Largely Optimized Thermoelectric Performance in (Ag, S) Coalloyed Cu₂Te Thermoelectric Materials

Cu2Te-based compounds are expected to exhibit superior thermoelectric performance compared to Cu2S and Cu2Se due to the larger atomic mass and more covalent bonding of Te atoms, such as chalcogenide selenide and chalcogenide lead. However, the currently reported figure of merit (ZT) for Cu2Te is still lower than that of Cu2S and Cu2Se. In this work, the thermoelectric transport properties are studied and optimized by two-step coalloying of Cu2Te-based materials. An improved average power factor of 7.21 μW cm-1 K-2 is obtained between room temperature and 773 K because of the largely optimized carrier concentration and Seebeck coefficient. Additionally, the total thermal conductivity decreases to 0.55 W m-1 K-1 for Ag0.7Cu1.3Te0.94S0.06 W m-1 K-1 at room temperature, and the lowest thermal conductivity of 0.49 W m-1 K-1 is obtained in Ag0.7Cu1.3Te0.92S0.08 at 523 K because of the tuned carrier concentration and increased entropy. Combined with the simultaneous optimization of electrical transport properties and thermal transport properties, (Ag, S) coalloyed Cu2Te shows a maximum ZT of 1.4 at 773 K, which is 460% higher than that of Cu2Te at the corresponding temperature.