Rare earth-based half-Heusler compounds are potential thermoelectric materials with inherently low thermal conductivity. Here, LuNiSb-based compounds were successfully prepared and their electrical and thermal transport properties were simultaneously improved via aliovalent doping of Sn and Co. In addition to optimizing the carrier concentration, a huge suppression of lattice thermal conductivity κL (∼40% at 300 K) was observed, despite the atomic mass and radius of Sn and Co having only small differences compared with those of the substituted matrix atoms. With the help of first-principles calculations, it is discovered that the suppression of κL mainly originates from the deceleration of optical phonons and the enhancement of phonon–phonon (p–p) scattering phase space. Compared with Co-doped LuNiSb-based compounds, Sn-doped ones exhibit better electrical performance, which is probably because of the weaker perturbation of the valence band. Finally, a peak zT of about 0.4 was obtained at 775 K for LuNiSb0.92Sn0.08. This work highlights the simultaneous optimization of electrical and thermal transport properties only by aliovalent doping, which helps develop high-performance thermoelectrics.
