La(0.6)Sr(0.4)Co(1- y)FeyO(3 - delta) (LSCF) mixed-conducting perovskite oxides, a SOFC cathode candidate material, exhibit oxygen nonstoichiometry under reducing atmosphere and elevated temperatures. Reduction of the B-site transition metals and formation of oxygen vacancies result in chemical expansion of the LSCF lattice. Knowledge of both thermal and chemical lattice expansion as a function of composition is an essential tool to tailor mismatches between different materials exposed to reducing and high temperature environments and avoid mechanical failure of the device. In this paper, thermal and chemical expansion coefficients were determined by measurement of the lattice parameters by HT-XRD as a function of pO(2) (in the range of 10(-4) to 1 bar), temperature (773-1173 K) and B-site composition. The lattice parameters were correlated with the previously investigated oxygen nonstoichiometry of the LSCF series. While the thermal expansion coefficient increases almost linearly with increasing Co content, the chemical expansion coefficient appears to be independent of B-site composition. (C) 2013 Elsevier B.V. All rights reserved.