High-Entropy Perovskites: An Emergent Class of Oxide Thermoelectrics with Ultralow Thermal Conductivity

Although SrTiO3-based perovskites showed a lot of promise as n-type thermoelectric (TE) materials, they demonstrated a low figure of merit value primarily because of their high lattice thermal conductivity (kl). Researchers found it difficult to reduce kl, as a popular route like nanostructuring did not work well with these perovskites possessing low phonon mean free paths. Here, we put forward a novel strategy of designing high-entropy perovskite (HEP) oxides having five transition metals in the B site to induce more anharmonicity causing enhanced multiphonon scattering in order to decrease kl. Using detailed thermodynamic calculations, we designed and synthesized a highly dense Sr(Ti0.2Fe0.2Mo0.2Nb0.2Cr0.2)O3 HEP ceramic. An ultralow thermal conductivity of 0.7 W/mK at 1100 K was achieved in this n-type rare-earth-free HEP oxide TE material. The concept of designing HEPs to achieve ultralow thermal conductivity potentially opens up a new avenue for enhancing TE performance of environmentally benign bulk oxides for high-temperature TE power generation.