Uncovering High Thermoelectric Figure of Merit in (Hf,Zr)NiSn Half-Heusler Alloys

TL;DR

This paper reports a significant increase in the thermoelectric figure of merit (ZT) in (Hf,Zr)NiSn Half-Heusler alloys through annealing, improving structural order and electrical properties without nanostructuring.

Contribution

It demonstrates that annealing can enhance ZT in (Hf,Zr)NiSn alloys by improving structural order, achieving ZT~1.2 without nanostructuring, which is a novel approach.

Findings

ZT~1.2 achieved in annealed (Hf,Zr)NiSn alloys

Increase in power factor and carrier mobility

Decrease in charge carrier density

Abstract

Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler phases (R=Hf, Zr, Ti) are the most studied in view of their thermal stability. The highest dimensionless figure of merit (ZT) obtained is ~1 in the temperature range ~450-900oC, primarily achieved in nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an appreciable increase in the power factor, decrease in charge carrier density, and increase in carrier mobility. The findings are attributed to the improvement of structural order. Present approach may be applied to optimize the functional properties of Heusler-type alloys.