Optimization of hot-press conditions of Zn4Sb3 for high thermoelectric performance

Thermoelectric p-type semiconductive ɛ-Zn4Sb3 was hot-pressed at 748 K under 49 MPa for 5 h in vacuum from three kinds of raw powder having different average particle sizes (12.1, 19.5 and 44.3 μm) in order to study the effect of particle size on electrical and mechanical properties. Electrical resistance and Seebeck coefficient were measured over the temperature range from 323 to 673 K. Of the three powders, the 44.3 μm powder yielded the lowest electrical resistance ɛ-Zn4Sb3. This was not due to the reduced grain boundary resistance, but rather, the lower oxygen contamination. The Seebeck coefficient showed no distinctive dependence on starting particle size below 600 K. Above this temperature, however, the Zn4Sb3 specimen derived from 44.3 μm powder exhibited the highest coefficient. Both bending strength and fracture toughness improved by reducing the starting particle size. The 12.1 μm powder yielded the highest strength (82.7 MPa) and the highest fracture toughness (0.95 M N m−1.5).