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 Gd5(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, Gd5(SixGe1−x)4 for image, 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 Gd5(SixGe1−x)4.