Thermoelectric Performance Optimization and Phase Transition of GeTe by Alloying with Orthorhombic CuSbSe₂

GeTe-based compounds are promising thermoelectric materials at medium temperature, while the performance of the GeTe matrix is at the mercy of its high hole concentration and high thermal conductivity. This work reports the thermoelectric performance optimization of GeTe by alloying with CuSbSe2. With only 5% CuSbSe2 being introduced, the p-type hole concentration is greatly decreased from ∼1021 to ∼1020 cm–3, and the thermal conductivity at room temperature is reduced by more than 70%. Interestingly, the alloying of CuSbSe2 also induces a crystal structure transition of GeTe which results in the cubic structure of GeTe at room temperature, in spite of the noncubic structure of orthorhombic CuSbSe2. Owing to the phase transition and carrier concentration optimization, the thermoelectric performance is largely improved relative to the pristine compound. Eventually, a ZTmax ∼ 1.65 is achieved at 630 K. It is also indicated that the performance of GeTe–CuSbSe2 could be further improved by the careful tuning of carrier concentration.