N; Michalikoya, J; Yamasaki, M; Kawamura, Y Author Full Names: Matsushita, Masafumi; Bednarcik, Jozef; Sakata, Yuya; Akamatsu, Shutaro; Nishiyama, Norimasa; Michalikoya, Jana; Yamasaki, Michiaki; Kawamura, Yoshihito
Source:
PHYSICA B-CONDENSED MATTER, 461 147-153; 10.1016/j.physb.2014.12.021 MAR 15 2015
Abstract:
Phase transformation of the long period stacking order (LPSO) synchronized with the chemical concentration in Mg85Zn6Y9 has been investigated during both heating and cooling via in situ X-ray diffraction analysis. With increasing temperature, above 800 K, 10H-type LPSO phase collapsed firstly. 10H structural modulation collapsed earlier than the chemical modulation of 5 layers per period. The in plane ordering consisted of aligned L1(2)-type clusters vanished before the collapse of chemical and structural modulation of 18R-type LPSO. After, the chemical and structural modulation of 18R-type LPSO show synchronize collapse. During cooling, the 14H-type LPSO emerged in addition to the 18R-type LPSO. The growths of chemical and structural modulation start at the same temperature. After that, the formation of in plane order consisting of aligned L1(2)-type Zn-Y clusters emerged. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Natural quasicrystal with decagonal symmetry
Authors:
Bindi, L; Yao, N; Lin, C; Hollister, LS; Andronicos, CL; Distler, VV; Eddy, MP; Kostin, A; Kryachko, V; MacPherson, GJ; Steinhardt, WM; Yudovskaya, M; Steinhardt, PJ Author Full Names: Bindi, Luca; Yao, Nan; Lin, Chaney; Hollister, Lincoln S.; Andronicos, Christopher L.; Distler, Vadim V.; Eddy, Michael P.; Kostin, Alexander; Kryachko, Valery; MacPherson, Glenn J.; Steinhardt, William M.; Yudovskaya, Marina; Steinhardt, Paul J.
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep09111 MAR 13 2015
Abstract:
We report the first occurrence of a natural quasicrystal with decagonal symmetry. The quasicrystal, with composition Al71Ni24Fe5, was discovered in the Khatyrka meteorite, a recently described CV3 carbonaceous chondrite. Icosahedrite, Al63Cu24Fe13, the first natural quasicrystal to be identified, was found in the same meteorite. The new quasicrystal was found associated with steinhardtite (Al38Ni32Fe30), Fe-poor steinhardtite (Al50Ni40Fe10), Al-bearing trevorite (NiFe2O4) and Al-bearing taenite (FeNi). Laboratory studies of decagonal Al71Ni24Fe5 have shown that it is stable over a narrow range of temperatures, 1120 K to 1200 K at standard pressure, providing support for our earlier conclusion that the Khatyrka meteorite reached heterogeneous high temperatures [1100 < T(K) <= 1500] and then rapidly cooled after being heated during an impact-induced shock that occurred in outer space 4.5 Gya. The occurrences of metallic Al alloyed with Cu, Ni, and Fe raises new questions regarding conditions that can be achieved in the early solar nebula.

Title:
Group-theoretical analysis of aperiodic tilings from projections of higher-dimensional lattices B-n
Authors:
Koca, M; Koca, NO; Koc, R Author Full Names: Koca, Mehmet; Koca, Nazife Ozdes; Koc, Ramazan
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 175-185; 10.1107/S2053273314025492 2 MAR 2015
Abstract:
A group-theoretical discussion on the hypercubic lattice described by the affine Coxeter-Weyl group W-a(B-n) is presented. When the lattice is projected onto the Coxeter plane it is noted that the maximal dihedral subgroup D-h of W(B-n) with h = 2n representing the Coxeter number describes the h-fold symmetric aperiodic tilings. Higher-dimensional cubic lattices are explicitly constructed for n = 4, 5, 6. Their rank-3 Coxeter subgroups and maximal dihedral subgroups are identified. It is explicitly shown that when their Voronoi cells are decomposed under the respective rank-3 subgroupsW(A(3)), W(H-2) x W(A(1)) and W(H-3) one obtains the rhombic dodecahedron, rhombic icosahedron and rhombic triacontahedron, respectively. Projection of the lattice B-4 onto the Coxeter plane represents a model for quasicrystal structure with eightfold symmetry. The B-5 lattice is used to describe both fivefold and tenfold symmetries. The lattice B-6 can describe aperiodic tilings with 12-fold symmetry as well as a three-dimensional icosahedral symmetry depending on the choice of subspace of projections. The novel structures from the projected sets of lattice points are compatible with the available experimental data.

Title:
Thermodynamic and neutron diffraction studies on multiferroic NdMn2O5
Authors:
Chattopadhyay, S; Baledent, V; Auban-Senzier, P; Pasquier, C; Doubroysky, C; Greenblatt, M; Foury-Leylekian, P Author Full Names: Chattopadhyay, S.; Baledent, V.; Auban-Senzier, P.; Pasquier, C.; Doubroysky, C.; Greenblatt, M.; Foury-Leylekian, P.
Source:
PHYSICA B-CONDENSED MATTER, 460 214-217; SI 10.1016/j.physb.2014.11.074 MAR 1 2015
Abstract:
Magnetically frustrated RMn2O5 oxides have attracted considerable attention in recent years, because most of the members of this family show spin ordering induced dielectric polarization along with strong magneto-electric coupling. Although the true origin of the ferroelectricity is still a matter of debate, it has been observed that the magneto-electric phase diagram can be substantially tuned with the variation of rare earth elements. In this work, we have chosen NdMn2O5 as the compound of our interest since it lies exactly in between the ferroelectric and non-ferroelectric members of this family and also, because there are few investigations performed on RMn2O5 systems with large rare earth atoms. With the combination of heat capacity, magnetic susceptibility, dielectric permittivity, powder X-ray diffraction, and powder neutron diffraction measurements, it has been found that NdMn2O5 undergoes an incommensurate magnetic ordering around 30 K followed by a possible ferroelectric-like transition at similar to 26 K. Another lock-in kind of magnetic transition appears when the temperature is decreased to similar to 15 K. With further lowering of temperature, an antiferromagnetic ordering, which is presumably associated with the Nd3+, is achieved near 4 K. This study thus sheds light on a new compound of the RMn2O5 series presenting different multiferroic properties. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Generalized Penrose tiling as a quasilattice for decagonal quasicrystal structure analysis
Authors:
Chodyn, M; Kuczera, P; Wolny, J Author Full Names: Chodyn, Maciej; Kuczera, Pawel; Wolny, Janusz
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 71 161-168; 10.1107/S2053273314024917 2 MAR 2015
Abstract:
The generalized Penrose tiling is, in fact, an infinite set of decagonal tilings. It is constructed with the same rhombs (thick and thin) as the conventional Penrose tiling, but its long-range order depends on the so-called shift parameter (s is an element of < 0; 1)). The structure factor is derived for the arbitrarily decorated generalized Penrose tiling within the average unit cell approach. The final formula works in physical space only and is directly dependent on the s parameter. It allows one to straightforwardly change the long-range order of the refined structure just by changing the s parameter and keeping the tile decoration unchanged. This gives a great advantage over the higher-dimensional method, where every change of the tiling (change in the s parameter) requires the structure model to be built from scratch, i.e. the fine division of the atomic surfaces has to be redone.

Title:
Analytical electron microscopy study on gallium nitride systems doped with manganese and iron
Authors:
Meingast, A; Quezada, AN; Devillers, T; Kovacs, A; Albu, M; Fladischer, S; Bonanni, A; Kothleitner, G Author Full Names: Meingast, Arno; Quezada, Andrea Navarro; Devillers, Thibaut; Kovacs, Andras; Albu, Mihela; Fladischer, Stefanie; Bonanni, Alberta; Kothleitner, Gerald
Source:
SEMICONDUCTOR SCIENCE AND TECHNOLOGY, 30 (3):10.1088/0268-1242/30/3/035002 MAR 2015
Abstract:
Modulated structures of gallium nitride (GaN) doped with transition metal ions (here Fe, Mn) are investigated by analytical (scanning) transmission electron microscopy to gain insight into the structural arrangement and chemical composition of the material, known to be critically correlated to the magnetic response and hence the functionality of these technologically relevant systems. Three classes of samples are considered: (i) homogeneous (dilute) (Ga, Mn) N; (ii) delta-Mn-doped (Ga, delta-Mn) N and phase separated (Ga, Fe) N, containing Fe-rich nanocrystals. The combination of various microscopic techniques employed, allows for a quantitative determination of the distribution of the magnetic ions in the samples, providing essential information on the structural and chemical asset of these systems.

Title:
Direct observation of single-electron solitons and Friedel oscillations in a quasi-one dimensional material with incommensurate charge-density waves
Authors:
Brun, C; Brazovskii, S; Wang, ZZ; Monceau, P Author Full Names: Brun, Christophe; Brazovskii, Serguei; Wang, Zhao-Zhong; Monceau, Pierre
Source:
PHYSICA B-CONDENSED MATTER, 460 88-92; SI 10.1016/j.physb.2014.11.046 MAR 1 2015
Abstract:
We have performed scanning tunneling microscopy experiments in the quasi-one dimensional charge density wave (CDW) system NbSe3, where we could image and study in detail individual solitons corresponding to the self-trapping of a single electron. Our analysis shows that the type of soliton we observed is an "Amplitude Soliton", characterized by a vanishing CDW amplitude at the soliton center and by a pi-shift of its phase along the chain direction. Pairs of solitons or multiple solitons were also observed. Such observations could be made only in the high-temperature COW phase. Additionally, one-dimensional Friedel oscillations around charged defects could also be imaged and are found to be superimposed to the COW. The distinction between amplitude solitons and Friedel oscillations can be made without any ambiguity. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Topological Hofstadter insulators in a two-dimensional quasicrystal
Authors:
Tran, DT; Dauphin, A; Goldman, N; Gaspard, P Author Full Names: Tran, Duc-Thanh; Dauphin, Alexandre; Goldman, Nathan; Gaspard, Pierre
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085125 FEB 27 2015
Abstract:
We investigate the properties of a two-dimensional quasicrystal in the presence of a uniform magnetic field. In this configuration, the density of states (DOS) displays a Hofstadter-butterfly-like structure when it is represented as a function of the magnetic flux per tile. We show that the low-DOS regions of the energy spectrum are associated with chiral edge states, in direct analogy with the Chern insulators realized with periodic lattices. We establish the topological nature of the edge states by computing the topological Chern number associated with the bulk of the quasicrystal. This topological characterization of the nonperiodic lattice is achieved through a local (real-space) topological marker. This work opens a route for the exploration of topological-insulating materials in a wide range of nonperiodic lattice systems, including photonic crystals and cold atoms in optical lattices.

Title:
Effects of Initial States on the Spinodal Decomposition of Quenched and Melt-Spun Cu-15Ni-8Sn Alloy
Authors:
Kondo, SI; Masusaki, A; Ogawa, K; Morimura, T; Nakashima, H Author Full Names: Kondo, Shin-ichiro; Masusaki, Akinori; Ogawa, Kento; Morimura, Takao; Nakashima, Hiromichi
Source:
MATERIALS TRANSACTIONS, 56 (1):23-29; 10.2320/matertrans.M2014234 JAN 2015
Abstract:
We investigate early stages of spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a non-melt-spun alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350 degrees C for 120 min, whereas they are found in the quenched sample after a heat treatment at 350 degrees C for 60 min. TEM observations of a quenched sample after aging at 350 degrees C for 60 mm indicate the presence of a modulated structure (lambda = 5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (lambda: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt-spun samples, cluster size was much smaller as a result of a high cooling rate (approximate to 8 x 10(5)degrees C/s).

Update: 2-Apr-2015


Title:
First-principles study of structurally modulated multiferroic CaMn7O12
Authors:
Cao, K; Johnson, RD; Perks, N; Giustino, F; Radaelli, PG Author Full Names: Cao, Kun; Johnson, Roger D.; Perks, Natasha; Giustino, Feliciano; Radaelli, Paolo G.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064422 FEB 27 2015
Abstract:
study the electronic and magnetic structures of multiferroic CaMn7O12 by first-principles calculations, based on the experimentally determined modulated crystal structure. We confirm the presence of a 3d orbital modulation of the Mn2 (Mn3+) sites, previously inferred from the Jahn-Teller crystal distortions. Our results indicate that in the multiferroic phase themagnetic structure of the Mn3 (Mn4+) sites is anharmonically modulated via orbitally mediated coupling with the structural modulation, and that the Dzyaloshinskii-Moriya and exchange striction mechanisms contribute equally to the polarization.

Title:
Disorder from order among anisotropic next-nearest-neighbor Ising spin chains in SrHo2O4
Authors:
Wen, JJ; Tian, W; Garlea, VO; Koohpayeh, SM; McQueen, TM; Li, HF; Yan, JQ; Rodriguez-Rivera, JA; Vaknin, D; Broholm, CL Author Full Names: Wen, J. -J.; Tian, W.; Garlea, V. O.; Koohpayeh, S. M.; McQueen, T. M.; Li, H. -F.; Yan, J. -Q.; Rodriguez-Rivera, J. A.; Vaknin, D.; Broholm, C. L.
Source:
PHYSICAL REVIEW B, 91 (5):10.1103/PhysRevB.91.054424 FEB 26 2015
Abstract:
We describe why Ising spin chains with competing interactions in SrHo2O4 segregate into ordered and disordered ensembles at low temperatures (T). Using elastic neutron scattering, magnetization, and specific heat measurements, the two distinct spin chains are inferred to have Neel (up arrow down arrow up arrow down arrow) and double-Neel (up arrow up arrow down arrow down arrow) ground states, respectively. Below T-N = 0.68(2) K, the Neel chains develop three-dimensional long range order (LRO), which arrests further thermal equilibration of the double-Neel chains so they remain in a disordered incommensurate state for T below T-S = 0.52(2) K. SrHo2O4 distills an important feature of incommensurate low dimensional magnetism: kinetically trapped topological defects in a quasi-d-dimensional spin system can preclude order in d + 1 dimensions.

Title:
Quantum critical behavior in heavily doped LaFeAsO1-xHx pnictide superconductors analyzed using nuclear magnetic resonance
Authors:
Sakurai, R; Fujiwara, N; Kawaguchi, N; Yamakawa, Y; Kontani, H; Iimura, S; Matsuishi, S; Hosono, H Author Full Names: Sakurai, R.; Fujiwara, N.; Kawaguchi, N.; Yamakawa, Y.; Kontani, H.; Iimura, S.; Matsuishi, S.; Hosono, H.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064509 FEB 19 2015
Abstract:
We studied the quantum critical behavior of the second antiferromagnetic (AF) phase in the heavily electron-doped high-T-c pnictide, LaFeAsO1-x H-x, by using a As-75 and H-1 nuclear magnetic resonance (NMR) technique. In the second AF phase, we observed a spatially modulated spin-density-wave-like state up to x = 0.6 from the NMR spectral line shape and detected a low-energy excitation gap from the nuclear relaxation time T-1 of As-75. The excitation gap closes at the AF quantum critical point (QCP) at x approximate to 0.49. The superconducting phase in a lower-doping regime contacts the second AF phase only at the AF QCP, and both phases are segregated from each other. The absence of AF critical fluctuations and the enhancement of the in-plane electric anisotropy are key factors for the development of superconductivity.

Title:
Disruption of quantum oscillations by an incommensurate charge density wave
Authors:
Zhang, Y; Maharaj, AV; Kivelson, S Author Full Names: Zhang, Yi; Maharaj, Akash V.; Kivelson, Steven
Source:
PHYSICAL REVIEW B, 91 (8):10.1103/PhysRevB.91.085105 FEB 9 2015
Abstract:
Because a material with an incommensurate charge density wave (ICDW) is only quasiperiodic, Bloch's theorem does not apply and there is no sharply defined Fermi surface. We will show that, as a consequence, there are no quantum oscillations which are truly periodic functions of 1/B (where B is the magnitude of an applied magnetic field). For a weak ICDW, there exist broad ranges of 1/B in which approximately periodic variations occur, but with frequencies that vary inexorably in an unending cascade with increasing 1/B. For a strong ICDW, e.g., in a quasicrystal, no quantum oscillations survive at all. Rational and irrational numbers really are different.

Title:
Direct observation of Ca-Na ordering and structure polarity in Ca-rich intermediate plagioclase feldspar with incommensurate modulated structure
Authors:
Xu, HF Author Full Names: Xu, Huifang
Source:
AMERICAN MINERALOGIST, 100 (2-3):510-515; 10.2138/am-2015-5022 FEB-MAR 2015
Abstract:
Ca-Na ordering and structural polarity of subcells in an intermediate plagioclase with modulated structure have been observed using Z-contrast imaging with an aberration-corrected scanning transmission electron microscope. Neighboring lamellar domains with I1 symmetry are related by inversion twin operation, instead of anti-phase domain boundaries (or APBs) as in all previously reported structure models. The boundaries between lamellar domains have I (1) over bar symmetry instead of C (1) over bar symmetry. Modulated plagioclase has unique Ca-Na and Al-Si ordering structure that is different from those in end-member structures of anorthite and low albite. The modulated structures of intermediate plagioclase are not metastable structures formed during phase transition, but instead thermodynamically stable structures at low temperature due to Ca-Na ordering within the subcells with I1 symmetry.

Update: 26-Mar-2015


Title:
Charge order and resistivity transition of Zn-doped cuprate superconductors
Authors:
de Mello, EVL; Mockli, D Author Full Names: de Mello, E. V. L.; Moeckli, David
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (9):10.1088/0953-8984/27/9/095702 MAR 11 2015
Abstract:
Impurity doping using Zn atoms was largely studied in cuprates because this process substantially reduces the superconducting critical temperature T-c without any effect on the pseudogap onset T*. Earlier theories missed the recently established ubiquitous presence of incommensurate charge modulations in these materials. The charge order is a consequence of a phase separation transition which we describe by a continuity equation of the local free energy density. The Zn atoms generate a local magnetic moment, freezing their neighbors' spins, slowing down the electronic segregation process. Then the Zn-doped properties are that of a granular superconductor whose size of the charge order modulations are dictated by the degree of phase separation.

Title:
Effect of Li on structure and electrochemical hydrogen storage properties of Ti55V10Ni35 quasicrystal alloy
Authors:
Liu, CF; Duan, YH; Ouyang, ZT; Shang, JM; Liu, K; Xing, C; Fu, YG; Liu, WQ; Wang, LM Author Full Names: Liu, Chaofan; Duan, Yuhan; Ouyang, Zhongtao; Shang, Jinming; Liu, Kun; Xing, Cheng; Fu, Yuegang; Liu, Wanqiang; Wang, Limin
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 40 (7):3015-3022; 10.1016/j.ijhydene.2014.12.133 FEB 23 2015
Abstract:
The Ti55V10Ni35 quasicrystal ribbons are synthesized by arc melting and subsequent melt-spinning technique and then Li atoms are infiltrated into this quasicrystal material by the way of electroosmosis. X-ray diffraction results indicate that the pristine quasicrystal Ti55V10Ni35 mainly consists of the icosahedral quasicrystal (I-phase), V-based solid solution phase with BBC structure and face centered cubic (FCC) phase with Ti2Ni-type structure. After infiltrating some amount of Li atoms into Ti55V10Ni35 quasicrystal lattice voids at different electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 respectively, phase structure investigations show that the main phase structures do not change greatly except for the additional lithium phase, which demonstrates that Li does not destroy the phase structure of Ti55V10Ni35 quasicrystal. Ti55V10Ni35 alloy shows the best discharge capacity is 219.8 mAh g(-1) at a current density of 30 mA g(-1). The negative electrode made by Ti55V10Ni35 Li quasicrystal alloys (Li atoms are infiltrated into Ti55V10Ni35 quasicrystal alloy at different the electroosmosis current density (A/mg) of 0.3, 0.6 and 0.9 has a maximum discharge capacity of 257.7 mAh g(-1), 301.8 mAh g(-1) and 238.7 mAh g(-1) at a discharge current density of 30 mA g(-1), respectively. And the high rate discharge ability of alloy electrodes is higher than that of Ti55V10Ni35 quasicrystal alloy at 240 mA g(-1). The Effect of Li on structure of Ti55V10Ni35 quasicrystal has been discussed by measuring the place, mass ratio and chemical state that Li infiltrated into quasicrystal Ti55V10Ni35 lattice. In addition, the electrochemical reaction kinetics of Ti55V10Ni35-Li quasicrystal alloy electrodes is also studied by measuring both the electrochemical impedance spectroscopy and hydrogen diffusion coefficient. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Title:
Density-matrix renormalization group study of the extended Kitaev-Heisenberg model
Authors:
Shinjo, K; Sota, S; Tohyama, T Author Full Names: Shinjo, Kazuya; Sota, Shigetoshi; Tohyama, Takami
Source:
PHYSICAL REVIEW B, 91 (5):10.1103/PhysRevB.91.054401 FEB 4 2015
Abstract:
We study an extended Kitaev-Heisenberg model including additional anisotropic couplings by using the two-dimensional density-matrix renormalization group method. Calculating the ground-state energy, entanglement entropy, and spin-spin correlation functions, we make a phase diagram of the extended Kitaev-Heisenberg model around the spin-liquid phase. We find a zigzag antiferromagnetic phase, a ferromagnetic phase, a 120. antiferromagnetic phase, and two kinds of incommensurate phases around the Kitaev spin-liquid phase. Furthermore, we study the entanglement spectrum of the model, and we find that entanglement levels in the Kitaev spin-liquid phase are degenerate forming pairs, but those in the magnetically ordered phases are nondegenerate. The Schmidt gap defined as the energy difference between the lowest two levels changes at the phase boundary adjacent to the Kitaev spin-liquid phase. However, we find that phase boundaries between magnetically ordered phases do not necessarily agree with the change of the Schmidt gap.

Title:
Modification of the phase composition and structure of the quasicrystalline Al-Cu-Fe alloy prepared by plasma spraying
Authors:
Lepeshev, AA; Bayukov, OA; Rozhkova, EA; Karpov, IV; Ushakov, AV; Fedorov, LY Author Full Names: Lepeshev, A. A.; Bayukov, O. A.; Rozhkova, E. A.; Karpov, I. V.; Ushakov, A. V.; Fedorov, L. Yu.
Source:
PHYSICS OF THE SOLID STATE, 57 (2):255-259; 10.1134/S1063783415020249 FEB 2015
Abstract:
The structural-phase state of quasicrystalline coatings of the Al-Cu-Fe alloy produced under different thermal conditions of plasma spraying (different contact temperatures T (k) of the substrate) has been investigated. It has been shown that sprayed coatings are heterophase with the dominant content of the icosahedral psi and cubic beta phases, the formation and fractional ratio of which depend on spraying conditions. The distribution of probabilities P(QS) of quadrupole splitting in experimental gamma-resonance spectra has been analyzed. The dependence of hyperfine interaction parameters (QS, A) on spraying conditions of the coating has been established. Five nonequivalent positions of resonant iron atoms, the appearance and filling of which are determined by spraying conditions, have been revealed.

Title:
Incommensurate Structure and Phase Transitions in Epitaxial Multiferroic Films
Authors:
Gareeva, ZV; Popkov, AF; Kulagin, NE; Soloviov, SV; Zvezdin, AK Author Full Names: Gareeva, Z. V.; Popkov, A. F.; Kulagin, N. E.; Soloviov, S. V.; Zvezdin, A. K.
Source:
FERROELECTRICS, 475 (1):1-9; SI 10.1080/00150193.2015.994973 JAN 25 2015
Abstract:
We investigate transformations of space modulated structure in BiFeO3 films induced by change of magnetic anisotropy, strain, or temperature and applied magnetic field. We show that critical field of the transition between incommensurate and commensurate structures is lower in films as compared with single crystals. There are two incommensurate phases at H parallel to[111]: plane and conical cycloidal phases with the second order transition between them. An important feature of this transition is softening of spin wave activation mode localized on spin cycloid. Cycloidal spin wave spectrum contains a countable number of branches, thus BiFeO3 can be considered as a magnonic crystal.

