Synergistic optimization of thermoelectric performance in p-type Ag2Te through Cu substitution

Abstract Superionic conductors, which exhibit liquid-like phonon transport but crystal-like carrier transport, have attracted great attention and broad research interest in the thermoelectric community. Ag 2 Te is a superionic conductor; however, its small band gap and large Ag vacancy formation energy impede its application as a prominent p-type thermoelectric material. In this work, synergistic optimization of the thermoelectric performance of Ag 2 Te through Cu substitution is realized through a combination of experimental and theoretical efforts. For the electrical transport, Cu substitution systematically increases the band gap of Ag 2 Te and reduces the cation vacancy formation energy. These two beneficial effects simultaneously increase the electrical conductivity and suppress the bipolar effect, thereby greatly enhancing the p-type electrical transport properties of Ag 2 Te. For the thermal transport, alloying Cu 2 Te with Ag 2 Te significantly reduces the thermal conductivity through not only point defect scattering but also softening of the interatomic interactions. The latter is attributed to the relatively small Cu atoms vibrating in the oversized 8c sites. This two-fold optimization results in maximum thermoelectric figure of merit zT values of over 1.3 at 773 K for both Ag 1.2 Cu 0.8 Te and AgCuTe, demonstrating the great potential of Ag 2− x Cu x Te as a promising p-type thermoelectric material system.