On the distribution of tetrelide atoms (Si, Ge) in Gd5(SixGe1-x)4

A crystallographic study of the Si/Ge site preferences in the Si-rich regime of Gd-5(SixGe1-x)(4) and a crystal chemical analysis of these site preferences for the entire range is presented. The room temperature crystal structure of Gd5Si4 as well as four pseudobinary phases, Gd-5(SixGe1-x)(4) for x >= 0.6, is reported. All structures are orthorhombic (space group Pnma), Gd5Si4-type and show decreasing volume as the Si concentration increases. Refinements of the site occupancies for the three crystallographic sites for Si/Ge atoms in the asymmetric unit reveal a nonrandom, but still incompletely ordered arrangement of Si and Ge atoms. The distribution of Si and Ge atoms at each site impacts the fractions of possible homonuclear and heteronuclear Si-Si, Si-Ge and Ge-Ge dimers in the various structures. This distribution correlates with the observed room temperature crystal structures for the entire series of Gd-5(SixGe1-x)(4). (c) 2006 Elsevier Inc. All rights reserved.