Update: 19-Mar-2015


Title:
Electrochemical hydrogen storage properties of Ti1.4V0.6Ni quasicrystal and TiH composite materials
Authors:
Liu, K; Shang, JM; Ouyang, ZT; Duan, YH; Xing, C; Fu, YG; Liang, F; Lin, J; Liu, WQ; Wang, LM Author Full Names: Liu, Kun; Shang, Jinming; Ouyang, Zhongtao; Duan, Yuhan; Xing, Cheng; Fu, Yuegang; Liang, Fei; Lin, Jing; Liu, Wanqiang; Wang, Limin
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 630 158-162; 10.1016/j.jallcom.2015.01.062 MAY 5 2015
Abstract:
In this study, we use arc-melting and subsequent melt-spinning techniques to prepare Ti1.4V0.6Ni alloy ribbons. The Ti1.4V0.6Ni + xTiH (x = 5, 10, 15 and 20 wt.%) mixture powders are obtained by mechanical ball-milling. Also, we investigate the structure and electrochemical hydrogen storage properties of composite materials. Besides I-phase, FCC and BCC phase, the XRD of composite materials indicates it contains TiH phase. After adding TiH, the discharge capacities of Ti1.4V0.6Ni alloy electrode increase first and then decrease with increasing amount of Ti. The achieved maximum discharge capacity is about 339.8 mA h/g (x = 15 wt.%) at the first discharge cycle. Additionally, composite materials lead to significant improvement in the high-rate dischargeability (HRD) as well as the cyclic stability. (C) 2015 Elsevier B.V. All rights reserved.

Title:
Wave propagation of phonon and phason displacement modes in quasicrystals: Determination of wave parameters
Authors:
Chellappan, V; Gopalakrishnan, S; Mani, V Author Full Names: Chellappan, Vinita; Gopalakrishnan, S.; Mani, V.
Source:
JOURNAL OF APPLIED PHYSICS, 117 (5):10.1063/1.4907212 FEB 7 2015
Abstract:
The paper presents the study of wave propagation in quasicrystals. Our interest is in the computation of the wavenumber (k(n)) and group speed (c(g)) of the phonon and phason displacement modes of one, two, and three dimensional quasicrystals. These wave parameter expressions are derived and computed using the elasto-hydrodynamic equations for quasicrystals. For the computation of the wavenumber and group speeds, we use Fourier transform approximation of the phonon and the phason displacement modes. The characteristic equations obtained are a polynomial equation of the wavenumber (k(n)), with frequency as a parameter. The corresponding group speeds (c(g)) for different frequencies are then computed from the wavenumber k(n). The variation of wavenumber and group speeds with frequency is plotted for the 1-D quasicrystal, 2-D decagonal Al-Ni-Co quasicrystals, and 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. From the wavenumber and group speeds plots, we obtain the cut-off frequencies for different spatial wavenumber eta(m). The results show that for 1-D, 2-D, and 3-D quasicrystals, the phonon displacement modes are non-dispersive for low values of eta(m) and becomes dispersive for increasing values of eta(m). The cut-off frequencies are not observed for very low values of eta(m), whereas the cut-off frequency starts to appear with increasing eta(m). The group speeds of the phason displacement modes are orders of magnitude lower than that of the phonon displacement modes, showing that the phason modes do not propagate, and they are essentially the diffusive modes. The group speeds of the phason modes are also not influenced by eta(m). The group speeds for the 2-D quasicrystal at 35 kHz is also simulated numerically using Galerkin spectral finite element methods in frequency domain and is compared with the results obtained using wave propagation analysis. The effect of the phonon and phason elastic constants on the group speeds is studied using 3-D icosahedral Al-Pd-Mn and Zn-Mg-Sc quasicrystals. It is also shown that the phason elastic constants and the coupling coefficient do not affect the group speeds of the phonon displacement modes. (C) 2015 AIP Publishing LLC.

Update: 12-Mar-2015


Title:
Spin-Glass Behavior and Incommensurate Modulation in High-Pressure Perovskite BiCr0.5Ni0.5O3
Authors:
Arevalo-Lopez, AM; Dos Santos-Garcia, AJ; Levin, JR; Attfield, JP; Alario-Franco, MA Author Full Names: Arevalo-Lopez, Angel M.; Dos Santos-Garcia, Antonio J.; Levin, Jessica R.; Attfield, J. Paul; Alario-Franco, Miguel A.
Source:
INORGANIC CHEMISTRY, 54 (3):832-836; 10.1021/ic502012p FEB 2 2015
Abstract:
The BiCr0.5Ni0.5O3 perovskite has been obtained at high pressure. Neutron and synchrotron diffraction data show a Pnma orthorhombic structure with a = 5.5947(1) angstrom, b = 7.7613(1) angstrom, and c = 5.3882(1) angstrom at 300 K and random B-site Cr/Ni distribution. Electron diffraction reveals an incommensurate modulation parallel to the b axis. The combination of either Cr-O-Ni (J > 0) or Cr-O-Cr/Ni-O-Ni (J < 0) nearest-neighbor spin interactions results in a random-bond spin-glass configuration. Magnetization, neutron diffraction, and muon-spin-relaxation measurements demonstrate that variations in the local bonding and charge states contribute to the magnetic frustration.

Title:
Structural Modulations in the Rare-Earth Metal Digermanides REAl1-x,Ge-2 (RE = Gd-Tm, Lu, Y; 0.8
Authors:
Zhang, JL; Wang, YM; Bobev, S Author Full Names: Zhang, Jiliang; Wang, Yingmin; Bobev, Svilen
Source:
INORGANIC CHEMISTRY, 54 (3):722-732; 10.1021/ic501002j FEB 2 2015
Abstract:
Rare-earth metal aluminum germanides with the general formula REAl1-xGe2 (RE = Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y) have been synthesized by direct fusion of the corresponding elements. The structures have been studied by single-crystal X-ray diffraction and selected-area electron diffraction (SAED). The average structure represents a randomly stuffed variant of the orthorhombic ZrSi2 structure type, also known as the CeNi1-xSi2 type (Pearson symbol oC16; space group Cmcm). The SAED patterns for selected members of the family suggest the coexistence of commensurate and incommensurate structural modulations. The most prominent model for long-range vacancy ordering is the Tb4FeGe8 type (Pearson symbol mP26; space group P2(1)/n), which is the commensurate 4-fold superstructure of CeNi1-xSi2 (x = 3/4). Short-range correlations cause additional deviations in the 4-fold superlattice. These results shed more light on the structural complexity as a function of the aluminum vacancies and size of the rare-earth metal. Magnetic susceptibility measurements are presented and discussed. The measured ordering temperatures and calculated ones based on empirical rules and Ruderman-Kittel-Kasuya-Yosida interactions are shown to be in close agreement.

Title:
Fabrication and structural characterization of bismuth niobate thin films grown by chemical solution deposition
Authors:
Goncalves, LF; Cortes, JA; Ranieri, MGA; Destro, FB; Ramirez, MA; Simoes, AZ Author Full Names: Goncalves, L. F.; Cortes, J. A.; Ranieri, M. G. A.; Destro, F. B.; Ramirez, M. A.; Simoes, A. Z.
Source:
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 26 (2):1142-1150; 10.1007/s10854-014-2518-6 FEB 2015
Abstract:
Bi3NbO7 (BNO) thin films were deposited on Pt/TiO2/SiO2/Si (100) substrates at room temperature from the polymeric precursor method. X-ray powder diffraction and transmission electron microscopy were used to investigate the formation characteristics and stability range of the tetragonal modification of a fluorite-type solid solution. The results showed that this tetragonal, commensurately modulated phase forms through the intermediate formation of the incommensurately modulated cubic fluorite phase followed by the incommensurate-commensurate transformation. The 200 nm thick BNO films exhibit crystalline structure, a dielectric constant of 170, capacitance density of 200 nF/cm(2), dielectric loss of 0.4 % at 1 MHz, and a leakage current density of approximately 1 x 10(-7) A/cm(2) at 5 V. They show breakdown strength of about 0.25 MV/cm. The leakage mechanism of BNO film in high field conduction is well explained by the Schottky and Poole-Frenkel emission models. The 200 nm thick BNO film is suitable for embedded decoupling capacitor applications directly on a printed circuit board.

Title:
On the Origin of Nanochessboard Super lattices in A-Site-Deficient Ca-Stabilized Nd2/3TiO3
Authors:
Azough, F; Kepaptsoglou, D; Ramasse, QM; Schaffer, B; Freer, R Author Full Names: Azough, Feridoon; Kepaptsoglou, Demie; Ramasse, Quentin M.; Schaffer, Berhnard; Freer, Robert
Source:
CHEMISTRY OF MATERIALS, 27 (2):497-507; 10.1021/cm5036985 JAN 27 2015
Abstract:
A-site deficient Nd2/3TiO3 ceramics stabilized with CaTiO3, with an overall composition of 0.9 Nd2/3TiO3-0.1 CaTiO3, were synthesized by the mixed oxide route. Synchrotron X-ray diffraction was used to identify the basic perovskite structure and revealed cross-type superlattice reflections. An incommensurate superlattice structure with dimensions of a approximate to b approximate to 20ap and c = 2a(p) (where a(p) is the cell parameter for the parent perovskite phase) was identified, giving rise to contrast features resembling a nanochessboard pattern in electron microscopy images. The superlattice was further characterized by aberration-corrected scanning transmission electron microscopy (STEM): atomically resolved lattice images were obtained along ?100? orientations to visualize the A-site (Ca, Nd, and vacancies) and B-site (Ti) cation column intensities, in correlation with observations of the nanochessboard superlattice. Electron energy loss spectroscopy (EELS) was used to precisely determine the distribution of Nd and Ca across the structure, confirming the absence of long-range elemental segregation or phase separation across the nanochessboard superstructure. Closer inspection of the chemical maps in two orthogonal directions, however, suggests the presence of localized ordering of cations and vacancies. The chessboard pattern superlattice is thus likely to be caused by periodic octahedral tilt distortions of the O sublattice, possibly induced by these short-range chemical variations, as a result of a complex interplay between cation and vacancy ordering in three dimensions.

Title:
Cation ordering in A-site-deficient Li-ion conducting perovskites La(1-x)/3LixNbO3
Authors:
Gao, X; Fisher, CAJ; Ikuhara, YH; Fujiwara, Y; Kobayashi, S; Moriwake, H; Kuwabara, A; Hoshikawa, K; Kohama, K; Iba, H; Ikuhara, Y Author Full Names: Gao, Xiang; Fisher, Craig A. J.; Ikuhara, Yumi H.; Fujiwara, Yasuyuki; Kobayashi, Shunsuke; Moriwake, Hiroki; Kuwabara, Akihide; Hoshikawa, Keigo; Kohama, Keiichi; Iba, Hideki; Ikuhara, Yuichi
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 3 (7):3351-3359; 10.1039/c4ta07040b 2015
Abstract:
Cation-deficient perovskites exhibit complex local atomic arrangements which cannot be adequately described by average crystal structure models. By combining reciprocal-space electron diffraction analysis and direct observations of atom positions using state-of-the-art scanning transmission electron microscopy, we clarify the nature of the cation ordering within A-site-deficient perovskite single crystals of La(1-x)/3LixNbO3 (x = 0 and x = 0.04). Both materials are found to have complex modulated crystal structures with two types of A-cation ordering, namely a long-range layer ordering in alternate (001)(p) planes and a short-range (intra-domain) columnar ordering within La-rich (001)(p) layers. The columnar ordering (occupational modulation) produces modulated displacements of Nb and O atoms. It is also found that substitution of even a small amount of Li for La can affect significantly the columnar ordering, leading to a series of structural and microstructural changes that are likely to have a deleterious effect on the Li-ion conductivity of this material.

Title:
Magnetic resonance and spin-reorientation transitions in the Nd0.75Ho0.25Fe3(BO3)(4) multiferroic
Authors:
Kobets, MI; Dergachev, KG; Gnatchenko, SL; Khatsko, EN; Bezmaternykh, LN; Gudim, IA Author Full Names: Kobets, M. I.; Dergachev, K. G.; Gnatchenko, S. L.; Khatsko, E. N.; Bezmaternykh, L. N.; Gudim, I. A.
Source:
LOW TEMPERATURE PHYSICS, 41 (1):75-79; 10.1063/1.4906338 JAN 2015
Abstract:
A presentation of experimental study results obtained by antiferromagnetic resonance (AFMR) of the high-frequency properties of the multiferroic Nd0.75Ho0.25Fe3(BO3)(4) in a broad range of temperatures and frequencies. We studied the effect of substituting the Nd3+ ions with Ho3+, on the resonance properties of the Nd0.75Ho0.25Fe3(BO3)(4) solid solution. In addition, we investigated the particularities of magnetic-field induced spin-reorientation phase transitions for H parallel to c and H parallel to a directions, in which the anisotropy of the magnetic system is measured from "easy-axis" anisotropy to "easy-plane." The AFMR modes of a Fe3+ subsystem are revealed. New information about the most important characteristics of AFM is obtained, including: frequency-field dependence of the AFMR spectrum, gaps in the spin-wave spectrum, effective magnetic anisotropy values, and fields of spin-reorientation transitions. It is shown that "easy-plane" anisotropy prevails in this magnet, with a weak anisotropy in the basal plane. For the first time there are observed features in the AFMR spectra that could be tied to the presence of a spatially modulated spin structure (incommensurate phase) in AFM Nd0.75Ho0.25Fe3(BO3)(4). (C) 2015 AIP Publishing LLC.

Title:
Single-molecule probing of incommensurate biphenyl (vol 36, pg 448, 2010)
Authors:
Pars, M; Palm, V; Kikas, J Author Full Names: Paers, M.; Palm, V.; Kikas, J.
Source:
LOW TEMPERATURE PHYSICS, 41 (1):80-80; 10.1063/1.4906339 JAN 2015

Title:
Effect of shape on the self-assembly of faceted patchy nanoplates with irregular shape into tiling patterns
Authors:
Millan, JA; Ortiz, D; Glotzer, SC Author Full Names: Millan, Jaime A.; Ortiz, Daniel; Glotzer, Sharon C.
Source:
SOFT MATTER, 11 (7):1386-1396; 10.1039/c4sm01612b 2015
Abstract:
Recent reports of the synthesis and assembly of faceted nanoplates with a wide range of shapes and composition motivates the possibility of a new class of two-dimensional materials with specific patterns targeted for a host of exciting properties. Yet, studies of how nanoplate shape controls their assembly knowledge necessary for their inverse design from target structures - has been performed for only a handful of systems. By constructing a general framework in which many known faceted nanoplates may be described in terms of four anisotropy dimensions, we discover design rules to guide future synthesis and assembly. We study via Monte Carlo simulations attractive polygons whose shape is altered systematically under the following four transformations: faceting, pinching, elongation and truncation. We report that (i) faceting leads to regular porous structures (ii) pinching stabilizes complex structures such as dodecagonal quasicrystals (iii) elongation leads to asymmetric phase behavior, where low and high aspect ratio nanoplates self-assemble completely different structures and (iv) low and high degrees of truncation transform a complex self-assembler into a disk-like assembler, providing design ideas that could lead to switchable structures. We provide important insight into how the shape and attractive interactions of a nanoplate can be exploited or designed to target specific classes of structures, including space-filling, porous, and complex tilings.

Title:
Ultrathin Two-Dimensional Inorganic Materials: New Opportunities for Solid State Nanochemistry
Authors:
Sun, YF; Gao, S; Lei, FC; Xiao, C; Xie, Y Author Full Names: Sun, Yongfu; Gao, Shan; Lei, Fengcai; Xiao, Chong; Xie, Yi
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 48 (1):3-12; 10.1021/ar500164g JAN 2015
Abstract:
CONSPECTUS: The ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called "nanochemistry" for short, primarily studies the microstructures and macroscopic properties of a nanomaterial's aggregation states. Due to abundant microstructures in the aggregation states, it is only possible to build a simple but imprecise correlation between the microscopic morphology and the macroscopic properties of the nanostructures. Notably, atomically thin two-dimensional inorganic materials provide an ideal platform to establish clear structure-property relationships in the field of solid state nanochemistry, thanks to their homogeneous dispersion without the assistance of a capping ligand. In addition, their atomic structures including coordination number, bond length, and disorder degree of the examined atoms can be clearly disclosed by X-ray absorption fine structure spectroscopy. Also, their more exposed interior atoms would inevitably induce the formation of various defects, which would have a non-negligible effect on their physicochemical properties. Based on the obtained atomic and defect structural characteristics, density-functional calculations are performed to study their electronic structures. Then, after the properties of the individual ultrathin two-dimensional materials or their assembled highly oriented thin film-based nanodevices are measured, the explicit relationship between atomic, defect, and electronic structure and intrinsic properties could be established. In this Account, we focus on our recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations. In addition, we summarize the close correlation between atomic, defect, and electronic structure variations and the optoelectronic, electrical, magnetic, and thermal properties of ultrathin two-dimensional materials. Finally, we also propose the major challenges and opportunities that face solid state nanochemistry. We believe that all the past achievements in ultrathin two-dimensional materials could bring new opportunities for solid state nanochemistry.

Update: 5-Mar-2015


Title:
An enhancement ZT and spin state transition of Ca3Co4O9 with Pb doping
Authors:
Demirel, S; Altin, E; Oz, E; Altin, S; Bayri, A Author Full Names: Demirel, S.; Altin, E.; Oz, E.; Altin, S.; Bayri, A.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 627 430-437; 10.1016/j.jallcom.2014.11.200 APR 5 2015
Abstract:
We reported the structural, electrical, thermal and magnetic properties of Pb-doped Ca3Co4O9 in the range of 300-5 K. DTA analysis showed that the stability of the Ca3Co4O9 was increased with Pb doping. According to XRD analysis, it is found that Pb ions were successfully doped in the Ca3Co4O9 structure. The temperature of resistivity minima, T-min, increased by increasing the Pb doping level and it is seen that incommensurate spin density wave state becomes more stable with Pb doping. The enhancement of thermopower was explained that Pb doping in Ca sites caused a decrease of Co4+ fraction such that Co4+ ions transformed into Co3+ or Co2+. The room temperature ZT value of the polycrystalline sample reaches about 16 times larger value than that of the un-doped polycrystalline sample which is the promising candidate for high temperatures in the thin film applications. According to magnetic susceptibility measurement, the increase of effective magnetic moment by Pb concentration was explained by spin state transition of Co3+ from low spin to intermediate spin and high spin state together with some orbital angular momentum contribution which comes from T-5(2) term due to a decrease of the ligand field splitting energy. (C) 2014 Elsevier B. V. All rights reserved.

Title:
Localized Electron Magnetism in the Icosahedral Au-Al-Tm Quasicrystal and Crystalline Approximant
Authors:
Nakayama, M; Tanaka, K; Matsukawa, S; Deguchi, K; Imura, K; Ishimasa, T; Sato, NK Author Full Names: Nakayama, Mika; Tanaka, Katsumasa; Matsukawa, Shuya; Deguchi, Kazuhiko; Imura, Keiichiro; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (2):10.7566/JPSJ.84.024721 FEB 15 2015
Abstract:
We report the magnetic, thermal, and transport properties of the Au-Al-Tm quasicrystal, which is isostructural to the first and only quasicrystal Au-Al-Yb that shows a novel quantum critical behavior. The Tm-based quasicrystal undergoes a spin-glass-like freezing below T-f similar to 0.4 K. We also synthesize the Au-Al-Tm approximant to the quasicrystal and find that it shows a similar spin-glass-like freezing below T-f similar to 0.3 K. Both the quasicrystal and the approximant follow the Curie-Weiss law in a wide temperature range above T-f, indicating that the 4f electrons are well localized on the vertices of the icosahedron. The interspin interaction is antiferromagnetic and its magnitude is as small as similar to 1 K. The spin-glass-like freezing is presumably driven by the combined effect of the chemical disorder of Au/Al ions and the frustrated nature of the icosahedron. On the basis of these results, we discuss a possible origin of the unusual quantum criticality observed in the Yb-based system.

Title:
Superconductivity of Au-Ge-Yb Approximants with Tsai-Type Clusters
Authors:
Deguchi, K; Nakayama, M; Matsukawa, S; Imura, K; Tanaka, K; Ishimasa, T; Sato, NK Author Full Names: Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (2):10.7566/JPSJ.84.023705 FEB 15 2015
Abstract:
We report the emergence of bulk superconductivity in Au64.0Ge22.0Yb14.0 and Au63.5Ge20.5Yb16.0 below 0.68 and 0.36 K, respectively. This is the first observation of superconductivity in Tsai-type crystalline approximants of quasicrystals. The Tsai-type cluster center is occupied by Au and Ge ions in the former approximant, and by an Yb ion in the latter. For magnetism, the latter system shows a larger magnetization than the former. To explain this observation, we propose a model that the cluster-center Yb ion is magnetic. The relationship between the magnetism and the superconductivity is also discussed.

Title:
Incommensurate magnetic structure, Fe/Cu chemical disorder, and magnetic interactions in the high-temperature multiferroic YBaCuFeO5
Authors:
Morin, M; Scaramucci, A; Bartkowiak, M; Pomjakushina, E; Deng, G; Sheptyakov, D; Keller, L; Rodriguez-Carvajal, J; Spaldin, NA; Kenzelmann, M; Conder, K; Medarde, M Author Full Names: Morin, M.; Scaramucci, A.; Bartkowiak, M.; Pomjakushina, E.; Deng, G.; Sheptyakov, D.; Keller, L.; Rodriguez-Carvajal, J.; Spaldin, N. A.; Kenzelmann, M.; Conder, K.; Medarde, M.
Source:
PHYSICAL REVIEW B, 91 (6):10.1103/PhysRevB.91.064408 FEB 6 2015
Abstract:
Motivated by the recent observations of incommensurate magnetic order and electric polarization in YBaCuFeO5 up to temperatures T-N2 as high as 230 K [B. Kundys et al., Appl. Phys. Lett. 94, 072506 (2009); Y. Kawamura et al., J. Phys. Soc. Jpn 79, 073705 (2010)], we report here for the first time a model for the incommensurate magnetic structure of this material, which we complement with ab initio calculations of the magnetic exchange parameters. Using neutron powder diffraction, we show that the appearance of polarization below TN2 is accompanied by the replacement of the high-temperature collinear magnetic order by a circular inclined spiral with propagation vector k(i) = (1/2,1/2,1/2 +/- q). Moreover, we find that the polarization approximately scales with the modulus of the magnetic modulation vector q down to the lowest temperature investigated (similar to 3 K). Further, we observe occupational Fe/Cu disorder in the FeO5-CuO5 bipyramids, although a preferential occupation of such units by Fe-Cu pairs is supported by the observed magnetic order and by density functional calculations. We calculate exchange coupling constants for different Fe/Cu distributions and show that, for those containing Fe-Cu dimers, the resulting magnetic order is compatible with the experimentally observed collinear magnetic structure [k(c) = (1/2,1/2,1/2), T-N2 > T > T-N1 = 440 K]. Based on these results, we discuss possible origins for the incommensurate modulation and its coupling with ferroelectricity.

Title:
Critical behaviour of Sn2P2S6 and Sn2P2(Se0.28S0.72)(6) crystals under high hydrostatic pressures
Authors:
Zapeka, B; Kostyrko, M; Martynyuk-Lototska, I; Vlokh, R Author Full Names: Zapeka, B.; Kostyrko, M.; Martynyuk-Lototska, I.; Vlokh, R.
Source:
PHILOSOPHICAL MAGAZINE, 95 (4):382-393; 10.1080/14786435.2015.1006295 FEB 1 2015
Abstract:
Basing on the temperature dependences of optical birefringence for Sn2P2S6 and Sn2P2(Se0.28S0.72)(6) crystals subjected to hydrostatic pressures, we prove unambiguously that Sn2P2S6 reveals a tricritical point on its (p, T)- phase diagram with the coordinates (p, T) = (4.3kbar, 259K), so that the second-order phase transition transforms into the first-order one whenever the pressure increases above 4.3kbar. We also find that increasing hydrostatic pressure applied to Sn2P2(Se0.28S0.72)(6) leads to the change in the phase transition character from tricritical to first order. Further increase in the pressure up to ~2.5kbar imposes splitting of the first-order paraelectric-to-ferroelectric phase transition into two phase transitions, a second-order paraelectric-to-incommensurate one and a first-order incommensurate-to-ferroelectric transition.

