Microwave synthesis and enhancement of thermoelectric performance in HfxTi1−xNiSn0.97Sb0.03 half-Heusler bulks

Abstract

We obtained TiNiSn-based half-Heusler HfxTi1−xNiSn0.97Sb0.03 bulks with 85%–96% relative densities via 5-min microwave synthesis and 20-min microwave sintering in sealed vacuum. The phase composition and microstructure of samples were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). Thermoelectric (TE) properties were measured, i.e., Seebeck coefficient (S), electrical resistivity (ρ), and thermal conductivity (κ) through Seebeck coefficient/resistance analysis system (S/RAs) and laser flash thermal analyzer (LFT). The results show that the nearly single phase exists after microwave sintering. The grain sizes and the number of grain boundaries decrease with increase in Hf-doping amount due to an increase in point defects. The matrix grains for Hf0.1Ti0.9NiSn0.97Sb0.03 are ~ 10 μm. The nanoscle pores and precipitates are present as second phases in matrix grain. The real composition for Hf0.1Ti0.9NiSn0.97Sb0.03 matrix grain is Hf3.51Ti28.76Ni34.76Sn31.55Sb1.43. The variation trends of electrical resistivity, Seebeck coefficient, power factor, and thermal conductivity were analyzed in detail. The maximum figure of merit (ZT) of 0.46 is obtained for Hf0.1Ti0.9NiSnSn0.97Sb0.03 at 723 K. The innovation route exhibits advantages for predation of TE bulks when compared to the conventional methods, especially in terms of efficiency while it still maintains TE performance.