Phase Equilibria in Aluminium–Ruthenium–Silicon System near 1200 Kelvin
Koichi Kitahara, Hiroyuki Takakura, Yutaka Iwasaki, Kaoru Kimura
MATERIALS TRANSACTIONS 65 1 18 - 26 2024年01月01日 [査読有り]
Crystal structures of five compounds in the aluminium–ruthenium–silicon system
Koichi Kitahara, Hiroyuki Takakura, Yutaka Iwasaki, Kaoru Kimura
Acta Crystallographica Section E Crystallographic Communications 79 10 946 - 951 2023年09月29日 [査読有り]
Single crystals of five compounds with approximate compositions ∼Ru16(Al0.78Si0.22)47, (I), ∼Ru9(Al0.70Si0.30)32, (II), ∼Ru10(Al0.67Si0.33)41, (III), ∼Ru(Al0.57Si0.43)5, (IV), and ∼Ru2(Al0.46Si0.54)9, (V), were obtained from polycrystalline lumps mainly composed of the target compounds, and their crystal structures were determined by means of single-crystal X-ray diffraction. The crystal structure of (I) can be related to that of a cubic rational crystalline approximant to an icosahedral quasicrystal through crystallographic shear and then unit-cell twinning. The crystal structure of (II) is isotypic with that of a phase with composition ∼Fe9(Al,Si)32. The crystal structure of (III) is comprised of edge-sharing Ru(Al,Si)9–11 polyhedra with disordered chains along edges of polyhedra. The crystal structure of (IV) is of the LiIrSn4 type. The crystal structure of (V) can be viewed as a crystallographic shear structure derived from that of (IV).
Formation and structure of 1/1 cubic approximants in the Cd-Mg-Ce system: The identification of a new structural variant
Farid Labib, Nobuhisa Fujita, Hiroyuki Takakura, Satoshi Ohhashi, Takayuki Shiino, An-Pang Tsai, Ryuji Tamura
Journal of Alloys and Compounds 954 170151 - 170151 2023年09月 [査読有り]
Magnetic properties of the quasicrystal approximant Au65Ga21Tb14
Kazuhiro Nawa, Maxim Avdeev, Asuka Ishikawa, Hiroyuki Takakura, Chin-Wei Wang, Daisuke Okuyama, Ryo Murasaki, Ryuji Tamura, Taku J. Sato
Physical Review Materials 7 5 2023年05月31日 [査読有り]
Atomic structure of the unique antiferromagnetic 2/1 quasicrystal approximant
Farid Labib, Hiroyuki Takakura, Asuka Ishikawa, Ryuji Tamura
Physical Review B 107 18 2023年05月15日 [査読有り]
Growth and characterisation of single grain Al-Cu-Ru icosahedral quasicrystals from self-fluxes
Kotoba Toyonaga, Ryosei Shibata, Tsunetomo Yamada, Marc de Boissieu, Olivier Peréz, Pierre Fertey, Hiroyuki Takakura
Philosophical Magazine 100 17 2220 - 2243 2020年09月01日 [査読有り]
The structure solution of the F-type i-ZnMgHf from the X-ray diffraction
Ireneusz Buganski, Kotoba Toyonaga, Hiroyuki Takakura, Tsunetomo Yamada, Marc de Boissieu, Olivier Perez, Pierre Fertey, Janusz Wolny
Materials Science and Technology 36 9 989 - 995 2020年06月12日 [査読有り]
The atomic structure of the Bergman-type icosahedral quasicrystal based on the Ammann–Kramer–Neri tiling
Ireneusz Buganski, Janusz Wolny, Hiroyuki Takakura
Acta Crystallographica Section A Foundations and Advances 76 2 180 - 196 2020年02月11日 [査読有り]
In this study, the atomic structure of the ternary icosahedral ZnMgTm quasicrystal (QC) is investigated by means of single-crystal X-ray diffraction. The structure is found to be a member of the Bergman QC family, frequently found in Zn–Mg–rare-earth systems. Theab initiostructure solution was obtained by the use of theSuperflipsoftware. The infinite structure model was founded on the atomic decoration of two golden rhombohedra, with an edge length of 21.7 Å, constituting the Ammann–Kramer–Neri tiling. The refined structure converged well with the experimental diffraction diagram, with the crystallographicRfactor equal to 9.8%. The Bergman clusters were found to be bonded by four possible linkages. Only two linkages,bandc, are detected in approximant crystals and are employed to model the icosahedral QCs in the cluster approach known for the CdYb Tsai-type QC. Additional shortbandalinkages are found in this study. Short interatomic distances are not generated by those linkages due to the systematic absence of atoms and the formation of split atomic positions. The presence of four linkages allows the structure to be pictured as a complete covering by rhombic triacontahedral clusters and consequently there is no need to define the interstitial part of the structure (i.e.that outside the cluster). The 6D embedding of the solved structure is discussed for the final verification of the model.
