PNNL

Abstract

Using x-ray scattering, spectroscopy, and computational methods, we show that oxidation of the UO2 (111) surface results in a self-organized arrangement of oxygen interstitials with three-layer periodicity, producing a nanoscale oscillatory oxidation front with uranium in three oxidation states: IV, V, and VI. This complex diffusion profile is driven by the transfer of the lowest energy U5f electrons from multiple U atoms into the O2p band. Our results contrast with all previous bulk structural oxidation models and the simple exponential oxidation front expected from classical diffusion.