Thermoelectric properties of the TiX(Zr0.5Hf0.5)1 − XNiSn half-Heusler compounds

The effect of Ti substitution on the thermoelectric properties of (Zr, Hf)NiSn half-Heusler compounds, TiX(Zr0.5Hf0.5)1 − XNiSn (X = 0-0.7), is reported. The sintered polycrystalline samples were obtained by hot-pressing the milled powder after arc melting. It was shown that the substitution of Ti for (Zr, Hf) resulted in a significant reduction of the thermal conductivity to as low as 3.1 Wm−1 K−1 at room temperature. We also found that the Seebeck coefficient was enhanced remarkably by Ti substitution. Furthermore, the doping with Sb for the Sn sites in (Ti, Zr, Hf)NiSn led to reduction in electric resistivity and, accordingly, to enhancement of the power factor. In the Sb doped (Ti, Zr, Hf)NiSn compounds, Ti0.5(Zr0.5Hf0.5)0.5NiSn0.998Sb0.002, the dimensionless figure of merit, ZT, increased with increasing temperature, showing its maximum value of 1.5 at 700 K. In view of their potential, these materials are of interest in regard to thermoelectric power generation.