Update: 6-Sep-2018


Title:
Effects of Mg-Zn-Y quasicrystal addition on the microstructures, mechanical performances and corrosion behaviors of as-cast AM60 magnesium alloy
Authors:
Jia, P; Wu, M; Zhang, JY; Hu, X; Teng, XY; Zhao, DG; Wei, T; Dong, DH; Liu, Q; Wang, Y Author Full Names: Jia, Peng; Wu, Ming; Zhang, Jinyang; Hu, Xun; Teng, Xinying; Zhao, Degang; Wei, Tao; Dong, Dehua; Liu, Qing; Wang, Yi
Source:
MATERIALS RESEARCH EXPRESS, 5 (10):10.1088/2053-1591/aada70 OCT 2018
Abstract:
In this work, the as-cast Mg-50Zn-5Y (mass fraction) master alloy containing Mg42Zn50Y8(mole fraction) icosahedral quasicrystal phase (I-phase) was prepared. The influences of addition amount of the Mg-50Zn-5Y master alloy on the microstructure, mechanical performances and corrosion properties of AM60 alloys were studied, aiming to investigate the structure-activity relationship for optimizing the microstructures and properties of AM60 alloys. The results indicated that the continuous reticulation structure could be broken and the precipitated phases could be significantly refined by adding the Mg-50Zn-5Y quasicrystal master alloy. The quasicrystal-reinforced AM60 alloys exhibited better mechanical properties and corrosion resistance than unmodified one. The modified AM60 alloy with 6 wt% of the Mg-50Zn-5Y quasicrystal master alloy had the optimal mechanical performances and corrosion resistance such as a Brinell hardness of 74 HB (increased by 37.0%), an ultimate tensile strength of 205 MPa (increased by 24.3%), a yield strength of 99 MPa (increased by 32.0%) as well as a corrosion rate of 1.35 x 10(-2)mm.year(-1)(decreased by 93.1%). The broken of the continuous reticulation structure and the refinement of the precipitated phases were responsible for the improvement of mechanical performances and corrosion resistance.

Title:
Preparation and electrochemical hydrogen storage properties of MWCNTs-doped Ti49Zr26Ni25 alloy containing quasicrystal phase
Authors:
Liu, H; Zhai, XJ; Li, Z; Tao, X; Liu, WQ; Zhao, JX; Jiang, DY; Gao, S Author Full Names: Liu, Heng; Zhai, Xiaojie; Li, Zhe; Tao, Xing; Liu, Wanqiang; Zhao, Jianxun; Jiang, Dayong; Gao, Shang
Source:
SOLID STATE SCIENCES, 83 17-22; 10.1016/j.solidstatesciences.2018.06.012 SEP 2018
Abstract:
Mechanical alloying technique and subsequent annealing were used to prepare the Ti49Zr26Ni25 quasicrystal. Composite materials of multi-walled carbon nanotubes (MWCNT5) doped Ti49Zr26Ni25 alloys were obtained via ball-milling to improve the hydrogen storage performance of Ti49Zr26Ni25. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were used to analyze the structural properties of the samples. The phase structures of the composite alloys were composed of icosahedral quasicrystal phase and Ti2Ni-type phase. Smaller alloy particles were obtained after doping MWCNT5. Moreover, a three-electrode battery system was carried out to test the electrochemical properties. The composites showed higher discharge capacity, stronger HRD, better cyclic stability and lower charge-transfer resistance than the original Ti49Zr26Ni25 alloy. In the composite electrodes, the optimal discharge capacity of 254.2 mAh/g and the highest capacity retention of 63.1% were achieved for 5 wt% additive content of MWCNTs. The electro-catalytic function of MWCNT5, the reduction of particle size and raise of specific surface area for Ti49Zr26Ni25 alloy may provide larger electrochemically accessible area and rapid channel for hydrogen transportation, which are crucial for improving the electrochemical performance of the alloy.

Title:
A molecular overlayer with the Fibonacci square grid structure
Authors:
Coates, S; Smerdon, JA; McGrath, R; Sharma, HR Author Full Names: Coates, Sam; Smerdon, Joseph A.; McGrath, Ronan; Sharma, Hem Raj
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-05950-7 AUG 24 2018
Abstract:
Quasicrystals differ from conventional crystals and amorphous materials in that they possess long-range order without periodicity. They exhibit orders of rotational symmetry which are forbidden in periodic crystals, such as five-, ten-, and twelve-fold, and their structures can be described with complex aperiodic tilings such as Penrose tilings and Stampfli-Gaehler tilings. Previous theoretical work explored the structure and properties of a hypothetical four-fold symmetric quasicrystal-the so-called Fibonacci square grid. Here, we show an experimental realisation of the Fibonacci square grid structure in a molecular overlayer. Scanning tunnelling microscopy reveals that fullerenes (C-60) deposited on the two-fold surface of an icosahedral Al-Pd-Mn quasicrystal selectively adsorb atop Mn atoms, forming a Fibonacci square grid. The site-specific adsorption behaviour offers the potential to generate relatively simple quasicrystalline overlayer structures with tunable physical properties and demonstrates the use of molecules as a surface chemical probe to identify atomic species on similar metallic alloy surfaces.

Update: 29-Aug-2018


Title:
Incommensurate phase of the stuffed tridymite derivative BaSrFe4O8
Authors:
Ishii, Y; Kawaguchi, S; Asai, K; Mori, S Author Full Names: Ishii, Y.; Kawaguchi, S.; Asai, K.; Mori, S.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 265 314-318; 10.1016/j.jssc.2018.06.007 SEP 2018
Abstract:
We demonstrate a new modulation for a high-temperature polymorph of BaSrFe4O8 via synchrotron powder X-ray diffraction and transmission electron microscopy (TEM) experiments. Although the powder X-ray diffraction pattern was successfully analyzed using a structure model of space group Pnna, an unusually large isotropic atomic displacement parameter (U-iso) was observed for the O1 atom. A split atom model that was applied to the O1 site and the adjacent Ba/Sr site, both of which are on the two-fold axis along the c-axis, indicated that positional disorder occurred in these atoms along the c-axis. The electron diffraction pattern and high-resolution TEM observations combined with the structure refinements revealed an incommensurate structure with a modulation vector q = 0.4270(1)a* and a displacement vector perpendicular to the alpha-axis, which gave rise to the large U-iso value of the O1 atom. The modulation observed in this study may be a signature of structural instability, which has commonly been discussed in the stuffed tridymite-type oxides.

Title:
Spontaneous and field-induced magnetic phase transitions in Dy2Co3Al9: Effects of exchange frustration
Authors:
Gorbunov, DI; Henriques, MS; Qureshi, N; Ouladdiaf, B; Mejia, CS; Gronemann, J; Andreev, AV; Petricek, V; Green, EL; Wosnitza, J Author Full Names: Gorbunov, D. I.; Henriques, M. S.; Qureshi, N.; Ouladdiaf, B.; Mejia, C. Salazar; Gronemann, J.; Andreev, A. V.; Petricek, V.; Green, E. L.; Wosnitza, J.
Source:
PHYSICAL REVIEW MATERIALS, 2 (8):10.1103/PhysRevMaterials.2.084406 AUG 15 2018
Abstract:
Due to the long-range oscillatory character of RKKY exchange interactions, for Dy2Co3Al9 there exist positive and negative couplings between the Dy magnetic moments that lead to magnetic frustration. As a result, the ground state can be easily perturbed, and the system displays a number of spontaneous and field-induced phase transitions. We performed magnetization, magnetic-susceptibility, specific-heat, and electrical-resistivity measurements as well as neutron-diffraction experiments on a single crystal. We find two transitions to distinct incommensurate antiferromagnetic phases at 6.2 and 5.2 K that evolve to a commensurate phase at 3.7 K. In applied magnetic field, new phases emerge. Field-dependent magnetization exhibits a multistep metamagnetic process with sharp transitions accompanied by pronounced magnetoresistance changes. The large number of phases and their complex magnetic structures suggest that the physical properties of Dy2Co3Al9 are ruled by exchange frustration in the presence of a large magnetocrystalline anisotropy.

Title:
Effect of Mg-Based Quasicrystals Addition on Microstructure and Mechanical Properties of AM50 Magnesium Alloy
Authors:
Ma, DZ; Wang, F; Wang, Z; Liu, Z; Mao, PL Author Full Names: Ma Dezhi; Wang Feng; Wang Zhi; Liu Zheng; Mao Pingli
Source:
RARE METAL MATERIALS AND ENGINEERING, 47 (7):2166-2171; JUL 2018
Abstract:
The Mg-48Zn-13Y (MZY) quasicrystal master alloy with high volume fraction of the quasicrystalline phase was prepared by a conventional solidification method. The influences of the MZY quasicrystal on microstructures and mechanical properties of AM50 alloys were investigated by OM, SEM, EDS, XRD and tensile tests. The results indicate that with addition of the MZY quasicrystal to AM50 alloy, the Mg3Zn6Y quasicrystal phase can be retained in AM50 matrix alloy, and the microstructures are obviously refined. The beta phase in the microstructures is changed from coarse and continuous net-like to discontinuous strip-like and granular, and the amount is decreased. When the content of the MZY quasicrystal is 6%, the microstructure is greatly refined, and the ultimate tensile strength, yield strength and elongation of the alloy reach to the maximum, 202.92 MPa, 100.57 MPa and 10.8%, respectively, which are improved by 24.59%, 74.9% and 66.15%, respectively, compared with those of AM50 alloy. Mechanical properties of AM50 magnesium alloy can be improved significantly by addition of the MZY quasicrystal, which results from the microstructure refinement, the optimization of the morphology and amount of the beta phase, and the dispersion strengthening effect of the quasicrystal phase having good wettability with the magnesium alloy substrate.

Update: 22-Aug-2018


Title:
Formation of modulated structures induced by oxygen vacancies in alpha-Fe2O3 nanowires
Authors:
Li, T; Feng, HL; Wang, YQ; Wang, C; Zhu, WH; Yuan, L; Zhou, GW Author Full Names: Li, Tao; Feng, Honglei; Wang, Yiqian; Wang, Chao; Zhu, Wenhui; Yuan, Lu; Zhou, Guangwen
Source:
JOURNAL OF CRYSTAL GROWTH, 498 10-16; 10.1016/j.jcrysgro.2018.05.031 SEP 15 2018
Abstract:
Two modulated structures caused by long-range ordering of oxygen vacancies have been observed in alpha-Fe2O3 nanowires (NWs) produced after oxidation of Fe, one being ten times (30 (3) over bar0) interplanar spacing and the other being six times (11 (2) over bar0) interplanar spacing. Both types of oxygen vacancy ordering structures have a similar modulation periodicity of 1.45 or 1.50 nm with corresponding atomic ratios of Fe and O (Fe/O) of 0.7407 and 0.7273, respectively. The Fe/O ratios in the NWs with oxygen-vacancy ordering are very close to that of Fe3O4 (0.7500). The similar Fe/O ratio between NWs and Fe3O4 may explain the similar modulation periodicity of different oxygen-vacancy orderings. Electron energy-loss spectroscopy studies show that the Fe/O ratio of NWs is close to that of Fe3O4 when oxygen atoms are not sufficient, which makes the NWs energetically favorable. The elucidation of the mechanism governing the formation of the modulated structures in alpha-Fe2O3 NWs is critical for controlling the microstructure and correspondingly physicochemical properties of NWs.

Title:
Investigation of a nano-scale, incommensurate, modulated domain in a Ti-Fe alloy
Authors:
Zheng, YF; Huber, D; Fraser, HL Author Full Names: Zheng, Yufeng; Huber, Daniel; Fraser, Hamish L.
Source:
SCRIPTA MATERIALIA, 154 220-224; 10.1016/j.scriptamat.2018.06.010 SEP 2018
Abstract:
The microstructure of a Ti-Fe compositional gradient sample was investigated using transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Different combinations of phases were observed to form depending on the local concentration of Fe. Interestingly, a nano-scale incommensurate modulated domain was detected in the alloy containing approximately 13.8 to 33.9 wt% Fe using selected area diffraction (SAD). The observed disordered structure with no fixed long range periodicity in the nano-scale incommensurate modulated domain in aberration-corrected HAADF-STEM imaging was found not related to the shuffle mechanism of the to phase. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Electronic phase separation and magnetic-field-induced phenomena in molecular multiferroic (ND4)(2)FeCl5 center dot D2O
Authors:
Tian, W; Cao, HB; Clune, AJ; Hughey, KD; Hong, T; Yan, JQ; Agrawal, HK; Singleton, J; Sales, BC; Fishman, RS; Musfeldt, JL; Fernandez-Baca, JA Author Full Names: Tian, W.; Cao, H. B.; Clune, Amanda J.; Hughey, Kendall D.; Hong, Tao; Yan, J. -Q.; Agrawal, Harish K.; Singleton, John; Sales, B. C.; Fishman, Randy S.; Musfeldt, J. L.; Fernandez-Baca, J. A.
Source:
PHYSICAL REVIEW B, 98 (5):10.1103/PhysRevB.98.054407 AUG 8 2018
Abstract:
Electronic phase separation has been increasingly recognized as an important phenomenon in understanding many of the intriguing properties displayed in transition metal oxides. It is believed to produce fascinating functional properties in otherwise chemically homogenous electronic systems, e.g., colossal magnetoresistance manganites and high-T-c cuprates. While many well-known electronically phase-separated systems are oxides, it has been argued that the same phenomenon should occur in other electronic systems with strong competing interactions. Here we report the observation of electronic phase separation in molecular (ND4)(2)FeCl5 center dot D2O, a type-II multiferroic. We show that two magnetic phases, one of which is commensurate and the other of which is incommensurate, coexist in this material. Their evolution under applied magnetic field produces emergent properties. In particular, our measurements reveal a field-induced exotic state linked to a direct transition from a paraelectric/paramagnetic phase to a ferroelectric/antiferromagnetic phase, a collective phenomenon that hasn't been seen in other magnetic multiferroics.

Title:
Incommensurately Modulated Structures in Zr-rich PZT: Periodic Nanodomains, Reciprocal Configuration, and Nucleation
Authors:
Fu, ZQ; Chen, XF; Lu, P; Zhu, CX; Nie, HC; Xu, FF; Wang, GS; Dong, XL Author Full Names: Fu, Zhengqian; Chen, Xuefeng; Lu, Ping; Zhu, Chenxi; Nie, Henchang; Xu, Fangfang; Wang, Genshui; Dong, Xianlin
Source:
CRYSTAL GROWTH & DESIGN, 18 (8):4395-4402; 10.1021/acs.cgd.8b00369 AUG 2018
Abstract:
Zr-rich PZT is one of the most representative materials with compositions located at the ferroelectric-antiferroelectric (FE-AFE) phase boundary. The study of its incommensurately modulated structure (IMS) is of fundamental importance in understanding the origin of its high-performance stored-energy properties and phase transformation between FE and AFE. In this study, the structural features of the IMS were investigated in detail by transmission electron microscopy. The IMS appears as submicron domains assembled by periodic arrays of two-dimensional nanodomains along a <111> direction with the domain width of about 30 {111} spacings. The nanodomains have dual attributes of both antiphase domains and electric domains. The displacement vector across the periodic antiphase boundaries was determined to be R = [001]. The reciprocal lattice of IMS was constructed and characterized by a set of strong basic reflections of pseudocubic unit cell together with 1/2{ooe} superlattice reflections where 1/2(ooe) superlattice reflections (located on the (001) reciprocal planes) do not split, while both 1/2(eoo) and 1/2(oeo) superlattice reflections (located on (100) and (010) reciprocal planes, respectively) split. In addition, the growth process of IMS and the visibility conditions for the periodic nanodomains and superlattice reflections splitting are presented.

Title:
Modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering
Authors:
Nagata, T; Ikeda, N Author Full Names: Nagata, T.; Ikeda, N.
Source:
AIP ADVANCES, 8 (7):10.1063/1.5026921 JUL 2018
Abstract:
We report the modulation in charge ordering structure of ferroelectric YbFe2O4 by magnetic ordering from x-ray diffraction experiments and magnetic measurements. The incommensurate modulation was observed on (n n 3m+3/2) type diffraction signal around magnetic ordering temperature where n and m are integer. The modulation was also observed on charge ordering signal, indicating spin-charge coupling. The incommensurate modulation was observed only on (n/3 n/3 3m) type charge ordering signal. This selectivity can be explained by polar charge ordering models. (C) 2018 Author(s).

Update: 15-Aug-2018


Title:
Research on the formation of M1-type alite doped with MgO and SO3-A route to improve the quality of cement clinker with a high content of MgO
Authors:
Zhou, H; Gu, XM; Sun, JF; Yu, ZQ; Huang, H; Wang, QQ; Shen, XD Author Full Names: Zhou, Hao; Gu, Xiaomei; Sun, Jinfeng; Yu, Zhuqing; Huang, Hong; Wang, Qianqian; Shen, Xiaodong
Source:
CONSTRUCTION AND BUILDING MATERIALS, 182 156-166; 10.1016/j.conbuildmat.2018.06.078 SEP 10 2018
Abstract:
This paper discusses the effect of SO3 dopants on the M-1 polymorph formation and mechanical properties of alite containing a high content of MgO. The structure of the M-1 alite is identified by XRD, high-temperature XRD and TEM analysis. A characteristic XRD pattern of M-1 alite doped with MgO and SO3 is determined, and TEM results show that M-1 alite has an incommensurate modulated structure feature with 2.4 times the subcell dimension along [(2) over bar1 0 ](H)* and could be expressed as ha* + kb* + lc* + m/[2.4 (-2a* + b*)], where m = +/- 1. The First-Principles method is used to simulate the structure of M-1 alite, and the calculated Delta Cohesive Energy is approximately 11-12 eV between the M-1 and M-3 alite. Quantitative analysis is performed by the Rietveld method. The SO3/MgO (mass ratio from SO3 to MgO) and M-1% in alite (M1-C3S%/M1-C3S%+M3-C3S% x 100%) are shown to have a strong linear relationship, which can be defined as M1-C3S%/M1-C3S%+M3-C3S% x 100% = 24.73 + 108.11 * SO3/MgO (%). Mechanical properties results show that appropriate SO3 dopant can improve the compressive strength of alite containing high MgO while over dosed SO3 will lead to a contrary effect because of the decomposition of alite. The relationship between M-1% in the alite and the compressive strengths at different ages is also given. The optimal M-1% in alite is approximately 68% and the best SO3/MgO ratio is approximately 0.43 because the compressive strength could be maximized at each age. (C) 2018 Elsevier Ltd. All rights reserved.

Title:
Incommensurately Modulated Structures and Luminescence Properties of the AgxSm(2-x)/3WO4 (x=0.286, 0.2) Scheelites as Thermographic Phosphors
Authors:
Morozov, V; Deyneko, D; Basoyich, O; Khaikina, EG; Spassky, D; Morozov, A; Chernyshev, V; Abakumov, A; Hadermann, J Author Full Names: Morozov, Vladimir; Deyneko, Dina; Basoyich, Olga; Khaikina, Elena G.; Spassky, Dmitry; Morozov, Anatolii; Chernyshev, Vladimir; Abakumov, Artem; Hadermann, Joke
Source:
CHEMISTRY OF MATERIALS, 30 (14):4788-4798; 10.1021/acs.chemmater.8b02029 JUL 24 2018
Abstract:
Ag+ for Sm3+ substitution in the scheelite-type AgxSm(2-x)/3 square(1-2x)/3WO4 tungstates has been investigated for its influence on the cation-vacancy ordering and luminescence properties. A solid state method was used to synthesize the x = 0.286 and x = 0.2 compounds, which exhibited (3 + 1)D incommensurately modulated structures in the transmission electron microscopy study. Their structures were refined using high resolution synchrotron powder X-ray diffraction data. Under near-ultraviolet light, both compounds show the characteristic emission lines for (4)G(5/2) -> H-6(J) (J = 5/2, 7/2, 9/2, and 11/2) transitions of the Sm3+ ions in the range 550-720 nm, with the J = 9/2 transition at the similar to 648 nm region being dominant for all photoluminescence spectra. The intensities of the (4)G(5/2) -> H-6(9/2) and (4)G(5/2) -> H-6(7/2) bands have different temperature dependencies. The emission intensity ratios (R) for these bands vary reproducibly with temperature, allowing the use of these materials as thermographic phosphors.

Update: 8-Aug-2018


Title:
Effects of Microstructure of Quasicrystal Alloys on Their Mechanical and Tribological Performance
Authors:
Lee, K; Dai, W; Naugle, D; Liang, H Author Full Names: Lee, Kyungjun; Dai, Wei; Naugle, Donald; Liang, Hong
Source:
JOURNAL OF TRIBOLOGY-TRANSACTIONS OF THE ASME, 140 (5):10.1115/1.4039528 SEP 2018
Abstract:
The current design of materials against wear considers hardness as the sole material property. As a result, the brittleness associated with increased hardness leads to severe damage. The purpose of this research is to understand the nature of conflicts between hardness and toughness of a new alloy composite. First, we designed Al-Cu-Fe alloys containing crystal structures of lambda, beta, and quasi-crystalline i-phase. These and their combination with others lead to a set of alloys with various hardness and fracture toughness. Experimental study was carried out using a noble and hard tungsten carbide (WC) ball against sample disks. The WC ball did not produce any wear. The wear rate of those alloys was found to be dependent not only on their hardness, but also the toughness, an alternative to the well-accepted Archard-based equations.

Title:
Re-entrant charge order in overdoped (Bi,Pb)(2.12)Sr1.88CuO6+delta outside the pseudogap regime
Authors:
Peng, YY; Fumagalli, R; Ding, Y; Minola, M; Caprara, S; Betto, D; Bluschke, M; De Luca, GM; Kummer, K; Lefrancois, E; Salluzzo, M; Suzuki, H; Le Tacon, M; Zhou, XJ; Brookes, NB; Keimer, B; Braicovich, L; Grilli, M; Ghiringhelli, G Author Full Names: Peng, Y. Y.; Fumagalli, R.; Ding, Y.; Minola, M.; Caprara, S.; Betto, D.; Bluschke, M.; De Luca, G. M.; Kummer, K.; Lefrancois, E.; Salluzzo, M.; Suzuki, H.; Le Tacon, M.; Zhou, X. J.; Brookes, N. B.; Keimer, B.; Braicovich, L.; Grilli, M.; Ghiringhelli, G.
Source:
NATURE MATERIALS, 17 (8):697-+; 10.1038/s41563-018-0108-3 AUG 2018
Abstract:
In the underdoped regime, the cuprate high-temperature superconductors exhibit a host of unusual collective phenomena, including unconventional spin and charge density modulations, Fermi surface reconstructions, and a pseudogap in various physical observables. Conversely, overdoped cuprates are generally regarded as conventional Fermi liquids possessing no collective electronic order. In partial contradiction to this widely held picture, we report resonant X-ray scattering measurements revealing incommensurate charge order reflections for overdoped (Bi,Pb)(2.12)Sr1.88CuO6+delta (Bi2201), with correlation lengths of 40-60 lattice units, that persist up to temperatures of at least 250 K. The value of the charge order wavevector decreases with doping, in line with the extrapolation of the trend previously observed in underdoped Bi2201. In overdoped materials, however, charge order coexists with a single, unreconstructed Fermi surface without nesting or pseudogap features. The discovery of re-entrant charge order in Bi2201 thus calls for investigations in other cuprate families and for a reconsideration of theories that posit an essential relationship between these phenomena.

Title:
Incommensurate atomic and magnetic modulations in the spin-frustrated beta-NaMnO2 triangular lattice
Authors:
Orlandi, F; Aza, E; Bakaimi, I; Kiefer, K; Klemke, B; Zorko, A; Arcon, D; Stock, C; Tsibidis, GD; Green, MA; Manuel, P; Lappas, A Author Full Names: Orlandi, Fabio; Aza, Eleni; Bakaimi, Ioanna; Kiefer, Klaus; Klemke, Bastian; Zorko, Andrej; Arcon, Denis; Stock, Christopher; Tsibidis, George D.; Green, Mark A.; Manuel, Pascal; Lappas, Alexandros
Source:
PHYSICAL REVIEW MATERIALS, 2 (7):10.1103/PhysRevMaterials.2.074407 JUL 24 2018
Abstract:
The layered beta-NaMnO2, a promising Na-ion energy-storage material, has been investigated for its triangular lattice capability to promote complex magnetic configurations that may release symmetry restrictions for the coexistence of ferroelectric and magnetic orders. The complexity of the neutron powder diffraction patterns underlines that the routinely adopted commensurate structural models are inadequate. Instead, a single-phase superspace symmetry description is necessary, demonstrating that the material crystallizes in a compositionally modulated q = (0.077(1), 0, 0) structure. Here Mn3+ Jahn-Teller distorted MnO6 octahedra form corrugated layer stacking sequences of the beta-NaMnO2 type, which are interrupted by flat sheets of the alpha-like oxygen topology. Spontaneous long-range collinear antiferromagnetic order, defined by the propagation vector k = (1/2,1/2,1/2), appears below T-N1 = 200 K. Moreover, a second transition into a spatially modulated proper-screw magnetic state (k +/- q) is established at T-N2 = 95 K, with an antiferromagnetic order parameter resembling that of a two-dimensional (2D) system. The evolution of Na-23 NMR spin-lattice relaxation identifies a magnetically inhomogeneous state in the intermediate T region (T-N2 < T < T-N1), while its strong suppression below T-N2 indicates that a spin gap opens in the excitation spectrum. High-resolution neutron inelastic scattering confirms that the magnetic dynamics are indeed gapped (Delta similar to 5 meV) in the low-temperature magnetic phase, while simulations on the basis of the single-mode approximation suggest that Mn spins residing on adjacent antiferromagnetic chains, establish sizable 2D correlations. Our analysis points out that novel structural degrees of freedom promote cooperative magnetism and emerging dielectric properties in this nonperovskite type of manganite.

Update: 1-Aug-2018


Title:
Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field-orientation-dependent Pt-195 NMR
Authors:
Tokunaga, Y; Nakamura, A; Aoki, D; Shimizu, Y; Homma, Y; Honda, F; Sakai, H; Hattori, T; Kambe, S Author Full Names: Tokunaga, Y.; Nakamura, A.; Aoki, D.; Shimizu, Y.; Homma, Y.; Honda, F.; Sakai, H.; Hattori, T.; Kambe, S.
Source:
PHYSICAL REVIEW B, 98 (1):10.1103/PhysRevB.98.014425 JUL 23 2018
Abstract:
Pt-195 NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below T-N = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes, estimated to be 59 kOe/mu B. Nuclear relaxation rate (1/T-1) measurement revealed the development of the antiferromagnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.

Title:
Imaging the magnetic structures of artificial quasicrystal magnets using resonant coherent diffraction of circularly polarized X-rays
Authors:
Sung, D; Jung, C; Cho, BG; Jo, W; Han, HS; Lee, KS; Bhat, V; Farmer, B; De Long, LE; Lee, KB; Keavney, DJ; Lee, DR; Song, C Author Full Names: Sung, Daeho; Jung, Chulho; Cho, Byeong-Gwan; Jo, Wonhyuk; Han, Hee-Sung; Lee, Ki-Suk; Bhat, Vinayak; Farmer, Barry; De Long, L. E.; Lee, Ki Bong; Keavney, D. J.; Lee, Dong Ryeol; Song, Changyong
Source:
NANOSCALE, 10 (27):13159-13164; 10.1039/c8nr03733g JUL 21 2018
Abstract:
Unraveling nanoscale spin structures has long been an important activity addressing various scientific interests, that are also readily adaptable to technological applications. This has invigorated the development of versatile nanoprobes suitable for imaging specimens under native conditions. Here we have demonstrated the resonant coherent diffraction of an artificial quasicrystal magnet with circularly polarized X-rays. The nanoscale magnetic structure was revealed from X-ray speckle patterns by comparing with micromagnetic simulations, as a step toward understanding the intricate relationship between the chemical and spin structures in an aperiodic quasicrystal lattice. Femtosecond X-ray pulses from free electron lasers are expected to immediately extend the current work to nanoscale structure investigations of ultrafast spin dynamics, surpassing the present spatio-temporal resolution.

Title:
Structure and properties of composites based on polyphenylene sulfide reinforced with Al-Cu-Fe quasicrystalline particles
Authors:
Chukov, DI; Stepashkin, AA; Tcherdyntsev, VV; Olifirov, LK; Kaloshkin, SD Author Full Names: Chukov, D. I.; Stepashkin, A. A.; Tcherdyntsev, V. V.; Olifirov, L. K.; Kaloshkin, S. D.
Source:
JOURNAL OF THERMOPLASTIC COMPOSITE MATERIALS, 31 (7):882-895; 10.1177/0892705717729015 JUL 2018
Abstract:
Structural, mechanical, and thermal properties of polyphenylene sulfide (PPS) filled with Al-Cu-Fe quasicrystals particles were studied. It was shown that the introducing of quasicrystalline fillers into the polymer matrix results in the increase in Young's modulus, hardness, and toughness of the polymer. Quasicrystalline fillers can improve thermal properties of PPS, including heat resistance index, Vicat softening temperature, thermal diffusivity, and thermal conductivity.

Title:
Cylindrical bending analysis of a layered two-dimensional piezoelectric quasicrystal nanoplate
Authors:
Li, Y; Yang, LZ; Gao, Y; Pan, EN Author Full Names: Li, Yang; Yang, Lianzhi; Gao, Yang; Pan, Ernian
Source:
JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 29 (12):2660-2676; 10.1177/1045389X18770920 JUL 2018
Abstract:
The piezoelectric effect is a significant property of quasicrystal. In this article, the exact solution is derived for a layered piezoelectric quasicrystal nanoplate with nonlocal effect in cylindrical bending. Based on the nonlocal theory and the pseudo-Stroh formalism, the exact solution for a homogeneous simply supported nanoplate is obtained. With the aid of the propagator matrix, the exact solution for a multilayered nanoplate is achieved. Numerical examples are carried out to reveal the influences of span-to-thickness ratio, nonlocal parameter, and stacking sequence on piezoelectric quasicrystal nanoplates with their top surface subjected to two loadings. One is a z-direction mechanical loading and the other is an electric potential loading. These results can be served as benchmarks for the design, numerical modeling, and simulation of layered two-dimensional piezoelectric quasicrystal nanoplates under cylindrical bending.

Title:
EVOLUTION OF THE PHASES OF QUASICRYSTALLINE ALLOYS ICOSAHEDRAL/DECAGONAL Al62.2Cu25.3Fe12.5/Al65Ni15Co20 AND OXIDATIVE BEHAVIOR
Authors:
Jamshidi, LCLA; Rodbari, RJ Author Full Names: Lucena Agostinho Jamshidi, Lourdes Cristina; Rodbari, Reza Jamshidi
Source:
JOURNAL OF THE CHILEAN CHEMICAL SOCIETY, 63 (2):3928-3933; 10.4067/s0717-97072018000203928 JUN 2018
Abstract:
In this paper, we present an approach and investigation on the evolution of the icosahedral and decagonal phases of quasicrystalline alloys Al62.2Cu25.3Fe12.5 E Al65Ni15Co20, the oxidation behavior in them. The quantification of the quasicrystalline and crystalline phases present in the quasicrystals provides important information in the mass transport by diffusion, as well as the phase transformations that occurred. For this purpose, X-ray diffraction (XRD) and Rietveld Method Quantification, Scanning Electron Microscopy (SEM) / Dispersive Energy Spectroscopy (EDS), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis). The results showed structural aspects of the two compositions of quasicrystals, these were elaborated and obtained in an arc induction furnace. The oxidation of the alloy Al62.2Cu25.3Fe12.5 showed intermetallic phases with associations of the elements of the alloy and above 735 degrees C was observed that the crystalline phase is stable in the icosahedral phase. The quasicrystals Al65Ni15Co20, with the interaction of oxygen, happens in the surface of symmetry 10 times plane perpendicular vector. The formation of a thin film of the aluminum oxide with a well ordered hexagonal shape structure, with a domain opposite the decagonal phase with lateral size at about 35 angstrom.

Title:
Electric-field-induced phase transition and pinched P-E hysteresis loops in Pb-free ferroelectrics with a tungsten bronze structure
Authors:
Li, K; Zhu, XL; Liu, XQ; Ma, X; Sen Fu, M; Kroupa, J; Kamba, S; Chen, XM Author Full Names: Li, Kun; Zhu, Xiao Li; Liu, Xiao Qiang; Ma, Xiao; Sen Fu, Mao; Kroupa, Jan; Kamba, Stanislav; Chen, Xiang Ming
Source:
NPG ASIA MATERIALS, 10 10.1038/s41427-018-0013-x APR 5 2018
Abstract:
Antiferroelectrics are of interest due to their high potential for energy storage. Here, we report the discovery of pinched, polarization-vs.-electric field (P-E) hysteresis loops in the lead-free tungsten bronze ferroelectrics Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30, while a broad, single P-E hysteresis loop was observed in the analogue compound Ba4Nd2Ti4Nb6O30. Pinched P-E loops are similar to antiferroelectric hysteresis loops, but in perovskites, they are mostly caused by an extrinsic, internal bias field due to defects, which block domain wall motion. We show that the pinched P-E loops are caused by an intrinsic effect, i.e., by the electric-field-induced phase transition from a non-polar incommensurate to a polar commensurately modulated crystal structure. The in situ electron diffraction results show the coexistence of commensurate polar structural modulation and incommensurate non-polar modulation during the ferroelectric transition and within the ferroelectric phase below the transition temperature. This phase coexistence is the reason for the small remanent polarization. An external electric field transforms the incommensurate component into a commensurate one, and the polarization increases. This new mechanism for pinched P-E hysteresis loops in ferroelectrics not only indicates a new direction for the development of Pb-free ferroelectric materials for energy storage but also significantly contributes to the physical understanding of ferroelectricity in materials with a tungsten bronze structure.

Update: 26-Jul-2018


Title:
Charge density wave phase, Mottness, and ferromagnetism in monolayer 1T-NbSe2
Authors:
Pasquier, D; Yazyev, OV Author Full Names: Pasquier, Diego; Yazyev, Oleg V.
Source:
PHYSICAL REVIEW B, 98 (4):10.1103/PhysRevB.98.045114 JUL 10 2018
Abstract:
The recently investigated 1T polymorph of monolayer NbSe2 revealed an insulating behavior suggesting a star-of-David phase with root 13 x root 13 periodicity associated with a Mott insulator, reminiscent of 1 T-TaS2. We examine this novel two-dimensional material from first principles. We find an instability towards the formation of an incommensurate charge density wave (CDW) and establish the star-of-David phase as the most stable commensurate CDW. The Mottness in the star-of-David phase is confirmed and studied at various levels of theory: the spin-polarized generalized gradient approximation (GGA) and its extension involving the on-site Coulomb repulsion (GGA+U), as well as the dynamical mean-field theory. Finally, we estimate Heisenberg exchange couplings in this material and find a weak nearest-neighbor ferromagnetic coupling, at odds with most Mott insulators. We point out the close resemblance between this star-of-David phase and flat-band ferromagnetism models.

Title:
Multi-orbital nature of the spin fluctuations in Sr2RuO4
Authors:
Boehnke, L; Werner, P; Lechermann, F Author Full Names: Boehnke, Lewin; Werner, Philipp; Lechermann, Frank
Source:
EPL, 122 (5):10.1209/0295-5075/122/57001 JUN 2018
Abstract:
The spin susceptibility of strongly correlated Sr2RuO4 is known to display a rich structure in reciprocal space, with a prominent peak at Q(i) = (0.3,0.3,0). It is still debated if the resulting incommensurate spin-density-wave fluctuations foster unconventional superconductivity at low temperature or compete therewith. By means of density functional theory combined with dynamical mean-field theory, we reveal the realistic multi-orbital signature of the (dynamic) spin susceptibility beyond existing weak-coupling approaches. The experimental fluctuation spectrum up to 80 meV is confirmed by theory. Furthermore, the peak at Q(i) is shown to carry nearly equal contributions from each of the Ru(4d)-t(2)g orbitals, pointing to a cooperative effect resulting in the dominant spin fluctuations. Copyright (C) EPLA, 2018

Title:
Quasicrystal seen to superconduct
Authors:
Jarman, S Author Full Names: Jarman, Sam
Source:
PHYSICS WORLD, 31 (5):4-4; MAY 2018

Update: 18-Jul-2018


Title:
Persistent low-energy phonon broadening near the charge-order q vector in the bilayer cuprate Bi2Sr2CaCu2O8+delta
Authors:
He, Y; Wu, S; Song, Y; Lee, WS; Said, AH; Alatas, A; Bosak, A; Girard, A; Souliou, SM; Ruiz, A; Hepting, M; Bluschke, M; Schierle, E; Weschke, E; Lee, JS; Jang, H; Huang, H; Hashimoto, M; Lu, DH; Song, D; Yoshida, Y; Eisaki, H; Shen, ZX; Birgeneau, RJ; Yi, M; Frano, A Author Full Names: He, Y.; Wu, S.; Song, Y.; Lee, W-S; Said, A. H.; Alatas, A.; Bosak, A.; Girard, A.; Souliou, S. M.; Ruiz, A.; Hepting, M.; Bluschke, M.; Schierle, E.; Weschke, E.; Lee, J-S; Jang, H.; Huang, H.; Hashimoto, M.; Lu, D-H; Song, D.; Yoshida, Y.; Eisaki, H.; Shen, Z-X; Birgeneau, R. J.; Yi, M.; Frano, A.
Source:
PHYSICAL REVIEW B, 98 (3):10.1103/PhysRevB.98.035102 JUL 2 2018
Abstract:
We report a persistent low-energy phonon broadening around qB similar to 0.28 reciprocal lattice unit (r.l.u.)along the Cu-O bond direction in the high-T-c cuprate Bi2Sr2CaCu2O8+delta (Bi-2212). We show that such broadening exists both inside and outside the conventional charge-density wave (CDW) phase, via temperature-dependent measurements in both underdoped and heavily overdoped samples. Combining inelastic hard x-ray scattering, diffuse scattering, angle-resolved photoemission spectroscopy, and resonant soft x-ray scattering at the Cu L-3-edge, we exclude the presence of a CDW in the heavily overdoped Bi-2212 similar to that observed in the underdoped systems. Finally, we discuss the origin of such anisotropic low-energy phonon broadening and its potential precursory role to the CDW phase in the underdoped region.

Title:
Exploiting superspace to clarify vacancy and Al/Si ordering in mullite
Authors:
Klar, PB; Etxebarria, I; Madariaga, G Author Full Names: Klar, Paul Benjamin; Etxebarria, Inigo; Madariaga, Gotzon
Source:
IUCRJ, 5 497-509; 10.1107/S2052252518007467 4 JUL 2018
Abstract:
Synchrotron single-crystal X-ray diffraction has revealed diffuse scattering alongside sharp satellite reflections for different samples of mullite (Al4+2xSi2-2xO10-x). Structural models have been developed in (3+1)-dimensional superspace that account for vacancy ordering and Al/Si ordering based on harmonic modulation functions. A constraint scheme is presented which explains the crystal-chemical relationships between the split sites of the average structure. The modulation amplitudes of the refinements differ significantly by a factor of similar to 3, which is explained in terms of different degrees of ordering, i.e. vacancies follow the same ordering principle in all samples but to different extents. A new approach is applied for the first time to determine Al/Si ordering by combining density functional theory with the modulated volumes of the tetrahedra. The presence of Si-Si diclusters indicates that the mineral classification of mullite needs to be reviewed. A description of the crystal structure of mullite must consider both the chemical composition and the degree of ordering. This is of particular importance for applications such as advanced ceramics, because the physical properties depend on the intrinsic structure of mullite.

Title:
Sr2Pt8-x As: a layered incommensurately modulated metal with saturated resistivity
Authors:
Martino, E; Arakcheeva, A; Autes, G; Pisoni, A; Bachmann, MD; Modic, KA; Helm, T; Yazyev, OV; Moll, PJW; Forro, L; Katrych, S Author Full Names: Martino, Edoardo; Arakcheeva, Alla; Autes, Gabriel; Pisoni, Andrea; Bachmann, Maja D.; Modic, Kimberly A.; Helm, Toni; Yazyev, Oleg, V; Moll, Philip J. W.; Forro, Laszlo; Katrych, Sergiy
Source:
IUCRJ, 5 470-477; 10.1107/S2052252518007303 4 JUL 2018
Abstract:
The high-pressure synthesis and incommensurately modulated structure are reported for the new compound Sr2Pt8-xAs, with x = 0.715 (5). The structure consists of Sr2Pt3 As layers alternating with Pt-only corrugated grids. Ab initio calculations predict a metallic character with a dominant role of the Pt d electrons. The electrical resistivity (rho) and Seebeck coefficient confirm the metallic character, but surprisingly, rho showed a near-flat temperature dependence. This observation fits the description of the Mooij correlation for electrical resistivity in disordered metals, originally developed for statistically distributed point defects. The discussed material has a long-range crystallographic order, but the high concentration of Pt vacancies, incommensurately ordered, strongly influences the electronic conduction properties. This result extends the range of validity of the Mooij correlation to long-range ordered incommensurately modulated vacancies. Motivated by the layered structure, the resistivity anisotropy was measured in a focused-ion-beam micro-fabricated well oriented single crystal. A low resistivity anisotropy indicates that the layers are electrically coupled and conduction channels along different directions are intermixed.

Title:
A Markov theoretic description of stacking-disordered aperiodic crystals including ice and opaline silica
Authors:
Hart, AG; Hansen, TC; Kuhs, WF Author Full Names: Hart, A. G.; Hansen, T. C.; Kuhs, W. F.
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 357-372; 10.1107/S2053273318006083 4 JUL 2018
Abstract:
This article reviews the Markov theoretic description of one-dimensional aperiodic crystals, describing the stacking-faulted crystal polytype as a special case of an aperiodic crystal. Under this description the centrosymmetric unit cell underlying a topologically centrosymmetric crystal is generalized to a reversible Markov chain underlying a reversible aperiodic crystal. It is shown that for the close-packed structure almost all stackings are irreversible when the interaction reichweite s > 4. Moreover, the article presents an analytic expression of the scattering cross section of a large class of stacking-disordered aperiodic crystals, lacking translational symmetry of their layers, including ice and opaline silica (opal CT). The observed stackings and their underlying reichweite are then related to the physics of various nucleation and growth processes of disordered ice. The article discusses how the derived expressions of scattering cross sections could significantly improve implementations of Rietveld's refinement scheme and compares this Q-space approach with the pair-distribution function analysis of stacking-disordered materials.

Title:
Primitive substitution tilings with rotational symmetries
Authors:
Say-awen, ALD; De las Penas, MLAN; Frettloh, D Author Full Names: Say-awen, April Lynne D.; De las Penas, Ma Louise Antonette N.; Frettloeh, Dirk
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 388-398; 10.1107/S2053273318006745 4 JUL 2018
Abstract:
This work introduces the idea of symmetry order, which describes the rotational symmetry types of tilings in the hull of a given substitution. Definitions are given of the substitutions sigma(6) and sigma(7) which give rise to aperiodic primitive substitution tilings with dense tile orientations and which are invariant under six- and sevenfold rotations, respectively; the derivation of the symmetry orders of their hulls is also presented.

Title:
A phenomenological model for structural phase transitions in incommensurate alkane/urea inclusion compounds
Authors:
Couzi, M; Guillaume, F; Harris, KDM Author Full Names: Couzi, Michel; Guillaume, Francois; Harris, Kenneth D. M.
Source:
ROYAL SOCIETY OPEN SCIENCE, 5 (6):10.1098/rsos.180058 JUN 2018
Abstract:
n-Alkane/urea inclusion compounds are crystalline materials in which n-alkane 'guest' molecules are located within parallel one-dimensional 'host' tunnels formed by a helical hydrogen-bonded arrangement of urea molecules. The periodic repeat distance of the guest molecules along the host tunnels is incommensurate with the periodic repeat distance of the host substructure. The structural properties of the high-temperature phase of these materials (phase I), which exist at ambient temperature, are described by a (3 + l)-dimensional superspace. Recent publications have suggested that, in the prototypical incommensurate composite systems, n-nonadecane/urea and n-hexadecane/urea, two low-temperature phases II and 'III' exist and that one or both of these phases are described by a (3 + 2)dimensional superspace. We present a phenomenological model based on symmetry considerations and developed in the frame of a pseudo-spin-phonon coupling mechanism, which accounts for the mechanisms responsible for the I <-> II <-> 'III' phase sequence. With reference to published experimental data, we demonstrate that, in all phases of these incommensurate materials, the structural properties are described by (3 + l)-dimensional superspace groups. Around the temperature of the II <-> 'III' transition, the macroscopic properties of the material are not actually associated with a phase transition, but instead represent a 'crossover' between two regimes involving different couplings between relevant order parameters.

Title:
Microstructural analysis, micro-hardness and wear resistance properties of quasicrystalline Al-Cu-Fe coatings on Ti-6Al-4V alloy
Authors:
Fatoba, OS; Akinlabi, SA; Akinlabi, ET; Gharehbaghi, R Author Full Names: Fatoba, O. S.; Akinlabi, S. A.; Akinlabi, E. T.; Gharehbaghi, R.
Source:
MATERIALS RESEARCH EXPRESS, 5 (6):10.1088/2053-1591/aaca70 JUN 2018
Abstract:
The need for engineering components with suitable functionality under harsh wear and aggressive environment subjected to high risk of deterioration, has led to the demand for surface treatment processes and high-performance materials. Ti-6Al-4V is one of the mostly used titanium alloys with more than 70% of the industrial applications in the aerospace, marine and automotive industries. Despite the exceptional properties of Ti-6Al-4V alloy, their low hardness, high susceptibility to corrosion, poor thermal stability and poor tribological properties have limited their viability in the field of engineering. In this research, laser metal deposition technique by incorporating quasicrystal-line Al-Cu-Fe coatings can be very beneficial in enhancing the surface properties of Ti-6Al-4V alloy. A 3 kW continuous wave ytterbium laser system (YLS) attached to a KUKA robot which controls the movement of the cladding process was utilized for the fabrication of the coatings. The titanium alloy cladded surfaces were investigated for its microstructure, mechanical and wear resistance properties at different laser processing conditions. The obtained results illustrated that geometrical properties height and width of the deposit increase with an increase in laser power. Increase in scanning speed results in a decrease in the geometrical properties. Ti reacted with increased amount of Al and Fe and less amount of Cu powders to form Al2Ti, Fe0.975Ti, Al0.9Fe3.1Ti0.025 and AlCu2Ti. The optimum performances were obtained for an alloy composition of Ti-6A-4V/Al-Cu-5Fe composite, at laser power of 800 W and scanning speed of 1.0 m min(-1). Its performance enhancement compared to the unprotected substrate comprised a significant increase in hardness from 302 to 2740 HV which translates to 89.14% in hardness values above that of the substrate. Coatings with higher hardness levels were achieved mainly due to the larger fraction of hard-intermetallic phases at lower laser scanning speeds. Finally, Ti-6Al-4V/Al-Cu-5Fe coating at laser power of 800 W and scanning speed of 1.0 m min(-1) shows the highest wear resistance performance compared to the substrate. Ti-6Al-4V/ Al-Cu-5Fe coating was 2.8 times the wear resistance performance of the substrate.

