Optimized Carrier Concentration and Reduced Thermal Conductivity in Cu-Deficient CuGaTe2 Alloyed with AgSbTe2 for Superior Thermoelectric Performance

As a mid-temperature thermoelectric material, CuGaTe2 features a distinctive crystal structure, environmentally friendly and high tunability, all of which contribute to its promising thermoelectric performance. However, due to its intrinsically low electrical conductivity and high lattice thermal conductivity, the thermoelectric performance of pristine CuGaTe2 is unsatisfactory. In this work, Cu-deficient Cu0.96GaTe2 was alloyed with different contents of AgSbTe2 via a combined approach involving melting, ball milling, and spark plasma sintering. The Cu-poor condition introduces Cu vacancies, thereby providing more hole carriers. AgSbTe2 alloying leads to a further increase in the carrier concentration. Despite of the decrease in carrier mobility, the electrical conductivity was evidently enhanced. On the other hand, Sb doping increases the density of states at the Fermi level, leading to enhancement of the Seebeck coefficient. Moreover, Cu vacancies and AgSbTe2 alloying both cause a significant decrease in sound velocity, thereby decreasing the lattice thermal conductivity to an ultralow value of 0.29 W m–1 K–1 at 743 K. Finally, the optimized (Cu0.96GaTe2)0.9(AgSbTe2)0.1 sample demonstrates the highest thermoelectric performance, achieving an average zT of 0.41, which represents a 215.4% improvement over pristine CuGaTe2. Its peak zT reaches 1.39 at 743 K, corresponding to a 124.2% improvement relative to pristine CuGaTe2.