Title:
Phase Diagram of (Li1-xFex)OHFeSe: A Bridge between Iron Selenide and Arsenide Superconductors
Authors:
Dong, XL; Zhou, HX; Yang, HX; Yuan, J; Jin, K; Zhou, F; Yuan, DN; Wei, LL; Li, JQ; Wang, XQ; Zhang, GM; Zhao, ZX Author Full Names: Dong, Xiaoli; Zhou, Huaxue; Yang, Huaixin; Yuan, Jie; Jin, Kui; Zhou, Fang; Yuan, Dongna; Wei, Linlin; Li, Jianqi; Wang, Xinqiang; Zhang, Guangming; Zhao, Zhongxian
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 137 (1):66-69; 10.1021/ja511292f JAN 14 2015
Abstract:
Previous experimental results have shown important differences between iron selenide and arsenide superconductors which seem to suggest that the high-temperature superconductivity in these two subgroups of iron-based families may arise from different electronic ground states. Here we report the complete phase diagram of a newly synthesized superconducting (SC) system, (Li1-xFex)OHFeSe, with a structure similar to that of FeAs-based superconductors. In the non-SC samples, an antiferromagnetic (AFM) spin-density-wave (SDW) transition occurs at similar to 127 K. This is the first example to demonstrate such an SDW phase in an FeSe-based superconductor system. Transmission electron microscopy shows that a well-known O5xO5 iron vacancy ordered state, resulting in an AFM order at similar to 500 K in A(y)Fe(2-x)Se(2) (A = metal ions) superconductor systems, is absent in both non-SC and SC samples, but a unique superstructure with a modulation wave vector q = 1/2(1,1,0), identical to that seen in the SC phase of KyFe2-xSe2, is dominant in the optimal SC sample (with an SC transition temperature T-c = 40 K). Hence, we conclude that the high-T-c superconductivity in (Li1-xFex)OHFeSe stems from the similarly weak AFM fluctuations as FeAs-based superconductors, suggesting a universal physical picture for both iron selenide and arsenide superconductors.

Title:
Row of shear cracks moving in one-dimensional hexagonal quasicrystalline materials
Authors:
Tupholme, GE Author Full Names: Tupholme, G. E.
Source:
ENGINEERING FRACTURE MECHANICS, 134 451-458; 10.1016/j.engfracmech.2014.07.002 JAN 2015
Abstract:
Representations for the stress fields created around an infinite row of collinear, antiplane shear cracks moving within one-dimensional hexagonal quasicrystals, and the resulting stress intensity factors and the J-integral, are determined in closed-form and discussed, using an extended method of dislocation layers. The solutions for a finite quasicrystalline plate containing a single moving crack and a plate with a moving edge crack are also provided by this analysis. (C) 2014 Elsevier Ltd. All rights reserved.

Update: 26-Feb-2015


Title:
Electrochemical hydrogen storage properties of TixV65-xNi35 (x=45, 55) alloys produced by rapid-quenching
Authors:
Liu, CF; Liu, WQ; Wang, LM; Liang, F; Lin, J; Shen, Y; Jiang, DY Author Full Names: Liu, Chaofan; Liu, Wanqiang; Wang, Limin; Liang, Fei; Lin, Jing; Shen, Yu; Jiang, Dayong
Source:
MATERIALS LETTERS, 141 291-293; 10.1016/j.matlet.2014.11.108 FEB 15 2015
Abstract:
Electrochemical discharge performances of TixV65-xNi35 (x=45, 55) alloy are measured by electrochemical measurements at galvanostatic conditions, and alloy ribbon is prepared by rapid-quenching under argon atmosphere. XRD analysis of TixV65-xNi35 (x=45) alloy shows that the Ti45V20Ni35 (x=45) is mostly the amorphous phase, V-based solid solution phase with BCC structure phase and a negligible amount of (Ni, V) phase. While x=55, namely the Ti55V10Ni35 alloy, mainly consists of the icosahedral quasicrystal (I-phase), face centered cubic (FCC) phase with Ti2Ni-type structure and V-based solid solution phase with BCC structure phase. In the electrochemical tests, the maximum discharge capacity of Ti45V20Ni35 is about 150.4 mAh/g at a current density of 30 mA/g. However, Ti55V10Ni35 alloy shows that the best discharge capacity is 221.8 mAh/g under the same condition. In addition, it exhibits extraordinary cycling stability of 87.2% at 30 charge-discharge cycles. It can be found that the discharge capacity of the amorphous electrode is lower than those of the I-phase ones under the similar composition levels. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Strain-induced dimensionality crossover of precursor modulations in Ni2MnGa
Authors:
Nie, ZH; Wang, YD; Shang, SL; Zeng, QS; Ren, Y; Liu, DM; Yang, WG; Wang, Y; Liu, ZK Author Full Names: Nie, Zhihua; Wang, Yandong; Shang, Shunli; Zeng, Qiaoshi; Ren, Yang; Liu, Dongmei; Yang, Wenge; Wang, Yi; Liu, Zi-Kui
Source:
APPLIED PHYSICS LETTERS, 106 (2):10.1063/1.4906333 JAN 12 2015
Abstract:
Precursor modulations often occur in functional materials like magnetic shape memory alloys, ferroelectrics, and superconductors. In this letter, we have revealed the underlying mechanism of the precursor modulations in ferromagnetic shape memory alloys Ni2MnGa by combining synchrotron-based x-ray diffraction experiments and first-principles phonon calculations. We discovered the precursor modulations along [011] direction can be eliminated with [001] uniaxial loading, while the precursor modulations or premartensite can be totally suppressed by hydrostatic pressure condition. The TA(2) phonon anomaly is sensitive to stress induced lattice strain, and the entire TA(2) branch is stabilized along the directions where precursor modulations are eliminated by external stress. Our discovery bridges precursor modulations and phonon anomalies, and sheds light on the microscopic mechanism of the two-step superelasticity in precursor martensite. (C) 2015 AIP Publishing LLC.

Title:
Static friction scaling of physisorbed islands: the key is in the edge
Authors:
Varini, N; Vanossi, A; Guerra, R; Mandelli, D; Capozza, R; Tosatti, E Author Full Names: Varini, Nicola; Vanossi, Andrea; Guerra, Roberto; Mandelli, Davide; Capozza, Rosario; Tosatti, Erio
Source:
NANOSCALE, 7 (5):2093-2101; 10.1039/c4nr06521b 2015
Abstract:
The static friction preventing the free sliding of nanosized rare gas solid islands physisorbed on incommensurate crystalline surfaces is not completely understood. Simulations modeled on Kr/Pb(111) highlight the importance and the scaling behavior of the island's edge contribution to static friction.

Update: 19-Feb-2015


Title:
Distinct itinerant spin-density waves and local-moment antiferromagnetism in an intermetallic ErPd2Si2 single crystal
Authors:
Li, HF; Cao, CD; Wildes, A; Schmidt, W; Schmalzl, K; Hou, BY; Regnault, LP; Zhang, C; Meuffels, P; Loser, W; Roth, G Author Full Names: Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Loeser, Wolfgang; Roth, Georg
Source:
SCIENTIFIC REPORTS, 5 10.1038/srep07968 JAN 22 2015
Abstract:
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q(+/-) = (H +/- 0.557(1), 0, L +/- 0.150(1)) and Q(C) = (H +/- 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature-and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q(+/-)modulation may be attributed to localized 4f moments while the Q(C) correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix.

Title:
Exploring the magnetic phase diagram of dysprosium with neutron diffraction
Authors:
Yu, J; LeClair, PR; Mankey, GJ; Robertson, JL; Crow, ML; Tian, W Author Full Names: Yu, J.; LeClair, P. R.; Mankey, G. J.; Robertson, J. L.; Crow, M. L.; Tian, W.
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014404 JAN 5 2015
Abstract:
With one of the highest intrinsic magnetic moments (10.6 mu(B)/atom) among the heavy rare-earth elements, dysprosium exhibits a rich magnetic phase diagram, including several modulated magnetic phases. Aided by the Ruderman-Kittel-Kasuya-Yosida interaction, the magnetic modulations propagate coherently over a long range. Neutron diffraction experiments were performed to determine the microscopic magnetic origin of the field induced phases in bulk Dy as a function of temperature, covering regions of the well-known ferromagnetic, helical antiferromagnetic, fan phases, and several possible new phases suggested by previous studies. A short-range ordered fan phase was identified as the intermediate state between ferromagnetism and long-range ordered fan. In a field of 1 T applied along the a axis, the temperature range of a coexisting helix/fan phase was determined. The magnetic phase diagram of Dy was thus refined to include the detailed magnetic origin and the associated phase boundaries. Based on the period of the magnetic modulation and the average magnetization, the evolution of the spin arrangement upon heating was derived quantitatively for the modulated magnetic phases.

Title:
Coupling between an incommensurate antiferromagnetic structure and a soft ferromagnet in the archetype multiferroic BiFeO3/cobalt system
Authors:
Elzo, M; Moubah, R; Blouzon, C; Sacchi, M; Grenier, S; Belkhou, R; Dhesi, S; Colson, D; Torres, F; Kiwi, M; Viret, M; Jaouen, N Author Full Names: Elzo, Marta; Moubah, Reda; Blouzon, Camille; Sacchi, Maurizio; Grenier, Stephane; Belkhou, Rachid; Dhesi, Sarnjeet; Colson, Dorothee; Torres, Felipe; Kiwi, Miguel; Viret, Michel; Jaouen, Nicolas
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014402 JAN 5 2015
Abstract:
Multiferroic materials are mostly antiferromagnets, often containing incommensurate magnetic arrangements stemming from the magnetoelectric interaction. Using soft x-ray resonant magnetic scattering, we show that these long-range structures induce a magnetization wriggle in cobalt layers deposited on top of BiFeO3 single crystals. This is understood using a simple interface exchange interactions model. It leads to the appearance of a magnetic anisotropy axis, which, in the particular BiFeO3/Co system, can be manipulated using an electric field. More generally, it is demonstrated here that through interfacial magnetic exchange, antiferromagnets can leave an imprint revealing some of their hidden properties, thus providing much richer effects than mere exchange bias.

Title:
Modulated spin structure responsible for the magnetic-field-induced polarization switching in multiferroic TbMn2O5
Authors:
Lee, JH; Jang, HM Author Full Names: Lee, Jung-Hoon; Jang, Hyun Myung
Source:
PHYSICAL REVIEW B, 91 (1):10.1103/PhysRevB.91.014403 JAN 5 2015
Abstract:
Orthorhombic TbMn2O5 (o-TMO) is a well-known multiferroic manganite with the remarkable property of polarization switching at 3 K under a bias magnetic (H) field along the a axis of Pb2(1)m. To theoretically account for this outstanding observation, we have proposed a modulated spin structure under the saturated bias H field by considering the relative strength of the three relevant exchange parameters in o-TMO. The proposed modulated structure based on density-functional theory (DFT) calculations is described in terms of the spin angle phi between the neighboring Mn4+-Mn3+ spin moments on the a-b plane. We have shown that the computed DFT polarization plotted as a function of f satisfactorily accounts for the observed H-field-induced polarization switching. We have further theoretically shown that the square of the critical field strength (H-c) needed for the polarization switching is inversely proportional to the degree of the extrinsic magnetoelectric coupling. The computed partial charge density demonstrates that the H-field-induced polarization switching also accompanies with the switching in the sign of the excess valence-electron density.

Title:
Molecular disorder effects in the thermal conductivity of solid thiophene
Authors:
Vdovichenko, GA; Krivchikov, AI; Korolyuk, OA; Romantsova, OO Author Full Names: Vdovichenko, G. A.; Krivchikov, A. I.; Korolyuk, O. A.; Romantsova, O. O.
Source:
LOW TEMPERATURE PHYSICS, 40 (12):1112-1115; 10.1063/1.4904001 DEC 2014
Abstract:
The temperature dependence of the thermal conductivity kappa(T) of solid thiophene is measured in a sequence of stable orientationally disordered phases with different degrees of orientational ordering of the molecules: in orientational glass (V-g); in phase V with large angular librational molecular vibrations; in incommensurate phase IV with a static orientational disorder; and in orientationally disordered crystalline phase III with dynamic orientational disorder of the molecules. Measurements are made at the saturated vapor pressure in a temperature range of 2-180 K. It is found that the thermal conductivity of thiophene is practically independent of temperature in phases III and V with dynamic orientational disorder of the molecules. In the orientational glass state and in the incommensurate state, the temperature dependence of the thermal conductivity of thiophene has a form typical of crystals with a long-range orientational order. A distinct hysteresis of the thermal conductivity is found at temperatures slightly below the temperature of the transition from phase IV into phase V. (C) 2014 AIP Publishing LLC.

Update: 12-Feb-2015


Title:
Magnetic and structural phase transitions and the tetragonality of thermoelastic martensite in quasi-binary Heusler alloys Ni2+x Mn1-x Ga
Authors:
Pushin, VG; Kourov, NI; Korolev, AV; Marchenkova, EB; Kuranova, NN; Belosludtseva, ES Author Full Names: Pushin, V. G.; Kourov, N. I.; Korolev, A. V.; Marchenkova, E. B.; Kuranova, N. N.; Belosludtseva, E. S.
Source:
PHYSICS OF THE SOLID STATE, 57 (1):45-52; 10.1134/S1063783415010242 JAN 2015
Abstract:
This paper reports on the results of investigations into the structure of martensite and the electronic and magnetic properties of Ni2 + x Mn1 - x Ga alloys in the concentration range 0.12 a parts per thousand currency sign x a parts per thousand currency sign 0.39. The concentration dependences of the critical temperatures and the anomalous behavior of the degree of tetragonal distortion of the martensite have been discussed, as well as the changes in the parameters characterizing the electronic and magnetic subsystems in the thermoelastic martensitic transition L2(1) a dagger' M, which occurs in atomically ordered L2(1)-type alloys upon doping in the range 0.12 a parts per thousand currency sign x a parts per thousand currency sign 0.39 at different temperatures. The temperature and concentration dependences of the magnetic properties have been determined for the state of the single-phase L2(1) austenite (at T > T (C) and A (f)) and martensite (at T > T (C) and M (f)), which undergoes the transition from a modulated 10M- or 14M-type structure to a nonmodulated (NM) tetragonal structure.

Title:
The Synthesis, Structure, and Electrical Characterization of (SnSe)(1.2)TiSe2
Authors:
Merrill, DR; Moore, DB; Ditto, J; Sutherland, DR; Falmbigl, M; Winkler, M; Pernau, HF; Johnson, DC Author Full Names: Merrill, Devin R.; Moore, Daniel B.; Ditto, Jeffrey; Sutherland, Duncan R.; Falmbigl, Matthias; Winkler, Markus; Pernau, Hans-Fridtjof; Johnson, David C.
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, (1):83-91; 10.1002/ejic.201402814 JAN 2015
Abstract:
(SnSe)(1.2)TiSe2 was found to self-assemble from a precursor containing modulated layers of Sn-Se and Ti-Se over a surprisingly large range of layer thicknesses and compositions. The constituent lattices form an alternating layer superstructure with rotational disorder present between the layers. This compound was found to have the highest Seebeck coefficient measured for analogous TiX2 containing misfit layered compounds to date, suggesting potential for low-temperature thermoelectric applications. Electrical characterization suggests that electrons transferred from SnSe to TiSe2 are responsible for the higher carrier concentration observed relative to bulk TiSe2. The transfer of charge from one constituent to the other may provide a mechanism for doping layered dichalcogenides for various applications without negatively affecting carrier mobility.

Title:
Very large thermal rectification in bulk composites consisting partly of icosahedral quasicrystals
Authors:
Takeuchi, T Author Full Names: Takeuchi, Tsunehiro
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (6):10.1088/1468-6996/15/6/064801 DEC 2014
Abstract:
The bulk thermal rectifiers usable at a high temperature above 300 K were developed by making full use of the unusual electron thermal conductivity of icosahedral quasicrystals. The unusual electron thermal conductivity was caused by a synergy effect of quasiperiodicity and by a narrow pseudogap at the Fermi level. The rectification ratio, defined by TRR = vertical bar J(large)vertical bar/vertical bar J(small)vertical bar, reached vary large values exceeding 2.0. This significant thermal rectification would lead to new practical applications for the heat management.

Update: 5-Feb-2015


Title:
Microstructure evolution and mechanical properties of quasicrystal-reinforced Mg-Zn-Gd alloy processed by cyclic extrusion and compression
Authors:
Tian, Y; Huang, H; Yuan, GY; Ding, WJ Author Full Names: Tian, Yuan; Huang, Hua; Yuan, Guangyin; Ding, Wenjiang
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 626 42-48; 10.1016/j.jallcom.2014.11.167 MAR 25 2015
Abstract:
Mg-1.5Zn-0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and subjected to cyclic extrusion and compression (CEC) at 350 degrees C to investigate the microstructure evolution during CEC and its effect on the mechanical properties. It is observed that, during CEC, the microstructure of the alloy was greatly refined by dynamic recrystallization (DRX), large numbers of I-phase particles precipitated and then grew up, the texture of the alloy was obviously weakened. These changes in microstructure improved the mechanical properties of the alloy significantly and the alloy processed by 8 passes CEC exhibited outstanding plasticity of 31.4% and moderate yield strength of 161 MPa. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Substitution rules for icosahedral quasicrystals
Authors:
Madison, AE Author Full Names: Madison, Alexey E.
Source:
RSC ADVANCES, 5 (8):5745-5753; 10.1039/c4ra09524c 2015
Abstract:
An original well-defined substitution algorithm on how to construct the icosahedral packings is proposed, simple inflation/deflation rules for icosahedral quasicrystals are described, and natural local matching rules are derived.

Update: 29-Jan-2015


Title:
The modulated antiferromagnetic structures in multiferroic FeVO4: A Fe-57 Mossbauer spectroscopy investigation
Authors:
Colson, D; Forget, A; Bonville, P Author Full Names: Colson, D.; Forget, A.; Bonville, P.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 378 529-534; 10.1016/j.jmmm.2014.11.078 MAR 15 2015
Abstract:
We present an investigation of the two incommensurate magnetic phases in the multiferroic material FeVO4 using magnetic susceptibility and Fe-57 Mossbauer spectroscopy measurements. The susceptibility shows anomalies at the phase transitions at 15.7 and 23 K. We devise Mossbauer lineshapes appropriate for planar elliptical and collinear modulated magnetic structures and show that they reproduce very well the Mossbauer spectra in FeVO4, in full qualitative agreement with a previous neutron diffraction study. Quantitatively, our spectra provide precise determinations of the characteristics of the elliptical and modulated structures which match rather well the neutron diffraction results. We find that the hyperfine field elliptical modulation persists as T -> 0, which we attribute to an anisotropy of the hyperfine interaction since a moment modulation is forbidden at T=0 for a spin only ion like Fe3+. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Crystal Structure of Superconducting 1/1 Cubic Au-Ge-Yb Approximant with Tsai-Type Cluster
Authors:
Deguchi, K; Nakayama, M; Matsukawa, S; Imura, K; Tanaka, K; Ishimasa, T; Sato, NK Author Full Names: Deguchi, Kazuhiko; Nakayama, Mika; Matsukawa, Shuya; Imura, Keiichiro; Tanaka, Katsumasa; Ishimasa, Tsutomu; Sato, Noriaki K.
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (1):10.7566/JPSJ.84.015002 JAN 15 2015
Abstract:
We report the synthesis of a single-phase sample of the superconducting crystalline approximant Au64.0Ge22.0Yb14.0 and present a structure model refined by Rietveld analysis for X-ray diffraction data.

Title:
Semimetallic Band Structure and Cluster-Based Description of a Cubic Quasicrystalline Approximant in the Al-Cu-Ir System
Authors:
Kitahara, K; Takagiwa, Y; Kimura, K Author Full Names: Kitahara, Koichi; Takagiwa, Yoshiki; Kimura, Kaoru
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 84 (1):10.7566/JPSJ.84.014703 JAN 15 2015
Abstract:
Density functional calculations were performed for a cubic quasicrystalline approximant in the Al-Cu-Ir system. A semimetallic band structure was developed and analyzed on the basis of Wannier functions constructed from the valence and a part of the conduction band manifold. The Wannier functions were s-and p-like orbitals centered on either the centers of conventional clusters or the icosahedron-like vertices of pseudo-Mackay clusters, and d-like orbitals centered on the transition metals. Grouping the orbitals according to their center, we considered a small cluster for each group of the orbitals. Most of the orbitals contribute to the density of states only within the valence bands, i.e., they are valence states. The exceptions are some of p-like orbitals centered on the icosahedron-like vertices of the pseudo-Mackay clusters, and they contribute to both valence and conduction bands. Each of these p-like orbitals forms a covalent bond with one centered on the neighboring small cluster. The resulting bonding and antibonding orbitals are valence and conduction states, respectively. The number of valence bands (173) of our Al39Cu8Ir15 model was then decomposed in terms of the numbers of transition metals (23), clusters (16), and covalent bonds between the clusters (6) as 23 x 5 + 16 x 4 -6 = 173. The description for the valence-band formation may also be applicable to some of the group 13 element-transition metal intermetallic compounds, such as RuAl2.

Title:
Detailed study of the magnetic ordering in FeMnP0.75Si0.25
Authors:
Hoglin, V; Hudl, M; Caron, L; Beran, P; Solby, MH; Nordblad, P; Andersson, Y; Sahlberg, M Author Full Names: Hoglin, Viktor; Hudl, Matthias; Caron, Luana; Beran, Premysl; Solby, Magnus H.; Nordblad, Per; Andersson, Yvonne; Sahlberg, Martin
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 221 240-246; 10.1016/j.jssc.2014.10.013 JAN 2015
Abstract:
Magnetic and crystallographic properties of FeMnP0.75Si0.25 in the hexagonal Fe2P-type structure have been investigated by X-ray powder diffraction, neutron powder diffraction and magnetic measurements. The room temperature diffractograms reveal co-existence of two distinct structural phases in the samples with small, but significant, differences only in the unit cell dimensions. The volume ratio between the two phases is governed by the annealing conditions. One of the phases orders ferromagnetically (T-C=250 K) and the other in an incommensurate antiferromagnetic structure at low temperatures (q(x) = 0.363(1), T-N=150 K). (C) 2014 Elsevier Inc. All rights reserved.

Title:
Multiple twins of a decagonal approximant embedded in S-Al2CuMg phase resulting in pitting initiation of a 2024Al alloy
Authors:
Wang, J; Zhang, B; Zhou, YT; Ma, XL Author Full Names: Wang, J.; Zhang, B.; Zhou, Y. T.; Ma, X. L.
Source:
ACTA MATERIALIA, 82 22-31; 10.1016/j.actamat.2014.09.001 JAN 1 2015
Abstract:
The pitting of Al-Cu-Mg alloy is believed to originate from the local dissolution of S-Al2CuMg particles, and the dissolution activity differs from one particle to another. Nevertheless, the initial site where the dissolution of the S phase preferentially occurs and the cause of the heterogeneity in the electrochemical dissolution activity remain unknown, hindering our understanding of pitting initiation of Al-Cu-Mg alloys. In this work, we have applied in situ ex-environmental transmission electron microscopy and identified a large number of nanosized Al20Cu2Mn3 approximants of the decagonal quasicrystal embedded in the S phase. We find that the S phase with Al20Cu2Mn3 inclusions is more active than those free of the approximants. Such a preference is clarified to result from the decomposition of Al20Cu2Mn3 approximant prior to the dissolution of the S phase. In addition, we also find that the electrochemical behavior of Al20Cu2Mn3 approximants is different. The approximants with multiple twins are more active than those with few planar defects. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
New RMnO3+delta (R=Y, Ho; delta approximate to 0.35) phases with modulated structure
Authors:
Parkkima, O; Malo, S; Hervieu, M; Rautama, EL; Karppinen, M Author Full Names: Parkkima, Outi; Malo, Sylvie; Hervieu, Maryvonne; Rautama, Eeva-Leena; Karppinen, Maarit
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 221 109-115; 10.1016/j.jssc.2014.09.012 JAN 2015
Abstract:
A series of hexagonal RMnO3 (R=Y, Ho-Lu) compounds are first annealed in various highly oxidizing conditions to show that for the largest R constituents, Y and Ho, it is possible to load the phases with large amounts of excess oxygen. Within the oxygen-annealed samples we identify new heavily-oxygenated phases, that is, YMnO3.33 and HoMnO3.34. The former is then thoroughly characterized by thermogravimetric analysis, X-ray diffraction and electron diffraction. These studies evidence a hexagonal sub-cell (a(s) approximate to 3.578 angstrom (a(H)/root 3), c(S)approximate to 11.18 angstrom, space group P6(3)mc) and satellites, associated with two modulation vectors q(1)(->*)approximate to 0.41 a(S)(->*)+ 0.41 b(S)(->*)+1/3 c(S)(->*) and q(2)(->*) = (1/2). The results are interpreted by the formation of a modulated composite structure, resulting from the evolution of the hexagonal parent YMnO3+delta structure toward a reduced pyrochlore-type structure Y2Mn2O7-x, in long-and short-range ordering. (C) 2014 Elsevier Inc. All rights reserved.

