Anomalous reduction of lattice thermal conductivity in half-Heusler ZrCoSb
The reduction of lattice thermal conductivity can be realized by introducing large mass contrast through atomic substitution within pristine compounds. Such process are usually termed as “point-defect scattering” and has been proved effective to improve the thermoelectric figure-of-merit (zT). Recently we synthesized two sets of half-Heusler compounds: ZrCoSb1-xSnx and Zr1-yTiyCoSb, and compared their lattice thermal conductivity with respect to the substitution level. Contrary to the general concept that larger mass difference are more effective in phonon scattering, we find a much lower lattice thermal conductivity in compounds with Sn substituting at the Sb site than the ones with Ti substituting at the Zr site. To understand the origin of the anomalous phonon scattering in the Sn-containing compounds, we systematically investigated the transport properties and microstructural features. Our results reveal the origin of the reduced lattice thermal conductivity with Sn doping, which are illuminating for materials designs for subsequent zT optimization.