Crystal structure, electronic conductivity and oxygen exchange kinetics of high-entropy perovskites La0.2Pr0.2Nd0.2Sm0.2Sr0.2Co1-xFexO3-δ (x=0, 0.5, 1)

High-entropy perovskites (HEPs) are attracting increasing attention as air electrode materials for solid oxide cells (SOCs). In this work, three different HEPs from the series La0.2Pr0.2Nd0.2Sm0.2Sr0.2Co1-xFexO3-delta (x = 0, 0.5, 1) are synthesized using the citric acid-ethylenediaminetetraacetate (EDTA) method. X-ray diffraction analysis finds crystal structures with the orthorhombic space group 62 (Pnma) at room temperature. The lattice distortion increases with increased Fe-substitution at the B-site. The electrical conductivity (sigma(e)) is determined at temperatures from 600 to 850 degrees C and oxygen partial pressures (pO(2)) between 0.001 and 0.15 bar. For the pure cobaltate, sigma(e) is 1469 S cm(-1) at 800 degrees C and 0.15 bar pO(2). The conductivity is significantly reduced with Fe-doping, reaching 87 S cm(-1) for the pure ferrate at 800 degrees C. The chemical oxygen surface exchange coefficient (k(chem)) and the chemical oxygen diffusion coefficient (D-chem) are determined by the electrical conductivity relaxation technique. D-chem is found to be quite independent of B-site doping and pO(2), with values of approx. 5 x 10(-6) cm(2) s(-1) at 800 degrees C. In contrast, k(chem) is strongly influenced by the B-site composition, which results in an increase of more than one order of magnitude from the ferrate (3.4 x 10(-5) cm s(-1)) to the cobaltate (7.7 x 10(-4) cm s(-1)) at 800 degrees C and 0.001 bar pO(2). This clearly demonstrates the beneficial effects of Co on the electronic conductivity as well as on the catalytic activity for the oxygen surface exchange reaction.