Title:
Closely related magnetic and dielectric transitions in the "114" magnetoelectric Zn-doped CaBaCo4O7
Authors:
Seikh, MM; Caignaert, V; Suard, E; Meher, KRSP; Maignan, A; Raveau, B Author Full Names: Seikh, Md Motin; Caignaert, V.; Suard, E.; Meher, K. R. S. Preethi; Maignan, A.; Raveau, B.
Source:
JOURNAL OF APPLIED PHYSICS, 116 (24):10.1063/1.4905033 DEC 28 2014
Abstract:
We report on the impact of zinc doping upon the magneto-electric properties of CaBaCo4O7. We show that the presence of less than 1% Zn at the Co sites decreases T-C from 64K to 48K and generates two magnetic transitions, concomitant with changes of slope of dielectric permittivity, at 54K and 77K, respectively. Powder neutron diffraction and magnetic data show the existence of an incommensurate magnetic phase and a spin-flop transition in this temperature range. The crossover of the magnetodielectric effect of this oxide, from positive below 50K to negative above this temperature emphasizes the primordial role of the incommensurate magnetic phase in the evolution of these properties. (C) 2014 AIP Publishing LLC.

Title:
Tiling Phosphorene
Authors:
Guan, J; Zhu, Z; Tomanek, D Author Full Names: Guan, Jie; Zhu, Zhen; Tomanek, David
Source:
ACS NANO, 8 (12):12763-12768; 10.1021/nn5059248 DEC 2014
Abstract:
We present a scheme to categorize the structure of different layered phosphorene allotropes by mapping their nonplanar atomic structure onto a two-color 2D triangular tiling pattern. In the buckled structure of a phosphorene monolayer, we assign atoms in top positions to dark tiles and atoms in bottom positions to light tiles. Optimum sp(3) bonding is maintained throughout the structure when each triangular tile is surrounded by the same number N of like-colored tiles, with 0 = N = 2. Our ab initio density functional calculations indicate that both the relative stability and electronic properties depend primarily on the structural index N. The proposed mapping approach may also be applied to phosphorene structures with nonhexagonal rings and 2D quasicrystals with no translational symmetry, which we predict to be nearly as stable as the hexagonal network.

Title:
Spatial control of functional properties via octahedral modulations in complex oxide superlattices
Authors:
Moon, EJ; Colby,; Wang, Q; Karapetrova, E; Schleputz, CM; Fitzsimmons, MR; May, SJ Author Full Names: Moon, E. J.; R., Colby; Wang, Q.; Karapetrova, E.; Schlepuetz, C. M.; Fitzsimmons, M. R.; May, S. J.
Source:
NATURE COMMUNICATIONS, 5 10.1038/ncomms6710 DEC 2014
Abstract:
Control of atomic structure, namely the topology of the corner-connected metal-oxygen octahedra, has emerged as an important route to tune the functional properties at oxide interfaces. Here we investigate isovalent manganite superlattices (SLs), [(La0.7Sr0.3MnO3) n/(Eu0.7Sr0.3MnO3) n] x m, as a route to spatial control over electronic bandwidth and ferromagnetism through the creation of octahedral superstructures. Electron energy loss spectroscopy confirms a uniform Mn valence state throughout the SLs. In contrast, the presence of modulations of the MnO6 octahedral rotations along the growth direction commensurate with the SL period is revealed by scanning transmission electron microscopy and X-ray diffraction. We show that the Curie temperatures of the constituent materials can be systematically engineered via the octahedral superstructures leading to a modulated magnetization in samples where the SL period is larger than the interfacial octahedral coupling length scale, whereas a single magnetic transition is observed in the short-period SLs.

Title:
Magnetic structure and domain conversion of the quasi-2D frustrated antiferromagnet CuCrO2 probed by NMR
Authors:
Sakhratov, YA; Svistov, LE; Kuhns, PL; Zhou, HD; Reyes, AP Author Full Names: Sakhratov, Yu A.; Svistov, L. E.; Kuhns, P. L.; Zhou, H. D.; Reyes, A. P.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 119 (5):880-890; 10.1134/S1063776114110181 NOV 2014
Abstract:
We have carried out Cu-63,Cu-65 NMR spectra measurements in a magnetic field up to about 15.5 T on a single crystal of the multiferroic triangular-lattice antiferromagnet CuCrO2. The measurements were performed for perpendicular and parallel orientations of the magnetic field with respect to the c axis of the crystal, and the detailed angle dependence of the spectra on the magnetic field direction in the ab plane was studied. The shape of the spectra can be well described in the model of spiral spin structure proposed by recent neutron diffraction experiments. When the field is rotated perpendicular to the crystal c axis, we observed, directly for the first time, a remarkable reorientation of the spin plane simultaneous with rotation of the incommensurate wavevector, by quantitatively deducing the conversion of the energetically less favorable domain to a more favorable one. At high enough fields parallel to the c axis, the data are consistent with either a field-induced commensurate spiral magnetic structure or an incommensurate spiral magnetic structure with a disorder in the c direction, suggesting that high fields may have influence on interplanar ordering.

Title:
Modeling quasi-lattice with octagonal symmetry
Authors:
Girzhon, VV; Smolyakov, OV; Zakharenko, MI Author Full Names: Girzhon, V. V.; Smolyakov, O. V.; Zakharenko, M. I.
Source:
JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 119 (5):854-860; 10.1134/S1063776114110053 NOV 2014
Abstract:
We prove the possibility to use the method of modeling of a quasi-lattice with octagonal symmetry similar to that proposed earlier for the decagonal quasicrystal. The method is based on the multiplication of the groups of basis sites according to specified rules. This model is shown to be equivalent to the method of the periodic lattice projection, but is simpler because it considers merely two-dimensional site groups. The application of the proposed modeling procedure to the reciprocal lattice of octagonal quasicrystals shows a fairly good matching with the electron diffraction pattern. Similarly to the decagonal quasicrystals, the possibility of three-index labeling of the diffraction reflections is exhibited in this case. Moreover, the ascertained ratio of indices provides information on the intensity of diffraction reflections.

Title:
Single-Crystal Neutron Diffraction Study of Superstructure Ordering and Domain Behaviour in Brownmillerite-Type Ca2Fe2O5
Authors:
Auckett, JE; Studer, AJ; Ling, CD Author Full Names: Auckett, Josie E.; Studer, Andrew J.; Ling, Chris D.
Source:
AUSTRALIAN JOURNAL OF CHEMISTRY, 67 (12):1824-1828; 10.1071/CH14358 2014
Abstract:
We show that large single crystals of brownmillerite-type Ca2Fe2O5 can be grown using the floating-zone method under ambient pressure conditions, provided that the feed rods are pre-annealed to a very high density. Neutron diffraction data collected from these crystals show the emergence of a long-range ordered incommensurate phase at high temperature. The observation of this phase for the first time using neutrons proves that the incommensurate ordering of tetrahedral chains upon heating Ca2Fe2O5 is a truly long-range and bulk phenomenon. The results are used to compare and contrast the structures of Ca2Fe2O5 and Sr2Fe2O5, and are consistent with experimental observations of significantly higher oxide ionic conduction in the latter material.

Update: 21-Jan-2015


Title:
The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds
Authors:
Mariette, C; Guerin, L; Rabiller, P; Chen, YS; Bosak, A; Popov, A; Hollingsworth, MD; Toudic, B Author Full Names: Mariette, Celine; Guerin, Laurent; Rabiller, Philippe; Chen, Yu-Sheng; Bosak, Alexei; Popov, Alexander; Hollingsworth, Mark D.; Toudic, Bertrand
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):5-11; 10.1515/zkri-2014-1773 JAN 2015
Abstract:
n-Dodecane/urea is a member of the prototype series of n-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below T-c=248 K there appears a phase with rank four superspace group P6(1)22(00 gamma), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio gamma=C-h/C-g (C-host/C-guest), is found to be 0.632 +/- 0.005. Below T-c1=123 K, a monoclinic modulated phase is created with a constant shift along c of the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P12(1)1(alpha 0 gamma). Analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.

Title:
Incommensurate modulations in stoichiometric Ni2MnGa ferromagnetic shape memory alloy: an overview
Authors:
Singh, S; Barman, SR; Pandey, D Author Full Names: Singh, Sanjay; Barman, S. R.; Pandey, Dhananjai
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):13-22; 10.1515/zkri-2014-1784 JAN 2015
Abstract:
This article presents a brief overview of our recent work on the nature of long period modulation in the premartensite and martensite phases of Ni2MnGa ferromagnetic shape memory alloy using high resolution synchrotron x-ray powder diffraction patterns. The commensurate structure model using the Pnnm space group is unable to account for the peak positions of the satellite reflections that appear due to modulations correctly. LeBail and Rietveld refinements using the (3+1)-D super space group Immm(00 gamma)s00 show that the peak positions of all the reflections, including the satellites, can be explained satisfactorily using incommensurate modulations for both the premartensite and martensite phases. The incommensurate modulation vectors are found to be q=0.33761(5)c*=(1/3+delta(1))c* and 0.43160(3)c*=(3/7+delta(2))c*, where delta(1) and delta(2) are the degrees of incommensuration for the premartensite and martensite phases, respectively. The periodicity of the closest rational approximant of the premartensite and martensite phases are confirmed to be 3 M and 7 M, respectively, in agreement with single crystal diffraction results.

Title:
Insights from STEM and NBED studies into the local structure and growth mechanism of misfit layered compounds prepared using modulated reactants
Authors:
Hausler, I; Atkins, R; Falmbigl, M; Rudin, SP; Neumann, W; Johnson, DC Author Full Names: Haeusler, Ines; Atkins, Ryan; Falmbigl, Matthias; Rudin, Sven P.; Neumann, Wolfgang; Johnson, David C.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):45-54; 10.1515/zkri-2014-1761 JAN 2015
Abstract:
X-ray diffraction and transmission electron microscopy were used to probe the structure of the misfit compound [(SnSe)(1.15)](1)(VSe2)(1) grown using an elementally modulated precursor. The specular X-ray diffraction pattern contained only 00l reflections, which yielded a c lattice parameter of 1.203(1) nm. Cross-section STEM revealed alternating layers of SnSe and VSe2, in agreement with the structure model refined from the X-ray diffraction pattern using Rietveld refinement. Plan-view transmission electron microscopy revealed the in-plane grain structure of the films, yielding grain sizes in agreement with previously reported in plane X-ray diffraction studies and the cross-section STEM images. The plan view images also contained Moire fringes resulting from grains with different relative tilting on both sides of interfaces as well as Moire fringes resulting from different relative rotations between domains. An energy-filtered nano-beam electron diffraction pattern obtained from at least one domain in the [(SnSe)(1.15)](1) (VSe2)(1) sample investigated in cross section contained a series of resolvable supercell reflections along the c axis that indicated that the supercell c-axis lattice parameter was a multiple of three times that determined using X-ray diffraction. Energy filtered NBED of plan-view samples showed diffraction patterns from select regions with 12-fold symmetry, indicating that the arrangement of the layers is not rotationally random from layer to layer. This suggests that during the self-assembly of the amorphous modulated elemental precursor, the SnSe and VSe2 constituent layers must nucleate off the adjacent interfaces of the growing crystal, yielding layers that are locally rotationally aligned with growing crystal. Different processing conditions during the precursor to crystal self-assembly might enable the domain size and/or the extent of order to be controlled.

Title:
The modulated structure of labradorite
Authors:
Boysen, H; Kek, S Author Full Names: Boysen, Hans; Kek, Stefan
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):23-35; 10.1515/zkri-2014-1749 JAN 2015
Abstract:
The crystal structure of labradorite is characterized by two modulation waves with largely different periods of about 1500 angstrom and 50 angstrom, giving rise to s- and e-satellites, respectively. The problems to determine the true structure by diffraction methods are discussed. Since each s-lamella has its own e-modulation, common experiments are not sufficient. Using only s-satellites around main reflections assumes e-averaged structures of the s-lamellae. On the other hand, using only averaged e-satellites and main reflections integrated over the s-satellites leads to a hypothetical, idealised structure such as if there were no s-modulation. For this reason the analysis of an extensive data set, including e-satellites up to third order, cannot resolve the Ca/Na modulation unambiguously, although the Si/Al modulation can be determined consistently from directly refined occupancies and T-O bond lengths.

Title:
LEED studies on modulated surface structures
Authors:
Moritz, W Author Full Names: Moritz, Wolfgang
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 230 (1):37-43; 10.1515/zkri-2014-1787 JAN 2015
Abstract:
The problems occurring in structure analyses of modulated surfaces by LEED or X-ray diffraction are briefly discussed. In previous LEED studies of modulated surfaces a commensurate unit cell and Fourier coefficients to describe the modulation function has been used. The wave length of the modulation and the size of the supercell are limited in this way by the computational effort of the multiple scattering calculations. To overcome this problem an approximation is proposed allowing the analysis of commensurate or incommensurate surface modulations with long wave lengths.

Title:
Density-wave instabilities of fractionalized Fermi liquids
Authors:
Chowdhury, D; Sachdev, S Author Full Names: Chowdhury, Debanjan; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (24):10.1103/PhysRevB.90.245136 DEC 22 2014
Abstract:
Recent experiments in the underdoped regime of the hole-doped cuprates have found evidence for an incommensurate charge density-wave state. We present an analysis of the charge ordering instabilities in a metal with antiferromagnetic correlations, where the electronic excitations are coupled to the fractionalized excitations of a quantum fluctuating antiferromagnet on the square lattice. The resulting charge density-wave state emerging out of such a fractionalized Fermi liquid (FL*)has wave vectors of the form (+/- Q(0),0),(0, +/- Q(0)), with a predominantly d-form factor, in agreement with experiments on a number of different families of the cuprates. In contrast, as previously shown, the charge density-wave instability of a nearly antiferromagnetic metal with a large Fermi surface, interacting via short-range interactions, has wave vectors of the type (+/- Q(0), +/- Q(0)). Our results show that the observed charge density-wave appears as a low-energy instability of a fractionalized metallic state linked to the proximity to an antiferromagnetic insulator, and the pseudogap regime can be described by such a metal at least over intermediate length and energy scales.

Title:
BaGe6 and BaGe6-x : Incommensurately Ordered Vacancies as Electron Traps
Authors:
Akselrud, L; Wosylus, A; Castillo, R; Aydemir, U; Prots, Y; Schnelle, W; Grin, Y; Schwarz, U Author Full Names: Akselrud, Lev; Wosylus, Aron; Castillo, Rodrigo; Aydemir, Umut; Prots, Yurii; Schnelle, Walter; Grin, Yuri; Schwarz, Ulrich
Source:
INORGANIC CHEMISTRY, 53 (24):12699-12705; 10.1021/ic5021065 DEC 15 2014
Abstract:
We report the high-pressure high-temperature synthesis of the germanium-based framework compounds BaGe6 (P = 15 GPa, T = 1073 K) and BaGe6-x (P = 10 GPa, T = 1073 K) which are metastable at ambient conditions. In BaGe6-x, partial fragmentation of the BaGe6 network involves incommensurate modulations of both atomic positions and site occupancy. Bonding analysis in direct space reveals that the defect formation in BaGe6-x is associated with the establishment of free electron pairs around the defects. In accordance with the electron precise composition of BaGe6-x for x = 0.5, physical measurements evidence semiconducting electron transport properties which are combined with low thermal conductivity.

Title:
Structural phase transition associated with van Hove singularity in 5d transition metal compound IrTe2
Authors:
Qian, T; Miao, H; Wang, ZJ; Shi, X; Huang, YB; Zhang, P; Xu, N; Zeng, LK; Ma, JZ; Richard, P; Shi, M; Xu, G; Dai, X; Fang, Z; Fang, AF; Wang, NL; Ding, H Author Full Names: Qian, T.; Miao, H.; Wang, Z. J.; Shi, X.; Huang, Y. B.; Zhang, P.; Xu, N.; Zeng, L. K.; Ma, J. Z.; Richard, P.; Shi, M.; Xu, G.; Dai, X.; Fang, Z.; Fang, A. F.; Wang, N. L.; Ding, H.
Source:
NEW JOURNAL OF PHYSICS, 16 10.1088/1367-2630/16/12/123038 DEC 15 2014
Abstract:
We have investigated the electronic states of IrTe2 by using angle-resolved photoemission spectroscopy to elucidate the origin of the structural phase transition. Both the Ir 4f and Te 4d core level spectra exhibit dramatic splitting below the phase transition temperature T-s, suggesting that there exist two inequivalent Ir and Te sites with distinctly different electronic states in the distorted phase. The band related to the saddle points at the Fermi level (E-F) is strongly reconstructed, which removes the van Hove singularity from E-F below T-s. The wavevector connecting the adjacent saddle points is consistent with the in-plane superstructure modulation wavevector. These results indicate that the phase transition in IrTe2 is intimately associated with the saddle points. As the van Hove singularity mainly originates from the Te p(x)+p(y) orbitals, the Te 5p electronic states play a dominant role in the structural phase transition.

Title:
Diagnostics of a spatial spin-modulated structure using nuclear magnetic resonance and Mossbauer spectroscopy
Authors:
Rusakov, VS; Pokatilov, VS; Sigov, AS; Matsnev, ME; Gubaidulina, TV Author Full Names: Rusakov, V. S.; Pokatilov, V. S.; Sigov, A. S.; Matsnev, M. E.; Gubaidulina, T. V.
Source:
JETP LETTERS, 100 (7):463-469; 10.1134/S0021364014190102 DEC 2014
Abstract:
Methods of the diagnostics of the spatial spin-modulated structure of the cycloidal type in multiferroics based on nuclear magnetic resonance and Mossbauer spectroscopy have been considered. It has been established that Mossbauer spectroscopy makes it possible to determine the anharmonicity parameter of the spatial spin-modulated structure of the cycloidal type with no worse accuracy than nuclear magnetic resonance with higher resolution. Mossbauer spectroscopy, being sensitive to the hyperfine quadrupole interaction of the nucleus in the excited state, makes it possible to obtain additional information on the features of the spatial spin-modulated structure.

Title:
Effects of Au-Addition on Plastic Deformation Ability of Zr-Cu-Ni-Al Bulk Metallic Glasses
Authors:
Yamada, M; Yamasaki, T; Fujita, K; Yokoyama, Y; Kim, DH Author Full Names: Yamada, Masahiro; Yamasaki, Tohru; Fujita, Kazutaka; Yokoyama, Yoshihiko; Kim, Do Hyang
Source:
JOURNAL OF THE JAPAN INSTITUTE OF METALS, 78 (12):449-458; 10.2320/jinstmet.J2014042 DEC 2014
Abstract:
Effects of Au-addition on plastic deformation ability of Zr-Cu-Ni-Al bulk metallic glasses (BMGs) during compression and tensile tests have been examined. Zr65Cu20Ni5Al10 BMG(Zr-65) and Zr60+xCu22-xNi5Al10Au3(x= 0, 5, 6.5, 8, 9 at.) BMGs (Zr60Au3-Zr69Au3) have been prepared by a tilt casting method. By the Au. addition on the BMGs containing Zr. content of 65 at. and more, precipitation of icosahedral quasicrystalline phase (I. phase) in supercooled liquids was observed, resulting in large increase of viscosity in the supercooled liquids. Compression and tensile tests were carried out in these BMGs under various strain rates of 1 similar to 5x10 (4)/s at room temperature. In the compression test of the Zr65 BMG, plastic strain at fracture was about 10. and only several localized shear bands were observed. In the Zr65Au3 and Zr66.5Au3 BMGs, plastic strains at fracture were largely increased to 20. and above. In these cases, initial plastic strains of about 5. with large number of shear band were observed as macroscopically homogeneous deformation, and successive plastic strains along main shear band was observed. In the tensile test, large plastic strain at fracture of about 0.5% was also observed for the Zr66.5Au3 BMG. By transmission electron microscopic observations of the Au. addition BMGs, precipitation of nano. crystallites having about 10 nm in diameter was observed near the fractured surfaces of the compressive and tensile test specimens. Viscosity of supercooled liquids in shear bands was estimated by the stress. drop of serrations in the compressive stress. strain curves. It is considered that the large increase of the plastic strain is due to the drastic increase of the viscosity of the supercooled liquids formed inside shear bands during plastic deformation.

Title:
Spin reorientation and magnetic structure of HoCo12B6 ferrimagnetic compound
Authors:
Diop, LVB; Isnard, O Author Full Names: Diop, L. V. B.; Isnard, O.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 27 (2):10.1088/0953-8984/27/2/026004 JAN 21 2014
Abstract:
The magnetic phase diagram is determined by combining magnetization measurements, ac susceptibility and neutron diffraction. The crystal and magnetic structures are also investigated. The HoCo12B6 compound exhibits ferrimagnetic behavior below T-C = 147 K. Two antiferromagnetically coupled sublattices cancel out at the compensation temperature T-Comp = 46 K. HoCo12B6 undergoes a spin reorientation transition at T-SR = 76 K; the easy magnetization axis changes from axial to basal plane upon heating. The magnitude of the magnetic moments and their orientation are described and discussed. It is revealed that HoCo12B6 compound exhibits a commensurate magnetic structure below T-SR and an incommensurate one slightly above T-SR. Significantly different magnetic moments have been observed on the two Co crystal sites, a very low magnetic moment of 0.14(mu B) being refined on the Co 18 g position. In addition, the second order crystal electric-field parameter A(2)(0) at the rare-earth site is determined. This result is discussed and used to explain the observed spin reorientation transition by a competition between the Co and Ho sublattice anisotropy.

15-Jan-2015


Title:
A modulation wave approach to the order hidden in disorder
Authors:
Withers, R.
Source:
IUCrJ (2015) 2, 74-84
Abstract:
The usefulness of a modulation wave approach to understanding and interpreting the highly structured continuous diffuse intensity distributions characteristic of the reciprocal spaces of the very large family of inherently flexible materials which exhibit ordered `disorder' is pointed out. It is shown that both longer range order and truly short-range order are simultaneously encoded in highly structured diffuse intensity distributions. The long-range ordered crystal chemical rules giving rise to such diffuse distributions are highlighted, along with the existence and usefulness of systematic extinction conditions in these types of structured diffuse distributions.

Title:
Superspace crystallography: a key to the chemistry and properties
Authors:
Pinheiro, C. B; Abakumov, A. M.
Source:
IUCrJ (2015) 2, 137-154
Abstract:
An overview is given of the recent advances in the field of modulated molecular and inorganic crystals with an emphasis on the links between incommensurability, intermolecular and interatomic interactions and, wherever possible, the properties of the materials. The importance of detailed knowledge on the modulated structure for understanding the crystal chemistry and the functional properties of modulated phases is shown using selected examples of incommensurate modulations in organic molecular compounds and inorganic complex oxides.

Title:
Computational self-assembly of a one-component icosahedral quasicrystal
Authors:
Engel, M; Damasceno, PF; Phillips, CL; Glotzer, SC Author Full Names: Engel, Michael; Damasceno, Pablo F.; Phillips, Carolyn L.; Glotzer, Sharon C.
Source:
NATURE MATERIALS, 14 (1):109-116; 10.1038/NMAT4152 JAN 2015
Abstract:
Icosahedral quasicrystals (IQCs) are a form of matter that is ordered but not periodic in any direction. All reported IQCs are intermetallic compounds and either of face-centred-icosahedral or primitive-icosahedral type, and the positions of their atoms have been resolved from diffraction data. However, unlike axially symmetric quasicrystals, IQCs have not been observed in non-atomic (that is, micellar or nanoparticle) systems, where real-space information would be directly available. Here, we show that an IQC can be assembled by means of molecular dynamics simulations from a one-component system of particles interacting via a tunable, isotropic pair potential extending only to the third-neighbour shell. The IQC is body-centred, self-assembles from a fluid phase, and in parameter space neighbours clathrates and other tetrahedrally bonded crystals. Our findings elucidate the structure and dynamics of the IQC, and suggest routes to search for it and design it in soft matter and nanoscale systems.

Title:
ICOSAHEDRAL QUASICRYSTALS Assembled with one component
Authors:
Boissieu, M Author Full Names: de Boissieu, Marc
Source:
NATURE MATERIALS, 14 (1):18-19; 10.1038/nmat4183 JAN 2015

Title:
Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement
Authors:
de Nijs, B; Dussi, S; Smallenburg, F; Meeldijk, JD; Groenendijk, DJ; Filion, L; Imhof, A; van Blaaderen, A; Dijkstra, M Author Full Names: de Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, Marjolein
Source:
NATURE MATERIALS, 14 (1):56-60; 10.1038/NMAT4072 JAN 2015
Abstract:
Icosahedral symmetry, which is not compatible with truly long-range order, canbefoundinmany systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids(1-12). To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential(1,3,6-12). Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure (13,14). Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.

