Ultra-low Thermal Conductivity in a Perovskite Oxide Thermoelectric through Entropy Engineering

High entropy thermoelectric oxides offer a route towards highly efficient thermoelectric energy conversion as the materials frustrate parasitic phonon transport. Here, entropy-stabilised perovskite oxide thermoelectrics (Ca_0.33Sr_0.33Ba_0.33)(Ti_0.5-xZr_0.5-xNbx)O₃ (x = 0, 0.1, 0.2, 0.33) were prepared via solid-state reaction with sintering at 1673 K under a reducing atmosphere. The products contained two high entropy perovskite phases with homogeneous elemental distributions at the nanoscale. Through optimising the Nb content, the Seebeck coefficient was increased, yielding an enhanced power factor of 39.5 μW m^-1 K^-2 at 873 K. High resolution transmission electron microscopy revealed the presence of a large number of defects of different dimensionality, which enhanced phonon scattering. A glass-like, ultra-low thermal conductivity of 1.6 – 1.9 W m^-1 K^-1 was achieved from room temperature to 873 K, amongst the lowest reported values for perovskite oxides. This work highlights the design of high entropy oxide perovskites based on non-toxic components having both high Seebeck coefficients and ultra-low thermal conductivity.