Update: 11-Jul-2018


Title:
Al-Fe-Ge: New ternary compounds and phase equilibria at 800 degrees C
Authors:
Reisinger, GR; Effenberger, HS; Richter, KW Author Full Names: Reisinger, Gabriel R.; Effenberger, Herta S.; Richter, Klaus W.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 762 849-857; 10.1016/j.jallcom.2018.05.214 SEP 25 2018
Abstract:
The isothermal sections of Al-Fe-Ge at 800 degrees C and 780 degrees C were studied by a combination of SEM/EDX with X-ray powder diffraction. Two new ternary compounds were structurally characterised by means of single-crystal XRD measurements: Al3-xFeGe2+x, I4/mcm, a = 6.2303(11) angstrom, c = 9.710(2) angstrom, V = 376.9 angstrom(3), Z = 4, R-int = 0.031, wR(2) = 0.038 and Al1+xFeGe1-x, Fddd, a = 8.627(2) angstrom, b = 4.9139(8) angstrom, c = 16.369(3) angstrom, V = 693.9 angstrom(3), Z = 16, R-int = 0.039, wR(2) = 0.053, which crystallise in the Ga5Pd and CuMg2 structure types, respectively. Considerable solid solution ranges mainly based on Al/Ge substitution were found for all binary and ternary phases present in this section. An apparently incommensurate superstructure of Al5Fe2 is triggered by Ge-additions. (C) 2018 Elsevier B.V. All rights reserved.

Title:
Liquid Exfoliation of Icosahedral Quasicrystals
Authors:
Yadav, TP; Woellner, CF; Sinha, SK; Sharifi, T; Apte, A; Mukhopadhyay, NK; Srivastava, ON; Vajtai, R; Galvao, DS; Tiwary, CS; Ajayan, PM Author Full Names: Yadav, Thakur Prasad; Woellner, Cristiano F.; Sinha, Shyam K.; Sharifi, Tiva; Apte, Amey; Mukhopadhyay, Nilay Krishna; Srivastava, Onkar Nath; Vajtai, Robert; Galvao, Douglas S.; Tiwary, Chandra Sekhar; Ajayan, Pulickel M.
Source:
ADVANCED FUNCTIONAL MATERIALS, 28 (26):10.1002/adfm.201801181 JUN 27 2018
Abstract:
The realization of quasicrystals has attracted a considerable attention due to their unusual structures and properties. The concept of quasicrystals in the atomically thin materials is even more appealing due to the in-plane covalent bonds and weak interlayer interactions. Here, it is demonstrated that 2D quasicrystals can be created/isolated from bulk phases because of long-range interlayer ordered aperiodic arrangements. An ultrasonication-assisted exfoliation of polygrained icosahedral Al-Pd-Mn quasicrystals at room temperature shows the formation of a large area of mono- and few layers in threefold quasicrystalline plane. The formation of these layers from random grain orientation consistently indicates that the threefold plane is most stable in comparison to the twofold and fivefold planes in icosahedral clusters. The above experimental observations are further supported with help of theoretical simulations. The mono- and few-layered aperiodic planes render plentiful active sites for the catalysis of hydrogen evolution reaction. The threefold 2D quasicrystalline plane exhibits a hydrogen evolution reaction overpotential of approximate to 100 mV (160 times less than bulk counterpart) and long-term durability. These systems constitute the first demonstration of quasicrystalline monolayer ordering in a free-standing thin layer without requiring the support of periodic or aperiodic substrate.

Title:
Light Localization in Local Isomorphism Classes of Quasicrystals
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, Chaney; Steinhardt, Paul J.; Torquato, Salvatore
Source:
PHYSICAL REVIEW LETTERS, 120 (24):10.1103/PhysRevLett.120.247401 JUN 14 2018
Abstract:
We study a continuum of photonic quasicrystal heterostructures derived from local isomorphism (LI) classes of pentagonal quasicrystal tilings. These tilings are obtained by direct projection from a five-dimensional hypercubic lattice. We demonstrate that, with the sole exception of the Penrose LI class, all other LI classes result in degenerate, effectively localized states, with precisely predictable and tunable properties (frequencies, frequency splittings, and densities). We show that localization and tunability are related to a mathematical property of the pattern known as "restorability," i.e., whether the tiling can be uniquely specified given only a set of rules that fix all allowed clusters smaller than some bound.

Title:
First-principles study of elastic and slip properties of non-canonical beta-based Al-Cu-Fe approximants
Authors:
Medvedeva, NI; Shalaeva, EV Author Full Names: Medvedeva, N. I.; Shalaeva, E. V.
Source:
PHILOSOPHICAL MAGAZINE, 98 (23):2135-2150; 10.1080/14786435.2018.1478145 2018
Abstract:
Ab initio calculations were carried out to compare the mechanical properties of beta-based non-canonical Al-Cu-Fe approximants of quasicrystals with cubic (beta), monoclinic (eta) and orthorhombic (xi 1, xi 2) structures, which all demonstrate high strengthening. The aim was to elucidate the competitive effects of the eta- and xi-ordering and iron content on deformation behaviour of these phases. We found that the Young's modulus, polycrystalline shear modulus, mechanical stability and shear elastic modulus G(n,m) for different slip planes decrease for beta-Al50Cu1-xFex with lowering iron content, but they grow from beta-Al50Cu31.25Fe18.75 to the ordered eta-Al50Cu45Fe5, and xi 2-Al45.5Cu50Fe4.5 that indicates a growing resistance to plastic deformation due to ordering and agrees well with our experimental finding. The preferable slip systems were predicted based on the calculated generalised stacking fault (GSF) energies in beta-(Cu,Fe)Al and eta-(Cu,Fe)Al with similar Fe concentration. The GSF energies confirmed also that the strengthening observed in eta-phase is related to ordering rather than the Fe effect in consistence with a stronger covalent bonding in eta-phase.

Title:
Interpretation of some Yb-based valence-fluctuating crystals as approximants to a dodecagonal quasicrystal
Authors:
Ishimasa, T; Mihalkovic, M; Deguchi, K; Sato, NK; de Boissieu, M Author Full Names: Ishimasa, Tsutomu; Mihalkovic, Marek; Deguchi, Kazuhiko; Sato, Noriaki K.; de Boissieu, Marc
Source:
PHILOSOPHICAL MAGAZINE, 98 (22):2018-2034; 10.1080/14786435.2018.1470339 2018
Abstract:
The hexagonal ZrNiAl-type (space group: P (6) over bar 2m) and the tetragonal Mo2FeB2-type (space group: P4/mbm) structures, which are formed in the same Yb-based alloys and exhibit physical properties related to valence-fluctuation, can be regarded as approximants of a hypothetical dodecagonal quasicrystal. Using Pd-Sn-Yb system as an example, a model of quasicrystal structure has been constructed, of which five-dimensional crystal (space group: P12/mmm, a(DD) = 5.66 angstrom and c = 3.72 angstrom) consists of four types of acceptance regions located at the following crystallographic sites; Yb [0 0 0 0 0], Pd[1/3 0 1/3 0 1/2], Pd[1/3 1/3 1/3 1/3 0] and Sn[1/2 00 1/2 1/2]. In the three-dimensional space, the quasicrystal is composed of three types of columns, of which c-projections correspond to a square, an equilateral triangle and a three-fold hexagon. They are fragments of two known crystals, the hexagonal alpha-YbPdSn and the tetragonal Yb2Pd2Sn structures. The model of the hypothetical quasicrystal may be applicable as a platform to treat in a unified manner the heavy fermion properties in the two types of Yb-based crystals.

Update: 4-Jul-2018


Title:
Evolution of Magneto-Orbital order Upon B-Site Electron Doping in Na1-xCaxMn7O12 Quadruple Perovskite Manganites
Authors:
Johnson, RD; Mezzadri, F; Manuel, P; Khalyavin, DD; Gilioli, E; Radaelli, PG Author Full Names: Johnson, R. D.; Mezzadri, F.; Manuel, P.; Khalyavin, D. D.; Gilioli, E.; Radaelli, P. G.
Source:
PHYSICAL REVIEW LETTERS, 120 (25):10.1103/PhysRevLett.120.257202 JUN 19 2018
Abstract:
We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the wellknown pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic, and orbital ordering across a wide range of compounds.

Title:
Magnetoelastic phase diagram of TbNi2B2C
Authors:
Toft-Petersen, R; Jensen, TBS; Jensen, J; von Zimmermann, M; Sloth, S; Isaksen, FW; Christensen, NB; Chen, YZ; Siemensmeyer, K; Kawano-Furukawa, H; Takeya, H; Abrahamsen, AB; Andersen, NH Author Full Names: Toft-Petersen, Rasmus; Jensen, Thomas Bagger Stibius; Jensen, Jens; von Zimmermann, Martin; Sloth, Steffen; Isaksen, Frederik Werner; Christensen, Niels Bech; Chen, Yunzhong; Siemensmeyer, Konrad; Kawano-Furukawa, Hazuki; Takeya, Hiroyuki; Abrahamsen, Asger Bech; Andersen, Niels Hessel
Source:
PHYSICAL REVIEW B, 97 (22):10.1103/PhysRevB.97.224417 JUN 15 2018
Abstract:
The magnetic phase diagram of the quaternary borocarbide TbNi2B2C is investigated by direct means and by studying magnetically induced modifications of the crystal structure. Detailed superconducting quantum interference device measurements reveal a complex phase diagram with five distinct magnetic phases. The phase boundaries aremapped out comprehensively. Synchrotron hard x-raymeasurements in appliedmagnetic fields are employed to probe the magnetoelastic distortions throughout the phase diagram. The determination of the wave vectors of these field-induced lattice deformations suggests a range of commensurate spin-slip-type magnetic structures at low temperatures with wave vectors of the form (q, 0,0) with q = 6/11 and 5/9. The proposed magnetic structures yield values of magnetization well in-line with observations. The scattering intensity due to the magnetoelastic deformations exhibits a drastic jump at the phase boundary at 1.3 T and low temperatures.

Title:
Lattice Correspondence and Growth Structures of Monoclinic Mg4Zn7 Phase Growing on an Icosahedral Quasicrystal
Authors:
Singh, A; Rosalie, JM Author Full Names: Singh, Alok; Rosalie, Julian M.
Source:
CRYSTALS, 8 (5):10.3390/cryst8050194 MAY 2018
Abstract:
Mg4Zn7 phase, with a monoclinic unit cell, a layered structure and a unique axis showing pseudo-tenfold symmetry, grows over icosahedral quasicrystalline phase in a manner similar to a decagonal quasicrystal. In this study, the relationship of this phase to icosahedral quasicrystal is brought out by a transmission electron microscopy study of Mg4Zn7 phase growing on icosahedral phase in a cast Mg-Zn-Y alloy. Lattice correspondences between the two phases have been determined by electron diffraction. Planes related to icosahedral fivefold and pseudo-twofold symmetry are identified. Possible orthogonal cells bounded by twofold symmetry-related planes have been determined. Mg4Zn7 phase growing on an icosahedral phase exhibits a number of planar faults parallel to the monoclinic axis, presumably to accommodate the quasiperiodicity at the interface. Two faults were identified, which were on {200} and {201} planes. Their structures have been determined by high resolution imaging in TEM. They produce two different unit cells at the interface.

Title:
Crystallographic features of the approximant H (Mn7Si2V) phase in the Mn-Si-V alloy system
Authors:
Nakayama, K; Komatsuzaki, T; Koyama, Y Author Full Names: Nakayama, Kei; Komatsuzaki, Takumi; Koyama, Yasumasa
Source:
PHILOSOPHICAL MAGAZINE, 98 (20):1823-1847; 10.1080/14786435.2018.1459058 2018
Abstract:
The intermetallic compound H (Mn7Si2V) phase in the Mn-Si-V alloy system can be regarded as an approximant phase of the dodecagonal quasicrystal as one of the two-dimensional quasicrystals. To understand the features of the approximant H phase, in this study, the crystallographic features of both the H phase and the (sigma H) reaction in Mn-Si-V alloy samples were investigated, mainly by transmission electron microscopy. It was found that, in the H phase, there were characteristic structural disorders with respect to an array of a dodecagonal structural unit consisting of 19 dodecagonal atomic columns. Concretely, penetrated structural units consisting of two dodecagonal structural units were presumed to be typical of such disorders. An interesting feature of the (sigma H) reaction was that regions with a rectangular arrangement of penetrated structural units (RAPU) first appeared in the sigma matrix as the initial state, and H regions were then nucleated in contact with RAPU regions. The subsequent conversion of RAPU regions into H regions eventually resulted in the formation of the approximant H state as the final state. Furthermore, atomic positions in both the H structure and the dodecagonal quasicrystal were examined using a simple plane-wave model with 12 plane waves.

Update: 27-Jun-2018


Title:
Photoinduced discommensuration of the commensurate charge-density wave phase in 1T-TaS2
Authors:
Tanimura, K Author Full Names: Tanimura, Katsumi
Source:
PHYSICAL REVIEW B, 97 (24):10.1103/PhysRevB.97.245115 JUN 11 2018
Abstract:
The dynamics induced by femtosecond-laser excitation of the commensurate phase of the charge-density wave (CDW) in 1T -TaS2 have been studied using both time-resolved electron diffraction and the time-resolved spectroscopy of coherent-phonon dynamics. Electron diffraction results show that the commensurate CDW phase is transformed into a new phase with CDW order that is similar to the nearly commensurate phase with threshold-type transition rates; the threshold excitation density of 0.2 per 13 Ta atoms is evaluated. Coherent-phonon spectroscopy results show that, together with the amplitude mode of CDW with a frequency of 2.41 THz, two other modes with frequencies of 2.34 and 2.07 THz are excited in the photoexcited commensurate CDW phase over a timescale of several tens of picoseconds after excitation. Spectroscopic, temporal, and excitation-intensity dependent characteristics of the three coherent phonons reveal that a photoinduced decomposition of the commensurate CDW order into an ensemble of domains with different CDW orders is induced before the CDW-phase transition occurs. The physics underlying the photoinduced decomposition and evolution into discommensurations responsible for the CDW-order transformation are discussed.

Title:
Adaptive modulation in the Ni2Mn1.4In0.6 magnetic shape-memory Heusler alloy
Authors:
Devi, P; Singh, S; Dutta, B; Manna, K; D'Souza, SW; Ikeda, Y; Suard, E; Petricek, V; Simon, P; Werner, P; Chadhov, S; Parkin, SSP; Felser, C; Pandey, D Author Full Names: Devi, P.; Singh, Sanjay; Dutta, B.; Manna, K.; D'Souza, S. W.; Ikeda, Y.; Suard, E.; Petricek, V; Simon, P.; Werner, P.; Chadhov, S.; Parkin, Stuart S. P.; Felser, C.; Pandey, D.
Source:
PHYSICAL REVIEW B, 97 (22):10.1103/PhysRevB.97.224102 JUN 11 2018
Abstract:
The origin of incommensurate structural modulation in Ni-Mn based Heusler-type magnetic shape-memory alloys (MSMAs) is still an unresolved issue in spite of intense focus on it due to its role in the magnetic field induced ultrahigh strains. In the archetypal MSMA Ni2MnGa, the observation of "nonuniform displacement" of atoms from their mean positions in the modulated martensite phase, premartensite phase, and charge density wave as well as the presence of phason broadening of satellite peaks has been taken in support of the electronic instability model linked with a soft acoustic phonon. We present here results of a combined high-resolution synchrotron x-ray powder diffraction (SXRPD) and neutron powder diffraction (NPD) study on Ni2Mn1.4In0.6 using a (3+1)D superspace group approach, which reveals not only uniform atomic displacements in the modulated structure of the martensite phase with physically acceptable ordered magnetic moments in the antiferromagnetic phase at low temperatures, but also the absence of any premartensite phase and phason broadening of the satellite peaks. Our HRTEM studies and first-principles calculations of the ground state also support uniform atomic displacements predicted by powder diffraction studies. All these observations suggest that the structural modulation in the martensite phase of Ni(2)Mn(1.4)In(0.6 )MSMA can be explained in terms of the adaptive phase model. The present study underlines the importance of superspace group analysis using complementary SXRPD and NPD in understanding the physics of the origin of modulation as well as the magnetic and the modulated ground states of the Heusler-type MSMAs. Our work also highlights the fact that the mechanism responsible for the origin of modulated structure in different Ni-Mn based MSMAs may not be universal and it must be investigated thoroughly in different alloy compositions.

Title:
Breakdown of Magnetic Order in the Pressurized Kitaev Iridate beta-Li2IrO3
Authors:
Majumder, M; Manna, RS; Simutis, G; Orain, JC; Dey, T; Freund, F; Jesche, A; Khasanov, R; Biswas, PK; Bykova, E; Dubrovinskaia, N; Dubrovinsky, LS; Yadav, R; Hozoi, L; Nishimoto, S; Tsirlin, AA; Gegenwart, P Author Full Names: Majumder, M.; Manna, R. S.; Simutis, G.; Orain, J. C.; Dey, T.; Freund, F.; Jesche, A.; Khasanov, R.; Biswas, P. K.; Bykova, E.; Dubrovinskaia, N.; Dubrovinsky, L. S.; Yadav, R.; Hozoi, L.; Nishimoto, S.; Tsirlin, A. A.; Gegenwart, P.
Source:
PHYSICAL REVIEW LETTERS, 120 (23):10.1103/PhysRevLett.120.237202 JUN 8 2018
Abstract:
Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate beta-Li2IrO3 is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Neel temperature of beta-Li2IrO3 increases with the slope of 0.9 K/GPa upon initial compression, but the reduction in the polarization field Hc reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate the classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange Gamma under pressure.

Title:
Dynamically enhanced magnetic incommensurability: Effects of local dynamics on nonlocal spin correlations in a strongly correlated metal
Authors:
Vilardi, D; Taranto, C; Metzner, W Author Full Names: Vilardi, Demetrio; Taranto, Ciro; Metzner, Walter
Source:
PHYSICAL REVIEW B, 97 (23):10.1103/PhysRevR.97.235110 JUN 7 2018
Abstract:
We compute the spin susceptibility of the two-dimensional Hubbard model away from half-filling, and analyze the impact of frequency-dependent vertex corrections as obtained from the dynamical mean field theory (DMFT). We find that the local dynamics captured by the DMFT vertex strongly affects nonlocal spin correlations, and thus the momentum dependence of the spin susceptibility. While the widely used random-phase approximation yields commensurate Neel-type antiferromagnetism as the dominant instability over a wide doping range, the vertex corrections favor incommensurate ordering wave vectors away from(pi,pi). Our results indicate that the connection between the magnetic ordering wave vector and the Fermi surface geometry, familiar for weakly interacting systems, can hold in a strongly correlated metal, too.

Title:
Structural phase transitions in YPtGe2 and GdPtGe2
Authors:
Janka, O; Hoffmann, RD; Heying, B; Pottgen, R Author Full Names: Janka, Oliver; Hoffmann, Rolf-Dieter; Heying, Birgit; Poettgen, Rainer
Source:
DALTON TRANSACTIONS, 47 (17):6075-6088; 10.1039/c8dt00815a MAY 7 2018
Abstract:
The germanides YPtGe2 and GdPtGe2 were synthesized from REGe2 precursor compounds and platinum by arc-melting and their structures were studied on the basis of temperature-dependent single crystal X-ray diffraction data. At room temperature both germanides adopt the orthorhombic YIrGe2 type structure, space group Immm, with enhanced U-11 displacement parameters for the Ge1 atoms. Below 174 and 145 K, respectively, satellite reflections emerge in the diffraction patterns, giving rise to modulations. The low-temperature structures were refined in the superspace group Pnnn(1/2,1/2,gamma)qq0 (48.1.11.3). The structural phase transition is also evident in the magnetic susceptibility, specific heat and resistivity data. The high-and low-temperature modifications are discussed on the basis of a group-subgroup scheme.

Update: 20-Jun-2018


Title:
Preparation and nanoscopic plastic deformation of toughened Al-Cu-Fe-based quasicrystal/vanadium multilayered coatings
Authors:
Chang, SY; Chen, BJ; Hsiao, YT; Wang, DS; Chen, TS; Leu, MS; Lai, HJ Author Full Names: Chang, Shou-Yi; Chen, Bo-Jien; Hsiao, Yu-Ting; Wang, Ding-Shiang; Chen, Tai-Sheng; Leu, Ming-Sheng; Lai, Hong-Jen
Source:
MATERIALS CHEMISTRY AND PHYSICS, 213 277-284; 10.1016/j.matchemphys.2018.04.045 JUL 1 2018
Abstract:
Ductile vanadium layers were alternately deposited with brittle aluminum-copper-iron-based quasicrystal-alloy layers to form multilayered coatings. The in-situ transmission electron microscopic observations of nanopillar compression revealed that the as-deposited single-layered amorphous aluminum-copper-iron alloy slightly deformed via shear banding. After annealing at 800 degrees C, brittle quasicrystal and intermetallic compounds were formed, so the single-layered coating cracked and peeled. In comparison, the multilayered coatings were effectively toughened. The multilayered nanopillars plastically deformed via dislocation activities and were work hardened owing to confined dislocation gliding. The as-deposited multilayered structure (amorphous alloy/crystalline vanadium) had a low 10% flow stress of 1.72 GPa, while the annealed multilayered structure (quasicrystal/vanadium) presented a high flow stress of 2.58 GPa owing to quasicrystal strengthening. Dislocation clusters were in-situ observed to glide laterally in the crystalline vanadium layers and move vertically through the vanadium and quasicrystal layers, yielding an improved plasticity. (C) 2018 Elsevier B.V. All rights reserved.

Title:
Growth of two-dimensional decagonal colloidal quasicrystals
Authors:
Martinsons, M; Schmiedeberg, M Author Full Names: Martinsons, M.; Schmiedeberg, M.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (25):10.1088/1361-648X/aac503 JUN 27 2018
Abstract:
The growth of quasicrystals, i.e. structures with long-range positional order but no periodic translational symmetry, is more complex than the growth of periodic crystals. By employing Brownian dynamics simulations in two dimensions for colloidal particles that interact according to an isotropic pair potential with two incommensurate lengths, we study the growth of quasicrystalline structures by sequentially depositing particles at their surface. We quantify the occurrence of quasicrystalline order as a function of the temperature and the rate of added particles. In addition, we explore defects like local triangular order or gaps within the quasicrystalline structure. Furthermore, we analyze the shapes of the surfaces in grown structures which tend to build straight lines along the symmetry axes of the quasicrystal. Finally, we identify phasonic flips which are rearrangements of the particles due to additional degrees of freedom. The number of phasonic flips decreases with the distance to the surface.

Title:
Identification of a secondary phase Ga2O3(ZnO)m in Ga-doped ZnO thermoelectric materials by a (3+1)-dimensional superspace model
Authors:
Michiue, Y; Mori, T Author Full Names: Michiue, Yuichi; Mori, Takao
Source:
JOURNAL OF APPLIED CRYSTALLOGRAPHY, 51 924-927; 10.1107/S1600576718004119 3 JUN 2018
Abstract:
A unified structure model for the homologous compounds Ga2O3(ZnO)(m) in (3 + 1)-dimensional superspace was modified by refinements for samples of Ga2O3:ZnO = 1:n (n = 15, 23, 28, 33, 38). The first-order sine terms in the modulation functions decreased with increasing phase index m. The diffraction intensities of the thermoelectric material Ga2O3:ZnO = 1:98 were best fitted by a two-phase model containing the wurtzite structure (Ga-doped ZnO) and the homologous compound Ga2O3(ZnO)(s), where s = 38.

