The effect of A-site cation (Ln = La, Pr, Sm) on the crystal structure, conductivity and oxygen reduction properties of Sr-doped ferrite perovskites

Abstract

The influence of A-site cation (Ln=La, Pr, Sm) on the crystal structure of Sr-doped ferrite perovskites (Ln0.8Sr0.2FeO3−δ, LnSF) was studied and the results used to interpret the differences in electronic conductivity. The electronic conductivity decreased with decreasing A-site cation radius, i.e. in the order La>Pr>Sm between 573K and 1173K, whereas the ionic conductivity increased in the order La<Sm<Pr between 923K and 1073K. The ionic conductivity of Pr0.8Sr0.2FeO3−δ (PSF) was more than one order of magnitude higher than that of La0.8Sr0.2FeO3−δ (LSF) at 973K.To evaluate these materials as cathode materials for solid oxide fuel cells (SOFCs), the chemical compatibility of LnSF with yttria-stabilized zirconia (YSZ) was investigated. Despite significant differences in ionic and electronic conductivity, the performance of the symmetric cells with composite cathodes formed by infiltration of doped LnFeO3 into YSZ and calcination to 1123K were essentially independent of the transport properties of the cathode materials, exhibiting an identical impedance of 0.08Ω∙cm2 at 973K.