Synthesis and electrical properties of Ln0.6Ca0.4FeO3−δ (LnPr, Nd, Sm) as cathode materials for IT-SOFC

Fine powders of Ln0.6Ca0.4FeO3−δ (LnPr, Nd, Sm) were prepared by a glycine-nitrate process (GNP). The preparation process, thermal properties, phase constituents, and microstructure of the samples were characterized by FT-IR, TG-DSC, XRD and TEM, respectively. The results show that all of the powders have perovskite-type structure with orthorhombic symmetry and mean particle size of 25 nm. The relative density of Pr0.6Ca0.4FeO3−δ and Nd0.6Ca0.4FeO3−δ decreased with sintering temperature, while increased for Sm0.6Ca0.4FeO3−δ. The DC four-probe measurement indicated that both Pr0.6Ca0.4FeO3−δ and Nd0.6Ca0.4FeO3−δ exhibit fairly high electrical conductivity, over 100 S cm−1 at T > 650 °C, high enough for application as cathode materials for IT-SOFC. The temperature dependence of the conductivity for Nd0.6Ca0.4FeO3−δ consists of two straight lines with activation energies of 160.2 and 18.6 kJ mol−1, respectively, for the sample sintered at 1100 °C for 2 h. The conduction mechanism of the materials is discussed in terms of non-stoichiometry.