Title:
Frustration and multicriticality in the antiferromagnetic spin-1 chain
Authors:
Pixley, JH; Shashi, A; Nevidomskyy, AH Author Full Names: Pixley, J. H.; Shashi, Aditya; Nevidomskyy, Andriy H.
Source:
PHYSICAL REVIEW B, 90 (21):10.1103/PhysRevB.90.214426 DEC 15 2014
Abstract:
The antiferromagnetic spin-1 chain has a venerable history and has been thought to be well understood. Here, we show that inclusion of both next-nearest-neighbor (alpha) and biquadratic (beta) interactions results in a rich phase diagram with a multicritical point that has not been observed before. We study the problem using a combination of the density matrix renormalization group (DMRG), an analytic variational matrix product state wave function, and conformal field theory. For negative beta < beta*, we establish the existence of a spontaneously dimerized phase, separated from the Haldane phase by the critical line alpha(c) (beta) of second-order phase transitions. In the opposite regime, beta > beta*, the transition from the Haldane phase becomes first order into the next-nearest-neighbor (NNN) AKLT phase. Based on the field theoretical arguments and DMRG calculations, we find that these two regimes are separated by a multicritical point (beta*, alpha*) of a different universality class, described by the level-4 SU(2) Wess-Zumino-Witten conformal theory. From the DMRG calculations, we estimate this multicritical point to lie in the range -0.2 < beta* < -0.15 and 0.47 < alpha* < 0.53. We further find that the dimerized and NNN-AKLT phases are separated from each other by a line of first-order phase transitions that terminates at the multicritical point. We establish that transitions out of the Haldane phase into the dimer or NNN-AKLT phases are topological in nature and occur either with or without closing of the bulk gap, respectively. We also study short-range incommensurate-to-commensurate transitions in the resulting phase diagram. Inside the Haldane phase, we show the existence of two incommensurate crossovers: the Lifshitz transition and the disorder transition of the first kind, marking incommensurate correlations in momentum and real space, respectively. Notably, these crossover lines stretch across the entire (beta, alpha) phase diagram, merging into a single incommensurate-to-commensurate transition line for negative beta less than or similar to beta* inside the dimer *phase*. This behavior is qualitatively similar to that seen in classical frustrated two-dimensional spin models, by way of the quantum (1+ 1) D to classical 2D correspondence.

Title:
Isothermal section of Mg-rich corner in Mg-Zn-Al ternary system at 335 degrees C
Authors:
Ren, YP; Sun, SN; Wang, LQ; Guo, Y; Li, HX; Li, S; Qin, GW Author Full Names: Ren, Yu-ping; Sun, Shi-neng; Wang, Li-qing; Guo, Yun; Li, Hong-xiao; Li, Song; Qin, Gao-wu
Source:
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA, 24 (11):3405-3412; 10.1016/S1003-6326(14)63483-X NOV 2014
Abstract:
The phase equilibria and compositions at the Mg-rich corner of the Mg-Zn-Al ternary system at 335 degrees C were systemically investigated through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). It is experimentally testified that the alpha-Mg solid solution is not in equilibrium with the Mg-32(Al, Zn)(49) (tau) ternary intermetallic compound or q quasicrystalline phase, but only in equilibrium with one ternary intermetallic compound Al5Mg11Zn4 (phi). The whole composition range of the phi phase was also obtained at 335 degrees C, i.e., 52.5%-56.4% Mg, 13.6%-24.0% Al, 19.6%-33.9% Zn (mole fraction). The solubility of Al in the MgZn phase is remarkably more than that in the Mg7Zn3 phase, and the maximum is about 8.6% Al. Aluminum and zinc are simultaneously soluble in the alpha-Mg solid solution.

Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, *incommensurately modulated* alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the *incommensurately modulated* alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features *satellite reflections* of first order with very low intensities.

Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a *modulated structure* that represents a transitory *phase*. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.

Update: 8-Jan-2015


Title:
Incommensurate-to-incommensurate phase transition in Eu metal at high pressures
Authors:
Husband, RJ; Loa, I; Munro, KA; McBride, EE; Evans, SR; Liermann, HP; McMahon, MI Author Full Names: Husband, R. J.; Loa, I.; Munro, K. A.; McBride, E. E.; Evans, S. R.; Liermann, H. -P.; McMahon, M. I.
Source:
PHYSICAL REVIEW B, 90 (21):10.1103/PhysRevB.90.214105 DEC 8 2014
Abstract:
High pressure x-ray powder-diffraction experiments were performed on europium metal up to similar to 70 GPa. Above 38 GPa, europium transforms from the incommensurately modulated Eu-IV phase to a second phase with an incommensurately modulated crystal structure, Eu-V. This is a previously unseen incommensurately modulated to incommensurately modulated transition in the elements at high pressure. High-pressure high-temperature experiments were also performed up to 449 K in order to make an initial estimate of the positions of the phase boundaries of the incommensurate phases.

Title:
Toward the Understanding of Modulation in Molecular Materials: Barluenga's Reagent and its Analogues.
Authors:
Kim, Y; Mckinley, EJ; Christensen, KE; Rees, NH; Thompson, AL Author Full Names: Kim, Yejin; Mckinley, Emma J.; Christensen, Kirsten E.; Rees, Nicholas H.; Thompson, Amber L.
Source:
CRYSTAL GROWTH & DESIGN, 14 (12):6294-6301; 10.1021/cg500983s DEC 2014
Abstract:
Investigations into the phase transition of Barluengas reagent revealed a transient incommensurately modulated phase; the structures are presented herein. To understand the origin of the modulated phase and the chemistry that can affect it, analogues of Barluengas reagent were synthesized and studied. In this context, the halogen and anion can easily be exchanged. Studying different analogues led to the development of the Ratchet Model to describe the behavior in the solid state leading to a better understanding of modulation in this class of molecular crystal structure.

Title:
Breakdown of the Fermi arcs in underdoped cuprates by incommensurate charge density waves
Authors:
Gor'kov, LP Author Full Names: Gor'kov, L. P.
Source:
JETP LETTERS, 100 (6):403-406; 10.1134/S0021364014180040 NOV 2014
Abstract:
Interactions between the coherent excitations on disconnected arcs along a "bare" Fermi surface (the socalled Fermi arcs FAs) seen by angle-resolved photo emission spectroscopy (ARPES) in several underdoped (UD) cuprates and incommensurate charge density wave (IC CDW) ordering at lowering of the temperature have been studied. The carriers on FAs scatter strongly on the short-wavelength potential of CDW. The large momentum transfer relates FAs with the electronic states lying deeply under the chemical potential thus involving into consideration the Fermi liquid interactions. At low temperatures IC CDW may fully destroy low lying excitations on the Fermi arcs, leaving electrons on the pocket at the I" point as the only charged elementary excitations in the CDW phase in UD cuprates. The results infer competition between superconducting and CDW order parameters.

Title:
Magnetic shape memory effect and highly mobile twin boundaries
Authors:
Heczko, O Author Full Names: Heczko, O.
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 30 (13A):1559-1578; 10.1179/1743284714Y.0000000599 NOV 2014
Abstract:
The magnetic shape memory effect can be classified as an example of the multiferroic effect combining ferro-elasticity and (ferro) magnetism. After short overview of all known effects the focus is on magnetic field induced structure reorientation (MIR) in the martensite of Ni-Mn-Ga. In this material giant deformations of up to 12% have been observed in moderate magnetic fields. The phenomenology of the effect is first discussed and a model presented. The properties of Ni-Mn-Ga relevant to MIR are then considered. One necessary condition for MIR is a highly mobile twin boundary or interface between two differently oriented martensite variants (ferroelastic domains). In 10M modulated martensite, two types of mobile twin boundary (type I and type II) are observed with complex layered microstructures consisting of a hierarchy of twinning systems. The boundaries strongly differ according to the magnitude and temperature dependence of the twinning stress. Finally, the nature of these boundaries and their different behaviour is reviewed.

Title:
Linear magneto-optical effect in the incommensurate phase of antiferromagnetic LiNiPO4
Authors:
Kharchenko, YM; Miloslavskaya, OV; Kharchenko, MF Author Full Names: Kharchenko, Yu. M.; Miloslavskaya, O. V.; Kharchenko, M. F.
Source:
LOW TEMPERATURE PHYSICS, 40 (11):1029-1031; 10.1063/1.4901407 NOV 2014
Abstract:
A linear magneto-optical effect, birefringence of linearly polarized light that is directly proportional to magnetic field strength, is observed in magnetoelectric crystals of the orthophosphate LiNiPO4. This effect is especially pronounced in the incommensurate antiferromagnetic phase of the crystal. The linear magneto-optical effect indicates that the magnetic symmetry groups of the incommensurate, as well as the commensurate, phases of antiferromagnetic LiNiPO4 lack an anti-inversion operation. This fact is consistent with the existence of ultraweak ferromagnetism in the crystal and indicates that this antiferromagnet has more complicated magnetic structures than those found in neutron diffraction experiments. (C) 2014 AIP Publishing LLC.

Title:
Mechanical Alloying of Al73Cu11Cr16 Alloy from Ion Irradiated Powders
Authors:
Medvedeva, EV; Tcherdyntsev, VV; Makhin'ko, FF; Gushchina, NV; Ovchinnikov, VV Author Full Names: Medvedeva, E. V.; Tcherdyntsev, V. V.; Makhin'ko, F. F.; Gushchina, N. V.; Ovchinnikov, V. V.
Source:
ACTA PHYSICA POLONICA A, 126 (4):979-983; OCT 2014
Abstract:
Al73Cu11Cr16 alloys were prepared by mechanical alloying of the irradiated by Ar+ ions elemental powders. Evolution of alloy structure at ball milling, as well as during the further annealing, was investigated using X-ray diffraction and differential scanning calorimetry. It was shown that ball milling leads to the Cu dissolution in Al and Cr and to the formation of Al2Cu intermetallic phase. An increase of the milling duration leads to an increase of the Al2Cu phase content in the samples. Ion irradiation of initial elemental powders results in an increase of their interaction rate at milling. In the case of irradiated powders using as initial materials, a content of Al2Cu phase after milling is higher than in the case of using non-irradiated elemental powders. No effect of irradiation of initial elemental powders on the phase transformation at heating was observed. The annealing results in the decomposition of Al- and Cr-based supersaturated solid solutions. An increase in the Al2Cu phase content at heating was observed only in the samples, which were milled for 4 h. In the samples milled for 14 h, nearly no increase in Al2Cu phase content at heating was observed. Heating up to 500-600 degrees C results in the single-phase decagonal quasicrystalline phase formation for all of the studied samples.

Update: 1-Jan-2015


Title:
Brillouin scattering, DSC, dielectric and X-ray diffraction studies of phase transitions in antiferroelectric PbHfO3:Sn
Authors:
Maczka, M; Kim, TH; Gagor, A; Jankowska-Sumara, I; Majchrowski, A; Kojima, S Author Full Names: Maczka, Miroslaw; Kim, Tae Hyun; Gagor, Anna; Jankowska-Sumara, Irena; Majchrowski, Andrzej; Kojima, Seiji
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 622 935-941; 10.1016/j.jallcom.2014.11.020 FEB 15 2015
Abstract:
Specific heat, dielectric, powder X-ray diffraction and Brillouin scattering studies of phase transitions in antiferroelectric PbHf0.975Sn0.025O3 crystal were performed. The specific heat data revealed clear anomalies at T-1 = 473.5 and T-2 = 426.3 K on cooling, which could be attributed to onset of first order phase transitions from the paraelectric (PE) phase to an intermediate antiferroelectric phase (AFE2) and the AFE2 phase to another antiferroelectric phase (AFE1), respectively. The estimated entropy changes at T-1 and T-2 pointed to mainly an order-disorder and displacive character of these transitions, respectively. X-ray diffraction data showed a complex superstructure of the intermediate phase with a = 11.895(6) angstrom, b = 11.936(4) angstrom, c = 8.223(3)angstrom at 453 K. Brillouin studies revealed pronounced softening of longitudinal acoustic (LA) mode in the PE phase associated with its broadening. The broadening and softening exhibited maximum values at T-1. Additional acoustic anomalies, that is, abrupt frequency shifts for LA and transverse acoustic (TA) modes were also observed at T-2. Brillouin scattering data also showed presence of a broad central peak (CP) that exhibited highest intensity at T-1. The observed temperature dependences of acoustic modes and CP indicate order-disorder character of the FE to AFE2 phase transition and importance of polar precursor clusters in the PE phase. The obtained data also suggest that the intermediate antiferroelectric phases in Sn4+ doped PbHfO3 and PbZrO3 may have very similar structures with incommensurate modulations. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Atomic structure solution of the complex quasicrystal approximant Al77Rh15Ru8 from electron diffraction data
Authors:
Samuha, S; Mugnaioli, E; Grushko, B; Kolb, U; Meshi, L Author Full Names: Samuha, Shmuel; Mugnaioli, Enrico; Grushko, Benjamin; Kolb, Ute; Meshi, Louisa
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 999-1005; 10.1107/S2052520614022033 6 DEC 2014
Abstract:
The crystal structure of the novel Al77Rh15Ru8 phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al77Rh15Ru8 E-phase is orthorhombic [Pbma, a = 23.40 (5), b = 16.20 (4) and c = 20.00 (5) angstrom] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the epsilon(6)-phase formed in Al-Rh-Ru at close compositions.

Title:
Field-Induced Spin-Flop in Antiferromagnetic Semiconductors with Commensurate and Incommensurate Magnetic Structures: Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS)
Authors:
Brant, JA; dela Cruz, C; Yao, JL; Douvalis, AP; Bakas, T; Sorescu, M; Aitken, JA Author Full Names: Brant, Jacilynn A.; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P.; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A.
Source:
INORGANIC CHEMISTRY, 53 (23):12265-12274; 10.1021/ic5011693 DEC 1 2014
Abstract:
Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors k(m) = [(1)/(2), (1)/(2), (1)/(2)] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mossbauer spectroscopy confirmed the presence of Fe2+ and Sn4+ as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy.

Title:
Structure and Magnetic Behaviours of Melt-Spun Ti1.4V0.6Ni Alloy Containing Icosahedral Quasicrystalline Phase
Authors:
Hu, W; Yin, C; Ma, ZY; Liu, WQ; Wang, LM Author Full Names: Hu, W.; Yin, C.; Ma, Z. Y.; Liu, W. Q.; Wang, L. M.
Source:
ASIAN JOURNAL OF CHEMISTRY, 26 (17):5821-5823; A SEP 2014
Abstract:
The ribbons of Ti1.4V0.6Ni and TiVNi alloys were synthesized by arc-melting and subsequent melt-spinning techniques. The structures and magnetic properties were investigated. The results showed that the icosahedral quasicrystal (I-phase), Ti2Ni-type face centered cubic (FCC) phase and body centered cubic (BCC) structural solid solution phase existed in Ti1.4V0.6Ni alloy and the Ti2Ni-type FCC phase and BCC solid solution phase presented in TiVNi alloy. The relationships of M-H (magnetization -magnetic field) and M-T (magnetization-temperature) of the alloy ribbons were investigated by using SQUID (superconductivity quantum interference device). The results demonstrated that the magnetic behaviour was different, which is the Ti1.4V0.6Ni alloy ribbons exhibited higher ferromagnetic properties than those of TiVNi alloy ribbons both at 15 and 300 K.

Update: 25-Dec-2014


Title:
In situ transmission electron microscopy investigation of quasicrystal-crystal transformations in Mg-Zn-Y alloys
Authors:
Liu, JF; Yang, ZQ; Ye, HQ Author Full Names: Liu, J. F.; Yang, Z. Q.; Ye, H. Q.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 621 179-188; 10.1016/j.jallcom.2014.09.177 FEB 5 2015
Abstract:
Evolution of icosahedral quasicrystals (IQC) in Mg-Zn-Y alloys during annealing was investigated by in situ transmission electron microscopy (TEM), in combination with differential thermal analysis and X-ray diffraction. In bulk samples, the IQC phase transformed to face-centered cubic phase W and hexagonal phase H at 720 K and 727 K, respectively. In TEM samples, IQC started to transform to W at 673 K and H at 688 K during heating, and H transformed to W at 623 K on cooling. Quantitative analysis of the in situ transformation process reveals that growth of both H and W is controlled by diffusion, agreeing with the Avrami's model. The transformed products have specific orientation relationships with the parent phases: 3-fold(IQC)//[0001](H)//[111](W) and 2- fold(IQC)//11 (2) over bar0](H)//[0 (1) over bar1](W). The specific orientation relationships are attributed to close structural correlation among icosahedron, distorted icosahedron and cuboctahedron in IQC, H and W phases. The close structure relationship among IQC, H and W phases on the unit-cell level plays an important role in the phase transformations. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Microstructure and tensile properties of as-extruded Mg-Li-ZnGd alloys reinforced with icosahedral quasicrystal phase
Authors:
Zhang, Y; Zhang, J; Wu, GH; Liu, WC; Zhang, L; Ding, WJ Author Full Names: Zhang, Yang; Zhang, Jie; Wu, Guohua; Liu, Wencai; Zhang, Liang; Ding, Wenjiang
Source:
MATERIALS & DESIGN, 66 162-168; 10.1016/j.matdes.2014.10.049 A FEB 5 2015
Abstract:
Mg-Li-Zn-Gd alloys reinforced with icosahedral quasicrystal phase (I-phase) were prepared by casting and deformed by hot extrusion. The microstructure and tensile properties of as-extruded Mg-Li-Zn-Gd alloys were investigated. It is found that I-phase formed in as-cast Mg-Li-Zn-Gd alloys and was broken into small particles during extrusion. After hot extrusion, both alpha-Mg and beta-Li phases were elongated along the extrusion direction. Dynamic recrystallization occurred in as-extruded Mg-Li-Zn-Gd alloys. Compared with Mg-9Li (L9) alloy, the improvement in mechanical properties especially the tensile strength of the as-extruded Mg-Li-Zn-Gd alloys was mainly ascribed to the formation of I-phase and their volume fraction. Moreover, the finely recrystallized grain structure can also attribute to the strength enhancement of the alloy. (C) 2014 Elsevier Ltd. All rights reserved.

Title:
Field dependence of the magnetic structure of TbMn2O5
Authors:
Chatterji, T; Brown, PJ Author Full Names: Chatterji, T.; Brown, P. J.
Source:
JOURNAL OF APPLIED PHYSICS, 116 (20):10.1063/1.4902840 NOV 28 2014
Abstract:
The evolution of the magnetic propagation vector of the magnetically ordered phases of TbMn2O5 has been studied as a function of magnetic field applied parallel to both [010] and [100] axes. The results have been used to construct (H, T) phase diagrams showing the regions of stability of the three distinct phases IC1, C, and IC2 known to exist in zero field. Application of magnetic field along [010] increases the stability range of the commensurate C phase at the expense of the two incommensurate phases IC1 and IC2, whereas applying the field along [100] has the opposite effect. The evolution with field of the magnetic structure of the C phase has been determined from the integrated intensities of sets of magnetic reflections measured with different field values. With the field along [010], there are no significant changes in structure in fields up to 6 T. Applying the field parallel to [100] leads to an apparently continuous increase in the z component of the propagation vector from 0.25 in zero field to approximate to 0.3 in 6 T. This change is accompanied by increasing ferromagnetic polarisation of the Tb sublattices. Polarised neutron measurements made on the fundamental reflections show that there is no significant ferromagnetic polarisation of any the Mn sublattices in fields of up to 6 T. (C) 2014 AIP Publishing LLC.

Title:
Structural Evolution of GdBaCo2O5+delta (delta=7/18) at Elevated Temperatures
Authors:
Ishizawa, N; Asaka, T; Kudo, T; Fukuda, K; Yasuhara, A; Abe, N; Arima, T Author Full Names: Ishizawa, Nobuo; Asaka, Toru; Kudo, Tatsunari; Fukuda, Koichiro; Yasuhara, Akira; Abe, Nobuyuki; Arima, Taka-hisa
Source:
CHEMISTRY OF MATERIALS, 26 (22):6503-6517; 10.1021/cm503132e NOV 25 2014
Abstract:
The structural chemistry of the double-layered perovskite-type gadolinium barium cobaltate, GdBaCo2O5+delta (0 < delta < 1/2), is not well-known, in comparison to the representative end-member phases alpha at delta = 0 and beta at delta = 1/2. This study unveils the structural evolution of the room-temperature stable phase gamma at delta = 7/18, using in situ single-crystal X-ray diffraction at elevated temperatures and electron microscopy. The gamma phase is essentially charge-ordered with Co3+ and Co2+ in a ratio of 8:1 and is incommensurately modulated in the five-dimensional superspace. The approximant of the modulated structure reveals the presence of island-like charge-ordered square cell domains interleaved with a discommensurate zone. The gamma phase underwent a reversible first-order phase transition at similar to 380 K to the commensurate phase beta, without any change in composition at delta = 7/18. The charge ordering of Co in gamma ceased in beta, in combination with a redistribution of oxygen atoms (O3) in the [GdO delta] layer and a change in the spin state of Co. Further heating of beta induced partial oxygen detachment at similar to 700 K, causing a change in d from 7/18 (similar to 0.389) to 0.19 in the nitrogen flow atmosphere. The crystal irreversibly turned into a tetragonal prototypal phase a. A peristaltic oxygen transport mechanism in GdBaCo2O5+delta (0 <= delta <= 1/2) accompanied by electron transfer and resulting in polaronic local structure relaxation is also proposed. This mechanism underpins a usefulness of the compound for application to solid oxide fuel cells as revealed in recent years.

Update: 18-Dec-2014


Title:
Automated effective band structures for defective and mismatched supercells
Authors:
Brommer, P; Quigley, D Author Full Names: Brommer, Peter; Quigley, David
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 26 (48):10.1088/0953-8984/26/48/485501 DEC 3 2014
Abstract:
In plane-wave density functional theory codes, defects and incommensurate structures are usually represented in supercells. However, interpretation of E versus (k) over right arrow band structures is most effective within the primitive cell, where comparison to ideal structures and spectroscopy experiments are most natural. Popescu and Zunger recently described a method to derive effective band structures (EBS) from supercell calculations in the context of random alloys. In this paper, we present bs_sc2pc, an implementation of this method in the CASTEP code, which generates an EBS using the structural data of the supercell and the underlying primitive cell with symmetry considerations handled automatically. We demonstrate the functionality of our implementation in three test cases illustrating the efficacy of this scheme for capturing the effect of vacancies, substitutions and lattice mismatch on effective primitive cell band structures.

Title:
Wear assessment of composite surface layers in Al-6Mg alloy reinforced with AlCuFe quasicrystalline particles: Effects of particle size, microstructure and hardness
Authors:
Mordyuk, BN; Prokopenko, GI; Milman, YV; Iefimov, MO; Grinkevych, KE; Sameljuk, AV; Tkachenko, IV Author Full Names: Mordyuk, B. N.; Prokopenko, G. I.; Milman, Yu. V.; Iefimov, M. O.; Grinkevych, K. E.; Sameljuk, A. V.; Tkachenko, I. V.
Source:
WEAR, 319 (1-2):84-95; 10.1016/j.wear.2014.07.011 NOV 15 2014
Abstract:
Aluminium alloys reinforced with ceramic, intermetallic or quasicrystalline particles can fill the needs of automotive and aerospace industries due to their superior properties. In this paper, near-surface layers in Al-6Mg alloy specimens were modified using an ultrasonic impact treatment (UIT) process, which induces mechanical mixing of matrix and reinforces quasicrystalline (QC) Al63Cu25Fe12 particles to be introduced into a zone of severe plastic deformation. The wear and friction behaviours of the matrix alloy and QC reinforced layers were investigated in quasi-static and dynamic conditions with particular attention to the effects of QC particles size and test type on wear resistance and microhardness of subsurface composite layers in Al-6Mg alloy. XRD and SEM analyses show that the layers of 40-50 mu m dispersed fine QC(F) (0.5-3 mu m) or coarse QC(C) (similar to 15 mu m) particles, with volume fractions V-f of about 9% and 22%, respectively. In comparison to the annealed Al-6Mg alloy, noticeable increment in wear resistance was registered only for the composite layer reinforced with QC(F) particles. On the contrary, the QC(C) particles being fractured at the fabrication process and/or at the wear tests facilitate three-body abrasive wear conditions and deteriorate the wear resistance of the alloy. SEM and confocal laser microscopy show changes in wear mechanism from microcutting/ploughing in the QC(F) reinforced layer to microcracking/fracturing in the case of QC(C) reinforcement. Fine QC(F) particles are preferred for better wear resistance both at the quasi-static and dynamic conditions. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Photocatalytic and magnetic behaviors of BiFeO3 thin films deposited on different substrates
Authors:
Xu, HM; Wang, HC; Shen, Y; Lin, YH; Nan, CW Author Full Names: Xu, Hao-Min; Wang, Huan-Chun; Shen, Yang; Lin, Yuan-Hua; Nan, Ce-Wen
Source:
JOURNAL OF APPLIED PHYSICS, 116 (17):10.1063/1.4901066 NOV 7 2014
Abstract:
Single phase polycrystalline BiFeO3 thin films were grown on three different substrates via chemical solution deposition. Our results indicate that the band gap of as-prepared BiFeO3 films can be tuned (2.02-2.67eV) by the grain size effects caused by the substrates. These BiFeO3 films show good photocatalytic properties by the degradation of Congo red solution under visible-light irradiation (lambda>400 nm). Additionally, weak ferromagnetic behaviors can be observed at room temperature in all the films, which should be correlated to the destruction of the incommensurate cycloid spin structure of BiFeO3 phase and the coexistence of Fe3+ and Fe2+ as confirmed by X-ray photoelectron spectroscopy. (C) 2014 AIP Publishing LLC.

