Thermoelectric Transport in Cu_7PSe_6 with High Copper Ionic Mobility

Building on the good thermoelectric performances of binary superionic compounds like Cu_2Se, Ag_2Se and Cu_2S, a better and more detailed understanding of phonon-liquid electron-crystal (PLEC) thermoelectric materials is desirable. In this work we present the thermoelectric transport properties of the compound Cu_7PSe_6 as the first representative of the class of argyrodite-type ion conducting thermoelectrics. With a huge variety of possible compositions and high ionic conductivity even at room temperature, the argyrodites represent a very good model system to study structure–property relationships for PLEC thermoelectric materials. We particularly highlight the extraordinary low thermal conductivity of Cu_7PSe_6 below the glass limit, which can be associated with the molten copper sublattice leading to a softening of phonon modes