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The GdBaCo(2)O(5+delta)-Sm(0.2)Ce(0.8)O(1.9) (GBCO-SDC) composite cathodes were prepared, their thermogravimetric measurement, thermal expansion coefficient (TEC), electrical conductivity and electrochemical performance were studied as function of temperature and SDC content. The adjustment of TEC to electrolyte, which is one of the main problems of GBCO cathode, could be achieved to lower TEC values with more SDC addition, while maintaining reasonable high electrical conductivity. By means of DC polarization and AC impedance spectroscopy, the electrochemical performance of GBCO-SDC composite cathodes on SDC electrolyte was examined. Results indicated that the proper addition of SDC could improve the performance of GBCO cathode. The optimum content of SDC in the composite cathodes was 40 wt.% with the polarization resistance (Rp) of 1.39 Omega cm(2) at 500 degrees C, which was significantly lower than that of pure GBCO cathode (7.26 Omega cm(2)). (C) 2010 Elsevier B.V. All rights reserved.