Half Heusler Alloys for Efficient Thermoelectric Power Conversion

TL;DR

This paper reports a significant increase in the thermoelectric figure of merit (ZT) for Half-Heusler alloys through elemental substitution and nanoparticle embedding, leading to improved power conversion efficiency suitable for environmentally friendly energy applications.

Contribution

The study demonstrates a novel approach to enhance ZT in Half-Heusler alloys by combining elemental substitution and nanoparticle embedment, achieving higher efficiency without microstructure tuning.

Findings

ZT~1.3 achieved near 850 K in n-type alloys

Power conversion efficiency estimated at 13% for the new modules

High ZT obtained without microstructure tuning

Abstract

Half-Heusler (HH) phases (space group F43m, Clb) are increasingly gaining attention as promising thermoelectric materials in view of their thermal stability, scalability, and environmental benignity as well as efficient power output. Until recently, the verifiable dimensionless figure of merit (ZT) of HH phases has remained moderate near 1, which limits the power conversion efficiency of these materials. We report herein ZT~1.3 in n-type (Hf,Zr)NiSn alloys near 850 K developed through elemental substitution and simultaneously embedment of nanoparticles in the HH matrix, obtained by annealing the samples close to their melting temperatures. Introduction of mass fluctuation and scattering centers play a key role in the high ZT measured, as shown by the reduction of thermal conductivity and increase of thermopower. Based on computation, the power conversion efficiency of a n-p couple module based on the new n-type (Hf,Zr,Ti)NiSn particles-in-matrix composite and recently reported high-ZT p-type HH phases is expected to reach 13%, comparable to that of state-of-the-art materials, but with the mentioned additional materials and environmental attributes. Since the high efficiency is obtained without tuning the microstructure of the Half-Heusler phases, it leaves room for further optimization.