Improved thermoelectric properties of doped A0.5B0.5NiSn (A, B = Ti, Zr, Hf) with a special quasirandom structure

MNiSn (Ti, Hf, Zr) is used as the parent material in constructing special quasirandom structure-based half-Heusler compounds that experimentally mimic atomic occupation disorders. We randomly doped Ti, Hf, and Zr with an occupation probability of 50% to obtain Ti0.5Zr0.5NiSn, Ti0.5Hf0.5NiSn, and Zr0.5Hf0.5NiSn, respectively. We systematically studied the electronic structure and thermoelectric transport properties of these compounds by referring to density functional theory and the semiclassical Boltzmann transport equation. Compared with the parent compound MNiSn (M = Ti, Zr, Hf), the substituted compounds retain the characteristic of semiconductivity. The lattice thermal conductivity of the three compounds is about 2.5 Wm−1 K−1 at about 1000 K, which is lower than that of their corresponding parent materials (5.0–6.0 Wm−1 K−1). The maximum thermoelectric figures of merit for Ti0.5Zr0.5NiSn (0.57), Ti0.5Hf0.5NiSn (0.55), and Zr0.5Hf0.5NiSn (0.58) are higher than those of their parent compounds TiNiSn (0.35), ZrNiSn (0.496), and HfNiSn (0.473). The increase in thermoelectric figure of merit is due to low lattice thermal conductivity and high power factor. Therefore, the three predicted compounds can be considered candidate thermoelectric materials that can be used at a carrier concentration of 1020–1022 cm−3 and a temperature of 900–1200 K.