Title:
Formation of less-known structurally complex zeta(b) and orthorhombic quasicrystalline approximant epsilon(n) on solidification of selected Al-Pd-Cr alloys
Authors:
Adamech, M; Cernickova, I; Duriska, L; Kolesar, V; Drienovsky, M; Bednarcik, J; Svoboda, M; Janovec, J Author Full Names: Adamech, M.; Cernickova, I.; Duriska, L.; Kolesar, V.; Drienovsky, M.; Bednarcik, J.; Svoboda, M.; Janovec, J.
Source:
MATERIALS CHARACTERIZATION, 97 189-198; 10.1016/j.matchar.2014.10.001 NOV 2014
Abstract:
The evolution of phases was investigated on cooling of Al71Pd24Cr5, Al73Pd20Cr7, and Al73Pd23Cr4 alloys from 1350 degrees C down to ambient temperature with the rate of 10 degrees C.min(-1). To perform the investigation, differential thermal analysis, synchrotron X-ray powder diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used. In all the investigated alloys structurally complex phases epsilon(n) (epsilon(6) + epsilon(28)) and zeta(b), as well as the delta-phase were identified. Based on the results of differential thermal analysis, sequences of phase transformations were determined. The Al71Pd24Cr4 alloy started to solidify at 1031.4 degrees C through beta. Primary dendrites of zeta(b) were observed in Al73Pd20Cr7 and Al73Pd23Cr4 alloys. In the second step of solidification delta and/or zeta(b) were formed. The peritectic reaction, liquid + zeta(b) + delta -> epsilon(n) + zeta(b) + delta, leading to the formation of the quasicrystalline approximant epsilon(n) (epsilon(6) + epsilon(28)) took place in the final step of solidification at approximately 792 degrees C. (C) 2014 Published by Elsevier Inc.

Title:
Microstructure and compression deformation behavior in the quasicrystal-reinforced Mg-8Zn-1Y alloy solidified under super-high pressure
Authors:
Dong, Y; Lin, XP; Xu, R; Zheng, RG; Fan, ZB; Liu, SJ; Wang, Z Author Full Names: Dong Yun; Lin Xiaoping; Xu Rui; Zheng Runguo; Fan Zhibin; Liu Shijun; Wang Zhe
Source:
JOURNAL OF RARE EARTHS, 32 (11):1048-1055; 10.1016/S1002-0721(14)60182-4 NOV 2014
Abstract:
The microstructure of Mg-8Zn-1Y alloy solidified under super-high pressure was analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). And, compression deformation behavior at room-temperature was studied. The results showed that the microstructure of Mg-8Zn-1Y alloy solidified under ambient pressure and super-high pressure was both mainly composed of alpha-Mg and quasicrystal I-Mg3Zn6Y. Solidification under super-high pressure contributed to refining solidified microstructure and changing morphology of the intergranular second phase. The morphology of intergranular second phase (quasicrystal I-Mg3Zn6Y) was transformed from continuous network (ambient pressure) to long island (high pressure) and finally to granular (super-high pressure) with the increase in pressure. The compressive strength, yield strength and rupture strain of the samples solidified under ambient pressure were significantly improved from 262.6 MPa, 244.4 MPa and 13.3% to 437.3 MPa, 368.9 MPa and 24.7% under the pressure of 6 GPa, respectively. Under ambient pressure, cleavage plane on compressive fracture was large and smooth. When it was solidified under the pressure ranging from 4 to 6 GPa, cleavage plane on compressive fracture was small and coarse. In addition, dimple, tear ridge and lobate patterns existed.

Title:
Anti-plane problem analysis for icosahedral quasicrystals under shear loadings
Authors:
Li, W; Chai, YZ Author Full Names: Li Wu; Chai Yu-Zhen
Source:
CHINESE PHYSICS B, 23 (11):10.1088/1674-1056/23/11/116201 NOV 2014
Abstract:
The present paper is concerned with the longitudinal shear elasticity of three-dimensional icosahedral quasicrystals. By virtue of the Dugdale hypothesis along with the method of complex potential theory, it involves two defect problems of the icosahedral quasicrystals. The first one is the calculation of stress intensity factors and the size of the cohesive force zone in a half-infinite crack. Meanwhile, the crack tip tearing displacements can be exactly derived. The other is the demonstration of the generalized stress intensity factors induced by a sharp V-notch as an extension of a crack. The generalized E-integral around the notch tip gives the energy release rate when the V-notch degenerates into a crack. Apart from their own usefulness in carrying out some simplified crack analyses, the results obtained in this work can particularly serve as a basis for fracture mechanics of anti-plane defect problems of icosahedral quasicrystals.

Title:
Tailoring microstructure of Mg-Zn-Y alloys with quasicrystal and related phases for high mechanical strength
Authors:
Singh, A Author Full Names: Singh, Alok
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044803 AUG 2014
Abstract:
The occurrence of a stable icosahedral (i-) phase, which is quasicrystalline with an icosahedral (fivefold) symmetry, on the equilibrium phase diagram of Mg-Zn-RE (RE = Y, Gd, Tb, Dy, Ho or Er) alloys opened up an interesting possibility of developing a new series of magnesium alloys for structural applications. Alloys based on the i-phase have been studied for the past 14 years. Ultra-high strengths combined with good ductility have been shown. Here we show two strategies for tailoring microstructures for very high strengths in Mg-Zn-Y alloys. One of them involves strengthening by a fine distribution of rod-like beta(')(1) precipitates, where the matrix grain size is not critical. The alloy is solutionized at a high temperature of 480 degrees C to dissolve a large part of the i-phase, followed by a high temperature extrusion (similar to 430 degrees C) and a low temperature ageing to reprecipitate phases with fine size distribution. At first, phase transformations involved in this procedure are described. The closeness of the structure of the beta(')(1) precipitates to the i-phase is brought out. By this procedure, tensile yield strengths of over 370 MPa are obtained in grain sizes of 20 mu m. In another strategy, the alloys are chill cast and then extruded at low temperatures of about 250 degrees C. Ultra-fine grains are produced by enhanced recrystallization due to presence of the i-phase. At the same time nano-sized precipitates are precipitated dynamically during extrusion from the supersaturated matrix. Ultra-high tensile strengths of up to 400 MPa are obtained in combination with ductility of 12 to 16%. Analysis of the microstructure shows that strengthening by the i-phase occurs by enhanced recrystallization during extrusion. It produces ultra-fine grain sizes to give very high strengths, and moderate texture for good ductility. Fine distribution of the i-phase and precipitates contribute to strengthening and provide microstructre stability. Ultra-high strength over a very wide range of grain sizes is thus demonstrated, by utilizing different strengthening effects.

Title:
Metallic-covalent bonding conversion and thermoelectric properties of Al-based icosahedral quasicrystals and approximants
Authors:
Takagiwa, Y; Kimura, K Author Full Names: Takagiwa, Yoshiki; Kimura, Kaoru
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044802 AUG 2014
Abstract:
In this article, we review the characteristic features of icosahedral cluster solids, metallic-covalent bonding conversion (MCBC), and the thermoelectric properties of Al-based icosahedral quasicrystals and approximants. MCBC is clearly distinguishable from and closely related to the well-known metal-insulator transition. This unique bonding conversion has been experimentally verified in 1/1-AlReSi and 1/0-Al12Re approximants by the maximum entropy method and Rietveld refinement for powder x-ray diffraction data, and is caused by a central atom inside the icosahedral clusters. This helps to understand pseudogap formation in the vicinity of the Fermi energy and establish a guiding principle for tuning the thermoelectric properties. From the electron density distribution analysis, rigid heavy clusters weakly bonded with glue atoms are observed in the 1/1-AlReSi approximant crystal, whose physical properties are close to icosahedral Al-Pd-TM (TM: Re, Mn) quasicrystals. They are considered to be an intermediate state among the three typical solids: metals, covalently bonded networks (semiconductor), and molecular solids. Using the above picture and detailed effective mass analysis, we propose a guiding principle of weakly bonded rigid heavy clusters to increase the thermoelectric figure of merit (ZT) by optimizing the bond strengths of intra-and intericosahedral clusters. Through element substitutions that mainly weaken the inter-cluster bonds, a dramatic increase of ZT from less than 0.01 to 0.26 was achieved. To further increase ZT, materials should form a real gap to obtain a higher Seebeck coefficient.

Title:
Magnetism in icosahedral quasicrystals: current status and open questions
Authors:
Goldman, AI Author Full Names: Goldman, Alan I.
Source:
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 15 (4):10.1088/1468-6996/15/4/044801 AUG 2014
Abstract:
Progress in our understanding of the magnetic properties of R-containing icosahedral quasicrystals (R = rare earth element) from over 20 years of experimental effort is reviewed. This includes the much studied R-Mg-Zn and R-Mg-Cd ternary systems, as well as several magnetic quasicrystals that have been discovered and investigated more recently including Sc-Fe-Zn, R-Ag-In, Yb-Au-Al, the recently synthesized R-Cd binary quasicrystals, and their periodic approximants. In many ways, the magnetic properties among these quasicrystals are very similar. However, differences are observed that suggest new experiments and promising directions for future research.

Update: 11-Dec-2014


Title:
Structural and electrical properties of a new ([SnSe](1.16))(1)(NbSe2)(1) polytype
Authors:
Alemayehu, MB; Falmbigl, M; Grosse, C; Ta, K; Fischer, SF; Johnson, DC Author Full Names: Alemayehu, Matti B.; Falmbigl, Matthias; Grosse, Corinna; Ta, Kim; Fischer, Saskia F.; Johnson, David C.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 619 861-868; 10.1016/j.jallcom.2014.09.084 JAN 15 2015
Abstract:
A new polytype of the misfit layer compound ([SnSe](1.16))(1)(NbSe2)(1) with extensive rotational disorder was prepared from designed modulated elemental reactants. This polytype, previously referred to as a ferecrystal due to the extensive rotational disorder, formed over a range of compositions and precursor thicknesses and the resulting c-axis lattice parameters ranged from 1.2210(4) to 1.2360(4) nm. These values bracket the value published for the crystalline misfit layer compound prepared at high temperature. The a- and b-axis in-plane lattice parameters of both the SnSe and NbSe2 constituents were incommensurate, which differs from the misfit layer compound formed via high temperature reaction that has a common b-axis lattice parameter for the two constituents. The in-plane area per unit cell of the ferecrystal is 1-2% larger than the compound formed at high temperature. The ferecrystalline ([SnSe](1.16))(1)(NbSe2)(1) compound is 1.6 times more conductive than the misfit layer compound. Hall effect measurements indicate that the ferecrystal is a p-type metal and that the higher conductivity is a consequence of higher mobility of carriers in the ferecrystalline compound. (C) 2014 Elsevier B.V. All rights reserved.

Title:
The Al-rich region of the Al-Fe-Mn alloy system
Authors:
Balanetskyy, S; Pavlyuchkov, D; Velikanova, T; Grushko, B Author Full Names: Balanetskyy, S.; Pavlyuchkov, D.; Velikanova, T.; Grushko, B.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 619 211-220; 10.1016/j.jallcom.2014.08.232 JAN 15 2015
Abstract:
Phase equilibria in the Al-rich region of the Al-Fe-Mn alloy system were studied at 1070, 1020, 950, 875, 800, 740, 695 and 650 degrees C. The continuous region of the bcc solid solution was estimated between the Al-Mn and Al-Fe terminals. Also the isostructural high-temperature Al-Mn and Al-Fe gamma(1)- phases (gamma-brass type structure) form continuous regions. The Al6Mn, high-temperature T-Al11Mn4 and low-temperature gamma(2) phases dissolve up to 9.0, 14.5 and 31.0 at.% Fe, respectively, while the M-Al13Fe4, Al5Fe2 and Al2Fe phases dissolve up to 15.5, 11.5 and 10.0 at.% Mn, respectively. The thermodynamically stable decagonal D-3-phase with periodicity of 1.25 nm in the specific direction and two periodic intermetallics designated phi(P6(3)/mmc; a = 0.7554, c = 0.7872 nm) and kappa (P6(3)/m; a = 1.7630, c = 1.2506 nm) were identified. An additional ternary phase of unknown structure was also revealed. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Neutron and X-ray Scattering Studies of Rb2CoCl4 and Successive Phase Transition in A(2)BX(4)-type Crystals
Authors:
Shigematsu, H; Nishiyama, K; Kawamura, Y; Mashiyama, H Author Full Names: Shigematsu, Hirotake; Nishiyama, Katsura; Kawamura, Yukihiko; Mashiyama, Hiroyuki
Source:
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 83 (12):10.7566/JPSJ.83.124601 DEC 15 2014
Abstract:
Soft phonon modes, which are related to the normal-incommensurate phase transition at T-i = 294 K and the lowest-temperature phase transition at T-3 = 66 K in Rb2CoCl4, have been measured by inelastic neutron scattering. For the normal-incommensurate phase transition, phonon dispersion curves have been determined in the low-temperature commensurate phases, and the phase mode has been observed far below T-i. The soft mode is fully overdamped above T-i. Moreover, another soft phonon mode, which contributes to the phase transition at T3, has been observed. Furthermore, the space group of the lowest phase is directly confirmed to be C1c1 by verifying extinction rules of X-ray diffraction. It has been recognized that the ratio of the ionic radius of A(+) to the average bond length B-X in the tetrahedral BX42- ion can control the phase transition sequence. Rb2CoCl4 belongs to the group in which this ratio is in the range from 0.69 to 0.85, and the transition temperature decreases loosely with increasing the lattice parameter ratio c(0)/a(0), where a(0) and c(0) are the lattice parameters of the normal phase.

Title:
Controllable 3D morphology and growth mechanism of quasicrystalline phase in directionally solidified Al-Mn-Be alloy
Authors:
Kang, HJ; Wang, TM; Lu, YP; Jie, JH; Li, XZ; Su, YQ; Guo, JJ Author Full Names: Kang, Huijun; Wang, Tongmin; Lu, Yiping; Jie, Jinchuan; Li, Xinzhong; Su, Yanqing; Guo, Jingjie
Source:
JOURNAL OF MATERIALS RESEARCH, 29 (21):2547-2555; 10.1557/jmr.2014.287 NOV 14 2014
Abstract:
Three-dimensional (3D) morphological evolution and growth mechanisms of primary I-phase particles have been investigated in directionally solidified Al-6Mn-2.5Be (wt%) alloy at a wide range of growth rates (100-1500 mu m/s). At relatively low growth rates (100-600 mu m/s), the I-phase particles exhibit faceted growth with strong anisotropy, forming a hierarchical flower-like aggregate with icosahedral morphological symmetry composed of several attached irregular polyhedrons or pentagonal dodecahedrons. At higher growth rates (e.g., 1000 mu m/s), the interface of the I-phases becomes unstable along the edges and corners of the pentagonal dodecahedron, thereby arousing growth perturbations. Correspondingly, a transition from faceted to nonfaceted growth occurs with increasing growth rate. Further increase of the growth rate leads to the formation of I-phase columnar dendrites' preferential growth along the 3-fold axis. The configurations of the flower-like aggregates can be adequately illustrated by a geometrical model in terms of the perfect and elongated pentagonal dodecahedrons. A growth mechanism for the flower-like aggregates has been proposed based on the clear understanding of the 3D morphological evolution of the I-phase particles.

Title:
Commensurate structural modulation in the charge- and orbitally ordered phase of the quadruple perovskite (NaMn3)Mn4O12
Authors:
Prodi, A; Daoud-Aladine, A; Gozzo, F; Schmitt, B; Lebedev, O; van Tendeloo, G; Gilioli, E; Bolzoni, F; Aruga-Katori, H; Takagi, H; Marezio, M; Gauzzi, A Author Full Names: Prodi, A.; Daoud-Aladine, A.; Gozzo, F.; Schmitt, B.; Lebedev, O.; van Tendeloo, G.; Gilioli, E.; Bolzoni, F.; Aruga-Katori, H.; Takagi, H.; Marezio, M.; Gauzzi, A.
Source:
PHYSICAL REVIEW B, 90 (18):10.1103/PhysRevB.90.180101 NOV 10 2014
Abstract:
By means of synchrotron x-ray and electron diffraction, we studied the structural changes at the charge order transition T-CO = 176 K in the mixed-valence quadruple perovskite (NaMn3)Mn4O12. Below T-CO we find satellite peaks indicating a commensurate structural modulation with the same propagation vector q = ( 1/2,0,-1/2) of the CE magnetic structure that orders at low temperatures, similarly to the case of simple perovskites such as La0.5Ca0.5MnO3. In the present case, the modulated structure, together with the observation of a large entropy change at T-CO, gives evidence of a rare case of full Mn3+/Mn4+ charge and orbital order, consistent with the Goodenough-Kanamori model.

Title:
Noncoplanar and Counterrotating Incommensurate Magnetic Order Stabilized by Kitaev Interactions in gamma-Li2IrO3
Authors:
Biffin, A; Johnson, RD; Kimchi, I; Morris, R; Bombardi, A; Analytis, JG; Vishwanath, A; Coldea, R Author Full Names: Biffin, A.; Johnson, R. D.; Kimchi, I.; Morris, R.; Bombardi, A.; Analytis, J. G.; Vishwanath, A.; Coldea, R.
Source:
PHYSICAL REVIEW LETTERS, 113 (19):10.1103/PhysRevLett.113.197201 NOV 6 2014
Abstract:
Materials that realize Kitaev spin models with bond-dependent anisotropic interactions have long been searched for, as the resulting frustration effects are predicted to stabilize novel forms of magnetic order or quantum spin liquids. Here, we explore the magnetism of gamma-Li2IrO3, which has the topology of a three-dimensional Kitaev lattice of interconnected Ir honeycombs. Using magnetic resonant x-ray diffraction, we find a complex, yet highly symmetric incommensurate magnetic structure with noncoplanar and counterrotating Ir moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally accounts for all key features of the observed magnetic structure. Our results provide strong evidence that gamma-Li2IrO3 realizes a spin Hamiltonian with dominant Kitaev interactions.

Title:
Original Crystal-Chemical Behaviors in (Ba,Sr)(2)Ln(Fe,Nb,Ta)(5)O-15 Tetragonal Tungsten Bronze: Anion-Driven Properties Evidenced by Cationic Substitutions
Authors:
Josse, M; Heijboer, P; Albino, M; Molinari, F; Porcher, F; Decourt, R; Michau, D; Lebraud, E; Veber, P; Velazquez, M; Maglione, M Author Full Names: Josse, Michael; Heijboer, Pierre; Albino, Marjorie; Molinari, Flora; Porcher, Florence; Decourt, Rodolphe; Michau, Dominique; Lebraud, Eric; Veber, Philippe; Velazquez, Matias; Maglione, Mario
Source:
CRYSTAL GROWTH & DESIGN, 14 (11):5428-5435; 10.1021/cg5006049 NOV 2014
Abstract:
From room-temperature composite multiferroics to relaxor to ferroelectric crossovers, many original behaviors were recently evidenced in compounds and/or solid solutions related to the Ba(2)LnFeNb(4)O(15) (Ln = rare earth) family of tetragonal tungsten bronze (TTB) materials. We show how an empirical crystal chemistry approach, while yielding unexpected results, allowed for a better understanding of these original and sometimes specific behaviors. A survey of the dielectric properties of four solid solutions derived from the Ba2NdFeNb4O15 ferroelectric TTB is presented. We also show how the diversity of compositions and chemical substitution patterns unveils the anionic driving force behind the relaxor to ferroelectric crossovers. We finally discuss the probable involvement of aperiodic modulations in these crossovers and the fact that these modulations may constitute an additional degree of freedom to control the properties of TTB structured functional materials.

Title:
Twelvefold symmetric quasicrystallography from the lattices F-4, B-6 and E-6
Authors:
Koca, NO; Koca, M; Koc, R Author Full Names: Koca, Nazife O.; Koca, Mehmet; Koc, Ramazan
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 605-615; 10.1107/S2053273314015812 6 NOV 2014
Abstract:
One possible way to obtain the quasicrystallographic structure is the projection of the higher-dimensional lattice into two- or three-dimensional subspaces. Here a general technique applicable to any higher-dimensional lattice is introduced. The Coxeter number and the integers of the Coxeter exponents of a Coxeter-Weyl group play a crucial role in determining the plane onto which the lattice is to be projected. The quasicrystal structures display the dihedral symmetry of order twice that of the Coxeter number. The eigenvectors and the corresponding eigenvalues of the Cartan matrix are used to determine the set of orthonormal vectors in n-dimensional Euclidean space which lead to suitable choices for the projection subspaces. The maximal dihedral subgroup of the Coxeter-Weyl group is identified to determine the symmetry of the quasicrystal structure. Examples are given for 12-fold symmetric quasicrystal structures obtained by projecting the higher-dimensional lattices determined by the affine Coxeter-Weyl groups W-a(F-4), W-a(B-6) and W-a(E-6). These groups share the same Coxeter number h = 12 with different Coxeter exponents. The dihedral subgroup D-12 of the Coxeter groups can be obtained by defining two generators R-1 and R-2 as the products of generators of the Coxeter-Weyl groups. The reflection generators R-1 and R-2 operate in the Coxeter planes where the Coxeter element R1R2 of the Coxeter-Weyl group represents the rotation of order 12. The canonical (strip, equivalently, cut-and-project technique) projections of the lattices determine the nature of the quasicrystallographic structures with 12-fold symmetry as well as the crystallographic structures with fourfold and sixfold symmetry. It is noted that the quasicrystal structures obtained from the lattices W-a(F-4) and W-a(B-6) are compatible with some experimental results.

Title:
A study of one-dimensional incommensurate modulated structure determination in high-resolution transmission electron microscopy
Authors:
Li, XM; Ge, BH; Li, FH; Luo, HQ; Wen, HH Author Full Names: Li, Xueming; Ge, Binghui; Li, Fanghua; Luo, Huiqian; Wen, Haihu
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 70 563-571; 10.1107/S2053273314012005 6 NOV 2014
Abstract:
The methods for determining incommensurate modulated structures (IMSs) in high-resolution transmission electron microscopy have been studied and improved to a level more perfect than before. This is demonstrated by means of the IMS determination for Bi2.31Sr1.69CuO6+ as an example. First, as previously, the projected potential map (PPM) of the IMS with resolution 0.2nm was obtained after image deconvolution from a [100] image. Secondly, the resolution of the PPM was enhanced to 0.1nm through phase extension combined with the electron-diffraction data so that the substitutional and displacive modulation functions could be determined. Thirdly, a (2+1)- dimensional structure model that corresponds to the [100] projected IMS was built for calculating the related partial structure factors that were utilized to correct the experimental electron-diffraction intensities for both main and satellite reflections. After three cycles of diffraction-intensity correction and phase extension, all unoverlapped atoms projected along the [100] direction in Bi2.31Sr1.69CuO6+ were resolved, and the modulations of substitution and displacement could be observed clearly. The substitution of Bi for Sr atoms at the Sr(O) columns was seen in the final PPM and verified by high-dimensional image simulation.