Title:
Commensurate versus incommensurate charge ordering near the superconducting dome in Ir1-xPtxTe2 revealed by resonant x-ray scattering
Authors:
Takubo, K; Yamamoto, K; Hirata, Y; Wadati, H; Mizokawa, T; Sutarto, R; He, F; Ishii, K; Yamasaki, Y; Nakao, H; Murakami, Y; Matsuo, G; Ishii, H; Kobayashi, M; Kudo, K; Nohara, M Author Full Names: Takubo, K.; Yamamoto, K.; Hirata, Y.; Wadati, H.; Mizokawa, T.; Sutarto, R.; He, F.; Ishii, K.; Yamasaki, Y.; Nakao, H.; Murakami, Y.; Matsuo, G.; Ishii, H.; Kobayashi, M.; Kudo, K.; Nohara, M.
Source:
PHYSICAL REVIEW B, 97 (20):10.1103/PhysRevB.97.205142 MAY 31 2018
Abstract:
The electronic-structural modulations of Ir1-xPtxTe2 (0 <= x <= 0.12) have been examined by resonant elastic x-ray scattering (REXS) and resonant inelastic x-ray scattering (RIXS) techniques at both the Ir and Te edges. Charge-density-wave-like superstructures with wave vectors of Q = (1/5 0 - 1/5), (1/8 0 - 1/8), and (1/6 0 - 1/6) are observed on the same sample of IrTe2 at the lowest temperature, the patterns of which are controlled by the cooling speeds. In contrast, superstructures around Q = (1/5 0 - 1/5) are observed for doped samples (0.02 <= x <= 0.05). The superstructure reflections persist to higher Pt substitution than previously assumed, demonstrating that a charge-density wave (CDW) can coexist with superconductivity. The analysis of the energy-dependent REXS and RIXS line shape reveals the importance of the Te 5p state rather than the Ir 5d states in the formation of the spatial modulation of these systems. The phase diagram reexamined in this work suggests that the CDW incommensurability may correlate with the emergence of superconducting states such as CuxTiSe2 and LixTaS2.

Title:
Dipole-dipole interactions and incommensurate order in perovskite structures
Authors:
Burkovsky, RG Author Full Names: Burkovsky, R. G.
Source:
PHYSICAL REVIEW B, 97 (18):10.1103/PhysRevB.97.184109 MAY 31 2018
Abstract:
Dipole-dipole (DD) interactions are known to play an important role in conditioning ferroelectricity in ABO(3) perovskite crystals. Their possible role in conditioning nonferroelectric (inhomogeneous) cation ordering is presently unexplored. I analyze the energy of DD interactions in perovskite structure for different inhomogeneous spatial patterns of electric dipoles localized at the lattice sites. I show that DD interactions can favor inhomogeneous ordering when other terms of the Hamiltonian allow large total polarizability of A sites, comparably large total polarizability of oxygen sites in A-O planes, and relatively weak total polarizability of oxygen sites in the B-O direction. These conditions are naturally expected in PbZrO3 crystals, for which the reason behind antiferroelectric and incommensurate inhomogeneous ordering is currently being debated.

Title:
Magnetic structure of Ho0.5Y0.5Mn6Sn6 compound studied by powder neutron diffraction
Authors:
Li, XY; Peng, LC; He, LH; Zhang, SY; Yao, JL; Zhang, Y; Wang, FW Author Full Names: Li, X-Y.; Peng, L-C.; He, L-H.; Zhang, S-Y.; Yao, J-L.; Zhang, Y.; Wang, F-W.
Source:
JOURNAL OF APPLIED PHYSICS, 123 (20):10.1063/1.5029707 MAY 28 2018
Abstract:
The crystallographic and magnetic structures of the HfFe6Ge6-type compound Ho0.5Y0.5Mn6Sn6 have been studied by powder neutron diffraction and in-situ Lorentz transmission electron microscopy. Besides the nonlinear thermal expansion of lattice parameters, an incommensurate conical spiral magnetic structure was determined in the temperature interval of 2-340 K. A spin reorientation transition has been observed from 50 to 300 K, where the alignment of the c-axis component of magnetic moments of the Ho sublattice and the Mn sublattice transfers from ferrimagnetic to ferromagnetic. Published by AIP Publishing.

Update: 13-Jun-2018


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

Update: 6-Jun-2018


Title:
Coexistence of charge density wave and incommensurate antiferromagnetism in the cubic phase of DyGe2.85 synthesised under high pressure
Authors:
Salamatin, DA; Sidorov, VA; Kichanov, SE; Velichkov, A; Salamatin, AV; Fomicheva, LN; Kozlenko, DP; Nikolaev, AV; Menzel, D; Budzynski, M; Tsvyashchenko, AV Author Full Names: Salamatin, D. A.; Sidorov, V. A.; Kichanov, S. E.; Velichkov, A.; Salamatin, A. V.; Fomicheva, L. N.; Kozlenko, D. P.; Nikolaev, A. V.; Menzel, D.; Budzynski, M.; Tsvyashchenko, A. V.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 755 10-14; 10.1016/j.jallcom.2018.04.319 JUL 30 2018
Abstract:
A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P <= 3.1 GPa), neutron powder diffraction and time-differential gamma-gamma perturbed angular correlations (TDPAC) using Cd-111 nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature T-CDW = 80 K with charge density wave formation and the second transition at T-N approximate to 18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them. (C) 2018 Elsevier B.V. All rights reserved.

Title:
PERFECTLY ORDERED QUASICRYSTALS AND THE LITTLEWOOD CONJECTURE
Authors:
Haynes, A; Koivusalo, H; Walton, J Author Full Names: Haynes, Alan; Koivusalo, Henna; Walton, James
Source:
TRANSACTIONS OF THE AMERICAN MATHEMATICAL SOCIETY, 370 (7):4975-4992; 10.1090/tran/7136 JUL 2018
Abstract:
Linearly repetitive cut and project sets are mathematical models for perfectly ordered quasicrystals. In a previous paper we presented a characterization of linearly repetitive cut and project sets. In this paper we extend the classical definition of linear repetitivity to try to discover whether or not there is a natural class of cut and project sets which are models for quasicrystals which are better than 'perfectly ordered'. In the positive direction, we demonstrate an uncountable collection of such sets (in fact, a collection with large Hausdorff dimension) for every choice of dimension of the physical space. On the other hand, we show that, for many natural versions of the problems under consideration, the existence of these sets turns out to be equivalent to the negation of a well-known open problem in Diophantine approximation, the Littlewood conjecture.

Title:
Improved electrochemical hydrogen storage capacity of Ti45Zr38Ni17 quasicrystal by addition of ZrH2
Authors:
Zhao, JX; Zhai, XJ; Tao, X; Li, Z; Wang, QS; Liu, WQ; Wang, LM Author Full Names: Zhao, Jianxun; Zhai, Xiaojie; Tao, Xing; Li, Zhe; Wang, Qingshuang; Liu, Wanqiang; Wang, Limin
Source:
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 34 (6):995-998; 10.1016/j.jmst.2017.10.006 JUN 2018
Abstract:
Ti45Zr38Ni17 + xZrH(2) (x = 5, 10, 15 and 20 wt%) composite materials are produced by ball milling for 20 min. The results of XRD measurement show that the composite materials contain icosahedral quasicrystal phase (I-phase), FCC phase with a Ti2Ni type crystal and C14 Laves phase. After adding ZrH2, the composite materials include not only the individual phases mentioned above, but also the ZrH phase. These composite materials are used as the negative electrode material of the nickel-metal hydride batteries. The electrochemical hydrogen storage characteristics of the material after adding ZrH is investigated. The Ti45Zr38Ni17 + xZrH(2) (x = 5, 10, 15 and 20 wt%) composite material has reached the maximum discharge capacity (83.2 mA h/g) when x equals 10. This maximum discharge capacity is much higher than that of Ti(45)Zr(38)Ni(17 )alloy without ZrH. After adding ZrH2, the high-rate discharge ability and the cycling stability are enhanced simultaneously. The improvement of the electrochemical properties can be attributed to the synergistic effects of ZrH2, and the synergistic effects in the composite electrodes are probably attributed to the entry of most of hydrogen atoms from weakly bond strength of the Zr-H to the I-phase structure in electrochemical reaction. (C) 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Title:
Epitaxial growth of a metastable icosahedral quasicrystal on a stable icosahedral quasicrystal substrate
Authors:
Leskovar, B; Sturm, S; Samardzija, Z; Ambrozic, B; Markoli, B; Naglic, I Author Full Names: Leskovar, Blaz; Sturm, Saso; Samardzija, Zoran; Ambrozic, Bojan; Markoli, Bostjan; Naglic, Iztok
Source:
SCRIPTA MATERIALIA, 150 92-95; 10.1016/j.scriptamat.2018.03.014 JUN 2018
Abstract:
This study confirms that the stable icosahedral quasicrystal (iQc) phase Al65Cu20Fe15(iQc-AlCuFe) can serve as a substrate for the nucleation of the metastable iQc-AlMnSi phase formed in rapidly solidified Al-Mn-Si alloys. The results reveal that a continuous, thin layer of the metastable iQc-AlMnSi phase can be formed on a stable iQc-AlCuFe particle. Electron backscatter diffraction patterns and selected-area electron diffraction patterns confirmed that epitaxy exists between the stable and the metastable iQc phases. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Magnetic field induced evolution of intertwined orders in the Kitaev magnet beta-Li2IrO3
Authors:
Rousochatzakis, I; Perkins, NB Author Full Names: Rousochatzakis, Ioannis; Perkins, Natalia B.
Source:
PHYSICAL REVIEW B, 97 (17):10.1103/PhysRevB.97.174423 MAY 24 2018
Abstract:
Recent scattering experiments in the 3D Kitaev magnet beta-Li2IrO3 have shown that a relatively weak magnetic field along the crystallographic b axis drives the system from its incommensurate counter-rotating order to a correlated magnet, with a significant uniform 'zigzag' component superimposing the magnetization along the field. Here it is shown that the zigzag order is not emerging from its linear coupling to the field (via a staggered, off-diagonal element of the g tensor) but from its intertwining with the incommensurate order and the longitudinal magnetization. The emerging picture explains all qualitative experimental findings at zero and finite fields, including the rapid decline of the incommensurate order with field and the so-called intensity sum rule. The latter are shown to be independent signatures of the smallness of the Heisenberg exchange J, compared to the Kitaev coupling K and the off-diagonal anisotropy Gamma. Remarkably, in the regime of interest, the field H* at which the incommensurate component vanishes, depends essentially only on J, which allows us to extract an estimate of J similar or equal to 4 K from reported measurements of H*. We also comment on recent experiments in pressurized beta-Li2IrO3 and conclude that J decreases with pressure.

Title:
Polarized neutron scattering study of the multiple order parameter system NdB4
Authors:
Metoki, N; Yamauchi, H; Matsuda, M; Fernandez-Baca, JA; Watanuki, R; Hagihala, M Author Full Names: Metoki, N.; Yamauchi, H.; Matsuda, M.; Fernandez-Baca, J. A.; Watanuki, R.; Hagihala, M.
Source:
PHYSICAL REVIEW B, 97 (17):10.1103.PhysRevB.97.174416 MAY 17 2018
Abstract:
Neutron polarization analysis has been carried out in order to clarify the magnetic structures of multiple order parameter f-electron system NdB4. We confirmed the noncollinear "all-in all-out" structure (Gamma(4)) of the in-plane moment, which is in good agreement with our previous neutron powder diffraction study. We found that the magnetic moment along the c-axis m(c) showed diagonally antiferromagnetic structure (Gamma(10)), inconsistent with previously reported "vortex" structure (Gamma(2)). The microscopic mixture of these two structures with (q) over right arrow 0 = (0,0,0) appears in phase II and remains stable in phases III and IV, where an incommensurate modulation coexists. The unusual magnetic ordering is phenomenologically understood via Landau theory with the primary order parameter Gamma(4) coupled with higher-order secondary order parameter Gamma(10). The magnetic moments were estimated to be 1.8 +/- 0.2 and 0.2 +/- 0.05 mu B at T = 7.5 K for Gamma(4) and Gamma(10), respectively. We also found along-penod incommensurate modulation of the (q) over right arrow1 = (0,0,1 /2) antiferromagnetic structure of m(c) with the propagation (q) over right arrow (s1)= (0.14, 0.14, 0.1) and <(q) over right arrow>(s2) = (0.2,0,0.1) in phase III and IV, respectively. The amplitude of sinusoidal modulation was about m(c) = 1.0 +/- 0.2 mu B at T=1.5 K. The local (0,0,1 /2) structure consists of in-plane ferromagnetic and out-of-plane antiferromagnetic coupling of m(c), opposite to the coexisting Gamma(10). The m(c) of Gamma(10) is significantly enhanced up to 0.6 mu B at T=1.5 K, which is accompanied by the incommensurate modulations. The Landau phenomenological approach indicates that the higher-order magnetic and/or multipole interactions based on the pseudoquartet f-electron state play important roles.

Title:
Structural and electronic properties of the alkali metal incommensurate phases
Authors:
Woolman, G; Robinson, VN; Marques, M; Loa, I; Ackland, GJ; Hermann, A Author Full Names: Woolman, Gavin; Robinson, Victor Naden; Marques, Miriam; Loa, Ingo; Ackland, Graeme J.; Hermann, Andreas
Source:
PHYSICAL REVIEW MATERIALS, 2 (5):10.1103/PhysRevMaterials.2.053604 MAY 11 2018
Abstract:
Under pressure, the alkali elements sodium, potassium, and rubidium adopt nonperiodic structures based on two incommensurate interpenetrating lattices. While all elements form the same "host" lattice, their "guest" lattices are all distinct. The physical mechanism that stabilizes these phases is not known, and detailed calculations are challenging due to the incommensurability of the lattices. Using a series of commensurate approximant structures, we tackle this issue using density functional theory calculations. In Na and K, the calculations prove accurate enough to reproduce not only the stability of the host-guest phases, but also the complicated pressure dependence of the host-guest ratio and the two guest-lattice transitions. We find Rb-IV to be metastable at all pressures, and suggest it is a high-temperature phase. The electronic structure of these materials is unique: they exhibit two distinct, coexisting types of electride behavior, with both fully localized pseudo anions and electrons localized in 1D wells in the host lattice, leading to low conductivity. While all phases feature pseudogaps in the electronic density of states, the perturbative free-electron picture applies to Na, but not to K and Rb, due to significant d-orbital population in the latter.

Update: 23-May-2018


Title:
Dzyaloshinskii-Moriya interaction and magnetic anisotropies in Uranium compounds
Authors:
Sandratskii, LM Author Full Names: Sandratskii, L. M.
Source:
PHYSICA B-CONDENSED MATTER, 536 512-515; 10.1016/j.physb.2017.11.014 MAY 1 2018
Abstract:
We report on the first-principles study of complex noncollinear magnetic structures in Uranium compounds. We contrast two cases. The first is the periodic magnetic structure of U2Pd2In with exactly orthogonal atomic moments, the second is an incommensurate plane spiral structure of UPtGe where the angle between atomic moments of nearest neighbors is also close to 90 degrees. We demonstrate that the hierarchy of magnetic interactions leading to the formation of the magnetic structure is opposite in the two cases. In U2Pd2In, the magnetic anisotropy plays the leading role, followed by the Dzyaloshinskii-Moriya interaction (DMI) interaction specifying the chirality of the structure. Here, the interatomic exchange interaction does not play important role. In UPtGe the hierarchy of the interactions is opposite. The leading interaction is the interatomic exchange interaction responsible for the formation of the incommensurate spiral structure followed by the DMI responsible for the selected chirality of the helix. The magnetic anisotropy is very weak that is a prerequisite for keeping the distortion of the helical structure weak.

Title:
Magnetic excitations in the orbital disordered phase of MnV2O4
Authors:
Matsuura, K; Sagayama, H; Uehara, A; Nii, Y; Kajimoto, R; Kamazawa, K; Ikeuchi, K; Ji, S; Abe, N; Arima, TH Author Full Names: Matsuura, Keisuke; Sagayama, Hajime; Uehara, Amane; Nii, Yoichi; Kajimoto, Ryoichi; Kamazawa, Kazuya; Ikeuchi, Kazuhiko; Ji, Sungdae; Abe, Nobuyuki; Arima, Taka-hisa
Source:
PHYSICA B-CONDENSED MATTER, 536 372-376; 10.1016/j.physb.2017.09.085 MAY 1 2018
Abstract:
We have investigated the temperature dependence of magnetic dynamics in a spinel-type vanadium oxide MnV2O4 by inelastic neutron scattering. The scattering intensity of excitation around 20 meV disappears in the collinear intermediate-temperature cubic-ferrimagnetic phase, which reveals that this excitation should be peculiar to the orbital ordered phase. We have found a weakly dispersive mode emergent from a non-integer wavevector (1.4,1.4,0) at 56 K, which lies in the cubic-ferrimagnetic phase between non-coplanar ferrimagnetic and paramagnetic phases. This indicates that the probable presence of an incommensurate instability in the simple collinear structure.

Title:
Magnetic and thermodynamic studies on the charge and spin ordering in the highly-doped La2-xSrxCoO4
Authors:
Yoshida, M; Ueta, D; Ikeda, Y; Yokoo, T; Itoh, S; Yoshizawa, H Author Full Names: Yoshida, Masahiro; Ueta, Daichi; Ikeda, Yoichi; Yokoo, Tetsuya; Itoh, Shinichi; Yoshizawa, Hideki
Source:
PHYSICA B-CONDENSED MATTER, 536 338-341; 10.1016/j.physb.2017.10.081 MAY 1 2018
Abstract:
We report magnetic studies on the charge and spin ordering in La2-xSrxCoO4 for x = 1/3, 0.60, and 0.75. The magnetic susceptibility displays a clear cusp which we attribute to a spin glass freezing transition in all three compositions stduied. The behaviors of the evaluated effective magnetic moment and Curie-Weiss temperature indicate that the antiferromagnetic (AFM) interaction among Co2+ ions surrounded by the non-magnetic Co3+ weakens with increasing the doping concentration x. In addition, we have found that the incommensurate AFM short range order is frozen at T-g which is further below the onset temperature TIC of the neutron intensity of the incommensurate AFM correlation.

Title:
Detailed study of the structure of the low-energy magnetic excitations in overdoped La1.75Sr0.25CuO4
Authors:
Ikeuchi, K; Kikuchi, T; Nakajima, K; Kajimoto, R; Wakimoto, S; Fujita, M Author Full Names: Ikeuchi, Kazuhiko; Kikuchi, Tatsuya; Nakajima, Kenji; Kajimoto, Ryoichi; Wakimoto, Shuichi; Fujita, Masaki
Source:
PHYSICA B-CONDENSED MATTER, 536 717-719; 10.1016/j.physb.2017.11.022 MAY 1 2018
Abstract:
To examine the detailed structure of low-energy magnetic excitations in a high-transition-temperature superconducting cuprate with heavily hole-doping, we performed inelastic neutron scattering experiments on La1.75Sr0.25CuO4. We observed clear dispersion relations of the previously reported incommensurate (IC) magnetic correlations at Qtet = (0.5 +/- d, 0.5)/(0.5, 0.5 +/- delta) [1]. In addition, we show the emergence of continuum magnetic excitations with a ring shape centered at G point Q(tet) = (0.5, 0.5) in a constant energy spectrum at Gamma = 50K. The radius of the ring (r = 0.109) is smaller than the incommensurability (delta = 0.118). This suggests that the origin of the ring-like excitations is different from that of the IC magnetic correlations, and the low-energy magnetic excitations of the La2-xSrxCuO4 system are inherently composed of these two kinds of excitations.

Title:
Fluctuation effects at the onset of the 2k(F) density wave order with one pair of hot spots in two-dimensional metals
Authors:
Sykora, J; Holder, T; Metzner, W Author Full Names: Sykora, Jachym; Holder, Tobias; Metzner, Walter
Source:
PHYSICAL REVIEW B, 97 (15):10.1103/PhysRevB.97.155159 APR 30 2018
Abstract:
We analyze quantum fluctuation effects at the onset of charge or spin density wave order in two-dimensional metals with an incommensurate 2k(F) wave vector connecting a single pair of hot spots on the Fermi surface. We compute the momentum and frequency dependence of the fermion self-energy near the hot spots to leading order in a fluctuation expansion (one loop). Non-Fermi liquid behavior with anomalous frequency scaling and a vanishing quasiparticle weight is obtained. The momentum dependence yields a divergent renormalization of the Fermi velocity and a flattening of the Fermi surface near the hot spots. Going beyond the leading-order calculation, we find that the one-loop result is not self-consistent. We show that any momentum-independent self-energy with a non-Fermi liquid frequency exponent wipes out the peak of the polarization function at the 2k(F) wave vector, and thus destroys the mechanism favoring 2k(F) density waves over those with generic wave vectors. However, a 2k(F) density wave quantum critical point might survive in presence of a sufficiently flat renormalized Fermi surface.

Title:
Refinement of the Modulated Structures of Pb-Free and Pb-Doped Bi-2223 HTSC
Authors:
Shcherban, O; Akselrud, L; Giannini, E; Gladyshevskii, R Author Full Names: Shcherban, O.; Akselrud, L.; Giannini, E.; Gladyshevskii, R.
Source:
ACTA PHYSICA POLONICA A, 133 (4):1027-1029; 10.12693/APhysPolA.133.1027 APR 2018
Abstract:
The incommensurate modulated structures of Pb-free and Pb-doped Bi-2223 phases were refined on single crystal X-ray diffraction data.

Update: 16-May-2018


Title:
First-principles study of giant thermoelectric power in incommensurate TlInSe2
Authors:
Ishikawa, M; Nakayama, T; Wakita, K; Shim, YG; Mamedov, N Author Full Names: Ishikawa, M.; Nakayama, T.; Wakita, K.; Shim, Y. G.; Mamedov, N.
Source:
JOURNAL OF APPLIED PHYSICS, 123 (16):10.1063/1.5011337 APR 28 2018
Abstract:
Ternary thallium compound TlInSe2 exhibits a giant Seebeck effect below around 410 K, where Tl atoms form one dimensional incommensurate (IC) arrays. To clarify the origin of large thermoelectric power in the IC phase, the electronic properties of Tl-atom super-structured TlInSe2 were studied using the first-principles calculations. It was shown that the super-structures induce strong binding states between Se-p orbitals in the nearest neighboring layers and produce large density of states near lower conduction bands, which might be one of the origins to produce large thermoelectric power. Published by AIP Publishing.

Title:
The Effect of Doping on the Corrosion Behavior of Quasi-Crystalline Alloys in the Al-Cu-Fe-Cr System
Authors:
Chugunov, DB; Klyuchagina, AN; Meshkov, LL; Osipov, AK Author Full Names: Chugunov, D. B.; Klyuchagina, A. N.; Meshkov, L. L.; Osipov, A. K.
Source:
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES, 54 (2):301-307; 10.1134/S2070205118020041 MAR 2018
Abstract:
The electrochemical behavior of five alloys of variable compositions in the Al65Cu25Fe10-N... Cr (N...) system in dependence on the number of QC phases in acidic and alkaline media has been investigated by the potentiodynamic method. It has been established that the samples' corrosion stabilities increase along with the increase of the solution pH. Higher stability was manifested by alloys with a predominant quasi-crystalline (dexagonal and icosahedral) structural component.

Update: 9-May-2018


Title:
Field-induced magnetic phase transitions and metastable states in Tb3Ni
Authors:
Gubkin, AF; Wu, LS; Nikitin, SE; Suslov, AV; Podlesnyak, A; Prokhnenko, O; Prokes, K; Yokaichiya, F; Keller, L; Baranov, NV Author Full Names: Gubkin, A. F.; Wu, L. S.; Nikitin, S. E.; Suslov, A. V.; Podlesnyak, A.; Prokhnenko, O.; Prokes, K.; Yokaichiya, F.; Keller, L.; Baranov, N. V.
Source:
PHYSICAL REVIEW B, 97 (13):10.1103/PhysRevB.97.134425 APR 26 2018
Abstract:
In this paper we report the detailed study of magnetic phase diagrams, low-temperature magnetic structures, and the magnetic field effect on the electrical resistivity of the binary intermetallic compound Tb3Ni. The incommensurate magnetic structure of the spin-density-wave type described with magnetic superspace group P112(1)/a1'(ab0)0ss and propagation vector k(IC) = [0.506, 0.299,0] was found to emerge just below Neel temperature T-N = 61 K. Further cooling below 58 K results in the appearance of multicomponent magnetic states: (i) a combination of k(1) = [1/2, 1/2, 0] and k(IC) in the temperature range 51 < T < 58 K; (ii) a mixed magnetic state of k(IC), k(1), and k(2) = [1/2, 1/4, 0] with the partially locked-in incommensurate component in the temperature range 48 < T < 51 K; and (iii) a low-temperature magnetic structure that is described by the intersection of two isotropy subgroups associated with the irreducible representations of two coupled primary order parameters (OPs) k(2) = [1/2, 1/4, 0] and k(3) = [1/2, 1/3, 0] and involves irreducible representations of the secondary OPs k(1) = [1/2, 1/2, 0] and k(4) = [1/2, 0, 0] below 48 K. An external magnetic field suppresses the complex low-temperature antiferromagnetic states and induces metamagnetic transitions towards a forced ferromagnetic state that are accompanied by a substantial magnetoresistance effect due to the magnetic superzone effect. The forced ferromagnetic state induced after application of an external magnetic field along the b and c crystallographic axes was found to be irreversible below 3 and 8 K, respectively.

