Thermoelectric properties of half-Heusler phases: ErNi_1-xCu_xSb, YNi_1-xCu_xSb and Zr_xHf_yTi_zNiSn

Our previous investigations on the half-Heusler phases, rare earth nickel antimonides and zirconium nickel stannides, have indicated that ErNiSb can be comparably promising to ZrNiSn for further thermoelectric investigations. These compounds crystallize in the cubic MgAgAs structure type and possess Seebeck coefficients up to +160 μV/K and -355 μV/K, respectively. Their thermal conductivities are approximately 60 mW/cm.K with their electrical conductivity curves resembling a semiconductor (350 S/cm and 250 S/cm for ErNiSb and ZrNiSn, respectively). The rare earth nickel antimonide compounds are synthesized as p-type materials, however, a careful analysis of their electronic band structures point out that n-type materials will possess larger effective masses and therefore larger Seebeck coefficients. Consequently, in order to improve the transport properties of these compounds and to achieve n-type materials, we investigated some of their solid solutions obtained by partial substitution of the transition metal element. Here, we report the transport properties of a wide range of solid solution members corresponding to the formula ErNi_1-xCu_xSb, YNi_1-xCu_xSb and Zr_xHf_yTi_zNiSn (x+y+z = 1).