Monte Carlo and molecular dynamics simulation of disorder in the Ag + fast ion conductors Pearceite and Polybasite

Abstract

The pearceite-polybasite group of minerals (i.e., pearceite, antimonpearceite, arsenpolybasite, and polybasite) of general stoichiometry [M 6I T 2III S7][Ag 9I CuIS4], with M = Ag+, Cu+ and T = As3+, Sb3+, occur relatively commonly in nature. All have recently been shown to exhibit Ag + fast ion conduction at rather low temperatures (only slightly above or below room temperature[1]). The average crystal structure determination of these materials shows the positions of the Ag+ ions to be smeared out or delocalized within sheets in an ordered framework structure comprised of the other ions. At the same time, strong and highly structured diffuse scattering has been observed, which contains diffuse peaks that are incommensurate with the diffraction peaks of the framework structure. In order to try to understand the origins of the fast ion conduction properties of these materials, we have used computer simulation of a model system (Monte Carlo and molecular dynamics (MD)) to analyze this observed diffuse scattering. Show more