Title:
Improved electrochemical hydrogen storage performance of Ti49Zr26Ni25 quasicrystal alloy by doping with mesoporous alpha-Fe2O3 particles
Authors:
Liu, H; Zhai, XJ; Li, Z; Tao, X; Liu, WQ; Zhao, JX Author Full Names: Liu, Heng; Zhai, Xiaojie; Li, Zhe; Tao, Xing; Liu, Wanqiang; Zhao, Jianxun
Source:
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 43 (15):7447-7455; 10.1016/j.ijhydene.2018.02.149 APR 12 2018
Abstract:
A Ti49Zr26Ni25 quasicrystal alloy was prepared by mechanical alloying and subsequent annealing. Mesoporous alpha-Fe2O3 particles were obtained via a hydro-thermal procedure using chitosan as the template. Composites of Ti49Zr26Ni25 mixed with different amounts of mesoporous alpha-Fe2O3 were synthesized to enhance the electrochemical properties of Ti49Zr26Ni25. The structural characteristics of the alloy and composites were investigated using XRD, SEM, TEM and BET analysis. The electrochemical properties of the composite electrodes were tested using a three-electrode battery system at room temperature. The discharge capacities for the composites were higher than those for the Ti49Zr26Ni25 alloy and reached a maximum (259.6 mAh/g) for 5% additive content of alpha-Fe2O3. Moreover, the composites showed enhanced high-rate dischargeability. The capacity decay rate and charge-transfer resistance decreased after alpha-Fe2O3 loading. The preferable performance of the composite alloys may be attributed to the doping of mesoporous alpha-Fe2O3, which may play a catalytic effect in the kinetics of the electrochemical reactions. The large surface area and mesoporous structure of alpha-Fe2O3 may also be advantageous for rapid transmission of hydrogen in the interior of the alloy, thus improving the discharge capacity of the alloy electrode. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Update: 2-May-2018


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

Update: 25-Apr-2018


Title:
Large-sized quasi-crystals with continuously adjustable compositions
Authors:
Li, ZJ; Zhao, LR; Pan, SP; Fan, CZ; Qiang, JB; Dong, C; Wang, LM Author Full Names: Li, Zijing; Zhao, Linran; Pan, Shaopeng; Fan, Changzeng; Qiang, Jianbing; Dong, Chuang; Wang, Li-Min
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 746 356-360; 10.1016/j.jallcom.2018.02.341 MAY 25 2018
Abstract:
The quasi-crystal-forming alloys with adjustable compositions were prepared by element-addition to a pre-existing pure quasi-crystalline system. The protocol alloy Zr40Ti40Ni20 was chosen as the parent alloy, and beryllium was used as the additive element. The quasi-crystal forming ability was found to be enhanced with Be content within a wide composition range of (Zr40Ti40Ni20)(100-x)Be-x (0 <= x <= 16). A maximum size of up to 10mm in diameter of pure quasi-crystalline rod was attained at a composition of (Zr40Ti40Ni20)(84)Be-16. Structural analyses show that Be-addition continuously reduces the interplanar spacing. The mechanism of the enhanced quasi-crystal forming ability was also discussed. (c) 2018 Elsevier B.V. All rights reserved.

Title:
Effects of crystalline electronic field and onsite interorbital interaction in Yb-based quasicrystal and approximant crystal
Authors:
Watanabe, S; Miyake, K Author Full Names: Watanabe, Shinji; Miyake, Kazumasa
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (18):10.1088/1361-648X/aab817 MAY 10 2018
Abstract:
To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb15Al34Au51 and approximant crystal (AC) Yb14Al35Au51 under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculations for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb15Al34Au51 is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.

Title:
Partially-devitrified icosahedral quasicrystalline phase in Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 amorphous alloys with near equi-atomic compositions
Authors:
Takeuchi, A; Amiya, K; Yubuta, K Author Full Names: Takeuchi, A.; Amiya, K.; Yubuta, K.
Source:
MATERIALS CHEMISTRY AND PHYSICS, 210 245-250; SI 10.1016/j.matchemphys.2017.10.057 MAY 1 2018
Abstract:
Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were investigated for their possibility to be formed into a high-entropy alloy (HEA) with a quasicrystalline (QC) structure that contains an icosahedral-(I-) phase. The melt-spun alloys quenched at a circumference speed of 39 m/s were formed into an amorphous single phase. The amorphous alloys annealed up to a temperature between the first and second crystallization temperatures exhibited mixed phases of I- and remaining amorphous phases. Observation of the Zr30Hf30Ni15Cu10Ti15 amorphous alloy heated up to 745 K with transmission electron microscope revealed the presence of precipitates with diameters ranging 10-20 nm. Nano-beam diffraction demonstrated that the precipitates were identified to be the I-phase with the five-, three and two-fold symmetries. The Ti33.33Zr33.33Hf13.33Ni20 and Zr30Hf30Ni15Cu10Ti15 alloys were not formed into a single quasicrystalline phase as HEAs, but the discussions of the current and early experimental data led to provide the way to approach high-entropy quasicrystalline alloys (HE-QCs). (C) 2017 Elsevier B.V. All rights reserved.

Title:
Phase diagram of antimony up to 31 GPa and 835 K
Authors:
Coleman, AL; Stevenson, M; McMahon, MI; Macleod, SG Author Full Names: Coleman, A. L.; Stevenson, M.; McMahon, M. I.; Macleod, S. G.
Source:
PHYSICAL REVIEW B, 97 (14):10.1103/PhysRevB.97.144107 APR 13 2018
Abstract:
X-ray powder diffraction experiments using resistively heated diamond anvil cells have been conducted in order to establish the phase behavior of antimony up to 31 GPa and 835 K. The dip in the melting curve at 5.7 GPa and 840 K is identified as the triple point between the Sb-I, incommensurate Sb-II, and liquid phases. No evidence of the previously reported simple cubic phase was observed. Determination of the phase boundary between Sb-II and Sb-III suggests the existence of a second triple point in the region of 13 GPa and 1200 K. The incommensurate composite structure of Sb-II was found to remain ordered to the highest temperatures studies-no evidence of disordering of the guest-atom chains was observed. Indeed, the modulation reflections that arise from interactions between the host and guest subsystems were found to be present to the highest temperatures, suggesting such interactions remain relatively strong in Sb even in the presence of increased thermal motion. Finally, we show that the incommensurately modulated structure recently reported as giving an improved fit to diffraction data from incommensurate Ba-IV can be rejected as the structure of Sb-II using a simple density argument.

Title:
Phase transitions in ferroelectric 4-amino-pyridinium tetrachloroantimonate(III) - revisited
Authors:
Gagor, A Author Full Names: Gagor, Anna
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 217-225; 10.1107/S2052520618003669 2 APR 2018
Abstract:
New X-ray diffraction studies on the crystal structure of ferroelectric [4-NH2C5H4NH][SbCl4] indicate that in the broad temperature range from 240 to 304 K covering the three intermediate phases, the crystal structure is modulated. Phase II is incommensurately modulated with modulation vector q = beta b*, beta varying from 0.60 to 0.66 and monoclinic C2/c(0 beta 0)s0 superspace group. Ferroelectric phase III is commensurate with q = 2/3b* and Cc(0 beta 0)0 symmetry. Polar phase IV is incommensurately modulated with beta varying from 0.66 to 0.70 and Cc(0 beta 0)0 superspace group. In all phases only first-order satellites are observed along the b* direction. Two types of periodic deformation are present in the structure of modulated phases. The 4-aminopyridinium cations are subjected to occupation modulation whereas [SbCl4](n)(-) chains are displacively modulated. The paraelectric-ferroelectric phase transition is an example of the incommensurate-commensurate transition of the lock-in type. A new mechanism for this transformation is proposed.

Title:
Revisiting the I(1)over-bar structures of high-temperature Ca-rich plagioclase feldspar - a single-crystal neutron and X-ray diffraction study
Authors:
Jin, SY; Wang, XP; Xu, HF Author Full Names: Jin, Shiyun; Wang, Xiaoping; Xu, Huifang
Source:
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 152-164; 10.1107/S2052520618003219 2 APR 2018
Abstract:
The I (1) over bar structures of four natural Ca-rich plagioclase feldspars formed at high temperature were analysed using single-crystal neutron and X-ray diffraction. The neutron time-of-flight Laue diffractometer at the ORNL Spallation Neutron Source (Tennessee, USA) combined with a single-crystal X-ray diffraction instrument were able to reveal some new details about these already intensively studied structures. The split oxygen atoms refined from the neutron diffraction data show the underlying mechanism of Ca-Na ordering and the anisotropic P (1) over bar ordering along the c-axis. The compositional ranges covered by the samples studied are quite rare for I (1) over bar structures. The incommensurately modulated e2 structure of some plagioclase samples can easily be confused with an I (1) over bar structure from the diffraction pattern, which puts some previously published I (1) over bar structures into question. An incomplete phase diagram for Ca-rich plagioclase feldspar is proposed to explain the rarity of the I (1) over bar structure in this compositional range, and a time-temperature-transformation diagram for the composition similar to An(66) is provided accordingly.

Update: 18-Apr-2018


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

Update: 11-Apr-2018


Title:
Thermal transport properties, magnetic susceptibility and neutron diffraction studies of the (Cr100-xAlx)(95)Mo-5 alloy system
Authors:
Muchono, B; Sheppard, CJ; Venter, AM; Prinsloo, ARE Author Full Names: Muchono, B.; Sheppard, C. J.; Venter, A. M.; Prinsloo, A. R. E.
Source:
PHYSICA B-CONDENSED MATTER, 537 212-224; 10.1016/j.physb.2018.02.018 MAY 15 2018
Abstract:
Previous electrical resistivity (rho) and specific heat (C-P) studies on the ternary (Cr100-xAlx)(95)Mo-5 alloy system suggested that it harbours two quantum critical points (QCPs). This study reports comprehensive investigations of this alloy system through Seebeck coefficient oSthorn, thermal conductivity (kappa) magnetic susceptibility o.thorn and neutron diffraction oNDthorn measurements in the concentration range 0 <= x 8.6. The results of (kappa) and (chi) show that spin-density-wave (SDW) antiferromagnetism is suppressed to temperatures below 2 K for concentrations in the range 1.4 <= x <= 4.4. Plots of dS= dT in the limit as T -> 2 K depict two minima, i. e. just above x = 1.4 and 4.4. This parameter has been used as a key indicator of quantum critical behaviour (QCB) in Cr alloys. Analyses against the Nordheim-Gorter relationship demonstrates a positive slope for the incommensurate (I) SDW alloys and a negative slope for the commensurate (C) SDW alloys. Extrapolations of these two slopes intercept at a concentration of 3.2 at.% Al indicating the occurrence of band structure modifications when Al is added into the Cr95Mo5 base alloy. The Lorenz number oLthorn for the alloys with x = 0 and 0.5 shows interesting anomalous behaviour associated with band structure effects and SDW magnetic ordering. ND measurements as a function of temperature confirm that alloys with x < 1.4 order in the incommensurate (I) SDW phase whilst alloys with x > 4.4 show commensurate (C) SDW order. Power law fits of the form T-N alpha(1.40 - x)(0.35) (+/-0.05) for the ISDW to P phase transition and T-N alpha (x- 4. 40)(0.63) (+/-0.03) for the P to CSDW phase transition rendered the critical exponents 0: 35 +/- 0: 05 and 0: 63 +/- 0: 03 respectively. Overall the results of S,.,. and ND corroborate the existence of two QCPs at x approximate to 1.4 and 4.4.

Title:
Microphases deriving from Ba2ZrF8 structure type: II: Crystal structure of Sr17Zr9F70 and Sr(17.145)ZT(9)F(70.29)
Authors:
Laval, JP; Rafik, H; Trolliard, G Author Full Names: Laval, Jean-Paul; Rafik, Hamid; Trolliard, Gilles
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 260 151-158; 10.1016/j.jssc.2018.01.005 APR 2018
Abstract:
In the domain Sr1-xZrxF2+2 (x) studied at 670 degrees C between the limits 0.333 <= x <= 0.353, Sr2ZrF8 (x = 0.333) cannot be obtained under our synthesis conditions but a new phase Sr17Zr9F70 (x = 0.346) is characterized which clearly shows a great analogy with Ba2ZrF8 and Pb2ZrF8 already described. It presents the same Pnma space group and derives from this basic type by the relation: a = 28.812(10) angstrom = 3 x a(Ba2ZrF8); b = 16.566(6) angstrom = 3 x b(Ba2ZrF8); c = 11.433(4)angstrom = c(Ba2ZrF8). The superlattice along a results from a change in the step of zigzag parallel rows of respectively Sr cations and ZrF8 polyhedra. The zigzag step is not composition-dependent but more likely depends on the size of the M2+ cation. The superlattice along b results from an ordered creation of Sr vacancies of multiplicity m = 3 (1 vacancy for 3 Sr) in some Sr raws which changes the Sr/Zr ratio from 2/1 to 1.889/1 (x = 0.346). Then the superstructure along b accommodates the change in stoichiometry in Sr within this phase from Sr18Zr9F72 (9 x "Sr2ZrF8") to Sr17Zr9F70. A second structure of close composition (x = 0.344) shows that the vacant Sr site can be partially occupied in a disordered way by a small proportion of Sr, giving a composition slightly closer to "Sr2ZrF8". Compared to Sr17Zr8F70, the over-stoichiometry mechanism is a solid solution model. For Zr contents comprised between x = 0.346 and 0.353, a series of modulated phases corresponding to various more or less ordered sequences of Sr cations and Sr vacancies along b are characterized by electron diffraction and TEM lattice imaging. They can be interpreted as intermediate between limit phases Sr17Zr9F70 (x = 0.346) and Sr11Zr6F46 (x = 0.353), of respective multiplicities m = 3 and m = 2 along the same b direction and of modulation vectors q = 1/3b* and q = 1/2b*. Several modulated phases with q modulation vector comprised between 1/3 b* and 1/2 b* can be characterized.

Title:
Stairlike Aurivillius Phases in the Pseudobinary Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) System: A Comprehensive Analysis Using Superspace Group Formalism
Authors:
Steciuk, G; Barrier, N; Pautrat, A; Boullay, P Author Full Names: Steciuk, Gwladys; Barrier, Nicolas; Pautrat, Alain; Boullay, Philippe
Source:
INORGANIC CHEMISTRY, 57 (6):3107-3115; 10.1021/acs.inorgchem.7b03026 MAR 19 2018
Abstract:
We report the possibility of extending the so-called stairlike Aurivilius phases in the pseudobinary Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) over a wide range of compositions. These phases are characterized by a discontinuous stacking of [Bi2O2] slabs and perovskite blocks, leading to long-period intergrowths stabilized as a single phase. When analyses from precession electron diffraction tomography and Xray and neutron powder diffraction are combined, the monoclinic incommensurately modulated structure with q = alpha a* + gamma c* previously proposed for the ABi(7)Nb(5)O(24) composition could be generalized to the Bi5Nb3O15-ABi(2)Nb(2)O(9) (A = Ba and Sr) compounds. Considering the compositions expressed as (A,Bi)(1-x)NbxO3-3x, the stacking sequence associated with compositions ranging from x = 2/5 to 3/8 is governed by the component gamma of the modulation vector and can be predicted following a Farey tree hierarchy independently to the A cation. The length of the steps, characteristic of the stairlike nature, is controlled by the alpha component and depends on the substitution ratio A/Bi and the nature of A (A = Ba and Sr). This study highlights the compositional flexibility of stairlike Aurivillius phases.

Title:
Kinetically Controlled Formation and Decomposition of Metastable [(BiSe)(1+delta)](m)[TiSe2](m) Compounds
Authors:
Lygo, AC; Hamann, DM; Moore, DB; Merrill, DR; Ditto, J; Esters, M; Orlowicz, J; Wood, SR; Johnson, DC Author Full Names: Lygo, Alexander C.; Hamann, Danielle M.; Moore, Daniel B.; Merrill, Devin R.; Ditto, Jeffrey; Esters, Marco; Orlowicz, Jacob; Wood, Suzannah R.; Johnson, David C.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (9):3385-3393; 10.1021/jacs.7b13398 MAR 7 2018
Abstract:
Preparing homologous series of compounds allows chemists to rapidly discover new compounds with predictable structure and properties. Synthesizing compounds within such a series involves navigating a free energy landscape defined by the interactions within and between constituent atoms. Historically, synthesis approaches are typically limited to forming only the most thermodynamically stable compound under the reaction conditions. Presented here is the synthesis, via self-assembly of designed precursors, of isocompositional incommensurate layered compounds[(BiSe)(1+delta)](m)[TiSe2](m) , with m = 1, 2, and 3. The structure of the BiSe bilayer in the m = 1 compound is not that of the binary compound, and this is the first example of compounds where a BiSe layer thicker than a bilayer in heterostructures has been prepared. Specular and in-plane X-ray diffraction combined with high-resolution electron microscopy data was used to follow the formation of the compounds during low-temperature annealing and the subsequent decomposition of the m = 2 and 3 compounds into [(BiSe)(1+delta)](1)[TiSe2](1) at elevated temperatures. These results show that the structure of the precursor can be used to control reaction kinetics, enabling the synthesis of kinetically stable compounds that are not accessible via traditional techniques. The data collected as a function of temperature and time enabled us to schematically construct the topology of the free energy landscape about the local free energy minima for each of the products.

Title:
The Mystery of the Auln 1:1 Phase and Its Incommensurate Structural Variations
Authors:
Folkers, LC; Simonov, A; Wang, F; Lidin, S Author Full Names: Folkers, Laura C.; Simonov, Arkadiy; Wang, Fei; Lidin, Sven
Source:
INORGANIC CHEMISTRY, 57 (5):2791-2796; 10.1021/acs.inorgchem.7b03206 MAR 5 2018
Abstract:
In this communication, the AuIn 1:1 phase (Naturwissenschaften, 1953, 40, 437, DOI: 10.1007/BF00590353), and its ordering behavior at various temperatures is investigated. To enable the growth of a X-ray suitable specimen, a tempering routine was established by the interpretation of a differential scanning calorimetry (DSC) study. In this way, good quality single crystals were grown and measured at the Crystal beamline at Synchrotron SOLEIL. From the acquired data, three variations of this structure could be found at temperatures of 400 degrees C and 300 degrees C and room temperature, with differing degrees of incommensurate modulation. Diffuse scattering found at 400 degrees C was interpreted with the help of a three-dimensional difference pair distribution function (3D-Delta PDF) study.

Title:
Formation of Quasicrystalline Phases and Their Close Approximants in Cast Al-Mn Base Alloys Modified by Transition Metals
Authors:
Stan-Glowinska, K Author Full Names: Stan-Glowinska, Katarzyna
Source:
CRYSTALS, 8 (2):10.3390/cryst8020061 FEB 2018
Abstract:
The aim of the presented research was to study the influence of Cr, Co, Ni, and Cu additions on the formation of quasicrystalline particles in the 94Al-6Mn base alloy during casting at intermediate cooling rates. Based on the obtained results, Cu and Ni enhance quasicrystalline phase nucleation compared to the unmodified binary composition. In the case of Cu addition, formation of a quasicrystalline phase takes place along whole thickness of the prepared casting, but its fraction and morphology depends on the cooling rates present in different parts of the sample. Based on the previous works on the beneficial effect of Fe addition, a quaternary alloy containing both Fe and Cu was prepared to evaluate the effect of the simultaneous presence of these elements on the microstructure of the obtained castings.

Title:
Possible nucleus of the Bergman cluster in the Zn-Mg-Y alloy system
Authors:
Nakayama, K; Nakagawa, M; Koyama, Y Author Full Names: Nakayama, Kei; Nakagawa, Masaya; Koyama, Yasumasa
Source:
PHILOSOPHICAL MAGAZINE, 98 (3):219-236; 10.1080/14786435.2017.1400703 2018
Abstract:
To understand the formation of the Bergman cluster in the F-type icosahedral quasicrystal (IQ), crystallographic relations between the quasicrystal and the intermetallic-compound H and Zn23Y6 phases in the ZnMgY alloy system were investigated mainly by transmission electron microscopy. It was found that, although sample rotations of about 1 degrees were required to obtain simple crystallographic relations, the orientation relationship was established among the cubic-Fmm Zn23Y6 structure, the hexagonal-P6(3)/mmc H structure and the F-type IQ; that is, [(1) over bar 1 3](c) // the five-fold axis in the IQ // N(2 (1) over bar(1) over bar0)(H), and [1 1 1](c) // the two-fold axis in the IQ // N(0 5 (5) over bar3)(H), where N(h k m l)(H) means the normal direction of the (h k m l)(H) plane in the H structure. The correspondences between atomic positions in the Bergman cluster and in the Zn23Y6 structure and between those in the cluster and in the H structure were investigated on the basis of the established relationship. As a result, an assembly of six short-penetrated-decagonal columns was identified as an appropriate nucleus in the formation of the Bergman cluster from these two structures.

Update: 4-Apr-2018


Title:
Spin wave propagation spectra in Octonacci one-dimensional magnonic quasicrystals
Authors:
Valeriano, AP; Costa, CH; Bezerra, CG Author Full Names: Valeriano, Analine P.; Costa, Carlos H.; Bezerra, Claudionor G.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 456 228-235; 10.1016/j.jmmm.2018.02.042 JUN 15 2018
Abstract:
In this paper, we study spin wave propagation in quasiperiodic magnonic superlattices that follow the so-called Octonacci quasiperiodic sequence, where the N-th stage can be obtained through the recurrence rule S-N = SN-1SN-2SN-1, for N >= 3, and starting with S-1 = A and S-2 = B. The multilayered magnonic nanostructure is composed of two simple cubic ferromagnetic materials, labeled A and B, which interact through bilinear and biquadratic exchange couplings at their interfaces. The ferromagnetic materials are described by the Heisenberg model, and a transfer matrix treatment is employed, with the calculations performed for the exchange-dominated regime, taking the random phase approximation (RPA) into account. The obtained numerical results show the effects of both (i) the Octonacci quasiperiodic sequence and (ii) the biquadratic exchange coupling on the band structure and transmission spectra of spin waves. Comparisons are also performed with the spectra found in other periodic and quasiperiodic structures. (C) 2018 Elsevier B.V. All rights reserved.

