N-Type TaCoSn-Based Half-Heuslers as Promising Thermoelectric Materials

Half-Heusler compounds are recognized as promising thermoelectric materials for high-temperature power generation, but their relatively high lattice thermal conductivity impedes further improvement of ZT. Here, we report the synthesis of a new half-Heusler compound TaCoSn with a low thermal conductivity. Experimentally, the pristine TaCoSn exhibits a low lattice thermal conductivity of ∼5.7 W m^-1 K^-1 at 300 K, which is lower than that of most of the other half-Heusler compounds. Phonon calculations by density functional theory indicate that the low phonon velocity, small Debye temperature, and large Grüneisen parameter are the contributors to the low thermal conductivity of TaCoSn. Importantly, intense point-defect scattering can be induced by alloying Nb at the Ta site, which further suppresses the thermal conductivity of TaCoSn. Additionally, Sb has been identified as an efficient dopant for supplying high electron concentration. Finally, the optimized n-type Ta_0.6Nb_0.4CoSn_0.94Sb_0.06 demonstrates a peak ZT above 0.7 at 973 K. Our work demonstrates that the TaCoSn-based half-Heuslers are promising thermoelectric materials.