Résumé
Single crystals of the Ag
6.69GeSe
5I
0.69 phase have been obtained by iodine transport of the iodine-partially substituted stoichiometric argyrodite compound Ag
7GeSe
5I. This phase crystallizes in the cubic space group
F
4
̄
3
m (argyrodite
γ-phase,
a=10.921(2) Å at −100°C,
a=10.972(3) Å at 25°C,
Z=4). It is highly disordered both at anion and cation sites. Crystal structure refinements were completed by an anharmonic Gram–Charlier development of the atomic displacement factors of iodine and silver atoms. The structure of Ag
6.69GeSe
5I
0.69 was determined at −100°C and +25°C and was refined to R(
F) values of 5.80 and 6.51%, respectively. Both iodine and selenium (Se1) anions have been found disordered and iodine is slightly defective on its crystallographic site. This is correlated to the disorder observed for the two Ag1 and Ag2 cations that provides this material with superionic conducting properties. Analysis of the joint probability density function allowed the visualization of the Ag
+ diffusion paths within the anionic framework.