Acta Crystallographica Section B

Structural Science

Volume 64, Part 1 (February 2008)

research papers

Acta Cryst. (2008). B64, 1-11 [ doi:10.1107/S0108768107059642 ]

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

S. Albert, S. Pillet, C. Lecomte, A. Pradel and M. Ribes

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 d¹⁰ Ag⁺ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined.

Keywords: argyrodite; superionic conductor; disorder; anharmonicity; silver-ion distribution.