Synthesis and Thermoelectric Properties of Cu12−xNixSb4S13 Tetrahedrites

Ni-doped tetrahedrites Cu12−xNixSb4S13 (x = 0.1–0.4) were prepared by mechanical alloying (MA) and sintered by hot pressing (HP). The tetrahedrite phase could be synthesized by MA without post-annealing, and was stable after HP without phase transition. As the Ni content increased, the lattice constant decreased from 1.0312 nm to 1.0246 nm, confirming that the Ni was successfully substituted for Cu sites. As the Ni content increased, the Seebeck coefficient increased but the electrical conductivity decreased because the carrier (hole) concentration decreased owing to the substitution of Ni2+ at the Cu+ site. The power factor of 1.0 mW m−1 K−2 was obtained at 723 K for the Ni-doped specimen with x = 0.1, and decreased with increasing Ni content. In addition, as the Ni content increased, the electronic thermal conductivity decreased, but the total thermal conductivity of the specimen with Ni content x = 0.2 showed the lowest value of 0.65–0.79 W m−1 K−1 at 323–723 K owing to the lowest lattice thermal conductivity of 0.38 W m−1 K−1 at 723 K. As a result, the dimensionless figure of merit ZT = 0.92 was obtained at 723 K for Cu11.8Ni0.2Sb4S13.