Update: 13-Apr-2017


Title:
Magnetic ordering and dielectric relaxation in the double perovskite YBaCuFeO5
Authors:
Lai, YC; Du, CH; Lai, CH; Liang, YH; Wang, CW; Rule, KC; Wu, HC; Yang, HD; Chen, WT; Shu, GJ; Chou, FC Author Full Names: Lai, Yen-Chung; Du, Chao-Hung; Lai, Chun-Hao; Liang, Yu-Hui; Wang, Chin-Wei; Rule, Kirrily C.; Wu, Hung-Cheng; Yang, Hung-Duen; Chen, Wei-Tin; Shu, G. J.; Chou, F-C
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (14):10.1088/1361-648X/aa5708 APR 12 2017
Abstract:
Using magnetization, dielectric constant, and neutron diffraction measurements on a high quality single crystal of YBaCuFeO5 (YBCFO), we demonstrate that the crystal shows two antiferromagnetic transitions at T-N1 similar to 475 K and T-N2 similar to 175 K, and displays a giant dielectric constant with a characteristic of the dielectric relaxation at T-N2. It does not show the evidence of the electric polarization for the crystal used for this study. The transition at T-N1 corresponds with a paramagnetic to antiferromagnetic transition with a magnetic propagation vector doubling the unit cell along three crystallographic axes. Upon cooling, at T-N2, the commensurate spin ordering transforms to a spiral magnetic structure with a propagation vector of (h/2 k/2 l/2 +/- delta), where h, k, and l are odd, and the incommensurability d is temperature dependent. Around the transition boundary at T-N2, both commensurate and incommensurate spin ordering coexist.

Title:
Stability of icosahedral quasicrystals in a simple model with two-length scales
Authors:
Jiang, K; Zhang, PW; Shi, AC Author Full Names: Jiang, Kai; Zhang, Pingwen; Shi, An-Chang
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (12):10.1088/1361-648X/aa586b MAR 29 2017
Abstract:
The phase behaviour of a free energy functional with two length scales is examined by comparing the free energy of different candidate phases including three-dimensional icosahedral quasicrystals. Accurate free energy of the quasicrystals has been obtained using the recently developed projection method. The results reveal that the icosahedral quasicrystal and body-centred-cubic spherical phase are the stable ordered phases of the model. Furthermore, the difference between the results obtained from the projection method and the one-mode approximation has been analyzed in detail. The present study extends previous results on two-dimensional systems, demonstrating that the interactions between density waves at two length scales can stabilize two-and three-dimensional quasicrystals.

Title:
Effects of Cu addition on the microstructure and mechanical properties of as-cast and heat treated Mg-6Zn-4Al magnesium alloy
Authors:
Zhu, SZ; Luo, TJ; Zhang, TG; Li, YJ; Yang, YS Author Full Names: Zhu, Shaozhen; Luo, Tianjiao; Zhang, Tingan; Li, Yingju; Yang, Yuansheng
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 689 203-211; 10.1016/j.msea.2017.02.061 MAR 24 2017
Abstract:
The microstructure and mechanical properties of as-cast and heat treated Mg-6Zn-4Al-xCu (x=0, 0.5, 1.0 and 1.5 wt%) alloys were investigated in this work. The results show that the grain sizes of the alloys decrease considerably with increasing Cu addition, and the eutectics are refined with 0.5% Cu addition. The icosahedral quasi-crystalline phase is observed in Mg-6Zn-4Al and Cu-containing alloys, and the MgAlCu phase forms in the Cu-containing alloys because of Cu addition. Compared with Mg-6Zn-4Al alloy, the Cu-containing alloys exhibit improved age-hardening response during single-aging treatment. In addition, high-density fine precipitates are formed in the matrix during double-aging treatment, resulting in remarkable improvement of the tensile strength. The double aged Mg-6Zn-4Al-0.5Cu alloy shows the relatively optimal tensile properties. The yield strength, ultimate tensile strength and elongation are 202 MPa, 312 MPa and 7%, respectively, which is attributed to the combined effects of fine grains and the uniform distribution of high-density fine precipitates. It is noticed that the ductility of as-aged Cu-containing alloys is lower than that of the as-aged Mg-6Zn-4Al alloy due to the stress concentration during the tensile stress caused by the residual phases distributed along the grain boundaries after solution treatment.

Title:
Phase behaviour of quasicrystal forming systems of core-corona particles
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (11):10.1063/1.4977934 MAR 21 2017
Abstract:
Using Monte Carlo simulations and free-energy calculations, we study the phase behaviour of a two-dimensional system of particles interacting with a hard core of diameter sigma(HD) and a repulsive square shoulder potential. The interest in this system lies in the formation of quasicrystals of different symmetries at specific square-shoulder widths delta as previously reported by Dotera et al. [Nature 506, 208 (2014)]. However, an insight into other possible periodic phases formed in these systems and the thermodynamic stability of both the periodic and quasicrystal phases is yet to be addressed. Here, we study the phase behaviour and map out the phase diagrams for three different shoulder widths delta = 1.27 sigma(HD), 1.40 sigma(HD), and 1.60 sigma(HD), where octadecagonal, dodecagonal, and decagonal quasicrystals were previously reported. In addition, we verify the thermodynamic stability of these quasicrystals with respect to their periodic approximants. In general, we find that the system at all three shoulder widths forms hexagonal phases in two distinct density ranges due to the two characteristic length scales in the interaction potential. Further, we find that the dodecagonal and octadecagonal quasicrystals are stable in between two crystal phase regimes. In contrast, the decagonal quasicrystal is not bounded by a low-density crystal phase regime due to the lower density of this quasicrystal. From the free-energy calculations, we find indications that the decagonal and dodecagonal quasicrystals are thermodynamically stable with respect to their approximants, and the octadecagonal quasicrystal is stabilised by a configurational entropy contribution. Published by AIP Publishing.

Title:
Enhancement of Ferroelectricity for Orthorhombic (TB0.861Mn0.121)MnO3-delta by Copper Doping
Authors:
Deng, JM; Farid, MA; Zhang, M; Yang, AM; Zhang, HX; Zhang, H; Tian, GF; Wu, MM; Liu, LJ; Sun, JL; Li, GB; Liao, FH; Lin, JH Author Full Names: Deng, Jianming; Farid, Muhammad Asim; Zhang, Meng; Yang, Aimei; Zhang, Hongxing; Zhang, Hao; Tian, Gengfang; Wu, Meimei; Liu, Laijun; Sun, Junliang; Li, Guobao; Liao, Fuhui; Lin, Jianhua
Source:
INORGANIC CHEMISTRY, 56 (6):3475-3482; 10.1021/acs.inorgchem.6b03024 MAR 20 2017
Abstract:
Copper-doped (Tb0.861MnO0.121)Mn0(3-delta) has been synthesized by the conventional solid state reaction method. X-ray, neutron, and electron diffraction data indicate that they crystallize in Pnma space group at room temperature. Two magnetic orderings are found for this series by neutron diffraction. One is the ICAM (incommensurate canted antiferromagnetic) ordering of Mn with a wave vector q(Mn) = (similar to 0.283, 0, 0) with a approximate to 5.73A,b approximate to 5.31 A, and c approximate to 7.41 A, and the other is the CAM (canted antiferromagneiic) ordering of both Tb and Mn in the magnetic space group Pn'a2(1)' with a approximate to 5.73 A, b approximate to 5.31 A, and c approximate to 7:41 A. A dielectric peak around 40 K is found for the samples doped with Cu, which is higher than that for orthorhombic TbMnO3.

Title:
Opening a nodal gap by fluctuating spin-density wave in lightly doped La2-xSrxCuO4
Authors:
Kapon, I; Ellis, DS; Drachuck, G; Bazalitski, G; Weschke, E; Schierle, E; Strempfer, J; Niedermayer, C; Keren, A Author Full Names: Kapon, Itzik; Ellis, David S.; Drachuck, Gil; Bazalitski, Galina; Weschke, Eugen; Schierle, Enrico; Strempfer, Joerg; Niedermayer, Christof; Keren, Amit
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104512 MAR 14 2017
Abstract:
We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La2-xSrxCuO4, which is on the edge of the antiferromagnetic phase. We found that a fluctuating incommensurate spin-density wave (SDW) with a bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of a charge-density wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.

Title:
E-type noncollinear magnetic ordering in multiferroic o-LuMnO3
Authors:
Mukherjee, S; Donni, A; Nakajima, T; Mitsuda, S; Tachibana, M; Kitazawa, H; Pomjakushin, V; Keller, L; Niedermayer, C; Scaramucci, A; Kenzelmann, M Author Full Names: Mukherjee, Saumya; Donni, Andreas; Nakajima, Taro; Mitsuda, Setsuo; Tachibana, Makoto; Kitazawa, Hideaki; Pomjakushin, Vladimir; Keller, Lukas; Niedermayer, Christof; Scaramucci, Andrea; Kenzelmann, Michel
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104412 MAR 13 2017
Abstract:
Multiferroic orthorhombic o-LuMnO3 exhibits large ferroelectric polarization induced by an E-type magnetic order. Recently, the E-type magnetic phase in LuMnO3 was proposed to feature magnetic moments tilted away from the collinear ordering. We employed neutron diffraction to determine the symmetry of the magnetic order in o-LuMnO3. We observed that below T-N = 39 K, the Mn3+ spins order into an incommensurate amplitudemodulated phase that obeys the Pbnm crystal symmetry and is paraelectric. The incommensurate phase locks into a commensurate phase at T-C = 35.5 K described by a fully antiferromagnetic and noncollinear E-type order. This noncollinear E-type ordering breaks the spatial inversion symmetry and induces a spontaneous polarization at TC. At T = 2 K, an appreciably large electric polarization was observed similar to that of other orthorhombic manganites featuring E-type magnetic order. We also present a Pbnm symmetry-allowed Dzyaloshinskii-Moriya interaction that explains the noncollinear E-type order in the commensurate phase. These results are in qualitative agreement with the type of distortions from collinear E-type antiferromagnetic order found using Monte Carlo simulation for rare-earth manganites

Title:
Sodium layer chiral distribution and spin structure of Na2Ni2TeO6 with a Ni honeycomb lattice
Authors:
Karna, SK; Zhao, Y; Sankar, R; Avdeev, M; Tseng, PC; Wang, W; Shu, GJ; Matan, K; Guo, GY; Chou, FC Author Full Names: Karna, Sunil K.; Zhao, Y.; Sankar, R.; Avdeev, M.; Tseng, P. C.; Wang, W.; Shu, G. J.; Matan, K.; Guo, G. Y.; Chou, F. C.
Source:
PHYSICAL REVIEW B, 95 (10):10.1103/PhysRevB.95.104408 MAR 8 2017
Abstract:
The nature of Na ion distribution, diffusion path, and the spin structure of P2-type Na2Ni2TeO6 with a Ni honeycomb lattice has been explored. The nuclear density distribution of Na ions reveals a two-dimensional (2D) chiral pattern within Na layers without breaking the original 3D crystal symmetry, which has been achieved uniquely via an inverse Fourier transform (iFT)-assisted neutron-diffraction technique. The Na diffusion pathway described by the calculated isosurface of the Na ion bond valence sum (BVS) map is found consistent to a chiral diffusion mechanism. The Na site occupancy and Ni2+ spin ordering were examined in detail with the neutron diffraction, magnetic susceptibility, specific heat, thermal conductivity, and transport measurements. Signatures of both strong incommensurate (ICM) and weak commensurate (CM) antiferromagnetic (AFM) spin ordering were identified in the polycrystalline sample studied, and the CM-AFM spin ordering was confirmed by using a single-crystal sample through the k scan in the momentum space corresponding to the AFM peak of (1/2,0,1).

