The argyrodite compound Ag7PSe6 exhibits a change in the slope of its temperature dependent electrical conductivity at a temperature noticeably lower than that at which its crystal structure changes from the P2(1)3 space group to the F43m space group. The related argyrodite compound Cu7PSe6 exhibits two discontinuous changes in conductivity coincident with crystal lattice transformations from the Pna2(1) to the P2(1)3 structure and from the P2(1)3 to the F43m structure. Both compounds are found to be mixed conductors. (c) 2008 Elsevier B.V. All rights reserved.