Title:
Dielectric Studies of Thiourea, SC(NH2)(2), Embedded into Molecular Sieves
Authors:
Baryshnikov, SV; Charnaya, EV; Milinskiy, AY Author Full Names: Baryshnikov, S. V.; Charnaya, E. V.; Milinskiy, A. Yu.
Source:
FERROELECTRICS, 471 (1):109-117; 10.1080/00150193.2014.963428 OCT 26 2014
Abstract:
Studies of temperature dependences of linear permittivity and third harmonic generation were carried out for ferroelectric thiourea, SC(NH2)(2), particles embedded into molecular sieves SBA-15 and \MC\M-41 with pore sizes of 7.5nm and 4.0nm, respectively. Temperatures of the ferroelectric phase transition and transition from the incommensurate phase into paraphase were shown to be higher than in bulk thiourea. The shifts of the transitions increased with decreasing pore size. Both phase transitions were strongly diffused. The obtained data evidenced that the third harmonic generation can be used to find temperatures of the diffused ferroelectric transition.

Update: 4-Dec-2014


Title:
B19 phase in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy
Authors:
Song, L; Xu, XJ; You, L; Liang, YF; Lin, JP Author Full Names: Song, L.; Xu, X. J.; You, L.; Liang, Y. F.; Lin, J. P.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 618 305-310; 10.1016/j.jallcom.2014.08.137 JAN 5 2015
Abstract:
The B19 phase is widely observed in the alpha(2) laths in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy, forming a modulated structure together with the alpha(2) phase. The distortion between the alpha(2) and B19 phases exists only along the [1 (1) over bar 0 0](alpha 2) direction and is very difficult to detect. Thin gamma laths precipitate regularly within the alpha(2) + B19 structure to accommodate the lattice misfit, whereas the sizes of the gamma laths are limited to a small scale. The B19 phase, however, is unstable and was eliminated after annealing at 900 degrees C for 30 min, followed by air-cooling. The pure alpha(2) phase observed in the air-cooled sample is not in the equilibrium state. The B19 phase can be a stable phase in some temperatures below 900 degrees C but be repressed under rapid cooling. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Microstructure of an Al-Mn-Be-B alloy
Authors:
Zupanic, F; Boncina, T Author Full Names: Zupanic, F.; Boncina, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 617 174-179; 10.1016/j.jallcom.2014.07.212 DEC 25 2014
Abstract:
The aim of this work was to determine the effect of boron on the solidification and processes taking place during heat treatment of an Al-Mn-Be-based alloy. Several phases formed upon slow cooling of the investigated alloy Al89Mn2Be2B7: BeB12, AlBeB, T-Al15Mn3Be2, Al6Mn and aluminium solid solution (Al-ss). An icosahedral quasicrystalline phase (IQC) was formed during rapid solidification by melt spinning; partly dissolving Be and B, while the remaining Be and B precipitated as a ternary compound AlBeB. The primary IQC persisted within the microstructure up to 400 degrees C, whilst at temperatures above 450 degrees C the initial microstructure started to transform quickly into AlBeB, Al6Mn and Al-ss, which appeared to be the stable phases below the alloy's solidus temperature. The hardness remained almost unchanged up to 400 degrees C, whilst at temperatures above 450 degrees C it dropped abruptly. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Incommensurate structure of a new Nowotny phase in Fe-Ge system
Authors:
Li, WF; Li, Y; Ma, XL; Zhang, ZD Author Full Names: Li, Wanfeng; Li, Ying; Ma, Xiuliang; Zhang, Zhidong
Source:
MATERIALS CHEMISTRY AND PHYSICS, 148 (3):490-493; 10.1016/j.matchemphys.2014.08.023 DEC 15 2014
Abstract:
We studied post-annealed Fe-Ge alloy by X-ray diffraction and transmission electron microscopy. A new Nowotny chimney ladder phase has been discovered in such Fe-Ge system. The crystal structure and the composition have been calculated based on selected area electron diffraction. The formation of the incommensurate structure is attributed to the shrinkage of the Ge sublattice to meet the 14 electrons rule. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Hydrogen Absorption and Structural Analysis of TiZrNiV Quasicrystals
Authors:
Lee, SH; Jo, Y; Kim, J Author Full Names: Lee, Sang-Hwa; Jo, Youngsoo; Kim, Jaeyong
Source:
JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 14 (12):9373-9376; 10.1166/jnn.2014.10126 DEC 2014
Abstract:
Ti-based quasicrystals are known to store a high capacity of hydrogen exceeding the density of liquid hydrogen. Because TiZrNi quasicrystals contain a large number of tetrahedral sites formed with Ti and Zr atoms that are chemically favorable to hydrogen, these materials retain strong advantages for hydrogen storage applications in structurally and chemically. In fact, TiZrNi quasicrystals are known to absorb hydrogen maximum of the hydrogen to host metal ratio (H/M) value of near 2.0. The critical disadvantage, however, is that the equilibrium vapor pressure of hydrogen is very low (less than 1 Torr). To overcome this engineering drawback, we added a small amount of vanadium (V) in Ti53-XZr27Ni20Vx, alloys (where x = 0 to 15) and rapidly quenched the molten ingots to form quasicrystals, and investigated the effects of V in terms of changes of structure, the H/M values, and an equilibrium vapor pressure of hydrogen. As the results, an equilibrium vapor pressure significantly increased from 0.84 to 2.16 Torr while the maximum H/M value decreased from 1.32 to 1.11 as increasing x = 0 to 8. After hydrogenation, the main peaks shifted evenly to the lower angle of 2 theta in X-ray diffraction patterns with uniform expansion of the quasilattice constants which demonstrates that hydrogen atoms homogeneously diffused into the samples. A Laves phase starts to form at x = 13 and the samples completely transformed to the phase at x = 15 suggesting the similarity between the quasicrystal and the Laves phase.

Title:
The electronic structure and magnetism of CaFeAs2: First principles calculations
Authors:
Wang, GT; Shi, XB; Zhang, L; Yi, X Author Full Names: Wang, Guangtao; Shi, Xianbiao; Zhang, Lin; Yi, Xia
Source:
SOLID STATE COMMUNICATIONS, 200 61-65; 10.1016/j.ssc.2014.09.025 DEC 2014
Abstract:
The electronic structure, magnetism and Fermi surface (FS) nesting of the recently discovered superconductive parent material CaFeAs2 are studied by the first-principles, based on the GGA and GGA+U methods. In the nonmagnetic state, the density of states at the Fermi level are mostly derived from the d(xy), d(yz) and d(zx) orbits, just like LaOFeAs. The Fermi surfaces consist of four hole like FS sheets around the Gamma-point, two electron like sheets near the Brillouin zone corner M-point, and small pockets near X-point. The hole like Fermi surfaces will strongly overlap with the electron like FS sheets, if they are shifted by the q-vector q = (pi, pi, 0). Such FS nesting will induce the magnetic instability and spin density wave (SDW), which has been confirmed to be more stable than other states by the calculated total energy. The calculated bare susceptibility chi(0)(q) peaked at M-point, and was obviously suppressed with the electron doping. This explains the emergence of the superconductivity in the electron-doped compound Ca1-xLaxFeAs2, because the electron doping suppressed the SDW and induced the superconductivity. (C) 2014 Elsevier Ltd. All rights reserved.

Title:
Superspace application on magnetic structure analysis of the Pb2MnWO6 double perovskite system
Authors:
Orlandi, F; Righi, L; Ritter, C; Pernechele, C; Solzi, M; Cabassi, R; Bolzoni, F; Calestani, G Author Full Names: Orlandi, Fabio; Righi, Lara; Ritter, Clemens; Pernechele, Chiara; Solzi, Massimo; Cabassi, Riccardo; Bolzoni, Fulvio; Calestani, Gianluca
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 2 (43):9215-9223; 10.1039/c4tc01450b NOV 21 2014
Abstract:
The commensurate crystal structure of the magnetic phase occurring below 7 K of the multiferroic Pb2MnWO6 perovskite has been solved by the introduction of the superspace approach. This lead based double perovskite is characterized by a complex ferrielectric non-centrosymmetric nuclear structure with orthorhombic symmetry stable in a wide temperature range. As indicated from the analysis of powder neutron diffraction data, the low temperature antiferromagnetic structure showing a propagation vector kappa = [1/4 0 0] is stabilized by a multi-step process involving the evolution from incommensurate to commensurate spin ordering with a concomitant change of the magnetic symmetry. The determination of the Pb2MnWO6 magnetic structure offers a meaningful example of the superspace application and provides a detailed phase diagram of the involved magnetic states. Nowadays this ordered perovskite could be considered as a new type of multiferroic material combining ferrielectric properties and a long period antiferromagnetic structure.

Title:
Synthesis and crystal structure of a series of incommensurately modulated composite oxohalide compounds
Authors:
Zimmermann, I; Corgnet, A; Johnsson, M; Lidin, S Author Full Names: Zimmermann, Iwan; Corgnet, Alexis; Johnsson, Mats; Lidin, Sven
Source:
DALTON TRANSACTIONS, 43 (42):15812-15817; 10.1039/c4dt02084g NOV 14 2014
Abstract:
Transparent, needle-like single crystals of the isostructural compounds [Sb4O7+3 delta X4][Zn-3](1+delta) = CL Br, I) delta approximate to 0.2 were obtained from chemical reactions in evacuated and sealed silica tubes. First, the average structure was solved in P211n but the model refined poorly and a lowering of the symmetry to the 3 + 1 dimensional space group P2(1)(alpha 0 gamma)0 gave a significantly better fit to the data. This model used second order positional modulations for all the atoms. Whereas Sb, Cl (Br, I) and most 0 positions were well behaved, there was a mismatch with Zn that was better described in a sub-cell, thus yielding a composite structure. The composite nature of the structure leads to a charge imbalance that is compensated by oxygen vacancies.

Title:
Complex magnetic ordering in CeGe1.76 studied by neutron diffraction
Authors:
Jayasekara, WT; Tian, W; Hodovanets, H; Canfield, PC; Bud'ko, SL; Kreyssig, A; Goldman, AI Author Full Names: Jayasekara, W. T.; Tian, W.; Hodovanets, H.; Canfield, P. C.; Bud'ko, S. L.; Kreyssig, A.; Goldman, A. I.
Source:
PHYSICAL REVIEW B, 90 (13):10.1103/PhysRevB.90.134423 OCT 29 2014
Abstract:
Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At T-N approximate to 7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector ( 0 0 tau) with tau approximate to 1/4 and the magnetic moment along the a axis of the orthorhombic unit cell. Below T-LI approximate to 5 K, the magnetic structure locks in to a commensurate structure with tau = 1/4 and the magnetic moment remains along the a axis. Below T* approximate to 4 K, we find additional half-integer and integer indexed magnetic Bragg peaks consistent with a second commensurately ordered antiferromagnetic state.

Title:
Feedback of superconducting fluctuations on charge order in the underdoped cuprates
Authors:
Chowdhury, D; Sachdev, S Author Full Names: Chowdhury, Debanjan; Sachdev, Subir
Source:
PHYSICAL REVIEW B, 90 (13):10.1103/PhysRevB.90.134516 OCT 24 2014
Abstract:
Metals interacting via short-range antiferromagnetic fluctuations are unstable to sign-changing superconductivity at low temperatures. For the cuprates, this leading instability leads to the well-known d-wave superconducting state. However, there is also a secondary instability to an incommensurate charge-density wave, with a predominantly d-wave form factor, arising from the same antiferromagnetic fluctuations. Recent experiments in the pseudogap regime of the hole-doped cuprates have found strong evidence for such a charge-density wave order and, in particular, the predicted d-wave form factor. However, the observed wave vector of the charge order differs from the leading instability in Hartree-Fock theory, and is that of a subleading instability. In this paper, we examine the feedback of superconducting fluctuations on these different charge-density wave states, and find that over at least a small temperature window, they prefer the experimentally observed wave vector.

Title:
Non-Fermi-liquid behavior at the onset of incommensurate 2k(F) charge- or spin-density wave order in two dimensions
Authors:
Holder, T; Metzner, W Author Full Names: Holder, Tobias; Metzner, Walter
Source:
PHYSICAL REVIEW B, 90 (16):10.1103/PhysRevB.90.161106 OCT 21 2014
Abstract:
We analyze the influence of quantum critical fluctuations on single-particle excitations at the onset of incommensurate 2k(F) charge- or spin-density wave order in two-dimensional metals. The case of a single pair of hot spots at high symmetry positions on the Fermi surface needs to be distinguished from the case of two hot spot pairs. We compute the fluctuation propagator and the electronic self-energy perturbatively in leading order. The energy dependence of the single-particle decay rate at the hot spots obeys non-Fermi-liquid power laws, with an exponent 2/3 in the case of a single hot spot pair, and exponent one for two hot spot pairs. The prefactors of the linear behavior obtained in the latter case are not particle-hole symmetric.

Title:
Structural and magnetic dynamics in the magnetic shape-memory alloy Ni2MnGa
Authors:
Mariager, SO; Dornes, C; Johnson, JA; Ferrer, A; Grubel, S; Huber, T; Caviezel, A; Johnson, SL; Eichhorn, T; Jakob, G; Elmers, HJ; Beaud, P; Quitmann, C; Ingold, G Author Full Names: Mariager, S. O.; Dornes, C.; Johnson, J. A.; Ferrer, A.; Gruebel, S.; Huber, T.; Caviezel, A.; Johnson, S. L.; Eichhorn, T.; Jakob, G.; Elmers, H. J.; Beaud, P.; Quitmann, C.; Ingold, G.
Source:
PHYSICAL REVIEW B, 90 (16):10.1103/PhysRevB.90.161103 OCT 10 2014
Abstract:
Magnetic shape-memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic, and structural order. To study these correlations we use time-resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni2MnGa film and reveal a set of time scales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300 fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320 fs, which is comparable to the quenching of the structural modulation.

Title:
Fine structure of the incommensurate antiferromagnetic fluctuations in single-crystalline LiFeAs studied by inelastic neutron scattering
Authors:
Qureshi, N; Steffens, P; Lamago, D; Sidis, Y; Sobolev, O; Ewings, RA; Harnagea, L; Wurmehl, S; Buchner, B; Braden, M Author Full Names: Qureshi, N.; Steffens, P.; Lamago, D.; Sidis, Y.; Sobolev, O.; Ewings, R. A.; Harnagea, L.; Wurmehl, S.; Buechner, B.; Braden, M.
Source:
PHYSICAL REVIEW B, 90 (14):10.1103/PhysRevB.90.144503 OCT 8 2014
Abstract:
We present an inelastic neutron scattering study on single-crystalline LiFeAs devoted to the characterization of the incommensurate antiferromagnetic fluctuations at Q = (0.5 +/- delta, 0.5 -/+ delta, ql). Time-of-flight measurements show the presence of these magnetic fluctuations up to an energy transfer of 60 meV, while polarized neutrons in combination with a longitudinal polarization analysis on a triple-axis spectrometer prove the pure magnetic origin of this signal. The normalization of the magnetic scattering to an absolute scale yields that magnetic fluctuations in LiFeAs are by a factor of 8 weaker than the resonance signal in nearly optimally Co-doped BaFe2As2, although a factor of 2 is recovered due to the split peaks owing to the incommensurability. The longitudinal polarization analysis indicates weak spin-space anisotropy with a slightly stronger out-of-plane component between 6 and 12 meV. Furthermore, our data suggest a fine structure of the magnetic signal most likely arising from superposing nesting vectors.

Title:
CeCu2Ge2: Challenging our understanding of quantum criticality
Authors:
Zeng, B; Zhang, QR; Rhodes, D; Shimura, Y; Watanabe, D; Baumbach, RE; Schlottmann, P; Ebihara, T; Balicas, L Author Full Names: Zeng, B.; Zhang, Q. R.; Rhodes, D.; Shimura, Y.; Watanabe, D.; Baumbach, R. E.; Schlottmann, P.; Ebihara, T.; Balicas, L.
Source:
PHYSICAL REVIEW B, 90 (15):10.1103/PhysRevB.90.155101 OCT 3 2014
Abstract:
In the zero temperature limit, the zero-point quantum fluctuations of certain degrees of freedom (or quantum criticality) are claimed to describe the collective fluctuations of systems undergoing a second-order phase transition. To date, some of the best studied examples of quantum phase transitions, and concomitant anomalous physical behavior, involve f-electron magnetism in heavy-fermion metals, where quantum criticality (QC) is ascribed to either the suppression of a spin-density wave (SDW) ground state or the Kondo effect. Here, we unveil evidence for a quantum phase transition in CeCu2Ge2 which displays both an incommensurate SDW ground state, and a strong renormalization of the quasiparticle effective masses (mu) due to the Kondo effect. For all angles theta between an external magnetic field (H) and the crystallographic c axis, the application of H leads to the suppression of the SDW state through a second-order phase transition at a theta-dependent critical field H-p(theta) leading to the observation of small Fermi surfaces (FSs) in the paramagnetic state. For the H vertical bar vertical bar c axis, these FSs are characterized by light mu's pointing also to the suppression of the Kondo effect at H-p with, surprisingly, no experimental evidence for QC. But as H is rotated towards the a axis, these mu's increase considerably becoming undetectable for theta > 56 degrees between H and the c axis. Around H-p(a) similar to 30 T the resistivity becomes alpha T which, coupled to the divergence of mu, indicates the existence of a field-induced QC point at H-p(a) (T = 0 K). This observation, suggesting FS hot spots associated with the SDW nesting vector, is at odds with current QC scenarios for which the continuous suppression of all relevant energy scales at H-p(theta, T) should lead to a line of quantum-critical points in the H-theta plane. Finally, we show that the complexity of its magnetic phase diagram(s) makes CeCu2Ge2 an ideal system to explore field-induced quantum tricritical and QC end points.

Title:
Competing Exchange Interactions on the Verge of a Metal-Insulator Transition in the Two-Dimensional Spiral Magnet Sr3Fe2O7
Authors:
Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, B Author Full Names: Kim, J. -H.; Jain, Anil; Reehuis, M.; Khaliullin, G.; Peets, D. C.; Ulrich, C.; Park, J. T.; Faulhaber, E.; Hoser, A.; Walker, H. C.; Adroja, D. T.; Walters, A. C.; Inosov, D. S.; Maljuk, A.; Keimer, B.
Source:
PHYSICAL REVIEW LETTERS, 113 (14):10.1103/PhysRevLett.113.147206 OCT 3 2014
Abstract:
We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr3Fe2O7, which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe4+ moments adopt incommensurate spiral order below T-N = 115 K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr3Fe2O7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals.

Title:
Oxide ion distribution, vacancy ordering and electrical behaviour in the Bi3NbO7-Bi3YbO6 pseudo-binary system
Authors:
Leszczynska, M; Liu, X; Wrobel, W; Malys, M; Dygas, JR; Norberg, ST; Hull, S; Krok, F; Abrahams, I Author Full Names: Leszczynska, M.; Liu, X.; Wrobel, W.; Malys, M.; Dygas, J. R.; Norberg, S. T.; Hull, S.; Krok, F.; Abrahams, I.
Source:
JOURNAL OF MATERIALS CHEMISTRY A, 2 (43):18624-18634; 10.1039/c4ta03225j 2014
Abstract:
Oxide ion distribution, vacancy ordering and electrical conductivity has been examined in the Nb/Yb double substituted bismuth oxide based system Bi3Nb1-xYbxO7-x, using X-ray and neutron powder diffraction, reverse Monte Carlo modelling of total neutron scattering data and a. c. impedance spectroscopy. Transference number measurements confirm the system to be predominantly ionically conducting above ca. 450 degrees C. Niobium rich compositions show incommensurate ordering of the fluorite subcell, while increasing ytterbium content results in a commensurate fluorite, with fully disordered cation and anion sublattices. Oxide ion distribution shows both compositional and thermal dependencies. The latter is discussed with respect to its effect on the thermal variation of cubic lattice parameter. Substitution of bismuth by niobium and ytterbium in the cation sublattice of bismuth oxide leads to the creation of Frenkel interstitial oxide ions, which increase the tetrahedral vacancy concentration. The high vacancy concentration is confirmed in both Rietveld and RMC analyses of neutron data. Examination of vacancy ordering, in the x - 0.6 composition, indicates a favouring of < 100 > vacancy pair alignment.

Update: 26-Nov-2014


Title:
Magnetic properties of nanoscaled paramelaconite Cu4O3-x (x=0.0 and 0.5)
Authors:
Djurek, D; Prester, M; Drobac, D; Ivanda, M; Vojta, D Author Full Names: Djurek, D.; Prester, M.; Drobac, Dj.; Ivanda, M.; Vojta, D.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 373 183-187; JAN 1 2015
Abstract:
Pure paramelaconite Cu4O3-x has been prepared in the form of nanoparticles with 56 nm in diameter. This mixed valency oxide crystallizes in a tetragonal lattice with 4 unit formulae and forms a pyrochlore structure which manifests in two stoichiometric forms; Cu4O3 and Cu4O2.5, the latter form having two oxygen vacancies per unit cell. Magnetic lattice consists of Cu spin 1/2, and both stoichiometric forms obey transition to the antiferromagnetic state at T-N=45-55 K. Defect free Cu4O3 is indicated by an inversion symmetry and exhibits both antiferromagnetic and ferromagnetic state, where the latter is supposedly due to the superexchange interaction in Cu-O(1n)-Cu bonds. An additional magnetic transition was observed in Cu4O3 at T=120 K, probably as a result of an incommensurate ordering. Absence of an inversion symmetry in the oxygen defect Cu4O2.5 results in a long range Dzyaloshinsky-Moriya interaction accompanied by the strong superparamagnetism. (C) 2014 Elsevier B.V. All rights reserved

Title:
Interacting magnetic cluster-spin glasses and strain glasses in Ni-Mn based Heusler structured intermetallics
Authors:
Entel, P; Gruner, ME; Comtesse, D; Sokolovskiy, VV; Buchelnikov, VD Author Full Names: Entel, Peter; Gruner, Markus E.; Comtesse, Denis; Sokolovskiy, Vladimir V.; Buchelnikov, Vasiliy D.
Source:
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251 (10):2135-2148; SI 10.1002/pssb.201451059 OCT 2014
Abstract:
Magnetic Ni-Mn based Heusler intermetallics show complex magnetic behavior in connection with martensitic transformations (see, for instance, the phase diagram of Ni-Co-Mn-Sn on the right-hand side). The cubic austenitic phase at high temperature shows long-range ferromagnetic order which can considerably be weakened by the appearance of competing antiferromagnetic interactions which are induced by Mn excess and chemical disorder. With decreasing temperature a martensitic/magnetostructural transformation takes place from cubic to non-modulated/modulated tetragonal/monoclinic or orthorhombic structure, where long-range ferromagnetic order can no longer be maintained, leading to superparamagnetic behavior. At still lower temperatures superparamagnetism changes to superspin glass because of strong competition of ferromagnetic and antiferromagnetic interactions and chemical disorder. In addition, disorder and local structural distortions can lead to strain glass in austenite, as observed for some nonmagnetic martensitic systems. The magnetic intermetallics are of technological importance in view of their functional properties involving magnetic shape-memory and exchangebias effects as well as magnetocaloric effects. The ` ferroic cooling' is of particular relevance since it avoids the use of ozone-depleting and greenhouse chemicals compared with conventional fluid-compression technology. Experimental phase diagram of Ni50-xCoxMn39Sn11 for 0 <= x <= 10. Here, TC is the Curie temperature of austenite; at T-M the system transforms to paramagnetic martensite and at T-S to superparamagnetic martensite (SPM) and then to superspin-glass martensite (SSG) at T-P. The possible strainglass phases (labeled by question marks) are predicted because of kinetic arrest phenomena and local distortions associated with the magnetostructural transition and ergodicity breaking by field-cooling/zero-field-cooling experiments. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Title:
Elastic fields around a nanosized elliptic hole in decagonal quasicrystals
Authors:
Li, LH; Yun, GH Author Full Names: Li Lian-He; Yun Guo-Hong
Source:
CHINESE PHYSICS B, 23 (10):10.1088/1674-1056/23/10/106104 OCT 2014
Abstract:
Based on the variational principle, a continuum theory of surface elasticity and new boundary conditions for quasicrystals is proposed. The effect of the residual surface stress on a decagonal quasicrystal that is weakened by a nanoscale elliptical hole is considered. The explicit expressions for the hoop stress along the edge of the hole are obtained using the Stroh formalism. The results show that the residual surface stress and the shape of the hole have a significant effect on the elastic state around the hole.

