Ba0.5Sr0.5Co1-yFeyO3-delta (y = 0-1-0-9) (BSCF) oxides have been evaluated as cathode materials for intermediate solid oxide fuel cells with La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) as electrolyte. The increase of iron content in BSCF materials results in an increase of the area-specific resistance (ASR), e.g. 0.04, 0.08 and 0.13 Omega cm(2) for compositions with y = 0.2, 0.4 and 0.6 respectively at 1073 K. The influence of iron content in BSCF oxides on the unit cell volume via high temperature X-ray diffraction, the overall electrical conductivity and the thermal expansion coefficient (TEC) has also been investigated The lattice cell parameters for the BSCF series increase as a function of the temperature and exhibit a non-linear behaviour, with a sudden increase at around 673 K due to the loss of lattice oxygen, which in turn is caused by the reduction of Co4+ and Fe4+ to lower oxidation states This was determined by O-2 temperature-programmed desorption and thermogravimetric analysis Such oxygen non-stoichiometry results in a significant thermal expansion and conductivity change for all compositions at the same temperature. (C) 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu.