Regulation of the Thermoelectric Properties of Perovskite RECoO3 Ceramics via High-Entropy Engineering

Entropy engineering has been demonstrated to be an effective strategy to regulate the thermoelectric properties of materials. In this work, we report a series of single-phase cubic (La0.25Sr0.25Ba0.25Ca0.25)CoO3 (LSBC), (La0.25Nd0.25Sr0.25Ba0.25)CoO3 (LNSB), and (La0.2Nd0.2Sr0.2Ba0.2Ca0.2)CoO3 (LNSBC) ceramics based on high-entropy design in the Re site of perovskite RECoO3. Electron microscopy results indicate that the three samples have high crystallinity and exhibit a clear pore structure with rich lattice defects. Electrical transport measurements show that LNSB and LNSBC show metallic conductive behaviors with the lowest resistivity of only 2.25 m Omega cm at 973 K, while LSBC exhibits a semiconductor-metal transition at around 650 K due to the lower average chemical valences in the RE site. Meanwhile, the low average chemical valences also cause the increasing proportion of Co4+ due to the requirement of charge neutrality of the samples, which inhibits their Seebeck coefficients. However, compared with the reported Co-based perovskite oxides, their thermal conductivities are greatly reduced owing to high-entropy enhanced lattice scattering. LSBC in particular obtains the lowest thermal conductivity of 1.25 W<middle dot>m-1<middle dot>K-1 at 937 K, while LNSB and LNSBC characterized by high carrier thermal conductivity exhibit a thermal conductivity of 1.52 W<middle dot>m-1<middle dot>K-1 at the same temperature. These findings reveal that high-entropy design in the RE site of perovskite RECoO3 ceramics enables the effective reduction of thermal conductivity and the maintenance of the excellent electrical properties simultaneously, which provides a novel route for the development of high-performance thermoelectric materials.