CRYSTAL-STRUCTURE OF GAMMA-AG8GETE6, A POTENTIAL MIXED ELECTRONIC-IONIC CONDUCTOR

γ Ag8GeTe6 belongs to space group F43m with Z – 4 and a = 11.58 ± 0.02 A. The arrangement of the tellurium atoms is almost precisely that of both the magnesium and copper atoms in the Friauf-Laves cubic phase of MgCu2. This arrangement produces 136 tetrahedra per unit cell, of which four are occupied by the Ge atoms. The remainder are divided among two 48-fold, two 16-fold and one 4-fold sets of positions. One of the 16-fold sets of tetrahedra which shares faces with the GeTe4 tetrahedra is empty. The Ag atoms are distributed over the remaining sets with 29 of the 32 in the unit cell being in the two 48-fold sets and 25 in just one of these. There are many routes whereby the Ag atoms may move through the crystal; in particular the two 48-fold sets themselves form such routes. Not all the Ag atoms are constrained to lie at the near-centers of the tetrahedra; some are closer to particular shared faces. There are substantial differences between the structure reported here and that reported earlier by Rysanek, Laruelle and Katty. © by Akademische Verlagsgesellschaft 1979