Significantly optimized thermoelectric properties in high-symmetry cubic Cu7PSe6 compounds via entropy engineering

Abstract

High-symmetry crystal structures are preferred for thermoelectrics because high structural symmetry usually yields good electron transport properties. Entropy engineering is an effective approach to improve the structural symmetry of low-symmetry materials, and thus to enhance their thermoelectric performance. In this study, via introducing Te into the argyrodite-type compound Cu₇PSe₆, the configurational entropy is significantly increased to successfully improve its initial low-symmetry cubic structure (P2₁3) to the high-symmetry cubic structure (F3m) at room temperature. Such improved structural symmetry leads to a high density-of-state effective mass but similar carrier mobility in the same carrier concentration range as compared with the pristine Cu₇PSe₆. Thus, significantly optimized electron transport properties are achieved in the Te-alloyed Cu₇PSe₆ samples. In particular, at room temperature, the power factor of the high-symmetry cubic Cu₇PSe_5.7Te_0.3 sample is about 15-times higher than that of the low-symmetry Cu₇PSe₆ matrix. Combining the well-maintained ultralow lattice thermal conductivity, a maximum ZT of around 0.55 at 600 K is obtained in Cu₇PSe_5.7Te_0.3. This work strongly shows that entropy engineering using multiple components is a very powerful strategy to discover or design novel high-performance TE materials starting from low-symmetry compounds.