Effects of Aging on Thermoelectric Properties of Tetrahedrite Cu₁₂Sb₄S₁₃

Abstract

Tetrahedrite Cu₁₂Sb₄S₁₃ was prepared by mechanical alloying and hot pressing. The phase transition, microstructure, and thermoelectric properties (electronic conductivity, Seebeck coefficient, power factor, thermal conductivity, and dimensionless figure of merit) were examined under various aging conditions (atmosphere, temperature, and time). When aged at temperatures above 723 K in air, various oxides (SbO₂, Sb₂O₃, and Sb₆O₇(SO₄)₂) and sulfides (Cu₉S₈, Cu₂S, Cu_1.96S, and CuSbS₂) were formed through oxidation, volatilization, and decomposition of the tetrahedrite phase. However, the tetrahedrite phase was stable up to 723 K in vacuum. The pristine specimen exhibited a dimensionless figure of merit of 0.86 at 723 K, resulting from a power factor of 0.95 mW·m⁻¹K⁻² and a thermal conductivity of 0.78 W·m⁻¹K⁻¹ at 723 K. For the specimens aged at 523–723 K for 10 h in air, the dimensionless figure of merit varied from 0.81 to 0.92 as the power factor ranged from 0.97 to 1.04 mW·m⁻¹K⁻² and the thermal conductivity ranged from 0.80 to 0.85 W·m⁻¹K⁻¹. However, the thermoelectric performance was slightly degraded when the specimen was aged at 723 K for 100 h because of a decreased power factor and increased thermal conductivity.