Thermoelectric Properties of Directionally Solidified Half-Heusler (M 0.5 a ,M 0.5 b )NiSn (Ma, Mb = Hf, Zr, Ti) Alloys

Abstract

To evaluate the effect of the substitution of the M-site atoms Ti, Zr, and Hf on thermoelectric properties, nearly single-phase (M0.5a,M0.5b)NiSn alloys (Ma, Mb = Hf, Zr, Ti) were fabricated by directional solidification. The lattice thermal conductivity can be most effectively reduced in the (Ti0.5,Hf0.5)NiSn alloy, probably due to the solid-solution effect, since the difference in atomic size and atomic mass are maximized between Ti and Hf. Moreover, we have found the phase separation between Ti-rich and Ti-poor half-Heusler phases in (Ti0.5,Hf0.5)NiSn and (Ti0.5,Zr0.5)NiSn alloys through observation of microstructure, chemical concentration measurement, and x-ray diffractometry.