Chemical expansion and oxygen non-stoichiometry of undoped and Gd-doped cerium oxide exposed to different partial pressures of oxygen was studied at 800 degrees C by dilatometry and thermo-gravimetry, respectively. The results were modeled in terms of isolated defects and defect complexes to successfully predict non-stoichiometry and chemical expansion behavior. A chemical expansion coefficient for isolated defects was determined using the model. A separate chemical expansion coefficient for defect complexes was found to match an empirically predicted value for lattice parameter versus dopant concentration from the literature showing that at room temperature, a considerable fraction of defects are in complexes. The chemical expansion coefficients used were the same for both the undoped and Gd-doped cerium oxide displaying consistency in the model. The results of the model are not only useful in interpreting strain behavior upon reduction in ceria based oxides, but are also useful in explaining conductivity behavior. (C) 2008 Elsevier Masson SAS. All rights reserved.