In this paper we investigate the electronic structure and the thermopower for $\mathrm{Ni}\left({\mathrm{Ti}}_{0.5}{\mathrm{Hf}}_{0.5}\right)\mathrm{Sn}$ and related half-Heusler compounds. Two different methods have been used to calculate the electronic structure, i.e., full potential linearized augmented plane wave method for ordered compounds and the Korringa-Kohn-Rostoker method within the coherent potential approximation for disordered alloys. We show that these methods give very close results if comparing the density of states obtained in both cases. Moreover, no peculiarities in the band structure have been revealed upon alloying the parent compounds and therefore the large value of the thermopower reported experimentally for $\mathrm{Ni}\left({\mathrm{Ti}}_{0.5}{\mathrm{Hf}}_{0.5}\right)\mathrm{Sn}$ with respect to NiTiSn or NiHfSn, does not have an origin in the electronic structure behavior. The thermopower calculations performed for different half-Heusler compounds rather suggest that the carrier concentration itself could be predominantly responsible for the large thermopower in $\mathrm{Ni}\left({\mathrm{Ti}}_{0.5}{\mathrm{Hf}}_{0.5}\right)\mathrm{Sn}$ as well as in other half-Heusler phases. Therefore, the large negative values of the Seebeck coefficient are not limited to some specified half-Heusler semiconductors but seem to be the rule for the $n$-type samples with moderately low carrier concentrations.

• Received 9 September 2005

DOI:https://doi.org/10.1103/PhysRevB.73.045121