Title:
Building 2D quasicrystals from 5-fold symmetric corannulene molecules
Authors:
Kalashnyk, N; Ledieu, J; Gaudry, E; Cui, C; Tsai, AP; Fournee, V Author Full Names: Kalashnyk, Nataliya; Ledieu, Julian; Gaudry, Emilie; Cui, Can; Tsai, An-Pang; Fournee, Vincent
Source:
NANO RESEARCH, 11 (4):2129-2138; 10.1007/s12274-017-1830-x APR 2018
Abstract:
The formation of long-range ordered aperiodic molecular films on quasicrystalline substrates is a new challenge that provides an opportunity for further surface functionalization. This aim can be realized through the smart selection of molecular building blocks, based on symmetry-matching between the underlying quasicrystal and individual molecules. It was previously found that the geometric registry between the C-60 molecules and the 5- and 10-fold surfaces was key to the growth of quasiperiodic organic layers. However, an attempt to form a quasiperiodic C-60 network on i-Ag-In-Yb substrates was unsuccessful, resulting in disordered molecular films. Here we report the growth of 5-fold symmetric corannulene C20H10 molecules on the 5-fold surfaces of i-Ag-In-Yb quasicrystals. Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) revealed long-range quasiperiodic order and 5-fold rotational symmetry in self-assembled corannulene films. Recurrent decagonal molecular rings were seen, resulting from the decoration of specific adsorption sites with local pentagonal symmetry by corannulenes, adsorbed with their bowl-openings pointing away from the surface. They were identified as (Ag, In)-containing rhombic triacontahedral (RTH) cluster centers and pentagonal Yb motifs, which cannot be occupied simultaneously due to steric hindrance. It is proposed that symmetry-matching between the molecule and specific substrate sites drives this organization. Alteration of the molecular rim by the introduction of CH substituents appeared to increase molecule mobility on the potential energy surface and facilitate trapping at these specific sites. This finding suggests that rational selection of molecular moiety enables the templated self-assembly of molecules leading to an ordered aperiodic corannulene layer.

Title:
SU(5) grand unified theory, its polytopes and 5-fold symmetric aperiodic tiling
Authors:
Koca, M; Koca, NO; Al-Siyabi, A Author Full Names: Koca, Mehmet; Koca, Nazife Ozdes; Al-Siyabi, Abeer
Source:
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS, 15 (4):10.1142/S0219887818500561 APR 2018
Abstract:
We associate the lepton-quark families with the vertices of the 4D polytopes 5-cell (0001) (A4) and the rectified 5-cell (0100) (A4) derived from the SU(5) Coxeter-Dynkin diagram. The off-diagonal gauge bosons are associated with the root polytope (1001) A(4) whose facets are tetrahedra and the triangular prisms. The edge-vertex relations are interpreted as the SU(5) charge conservation. The Dynkin diagram symmetry of the SU(5) diagram can be interpreted as a kind of particle-antiparticle symmetry. The Voronoi cell of the root lattice consists of the union of the polytopes (1000) (A4) + (0100) (A4) + (0010) (A4) + (0001) (A4) whose facets are 20 rhombohedra. We construct the Delone (Delaunay) cells of the root lattice as the alternating 5-cell and the rectified 5-cell, a kind of dual to the Voronoi cell. The vertices of the Delone cells closest to the origin consist of the root vectors representing the gauge bosons. The faces of the rhombohedra project onto the Coxeter plane as thick and thin rhombs leading to Penrose-like tiling of the plane which can be used for the description of the 5-fold symmetric quasicrystallography. The model can be extended to SO(10) and even to SO(11) by noting the Coxeter-Dynkin diagram embedding A(4) subset of D-5 subset of B-5. Another embedding can be made through the relation A(4) subset of D-5 subset of E-6 for more popular GUT's. Appendix A includes the quaternionic representations of the Coxeter-Weyl groups W(A(4)) subset of W(H-4) which can be obtained directly from W(E-8) by projection. This leads to relations of the SU(5) polytopes with the quasicrystallography in 4D and E-8 polytopes. Appendix B discusses the branching of the polytopes in terms of the irreducible representations of the Coxeter-Weyl group W(A(4)) approximate to S-5.

Title:
Charge Order and Superconductivity in Underdoped YBa2Cu3O7-delta under Pressure
Authors:
Putzke, C; Ayres, J; Buhot, J; Licciardello, S; Hussey, NE; Friedemann, S; Carrington, A Author Full Names: Putzke, Carsten; Ayres, Jake; Buhot, Jonathan; Licciardello, Salvatore; Hussey, Nigel E.; Friedemann, Sven; Carrington, Antony
Source:
PHYSICAL REVIEW LETTERS, 120 (11):10.1103/PhysRevLett.120.117002 MAR 16 2018
Abstract:
In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in T-c at the hole doping level where the CDW is strongest (n(p) similar or equal to 0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa2Cu3O7-d(delta) by measuring the temperature dependence of the Hall coefficient R-H(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases T-c by up to 10 K at 2.6 GPa, it has very little effect on R-H(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in T-c with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in T-c at n(p) similar or equal to 0.12 at ambient pressure is probably not caused by the CDW formation.

Update: 28-Mar-2018


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

Update: 21-Mar-2018


Title:
Two spin-canting textures in the antiferromagnetic phase AF1 of MnWO4 based on the new polar atomistic model in P2
Authors:
Park, SH; Liu, BQ; Behal, D; Pedersen, B; Schneidewind, A Author Full Names: Park, S-H; Liu, B-Q; Behal, D.; Pedersen, B.; Schneidewind, A.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (13):10.1088/1361-648X/aaaeae APR 4 2018
Abstract:
The low temperature antiferromagnetic (AF) phase of MnWO4 (the so-called AF1 phase) exhibits different spin-canting configurations at two Mn2+ sublattices of the (3 + 1)-dimensional magnetic structure. The suggested superspace group P2.1'(alpha, 1/2, gamma)0s is a significant consequence of the polar space group P2 true for the nuclear structure of MnWO4. Density functional theory calculations showed that its ground state prefers this two spin-canting system. The structural difference between two independent atomic sites for Mn (Mn-a, Mn-b) is too small to allow microscopically detectable electric polarisation. However, this hidden intrinsic polar character allows AF1 two commensurately modulated spin-canting textures. This is considered as the prerequisite onset of the improper ferroelectricity enhanced by the helical spin order in the multiferroic phase AF2 of MnWO4.

Title:
The incommensurately modulated crystal structure of roshchinite, Cu0.09Ag1.04Pb0.65Sb2.82As0.37S6.08
Authors:
Makovicky, E; Stoger, B; Topa, D Author Full Names: Makovicky, Emil; Stoger, Berthold; Topa, Dan
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (3-4):255-267; 10.1515/zkri-2017-2126 MAR 2018
Abstract:
The Pb-Ag-Sb sulfide roshchinite, Cu0.09Ag1.04Pb0.65Sb2.82As0.37S6.08, is a lillianite homologue N = 4 with a complex incommensurate superstructure in the 8.46 angstrom direction of the orthorhombic crystal lattice with a 19.0804(1) angstrom, b 8.4591(2) angstrom and c 12.9451(3) angstrom, superspace group Pbcn(0 sigma(2)0)00s, q = 0.41458(3) b*. A structure solution and refinement in (3+1) superspace, based on 10,019 observed reflections and 437 refined parameters was terminated at R-obs (wR) equal to 7.27 (8.07)% using satellites up to second order; R-obs is 4.82 for main reflections only. The Pb atoms in trigonal coordination prisms on planes of unit-cell twinning are semiperiodically replaced by antimony. The marginal columns of (311)(PbS) slabs of the Sb-Ag based structure which is based on PbS-like topology contain Sb, Ag(Cu) and mixed Ag/Sb sites in a complicated sequence. Central portions of the slabs are occupied by Sb-S crankshaft chains, best exposed on the (100) PbS planes, which run diagonally across the slabs. In these planes, in their majority the chains display Sb3S4 form and two opposing orientations, zig-zagging along the [010] direction. Every six chains, a parallel configuration of two chains occurs, but occasionally this interval is reduced to five chains. This, together with related compositional changes in the Pb- and Ag-Sb column, explains the one-dimensionally incommensurate character of roshchinite. Modestly elevated contents of As replacing Sb are the probable reason of modulation and non-commensurability in roshchinite.

Title:
The (3+3) commensurately modulated structure of the uranyl silicate mineral swamboite-(Nd), Nd-0.333[(UO2)(SiO3OH)](H2O)(2.41)
Authors:
Plasil, J; Petricek, V; Locock, AJ; Skoda, R; Burns, PC Author Full Names: Plasil, Jakub; Petricek, Vaclav; Locock, Andrew J.; Skoda, Radek; Burns, Peter C.
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (3-4):223-231; 10.1515/zkri-2017-2119 MAR 2018
Abstract:
The uranyl mineral swamboite has been redefined to swamboite-(Nd) and its structure has been solved and refined as a commensurate structure in six-dimensional superspace. The structure is monoclinic, superspace group P2(1)/m(a1, b1, g1) 00(-a1, b1, g1) 00 (a2,0,g2)0s, cell parameters a = 6.6560(3), b = 6.9881(5), c = 8.8059(6), c = 11.3361(16) angstrom, beta = 102.591(5)degrees, modulation wave-vectors q(1) = 1/3 1/3 0; q(2) = - 1/3 1/3 0; q(3) = 1/2 0 1/2. The structure was refined from 8717 reflections to a final R = 0.0610. The model includes modulation both of atomic positions and displacement parameters, as well as occupancy waves. The structure is based upon uranyl-silicate sheets of uranophane topology alternating with an inter-layer of partly occupied Nd3+ sites and H2O molecules. The strong (3 + 3) dimensional modulation of the structure originates from the distribution of the Nd-dominated sites and further accommodation of the suitable geometry within the sheets and charge distribution within the structure. The separation distances between the corres-ponding occupied Nd sites are rationals of the super-cell vectors corresponding to the modulation vectors of the structure. The case of swamboite-(Nd) is the first example of a modulated structure within the oxysalts of U6+.

Title:
Frustration and thermalization in an artificial magnetic quasicrystal
Authors:
Shi, D; Budrikis, Z; Stein, A; Morley, SA; Olmsted, PD; Burnell, G; Marrows, CH Author Full Names: Shi, Dong; Budrikis, Zoe; Stein, Aaron; Morley, Sophie A.; Olmsted, Peter D.; Burnell, Gavin; Marrows, Christopher H.
Source:
NATURE PHYSICS, 14 (3):309-+; 10.1038/s41567-017-0009-4 MAR 2018
Abstract:
Artificial frustrated systems offer a playground to study the emergent properties of interacting systems. Most work to date has been on spatially periodic systems, known as artificial spin ices when the interacting elements are magnetic. Here we have studied artificial magnetic quasicrystals based on quasiperiodic Penrose tiling patterns of interacting nanomagnets. We construct a low-energy configuration from a step-by-step approach that we propose as a ground state. Topologically induced emergent frustration means that this configuration cannot be constructed from vertices in their ground states. It has two parts, a quasione- dimensional 'skeleton' that spans the entire pattern and is capable of long-range order, surrounding ` flippable' clusters of macrospins that lead to macroscopic degeneracy. Magnetic force microscopy imaging of Penrose tiling arrays revealed superdomains that are larger for more strongly coupled arrays, especially after annealing the array above its blocking temperature.

Title:
Coordination numbers of the vertex graph of a Penrose tiling
Authors:
Shutov, A; Maleev, A Author Full Names: Shutov, Anton; Maleev, Andrey
Source:
ACTA CRYSTALLOGRAPHICA A-FOUNDATION AND ADVANCES, 74 112-122; 10.1107/S2053273318000062 2 MAR 2018
Abstract:
A new approach to study coordination shells and coordination sequences of quasiperiodic graphs is suggested. The structure of the coordination shells in the vertex graph of a Penrose tiling is described. An asymptotic formula for its coordination numbers is obtained. An essentially different behaviour of the coordination numbers for even and odd shells is revealed.

Title:
Deformation Behavior and Structure of i-Al-Cu-Fe Quasicrystalline Alloy in Vicinity of Nanoindenter Indentation
Authors:
Shalaeva, EV; Selyanin, IO; Smirnova, EO; Smirnov, SV; Novachek, DD Author Full Names: Shalaeva, E. V.; Selyanin, I. O.; Smirnova, E. O.; Smirnov, S. V.; Novachek, D. D.
Source:
PHYSICS OF THE SOLID STATE, 60 (2):312-319; 10.1134/S1063783418020233 FEB 2018
Abstract:
The nanoindentation tests have been carried out for the quasicrystalline polygrain Al62.4Cu25.3Fe12.3 alloy with the icosahedral structure i; the load P-displacement h diagrams have been used to estimate the contributions of plastic deformation (monotonic and intermittent), and the structures of the transverse microscopic sections have been studied in the vicinity of indentations by electron microscopy. It is shown that several systems of deformation bands are formed in the elasto-plastic zone in the vicinity of the indentations along the close-packed planes of the i lattice with the five-fold and two-fold symmetry axes; the bands often begin from cracks and manifest the signs of the dislocation structure. The traces of the phase transformation with the formation of the beta-phase areas are observed only in a thin layer under an indenter. The effects of intermittent deformation are up to 50% of the total inelastic deformation and are related to the plastic behavior of the quasicrystal-activation and passage of deformation bands and also the formation of undersurface micro- and nanosized cracks.

Update: 14-Mar-2018


Title:
Melt holding time as an important factor on the formation of quasicrystal phase in Mg67Zn30Gd3 alloy
Authors:
Zhang, JY; Jia, P; Zhao, DG; Teng, XY Author Full Names: Zhang, Jinyang; Jia, Peng; Zhao, Degang; Teng, Xinying
Source:
PHYSICA B-CONDENSED MATTER, 533 28-32; 10.1016/j.physb.2017.12.052 MAR 15 2018
Abstract:
In the present work, the content of icosahedral quasicrystal phase (I-phase) and melt holding time shows a mono peak curve: a small amount of I-phase and lots of Mg-3(Gd, Zn) phase are presented for t < 21 min, however a great deal of I-phase is observed for t > 21 min, and the volumetric fraction of I-phase has the maximum of 49.50% for t = 41 min. This strategy of formation of quasicrystal phase makes us realize that melt thermal treatment could significantly affect the phase types in Mg-Zn-Gd alloy.

Title:
Multi-q Mesoscale Magnetism in CeAuSb2
Authors:
Marcus, GG; Kim, DJ; Tutmaher, JA; Rodriguez-Rivera, JA; Birk, JO; Niedermeyer, C; Lee, H; Fisk, Z; Broholm, CL Author Full Names: Marcus, Guy G.; Kim, Dae-Jeong; Tutmaher, Jacob A.; Rodriguez-Rivera, Jose A.; Birk, Jonas Okkels; Niedermeyer, Christof; Lee, Hannoh; Fisk, Zachary; Broholm, Collin L.
Source:
PHYSICAL REVIEW LETTERS, 120 (9):10.1103/PhysRevLett.120.097201 FEB 28 2018
Abstract:
We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb2. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)mu(B)/Ce for T << T-N = 6.25(10)K with a wave vector q(1) = (eta, eta, 1/2) [eta = 0.136(2)]. For H parallel to c, harmonics appearing at 2q(1) evidence a striped magnetic texture below mu H-degrees(1) = 2.78(1)T. Above H-1, these are replaced by coupled harmonics at q(1) + q(2) = (2 eta, 0, 0) + c* until mu H-degrees(2) = 5.42(5)T, where satellites vanish and magnetization nonlinearly approaches saturation at 1.64(2)mu(B)/Ce for mu H-degrees approximate to 7T.

Title:
High-strength Mg-6Zn-1Y-1Ca (wt%) alloy containing quasicrystalline I-phase processed by a powder metallurgy route
Authors:
Medina, J; Perez, P; Garces, G; Stark, A; Schell, N; Adeva, P Author Full Names: Medina, J.; Perez, P.; Garces, G.; Stark, A.; Schell, N.; Adeva, P.
Source:
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 715 92-100; 10.1016/j.msea.2017.12.111 FEB 7 2018
Abstract:
A high-strength Mg-6Zn-1Y-1Ca (wt%) alloy has been processed by a powder metallurgy route. Rapidly solidified powders with a particle size below 100 tun were used as a way for preventing formation of ternary MgZnCa compounds during subsequent extrusion at 250 degrees C. The microstructure of the extruded alloy consists of an ultrafine-grain magnesium matrix, with an average grain size of 444 nm, embedding a high volume fraction of fine I-phase particles aligned along the extrusion direction. The alloy combines an excellent ductility (14% of elongation to failure) with a high strength (ultimate strength of 469 MPa and yield stress of 461 MPa) at room temperature, mainly due to grain size refinement (around 70% of the yield stress). The strength is kept high up to 150 degrees C (yield stress of 279 MPa). Above this temperature, the mechanical strength falls to very low values but the ability to deform plastically is considerably enhanced, exhibiting superplastic behaviour from 200 to 350 degrees C, with a maximum elongation of 477% at 350 degrees C.

Title:
Parallels in Structural Chemistry between the Molecular and Metallic Realms Revealed by Complex Intermetallic Phases
Authors:
Fredrickson, DC Author Full Names: Fredrickson, Daniel C.
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 51 (2):248-257; 10.1021/acs.accounts.7b00625 FEB 2018
Abstract:
CONSPECTUS: The structural diversity of intermetallic phases poses a great challenge to chemical theory and materials design. In this Account, two examples are used to illustrate how a focus on the most complex of these structures (and their relationships to simpler ones) can reveal how chemical principles underlie structure for broad families of compounds. First, we show how experimental investigations into the Fe-Al-Si system, inspired by host-guest like features in the structure of Fe25Al78Si20, led to a theoretical approach to deriving isolobal analogies between molecular and intermetallic compounds and a more general electron counting rule. Specifically, the Fe(8)Al(17.6)Si(7.4)compound obtained in these syntheses was traced to a fragmentation of the fluorite-type structure (as adopted by NiSi2), driven by the maintenance of 18-electron configurations on the transition metal centers.& para;& para;The desire to quickly generalize these conclusions to a broader range of phases motivated the formulation of the reversed approximation Molecular Orbital (raMO) approach. The application of raMO to a diverse series of compounds allowed us recognize the prevalence of electron pair sharing in multicenter functions isolobal to classical covalent bonds and to propose the 18 - n electron rule for transition metal-main group (T-E) intermetallic compounds. These approaches provided a framework for understanding the 14-electron rule of the Nowotny Chimney Ladder phases, a temperature-driven phase transition in GdCoSi2, and the bcc-structure of group VI transition metals.& para;& para;In the second story, we recount the development of the chemical pressure approach to analyzing atomic size and packing effects in intermetallic structures. We begin with how the stability of the Yb2Ag7-type structure of Ca2Ag7 over the more common CaCu(5 )type highlights the pressing need for approaches to assessing the role of atomic size in crystal structures, and inspired the development of the DFT-Chemical Pressure (CP) method. Examples of structural phenomena elucidated by this approach are then given, including the Y/Co(2 )dumbbell substitution in the Th2Zn17-type phase Y2Co17, and local icosahedral order in the Tsai-type quasicrystal approximant CaCd6. We next discuss how deriving relationships between the CP features of a structure and its phonon modes provided a way of both validating the method and visualizing how local arrangements can give rise to soft vibrational modes. The themes of structural mechanisms for CP relief and soft atomic motions merge in the discovery and elucidation of the incommensurately modulated phase CaPd5. In the conclusion of this Account, we propose combining raMO and CP methods for focused predictions of structural phenomena.

Title:
In Situ Synthesis and Single Crystal Synchrotron X-ray Diffraction Study of ht-Sn3Sb2: An Example of How Complex Modulated Structures Are Becoming Generally Accessible
Authors:
Lidin, S; Folkers, LC Author Full Names: Lidin, Sven; Folkers, Laura C.
Source:
ACCOUNTS OF CHEMICAL RESEARCH, 51 (2):223-229; 10.1021/acs.accounts.7b00508 FEB 2018
Abstract:
Recent developments in X-ray sources and detectors and the parallel development of software for nonstandard crystallography has made analysis of very complex structural problems accessible to nonexperts. Here, we report the successful solution of the structure of ht-Sn3Sb2, an analysis that presents several challenges but that is still manageable in a relatively straightforward way. This compound exists only in a narrow temperature regime and undergoes an unquenchable phase transformation on cooling to room temperature; it contains two elements with close to identical scattering factors, and the structure is incommensurately modulated with four symmetry dependent modulation wave vectors. In this study, an attempt was first made to synthesize the title compound by in-house crystal growth in the stability region of ht-Sn3Sb2, followed by cooling to room temperature. This is known to produce mutiply twinned stistaite and elemental tin, and this sample, freshly prepared, was then reheated in situ at the single crystal materials beamline Crystal at the synchrotron Soleil. This method was unsuccessful as reheating the sample led to loss of Sn from stistaite as revealed by a change in the measured modulation wave vector. The compound was instead successfully synthesized in situ at the beamline by the topochemical reaction of single crystalline stistaite and liquid tin. A well-formed crystal of stistaite was enclosed in a quartz capillary together with a large excess of tin and heated above the melting point of tin but below the melting point of ht-Sn3Sb2. The structure was probed by sychrotron X-ray diffraction using a wavelength close to the absorption edge of Sn to maximize elemental contrast. In the diffraction patterns, first order satellites were observed, making the structure of ht-Sn3Sb2 incommensurately modulated. Further analysis exposes four q-vectors running along the body diagonals of the cubic unit cell (q(1)' = alpha alpha alpha, q(2)' = -alpha alpha -alpha, q3' = -alpha -alpha alpha, q(4)' = alpha-alpha-alpha). To facilitate the analysis, the q vectors were instead treated as axial (q(1) = alpha 0 0, q(2) = 0 alpha 0, q(3) = 0 0 alpha) and an F-type extinction condition for satellites was introduced so that only reflections with hklmnp, mnp all odd or all even, were considered. Further, the modulation functions F(q(i)) were set to zero, and only modulation functions of the type F(q(i)') were refined. The final model uses the four modulation functions, F(q(1)'), F(q(2)'), F(q(3)'), and F(q(4)'), to model occupancy Sn/Sb and positional modulation. The model shows a structure that comprises small NaCl type clusters, typically 7 x 7 x 7 atoms in extension, interspersed between single layers of elemental tin. The terminating layers of tin are slightly puckered, emulating an incipient deformation toward the structure of the layers perpendicular to the [001] direction in elemental tin. It is notable that this model is complementary to that of stistaite. In stistaite, two-dimensionally infinite slabs of rock salt are interspersed between layers of antimony along the trigonal [001] direction, so that the terminating Sb layers are the puckered bilayers typical for elemental Sb. Since all modulation functions are simple first-order harmonics, the structural model describes a locally disordered and most probably dynamic ordering.

Update: 7-Mar-2018


Title:
Shear localization and size-dependent strength of YCd6 quasicrystal approximant at the micrometer length scale
Authors:
Song, G; Kong, T; Dusoe, KJ; Canfield, PC; Lee, SW Author Full Names: Song, Gyuho; Kong, Tai; Dusoe, Keith J.; Canfield, Paul C.; Lee, Seok-Woo
Source:
JOURNAL OF MATERIALS SCIENCE, 53 (9):6980-6990; 10.1007/s10853-018-2043-8 MAY 2018
Abstract:
Mechanical properties of materials are strongly dependent of their atomic arrangement as well as the sample dimension, particularly at the micrometer length scale. In this study, we investigated the small-scale mechanical properties of single-crystalline YCd6, which is a rational approximant of the icosahedral Y-Cd quasicrystal. In situ microcompression tests revealed that shear localization always occurs on {101} planes, but the shear direction is not constrained to any particular crystallographic directions. Furthermore, the yield strengths show the size dependence with a power law exponent of 0.4. Shear localization on {101} planes and size-dependent yield strength are explained in terms of a large interplanar spacing between {101} planes and the energetics of shear localization process, respectively. The mechanical behavior of the icosahedral Y-Cd quasicrystal is also compared to understand the influence of translational symmetry on the shear localization process in both YCd6 and Y-Cd quasicrystal micropillars. The results of this study will provide an important insight in a fundamental understanding of shear localization process in novel complex intermetallic compounds.

