Defect Structure and Transport in Oxygen excess Cerium Oxide-Uranium Oxide Solid Solutions

Abstract

Given the ease with which the binary oxides CeO₂ and UO₂ deviate from stoichiometry, these systems represent the paradigms for non- stoichiometry in the fluorite-related oxides with CeO₂ deviating in the direction of oxygen deficiency and UO₂ in the direction of oxygen excess. Nevertheless, important information concerning intrinsic ionic disorder in both systems and the defect structure of oxygen excess CeO₂ or oxygen deficient UO₂ is sorely lacking. In this study we report results of electrical measurements and defect modeling on cerium oxide-uranium oxide solid solutions which traverse the composition range from oxygen excess to oxygen deficiency for a series of isotherms ranging from ∿450–1200°C. The following features will be emphasized. Cerium dioxide may be induced to become oxygen excess under accessible experimental conditions by the addition of as little as 0.1% uranium. The Frenkel product is obtained for this system for the first time experimentally. Values for the electron mobility are obtained in a relatively straightforward manner. Subsequent articles by the authors will deal with (a) results obtained for a much broader range of compositions (including nearly pure UO₂), (b) implications of defect ordering on this type of analysis and (c) analysis of electronic carrier transport based on combined electrical conductivity and thermoelectric power measurements.