Titanium Doping to Enhance Thermoelectric Performance of 19‐Electron VCoSb Half‐Heusler Compounds with Vanadium Vacancies

Abstract

Abstract The 19‐electron VCoSb compounds are actually composites of an off‐stoichiometric half‐Heusler phase and impurities. Here the compositional adjustment is systematically studied in V 1− x CoSb to obtain single‐phase V 0.955 CoSb. Hall measurements suggest that such a V vacancy, as well as Ti doping, can optimize the carrier concentration, which decreases from ≈11.3 × 10 21 cm −3 for VCoSb to ≈6.3 × 10 21 cm −3 for V 0.755 Ti 0.2 CoSb. Low sound velocity contributes to the intrinsically low lattice thermal conductivity for VCoSb‐based materials. The high Ti‐dopant content results in enhanced point‐defect scattering, which further decreases the lattice thermal conductivity. Finally, the optimized n‐type V 0.855 Ti 0.1 CoSb is found to reach a peak ZT of ≈0.7 at 973 K. The work demonstrates that the VCoSb‐based half‐Heuslers are promising thermoelectric materials.