The thermal and chemical expansion properties of BaCo0.7Fe0.22Nb0.08O3-delta, a potential candidate for oxygen permeable membranes and cathodes in solid oxide fuel cells, are reported here. The average thermal expansion coefficient is about 14 x 10(-6) K-1 below 500 degrees C, about 19 x 10(-6) K-1 between 600 and 900 degrees C, and about 29 x 10(-6) K-1 between 900 and 1000 degrees C, which consists of the previous weight change in a thermal gravimetric analysis experiment. The transient behavior in the thermochemical expansion can be best fitted with Fick's second law for a small displacement from the equilibrium. The chemical diffusivity of oxygen and the surface exchange kinetics are successfully extracted. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3515070] All rights reserved.