Title:
Precipitation of binary quasicrystals along dislocations
Authors:
Yang, ZQ; Zhang, LF; Chisholm, MF; Zhou, XZ; Ye, HQ; Pennycook, SJ Author Full Names: Yang, Zhiqing; Zhang, Lifeng; Chisholm, Matthew F.; Zhou, Xinzhe; Ye, Hengqiang; Pennycook, Stephen J.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-018-03250-8 FEB 23 2018
Abstract:
Dislocations in crystals naturally break the symmetry of the bulk, introducing local atomic configurations with symmetries such as fivefold rings. But dislocations do not usually nucleate aperiodic structure along their length. Here we demonstrate the formation of extended binary quasicrystalline precipitates with Penrose-like random-tiling structures, beginning with chemical ordering within the pentagonal structure at cores of prismatic dislocations in Mg-Zn alloys. Atomic resolution observations indicate that icosahedral chains centered along [0001] pillars of Zn interstitial atoms are formed templated by the fivefold rings at dislocation cores. They subsequently form columns of rhombic and elongated hexagonal tiles parallel to the dislocation lines. Quasicrystalline precipitates are formed by random tiling of these rhombic and hexagonal tiles. Such precipitation may impact dislocation glide and alloy strength.

Title:
From Quasicrystals to Crystals with Interpenetrating Icosahedra in Ca-Au-Al: In Situ Variable-Temperature Transformation
Authors:
Pham, J; Meng, FQ; Lynn, M; Ma, T; Kreyssig, A; Kramer, MJ; Goldman, AI; Miller, GJ Author Full Names: Pham, Joyce; Meng, Fanqiang; Lynn, Matthew.; Ma, Tao; Kreyssig, Andreas; Kramer, Matthew J.; Goldman, Alan I.; Miller, Gordon J.
Source:
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 140 (4):1337-1347; 10.1021/jacs.7b10358 JAN 31 2018
Abstract:
The irreversible transformation from an icosahedral quasicrystal (i-QC) CaAu4.39Al1.61 to its cubic 2/1 crystalline approximant (CA) Ca13Au56.31 Al-(3)(21.69) (CaAu4.33(1)Al1.67, Pa (3) over bar (No. 205); Pearson symbol: cP728; a = 23.8934(4)), starting at similar to 570 degrees C and complete by similar to 650 degrees C, is discovered from in situ, high-energy, variable-temperature powder X-ray diffraction (PXRD), thereby providing direct experimental evidence for the relationship between QCs and their associated CAs. The new cubic phase crystallizes in a Tsai-type approximant structure under the broader classification of polar intermetallic compounds, in which atoms of different electronegativities, viz., electronegative Au + Al vs electropositive Ca, are arranged in concentric shells. From a structural chemical perspective, the outermost shell of this cubic approximant may be described as interpenetrating and edge-sharing icosahedra, a perspective that is obtained by splitting the traditional structural description of this shell as a 92-atom rhombic triacontahedron into an 80-vertex cage of primarily Au [Au59.86(2)Al17.14 square(3.00)] and an icosahedral shell of only Al [Al-10.5 square(1.5)]. Following the proposal that the cubic 2/1 CA approximates the structure of the i-QC and on the basis of the observed transformation, an atomic site analysis of the 2/1 CA, which shows a preference to maximize the number of heteroatomic Au-Al nearest neighbor contacts over homoatomic Al-Al contacts, implies a similar outcome for the i-QC structure. Analysis of the most intense reflections in the diffraction pattern of the cubic 2/1 CA that changed during the phase transformation shows correlations with icosahedral symmetry, and the stability of this cubic phase is assessed using valence electron counts. According to electronic structure calculations, a cubic 1/1 CA, "Ca24Au88Al (64)" (CaAu3.67Al2.67) is proposed.

Update: 1-Mar-2018


Title:
On the kinetic and equilibrium shapes of icosahedral Al71Pd19Mn10 quasicrystals
Authors:
Senabulya, N; Xiao, XH; Han, I; Shahani, AJ Author Full Names: Senabulya, Nancy; Xiao, Xianghui; Han, Insung; Shahani, Ashwin J.
Source:
SCRIPTA MATERIALIA, 146 218-221; 10.1016/j.scriptamat.2017.11.049 MAR 15 2018
Abstract:
The dynamics of growth and relaxation of icosahedral single quasicrystals in a liquid phase were investigated using in situ synchrotron-based X-ray tomography. Our 4D studies (i.e., space- and time-resolved) provide direct evidence that indicates the growth process of an Al71Pd19Mn10 quasicrystal is governed predominantly by bulk transport rather than attachment kinetics. This work is in agreement with theoretical predictions, which show that the pentagonal dodecahedron is not the minimum energy structure in Al-Pd-Mn icosahedral quasicrystals, but merely a growth shape characterized by non-zero anisotropic velocity. This transient shape transforms into a truncated dodecahedral Archimedian polyhedron once equilibrium has been attained. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
A Cesium Rare-Earth Silicate Cs3RESi6O15 (RE = Dy-Lu, Y, In): The Parent of an Unusual Structural Class Featuring a Remarkable 57 angstrom Unit Cell Axis
Authors:
Terry, R; Vinton, D; McMillen, CD; Kolis, JW Author Full Names: Terry, Rylan; Vinton, Daniel; McMillen, Colin D.; Kolis, Joseph W.
Source:
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 57 (8):2077-2080; 10.1002/anie.201708798 FEB 19 2018
Abstract:
The structure of Cs3RESi6O15, where RE=Dy-Lu, Y, In, is unusual in that it contains octahedrally coordinated rare-earth ions; their relative orientation dictates the structure, as they rotate about the c-axis supported by the cyclic Si6O15 framework. The repeat unit of the rotation is eight units generating a very long (ca. 57 angstrom) unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. Previous work showed for the smaller Sc3+ ion, the rotation of the octahedra is not sufficient to achieve closure at an integral repeat unit and an incommensurate structure results. The products are prepared as large, high quality single crystals using a high-temperature (650 degrees C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product.

Title:
Enhancement and destruction of spin-Peierls physics in a one-dimensional quantum magnet under pressure
Authors:
Rotundu, CR; Wen, JJ; He, W; Choi, Y; Haskel, D; Lee, YS Author Full Names: Rotundu, Costel R.; Wen, Jiajia; He, Wei; Choi, Yongseong; Haskel, Daniel; Lee, Young S.
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054415 FEB 15 2018
Abstract:
The application of pressure reveals a rich phase diagram for the quantum S = 1/2 spin chain material TiOCl. We performed x-ray diffraction on single-crystal samples in a diamond-anvil cell down to T = 4 K and pressures up to 14.5 GPa. Remarkably, the magnetic interaction scale increases dramatically with increasing pressure, as indicated by the high onset temperature of the spin-Peierls phase. The spin-Peierls phase was probed at similar to 6 GPa up to 215 K but possibly extends in temperature to above T = 300 K, indicating the possibility of a quantum singlet state at room temperature. Near the critical pressure for the transition to the more metallic phase, coexisting phases are exemplified by incommensurate order in two directions. Further comparisons are made with the phase diagrams of related spin-Peierls systems that display metallicity and superconductivity under pressure.

Title:
Effect of imperfections on the hyperuniformity of many-body systems
Authors:
Kim, J; Torquato, S Author Full Names: Kim, Jaeuk; Torquato, Salvatore
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054105 FEB 12 2018
Abstract:
A hyperuniform many-body system is characterized by a structure factor S(k) that vanishes in the small-wave-number limit or equivalently by a local number variance sigma(2)(N) (R) associated with a spherical window of radius R that grows more slowly than R-d in the large-R limit. Thus, the hyperuniformity implies anomalous suppression of long-wavelength density fluctuations relative to those in typical disordered systems, i.e., sigma(2)(N) (R) similar to R-d as R -> infinity. Hyperuniform systems include perfect crystals, quasicrystals, and special disordered systems. Disordered hyperuniform systems are amorphous states of matter that lie between a liquid and crystal [S. Torquato et al., Phys. Rev. X 5, 021020 (2015)], and have been the subject of many recent investigations due to their novel properties. In the same way that there is no perfect crystal in practice due to the inevitable presence of imperfections, such as vacancies and dislocations, there is no "perfect" hyperuniform system, whether it is ordered or not. Thus, it is practically and theoretically important to quantitatively understand the extent to which imperfections introduced in a perfectly hyperuniform system can degrade or destroy its hyperuniformity and corresponding physical properties. This paper begins such a program by deriving explicit formulas for S(k) in the small-wave-number regime for three types of imperfections: (1) uncorrelated point defects, including vacancies and interstitials, (2) stochastic particle displacements, and (3) thermal excitations in the classical harmonic regime. We demonstrate that our results are in excellent agreement with numerical simulations. We find that "uncorrelated" vacancies or interstitials destroy hyperuniformity in proportion to the defect concentration p. We show that "uncorrelated" stochastic displacements in perfect lattices can never destroy the hyperuniformity but it can be degraded such that the perturbed lattices fall into class III hyperuniform systems, where sigma(2)(N) (R) similar to Rd-alpha as R -> infinity and 0 < alpha < 1. By contrast, we demonstrate that certain "correlated" displacements can make systems nonhyperuniform. For a perfect (ground-state) crystal at zero temperature, increase in temperature T introduces such correlated displacements resulting from thermal excitations, and thus the thermalized crystal becomes nonhyperuniform, even at an arbitrarily low temperature. It is noteworthy that imperfections in disordered hyperuniform systems can be unambiguously detected. Our work provides the theoretical underpinnings to systematically study the effect of imperfections on the physical properties of hyperuniform materials.

Title:
Magnetoelectric and Raman spectroscopic studies of monocrystalline MnCr2O4
Authors:
Lin, GT; Wang, YQ; Luo, X; Ma, J; Zhuang, HL; Qian, D; Yin, LH; Chen, FC; Yan, J; Zhang, RR; Zhang, SL; Tong, W; Song, WH; Tong, P; Zhu, XB; Sun, YP Author Full Names: Lin, G. T.; Wang, Y. Q.; Luo, X.; Ma, J.; Zhuang, H. L.; Qian, D.; Yin, L. H.; Chen, F. C.; Yan, J.; Zhang, R. R.; Zhang, S. L.; Tong, W.; Song, W. H.; Tong, P.; Zhu, X. B.; Sun, Y. P.
Source:
PHYSICAL REVIEW B, 97 (6):10.1103/PhysRevB.97.064405 FEB 12 2018
Abstract:
MnCr2O4 that exhibits spin frustration and complex spiral spin order is of great interest from both fundamental as well as application-oriented perspectives. Unlike CoCr2O4, whose ground state presents the coexistence of commensurate spiral spin order (CSSO) and ferroelectric order, MnCr2O4 shows no multiferroicity. One reason is that the spiral spin order is highly sensitive to the oxygen concentration in MnCr2O4. Here, we have successfully grown high-quality single-crystalline MnCr2O4 by the chemical vapor transport method. We observe a first-order magnetic transition from the incommensurate spiral spin order (ICSSO) at 19.4 K to the CSSO at 17.4 K. This magnetic transition is verified by magnetization, specific heat, and magnetoelectric measurements, which also confirm that the ground state exhibits the coexistence of the CSSO and magnetoelectricity below 17.4 K. Interestingly, the temperature evolution of Raman spectra between 5.4 and 300 K suggests that the structure remains the same. We also find that the phase-transition temperature of the CSSO decreases as applied magnetic field increases up to 45 kOe.

Title:
Magnetic state selected by magnetic dipole interaction in the kagome antiferromagnet NaBa2Mn3F11
Authors:
Hayashida, S; Ishikawa, H; Okamoto, Y; Okubo, T; Hiroi, Z; Avdeev, M; Manuel, P; Hagihala, M; Soda, M; Masuda, T Author Full Names: Hayashida, Shohei; Ishikawa, Hajime; Okamoto, Yoshihiko; Okubo, Tsuyoshi; Hiroi, Zenji; Avdeev, Maxim; Manuel, Pascal; Hagihala, Masato; Soda, Minoru; Masuda, Takatsugu
Source:
PHYSICAL REVIEW B, 97 (5):10.1103/PhysRevB.97.054411 FEB 12 2018
Abstract:
We haved studied the ground state of the classical kagome antiferromagnet NaBa2Mn3F11. Strong magnetic Bragg peaks observed for d spacings shorter than 6.0 angstrom were indexed by the propagation vector of k(0) = (0,0,0). Additional peaks with weak intensities in the d-spacing range above 8.0 angstrom were indexed by the incommensurate vector of k(1) = [0.3209(2), 0.3209(2), 0] and k(2) = [0.3338(4), 0.3338(4), 0]. Magnetic structure analysis unveils a 120 degrees. structure with the tail-chase geometry having k(0) modulated by the incommensurate vector. A classical calculation of the Heisenberg kagome antiferromagnet with antiferromagnetic second-neighbor interaction, for which the ground state a k(0) 120 degrees. degenerated structure, reveals that the magnetic dipole-dipole (MDD) interaction including up to the fourth neighbor terms selects the tail-chase structure. The observed modulation of the tail-chase structure is attributed to a small perturbation such as the long-range MDD interaction or the interlayer interaction.

Title:
Magnetic structure of the swedenborgite CaBa(Co3Fe)O-7 derived by unpolarized neutron diffraction and spherical neutron polarimetry
Authors:
Qureshi, N; Diaz, MTF; Chapon, LC; Senyshyn, A; Schweika, W; Valldor, M Author Full Names: Qureshi, N.; Diaz, M. T. Fernandez; Chapon, L. C.; Senyshyn, A.; Schweika, W.; Valldor, M.
Source:
PHYSICAL REVIEW B, 97 (6):10.1103/PhysRevB.97.064404 FEB 9 2018
Abstract:
We present a study that combines polarized and unpolarized neutrons to derive the magnetic structure of the swedenborgite compound CaBa(Co3Fe)O-7. Integrated intensities from a standard neutron diffraction experiment and polarization matrices from spherical neutron polarimetry have been simultaneously analyzed revealing a complex order, which differs from the usual spin configurations on a kagome lattice. We find that the magnetic structure is well described by a combination of two one-dimensional representations corresponding to themagnetic superspace symmetry P2(1)' and it consists of spins rotating around an axis close to the [110] direction. Due to the propagation vector q = (1/300), this modulation has cycloidal and helicoidal character rendering this system a potential multiferroic. The resulting spin configuration can be mapped onto the classical root 3 x root 3 structure of a kagome lattice, and it indicates an important interplay between the kagome and the triangular layers of the crystal structure.

Title:
Atomic channel occupation in disordered eta-Al5Fe2 and in two of its low-temperatures phases, eta '' and eta '''
Authors:
Becker, H; Leineweber, A Author Full Names: Becker, Hanka; Leineweber, Andreas
Source:
INTERMETALLICS, 93 251-262; 10.1016/j.intermet.2017.09.021 FEB 2018
Abstract:
High-temperature, disordered n-Al5Fe2 intermetallic and its low-temperature long-range ordered structures have been investigated in the whole homogeneity range from 70.6 to 73.0 at.% Al based on selected area electron diffraction data and powder X-ray diffraction data. Using these data, the channel site occupation in the disordered eta phase has been revised and a composition-dependent model with mixed occupation of the channels by both Al and Fe atoms was derived. It leads to an average number of atoms per channel and unit cell of approx. 1.5 in the whole homogeneity range. Below about 350 degrees C, four different phases exhibiting long-range order of the channel atoms appear to exist. Here the atomic ordering in the Al-poorest and Al-richest of these low-temperature phases, eta '' and eta ''' is reported. Both these phases can be characterized as incommensurately modulated composite crystal structures. Thereby, in both phases, the first composite subsystem contains atoms of the framework structure generating channels which are filled by atoms described by the second composite subsystem. The subsystems of the eta '' phase have orthorhombic superspace groups Xmcm(00g)0s0 and Inunm(00g)0s0 keeping the basic metric of the parent eta phase. The subsystems of the eta ''' can be described by the monoclinic superspace groups P2(1)/c(0b0)00 and P2(1)/c(0b0)s0 providing a lattice correspondence a(m) = 1/2(a + b), b(m) = c and c(m) = a +b to the orthorhombic parent eta phase. Although the number of atoms per channel is approx. 1.5 in eta '' and eta ''' phases, the channels are differently correlated with each other which is attributed to different Fe content in the channels inherited from the channel occupation in the disordered eta phase.

Title:
Observation of a dodecagonal oxide quasicrystal and its complex approximant in the SrTiO3-Pt(111) system
Authors:
Schenk, S; Forster, S; Meinel, K; Hammer, R; Leibundgut, B; Paleschke, M; Pantzer, J; Dresler, C; Schumann, FO; Widdra, W Author Full Names: Schenk, Sebastian; Foerster, Stefan; Meinel, Klaus; Hammer, Rene; Leibundgut, Bettina; Paleschke, Maximilian; Pantzer, Jonas; Dresler, Christoph; Schumann, Florian O.; Widdra, Wolf
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (13):10.1088/1361-648X/aa5bdb APR 5 2017
Abstract:
We report on the formation of a SrTiO3-derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(111). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO3-derived OQC exhibits strong similarities to the BaTiO3-derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO3-derived OQC is 1.8% smaller. Coexisting with the OQC a large scale approximant structure with a monoclinic unit cell is identified. It demonstrates the extraordinary level of complexity that oxide approximant structures can reach.

Update: 21-Feb-2018


Title:
A non-uniformly loaded anti-plane crack embedded in a half-space of a one-dimensional piezoelectric quasicrystal
Authors:
Tupholme, G Author Full Names: Tupholme, G. E.
Source:
MECCANICA, 53 (4-5):973-983; 10.1007/s11012-017-0759-1 MAR 2018
Abstract:
Closed-form representations are obtained using an extension of the classical continuous dislocation layer method combined with a method of images for the components of the phonon and phason stress and electric displacement fields around a generally loaded strip crack in a half-space of one-dimensional hexagonal piezoelectric quasicrystalline material parallel to its free surface. Representative numerical data are presented graphically.

Title:
Similar local order in disordered fluorite and aperiodic pyrochlore structures
Authors:
Shamblin, J; Tracy, CL; Palomares, RI; O'Quinn, EC; Ewing, RC; Neuefeind, J; Feygenson, M; Behrens, J; Trautmann, C; Lang, M Author Full Names: Shamblin, Jacob; Tracy, Cameron L.; Palomares, Raul I.; O'Quinn, Eric C.; Ewing, Rodney C.; Neuefeind, Joerg; Feygenson, Mikhail; Behrens, Jason; Trautmann, Christina; Lang, Maik
Source:
ACTA MATERIALIA, 144 60-67; 10.1016/j.actamat.2017.10.044 FEB 1 2018
Abstract:
A major challenge to understanding the response of materials to extreme environments (e.g., nuclear fuels/waste forms and fusion materials) is to unravel the processes by which a material can incorporate atomic-scale disorder, and at the same time, remain crystalline. While it has long been known that all condensed matter, even liquids and glasses, possess short-range order, the relation between fully-ordered, disordered, and aperiodic structures over multiple length scales is not well understood. For example, when defects are introduced (via pressure or irradiation) into materials adopting the pyrochlore structure, these complex oxides either disorder over specific crystallographic sites, remaining crystalline, or become aperiodic. Here we present neutron total scattering results characterizing the irradiation response of two pyrochlores, one that is known to disorder (Er2Sn2O7) and the other to amorphize (Dy2Sn2O7) under ion irradiation. The results demonstrate that in both cases, the local pyrochlore structure is transformed into similar short range configurations that are best fit by the orthorhombic weberite structure, even though the two compositions have distinctly different structures, aperiodic vs. disordered-crystalline, at longer length scales. Thus, a material's resistance to amorphization may not depend primarily on local defect formation energies, but rather on the structure's compatibility with meso-scale modulations of the local order in a way that maintains long-range periodicity. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Title:
Cesium immobilization in (Ba,Cr)-hollandites: Effects on structure
Authors:
Tumurugoti, P; Sundaram, SK; Misture, ST Author Full Names: Tumurugoti, Priyatham; Sundaram, S. K.; Misture, Scott T.
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 258 72-78; 10.1016/j.jssc.2017.10.008 FEB 2018
Abstract:
Hollandites with compositions Ba1.15-xCs2xCr2.3Ti5.7O16 (0 <= x <= 1.15) intended for the immobilization of cesium (Cs) from nuclear waste have been prepared, characterized, and analyzed for Cs retention properties. Sol-gel synthesized powders were used for structural characterization using a combination of X-ray, neutron, and electron diffraction techniques. Phase-pure hollandites adopting tetragonal (I4/m) or monoclinic symmetry (I2/m) were observed to form in the compositional range 0 <= x <= 0.4. Structural models for the compositions, x = 0, 0.15, and 0.25 were developed from Rietveld analysis of powder diffraction data. Refined anisotropic displacement parameters (beta(ij)) for the Ba and Cs ions in the hollandite tunnels indicate local disorder of Ba/Cs along the tunnel direction. In addition, weak superlattice reflections were observed in X-ray and electron diffraction patterns that were due to the compositional modulation i.e., ordering of ions and vacancies along tunnel direction. Our overall observations suggest the phase-pure hollandites studied assumed supercell structures with ordered tunnel cations, which in turn have positional disorder in individual supercells.

Title:
Phase relations in the pseudo ternary system In2O3-TiO2-BO (B: Zn, Co and Ni) at 1200 degrees C in air
Authors:
Brown, F; Jacobo-Herrera, IE; Alvarez-Montano, VE; Kimizuka, N; Hirano, T; Sekine, R; Denholme, SJ; Miyakawa, N; Kudo, A; Iwase, A; Michiue, Y Author Full Names: Brown, Francisco; Edmundo Jacobo-Herrera, Ivan; Emmanuel Alvarez-Montano, Victor; Kimizuka, Noboru; Hirano, Tomonosuke; Sekine, Ryotaro; Denholme, Saleem J.; Miyakawa, Nobuaki; Kudo, Akihiko; Iwase, Akihide; Michiue, Yuichi
Source:
JOURNAL OF SOLID STATE CHEMISTRY, 258 865-875; 10.1016/j.jssc.2017.12.020 FEB 2018
Abstract:
Phase relations in the pseudo ternary systems In2O3-TiO2-ZnO, In2O3-TiO2-CoO and In2O3-TiO2-NiO at 1200 degrees C in air were determined by means of a classic quenching method. In6Ti6BO22 (B: Zn, Co and Ni) which has the monoclinic In(Fe1/4Ti3/4)O-27/8-type of structure with a 4-dimensional super space group exists in a stable form. There exist homologous phases In1-x(Ti1/2Zn1/2)(1-x)O-3(ZnO)(m) (m: natural number, 0 m (No. 166) for m = odd or P63/mmc (No. 194) for m = even in space group. Lattice constants for each of the homologous compounds as a hexagonal setting and In6Ti6BO22 as the monoclinic system were determined by means of the powder X-ray diffraction method at room temperature. The temperature dependence of resistivity for In1-x(Ti1/2Zn1/2)(1-x)(ZnO)(4) (0.15 <= x <= 1) showed semiconducting like behavior for all samples examined at T(K) = 2-300. The resistivity increased systematically with decreasing x (0.7 <= x <= 1), and it was found that samples where x <= 0.7 became insulators. The optical band gap E-g (eV) of In1+x(Ti1/2Zn1/2)(1-x)(ZnO)(4) has been estimated from the diffuse reflection spectra for the whole range of x (0.15 <= x <= 1). A minimum value of 2.0717 eV for x = 1 and a maximum one of 3.066 eV for x = 0.15 were observed. Dependence of the crystal structures of the InAO(3)(BO), In(Ti1/2B1/2)O-3(B'O) and stability of In6Ti6BO22 upon the constituent cations in the pseudo quaternary system In2O3-TiO2-A(2)O(3)-BO (A: Fe, Ga and Cr; B, B': Mg, Zn, Co, Ni, Ca and Sr) were discussed in terms of their ionic radii and site preference effects.

