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

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 Cu_0.96GaTe₂ 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 (Cu_0.96GaTe₂)_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.