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Atomic structures of ternary Yb–Cd–Mg icosahedral quasicrystals and a 1/1 approximant
Author(s) -
Yamada Tsunetomo,
Takakura Hiroyuki,
de Boissieu Marc,
Tsai An-Pang
Publication year - 2017
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520617013270
Subject(s) - isostructural , icosahedral symmetry , quasicrystal , crystallography , ternary operation , lattice constant , materials science , chemistry , diffraction , crystal structure , cluster (spacecraft) , physics , computer science , optics , programming language
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 Yb 13.3 Cd 70.3 Mg 16.5 , have been analysed by single‐crystal X‐ray diffraction. The structures of the iQCs were found to be isostructural to the parent i‐YbCd 5.7 , 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 YbCd 6 , 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.