Improved Thermoelectric Performance of P-Doped Half-Heusler Ti0.5Zr0.5CoSb0.5P0.5, Ti0.5Hf0.5CoSb0.5P0.5, and Zr0.5Hf0.5CoSb0.5P0.5 Compounds

We substituted the M site with two atoms of Ti, Zr, Hf and Sb atom with P atom in MCoSb half-Heusler compounds to obtain Ti0.5Zr0.5CoSb0.5P0.5, Ti0.5Hf0.5CoSb0.5P0.5, and Zr0.5Hf0.5CoSb0.5P0.5. Then, we systematically studied the electronic structure and TE transport properties of the three compounds by using density functional theory and the semiclassical Boltzmann transport equation. In contrast to their parent compound MCoSb (M=Ti, Zr, Hf), the substituted compounds retained the characteristic of indirect bandgap semiconductivity. The lattice thermal conductivity of these three compounds was lower than that of their corresponding parent material. The thermoelectric figure of merit of the three compounds was approximately 0.85, which was remarkably higher than that of their corresponding parent compounds (0.25). The increased in the thermoelectric figure of merit may be attributed to a reduction in lattice thermal conductivity and high power factor. Therefore, the three compounds with carrier concentrations of 10(20) and 10(21) cm(?3) are candidate thermoelectric materials that can be applied at the temperature of 900?1500 K.