Oxidation of crystalline UO2 studied using X-ray photoelectron spectroscopy and X-ray diffraction

Abstract

The oxidation of the (111) surface of crystalline UO₂via U₃O₇ to U₃O₈ has been studied by X-ray photoelectron spectroscopy and X-ray diffraction. Oxidation was carried out at 463 and 573 K in 1 Torr† of oxygen. The formation of UO_2+x and U₄O₉ was not observed under these conditions. Anisotropic growth of U₃O₈ revealed an epitaxial relationship between the cubic close-packed (111) plane of fluorite UO₂ and the (001) basal plane of orthorhombic U₃O₈. It is proposed that the clustering of oxygen interstitial atoms in the fluorite lattice is instrumental in its ultimate breakdown and may be identified within the network of oxygen atoms present in U₃O₈.