Microwave synthesis and enhancement of thermoelectric figure of merit in half-Heusler TiNiSbxSn1-x

The preparation of half-Heusler thermoelectric bulk is complex and time-consuming. In the present work, Sb doped TiNiSbxSn1-x bulks (x=0.01, 0.02, 0.03 and 0.04) were prepared via cold press forming, microwave synthesis and sintering in vacuumed sealed quartz in a few minutes. The microstructures of samples were characterized by using X-ray diffractometer (XRD) and scanning electron microscopy (SEM) techniques. The thermoelectric properties i.e. Seebeck coefficient (S), electrical resistivity (p) and thermal conductivity (kappa) were measured on Seebeck coefficient/resistance analysis system (S/RAs) and laser flash thermal analyzer (LFT). The results show that high purity single phase was obtained after microwave sintering. The point defects came from Sb doping and the in-suit nanostructures attributed to microwave sintering process were found to lead to special microstructure. The variation trends of S, p, kappa with temperature were analyzed. The influences of Sb doping to electrical and thermal properties were discussed. The electrical resistivity was decreased by similar to 84% at the cost of decreasing the Seebeck coefficient by similar to 25-30%. The maximum power factor of 2560 mu Wm(-1)K(-2) was achieved at 673 K. The lattice and total thermal conductivities are merely 1.1-1.3 and 3.8-4.0 Wm(-1)K(-1) respectively. The thermoelectric figure of merit for TiNiSb0.03Sn0.97 was enhanced from 0.30 (773 K) to 0.44 (673 K and 723 K) when compared to that of non-doped TiNiSn.