Title:
Formation of the Structure and Physicomechanical Properties of a Quasicrystalline Al-Cu-Fe Alloy upon Plasma Spraying
Authors:
Lepeshev, AA; Karpov, IV; Ushakov, AV Author Full Names: Lepeshev, A. A.; Karpov, I. V.; Ushakov, A. V.
Source:
PHYSICS OF THE SOLID STATE, 59 (3):438-442; 10.1134/S1063783417030210 MAR 2017
Abstract:
Quasicrystalline coatings prepared under various thermal conditions of spraying have been studied. Initial quasicrystalline powders with dispersion of 10-50 mu m were prepared in a low-pressure arc discharge plasma. The coatings have been sprayed on copper rings using a swinging plasmatron. It is found that the increase in the quenching rate of melt droplets increases the chemical homogeneity and leads to formation of nanostructured formations. The precipitation of nanostructured grains (d < 100 nm) in the sprayed alloy leads to an increase in the mechanical characteristics (hardness, deformation, and ductility) and can be considered as an additional factor of hardening of the material.

Title:
Mossbauer Studies of Spatial Spin-Modulated Structure and Hyperfine Interactions in Multiferroic (BiFe0.10Fe0.85Cr0.05O3)-Fe-57
Authors:
Pokatilov, VS; Rusakov, VS; Sigov, AS; Belik, AA; Matsnev, ME; Komarov, AE Author Full Names: Pokatilov, V. S.; Rusakov, V. S.; Sigov, A. S.; Belik, A. A.; Matsnev, M. E.; Komarov, A. E.
Source:
PHYSICS OF THE SOLID STATE, 59 (3):443-449; 10.1134/S1063783417030271 MAR 2017
Abstract:
Results of Mossbauer investigations on Fe-57 nuclei in multiferroic material (BiFe0.10Fe0.85Cr0.05O3)-Fe-57 in the temperature range from 5.2 to 300 K are presented. Bulk rhombohedral samples were obtained by solid-state synthesis at high pressure. Mossbauer spectra were analyzed using the model of spatial incommensurate spin-modulated structure of the cycloidal type. Information on the influence of substituting Cr cations for Fe cations on hyperfine spectral parameters was obtained: the shift and quadrupolar shift of a Mossbauer line, and isotropic and anisotropic contributions into the hyperfine magnetic field. The anharmonicity parameter m of the spatial spin-modulated structure increases almost 1.7 times at 5.2 K when BiFeO3 is doped with chromium. The data on m were used for calculation of the uniaxial magnetic anisotropy constants and their temperature dependences for pure and chromium-doped BiFeO3.ß

Update: 6-Apr-2017


Title:
Charge Density Wave in the New Polymorphs of RE2Ru3Ge5 (RE = Pr, Sm, Dy)
Authors:
Bugaris, DE; Malliakas, CD; Han, F; Calta, NP; Sturza, M; Krogstad, MJ; Osborn, R; Rosenkranz, S; Ruff, JPC; Trimarchi, G; Bud'ko, SL; Balasubramanian, M; Chung, DY; Kanatzidis, MG Author Full Names: Bugaris, Daniel E.; Malliakas, Christos D.; Han, Fei; Calta, Nicholas P.; Sturza, Mihai; Krogstad, Matthew J.; Osborn, Raymond; Rosenkranz, Stephan; Ruff, Jacob P. C.; Trimarchi, Giancarlo; Bud'ko, Sergey L.; Balasubramanian, Mahalingam; Chung, Duck Young; Kanatzidis, Mercouri G.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (11):4130-4143; 10.1021/jacs.7b00284 MAR 22 2017
Abstract:
A new polymorph of the RE2Ru3Ge5 (RE = Pr, Sm, Dy) compounds has been grown as single crystals via an indium flux. These compounds crystallize in tetragonal space group P4/mnc with the Sc2Fe3Si5-type structure, having lattice parameters a = 11.020(2) angstrom and c = 5.853(1) angstrom for RE = Pr, a = 10.982(2) angstrom and c = 5.777(1) angstrom for RE = Sm, and a = 10.927(2) angstrom and c = 5.697(1) angstrom for RE = Dy. These materials exhibit a structural transition at low temperature, which is attributed to an apparent charge density wave (CDW). Both the high-temperature average crystal structure and the low-temperature incommensufately Modulated crystal structure (for Sm2Ru3Ge5 as a representative) have been solved. The charge density wave order is manifested by periodic distortions of the one-dimensional zigzag Ge chains. From X-ray diffraction, charge transport (electrical resistivity, Hall effect, magnetoresistance), magnetic measurements, and heat capacity, the ordering temperatures (T-CDW) observed, in the Pr and Sm analogues are similar to 200 and similar to 175 K, respectively. The charge transport measurement results indicate an electronic state transition happening simultaneously with the CDW transition. X-ray absorption near-edge spectroscopy (XANES) and electronic band structure results are also reported.

Title:
Improved tensile properties of an equal channel angular pressed (ECAPed) Mg-8Sn-6Zn-2A1 alloy by prior aging treatment
Authors:
Cheng, WL; Tian, L; Wang, HX; Bian, LP; Yu, H Author Full Names: Cheng, Weili; Tian, Liang; Wang, Hongxia; Bian, Liping; Yu, Hui
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 687 148-154; 10.1016/jansea.2017.01.054 FEB 27 2017
Abstract:
This paper demonstrates that aging prior to ECAP (APE) can greatly enhance the tensile properties of an ECAPed Mg-8Sn-6Zn-2(wt%)Al (TZA862) alloy. Both fine Mg2Sn and icosahedral quasicrystal phase (I -phase) precipitates that formed during the APE treatment could reduce the average size of dynamically recrystallized (DRXed) grains as well as increase the fraction of fine particles after ECAP. Furthermore, the APE treatment resulted in increased basal texture intensity as well as a decreased amount of large non-deformed particles. Therefore, the tensile strength and ductility of ECAPed TZA862 alloy were improved simultaneously by the APE treatment.

Title:
Subpicometer-scale atomic displacements and magnetic properties in the oxygen-isotope substituted multiferroic DyMnO3
Authors:
Narayanan, N; Graham, PJ; Reynolds, N; Li, F; Rovillain, P; Hester, J; Kimpton, J; Yethiraj, M; McIntyre, GJ; Hutchison, WD; Ulrich, C Author Full Names: Narayanan, N.; Graham, P. J.; Reynolds, N.; Li, F.; Rovillain, P.; Hester, J.; Kimpton, J.; Yethiraj, M.; McIntyre, G. J.; Hutchison, W. D.; Ulrich, C.
Source:
PHYSICAL REVIEW B, 95 (7):10.1103/PhysRevB.95.075154 FEB 27 2017
Abstract:
We have investigated DyMn O-16(3) and its isotopically substituted counterpart DyMn O-18(3) by neutron powder diffraction, x-ray diffraction, and heat capacity measurements to investigate the mechanism leading to its magnetically induced electric polarization. O-18 isotope substitution does not influence the magnetic ordering temperature of the Mn ions T-N,(Mn) or the multiferroic ordering temperature T-l coinciding with the onset of the spin spiral phase; however, it does reduce the ordering temperature of Dy into its incommensurate magnetic state T-N,T-Dy from 7.0(1) K to 5.9(1) K. The temperature dependence of the magnetic propagation vector, q(IC), changes with O-18 substitution, while T-l remains almost constant, independent of q(IC). Pronounced changes in the lattice parameters occur at the various phase transitions. Furthermore, distinct subpicometer-scale distortions of the MnO6 octahedra and displacements of the Dy ions are observed below the ferroelectric phase transition at T-l in both samples, pointing toward the mechanism for electric polarization and its coupling to the orbital degrees of freedom.

Title:
Hyperuniformity of quasicrystals
Authors:
Oguz, EC; Socolar, JES; Steinhardt, PJ; Torquato, S Author Full Names: Oguz, Erdal C.; Socolar, Joshua E. S.; Steinhardt, Paul J.; Torquato, Salvatore
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054119 FEB 23 2017
Abstract:
Hyperuniform systems, which include crystals, quasicrystals, and special disordered systems, have attracted considerable recent attention, but rigorous analyses of the hyperuniformity of quasicrystals have been lacking because the support of the spectral intensity is dense and discontinuous. We employ the integrated spectral intensity Z(k) to quantitatively characterize the hyperuniformity of quasicrystalline point sets generated by projection methods. The scaling of Z(k) as k tends to zero is computed for one-dimensional quasicrystals and shown to be consistent with independent calculations of the variance, sigma(2)(R), in the number of points contained in an interval of length 2R. We find that one-dimensional quasicrystals produced by projection from a two-dimensional lattice onto a line of slope 1/tau fall into distinct classes determined by the width of the projection window. For a countable dense set of widths, Z(k) similar to k(4); for all others, Z(k) similar to k(2). This distinction suggests that measures of hyperuniformity define new classes of quasicrystals in higher dimensions as well.

Title:
Field-induced reentrant magnetoelectric phase in LiNiPO4
Authors:
Toft-Petersen, R; Fogh, E; Kihara, T; Jensen, J; Fritsch, K; Lee, J; Granroth, GE; Stone, MB; Vaknin, D; Nojiri, H; Christensen, NB Author Full Names: Toft-Petersen, Rasmus; Fogh, Ellen; Kihara, Takumi; Jensen, Jens; Fritsch, Katharina; Lee, Jooseop; Granroth, Garrett E.; Stone, Matthew B.; Vaknin, David; Nojiri, Hiroyuki; Christensen, Niels Bech
Source:
PHYSICAL REVIEW B, 95 (6):10.1103/PhysRevB.95.064421 FEB 21 2017
Abstract:
Using pulsed magnetic fields up to 30 T we have measured the bulk magnetization and electrical polarization of LiNiPO4 and have studied its magnetic structure by time-of-flight neutron Laue diffraction. Our data establish the existence of a reentrant magnetoelectric phase between 19 T and 21 T. We show that a magnetized version of the zero field commensurate structure explains the magnetoelectric response quantitatively. The stability of this structure suggests a field-dependent spin anisotropy. Above 21 T, amagnetoelectrically inactive, short-wavelength incommensurate structure is identified. Our results demonstrate the combination of pulsed fields with epithermal neutron Laue diffraction as a powerful method to probe even complex phase diagrams in strong magnetic fields.

Title:
Cell-quintupling: Structural phase transition in a molecular crystal, bis(trans-4-butylcyclohexyl) methanol
Authors:
Saito, K; Ikeda, T; Yamamura, Y; Saitoh, H; Hishida, M; Kobayashi, Y; Fujita, T; Ichikawa, J Author Full Names: Saito, Kazuya; Ikeda, Takaaki; Yamamura, Yasuhisa; Saitoh, Hideki; Hishida, Mafumi; Kobayashi, Yutaro; Fujita, Takeshi; Ichikawa, Junji
Source:
JOURNAL OF CHEMICAL PHYSICS, 146 (7):10.1063/1.4976318 FEB 21 2017
Abstract:
Astructural phase transition at 151.6 K of the title compound [bis(trans-4-butylcyclohexyl) methanol] is examined by X-ray diffraction crystallography, Fourier-transform infrared spectroscopy, and adiabatic calorimetry. A general consideration on possible superstructures indicates that a single modulation wave is sufficient to drive this cell-quintupling transition. The entropy of transition determined calorimetrically indicates that two conformations are dominant in the room-temperature phase in contrast to the fivefold disorder expected from the structure of the low-temperature phase. Published by AIP Publishing.

