The effect of Ag substitution in the mixed conductor Cu7PSe6

Cu7PSe6 is a mixed conductor that crystallizes in the simple cubic structure at room temperature. Structural transitions above and below room temperature are accompanied by step-like changes in electrical conductivity. The substitution of Ag+ for Cu+ in Cu7PSe6 stabilized the simple cubic structure over a wider range of temperatures than is observed for the pure compound. A disproportionate decrease in electrical conductivity accompanies modest levels of silver substitution. The prominent step in electrical conductivity associated with the low-temperature crystallographic phase transition disappears in (AgxCu1−x)7PSe6 solid solutions for a composition parameter x=0.20, replaced by two distinct changes in the slope of conductivity below room temperature.