Ultralow lattice thermal conductivity enables high thermoelectric performance in BaAg2Te2 alloys

Abstract

Due to the intrinsic low lattice thermal conductivity (κL), AB2X2 Zintl compounds with a P3-M1 crystal structure have been demonstrated as potential thermoelectric candidates. Recently, a novel AB2X2 compound with a Pnma crystal structure has been revealed to possess an even lower κL, which motivates this work to focus on BaAg2Te2 for its potential for thermoelectric applications. Impressively, pristine BaAg2Te2 shows a κL lower than ∼0.3 W/m-K in the entire temperature range, being the lowest one ever reported in AB2X2 thermoelectrics. Theoretically, such a low κL comes from intrinsically strong anharmonicity and low sound velocity. With help of Cu-alloying at Ag site for increasing carrier concentration and for reducing κL, a peak zT up to ∼1.3 is achieved in BaAgCuTe2 alloy, and its single-leg device with Ag as the electrode enables an output power of ∼120 mW under a temperature difference of ∼375 K, demonstrating BaAg2Te2 based alloys as promising thermoelectric materials.