Title:
Four-Dimensional Incommensurate Modulation and Luminescent Properties of Host Material Na3La(PO4)(2)
Authors:
Zhao, D; Ma, FX; Ma, SQ; Zhang, AY; Nie, CK; Huang, M; Zhang, L; Fan, YC Author Full Names: Zhao, Dan; Ma, Fa-Xue; Ma, Shu-Qi; Zhang, Ai-Yun; Nie, Cong-Kui; Huang, Min; Zhang, Lei; Fan, Yun-Chang
Source:
INORGANIC CHEMISTRY, 56 (4):1835-1845; 10.1021/acs.inorgchem.6b02241 FEB 20 2017
Abstract:
A series of orthophosphates Na(3)Ln(PO4)(2) (Ln = lanthanoids) have for a long time been known as good luminescent materials, yet their crystal structures have not been studied in full detail. In this work, compound Na3La(PO4)(2) was prepared using molten salt (flux) method and for the first time was structurally determined on X-ray single-crystal diffraction data. Interestingly, it crystallizes in the four-dimensional incommensurately modulated structure with orthorhombic superspace group Pca(21)(0 beta 0)000 and modulation wave vector q = 0.387b*. Furthermore, to evaluate the potentiality of Na3La(PO4)(2) to be used as a luminescent host material, 5 mol % Eu3+, Tb3+, and Dy3+ doped phosphors were prepared, respectively. The excitation spectra, emission spectra, decay time, quantum efficiency, and the color purity of prepared phosphors, Na3La0.95Eu0.05(PO4)(2), Na3La0.95Tb0.05(PO4)(2), and Na3La0.95Dy0.05(PO4)(2), were studied.

Title:
Anomalous lattice compression and magnetic ordering in CuO at high pressures: A structural study and first-principles calculations
Authors:
Kozlenko, DP; Druzbicki, K; Kichanov, SE; Lukin, EV; Liermann, HP; Glazyrin, KV; Savenko, BN Author Full Names: Kozlenko, D. P.; Druzbicki, K.; Kichanov, S. E.; Lukin, E. V.; Liermann, H. -P.; Glazyrin, K. V.; Savenko, B. N.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054115 FEB 17 2017
Abstract:
The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-ray powder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations. Anomalous lattice compression is observed, with enlargement of the lattice parameter a, reaching a maximum at P = 13 GPa, followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at high pressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the square fourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural properties and electronic structure of CuO was successfully elucidated in the framework of full-electronic density functional theory calculations with range-separated HSE06, and meta-generalized gradient approximation hybrid M06 functionals. The antiferromagnetic (AFM) ground state with a propagation vector q = (0.5,0, -0.5) remains stable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of the principal superexchange magnetic interactions were analyzed, and the pressure behavior of the Neel temperature as well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic state to the commensurate AFM ground state were evaluated. The estimated upper limit of the Neel temperature at P = 38 GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at room temperature and high pressure.

Title:
Fabrication of a Quasicrystal Electrode at a Low Processing Temperature via Electrohydrodynamic and Transfer Printing for use in Multifunctional Electronics
Authors:
Park, S; Park, S; Park, S; Ryu, H; Park, JJ Author Full Names: Park, Seoungwoong; Park, Siyong; Park, Sangki; Ryu, Hochung; Park, Jong-Jin
Source:
ADVANCED ELECTRONIC MATERIALS, 3 (2):10.1002/aelm.201600440 FEB 2017
Abstract:
Fabrication of a quasicrystal electrode at a low processing temperature via electrohydrodynamic and transfer printing for use in multifunctional electronics is demonstrated using an electrohydrodynamic narrow nozzle-to-substrate distance printing method to obtain a quasicrystal electrode (transferred electrode), which can increase electrode durability with a better surface roughness and lower processing cost with low-temperature processing, for use in multifunctional electronics.

Title:
Dynamic response of an icosahedral quasi-crystalline medium with a Griffith crack under mechanical loadings
Authors:
Qiao, LP; Wu, L; Fan, TY Author Full Names: Qiao, Liangping; Wu, Li; Fan, Tianyou
Source:
ADVANCES IN MECHANICAL ENGINEERING, 9 (2):10.1177/1687814016688850 FEB 1 2017
Abstract:
Elastodynamic response of three-dimensional icosahedral quasi-crystals under mechanical loadings is presented in this article. Two kinds of cases are considered here, in which the plane problem and anti-plane problem are included. The phonon and phason elastic fundamental fields along with their coupling effect in crack analysis are explicitly presented in terms of the theoretical and numerical analyses. Using the finite difference method, some numerical results of stresses, displacements, and normalized dynamic stress intensity factor are obtained. By comparing the results of quasi-crystals, this article reveals the influence of phonon and phason elastic fundamental fields, which occupy an important position in dynamic deformation behavior of quasi-crystals. Of course, phonon-phason coupling effect also should not be neglected.

Update: 30-Mar-2017


Title:
Shield-like tile and its application to the decagonal quasicrystal-related structures in Al-Cr-Fe-Si alloys
Authors:
Li, H; Ma, HK; Hou, LG; Guo, MX; He, ZB Author Full Names: Li, Hua; Ma, Haikun; Hou, Longgang; Guo, Mingxing; He, Zhanbing
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 701 494-498; 10.1016/j.jallcom.2017.01.105 APR 15 2017
Abstract:
A shield-like tile (SLT) consisting of one star tile and two hexagon tiles was used as one structural block to describe the tilings of quasicrystal approximants in our previous work [J. All. Compds. 647 (2015) 797- 801.] because of its merits compared with the hexagon-boat-star model. In this paper, we aim to elucidate the rules of connection and the orientations of SLTs. Two examples of high-angle annular dark field scanning transmission electron microscopy images are provided to support these rules. The SLT orientation mapping of the quasicrystal-related structures along the pseudo-tenfold axis was achieved, and the structural characterizations were revealed intuitively. Furthermore, some new quasicrystal approximants were discussed based on the changeable rows of SLTs. (C) 2017 Elsevier B.V. All rights reserved.

Title:
Nanoquasicrystalline Al-Fe-Cr-Ti alloy matrix/gamma-Al2O3 nanocomposite powders: The effect of the ball milling process
Authors:
Xu, W; Galano, M; Audebert, F Author Full Names: Xu, W.; Galano, M.; Audebert, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 701 342-349; 10.1016/j.jallcom.2016.11.412 APR 15 2017
Abstract:
Quasicrystalline aluminium alloys and aluminium based nanocomposites with the advantage of high strength over commercial aluminium alloys have been studied for many years. In this work a nano-quasicrystalline Al-Fe-Cr-Ti alloy powder and a nanocomposite consisting of a mixture of a nano-quasicrystalline alloy and nanosize gamma-Al2O3 powders were produced through mechanical milling with different milling speeds. It has been observed that a higher milling time or milling speed can improve the homogeneity of the gamma-Al2O3 distribution. The alpha-Al crystallite size decreases and the hardness increases with the milling time. The smallest crystallite size (14 nm) and the highest hardness value (638 HV10g) were obtained for the nanocomposite after 30 h of milling at 250 rpm. As the alpha-Al crystallite size is the main change in the microstructure during the ball milling process, the change in the hardness of the milled powders was found to follow a Hall-Fetch type relation with an exponent of 0.25. (C) 2016 Published by Elsevier B.V.

Title:
The effect of temperature, interaction range, and pair potential on the formation of dodecagonal quasicrystals in core-corona systems
Authors:
Pattabhiraman, H; Dijkstra, M Author Full Names: Pattabhiraman, Harini; Dijkstra, Marjolein
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (9):10.1088/1361-648X/aa5530 MAR 8 2017
Abstract:
A two-dimensional dodecagonal quasicrystal was previously reported by Dotera et al (2014 Nature 506 208) in a system of particles interacting with a hard core of diameter s and a repulsive square shoulder of diameter delta = 1.40 sigma. In the current work, we examine the formation of this quasicrystal using bond orientational order parameters, correlation functions and tiling distributions. We find that this dodecagonal quasicrystal forms from a fluid phase. We further study the effect of the width of the repulsive shoulder by simulating the system over a range of values of d. For the range of densities and temperatures considered, we observe the formation of the dodecagonal quasicrystal between delta = 1.30 sigma and 1.44 sigma. We also study the effect of shape of the interaction potential by simulating the system using three other interaction potentials with two length scales, namely hard-core plus a linear ramp, modified exponential, or Buckingham (exp-6) potential. We observe the presence of the quasicrystal in all three systems. However, depending on the shape of the potential, the formation of the quasicrystal takes place at lower temperatures (or higher interaction strengths). Using free-energy calculations, we demonstrate that the quasicrystal is thermodynamically stable in the square-shoulder and linear-ramp system.

Title:
New insights into the multiferroic properties of Mn3TeO6
Authors:
Ivanov, SA; Ritter, C; Nordblad, P; Tellgren, R; Weil, M; Carolus, V; Lottermoser, T; Fiebig, M; Mathieu, R Author Full Names: Ivanov, S. A.; Ritter, C.; Nordblad, P.; Tellgren, R.; Weil, M.; Carolus, V.; Lottermoser, Th; Fiebig, M.; Mathieu, R.
Source:
JOURNAL OF PHYSICS D-APPLIED PHYSICS, 50 (8):10.1088/1361-6463/aa5621 MAR 1 2017
Abstract:
Mn3TeO6 has a trigonal corundum related structure (space group R (3) over bar), and orders in an incommensurate antiferromagnetic (AFM) structure at T-N approximate to 24 K. A weak ferroelectric order below T* similar to 21 K has recently been reported. In order to investigate possible structural changes below T-N leading to the observed dipole order, we have performed a detailed study of the crystal and magnetic structures of Mn3TeO6 using neutron powder diffraction (NPD) in the temperature range of 5-40 K. Complementary low-temperature second harmonic generation (SHG) measurements were performed in order to confirm the reported dipole order at T*. No change in the rhombohedral symmetry associated with a possible displacive phase transition at T* was observed in the long-range *structural* correlations, and it appears that Mn3TeO6 keeps the same incommensurately modulated magnetic spin structure with the propagation vector k = (0; 0; 0.43) in the whole temperature range from 5 to 24 K.

