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

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 573 K and 1173 K, whereas the ionic conductivity increased in the order La < Sm < Pr between 923 K and 1073 K. 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 973 K.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 1123 K were essentially independent of the transport properties of the cathode materials, exhibiting an identical impedance of 0.08 Ω∙cm2 at 973 K.

► A-site cation effect on the properties of LnSF (Ln = La, Pr, Sm) was studied.
► Ionic conductivities of LnSF were carefully measured.
► Pr0.8Sr0.2FeO3 − δ showed the highest ionic conductivities at 923–1073 K.
► At 973 K, ionic conductivities of LnSF vary by approximately an order of magnitude.
► This does not affect the oxygen reduction reaction in an SOFC cathode prepared by infiltration.