Half-Heusler alloys based on TiNiSn are promising thermoelectric materials characterised by large power factors, good mechanical and thermal stabilities; but they are limited by large thermal conductivities. A variety of strategies have been used to disrupt their thermal transport, including alloying with heavy, generally expensive, elements and nanostructuring, enabling figures of merit, ZT ≥ 1 at elevated temperatures (>773 K). Here, we demonstrate an alternative strategy that is based around the partial segregation of excess Cu leading to grain-by-grain compositional variations, the formation of extruded Cu ‘wetting’ layers between grains and – most importantly – the presence of statistically distributed interstitials that reduce the thermal conductivity effectively through point-defect scattering. Our best TiNiCuySn (y ≤ 0.1) compositions have a temperature-averaged ZTdevice = 0.3-0.4 and estimated leg power outputs of 6-7 W cm-2 in the 323-773 K temperature range. This is a significant development as these materials were prepared using a straightforward processing method, do not contain any toxic, expensive or scarce elements and are therefore promising candidates for large scale production.
Barczak, S., Halpin, J., Buckman, J., Decourt, R., Pollet, M., Smith, R. I., MacLaren, D. A., & Bos, J-W. G. (2018). Grain by grain compositional variations and interstitial metals – a new route towards achieving high performance in half-Heusler thermoelectrics. ACS Applied Materials and Interfaces, 10(5), 4786–4793. https://doi.org/10.1021/acsami.7b14525