Title:
Competing electronic instabilities of extended Hubbard models on the honeycomb lattice: A functional renormalization group calculation with high-wave-vector resolution
Authors:
de la Pena, DS; Lichtenstein, J; Honerkamp, C Author Full Names: de la Pena, D. Sanchez; Lichtenstein, J.; Honerkamp, C.
Source:
PHYSICAL REVIEW B, 95 (8):10.1103/PhysRevB.95.085143 FEB 27 2017
Abstract:
We investigate the quantum many-body instabilities for electrons on the honeycomb lattice at half filling with extended interactions, motivated by a description of graphene and related materials. We employ a recently developed fermionic functional renormalization group scheme, which allows for highly resolved calculations of wave-vector dependences in the low-energy effective interactions. We encounter the expected anti-ferromagnetic spin densitywave for a dominant on-site repulsion between electrons, and charge orderwith different modulations for dominant pure nth nearest-neighbor repulsive interactions. Novel instabilities towards incommensurate charge density waves take place when nonlocal density interactions among several bond distances are included simultaneously. Moreover, for more realistic Coulomb potentials in graphene including enough nonlocal terms there is a suppression of charge order due to competition effects between the different charge ordering tendencies, and if the on-site term fails to dominate, the semimetallic state is rendered stable. The possibility of a topological Mott insulator being the favored tendency for dominating second-nearest-neighbor interactions is not realized in our results with high momentum resolution.

Title:
Quasiperiodic Frank-Kasper phases derived from the square-triangle dodecagonal tiling
Authors:
Sadoc, JF; Mosseri, R Author Full Names: Sadoc, Jean-Francois; Mosseri, Remy
Source:
STRUCTURAL CHEMISTRY, 28 (1):63-73; SI 10.1007/s11224-016-0846-2 FEB 2017
Abstract:
Frank-Kasper (F-K) phases form an important set of large-cell crystalline structures describing many intermetallic alloys. They are usually described in term of their atomic environments, with atoms having 12, 14, 15 and 16 neighbours, coded into the canonical Z(p) cells (with p the coordination number), the case p = 12 corresponding to a local icosahedral environment. In addition, the long-range structure is captured by the geometry of a network (called either "major skeleton" or "disclination network") connecting only the non-icosahedral sites (with p 6 not equal 12). Another interesting description, valid for the so-called layered F-K phases, amounts to give simple rules to decorate specific periodic 2d tilings made of triangles and squares and eventually get the 3d periodic F-K phases. Quasicrystalline phases can sometime be found in the vicinity, in the phase diagram, of the F-K crystalline alloys; it is therefore of interest to understand whether and how the standard F-K construction rules can be generalized on top of an underlying quasiperiodic structure. It is in particular natural to investigate how well square-triangle quasiperiodic tilings with dodecagonal symmetry, made of square and (equilateral) triangles, can be used as building frames to generate some F-K-like quasicrystalline structures. We show here how to produce two types of such structures, which are quasiperiodic in a plane and periodic in the third direction, and containing (or not) Z(16) sites.

Title:
Are periodicity and symmetry the properties of a discrete space? (On one paradox of cellular automata)
Authors:
Shevchenko, VY; Krivovichev, SV Author Full Names: Shevchenko, Vladimir Ya; Krivovichev, Sergey V.
Source:
STRUCTURAL CHEMISTRY, 28 (1):45-50; SI 10.1007/s11224-016-0844-4 FEB 2017
Abstract:
We consider a three-color cellular automaton (CA) that acts on a square lattice. In ternary numeral system, the CA has the number 111010011111110111011102010, which corresponds to 3704707887996 in the decimal system. With the finite size of the input row, CA-3704707887996 generates aperiodic structures with repeating self-similar patterns. In order to investigate the formation of periodic patterns by the CA-3704707887996, the input row was used that represents a periodic structure containing variable number of cells. The behavior of the CA-3704707887996 work for the input rows with periods up to 21 cells was studied. All generated patterns were analyzed from the viewpoint of their periodicity along the vertical direction. It was found out that the behavior of the system depending upon the length (l(input)) and structure of the periodic input row is strongly nonlinear. The complexity C of a pattern considered as a size of a unit cell increases exponentially with the increasing l(input) value and can be described by the function C = 1.8986 exp [0.3334 l(input)], with the correlation coefficient R-2 = 0.8967. As a rule, initially the CA generates a metastable aperiodic structure and then adopts a stable regime of generation of a stable periodic pattern. The abstract properties of the CA-3704707887996 have several important consequences for structural chemistry: (1) relatively simple schemes of local interactions of particles may result in the formation of very complex structures depending upon the initial conditions and abstract properties of the interactions; (2) symbolic complexity of the generated patterns increases exponentially depending upon the structure of initial conditions; (3) under certain initial conditions, explosive fluctuations of complexity are possible that lead to the formation of giant superstructures with extremely large periods; and (4) under certain conditions, the border between aperiodic and periodic structures virtually disappears.

Title:
Generalized reciprocal vector sets
Authors:
Gomez-Rodriguez, A; Aragon, JL Author Full Names: Gomez-Rodriguez, A.; Aragon, J. L.
Source:
STRUCTURAL CHEMISTRY, 28 (1):235-238; SI 10.1007/s11224-016-0848-0 FEB 2017
Abstract:
In this work, we present a short review on generalized reciprocal vectors, a field created by Alan L. Mackay. In particular, we discuss the concept of generalized reciprocal vectors, its relation with eutactic stars used in quasicrystallography and their calculation using Moore-Penrose pseudoinverses. Additionally, we propose a plain Gaussian algorithm for this same purpose.

Title:
Tiling approach for the description of the sevenfold symmetry in quasicrystals
Authors:
Madison, AE Author Full Names: Madison, A. E.
Source:
STRUCTURAL CHEMISTRY, 28 (1):57-62; SI 10.1007/s11224-016-0793-y FEB 2017
Abstract:
An example of substitution rules for the construction of heptagonal rhombic tilings is proposed. Rigorous inflation/deflation rules make it possible to expand the tiling up to infinity without additional ad hoc rearrangements. The derived tilings are self-similar and consist of characteristic patterns with seven-pointed stars surrounded by similar seven-pointed stars.

Title:
Mackay clusters and beyond in icosahedral quasicrystals seen from 6D space
Authors:
Sirindil, A; Quiquandon, M; Gratias, D Author Full Names: Sirindil, Abdullah; Quiquandon, Marianne; Gratias, Denis
Source:
STRUCTURAL CHEMISTRY, 28 (1):123-132; SI 10.1007/s11224-016-0843-5 FEB 2017
Abstract:
It is a great pleasure and honour for us to participate to the celebration of the 90th birthday of Alan Mackay, one of the most inspired crystallographers of our time who has been the authentic predecessor of the quasicrystal discovery. We discuss here several ways to construct Mackay-type atomic clusters and others for describing quasicrystalline structures from the standard 6D framework. We show that they are several simple solutions for both the 6D natural cluster and the original Mackay derivation that are consistent with special points of the basic icosahedral 6D lattice and the actually determined clusters in usual cubic 1/1 approximants of the icosahedral phases. This technique works as well for describing the two first shells of the so-called Bergman clusters but the situation is far more complicated for the so-called Tsai cluster that cannot be directly obtained from the icosahedral cut and projection of the simple 6D lattice special points without significantly large differences in the radii of the various orbits with respect to their actual positions in the YbCd icosahedral-type alloys. This shows that the 6D approach using special points as locations of the mean atomic surfaces-although very efficient for constructing initial simple models of the icosahedral phases-requires subsequent refinement techniques, especially in the actual locations and sizes of the various atomic orbits of the implied clusters, for leading to final acceptable structural models.

Title:
Kurt Bruckner's view on the Penrose tiling
Authors:
Steurer, W; Arlitt, S Author Full Names: Steurer, Walter; Arlitt, Sabine
Source:
STRUCTURAL CHEMISTRY, 28 (1):51-56; SI 10.1007/s11224-016-0790-1 FEB 2017
Abstract:
We demonstrate the potential of Kurt Bruckner's 'addition algorithm', which is based on the substitution rule for the generation of the Robinson triangle tiling, a variant of the Penrose tiling. The artist Kurt Bruckner developed his straightforward approach intuitively for the creation of quasiperiodic ornaments. This versatile method can be used for the construction of achiral, homochiral and racemic quasiperiodic ornaments, as well as for the generation of decorated two-level (two-color) Penrose tilings. Therefore, the underlying tiling is always the same kind of Penrose tiling, which is invariant under the action of specific mirror and black/white mirror operations in contrast to unit tiles that are decorated in specific ways. Compared to the underlying classical substitution method the advantage of Kurt Bruckner's approach is its simplicity and versatility for the creation of decorated tilings. Using a vector graphics editor, large and arbitrarily complex quasiperiodic ornaments can be easily generated manually.

Title:
Generalizing crystallography: a tribute to Alan L. Mackay at 90
Authors:
Hargittai, I Author Full Names: Hargittai, Istvan
Source:
STRUCTURAL CHEMISTRY, 28 (1):1-16; SI 10.1007/s11224-016-0766-1 FEB 2017
Abstract:
Alan L. Mackay, one of the rare generalists of our time, was a disciple and follower of J. Desmond Bernal. Mackay has contributed decisively to the development of the science of structures and taught generations to look at the broader picture when determining crystal and molecular structures. He was constantly seeking coherence and regularities in observations and in thought experiments and was aiming at creating concepts on the basis of those regularities. His inquiries prompted him to predict the existence of regular but not periodic crystal structures that are known today as quasicrystals.

Title:
The philosophical significance of Alan Mackay's theoretical discovery of quasicrystals
Authors:
Gilead, A Author Full Names: Gilead, Amihud
Source:
STRUCTURAL CHEMISTRY, 28 (1):249-256; SI 10.1007/s11224-016-0742-9 FEB 2017
Abstract:
Dan Shechtman was the first to discover an actual quasicrystal (on April 8, 1982). He was, however, not the first to discover the pure possibility of this novel structure (the theoretical discovery), which had been excluded from the range of the possibilities of crystals (as it had been fixed by both theoretical and empirical means in the beginning of the twentieth century). Penrose and Mackay, in particular, had contributed to the discovery of the pure possibilities of quasicrystals quite some time before their actual discovery. These pure possibilities are mathematical-structural, and like purely mathematical entities, they do not exist spatiotemporally and causally, whereas actual quasicrystals exist only spatiotemporally and causally. The pure possibilities of quasicrystals do not depend on their actualities, and without them, these actualities would have been theoretically groundless, meaningless, and could not be correctly identified if at all. Hence, Mackay's contribution to the meaning and theoretical basis of the discovery of actual quasicrystals is indispensable.

Title:
Microstructure and electrical resistivity in the GdNi5-xCux intermetallic series
Authors:
Bajorek, A; Chelkowska, G Author Full Names: Bajorek, Anna; Chelkowska, Grazyna
Source:
JOURNAL OF RARE EARTHS, 35 (1):71-78; 10.1016/S1002-0721(16)60176-X JAN 2017
Abstract:
The effect of the Ni/Cu substitution on the electrical resistivity and microstructure of the polycrystalline GdNi5-xCux series was studied. The value of temperature of phase transition (T-ph) estimated from temperature dependence of electrical resistance varied non-linearly across copper doping from 32.5 K (x=0.0) to 29.1 K (x=5.0). The value of residual resistivity (rho(o)) estimated at low temperature range decreased from 27.28 mu Omega cm (x=0.0) to 9.44 mu Omega cm (x=5.0), which was discussed as the influence of microstructure. In order to describe the temperature dependence of resistivity rho(T) a variety of approaches were applied due to different scattering mechanisms occurring at high and low temperature ranges. The change within rho(T) curvature was evidenced at low temperature range across copper doping. The temperature variation of the resistivity was quite peculiar for Cu-rich compounds (x=4.8, x=5.0), which might be correlated with the incommensurate magnetic structure derived from the weakly negative interaction between the nearest neighbours of Gd. The correlation between microstructure and resistivity was observed.

