Deeper understanding of thermal and chemical volume change in non-stoichiometric CeO2 - delta a is very important for the development of reactive ceria ceramics applied for thermochemical cycles. Dilatometric studies at 1538 K-1690 l< under reduced and air atmosphere were performed using polycrystalline ceria rods, which were produced from powder synthesized via Pechini-method. Based on chemical expansion and weight loss during reduction, the oxygen-deficiency parameter delta ranging between 0.02 and 0.09 was calculated. Above 1650 K, however, delta cannot be calculated from weight loss data due to initiating ceria evaporation. Log delta- vs. log p(o2) curves reveal a discontinuous development, which is interpreted in terms of defect complex formation. Cooling down CeO2 - delta from high temperatures under vacuum conditions results in unmixing and phase transformations according to the phase diagram going along with faint discontinuities in dilatometric curves. Rechiced ceria ceramics (delta = 0.02-0.09) consist of alpha-CeO1.985, coexisting with structurally related CeO1.778 and CeO1.714. while the expected beta-phase (CeO1.818) was not observed. The combination of dilatometric studies, XRD and thermal analyses on CeO2 - delta reoxidation shows a multi-step mechanism. CeO1.778 and CeO1.714 re-oxidize at temperatures of 373 K while the transformation from CeO1.985 to CeO2 requires temperatures >900 K. (C) 2017 Elsevier B.V. All rights reserved.