  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.
