Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural study

Abstract

A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475 K, in steps of 50 K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the F\bar 43m space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram–Charlier development of the Debye–Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d 10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined.