Solid-State Synthesis and Thermoelectric Properties of Tetrahedrites Cu12Sb4-yBiyS13

Tetrahedrite has low lattice thermal conductivity because of the lone-pair electrons of Sb, which cause the Cu atoms to vibrate at a low frequency and high amplitude. The synthesis of tetrahedrite compounds by conventional melting methods requires a long-time reaction and annealing. However, a homogeneous and solid-state synthesis can be conducted in a short time using mechanical alloying (MA) because the volatilization of the constituent elements is inhibited and a subsequent heat treatment is not necessary. In this study, Bi-doped tetrahedrites Cu12Sb4-yBiyS13 ( y = 0-0.4) were prepared by MA and hot pressing. X-ray diffraction analyses revealed that all specimens consisted of single-phase tetrahedrite. However, with increasing Bi content, skinnerite Cu3SbS3 was detected. The electrical conductivity increased and the Seebeck coefficient deceased with increasing Bi content as result of the substitution of Bi at Sb sites. In addition, the thermal conductivity increased as the Bi content increased because of the increase in electronic thermal conductivity. A high dimensionless figure of merit of 0.88 was obtained at 723 K for Cu12Sb3.9Bi0.1S13.