Oxygen deficiency, thermal and chemical expansion of La0.5Sr0.5Fe1-xCoxO3-delta (x=0, 0.5, 1) have been measured by thermogravimetry, dilatometry and high temperature X-ray diffraction. The rhombohedral perovskite materials transformed to a cubic structure at 350 +/- 50 degrees C. The thermal expansion of the materials up to the onset of thermal reduction was 14-18 x 10(-6) K-1. Above 500 degrees C in air (400 degrees C in N-2), chemical expansion contributed to the thermal expansion and the linear thermal expansion coefficients were significantly higher, 16-35 x 10(-6) K-1. The chemical expansion, epsilon(c), showed a maximum of 0.0045 for x=0.5 and 0.0041 for x=1 at 800-900 degrees C. The normalized chemical expansion, epsilon(c)/Delta delta, was 0.036 for x=0.5 and 0.035 for x=1 at 800 degrees C. The chemical expansion can be correlated with an increasing ionic radius of the transition metals with decreasing valence state. (c) 2006 Elsevier B.V. All rights reserved.