Rapid Microwave Synthesis and Sintering of ZrNiSn Half-Heusler Thermoelectric Alloy

The rapid microwave synthesis and sintering of ZrNiSn bulk was studied. The phase composition and microstructure of samples were characterized by X-ray diffractometer (XRD) and transmission electron microscope (TEM), respectively. The thermoelectric properties i.e. Seebeck coefficient (S), electrical resistivity (rho), and thermal conductivity (kappa) were measured through Seebeck coefficient/resistance analysis system (S/RAs) and laser flash thermal analyzer (LFT). The results show that a relatively high purity single phase of ZrNiSn alloy is synthesized within 4 similar to 5 min in microwave field, and a small amount of impurity Sn is almost eliminated by 30 min microwave sintering via secondary reaction. The variation trends of S, rho and power factor with temperature were analyzed. The electrical resistivity is relatively high, 13.7 similar to 16.9 mu Omega.m. The highest power factor is 1683 mu W.m(-1).K-2, lower than the previously reported, which should be attributed to the high electrical resistivity. The thermal conductivity is decreased with temperature, and its maximum value is 4.288 W.m(-1)K(-1). The lattice thermal conductivity is merely 2.86 similar to 3.96 W.m(-1).K-1. The microstructure analysis shows that the growth of ZrNiSn grain is inhibited during microwave sintering. A large number of nanometer grains are precipitated in the interior of ZrNiSn grain and on the boundary. The calculated thermoelectric figure of merit (ZT) is rapidly increased with temperature, and a maximum ZT of 0.25 is achieved at 573 similar to 673 K.