Enhancement of thermoelectric figure-of-merit at low temperatures by titanium substitution for hafnium in n-type half-Heuslers Hf[subscript0.75−x]Ti[subscript x]Zr[subscript 0.25]NiSn[subscript 0.99]Sb[subscript 0.01]

Abstract

The effect of titanium (Ti) substitution for hafnium (Hf) on thermoelectric properties of (Hf, Zr)-based n-type half-Heuslers: Hf[subscript 0.75−x]Ti[subscript x]Zr[subscript 0.25]NiSn[subscript 0.99]Sb[subscript 0.01], has been studied. The samples are made by arc melting followed by ball milling and hot pressing via the nanostructuring approach. A peak thermoelectric figure-of-merit (ZT) of ∼1.0 is achieved at 500 °C in samples with a composition of Hf[subscript 0.5]Zr[subscript 0.25]Ti[subscript 0.25]NiSn[subscript 0.99]Sb[subscript 0.01] due to a slight increase in carrier concentration and also a lower thermal conductivity caused by Ti. The ZT values below 500 °C of hot pressed Hf[subscript 0.5]Zr[subscript 0.25]Ti[subscript 0.25]NiSn[subscript 0.99]Sb[subscript 0.01] samples are significantly higher than those of the same way prepared Hf[subscript 0.75]Zr[subscript 0.25]NiSn[subscript 0.99]Sb[subscript 0.01] samples at each temperature, which are very much desired for mid-range temperature applications such as waste heat recovery in automobiles.