Powder metallurgically synthesized Cu12Sb4S13 tetrahedrites: phase transition and high thermoelectricity

Abstract

Cu₁₂Sb₄S₁₃ tetrahedrite with intrinsically low lattice thermal conductivity has been identified as a promising thermoelectric material with earth-abundant and environmental-friendly resource, but as a natural mineral its synthesis process has not been established. This work studied a powder metallurgical process combining mechanical alloying (MA) and spark plasma sintering (SPS) to synthesize Cu₁₂Sb₄S_13−x (x = 0, 0.1, 0.2, 0.3 and 0.4) compounds. It is found that single-phased Cu₁₂Sb₄S_13−x bulks could be synthesized by the MA-SPS process, but tended to become powdered naturally in air at room temperature. Interestingly, this weathering-like phenomenon could be effectively suppressed when the MA-SPS process was repeated. Consequently, a high ZT value of up to 0.65 at 723 K was achieved at a nominal composition of Cu₁₂Sb₄S_12.7, which is close to the best value of 0.70 obtained in Cu₁₂Sb₄S₁₃ tetrahedrites prepared by the melting method, although the present process is more simple and cost-effective. In addition, in this study temperature-dependent phase transitions were investigated to explore the reasons for the weathering-like phenomenon observed in synthetic Cu₁₂Sb₄S₁₃ tetrahedrites.