Substitution effect on thermoelectric properties of ZrNiSn based half-Heusler compounds

Thermoelectric properties of ZrNiSn based half-Heusler compounds, Zr0.7X0.3NiSn (X = Ti, Hf), ZrNi0.7Y0.3Sn (Y = Pd, Pt), and ZrNi1.05Sn were investigated from room temperature to 1000 K. All the substitutions and addition of the excess nickel drastically decreased the thermal conductivity. The experimental values at room temperature were in good agreement with those estimated by the disorder scattering theory. The thermal conductivity exhibited considerable increase above 700 K for all the samples. It was corresponding to the transition of electrical properties, indicating that the generated hole conduction at high temperatures provided the increase. The additional electronic thermal conductivity caused by the ambipolar diffusion effect is discussed.