Title:
Hybrid aluminium matrix composites containing boron carbide and quasicrystals: manufacturing and characterisation
Authors:
Khan, M; Zulfaqar, M; Ali, F; Subhani, T Author Full Names: Khan, Mahmood; Zulfaqar, Muhammad; Ali, Fahad; Subhani, Tayyab
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 33 (16):1955-1963; 10.1080/02670836.2017.1342017 2017
Abstract:
Hybrid composites of boron carbide (B4C) and Al62.5Cu25Fe12.5 quasicrystals (QCs) were prepared by ball milling and pressureless sintering in aluminium matrix to investigate their individual and hybrid effects on microstructural and mechanical properties. Hybrid composite contained B4C and QCs in 3 wt-% each, making a total of 6 wt-%. For reference, specimens of pure aluminium and two composites containing 6 wt-% B4C and 6 wt-% QCs were prepared. Microstructural characterisation was performed using optical, scanning electron microscopy and X-ray diffraction, while evaluation of mechanical properties was carried out by hardness and compression tests. Uniform dispersion of reinforcements in composites was observed along with significant increase in the mechanical properties. The composite containing 6 wt-% QCs demonstrated the highest hardness, while the hybrid composite showed better compressive properties.

Title:
Microstructure and mechanical properties of Mg-Zn-Y alloy under a steady magnetic field
Authors:
Zhang, L; Jin, F; Zhan, W; Hu, PH; Zhou, Q Author Full Names: Zhang, L.; Jin, F.; Zhan, W.; Hu, P. H.; Zhou, Q.
Source:
MATERIALS SCIENCE AND TECHNOLOGY, 33 (18):2197-2202; 10.1080/02670836.2017.1353662 2017
Abstract:
This study examined the effect of steady magnetic field on the microstructure and mechanical properties of Mg-Zn-Y alloy reinforced by icosahedral quasicrystal phase. Results show that the microstructure of Mg-Zn-Y alloy was further refined as the magnetic field intensity increased. However, the primary alpha-Mg gradually became coarse over a certain value. No significant effect on the refinement of icosahedral quasicrystal phase was observed. The (10 (1) over bar1) plane of the alloy treated by steady magnetic field was substituted by the (0002) plane as the primary plane. The (10 (1) over bar2) plane was intensified gradually as the intensity of the magnetic field increased. The mechanical properties of Mg-Zn-Y alloy also improved with steady magnetic field treatment.

Update: 15-Feb-2018


Title:
Relaxor nature in Ba5RZr3Nb7O30 (R = La, Nd, Sm) tetragonal tungsten bronze new system
Authors:
Feng, WB; Zhu, XL; Liu, XQ; Fu, MS; Ma, X; Jia, SJ; Chen, XM Author Full Names: Feng, Wen Bin; Zhu, Xiao Li; Liu, Xiao Qiang; Fu, Mao Sen; Ma, Xiao; Jia, Shu Jing; Chen, Xiang Ming
Source:
JOURNAL OF THE AMERICAN CERAMIC SOCIETY, 101 (4):1623-1631; 10.1111/jace.15332 APR 2018
Abstract:
Ba5RZr3Nb7O30(R=La, Nd, Sm) lead-free relaxor ferroelectrics were prepared by a standard solid-state reaction process, and the influence of A and B site ion occupation on the dielectric characteristics especially the relaxor nature were investigated systematically. Tetragonal tungsten bronze structure with space group P4/mbm was determined for all compositions, ion cross distribution by Ba2+ and R3+ in A1 site was observed, while A2 site was only occupied by Ba2+. Selected area electron diffraction patterns confirmed the existence of incommensurate superlattice modulation. Furthermore, temperature and frequency dependences of the dielectric properties showed a broad permittivity peak with strong frequency dispersion, following well the Vogel-Fulcher relationship. The maximum dielectric constant temperature increased gradually with decreasing A1 site ion size. Slim P-E hysteresis loops were obtained at room temperature for all compositions. Meanwhile, micro ferroelectric domains were observed in Ba5SmZr3Nb7O30. For Ba4R2Zr4Nb6O30 and Ba5RZr3Nb7O30 (R=Nd, Sm), the transition from normal ferroelectric to relaxor behavior originates from the increased t(A1), which is a result of cross distribution at A1 site. Compared with Ba5RTi3Nb7O30, Zr substitution at B site enhances the relaxor nature.

Title:
Crystallite size effect on the monoclinic deformation of the bcc crystal structure of chromium
Authors:
Przenioslo, R; Fabrykiewicz, P; Sosnowska, I; Wardecki, D; Slawinski, WA; Playford, HY; Hempelmann, R; Bukowski, M Author Full Names: Przenioslo, R.; Fabrykiewicz, P.; Sosnowska, I.; Wardecki, D.; Slawinski, W. A.; Playford, H. Y.; Hempelmann, R.; Bukowski, M.
Source:
PHYSICA B-CONDENSED MATTER, 530 183-190; 10.1016/j.physb.2017.10.086 FEB 1 2018
Abstract:
The modulated spin density wave magnetic orderings observed in chromium suggests that the crystal structure of chromium cannot be described by the cubic space group Im3m. Our experimental studies of polycrystalline and nanocrystalline chromium by synchrotron radiation (SR) and neutron powder diffraction show a hkl-dependent Bragg peak broadening which can be interpreted by the low-symmetry monoclinic space group P2(1)/n instead of the high symmetry cubic space group Im3m. Themonoclinic angle is beta(m) = 90.05(1)degrees and 90.29(1)degrees for polycrystalline Cr and nanocrystalline Cr, respectively. The relative monoclinic distortion observed in chromium is 5 times larger than those reported for several oxides: BiFeO3, alpha-Fe2O3, Cr2O3 and calcite. The symmetry of the magnetic transverse spin density wave (TSDW) and the longitudinal spin density wave (LSDW) observed in Cr are described by using the superspace groups P2(1)/n(0 beta 0)00 and P2'(1)/n'(0 beta 0)00, respectively. These superspace groups describe both the magnetic modulations and the atomic position modulations reported in the literature. The monoclinic symmetry of chromium is a robust effect which is observed in the paramagnetic as well as in the TSDW and LSDW phases.

Update: 7-Feb-2018


Title:
Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca3Ru2O7 with Fe substitution
Authors:
Zhu, M; Hong, T; Peng, J; Zou, T; Mao, ZQ; Ke, X Author Full Names: Zhu, M.; Hong, T.; Peng, J.; Zou, T.; Mao, Z. Q.; Ke, X.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 30 (7):10.1088/1361-648X/aaa626 FEB 21 2018
Abstract:
Bilayer ruthenate Ca-3(Ru(1-x)Fex)(2)O-7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii-Moriya interaction. Here we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurateto- commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on the temperature and the applied field orientation. We suggest that the observed field-induced metastability may be ascribable to the quenched kinetics at low temperature.

Title:
Two superstructures of Ce3Rh4Ge4
Authors:
Vosswinkel, D; Hoffmann, RD; Svitlyk, V; Hermes, W; Greiwe, M; Niehaus, O; Chevalier, B; Matar, SF; Al Alam, AF; Nakhl, M; Ouaini, N; Pottgen, R Author Full Names: Vosswinkel, Daniel; Hoffmann, Rolf-Dieter; Svitlyk, Volodymyr; Hermes, Wilfried; Greiwe, Magnus; Niehaus, Oliver; Chevalier, Bernard; Matar, Samir F.; Al Alam, Adel F.; Nakhl, Michel; Ouaini, Naim; Poettgen, Rainer
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (2):81-95; 10.1515/zkri-2017-2092 FEB 2018
Abstract:
Two different samples of Ce3Rh4Ge4 were synthesized from different starting compositions by melting of the elements in an arc-melting furnace followed by annealing sequences in a sealed tantalum ampoule in a muffle furnace. The structures of two different stacking variants were refined on the basis of temperature dependent single-crystal X-ray diffractometer data. At high temperature Ce3Rh4Ge4 adopts the U3Ni4Si4 type structure with strongly enhanced anisotropic displacement parameters for the Rh1 atoms. For the two different crystals, additional reflections start to appear at different temperatures. The first crystal showed additional reflections already at room temperature (stacking variant I) and the second one showed additional reflections emerging below 270 K (stacking variant II). Stacking variant I could be described with the (3 + 1)D superspace group I2/m(alpha 0 gamma)00; alpha = 1/2a*, gamma = 1/2c*; (Z = 2), 1252 F-2 values, 48 variables, wR = 0.0306 for the main and wR = 0.0527 for 440 1st order satellite reflections, similar to Pr3Rh4Ge4. For stacking variant II the (3 + 1) D superspace group is Immm(alpha 00)00s; alpha = 1/2a*; (Z = 2). The structure could be refined with 1261 F-2 values, 53 variables and residuals of wR = 0.0331 for the main reflections and wR = 0.1755 (R1(obs) = 0.0788) for the 1st order satellite reflections, [a = 406.2(1), b = 423.7(1) and c = 2497.1(1) pm]. The commensurate description could be transformed to a three-dimensional (3D)supercell with space group Pnma and Z = 4: a = 812.5(1), b = 423.7(1), c = 2497.1(2) pm, 1261 F-2 values, 69 variables and wR = 0.0525. The relation of the U3Ni4Si4 type structure, the (3 + 1) D modulated and the 3D supercells are discussed on the basis of group-subgroup schemes. Ab initio electronic structure calculations are in line with the diffraction experiments, revealing the lowest total energy for the Pnma phase.

Title:
Incommensurate Phonon Anomaly and the Nature of Charge Density Waves in Cuprates
Authors:
Miao, H; Ishikawa, D; Heid, R; Le Tacon, M; Fabbris, G; Meyers, D; Gu, GD; Baron, AQR; Dean, MPM Author Full Names: Miao, H.; Ishikawa, D.; Heid, R.; Le Tacon, M.; Fabbris, G.; Meyers, D.; Gu, G. D.; Baron, A. Q. R.; Dean, M. P. M.
Source:
PHYSICAL REVIEW X, 8 (1):10.1103/PhysRevX.8.011008 JAN 18 2018
Abstract:
While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wave vectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here, we investigate the temperature dependence of the low-energy phonons in the canonical CDW-ordered cuprate La1.875Ba0.125CuO4. We discover that the phonon softening wave vector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wave vector of 0.238 reciprocal lattice units (r.l.u.) below the ordering transition temperature to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that "214"-type cuprates can host CDW correlations at a similar wave vector to previously reported CDW correlations in non-214-type cuprates such as YBa2Cu3O6+delta. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.

Title:
The partial substitution of Y with Gd on microstructures and mechanical properties of as-cast and as-extruded Mg-10Zn-6Y-0.5Zr alloy
Authors:
Jiang, HS; Qiao, XG; Zheng, MY; Wu, K; Xu, C; Kamado, S Author Full Names: Jiang, H. S.; Qiao, X. G.; Zheng, M. Y.; Wu, K.; Xu, C.; Kamado, S.
Source:
MATERIALS CHARACTERIZATION, 135 96-103; 10.1016/j.matchar.2017.11.025 JAN 2018
Abstract:
Mg-10Zn-6Y-0.5Zr (wt%) alloy and Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy with medium RE content have been fabricated by conventional casting and indirect extrusion. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy shows a bimodal microstructure containing dynamic recrystallized (DRXed) grains with average grain size of 2 mu m and deformed regions. In addition to the fragmented W phase particle bands distributing along the extrusion direction, large amount of nano W phase and small amount of nano beta(2)' phase are precipitated in the matrix. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy exhibits completely dynamic recrystallized microstructure with average grain size of 3 mu m. The broken W phase particles are distributed homogeneously in the matrix. Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy exhibits yield strength of 341 MPa, ultimate tensile strength of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy shows lower yield strength of 247 MPa, ultimate tensile strength of 330 MPa and higher elongation to failure of 19.8%. The higher strength in the as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy is mainly attributed to higher area fraction of unDRXed regions with strong texture and the precipitation of nano W and beta(2)' phase. The fully recrystallized microstructure with weak texture and the formation of icosahedral quasi crystal phases with good coherent bond with alpha-Mg contribute to the good ductility of the as-extruded Mg-10Zn3Y-3Gd-0.5Zr alloy.

Update: 1-Feb-2018


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

Update: 25-Jan-2018


Title:
Discovery of superconductivity in quasicrystal
Authors:
Kamiya, K; Takeuchi, T; Kabeya, N; Wada, N; Ishimasa, T; Ochiai, A; Deguchi, K; Imura, K; Sato, NK Author Full Names: Kamiya, K.; Takeuchi, T.; Kabeya, N.; Wada, N.; Ishimasa, T.; Ochiai, A.; Deguchi, K.; Imura, K.; Sato, N. K.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-017-02667-x JAN 11 2018
Abstract:
Superconductivity is ubiquitous as evidenced by the observation in many crystals including carrier-doped oxides and diamond. Amorphous solids are no exception. However, it remains to be discovered in quasicrystals, in which atoms are ordered over long distances but not in a periodically repeating arrangement. Here we report electrical resistivity, magnetization, and specific-heat measurements of Al-Zn-Mg quasicrystal, presenting convincing evidence for the emergence of bulk superconductivity at a very low transition temperature of T-c congruent to 0: 05 K. We also find superconductivity in its approximant crystals, structures that are periodic, but that are very similar to quasicrystals. These observations demonstrate that the effective interaction between electrons remains attractive under variation of the atomic arrangement from periodic to quasiperiodic one. The discovery of the superconducting quasicrystal, in which the fractal geometry interplays with superconductivity, opens the door to a new type of superconductivity, fractal superconductivity.

Title:
Unidirectional spin density wave state in metallic (Sr1-xLax)(2)IrO4
Authors:
Chen, X; Schmehr, JL; Islam, Z; Porter, Z; Zoghlin, E; Finkelstein, K; Ruff, JPC; Wilson, SD Author Full Names: Chen, Xiang; Schmehr, Julian L.; Islam, Zahirul; Porter, Zach; Zoghlin, Eli; Finkelstein, Kenneth; Ruff, Jacob P. C.; Wilson, Stephen D.
Source:
NATURE COMMUNICATIONS, 9 10.1038/s41467-017-02647-1 JAN 9 2018
Abstract:
Materials that exhibit both strong spin-orbit coupling and electron correlation effects are predicted to host numerous new electronic states. One prominent example is the J(eff) = 1/2 Mott state in Sr2IrO4, where introducing carriers is predicted to manifest high temperature superconductivity analogous to the S = 1/2 Mott state of La2CuO4. While bulk super-conductivity currently remains elusive, anomalous quasiparticle behaviors paralleling those in the cuprates such as pseudogap formation and the formation of a d-wave gap are observed upon electron-doping Sr2IrO4. Here we establish a magnetic parallel between electron-doped Sr2IrO4 and hole-doped La2CuO4 by unveiling a spin density wave state in electron-doped Sr2IrO4. Our magnetic resonant X-ray scattering data reveal the presence of an incommensurate magnetic state reminiscent of the diagonal spin density wave state observed in the monolayer cuprate (La1-xSrx)(2)CuO4. This link supports the conjecture that the quenched Mott phases in electron-doped Sr2IrO4 and hole-doped La2CuO4 support common competing electronic phases.

Title:
Lattice Distortions in TlInSe2 Thermoelectric Material Studied by X-Ray Absorption Fine Structure
Authors:
Hosokawa, S; Stellhorn, JR; Ikemoto, H; Mimura, K; Wakita, K; Mamedov, N Author Full Names: Hosokawa, Shinya; Stellhorn, Jens Ruediger; Ikemoto, Hiroyuki; Mimura, Kojiro; Wakita, Kazuki; Mamedov, Nazim
Source:
PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 215 (1):10.1002/pssa.201700416 JAN 2018
Abstract:
Tl L-II and In K X-ray absorption fine structure (XAFS) measurements were performed on a TlInSe2 thermoelectric material in the temperature range of 25-300K including the incommensurate-commensurate phase transition temperature of about 135K. Most of the bond lengths obtained from the present XAFS measurements are in good agreement with existing X-ray diffraction data at room temperature, while only the Tl-Tl correlation shows inconsistent values indicating the commensurate properties of the Tl chains expected from the thermodynamic properties. The present XAFS data clearly support positional fluctuations of the Tl atoms found in three-dimensional atomic images reconstructed from X-ray fluorescence holography.

Title:
Hyperuniformity variation with quasicrystal local isomorphism class (vol 29, 204003, 2017)
Authors:
Lin, C; Steinhardt, PJ; Torquato, S Author Full Names: Lin, C.; Steinhardt, P. J.; Torquato, S.
Source:
JOURNAL OF PHYSICS-CONDENSED MATTER, 29 (47):10.1088/1361-648X/aa8430 NOV 29 2017

Update: 17-Jan-2018


Title:
Spin waves in planar quasicrystal of Penrose tiling
Authors:
Rychly, J; Mieszczak, S; Klos, JW Author Full Names: Rychly, J.; Mieszczak, S.; Klos, J. W.
Source:
JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 450 18-23; 10.1016/j.jmmm.2017.03.029 MAR 15 2018
Abstract:
We investigated two-dimensional magnonic structures which are the counterparts of photonic quasicrystals forming Penrose tiling. We considered the slab composed of Ni (or Py) disks embedded in Fe (or Co) matrix. The disks are arranged in quasiperiodic Penrose-like structure. The infinite quasicrystal was approximated by its rectangular section with periodic boundary conditions applied. This approach allowed us to use the plane wave method to find the frequency spectrum of eigenmodes for spin waves and their spatial profiles. The calculated integrated density of states shows more distinctive magnonic gaps for the structure composed of materials of high magnetic contrast (Ni and Fe) and relatively high filling fraction. This proves the impact of quasiperiodic long-range order on the spectrum of spin waves. We also investigated the localization of spin wave eingenmodes resulting from the quasiperiodicity of the structure. (C) 2017 Elsevier B.V. All rights reserved.

Title:
Defects in Static Elasticity of Quasicrystals
Authors:
Xu, Q; Lu, J; Li, W Author Full Names: Xu, Qin; Lu, Jing; Li, Wu
Source:
CRYSTALS, 7 (12):10.3390/cryst7120373 DEC 2017
Abstract:
A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The analytic and numerical solutions of dislocations and crack in quasicrystals are the core of the static and dynamic elasticity theory, and this paper gives a comprehensive review on the solutions for dislocations and crack with different configurations in different various important quasicrystalline systems. We review some results in linear elasticity of quasicrystals, referring to different boundary value problems. We also add some new achievements.

Title:
Structurally Complex Frank-Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability
Authors:
Degtyareva, VF; Afonikova, NS Author Full Names: Degtyareva, Valentina F.; Afonikova, Natalia S.
Source:
CRYSTALS, 7 (12):10.3390/cryst7120359 DEC 2017
Abstract:
Metal crystals with tetrahedral packing are known as Frank-Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number of valence electrons per atom. The significance of the electronic energy contribution is analyzed within the Fermi sphere-Brillouin zone interaction model for several typical examples: Cu4Cd3, Mg2Al3 with over a thousand atoms per cell, and for icosahedral quasicrystal approximants with 146-168 atoms per cell. Our analysis shows that to minimize the crystal energy, it is important that the Fermi sphere (FS) is in contact with the Brillouin zones that are related to the strong diffraction peaks: the zones either inscribe the FS or are circumscribed by the FS creating contact at edges or vertices.

Update: 11-Jan-2018


Title:
Influence of Ag replacement on supercooled liquid region and icosahedral phase precipitation of Zr65Al7.5Ni10Cu17.5-xAgx (x=0-17.5 at%) glassy alloys
Authors:
Li, MM; Inoue, A; Han, Y; Kong, FL; Zhu, SL; Shalaan, E; Al-Marzouki, F Author Full Names: Li, M. M.; Inoue, A.; Han, Y.; Kong, F. L.; Zhu, S. L.; Shalaan, E.; Al-Marzouki, F.
Source:
JOURNAL OF ALLOYS AND COMPOUNDS, 735 1712-1721; 10.1016/j.jallcom.2017.11.203 FEB 25 2018
Abstract:
The glass transition phenomenon for Zr65Al7.5Ni10Cu17.5-xAgx (x = 5-17.5 at%) glassy alloys was observed in the Ag content range below about 15% and the icosahedral phase precipitated as the heating-induced primary phase in the limited Ag content range. In the higher Ag content range where glass transition is not clearly observed, the primary precipitation phase changed to mixed phases of tetragonal Zr3Ag + tetragonal Zr2Ni + hexagonal Zr4Al3. The good correspondence between the appearance of glass transition and the icosahedral phase precipitation was recognized in the multicomponent glassy alloys containing the immiscible type atomic pairs of Ni-Ag and Cu-Ag. Although neither glass transition nor supercooled liquid region is observed for Zr65Al7.5Ni10Ag17.5 and no icosahedral phase is formed, a modified Zr65Al7.5Ni17.5Ag10 alloy with higher Ni/Ag content ratio exhibits glass transition and supercooled liquid region and the primary precipitates also changes to an icosahedral phase. The good correspondence can be interpreted on the basis of the previous knowledge that the appearance of glass transition and supercooled liquid state originates from icosahedral-like medium range ordered atomic configurations. Besides, the 6% Ag-containing alloy keeps high glass-forming ability which is high enough to form a bulk glassy alloy rod of 6 mm by suction casting. The close correlation between the appearance of glass transition phenomenon and the primary precipitation of icosahedral phase is expected to provide a useful knowledge on the role of icosahedral-like atomic configuration in the achievement of bulk glass-forming ability through the stabilization of supercooled liquid. (C) 2017 Elsevier B.V. All rights reserved.

Title:
The role of hydrogen bonds in order-disorder transition of a new incommensurate low temperature phase beta-[Zn-(C7H4NO4)(2)]center dot 3H(2)O
Authors:
Tabatabaee, M; Poupon, M; Eigner, V; Vanek, P; Dusek, M Author Full Names: Tabatabaee, Masoumeh; Poupon, Morgane; Eigner, Vaclav; Vanek, Premysl; Dusek, Michal
Source:
ZEITSCHRIFT FUR KRISTALLOGRAPHIE-CRYSTALLINE MATERIALS, 233 (1):17-25; 10.1515/zkri-2016-2013 JAN 2018
Abstract:
The room temperature structure with P2(1)/c symmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid. Acta Crystallogr. C. 2000, 56, 305). Here we report crystal structure of the low temperature phase beta-[Zn(pydcH)(2)]center dot 3H(2)O, pydc = C7H3NO4, resulting from the phase transition around 200 K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3 + 1)D incommensurately modulated structure. The modulated structure was solved in the superspace group X2(1)/c(0b0)s0, where X stands for a nonstandard centring vector (1/2, 0, 0, 1/2), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.

Title:
Spatially modulated magnetic structure of EuS due to the tetragonal domain structure of SrTiO3
Authors:
Rosenberg, AJ; Katmis, F; Kirtley, JR; Gedik, N; Moodera, JS; Moler, KA Author Full Names: Rosenberg, Aaron J.; Katmis, Ferhat; Kirtley, John R.; Gedik, Nuh; Moodera, Jagadeesh S.; Moler, Kathryn A.
Source:
PHYSICAL REVIEW MATERIALS, 1 (7):10.1103/PhysRevMaterials.1.074406 DEC 15 2017
Abstract:
The combination of ferromagnets with topological superconductors or insulators allows for new phases of matter that support excitations such as chiral edge modes and Majorana fermions. EuS, a wide-bandgap ferromagnetic insulator with a Curie temperature around 16 K, and SrTiO3 (STO), an important substrate for engineering heterostructures, may support these phases. We present scanning superconducting quantum interference device measurements of EuS grown epitaxially on STO that reveal micron-scale variations in ferromagnetism and paramagnetism. These variations are oriented along the STO crystal axes and only change their configuration upon thermal cycling above the STO cubic-to-tetragonal structural transition temperature at 105 K, indicating that the observed magnetic features are due to coupling between EuS and the STO tetragonal structure. We speculate that the STO tetragonal distortions may strain the EuS, altering the magnetic anisotropy on a micron scale. This result demonstrates that local variation in the induced magnetic order from EuS grown on STO needs to be considered when engineering new phases of matter that require spatially homogeneous exchange.


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