Synthesis And Thermoelectric Properties Of Ti-based Half-Heusler Compound

It is desirable for thermoelectric materials to have low thermal conductivity, low electrical resistivity and high Seebeck coefficient. The TiNiSn-based half-Heusler compound is one of the newly developed thermoelectric materials as prospective candidates for power generation.In this paper, single-phase Ti_1-x(Hf_0.919-zZr_0.081+zxNiSn_1-ySb_y, ( x=0.00 -0.25,y=0.00 — 0.01,z=0.00 — 0.05) compounds were synthesized by solid-state reaction and high-density bulk material was prepared by Spark Plasma Sintering(SPS). The effects of Hf and Zr substitution for Ti site and the doping with Sb for Sn site on the thermoelectric properties of TiNiSn half-Heusler compounds were investigated.The results shown that the substitution of a small amount Hf and trace Zr for Ti resulted in reduction of the thermal conductivity significantly and a remarkable enhancement of the Seebeck coefficient;The dimensionless figure of merit ZT of Ti_0.85(Hf_0.919Zr_0.081)_0.15NiSn reached a high maximum value of 0.56 at 700K and enhancement of ZT was 190—310% at same temperature compared with ternary TiNiSn compounds.We also found that the electrical conductivities, Seebeck coefficients increase and the thermal conductivities decrease with increasing Hf content of the proportions of Hf and Zr. Therefore ZT value has little change at the time of the low temperature, the high temperature is slightly enhanced.Doping of Sb on Sn site remarkably increase the electrical conductivities and power factor, but thermal conductivities are also increased. ZT value can be significantly enhance by controlling the Sb doping fraction.The greatest ZT value of 0.65 was obtained at 675 K for n-type Ti_0.85(Hf_0.919Zr_0.0810.15NiSn_0.996Sb_0.004 compound.