Thermoelectric and mechanical properties of Zn4Sb3 polycrystals sintered by spark plasma sintering

beta-Zn4Sb3 has attracted much interest as a thermoelectric material because of its potential for power-generation applications in a moderate temperature range (450 similar to 650 K). In general, three kinds of considerations have been reported for the fabrication of a polycrystalline beta-Zn4Sb3 bulk sample: (i) a problem in chemical stability, (ii) cracks in bulk specimens owing to a phase transition of the Zn4Sb3 composition resulting in stress during cooling, and (iii) the requirement for high bulk density. In this study, a pure Zn4Sb3 phase with a high define ZT(figure of merit) value was synthesized by using a vacuum melting process and a vacuum annealing process, followed by a spark plasma sintering (SPS) method. Fabricating a single-phase specimen with high bulk density by means of optimizing the SPS conditions (temperature and pressure) was significant for obtaining high performance in the Zn4Sb3 thermoelectric system. The maximum ZT value (0.98) was attained at a 573 K measurement temperature for the specimen sintered with the optimized SPS conditions (723 K, 40 MPa).