Thermoelectric behavior of (Ba_0.2Sr_0.2Ca_0.2La_0.2Na_0.2)CoO₃ high entropy cobaltate-based perovskite

Oxides are considered as promising thermoelectric materials due to their excellent thermal and chemical stability at elevated temperatures. However, their thermoelectric performances are hindered by high thermal conductivity due to the relatively simple structure compared to the layered or cage-like structure of intermetallics and chalcogenides. In this study, we have successfully crafted a novel cobaltate-based high-entropy oxide perovskite, (Ba_0.2Sr_0.2Ca_0.2La_0.2Na_0.2)CoO₃ (BSCLN), based on detailed thermodynamic calculation. XRD analysis of the as-synthesized ceramics confirms the formation of a cubic perovskite phase, while SEM-EDXS data reveals a dense microstructure with a uniform distribution of all the constituent elements. By employing high-entropy engineering in this cobaltate-based ceramic, we have managed to reduce thermal conductivity significantly while optimizing electrical conductivity. Five different elements populating the A-site induce extensive structural defects and disorder causing enhanced phonon scattering. This results in a glass-like low thermal conductivity of 1.43 W m^-1 K^-1 at 1023 K for the high-entropy cobaltate. Moreover, we have achieved a comparatively high electrical conductivity on the order of 10⁴ S m^-1. This study illustrates the effectiveness of introducing structural disorder through high-entropy engineering to enhance the overall thermoelectric performance of the material.