High-purity La 3-x Te 4 Material with Superior Thermoelectric Performance Synthesized via Te-vapor Transport and Solid-State Diffusion.

La 3-x Te 4 is a very promising high-temperature candidate applied in next-generation Radioisotope Thermoelectric Generators (RTGs). Conventional synthesis of such materials is based on the mechanochemical method, which makes the sample difficult to purify due to the high-energy ball milling. In this report, a novel synthetic method is developed, which utilizes Te-vapor transport and solid-phase diffusion to efficiently produce the RE 3-x Te 4 phases (RE = La, Ce, Pr, Nd). Notably, this method obviates the requirement for high-energy ball-milling instruments, conventionally indispensable in the mechanochemical syntheses. For as-synthesized La 2.74 Te 4 material, a high figure of merit of 1.5 is achieved at 1073 K, owning to the reduced electronic thermal conductivity with metal impurities well eliminated.