Quasi-random distribution of distorted nanostructures enhances thermoelectric performance of high-entropy chalcopyrite

Here, we suggest that the quasi-random distribution of distorted nanostructures (QDDN), which is unique in high-entropy materials, is the reason for superior thermoelectric properties. The general high entropy material consists of several atoms with disordered lattice in atomic scale. Our QDDN showed nanoscale disorder because the consisting atoms were not distributed fully randomly. The order of compositional distribution was found as 40–60 nm, which causes high level of lattice-strain-induced distortion. The underlying mechanism of phonon scattering by QDDN was clarified by theoretical analysis. The high level of lattice strain induced by QDDN causes strong phonon scattering in entire phonon spectrum. A low κ_lat of ∼0.38 W/m-K at 850 K was achieved in a CuGaTe₂-based high-entropy chalcopyrite material. However, the power factor was not significantly affected due to ther high crystallinity, despite the QDDN. Therefore, a zT of ∼1.56 at 850 K was attained in a Cu_0.8Ag_0.2[Ga_0.8In_0.2]_0.99Zn_0.01Te₂ compound, which represented a 132% enhancement from pure CuGaTe₂. These results elucidate recent zT increases in high-entropy materials and can be a step towards further enhancements of zT in thermoelectric materials.