A thin interlayer of samarium doped ceria (SDC) is applied as diffusion barrier between La(1-x)Sr(x)Co(y)Fe(1-y)O(3)x = 0.1-0.4, y = 0.2-0.8 (LSCF) cathode and La1.8Dy0.2Mo1.6W0.4O9 (LDMW82) electrolyte to obstruct Mo-Sr diffusion and solid state reaction in the intermediate temperature range of SOFC. We demonstrate the effectiveness of the diffusion barrier through contrasting the clearly defined interfaces of LSCF/SDC/LDMW82 against a rugged growing product layer of LSCF/LDMW82 in 800 degrees C thermal annealing, and analyze the product composition and the probable new phase. In addition, the measured polarization resistance is considerably lower for the half-cell with a diffusion barrier. Therefore, the electrochemical performance of the LSCF cathode is investigated on the SDC-protected LDMW82. The cell with LSCF (x = 0.4) persistently outperforms the one with x = 0.2 in polarization resistance because of its small low-frequency contribution. The activation energy of polarization resistance is also lower for La0.6Sr0.4CoyFe1-yO3 (112-135 kJ/mol), than that for La0.8Sr0.2CoYFe1-yO3 (156-164 kJ/mol). La0.6Sr0.4CoyFe1-yO3 y = 0.4-0.8 is the proper composition for the cathode interfaced to SDC/LDMW82. (C) 2009 Elsevier B.V. All rights reserved.