Update: 16-Mar-2017


Title:
Interfacial free energy and medium range order: Proof of an inverse of Frank's hypothesis
Authors:
Lee, GW; Cho, YC; Lee, B; Kelton, KF Author Full Names: Lee, Geun Woo; Cho, Yong Chan; Lee, Byeongchan; Kelton, Kenneth F.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054202 FEB 13 2017
Abstract:
We study the relation of crystal-liquid interfacial free energy and medium range order in the quasicrystal-forming Ti37Zr42Ni21 liquid from undercooling experiment and ab initio molecular dynamics (MD) simulation. Adding a small amount of Ag to the liquid significantly reduces the degree of undercooling, which is suggestive of small interfacial free energy, and thus very similar atomic configuration between the liquid and the icosahedral quasicrystal phases. Using ab initioMDstudy, we find that Ag atoms predominantly form a bond with Zr atoms in the short range and, further, Ag-Zr pairs are extended in the liquid, as amedium range orderwhich is identical to the global structural feature reported recently [Liu et al., Phys. Rev. Lett. 105, 155501 (2010)]. This result may expect extremely small undercooling if the icosahedral medium range order exists in a liquid forming an icosahedral quasicrystal, which implies the ambiguity of clear distinction of heterogeneous and homogeneous nucleation.

Title:
Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr(2)RuO4
Authors:
Zhu, M; Shanavas, KV; Wang, Y; Zou, T; Sun, WF; Tian, W; Garlea, VO; Podlesnyak, A; Matsuda, M; Stone, MB; Keavney, D; Mao, ZQ; Singh, DJ; Ke, X Author Full Names: Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (6):10.1103/PhysRevB.95.054413 FEB 10 2017
Abstract:
Sr2RuO4, an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector q(c) = ( 0.25 0.25 0) in Fe-doped Sr2RuO4, despite the magnetic fluctuations persisting at the incommensurate wave vectors q(ic) = ( 0.30.3L) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which showthat Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.

Title:
Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr2RuO4
Authors:
Zhu, M; Shanavas, KV; Wang, Y; Zou, T; Sun, WF; Tian, W; Garlea, VO; Podlesnyak, A; Matsuda, M; Stone, MB; Keavney, D; Mao, ZQ; Singh, DJ; Ke, X Author Full Names: Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.
Source:
PHYSICAL REVIEW B, 95 (5):10.1103/PhysRevB.95.054413 FEB 10 2017
Abstract:
Sr2RuO4, an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector q(c) = (0.25 0.25 0) in Fe-doped Sr2RuO4, despite the magnetic fluctuations persisting at the incommensurate wave vectors q(ic) = (0.30.3L) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which show that Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, Sr2RuO4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.

Title:
Incommensurate charge ordered states in the t-t '-J model
Authors:
Choubey, P; Tu, WL; Lee, TK; Hirschfeld, PJ Author Full Names: Choubey, Peayush; Tu, Wei-Lin; Lee, Ting-Kuo; Hirschfeld, P. J.
Source:
NEW JOURNAL OF PHYSICS, 19 10.1088/1367-2630/19/1/013028 JAN 20 2017
Abstract:
We study the incommensurate charge ordered states in the t-t'-J model using the Gutzwiller mean field theory on large systems. In particular, we explore the properties of incommensurate charge modulated states referred to as nodal pair density waves (nPDW) in the literature. nPDW states intertwine site and bond charge order with modulated d-wave pair order, and are characterized by a nonzero amplitude of uniform pairing; they also manifest a dominant intra-unit cell d-density wave form factor. To compare with a recent scanning tunneling microscopy (STM) study (Hamidian et al 2015 Nat. Phys. 12 150) of the cuprate superconductor BSCCO-2212, we compute the continuum local density of states (LDOS) at a typicalSTM tip height using the Wannier function based approach. By Fourier transforming Cu and O sub-lattice LDOS we also obtain bias-dependent intra-unit cell form factors and spatial phase difference. We find that in then PDW state the behavior of form factors and spatial phase difference as a function of energy agrees remarkably well with the experiment. This is in contrast to commensurate charge modulated states, which we show do not agree with experiment. We propose that then PDW states are good candidates for the charge density wave phase observed in the superconducting state of underdoped cuprates.

Update: 9-Mar-2017


Title:
Tuning Crystal Structures and Thermoelectric Properties through Al Doping in ReSi1.75
Authors:
Wang, F; Veremchuk, I; Lidin, S Author Full Names: Wang, Fei; Veremchuk, Igor; Lidin, Sven
Source:
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2017 (1):47-55; 10.1002/ejic.201600792 JAN 2017
Abstract:
Binary rhenium silicide, ReSi1.75, and its aluminium-doped variants have been synthesized. Their crystal structures were characterized by X-ray diffraction, solved and refined through the use of superspace group models. The binary un-doped ReSi1.75 is a commensurate (supercell) structure of the previously well-known MoSi2-type structure. Al doping renders an incommensurate structure that was solved and refined, and reported for the first time. The thermoelectric properties of these compounds were also measured, including their electrical resistivities, thermal conductivities, and Seebeck coefficients. Compared with the commensurate structure of binary ReSi1.75, the Al-doped incommensurate phase exhibits lower lattice thermal conductivity, lower electrical resistivity, a higher Seebeck coefficient, and ultimately a much higher figure of merit (ZT). The cause of the structural incommensuration by Al doping was studied through the use of first-principle calculations. The relationship between the incommensurability and the improved thermoelectric properties is also discussed.

Title:
The true structural periodicities and superspace group descriptions of the prototypical incommensurate composite materials: Alkane/urea inclusion compounds
Authors:
Couzi, M; Guillaume, F; Harris, KDM; Palmer, BA; Christensen, K; Collins, SP Author Full Names: Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.; Palmer, Benjamin A.; Christensen, Kirsten; Collins, Stephen P.
Source:
EPL, 116 (5):10.1209/0295-5075/116/56001 DEC 2016
Abstract:
The prototypical family of incommensurate composite materials are the n-alkane/urea inclusion compounds, in which n-alkane guest molecules are arranged in a periodic manner along one-dimensional tunnels in a urea host structure, with an incommensurate relationship between the periodicities of the host and guest substructures along the tunnel. We develop interpretations of the structural periodicities, superspace group descriptions and symmetry properties of the low-temperature phases of n-alkane/urea inclusion compounds, based in part on a high-resolution synchrotron single-crystal X-ray diffraction study of n-nonadecane/urea. Specifically, we prove that, on passing from phase I to phase II, the C-centering of the orthohexagonal unit cell is lost for both the host and guest substructures, and that the symmetries of all phases I, II and III are described completely by (3+1)-dimensional superspace groups. Copyright (C) EPLA, 2016

Title:
Commensurate-incommensurate transition and domain wall dynamics of adsorbed overlayers on a honeycomb substrate
Authors:
Elder, KR; Achim, CV; Granato, E; Ying, SC; Ala-Nissila, T Author Full Names: Elder, K. R.; Achim, C. V.; Granato, E.; Ying, S. C.; Ala-Nissila, T.
Source:
EPL, 116 (5):10.1209/0295-5075/116/56002 DEC 2016
Abstract:
We introduce an effective one-mode phase-field crystal model for studying the commensurate-incommensurate transition and domain wall dynamics of the (root 3 x root 3) R30 degrees. phase found in systems such as Xe/Pt(111), or Xe and Kr on graphite. The model allows us to study large systems where the domain walls can be separated over large macroscopic distances and at the same time incorporate the microscopic details of the domain wall structures. The resulting phase diagram shows that an intermediate stripe incommensurate phase always separates the commensurate phase from the honeycomb incommensurate phases. The energy of the domain wall crossing is investigated. We also find that near a step edge, the domain walls tend to align perpendicularly to the step edge, in agreement with recent experimental observations. Copyright (C) EPLA, 2016

Title:
Thermoelectric properties of layered calcium cobaltite Ca3Co4O9 from hybrid functional first-principles calculations
Authors:
Lemal, S; Varignon, J; Bilc, DI; Ghosez, P Author Full Names: Lemal, Sebastien; Varignon, Julien; Bilc, Daniel I.; Ghosez, Philippe
Source:
PHYSICAL REVIEW B, 95 (7):10.1103/PhysRevB.95.075205 FEB 9 2017
Abstract:
Using a combination of first-principles calculations based on density functional theory and Boltzmann semiclassical transport theory, we compute and study the properties of pristine layered calcium cobaltite Ca3Co4O9. We model the system with the B1WC hybrid functional. Two supercells of increasing size which approximate the incommensurate crystallographic structure of the compound are studied and we determine their structural, magnetic, and electronic properties. It is found that the B1WC hybrid functional is appropriate to reproduce the structural, electronic, and magnetic properties, which are then extensively discussed. From the electronic band structure, the Seebeck (S) and electrical resistivity (rho) tensors are computed using Boltzmann transport theory within the constant relaxation-time approximation. The differences between the diagonal components are detailed and reveal a strong in-plane anisotropy of the properties. The qualitative behavior of the averaged in-plane properties, S-// and rho(//), is consistent with the measurements reported in the literature. Our calculation clarifies and provides a broad picture of the evolution of the thermoelectric properties with both carrier density and temperature, and suggests that the change in S-// and rho(//) around 100 K is not necessarily related to the magnetic transitions occurring around 100 K.

Title:
Quasicrystalline nanocrystal superlattice with partial matching rules
Authors:
Ye, XC; Chen, J; Irrgang, ME; Engel, M; Dong, AG; Glotzer, SC; Murray, CB Author Full Names: Ye, Xingchen; Chen, Jun; Irrgang, M. Eric; Engel, Michael; Dong, Angang; Glotzer, Sharon C.; Murray, Christopher B.
Source:
NATURE MATERIALS, 16 (2):214-219; 10.1038/NMAT4759 FEB 2017
Abstract:
Expanding the library of self-assembled superstructures provides insight into the behaviour of atomic crystals and supports the development of materials with mesoscale order(1,2). Here we build on recent findings of soft matter quasicrystals (3-6) and report a quasicrystalline binary nanocrystal superlattice that exhibits correlations in the form of partial matching rules reducing tiling disorder. We determine a three-dimensional structure model through electron tomography(7,8) and direct imaging of surface topography. The 12-fold rotational symmetry of the quasicrystal is broken in sublayers, forming a random tiling of rectangles, large triangles and small triangles with 6-fold symmetry. We analyse the geometry of the experimental tiling and discuss factors relevant for the stabilization of the quasicrystal. Our joint experimental-computational study demonstrates the power of nanocrystal superlattice engineering and further narrows the gap between the richness of crystal structures found with atoms and in soft matter assemblies.

