Sm0.5−xGdxSr0.5CoO3−δ (SGSC, x=0, 0.1, 0.2, 0.3, 0.4, 0.5) powders were synthesized by a solution‐combustion method. SGSC formed the major perovskite phase with an orthorhombic symmetry after calcined at 1200°C. The electrical measurements indicated that the Gd3+content have a strong influence on the electrical conductivities of SGSC. It was found that the electrical conductivities of SGSC was firstly increased then decreased as the Gd3+ content changed from 0 to 0.5. The highest electrical conductivity with a value 1820 S/cm was obtained when the amount of Gd reached to 0.2.

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The perovskite oxides Ln 0.8 Sr 0.2 Cu 0.9 Fe 0.1 O 2.5-δ (LSCF, Ln=La, Pr, Nd, Sm, Gd) were synthesized by a Pechini-type gel method. The crystal structure, chemical stability and electrical conductivity of these oxides were investigated. The LSCF formed the major perovskite phase with a tetragonal symmetry after sintering at 800 o C. The LSCF was thermodynamically stable and chemically compatible to Sm 0.2 Ce 0.8 O 1.9 electrolyte below 1000 o C. The electrical conductivity of LSCF was measured by the dc fourterminal method. As the ionic radius of Ln 3+ decreased, the electrical conductivity significantly reduced from 632.7 S·cm −1 for La 0.8 Sr 0.2 Cu 0.9 Fe 0.1 O 2.5-σ to 14.7 S·cm −1 for Gd 0.8 Sr 0.2 Cu 0.9 Fe 0.1 O 2.5-σ at 700 o C.

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