A newly developed cathode material, Ba0.5Sr0.5Co0.8Fe0.2O3-delta, was synthesized and characterized. X-ray diffraction results identified it as a cubic perovskite structure. Thermogravimetric results showed that lattice oxygen loss was about 2% in weight between 50 and 1000 degrees C. Thermal expansion coefficient results in air and argon were extraordinarily high, with slope changes occurring at about 382 and 360 degrees C, respectively. Electrical conductivity values were sufficient for cathode application with the maximum of about 28.1 S cm(-1) at 500 degrees C in air and 17.3 S cm(-1) at 900 degrees C in N-2, correspondingly. Both thermal and electrical properties were closely associated with lattice oxygen behaviors and oxygen partial pressure. (c) 2005 The Electrochemical Society.