Superior electron transport in the single-crystalline TiCoSb-based half-Heuslers.

Half-Heuslers emerged as promising candidates for medium- and high-temperature thermoelectric power generation. However, polycrystalline half-Heuslers inevitably suffer from the defect-dominated scattering of electrons that greatly limits the optimization of their electronic properties. Herein, high-quality TiCoSb-based single-crystals with a dimension above 1 cm have been obtained. Benefitting from the improved electron mobility, an average power factor of ~37 μW cm K in the temperature range between 307 and 973 K has been realized in the n-type single-crystalline TiNbCoSb. In addition, Hf alloying results in the expansion of the weighted scattering phase space and enhances the anharmonic scattering rate, thereby effectively suppressing the lattice thermal conductivity. Eventually, co-doping of Nb/Ta and alloying of Hf effectively elevate the thermoelectric performance of TiCoSb single crystal, and a peak zT above 1.0 has been realized, which outperforms the previously reported polycrystalline (Ti, Zr, Hf)CoSb-based and ZrCoBi-based materials. Importantly, a single leg of TiCoSb-based single crystals exhibits a heat-to-electricity energy conversive efficiency of ~10.2% at a temperature difference of 700 K. Here, our findings reveal the promise of TiCoSb-based single crystals for thermoelectric power generation, and can potentially guide the future explorations of other single-crystalline half-Heuslers.