Title:
Two-coupled structural modulations in charge-density-wave state of SrPt2As2 superconductor
Authors:
Wang, L; Wang, Z; Shi, HL; Chen, Z; Chiang, FK; Tian, HF; Yang, HX; Fang, AF; Wang, NL; Li, JQ Author Full Names: Wang Li; Wang Zhen; Shi Hong-Long; Chen Zhen; Chiang Fu-Kuo; Tian Huan-Fang; Yang Huai-Xin; Fang Ai-Fang; Wang Nan-Lin; Li Jian-Qi
Source:
CHINESE PHYSICS B, 23 (8):10.1088/1674-1056/23/8/086103 AUG 2014
Abstract:
Transmission electron microscopy (TEM) study of SrPt2As2 reveals two incommensurate modulations appearing in the charge-density-wave (CDW) state below T-CDW approximate to 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q(1) = 0.62a on the a-b* plane and q(2) = 0.23a on the a-c* plane. The atomic displacements occur along the b-axis direction for q(1) and along the c-axis direction for q(2), respectively. Moreover, the correlation between q(1) and q(2) can be generally written as q(1) = (q(2) + a*)/2 in the CDW state, suggesting the presence of essential coupling between q(1) and q(2). A small fraction of Ir doping on the Pt site in Sr(Pt1-xIrx)(2)As-2 (x < 0.06) could moderately change these CDW modulations and also affect their superconductivities.

Update: 19-Nov-2014


Title:
The use of Nb in rapid solidified Al alloys and composites
Authors:
Audebert, F; Galano, M; Saporiti, F Author Full Names: Audebert, F.; Galano, M.; Saporiti, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 S621-S626; 1 10.1016/j.jallcom.2013.12.129 DEC 5 2014
Abstract:
The worldwide requirements for reducing the energy consumption and pollution have increased the demand of new and high performance lightweight materials. The development of nanostructured Al-based alloys and composites is a key direction towards solving this demand. High energy prices and decreased availability of some alloying elements open up the opportunity to use non-conventional elements in Al alloys and composites. In this work the application of Nb in rapid solidified Al-based alloys and Al alloys matrix composites is reviewed. New results that clarify the effect of Nb on rapid solidified Al alloys and composites are also presented. It is observed that Nb stabilises the icosahedral Al-Fe/Cr clusters, enhances the glass forming ability and shifts the icosahedral phase decomposition towards higher temperatures. Nb provides higher corrosion resistance with respect to the pure Al and Al-Fe-RE (RE: rare earth) alloys in the amorphous and crystalline states. The use of Nb as a reinforcement to produce new Al alloy matrix composites is explored. It is observed that Nb provides higher strength, ductility and toughness to the nanoquasicrystalline matrix composite. Nb appears as a new key element that can improve several properties in rapid solidified Al alloys and composites. (C) 2013 Elsevier B.V. All rights reserved.

Title:
Effect of Ti, Zr and Hf addition on microstructure and properties of rapidly solidified Al-Mn-Fe alloy
Authors:
Stan, K; Litynska-Dobrzynska, L; Ochin, P; Garzel, G; Wierzbicka-Miernik, A; Wojewoda-Budka, J Author Full Names: Stan, K.; Litynska-Dobrzynska, L.; Ochin, P.; Garzel, G.; Wierzbicka-Miernik, A.; Wojewoda-Budka, J.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 615 S607-S611; 1 10.1016/j.jallcom.2013.11.160 DEC 5 2014
Abstract:
In this work, the influence of alloying elements Ti, Zr and Hf on microstructure and properties of Al91Mn7Fe2 melt spun ribbons, strengthened with quasicrystalline particles was studied. It was found that Zr improves significantly the microhardness of the alloy in as spun state by precipitation of metastable L1(2)-Al3Zr phase in matrix grains. Both Hf and Zr additions retain higher microhardness values after annealing at 673 K by formation of stable Al3X precipitates, even though the quasicrystalline phase being the main strengthening phase in the alloy starts to decompose. Comparison of the results from differential scanning calorimetry, thermo-mechanical analysis and microhardness measurements after annealing showed correlation between phase transformations and mechanical properties. Based on TEM studies, drop of microhardness and increase in Young's modulus with temperature for all samples was attributed to significant change in samples microstructure, especially to decomposition of quasicrystalline particles and formation of different intermetallic phases. (C) 2013 Elsevier B.V. All rights reserved.

Title:
High-resolution electron microscopy and electron diffraction of perovskite-type superconducting copper oxides
Authors:
Oku, T Author Full Names: Oku, Takeo
Source:
NANOTECHNOLOGY REVIEWS, 3 (5):413-444; SI 10.1515/ntrev-2014-0003 OCT 2014
Abstract:
High-resolution electron microscopy and electron diffraction are quite useful for structural characterization of perovskite-type superconducting copper oxides on the atomic scale. Valuable information on the crystal structures and the microstructures could be obtained from observed high-resolution images if severe conditions such as thinner crystals and definite defocus values are satisfied. The structure images and electron diffraction patterns include information not only on accurate atomic coordinates of cations but also on ordered arrangements of oxygen atoms and oxygen vacancies. Crystal structures of the various perovskite-type copper oxides were analyzed from the observed structure images. Modulated structures, defects, intergowth, surfaces, and interfaces were also investigated.

Title:
Dual-phase glassy/nanoscale icosahedral phase materials in Cu-Zr-Ti-Pd system alloys
Authors:
Louzguine-Luzgin, DV; Churyumov, AY Author Full Names: Louzguine-Luzgin, Dmitri V.; Churyumov, A. Yu.
Source:
MATERIALS CHARACTERIZATION, 96 6-12; 10.1016/j.matchar.2014.07.014 OCT 2014
Abstract:
The present work is devoted to an investigation of the formation kinetics, stability and homogeneity area of the nanoscale icosahedral phase formed on heating in the dual-phase glassy/quasicrystalline phase Cu-Zr-Ti-Pd alloys. The data obtained indicate that the Cu-Zr-Ti-Pd icosahedral phase is not a Cu-rich part of the compositional homogeneity area of the Zr-Cu-Pd one. Moreover, Ti, as well as Pd, is found to be an important element stabilizing quasicrystalline phase in the Cu-Zr-Ti-Pd alloys. The formation criteria for Cu- and Zr/Hf-based icosahedral phases are discussed based on the quasilattice constant to average atomic diameter ratio. Deviation from a certain ratio leads to destabilization of the icosahedral phase. By using the isothermal calorimetry traces transformation kinetics above and below the glass-transition region was analyzed. Some difference in the transformation kinetics above and below the glass-transition region allows us to suggest that possible structure changes occur upon glass-transition. (C) 2014 Elsevier Inc. All rights reserved.

Title:
Partially amorphous (metamict) titanite: a silicate mineral in a natural radiation induced non-equilibrium phase
Authors:
Beirau, T Author Full Names: Beirau, Tobias
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE, 229 (8):543-549; 10.1515/zkri-2014-1745 AUG 2014
Abstract:
The present review will give a brief overview mainly focused on studies during the past 5 years on the mineral titanite (end-member composition CaTiSiO5) which could incorporate radioactive elements in its crystal structure. Aspects of investigations were the structural damage resulting from the radioactive decay, the thermally induced recrystallization process and the elastic properties of the mineral. During the radiation induced damage process, namely the metamictization, titanite becomes partially amorphous with coexisting defect enriched crystalline and aperiodic regions. Within these crystalline regions a P2(1)/c to C2/c phase transition (similar to at 500 K) occurs. Resulting from radiation induced structural damage, titanite shows elastic properties close to those of titanite glass. During recrystallization on annealing an initial softening of the titanite structure takes place (up to temperature similar to 950 K) resulting from the formation of soft interfaces. Thermal annealing at higher temperatures leads to increasing structural order and the hardening of the mineral.

Update: 13-Nov-2014


Title:
Multicomponent and High Entropy Alloys
Authors:
Cantor, B Author Full Names: Cantor, Brian
Source:
ENTROPY, 16 (9):4749-4768; 10.3390/e16094749 SEP 2014
Abstract:
This paper describes some underlying principles of multicomponent and high entropy alloys, and gives some examples of these materials. Different types of multicomponent alloy and different methods of accessing multicomponent phase space are discussed. The alloys were manufactured by conventional and high speed solidification techniques, and their macroscopic, microscopic and nanoscale structures were studied by optical, X-ray and electron microscope methods. They exhibit a variety of amorphous, quasicrystalline, dendritic and eutectic structures.

Title:
Structural origin of the different devitrification behaviors between ZrCu and ZrPd metallic glasses
Authors:
Huang, P; Zou, DH; Guo, GQ; Yang, L Author Full Names: Huang, Po; Zou, De-Hui; Guo, Gu-Qing; Yang, Liang
Source:
EPL, 107 (6):10.1209/0295-5075/107/66002 SEP 2014
Abstract:
The microstructures of Zr70Pd30 and Zr70Cu30 metallic glasses (MGs) were investigated via the synchrotron radiation techniques combined with the reverse Monte Carlo simulations. It is revealed that, compared with Zr70Cu30, Zr70Pd30 has more fruitful icosahedral-like clusters, which have a relatively high geometrical regularity closer to that of the ideal icosahedron. Therefore, clusters in Zr70Pd30 are prone to change into the structural units of icosahedral quasicrystal phase. This should be the structural origin of the amorphous-to-quasicrystal transformation found in Zr70Pd30 while such phase change never appears when heating Zr70Cu30 MG. This work provides an understanding of the devitrification mechanism from the atomic level in this class of glassy materials. Copyright (C) EPLA, 2014

Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha(1)-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, incommensurately modulated alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)-phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)-phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the incommensurately modulated alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features satellite reflections of first order with very low intensities.

Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S, 6S, 9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohepta[b]py ridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b]pyridin-1-yl)-1piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet this 'dried' structure is not a pure phase. It consists of semi-random layers of both child, parent and an interfacial layer which has a modulated structure that represents a transitory phase. Understanding the fact that a single 'dried' crystal can have the disordered layer structure described as well as understanding mechanistic relationships between the phases involved can have implications in understanding the effect of common large scale bulk drying procedures. During the development of BMS-927711, difficulties did arise during characterization of the dried bulk when using only routine solid-state analysis. The material is now better understood from this diffraction study. The diffraction experiments also reveal intermodulation satellites, which upon interpretation yield even more structural information about the crystal transformation. The model suggests the mechanism of transformation is laminar in which layers of the crystal are driven to approach a stable B-centered supercell phase of lower water content.

Update: 5-Nov-2014


Title:
High temperature X-ray diffraction study on incommensurate composite crystal MnSi gamma - (3+1)-dimensional superspace approach
Authors:
Kikuchi, Y; Nakajo, T; Hayashi, K; Miyazaki, Y Author Full Names: Kikuchi, Y.; Nakajo, T.; Hayashi, K.; Miyazaki, Y.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 616 263-267; 10.1016/j.jallcom.2014.07.106 DEC 15 2014
Abstract:
The (3 + 1)-dimensional crystal structure of a higher manganese silicide (MnSi gamma) phase is revealed using in situ high temperature powder X-ray diffraction (XRD) above room temperature. The compound consists of two tetragonal subsystems of [Mn] and [Si] with an irrational c-axis ratio gamma = c(Mn)/c(Si). The in situ XRD results show that the MnSi gamma phase is stable, in a vacuum of similar to 1 Pa, up to 1093 K and partially decomposes into the monosilicide (MnSi) phase with further increase in temperature. Refined a- and c(Mn)-axis lengths increase linearly and the thermal expansion coefficients are comparable with those of typical metallic electrode materials. In contrast, c(Si)-axis length changes its increment against temperature at T-BD similar to 773 K. As a result, the temperature dependence of gamma starts to decrease gradually above T-BD, from 1.7387(1) (at 773 K) to 1.7244(1) (at 1173 K). This finding implies that the MnSi gamma phase consecutively changes its irrational composition above T-BD, a typical temperature where the silicides exhibit a maximum figure-of-merit. An increase in hole carrier concentration is expected according to the valence electron counting concept. Although the nearest Mn-Mn and Mn-Si distances increase monotonically with temperature, the nearest Si-Si distance much increases by similar to 0.05 angstrom from 2.439(4) angstrom at 773 K to 2.493(7) angstrom at 1173 K. The latter increase is considered to be caused by the introduction of excited electron carriers into the anti-bonding orbital, due to the bipolar diffusion (BD). (C) 2014 Elsevier B.V. All rights reserved.

Title:
Effects of S-Se substitution and magnetic field on magnetic order in Fe0.5Ti(S,Se)(2) layered compounds
Authors:
Gubkin, AF; Sherokalova, EM; Keller, L; Selezneva, NV; Proshkin, AV; Proskurina, EP; Baranov, NV Author Full Names: Gubkin, A. F.; Sherokalova, E. M.; Keller, L.; Selezneva, N. V.; Proshkin, A. V.; Proskurina, E. P.; Baranov, N. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 616 148-154; 10.1016/j.jallcom.2014.06.195 DEC 15 2014
Abstract:
Powder neutron diffraction and specific heat measurements have been employed to study the evolution of an antiferromagnetic (AFM) structure in the intercalated Fe0.5TiS2-ySey compounds with S-Se substitution and under application of a magnetic field. In Fe0.5TiS2 (y = 0), the magnetic structure just below T-N similar or equal to 140 K is incommensurate while it becomes commensurate with further cooling below T-t similar or equal to 125 K. The presence of two magnetic phase transitions at T-t and T-N in Fe0.5TiS2 is confirmed by specific heat measurements. The field-induced AFM-FM transitions occurring in Fe0.5TiS2 within temperature interval T-t < T < T-N and below T-t are evidenced by neutron diffraction measurements under application of a magnetic field. Unlike Fe0.5TiS2 having a quadruplicated AFM structure, the compounds with the Se concentrations y > 0.5 are observed to exhibit an AFM structure with the doubled magnetic unit cell along a and c crystallographic directions of the monoclinic crystal lattice (I12/m1 space group). In the transition region around the critical Se concentration y(c) approximate to 0.5, the magnetic structure of Fe0.5TiS2-ySey is found to be incommensurate. The appearance of the AFM order with decreasing temperature in Fe0.5TiS2-ySey is accompanied by anisotropic deformations of the crystal lattice. At low temperatures, the Fe magnetic moments in all Fe0.5TiS2-ySey form an angle 14-16 degrees to the c crystallographic direction, which can be ascribed to the crystal field effects and spin-orbit couplings. (C) 2014 Elsevier B.V. All rights reserved.

Title:
Cu3Sn - understanding the systematic absences
Authors:
Muller, CJ; Lidin, S Author Full Names: Muller, Carola J.; Lidin, Sven
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 879-887; 10.1107/S205252061401806X 5 OCT 2014
Abstract:
The intermetallic compound Cu3Sn has previously been described as a long-period antiphase boundary superstructure of the Cu3Ti structure type. While the compound itself has been reported as a tenfold and an eightfold superstructure, ternary doped alloys show shorter repetitions. Interestingly, the diffraction patterns of these compounds show noncrystallographic absences that cannot be explained using the superstructure models. Since the compound exhibits phase broadening, these models are not satisfactory because the paucity of observed data does not allow for a refinement of the composition. Here, an alternative, superspace model in the orthorhombic space group Xmcm(0 beta 0)000 is proposed, with the centering vectors (0,0,0,0) and (1/2,0,0,1/2). The presence of the non-crystallographic absences is explained as a result of a dominating occupational modulation that is accompanied by a weaker displacive modulation. In consistency with the EDXS results, the composition has been refined to Cu3 + xSn from single-crystal X-ray diffraction data. It is further demonstrated that by varying the length and the direction of the modulation wavevector in the superspace model, the ternary Cu3Sn compounds and other colored hexagonal close packing (h.c.p.) structures can be produced.

Title:
Mackay icosahedron explaining orientation relationship of dispersoids in aluminium alloys
Authors:
Muggerud, AMF; Li, YJ; Holmestad, R; Andersen, SJ Author Full Names: Muggerud, Astrid Marie F.; Li, Yanjun; Holmestad, Randi; Andersen, Sigmund J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 888-896; 10.1107/S2052520614017880 5 OCT 2014
Abstract:
The orientation relations (ORs) of the cubic icosahedral quasicrystal approximant phase alpha-Al(Fe,Mn)Si have been studied after low temperature annealing of a 3xxx wrought aluminium alloy by transmission electron microscopy. From diffraction studies it was verified that the most commonly observed OR for the alpha-Al(Fe,Mn)Si dispersoids is [1 (1) over bar1]alpha // [1 (1) over bar1]Al, (5 (2) over bar(7) over bar)alpha // (011)Al. This orientation could be explained by assuming that the internal Mackay icosahedron (MI) in the alpha-phase has a fixed orientation in relation to Al, similar to that of the icosahedral quasi-crystals existing in this alloy system. It is shown that mirroring of the normal-to-high-symmetry icosahedral directions of the MI explains the alternative orientations, which are therefore likely to be caused by twinning of the fixed MI. Only one exception was found, which was related to the Bergman icosahedron internal to the T-phase of the Al-Mg-Zn system.

Title:
The ac-magnetic susceptibility and dielectric response of complex spin ordering processes in Mn3O4
Authors:
Thota, S; Singh, K; Nayak, S; Simon, C; Kumar, J; Prellier, W Author Full Names: Thota, Subhash; Singh, Kiran; Nayak, Sanjib; Simon, Ch.; Kumar, Jitendra; Prellier, Wilfrid
Source:
JOURNAL OF APPLIED PHYSICS, 116 (10):10.1063/1.4895054 SEP 14 2014
Abstract:
We report a meticulous study of the ac-magnetization dynamics (chi(ac)(T)), relative dielectric permittivity epsilon(r)(T), and magneto-dielectric (Delta epsilon(r)/epsilon(r)(H)) response of various complex magnetic transitions that occur below the ferrimagnetic Neel temperature T-N of Mn3O4. Besides the known sequence of transitions at T-N similar to 42.75 K, T-1 similar to 39 K, and T-2 similar to 34 K, the existence of a new anomaly reported recently at 38 K (T*) has been successfully probed by chi(ac)(T) and epsilon(r)(T) measurements. The effect of external dc-bias fields (H-DC) and driving frequency (f) on the above mentioned transitions has been investigated in consonance with the epsilon(r)(T) and Delta epsilon(r)/epsilon(r)(T, H) results. For the first time, we observed a clear hysteresis of about 5.15 K in the zero-field epsilon(r)(T) across the incommensurate-to-commensurate transition T-2 similar to 34 K, which provides evidence to the first-order nature of this transition. The Arrott plot (H/M vs. M-2) criterion has been used to distinguish the nature of all the sequential transitions that take place below T-N. (C) 2014 AIP Publishing LLC.

Title:
Structural changes and microstructures in stuffed tridymite-type compounds Ba1-xSrxAl2O4
Authors:
Tanaka, E; Ishii, Y; Teukasaki, H; Taniguchi, H; Mori, S Author Full Names: Tanaka, Eri; Ishii, Yui; Teukasaki, Hirofumi; Taniguchi, Hiroki; Mori, Shigeo
Source:
JAPANESE JOURNAL OF APPLIED PHYSICS, 53 (9):SI 10.7567/JJAP.53.09PB01 SEP 2014
Abstract:
Crystal structures and microstructures in Ba1-xSrxAl2O4 solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent (110) directions in the (001) plane, which appear in the P6(3) structure of Ba1-xSrxAl2O4 for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P2(1) structure in Ba1-xSrxAl2O4 with x = 0.7 was found to consist of a modulated structure with q = 0,1/2,0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P6(3) structure with a large structural fluctuation and a monoclinic P2(1) phase with the single-q modulated structure. (C) 2014 The Japan Society of Applied Physics

Title:
Strongly localized modes in one-dimensional defect-free magnonic quasicrystals
Authors:
Chen, CH; Qiu, RZ; Chang, CH; Hsueh, WJ Author Full Names: Chen, C. H.; Qiu, R. Z.; Chang, C. H.; Hsueh, W. J.
Source:
AIP ADVANCES, 4 (8):10.1063/1.4892164 AUG 2014
Abstract:
Signal storage in magnonic quasicrystals using a slow spin-wave mode, rather than the quasinormal mode of traditional periodic magnonic crystals, is proposed, which is analogous to the slow light mode in the field of optics. Compared to traditional materials, richer and more wavelength-selective sharp resonances are achieved using the quasicrystals with a fewer number of layers, because of the peculiar fractal transmission spectra of quasicrystals. The number of sharp resonance and the quality factor for the sharp resonances in the transmission spectra also increases as the generation order of the magnonic quasicrystal increases. This generic nature allows the storage of signals using spin wave, for a wide range of quasiperiodic systems. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Title:
Crystal structure and magnetic properties of Bi(0.8)A(0.2)FeO(3) (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy
Authors:
Rangi, M; Agarwal, A; Sanghi, S; Singh, R; Meena, SS; Das, A Author Full Names: Rangi, Manisha; Agarwal, Ashish; Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.
Source:
AIP ADVANCES, 4 (8):10.1063/1.4893241 AUG 2014
Abstract:
Bi(0.8)A(0.2)FeO(3) (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A(2+) results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ ruled out by Mossbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Title:
The alpha <-> beta phase transitions of Zn2P2O7 revisited: existence of an additional intermediate phase with an incommensurately modulated structure
Authors:
Stoger, B; Weil, M; Dusek, M Author Full Names: Stoeger, Berthold; Weil, Matthias; Dusek, Michal
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 539-554; SI 10.1107/S205252061401049X 3 JUN 2014
Abstract:
Zn2P2O7 crystallizes in a thortveitite-like structure and features temperature-dependent polymorphism. At high temperatures (T > 500 K), the aristotype phase beta-Zn2P2O7 (C2/m, Z = 2, a similar or equal to 6.60, b similar or equal to 8.28, c similar or equal to 4.53 angstrom, beta similar or equal to 105.4 degrees) is stable. At lower temperatures the lock-in phase alpha 1-Zn2P2O7 [at 350 K: I2/c, Z = 12, a = 20.1131 (13), b = 8.2769 (6), c = 9.109 (3) angstrom, beta = 106.338 (16)degrees], a sixfold superstructure with commensurate modulation vector q = (1/3, 0, 1/2), is stable. Between the stability ranges of the alpha(1)- and beta-phases exists the intermediate, *incommensurately modulated* alpha(2)-Zn2P2O7 phase with modulation wavevector q similar or equal to (0.33, 0, 0.40) and C2/m(alpha, 0, gamma)0s superspace group symmetry. The alpha(1) -> alpha(2) lock-in phase transition at T-L = 408 K is of first-order and features virtually no hysteresis. It is immediately followed by the second-order alpha(2) -> beta transition to the non-modulated phase at T-I similar or equal to 430 K. This transformation is sluggish and even at T = 500 K very weak satellite reflections of the alpha(2)- phase were observed. Both phase transitions were analyzed with differential scanning calorimetry and high-temperature powder and single-crystal X-ray diffraction. The crystal structures of the alpha(1)- and alpha(2)- phases were refined from single crystal data collected at T = 350, 400, 405, 410, 415, 420, 425, 430, 450 and 500 K. Different models describing the slow transition from the *incommensurately modulated* alpha(2)- to the non-modulated beta-phase were tested. In the model resulting in the best residuals, the bridging O atom of the [P2O7] group, which is located on a 2/m position in the basic structure, is described as an overlap of an atom ordered in internal space and one atom disordered around the mirror plane. The occupancy of the ordered atom decreases with temperature until at T = 500 K virtually only the disordered atom remains. Simultaneously, the amplitude of the modulation functions of the remaining atoms decreases, so that the T = 500 K structure can be considered as the C2/m aristotype structure, although the diffraction pattern still features *satellite reflections* of first order with very low intensities.

Title:
Understanding the structure details when drying hydrate crystals of pharmaceuticals - interpretations from diffuse scattering and inter-modulation satellites of a partially dehydrated crystal
Authors:
Chan, EJ; Gao, Q; Dabros, M Author Full Names: Chan, E. J.; Gao, Q.; Dabros, M.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 70 555-567; SI 10.1107/S2052520614005125 3 JUN 2014
Abstract:
Simplified models for the crystal lattice of the sesquihydrate form of the hemi-sulfate salt of (5S,6S,9R)-5-amino-6-(2,3-difluorophenyl)-6,7,8,9-tetrahydro-5H-cyclohep ta[b]pyridin9-yl 4-(2-oxo-2,3-dihydro-1H-imidazol[4,5b] pyridin-1-yl)-1-piperidine carboxylate (BMS-927711, C28H29F2N6O3+) are used to calculate diffuse diffraction features in order to develop a mechanistic understanding of the dehydration process with respect to disruption of the lattice, since a Bragg model cannot be established. The model demonstrates that what we observe when the water leaves the crystal is partial transformation from the parent form to a child form (a new form, less hydrated and structurally related to the parent). Yet t