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BaxSr1-xCo0.8Fe0.2O3-delta (0.3 <= x <= 0.7) composite oxides were prepared and characterized. The crystal structure, thermal expansion and electrical conductivity were studied by X-ray diffraction, dilatometer and four-point DC, respectively. For x <= 0.6 compositions, cubic perovskite structure was obtained and the lattice constant increased with increasing Ba content. Large amount of lattice oxygen was lost below 550 degrees C, which had significant effects on thermal and electrical properties. All the dilatometric curves had an inflection at about 350-500 degrees C, and thermal expansion coefficients were very high between 50 and 1000 degrees C with the value larger than 20 x 10(-6) degrees C-1. The conductivity were larger than 30 S cm(-1) above 500 degrees C except for x > 0.5 compositions. Furthermore, conductivity relaxation behaviors were also investigated at temperature 400-550 degrees C. Generally, Ba0.4Sr0.6Co0.8Fe0.2O3-delta and Ba0.5Sr0.5Co0.8Fe0.2O3-delta are potential cathode materials. (c) 2005 Elsevier Ltd. All rights reserved.