First-principles assisted design of high-entropy thermoelectric materials based on half-Heusler alloys

The deformation potential theory and semi-classical Boltzmann theory were combined to predict the thermoelectric performances of half-Heusler NaCuTe alloy and Li_0.5Na_0.5CuSe_0.5Te_0.5 high-entropy half-Heusler alloy through first-principles calculations. The former was constructed via the congener substitution method from LiCuSe alloy, while the latter was designed by the high-entropy engineering concept. The phonon spectrum and ab initio molecular dynamics simulations indicated that the three alloys display stable intermetallic compounds at ambient temperature. The electrical and thermal transport properties of p-type LiCuSe, NaCuTe, and Li_0.5Na_0.5CuSe_0.5Te_0.5 alloys were computed as a function of temperature and carrier concentration. The thermoelectric figure of merit for p-type Li_0.5Na_0.5CuSe_0.5Te_0.5 alloy was 1.005 and 3.443 at room temperature and 800 K, whereas that of p-type NaCuTe alloy achieved 2.488 at 800 K, which is obviously superior to most of the recently reported p-type half-Heusler thermoelectric materials. A comprehensive analysis of the phonon lifetime, Grüneisen parameters, phonon group velocities, and primitive cell phonon spectrum revealed that high-entropy engineering could introduce non-equivalent atoms and thus enhance phonon scattering, resulting in the reduction of lattice thermal conductivity. Furthermore, numerical simulations demonstrated that high-entropy engineering could improve the thermoelectric performances of half-Heusler alloys effectively, which provides a unique approach for the optimized design of novel thermoelectric materials.