Thermoelectric properties of high-entropy rare-earth cobaltates

High-entropy concept introduced with a promising paradigm to obtain exotic physical properties has motivated us to explore the thermoelectric properties of Sr-substituted high-entropy rare-earth cobaltates i.e., (LaNdPrSmEu)$_{1-x}$Sr$_x$CoO3 (0 \leq x \leq 0.10). The structural analysis of the samples synthesized using the standard solid-state route, confirms the orthorhombic structure with the Pbnm space group. The Seebeck coefficient and electrical resistivity decrease with rising Sr concentration as well as with an increase in temperature. The multiple A-site ions in high-entropy rare-earth cobaltates result in an improved Seebeck coefficient ({\alpha}) compared to La$_{0.95}$Sr$_{0.05}$CoO$_3$, associated with a decrease in the Co-O-Co bond angle, which further enhances the power factor. The random distribution of cations at the rare-earth site results in a significant lowering of phonon thermal conductivity. As a result, a maximum figure of merit (zT) of 0.23 is obtained at 350K for (LaNdPrSmEu)$_{0.95}$Sr$_{0.05}$CoO$_3$, which is one of the highest values of zT reported at this temperature for oxide materials. This study shows promise to decouple thermoelectric parameters using the high-entropy concept in several materials.