Enhancement of thermoelectric figure-of-merit at low temperatures by titanium substitution for hafnium in n-type half-Heuslers Hf0.75−xTixZr0.25NiSn0.99Sb0.01

The effect of titanium (Ti) substitution for hafnium (Hf) on thermoelectric properties of (Hf, Zr)-based n-type half-Heuslers: Hf0.75−xTixZr0.25NiSn0.99Sb0.01, 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 Hf0.5Zr0.25Ti0.25NiSn0.99Sb0.01 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 Hf0.5Zr0.25Ti0.25NiSn0.99Sb0.01 samples are significantly higher than those of the same way prepared Hf0.75Zr0.25NiSn0.99Sb0.01 samples at each temperature, which are very much desired for mid-range temperature applications such as waste heat recovery in automobiles.

Graphical AbstractFigure optionsDownload as PowerPoint slideHighlights
► Ti substitution boost thermoelectric performance of Hf–Zr based n-type half-Heuslers.
► ZT improvement at lower temperature is demonstrated.
► Peak ZT of 1.0 at 500 °C in n-type Hf0.5Ti0.25Zr0.25NiSn0.99Sb0.01 composition is observed.
► Increase in carrier concentration by Ti substitution causes the ZT improvement.
► The ZT enhancement beneficial for power generation applications is demonstrated.