Enhanced thermoelectric performance of n‐type TiCoSb half‐Heusler by Ta doping and Hf alloying

Abstract

Abstract The p‐type TiCoSb‐based half‐Heuslers are widely studied due to the good electrical transport properties after hole doping, while the pristine TiCoSb is intrinsically n‐type. It is thus desired to obtain a comparable n‐type counterpart through optimization of electron concentration. In this work, n‐type Ti 0.9− x Hf x Ta 0.1 CoSb half‐Heuslers were fabricated by arc melting, ball milling, and spark plasma sintering. An optimized carrier concentration, together with a decreased lattice thermal conductivity, was obtained by Ta doping at the Ti site, leading to a peak figure of merit (ZT) of 0.7 at 973 K in Ti 0.9 Ta 0.1 CoSb. By further alloying Hf at the Ti site, the lattice thermal conductivity was significantly reduced without deteriorating the power factor. As a result, a peak ZT of 0.9 at 973 K and an average ZT of 0.54 in the temperature range of 300–973 K were achieved in Ti 0.6 Hf 0.3 Ti 0.1 CoSb. This work demonstrates that n‐type TiCoSb‐based half‐Heuslers are promising thermoelectric materials.