Compositionally Engineered Non-Equimolar LaCoO$_3$-Based High-Entropy Perovskites with Enhanced Thermoelectric Performance

Abstract

The decoupling of phonon and electron transport remains a central challenge in the development of high-performance TE materials. Configurational-entropy maximization is widely invoked as a design principle for decoupling phonon and electron transport. This study investigates compositionally engineered LaCoO$_3$-based high-entropy perovskites to determine whether thermoelectric transport can be improved by tuning cation identity and concentration rather than maximizing configurational entropy. La$_{1-x}$Sr$_x$(CoFeMnCrNi)O$_3$ ($x=0.0$--$0.2$) and selected non-equimolar A- and B-site perovskite compositions were prepared by solid-state reaction. The obtained samples are predominantly single-phase, as confirmed by X-ray diffraction and Rietveld refinement, consistent with the calculated size-disorder parameters. Multication disorder introduces substantial mass and strain-field fluctuations that promote phonon scattering. All samples exhibit p-type, thermally activated electrical transport consistent with adiabatic SPH. Sr substitution progressively reduces the hopping barrier and $ρ$, whereas non-equimolar B-site engineering partially recovers electrical transport while retaining low k. La$_{0.9}$Sr$_{0.1}$Co$_{0.4}$Cr$_{0.3}$Ni$_{0.1}$Fe$_{0.1}$Mn$_{0.1}$O$_3$, featuring a Co-rich and Cr-rich B-site composition, combines Co-associated mixed valence and spin-state degeneracy that sustain a large alpha with Cr-mediated control of carrier concentration and a reduced polaron hopping barrier of 0.19eV. This composition achieves a power factor of 40--43 $μ$W/(m K$^2$) and a $zT\sim0.072$ at 1100K, approximately 2.7 times that of its equimolar analogue. These results demonstrate that targeted cation chemistry and mass contrast, rather than configurational-entropy maximization alone, provide an effective strategy for balancing electronic and phonon transport in multicomponent oxide TE.