Update: 22-Feb-2017


Title:
Critical scattering and incommensurate phase transition in antiferroelectric PbZrO3 under pressure
Authors:
Burkovsky, RG; Bronwald, I; Andronikova, D; Wehinger, B; Krisch, M; Jacobs, J; Gambetti, D; Roleder, K; Majchrowski, A; Filimonov, AV; Rudskoy, AI; Vakhrushev, SB; Tagantsev, AK Author Full Names: Burkovsky, R. G.; Bronwald, I.; Andronikova, D.; Wehinger, B.; Krisch, M.; Jacobs, J.; Gambetti, D.; Roleder, K.; Majchrowski, A.; Filimonov, A. V.; Rudskoy, A. I.; Vakhrushev, S. B.; Tagantsev, A. K.
Source:
Scientific Reports, 7 10.1038/srep41512 JAN 30 2017
Abstract:
Antiferroelectric lead zirconate is the key ingredient in modern ferroelectric and piezoelectric functional solid solutions. By itself it offers opportunities in new-type non-volatile memory and energy storage applications. A highly useful and scientifically puzzling feature of this material is the competition between the ferro- and antiferroelectric phases due to their energetic proximity, which leads to a challenge in understanding of the critical phenomena driving the formation of the antiferroelectric structure. We show that application of hydrostatic pressure drastically changes the character of critical lattice dynamics and enables the soft-mode-driven incommensurate phase transition sequence in lead zirconate. In addition to the long known cubic and antiferroelectric phases we identify the new non-modulated phase serving as a bridge between the cubic and the incommensurate phases. The pressure effect on ferroelectric and incommensurate critical dynamics shows that lead zirconate is not a single-instability-driven system.

Title:
Observation of a Charge Density Wave Incommensuration Near the Superconducting Dome in CuxTiSe2
Authors:
Kogar, A; de la Pena, GA; Lee, S; Fang, Y; Sun, SXL; Lioi, DB; Karapetrov, G; Finkelstein, KD; Ruff, JPC; Abbamonte, P; Rosenkranz, S Author Full Names: Kogar, A.; de la Pena, G. A.; Lee, Sangjun; Fang, Y.; Sun, S. X. -L.; Lioi, D. B.; Karapetrov, G.; Finkelstein, K. D.; Ruff, J. P. C.; Abbamonte, P.; Rosenkranz, S.
Source:
PHYSICAL REVIEW LETTERS, 118 (2):10.1103/PhysRevLett.118.027002 JAN 11 2017
Abstract:
X-ray diffraction was employed to study the evolution of the charge density wave (CDW) in CuxTiSe2 as a function of copper intercalation in order to clarify the relationship between the CDW and superconductivity. The results show a CDWincommensuration arising at an intercalation value coincident with the onset of superconductivity at around x = 0.055(5). Additionally, it was found that the charge density wave persists to higher intercalant concentrations than previously assumed, demonstrating that the CDW does not terminate inside the superconducting dome. A charge density wave peak was observed in samples up to x = 0.091(6), the highest copper concentration examined in this study. The phase diagram established in this work suggests that charge density wave incommensuration may play a role in the formation of the superconducting state.

Update: 16-Feb-2017


Title:
Multiple quasicrystal approximants with the same lattice parameters in Al-Cr-Fe-Si alloys
Authors:
He, ZB; Li, H; Ma, HK; Li, GW Author Full Names: He, Zhanbing; Li, Hua; Ma, Haikun; Li, Guowu
Source:
SCIENTIFIC REPORTS, 7 10.1038/srep40510 JAN 13 2017
Abstract:
By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns.

Title:
A general algorithm for generating isotropy subgroups in superspace
Authors:
Stokes, HT; Campbell, BJ Author Full Names: Stokes, Harold T.; Campbell, Branton J.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 4-13; 10.1107/S2053273316017629 1 JAN 2017
Abstract:
This paper presents a general algorithm for generating the isotropy subgroups of superspace extensions of crystallographic space groups involving arbitrary superpositions of multi-k order parameters from incommensurate and commensurate k vectors. Several examples are presented in detail in order to illuminate each step of the algorithm. The practical outcome is that one can now start with any commensurate parent crystal structure and generate a structure model for any conceivable incommensurate modulation of that parent, fully parameterized in terms of order parameters of irreducible representations at the relevant wavevectors. The resulting modulated structures have (3 + d)-dimensional superspace-group symmetry. Because incommensurate structures are now commonly encountered in the context of many scientifically and technologically important functional materials, the opportunity to apply the powerful methods of group representation theory to this broader class of structural distortions is very timely.

Title:
To superspace and beyond
Authors:
Senn, MS Author Full Names: Senn, Mark S.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 73 1-3; 10.1107/S2053273316019902 1 JAN 2017

Update: 8-Feb-2017


Title:
Field-induced magnetic states in holmium tetraboride
Authors:
Brunt, D; Balakrishnan, G; Wildes, AR; Ouladdiaf, B; Qureshi, N; Petrenko, OA Author Full Names: Brunt, D.; Balakrishnan, G.; Wildes, A. R.; Ouladdiaf, B.; Qureshi, N.; Petrenko, O. A.
Source:
PHYSICAL REVIEW B, 95 (2):10.1103/PhysRevB.95.024410 JAN 11 2017
Abstract:
A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at T-N1 = 7.1 K to an incommensurate state with a propagation vector (delta, delta, delta'), where delta = 0.02 and delta' = 0.43 and at T-N2 = 5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3)-type reflections between 18 and 24 kOe. This field range is marked by the previously reported M/M-sat = 1 3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M/M-sat approximate to 3/5. Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H-T phase diagram of HoB4 for the H parallel to c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.

Title:
Gapped excitation in dense Kondo lattice CePtZn
Authors:
Harriger, L; Disseler, SM; Gunasekera, J; Rodriguez-Rivera, J; Pixley, J; Manfrinetti, P; Dhar, SK; Singh, DK Author Full Names: Harriger, L.; Disseler, S. M.; Gunasekera, J.; Rodriguez-Rivera, J.; Pixley, J.; Manfrinetti, P.; Dhar, S. K.; Singh, D. K.
Source:
PHYSICAL REVIEW B, 95 (4):10.1103/PhysRevB.95.041102 JAN 10 2017
Abstract:
We report on neutron scattering and muon spin relaxation measurements of dense Kondo lattice CePtZn. The system develops long-range incommensurate magnetic order as the temperature is reduced below T-N = 1.75 K. Interestingly, a Q-independent gap at E = 0.65 meV in the energy spectrum is found to co-exist with the long-range magnetic order. The gap persists to a very high temperature of T similar or equal to 100 K. The Q-independent characteristic and its persistence to high temperature hint that the gapped excitation may be manifesting the excited state of the ground-state doublet of the crystal-field energy levels. However, the observed broadness in the linewidth with distinct temperature and field dependencies makes it a nontrivial phenomenon. Qualitative analysis of the experimental data suggests the possible co-existence of a local critical behavior, which is onset near the critical field of H similar or equal to 3 T, with the crystal-field excitation in the dynamic properties.

Title:
Mixed-mode crack tip loading and crack deflection in 1D quasicrystals
Authors:
Wang, Z; Scheel, J; Ricoeur, A Author Full Names: Wang, Zhibin; Scheel, Johannes; Ricoeur, Andreas
Source:
APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 122 (12):10.1007/s00339-016-0570-1 DEC 2016
Abstract:
Quasicrystals (QC) are a new class of materials besides crystals and amorphous solids and have aroused much attention of researchers since they were discovered. This paper presents a generalized fracture theory including the J-integral and crack closure integrals, relations between J(1), J(2) and the stress intensity factors as well as the implementation of the near-tip stress and displacement solutions of 1D QC. Different crack deflection criteria, i.e. the J-integral and maximum circumferential stress criteria, are investigated for mixed-mode loading conditions accounting for phonon-phason coupling. One focus is on the influence of phason stress intensity factors on crack deflection angles.

Update: 1-Feb-2017


Title:
Electronic structure and X-ray magnetic circular dichroism in the Ni-Mn-Ga Heusler alloys
Authors:
Antonov, VN; Bekenov, LV; Uba, S; Bonda, A; Uba, L Author Full Names: Antonov, V. N.; Bekenov, L. V.; Uba, S.; Bonda, A.; Uba, L.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 1826-1837; 10.1016/j.jallcom.2016.11.016 FEB 25 2017
Abstract:
The electronic structure and X-ray magnetic circular dichroism (XMCD) spectra of the Ni2MnGa and Cu doped Ni2MnGa Heusler alloys were investigated theoretically from first principles, using the fully relativistic Dirac linear MT-orbital (LMTO) band structure method. Densities of valence states, orbital and spin magnetic moments are analyzed and discussed. The electronic and magnetic structure of Ni-Mn-Ga Heusler alloys were investigated for the cubic austenitic and modulated 7M-like incommensurate martensitic phases. The X-ray absorption spectra ( XAS) and XMCD at the Mn, Ni, Ga, and Cu L-2,L-3,L- and Mn, Ni, and Ga K edges were investigated theoretically from first principles. The origin of the XMCD spectra in the Ni2MnGa compound is examined. The ab initio calculations reproduce well experimental XAS and XMCD spectra. The XAS at the Mn L-2,L-3 edges remains mostly unchanged through martensitic phase transition. A fingerprint of the martensitic phase transition has been found in the Ni L-2,L-3 XAS spectra. The experimental Ni L-3 XAS has a pronounced shoulder at the L-3 peak at around 853 eV. This peak is nearly suppressed in the martensitic state in comparison with the austenitic phase due to the lifting of the degeneracy in the Ni 3d related unoccupied electronic states. The XMCD of the martensitic phase is increased compared to the XMCD of the austenite phase at the Ni and Mn L-2,L-3 edges. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Incommensurately modulated structure and spectroscopic properties of CaGd2(MoO4)(4):Ho3+/Yb3+ phosphors for up-conversion applications
Authors:
Lim, CS; Atuchin, VV; Aleksandrovsky, AS; Molokeev, MS; Oreshonkov, AS Author Full Names: Lim, Chang Sung; Atuchin, Victor V.; Aleksandrovsky, Aleksandr S.; Molokeev, Maxim S.; Oreshonkov, Aleksandr S.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 737-746; 10.1016/j.jallcom.2016.06.134 FEB 25 2017
Abstract:
CaGd2(MoO4)(4):Ho3+/Yb3+ phosphors doped by Ho3+ and Yb3+ (Ho3+ = 0 and 0.05, and Yb3+ = 0, 0.35, 0.40, 0.45 and 0.50) were successfully synthesized by the microwave sol-gel method. The synthesized particles, being formed after heat-treatment at 900 degrees C for 16 h, showed a well crystallized morphology. All compounds are (3 + 2)D incommensurately modulated with superspace group I4(1)/alpha(alpha,beta,0)00(-beta,alpha,0)00. It was found that parameter (alpha(2) + beta(2))(1)/(2) is proportional to cell parameter a for all studied compositions and, therefore, modulation vector k is the same for all known CaRE2(MoO4)(4) compounds. The modulation vector invariance is a specific and valuable feature of this type of the structure. Under the excitation at 980 nm, the doped particles exhibited the yellow emission composed of green (545-nm) and red (655-nm) emission bands due to frequency upconversion (UC). The pump power dependence and CIE chromaticity of the UC emission were evaluated. The shape of UC bands in CaGd2(MoO4)(4):Ho3+/Yb3+ is dependent on the Yb content due to the influence of the crystal field affecting a holmium ion. 13 Raman-active modes of the CaGd2(MoO4)(4) lattice were identified via a comparison of experimental Raman spectra and the lattice dynamics simulation results. Four additional Raman lines were found in the region of stretching vibrations and, at least, two additional modes are present in the bending mode region. These additional modes are ascribed to incommensurate crystal lattice modulation. Luminescence bands of Ho ions are severely broadened due to a statistical disorder in the CaGd2-xYby (MoO4)(4) lattice. (C) 2016 Published by Elsevier B.V.