Atomic structures of ternary Yb-Cd-Mg icosahedral quasicrystals and a 1/1 approximant
Tsunetomo Yamada, Hiroyuki Takakura, Marc de Boissieu, An-Pang Tsai
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS 73 6 1125 - 1141 2017年12月 [査読有り][通常論文]
Atomic structures of ternary icosahedral (i) Yb-Cd-Mg quasicrystals (QCs) with five different Mg contents up to 46.4 at.% and a corresponding 1/1 approximant (AP), which has a composition of Yb13.3Cd70.3Mg16.5, have been analysed by single-crystal X-ray diffraction. The structures of the iQCs were found to be isostructural to the parent i-YbCd5.7, which consists of a so-called Tsai-type rhombic triacontahedron (RTH) cluster and double Friauf polyhedron, and that of the 1/1 AP was found to be isostructural to YbCd6, which is described by a body-centred packing of the same type of RTH cluster. In the iQCs, it was found that there are three types of Cd/Mg occupation, namely, Cd preferential site, Mg preferential site and Cd/Mg mixed site, and the occupation probabilities of Mg atoms at the Mg preferential site show a saturation behaviour around the Mg content of 20 at.%. This selective Mg occupation is identified as a cause of the non-linear increase in the icosahedral lattice constant with increasing Mg content. The 1/1 AP has a similar selective Mg occupation to that of the iQCs in terms of the shell structures of the Tsai-type RTH cluster. In both iQCs and the 1/1 AP, the Mg preferential sites have a smaller number of Yb atoms among their coordination numbers. Moreover, short-range order (s.r.o.) diffuse scattering was observed on the diffraction patterns of the iQCs at the positions corresponding to a face-centred-type (F-type) icosahedral superlattice. The F-type s.r.o. was found to result from the Mg substitution.
Atomic structure of the i-R-Cd quasicrystals and consequences for magnetism
T. Yamada, H. Takakura, T. Kong, P. Das, W. T. Jayasekara, A. Kreyssig, G. Beutier, P. C. Canfield, M. de Boissieu, A. I. Goldman
PHYSICAL REVIEW B 94 6 060103-1 - 060103-5 2016年08月 [査読有り][通常論文]
We report on the six-dimensional (6D) structural refinement of three members of the i-R-Cd quasicrystals (R = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-YbCd5.7 quasicrystal. However, our refinements suggest that the R occupancy on the Yb icosahedron sites within the Tsai-type atomic cluster is approximately 80%, with the balance taken up by Cd. Similarities between the i-R-Cd series and i-ScZn7.33, and their differences with i-YbCd5.7 and i-Ca15Cd85, indicate that there are at least two subclasses of Tsai-type icosahedral quasicrystals. We further show from x-ray resonant magnetic scattering (XRMS) measurements on a set of closely related Tb1-xYxCd6 1/1 approximants that the dilution of themagnetic R ions on the icosahedron within the Tsai-type cluster by nonmagnetic Y disrupts the commensurate magnetic ordering in the approximant phase.
Atomic structure and phason modes of the Sc-Zn icosahedral quasicrystal
Tsunetomo Yamada, Hiroyuki Takakura, Holger Euchner, Cesar Pay Gomez, Alexei Bosak, Pierre Fertey, Marc de Boissieu
IUCRJ 3 247 - 258 2016年07月 [査読有り][通常論文]
The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.
The quasiperiodic average structure of highly disordered decagonal Zn-Mg-Dy and its temperature dependence
Taylan Ors, Hiroyuki Takakura, Eiji Abe, Walter Steurer
ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS 70 2 315 - 330 2014年04月 [査読有り][通常論文]
A single-crystal X-ray diffraction structure analysis of decagonal Zn-Mg-Dy, a Frank-Kasper-type quasicrystal, was performed using the higher-dimensional approach. For this first Frank-Kasper (F-K) decagonal quasicrystal studied so far, significant differences to the decagonal Al-TM-based (TM: transition metal) phases were found. A new type of twofold occupation domain is located on certain edge centers of the five-dimensional unit cell. The structure can be described in terms of a two-cluster model based on a decagonal cluster (similar to 23 angstrom diameter) arranged on the vertices of a pentagon-Penrose tiling (PPT) and a star-like cluster covering the remaining space. This model is used for the five-dimensional refinements, which converged to an R value of 0.126. The arrangement of clusters is significantly disordered as indicated by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). In order to check the structure and stability at higher temperatures, in-situ high-temperature (HT) single-crystal X-ray diffraction experiments were conducted at 598 and 648 K (i.e. slightly below the decomposition temperature). The structure does not change significantly, however, the best quasiperiodic order is found at 598 K. The implication of these results on the stabilization mechanism of quasicrystals is discussed.
