Optimization of hot-press conditions of Zn4Sb3 for high thermoelectric performance I. Physical properties and thermoelectric performance

Thermoelectric Zn4Sb3 bulk specimens have been fabricated by hot pressing at various temperatures from 738 to 753 K either in a vacuum or under pressurized Ar. The bulk specimens consist of a single-phase p-type semiconductive ε-Zn4Sb3 compound. Compositional change due to Zn vaporization, anticipated during the high temperature processes, could be avoided by adding excess Zn to the starting powder. Bulk density, electric resistivity, Seebeck coefficient and thermal conductivity were evaluated. Observed bulk densities of 6.2-6.4 g/cm3 exceeded the value of 6.08 g/cm3 determined from X-ray diffraction data. Electric resistivity decreases with increasing hot-pressing temperature in the range from 323 to 673 K, and exhibits unusual temperature-dependent hysteresis. Seebeck coefficient and thermal conductivity values were much closer to previously reported data, with only slight differences among specimens measured at various hot-pressing temperatures. A material fabricated in a vacuum at 748 K, had a thermoelectric figure of merit (ZT) greater than 1, because it had small electric resistivity and thermal conductivity values. Application of a pressurized Ar atmosphere during hot pressing did not contribute to improved thermoelectric performance of Zn4Sb3 compound