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, Ti_x(Zr_0.5Hf_0.5)_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 as low as 3.1 W/mK at room temperature. We also found the remarkable enhancement of the Seebeck coefficient by Ti substitution. Furthermore, the doping with Sb on the Sn sites for (Ti,Zr,Hf)NiSn leaded to reduction in electric resistivity and, accordingly, to enhancement of the power factor. In the Sb doped (Ti,Zr,Hf)NiSn compounds, Ti_0.5(Zr_0.5Hf_0.5)_0.5NiSn_0.998Sb_{0.00 2}, the dimensionless figure of merit, ZT increased with increasing temperature showing its. maximum value 1.5 at 700 K. Because of their potential, it is expected that these materials are interesting in thermoelectric power generation.