Title:
Commensurate-incommensurate magnetic phase transition in the new Yb1-xLuxMn6Sn6 compounds
Authors:
Eichenberger, L; Venturini, G; Malaman, B; Nataf, L; Baudelet, F; Mazet, T Author Full Names: Eichenberger, L.; Venturini, G.; Malaman, B.; Nataf, L.; Baudelet, F.; Mazet, T.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 695 286-293; 10.1016/j.jallcom.2016.10.191 FEB 25 2017
Abstract:
We investigate the magnetic properties of the new Yb1-xLuxMn6Sn6 (0.00 <= x <= 1.00) alloys from AC/DC magnetization and powder neutron diffraction experiments. Room-temperature XANES measurements at Yb L-3 edge indicate that Yb is in an intermediate valent state (upsilon(Yb) similar to 2.6) in the whole Yb1-xLuxMn6Sn6 series. In these compounds only the Mn sublattice magnetically orders with an atomic Mn moment close to m(Mn) similar to 2.2 mu(B) at 2 K throughout the series. Lu substitution yields a crossover from ferromagnetism to antiferromagnetism of the Mn sublattice. In RMn6Sn6 compounds, this is the first time that such transition of the Mn sublattice is induced by substitution on the R site. The enhancement of the antiferromagnetic interactions likely results from modification in valence electron concentration since intermediate valent Yb is replaced by trivalent Lu. (C) 2016 Elsevier B.V. All rights reserved.

Title:
Pushing the limits of crystallography
Authors:
Wolny, J; Buganski, I; Kuczera, P; Strzalka, R Author Full Names: Wolny, Janusz; Buganski, Ireneusz; Kuczera, Pawel; Strzalka, Radoslaw
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 49 2106-2115; 10.1107/S160057671601637X 6 DEC 2016
Abstract:
A very serious concern of scientists dealing with crystal structure refinement, including theoretical research, pertains to the characteristic bias in calculated versus measured diffraction intensities, observed particularly in the weak reflection regime. This bias is here attributed to corrective factors for phonons and, even more distinctly, phasons, and credible proof supporting this assumption is given. The lack of a consistent theory of phasons in quasicrystals significantly contributes to this characteristic bias. It is shown that the most commonly used exponential Debye-Waller factor for phasons fails in the case of quasicrystals, and a novel method of calculating the correction factor within a statistical approach is proposed. The results obtained for model quasiperiodic systems show that phasonic perturbations can be successfully described and refinement fits of high quality are achievable. The standard Debye-Waller factor for phonons works equally well for periodic and quasiperiodic crystals, and it is only in the last steps of a refinement that different correction functions need to be applied to improve the fit quality.

Title:

Update: 19-Jan-2017


Title:
K8Nb7P7O39: a new type of complicated incommensurately modulated structure and photoluminescence properties of Eu3+-doped solid solutions
Authors:
Zhao, D; Cui, JY; Han, HX; Li, C Author Full Names: Zhao, Dan; Cui, Jun-Yan; Han, Hong-Xian; Li, Can
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 4 (48):11436-11448; 10.1039/c6tc03022j 2016
Abstract:
A new type of potassium niobium phosphate, K8Nb7P7O39, has been prepared and its structure has been determined by single crystal X-ray diffraction analysis. The results show that it crystallizes in a novel (3 + 1)-dimensional incommensurately modulated structure with a triclinic superspace group P (1) over bar(alpha beta gamma)O and modulation vector q = -0.35281a* + 0.17630b* + 0.25807c*. The structure of K8Nb7P7O39 contains [K-3.66](infinity) N, [K-4.34](infinity) N and [Nb7P7O39](infinity) N layers alternately stacked along the c-axis. In this structure, seven not fully occupied K atoms (six of them come from the [K-3.66](infinity) N layer and the remaining one comes from the [K-4.34]infinity N layer) are thought to be the dominant factors in driving the structural modulation. The strong occupational modulation in combination with positional modulation of these seven K atoms can be described by crenel-type modulation functions. Furthermore, elemental composition, UV-Vis absorption spectrum, SEM morphology and photoluminescence properties induced by Eu3+-doping have been studied for K8Nb7P7O39. The excitation spectrum covers a wide range from 362 to 465 nm and it matches well with the emission of near-UV InGaN-based LED chips and bluish-green LED chips, indicating that K8Nb7P7O39: Eu3+ has potential as a red-emitting phosphor for LED applications.

Title:
Generation of Basis Vectors for Magnetic Structures and Displacement Modes
Authors:
Davies, ZL; Wills, AS Author Full Names: Davies, Z. L.; Wills, A. S.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2016/3960145 2016
Abstract:
Increasing attention is being focused on the use of symmetry-adapted functions to describe magnetic structures, structural distortions, and incommensurate crystallography. Though the calculation of such functions iswell developed, significant difficulties can arise such as the generation of too many or too few basis functions to minimally span the linear vector space. We present an elegant solution to these difficulties using the concept of basis sets and discuss previous work in this area using this concept. Further, we highlight the significance of unitary irreducible representations in this method and provide the first validation that the irreducible representations of the crystallographic space groups tabulated by Kovalev are unitary.

Title:
K8Nb7P7O39: a new type of complicated incommensurately modulated structure and photoluminescence properties of Eu3+-doped solid solutions
Authors:
Zhao, D; Cui, JY; Han, HX; Li, C Author Full Names: Zhao, Dan; Cui, Jun-Yan; Han, Hong-Xian; Li, Can
Source:
JOURNAL OF MATERIALS CHEMISTRY C, 4 (48):11436-11448; 10.1039/c6tc03022j 2016
Abstract:
A new type of potassium niobium phosphate, K8Nb7P7O39, has been prepared and its structure has been determined by single crystal X-ray diffraction analysis. The results show that it crystallizes in a novel (3 + 1)-dimensional incommensurately modulated structure with a triclinic superspace group P (1) over bar(alpha beta gamma)O and modulation vector q = -0.35281a* + 0.17630b* + 0.25807c*. The structure of K8Nb7P7O39 contains [K-3.66](infinity) N, [K-4.34](infinity) N and [Nb7P7O39](infinity) N layers alternately stacked along the c-axis. In this structure, seven not fully occupied K atoms (six of them come from the [K-3.66](infinity) N layer and the remaining one comes from the [K-4.34]infinity N layer) are thought to be the dominant factors in driving the structural modulation. The strong occupational modulation in combination with positional modulation of these seven K atoms can be described by crenel-type modulation functions. Furthermore, elemental composition, UV-Vis absorption spectrum, SEM morphology and photoluminescence properties induced by Eu3+-doping have been studied for K8Nb7P7O39. The excitation spectrum covers a wide range from 362 to 465 nm and it matches well with the emission of near-UV InGaN-based LED chips and bluish-green LED chips, indicating that K8Nb7P7O39: Eu3+ has potential as a red-emitting phosphor for LED applications.

Title:
Generation of Basis Vectors for Magnetic Structures and Displacement Modes
Authors:
Davies, ZL; Wills, AS Author Full Names: Davies, Z. L.; Wills, A. S.
Source:
ADVANCES IN CONDENSED MATTER PHYSICS, 10.1155/2016/3960145 2016
Abstract:
Increasing attention is being focused on the use of symmetry-adapted functions to describe magnetic structures, structural distortions, and incommensurate crystallography. Though the calculation of such functions iswell developed, significant difficulties can arise such as the generation of too many or too few basis functions to minimally span the linear vector space. We present an elegant solution to these difficulties using the concept of basis sets and discuss previous work in this area using this concept. Further, we highlight the significance of unitary irreducible representations in this method and provide the first validation that the irreducible representations of the crystallographic space groups tabulated by Kovalev are unitary.

Update: 12-Jan-2017


Title:
Incommensurate spin density wave as a signature of spin-orbit coupling and precursor of topological superconductivity
Authors:
Farrell, A; Wu, PK; Kao, YJ; Pereg-Barnea, T Author Full Names: Farrell, Aaron; Wu, P. -K.; Kao, Y. -J.; Pereg-Barnea, T.
Source:
PHYSICAL REVIEW B, 94 (21):10.1103/PhysRevB.94.214424 DEC 22 2016
Abstract:
On a square lattice, the Hubbard model at half filling reduces to the Heisenberg model and exhibits antiferromagnetism. When doped away from half filling this model gives rise to d-wave superconductivity. This behavior is reminiscent of the phenomenology of the cuprate family with their high T(c)d-wave superconductivity and their antiferromagnetic parent compound. It is therefore interesting to study an extension of the Hubbard model which includes spin orbit coupling. We have previously studied this model away from half filling [see, for example, Farrell and Pereg-Barnea, Phys. Rev. B 89, 035112 (2014)] and found that the addition of spin-orbit coupling and Zeeman field leads to topological superconductivity with d + id pairing function. In this paper we are interested in the 'parent compound' of this state. Namely, we study the half filling, strong coupling limit of the square lattice Hubbard model with spin orbit coupling and Zeeman field. The strong coupling expansion of the model is a spin model which contains compass anisotropy and Dzyaloshinsky-Moriya interaction on top of the usual Heisenberg term. We analyze this spin model classically and find an incommensurate spin density wave (ISDW) for low Zeeman fields. This ISDWhas a wave vector (Q) over right arrow which deviates from (pi, pi) by an amount which is proportional to the spin-orbit coupling and can therefore serve as a signature. We study the stability of the ISDW phase using spin wave theory and find a stable and an unstable region. At higher but moderate Zeeman fields we find a tilted antiferromagnet and a ferromagnet at high Zeeman fields.

Title:
Anisotropic spin fluctuations in Sr2RuO4: Role of spin-orbit coupling and induced strain
Authors:
Cobo, S; Ahn, F; Eremin, I; Akbari, A Author Full Names: Cobo, Sergio; Ahn, Felix; Eremin, Ilya; Akbari, Alireza
Source:
PHYSICAL REVIEW B, 94 (22):10.1103/PhysRevB.94.224507 DEC 14 2016
Abstract:
We analyze the spin anisotropy of themagnetic susceptibility of Sr2RuO4 in the presence of spin-orbit coupling and anisotropic strain using quasi-two-dimensional tight-binding parametrization fitted to the angle-resolved photoemission spectroscopy results. Similar to the previous observations we find the in-plane polarization of the low-q magnetic fluctuations and the out-of-plane polarization of the incommensurate magnetic fluctuation at the nestingwave-vector Q(1) = (2/3 pi, 2/3 pi) but also nearly isotropic fluctuations nearQ(2) = (pi/6, pi/6). Furthermore, one finds that, apart from the high-symmetry direction of the tetragonal Brillouin zone, the magnetic anisotropy is maximal, i. e., chi(xx) not equal chi(yy) not equal chi(zz) reflected in the x polarization of the intraband nestingwave-vectorQ(3) = (pi/2, pi). This is a consequence of the orbital anisotropy of the t(2g) orbitals in momentum space. We also study how the magnetic anisotropy evolves in the presence of the strain and find strong Ising-like ferromagnetic fluctuations near the Lifshitz transition for the xy band.

