High Thermoelectric Performance and Oxidation Resistance of (Na, Ga) Codoped β-Zn4Sb3 Thermoelectric Materials Prepared by the NaCl Flux

β-Zn4Sb3 is a promising thermoelectric (TE) material, as it contains low-cost and environment-friendly elements. However, its application has long been limited due to the lower figure of merit (ZT), poor mechanical properties, and inferior thermodynamic stability. In this research, we successfully synthesized Na/Ga codoped β-Zn4Sb3 with high thermoelectric performance and stability. The power factor (PF) value of the Ga-doped sample is significantly improved by optimizing carrier concentration, the maximum value of 2.28 × 10–3 W m–1 K–2 is obtained at 690 K, and the maximum ZT reaches 1.73 at 690 K for the Zn4.1Sb3(NaCl)7Ga0.12 sample. Moreover, the TG-DSC and oxidation resistance tests show that Na and Ga codoped β-Zn4Sb3 possess good stability. This work provides an attractive method for improving the thermoelectric properties and stability of β-Zn4Sb3 through diatomic doping.