Valence Change Driven by Constituent Element Substitution in the Mixed-Valence Quasicrystal and Approximant Au-Al-Yb
Shuya Matsukawa, Katsumasa Tanaka, Mika Nakayama, Kazuhiko Deguchi, Keiichiro Imura, Hiroyuki Takakura, Shiro Kashimoto, Tsutomu Ishimasa, Noriaki K. Sato
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 83 3 034705-1 - 034705-5 2014年03月 [査読有り][通常論文]
Quantum criticality has been considered to be specific to crystalline materials such as heavy fermions. Very recently, however, the Tsai-type quasicrystal Au51Al34Yb15 has been reported to show unusual quantum critical behavior. To obtain a deeper understanding of this new material, we have searched for other Tsai-type cluster materials. Here, we report that the metal alloys Au44Ga41Yb15 and Ag47Ga38Yb15 are members of the 1/1 approximant to the Tsai-type quasicrystal and that both possess no localized magnetic moment. We suggest that the Au-Al-Yb system is located near the border of the divalent and trivalent states of the Yb ion; we also discuss a possible origin of the disappearance of magnetism, associated with the valence change, by the substitution of the constituent elements.
In-situ high-pressure X-ray diffraction on the Zn6Sc 1/1 periodic cubic approximant to a quasicrystal
Tsunetomo Yamada, Gaston Garbarino, Hiroyuki Takakura, Cesar Pay Gòmez, Ryuji Tamura, Marc de Boissieu
Zeitschrift für Kristallographie – Crystalline Materials 229 3 2014年01月 [査読有り]
Short- and long-range ordering during the phase transition of the Zn6Sc 1/1 cubic approximant
Tsunetomo Yamada, Holger Euchner, Cesar Pay Gómez, Hiroyuki Takakura, Ryuji Tamura, Marc de Boissieu
Journal of Physics: Condensed Matter 25 20 205405 - 205405 2013年05月22日 [査読有り]
Quantum critical state in a magnetic quasicrystal
Kazuhiko Deguchi, Shuya Matsukawa, Noriaki K. Sato, Taisuke Hattori, Kenji Ishida, Hiroyuki Takakura, Tsutomu Ishimasa
NATURE MATERIALS 11 12 1013 - 1016 2012年12月 [査読有り][通常論文]
Quasicrystals are metallic alloys that possess long-range, aperiodic structures with diffraction symmetries forbidden to conventional crystals. Since the discovery of quasicrystals by Schechtman et al. in 1984(1), there has been considerable progress in resolving their geometric structure. For example, it is well known that the golden ratio of mathematics and art occurs over and over again in their crystal structure. However, the characteristic properties of the electronic states-whether they are extended as in periodic crystals or localized as in amorphous materials-are still unresolved. Here we report the first observation of quantum (T = 0) critical phenomena of the Au-Al-Yb quasicrystal-the magnetic susceptibility and the electronic specific heat coefficient arising from strongly correlated 4f electrons of the Yb atoms diverge as T -> 0. Furthermore, we observe that this quantum critical phenomenon is robust against hydrostatic pressure. By contrast, there is no such divergence in a crystalline approximant, a phase whose composition is close to that of the quasicrystal and whose unit cell has atomic decorations (that is, icosahedral clusters of atoms) that look like the quasicrystal. These results clearly indicate that the quantum criticality is associated with the unique electronic state of the quasicrystal, that is, a spatially confined critical state. Finally we discuss the possibility that there is a general law underlying the conventional crystals and the quasicrystals.
Lattice dynamics of the Zn-Mg-Sc icosahedral quasicrystal and its Zn-Sc periodic 1/1 approximant
Marc De Boissieu, Sonia Francoual, Marek Mihalkovič, Kaoru Shibata, Alfred Q.R. Baron, Yvan Sidis, Tsutomu Ishimasa, Dongmei Wu, Thomas Lograsso, Louis Pierre Regnault, Franz Gähler, Satoshi Tsutsui, Bernard Hennion, Pierre Bastie, Taku J. Sato, Hiroyuki Takakura, Roland Currat, An Pang Tsai
Nature Materials 6 12 977 - 984 2007年12月 [査読有り][通常論文]
Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics ofquasicrystals.
Atomic structure of the binary icosahedral Yb–Cd quasicrystal
Hiroyuki Takakura, Cesar Pay Gómez, Akiji Yamamoto, Marc De Boissieu, An Pang Tsai
Nature Materials 6 58 - 63 2006年12月10日 [査読有り]
密度修正法による準結晶構造解析の研究
高倉 洋礼
日本結晶学会誌 44 2 114 - 120 The Crystallographic Society of Japan 2002年04月30日 [査読有り]
A novel density modification method has been applied to phase reconstruction of X-ray single crystal data of quasicrystals. This is based on the low density elimination (LDE) method that is an ab initio structure determination method for crystals in the real space. The location, size andshape of the occupation domains of quasicrystals in the n-dimensional (nD) unit cell are obtained without a prioi model structure. Therefore, the LDE method can be a substitute for the direct method for quasicrystals that are described as nD crystals. The structure solution can easily be found in the trial sets (normally 100 sets) and is confirmed by the subsequent analysis. The result is used as a starting model for constructing a detailed structure model of quasicrystals. The solution of several qusicrystalline structures including a model quasicrystal structure are exemplified.