Preparation of Tetrahedrite Cu12Sb4S13 by Mechanical Alloying and Hot Pressing

Tetrahedrite Cu12Sb4S13 was synthesized via mechanical alloying (MA) and consolidated using hot pressing (HP) as a solid-state route. Powders with a single phase of Cu12Sb4S13 could be successfully synthesized without post-annealing by controlling the process conditions of MA: 350 rpm for 24 h in an Ar atmosphere. A sintered tetrahedrite with density close to the theoretical density was obtained via HP at 723 K for 2 h under a pressure of 70 MPa. Thermogravimetric and calorimetric analyses confirmed weight loss and endothermic reactions at temperatures above 853 K, possibly due to the decomposition/melting of the tetrahedrite and the volatilization/melting of the constituent elements. The synthesized tetrahedrite is a nondegenerate semiconductor; its electrical conductivity increased with the increase in temperature. Its Seebeck coefficient also increased with the increase in temperature without showing intrinsic conduction up to 773 K. As the HP temperature increased, the power factor decreased because the decrease in the electrical conductivity prevailed over the increase in the Seebeck coefficient. The thermal conductivity had similar low values regardless of the HP temperature. The maximum dimensionless figure-of-merit, ZTmax = 0.87, was obtained at 723 K for the Cu12Sb4S13 hot-pressed at 723 K.