Exceptional Rare-Earth Half-Heusler Thermoelectrics With Sublattice Softening

Half-Heusler (HH) compounds are promising thermoelectric (TE) materials, but their intrinsically high lattice thermal conductivity (κ_L) limits TE performance. Here, we report sublattice softening-induced intrinsically low κ_L and exceptional thermoelectricity in the previously underexplored rare-earth (RE) containing HHs. Unlike conventional non-RE HHs, the softened RE-based lattice framework in RE-HHs enables vigorous atom vibration within the 4c sublattice, strengthening lattice anharmonicity and phonon damping. This effect can be further amplified when heavier elements occupy the 4c sublattice, effectively suppressing both acoustic and optical phonon propagation and resulting in a pronounced reduction in κ_L. Leveraging the low κ_L, we identify four RE-HHs-DyPtSb, Y_0.7Lu_0.3PtSb, Sc_0.6Lu_0.4PtSb, and Dy_0.7Y_0.3PtSb-with peak zT values exceeding 1.0. Notably, Dy_0.7Y_0.3PtSb achieves a maximum zT of 1.33 at 875 K. These findings underscore the promising potential of sublattice-softened RE-HHs as highly efficient thermoelectrics with broad compositional tunability.