Thermodynamic and transport studies of mixed oxides. The CeO2–UO2 system

Abstract

The electrical properties of CeO₂–UO₂ solid solutions are examined as a function of temperature, oxygen partial pressure and Ce/U ratio. A defect model is presented for this system which illustrates the manner in which CeO₂- and UO₂-rich solid solutions can be induced to cross over the stoichiometric composition to oxygen excess and deficiency, respectively, by the addition of the minor component and thereby give access to defect regimes not normally accessible. The electrical conductivity data for U-doped CeO₂ solid solutions are shown to be in good agreement with predictions and thereby enable derivation of key parameters including those controlling generation of oxygen frenkel defects, doubly ionized oxygen vacancies and electrons by reduction and electron mobilities. Independent confirmation of the model is obtained from oxygen self-diffusion measurements. Measurements on Ce-doped UO₂ give qualitative agreement with the model predictions but disagree in detail owing to significant defect clustering.