Effects of the Fe/Ni ratio in double half-Heusler composition HfFe1−xNixSb

Abstract

The effects of the Fe/Ni ratio in the double half-Heusler composition HfFe_xNi_1−xSb were investigated. By changing the chemical composition from Ni-rich to Fe-rich in HfFe_xNi_1−xSb, the Seebeck coefficient changes from negative to positive showing a clear n-type to p-type transition. In addition to very low lattice thermal conductivity (κ_L= 1.7 W m⁻¹ K⁻¹) for a half-Heusler material, achieving both p- and n-type materials with similar parent compositions is useful for developing thermoelectric modules as small differences in the thermal expansion coefficient and chemical stability prevent the degradation of thermoelectric modules. The highest thermoelectric figures of merit, zT, were 0.36 and 0.22 at 950 K for n- and p-type respectively.