Effect of Nanostructuring and High-Pressure Torsion Process on Thermal Conductivity of Carrier-Doped Chalcopyrite

Carrier-doped chalcopyrite (CuFeS2) has been shown to exhibit a high power factor exceeding 1 mW/K-2-m at room temperature. However, it has a relatively high thermal conductivity of 6 W/K-m in this temperature range. To reduce the thermal conductivity, nanostructuring by a ball-milling process and the high-pressure torsion (HPT) method have been applied to Zn0.03Cu0.97FeS2. While ball milling yielded a fine powder specimen with crystal grain size of about 20 nm, a subsequent synthesis process using spark plasma sintering at 720 K for 2 min caused crystal grain regrowth. The thermal conductivity of the ball-milled and spark-plasma-sintered sample was similar to that of a bulk sample above room temperature. The HPT-treated sample showed a significant drop in thermal conductivity over the entire temperature range. However, the electrical resistivity increased, resulting in a degradation of the overall thermoelectric performance. Annealing at 520 K after HPT was partly effective in recovering the electrical conductivity while retaining low thermal conductivity.