Density functional theory calculations of UO2 oxidation : Evolution of UO2+x, U4O9−y, U3O7, and U3O8.
Résumé
Formation of UO2+x derived from the fluorite structure was investigated by density functional theory (DFT) calculations. We identify stable line compounds at the U4O8.889, U3O7, and U3O7.333 compositions. Although the transition from fluorite to the layered U3O8 structure occurs at U3O7 or U3O7.333, the fluorite-derived compounds are favored up to UO2.5, that is, as long as the charge-compensation for adding oxygen atoms occurs via formation of U5+ ions, after which U3O8−y becomes more stable.