Title:
Vacancy pairing and superstructure in the high-pressure silicate K1.5Mg2Si2O7H0.5: a new potential host for potassium in the deep Earth
Authors:
Welch, MD; Bindi, L; Petricek, V; Plasil, J Author Full Names: Welch, M. D.; Bindi, L.; Petricek, V.; Plasil, J.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 822-827; 10.1107/S2052520616014049 6 DEC 2016
Abstract:
The high-pressure silicate K1.5Mg2Si2O7H0.5, synthesized and characterized by Welch et al. [(2012), Am. Mineral. 97, 1849-1857], has been re-examined with the aim of determining the nature of the superstructure noted in their study. The composition corresponds to a 1:1 combination of KMg2Si2O7H and K2Mg2Si2O7 end-members, but it is not a solid solution. Single-crystal X-ray diffraction data for one of the original K1.5Mg2Si2O7H0.5 crystals synthesized at 16 GPa/1573 K, has been collected using a much longer exposure time in order to improve the intensity statistics of weak superlattice reflections identified by Welch et al. (2012). The superstructure has been determined using a superspace approach as having the superspace group Cmcm(0,beta,0)00s and t(0) = 1/16 with refined parameters a = 8.7623 (10), b = 5.0703 (7), c = 13.2505 (11) angstrom, V = 588.69 (12) angstrom(3). This structure corresponds to one with the conventional space group Pbnm and unit-cell parameters a = 8.7623 (10), b = 20.281 (3), c = 13.2505 (11) angstrom, V=2354.7 (5) angstrom(3) and is based upon a super-sheet motif in which ordering involves rows of pairs of vacant interlayer K sites. This is the third topologically distinct structure type for the KMg2Si2O7H-K2Mg2Si2O7 join and suggests that there is very limited solid solution, and so it can be expected that each of the three structures (P6(3)cm, P (3) over bar 1m and Pbnm) has its own stability field, rather than being part of a continuous compositional series based upon a single structure type. As such, K1.5Mg2Si2O7H0.5 should be considered as a potentially significant host of K in the Earth's mantle.

Title:
Incommensurate density modulation in a Na-rich plagioclase feldspar: Z-contrast imaging and single-crystal X-ray diffraction study
Authors:
Xu, HF; Jin, SY; Noll, BC Author Full Names: Xu, Huifang; Jin, Shiyun; Noll, Bruce C.
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 72 904-915; 10.1107/S205252061601578X 6 DEC 2016
Abstract:
Plagioclase feldspars are the most abundant mineral in the Earth's crust. Intermediate plagioclase feldspars commonly display incommensurately modulated or aperiodic structures. Z-contrast images show both Ca-Na ordering and density modulation. The local structure of lamellae domains has I1-like symmetry. The neighboring lamellae domains are in an inversion twinning relationship. With a state-of-the-art X-ray diffraction unit, second-order satellite reflections (f-reflections) are observed for the first time in andesine (An(45)), a Na-rich e-plagioclase. The f-reflections indicate a structure with a density modulation which is close to a Ca-rich e-plagioclase. The similarity between this e-andesine structure and previously solved e-labradorite structure is confirmed. Refinement of the structure shows density modulation of similar to 7 mol% in compositional variation of the anorthite (An) component. The results from Z-contrast imaging and low-temperature single X-ray diffraction (XRD) provide a structure consistent with density modulation. The discovery of f-reflections in Na-rich e-plagioclase extends the composition range of e1 structure with density modulation to as low as at least An45, which is the lower end of the composition range of Boggild intergrowth. The new result supports the loop-shaped solvus for Boggild intergrowth, below which is a homogenous stable area for e1 structure in the phase diagram. The phase transition between e2 structure without density modulation and e1 structure with density modulation should happen at low temperature. There is a change in modulation period accompanying the phase transition, as well as higher occupancy of AL in the T(1)o site. The andesine with density modulation also indicates extremely slow cooling of its host rock.

Title:
Elasto-Dynamics of Quasicrystals
Authors:
Li, W; Fan, TY Author Full Names: Li, Wu; Fan, Tianyou
Source:
CRYSTALS, 6 (11):10.3390/cryst6110152 NOV 2016
Abstract:
A review on elasto-dynamics of quasicrystals (QCs) and their applications based on mathematical elasticity is given. In this study, recent studies on elasto-dynamics of QCs are reviewed, in which the focus of the problem lies in the role of phason variables and the coupling effect between phonons and phasons in the dynamic deformation process. On summarizing and describing the development of the elastic dynamics of QCs, this review mainly presents theelasto-dynamics of QCs and their application in a variety of research areas, ranging from problems with different QCs, including one-, two-, and three-dimensional QCs to various coupling problems. The plane elasticity and anti-plane elasticity of quasicrystals are included in this review.

Title:
Quasicrystals and Other Aperiodic Structures in Mineralogy
Authors:
Pina, CM; Lopez-Acevedo, V Author Full Names: Pina, Carlos M.; Lopez-Acevedo, Victoria
Source:
CRYSTALS, 6 (11):10.3390/cryst6110137 NOV 2016
Abstract:
In this article, we first present and discuss eighteenth-century descriptions of minerals that contributed decisively to the development of crystallography. Remarkably, these old crystallographic descriptions included morphologies with symmetries incompatible with an internal periodic order of atoms, which, however, have been recognised to be characteristics of quasicrystals. Moreover, we also review a number of studies of minerals with aperiodic crystal structures, including recently reported natural quasicrystals of extra-terrestrial origin. Finally, we discuss the current investigations addressing the search for new quasicrystalline minerals in nature.

Title:
Neutron diffraction study of low-temperature magnetic phase diagram of an isosceles-triangular-lattice Ising antiferromagnet CoNb2O6
Authors:
Kobayashi, S; Mitsuda, S; Hosaka, S; Tamatsukuri, H; Nakajima, T; Koorikawa, H; Prokes, K; Kiefer, K Author Full Names: Kobayashi, S.; Mitsuda, S.; Hosaka, S.; Tamatsukuri, H.; Nakajima, T.; Koorikawa, H.; Prokes, K.; Kiefer, K.
Source:
PHYSICAL REVIEW B, 94 (13):10.1103/PhysRevB.94.134427 OCT 27 2016
Abstract:
A low-temperature magnetic phase diagram under magnetic fields along the orthorhombic a axis of an isosceles-triangular-lattice antiferromagnet CoNb2O6 was investigated through single-crystal neutron diffraction measurements made at temperatures down to T = 0.5K. We produced a phase diagram that consists of three magnetically ordered phases, i.e., the antiferromagnetic (AF), the incommensurate sinusoidal magnetic (IC), and the induced ferromagnetic (IFM) phases, which were characterized by the propagation wave vectors Q = (01/20), (0 q 0), and (0 0 0), respectively. We found that a field-induced ferrimagnetic phase with Q = (01/40) that had been observed by previous neutron diffraction studies down to T = 1.8K [H. Weitzel et al., Phys. Rev. B 62, 12146 (2000)] does not exist as a single equilibrium phase, but rather it always coexists with the other ordered phases near the triple point where the AF, IC, and IFM phases meet. We also found that the relaxation time of the system becomes extremely long below T = 0.6 K in comparison with our observation time; this was considered to possibly be the reason for magnetization plateaus appearing at T = 0.5K. These plateaus have a half-saturation magnetization, from which another field-induced state was inferred in previous magnetization measurements [J. Phys. Soc. Jpn. 63, 2706 (1994)].

Title:
An Icosahedral Quasicrystal and Its 1/0 Crystalline Approximant in the Ca-Au-Al System
Authors:
Pham, J; Kreyssig, A; Goldman, AI; Miller, GJ Author Full Names: Pham, Joyce; Kreyssig, Andreas; Goldman, Alan I.; Miller, Gordon J.
Source:
INORGANIC CHEMISTRY, 55 (20):10425-10437; 10.1021/acs.inorgchem.6b01636 OCT 17 2016
Abstract:
A new icosahedral quasicrystalline phase, CaAu4.5-xAl1.5+x [0.11 <= x <= 0.40(6); CaAu4.4Al1.6, a(QC) = 5.383(4) angstrom, and Pm (3) over bar(5) over bar], and its lowest-order 1/0 cubic crystalline approximant phase, CaAu3+xAl1-x [0 <= x <= 0.31(1); a = 9.0766(5)-9.1261(8) angstrom, Pa (3) over bar (No. 205), and Pearson symbol cP40], have been discovered in the Ca-poor region of the Ca-Au-Al system. In the crystalline approximant, eight [Au3-xAl1+x] tetrahedra fill the unit cell, and each tetrahedron is surrounded by four Ca atoms, thus forming a three-dimensional network of {Ca-4/4[Au3-xAl1+x]} tetrahedral stars. A computational study of Au and Al site preferences concurs with the experimental results, which indicate a preference for near-neighbor Au-Al interactions over Au-Au and Al-Al interactions. Analysis of the electronic density of states and the associated crystal orbital Hamilton population curves was used to rationalize the descriptions of CaAu4.5-xAl1.5+x [0.11 <= x <= 0.46(6)] and CaAu3+xAl1-x [0 <= x <= 0.31(1)] as polar intermetallic species, whereby Ca atoms engage in polar covalent bonding with the electronegative, electron-deficient [Au3-xAl1+x] tetrahedral clusters and the observed phase width of the crystalline approximant.

Title:
Quantum Simulation of a 2D Quasicrystal with Cold Atoms
Authors:
Mace, N; Jagannathan, A; Duneau, M Author Full Names: Mace, Nicolas; Jagannathan, Anuradha; Duneau, Michel
Source:
CRYSTALS, 6 (10):10.3390/cryst6100124 OCT 2016
Abstract:
We describe a way to obtain a two-dimensional quasiperiodic tiling with eight-fold symmetry using cold atoms. One can obtain a series of such optical tilings, related by scale transformations, for a series of specific values of the chemical potential of the atoms. A theoretical model for the optical system is described and compared with that of the well-known cut-and-project method for the Ammann-Beenker tiling. The relation between the two tilings is discussed. This type of cold atom structure should allow the simulation of several important lattice models for interacting quantum particles and spins in quasicrystals.

Title:
Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x
Authors:
Hamidian, MH; Edkins, SD; Joo, SH; Kostin, A; Eisaki, H; Uchida, S; Lawler, MJ; Kim, EA; Mackenzie, AP; Fujita, K; Lee, J; Davis, JCS Author Full Names: Hamidian, M. H.; Edkins, S. D.; Joo, Sang Hyun; Kostin, A.; Eisaki, H.; Uchida, S.; Lawler, M. J.; Kim, E. -A.; Mackenzie, A. P. .; Fujita, K.; Lee, Jinho; Davis, J. C. Seamus
Source:
NATURE, 532 (7599):343-+; 10.1038/nature17411 APR 21 2016
Abstract:
The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density(1,2). Such a state has been created in ultracold Li-6 gas(3) but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase (4) of the copper oxide superconductors contains such a 'pair density wave' state(5-21). Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy (22-24) to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms(25) and at the Bi2Sr2CaCu2O8+x crystal supermodulation(26). Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors Q(P) approximate to (0.25, 0)2 pi/a(0) and (0, 0.25)2 pi/a(0) in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s' symmetry. This phenomenology is consistent with Ginzburg-Landau theory(5,13,14) when a charge density wave(5,27) with d-symmetry form factor(28-30) and wavevector Q(C) = Q(P) coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase (18-21).

Update: 4-Jan-2017


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


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