UO2 Oxidative Corrosion by Nonclassical Diffusion

Using x-ray scattering, spectroscopy, and density-functional theory, we determine the structure of the oxidation front when a UO2 (111) surface is exposed to oxygen at ambient conditions. In contrast to classical diffusion and previously reported bulk UO2+x structures, we find oxygen interstitials order into a nanoscale superlattice with three-layer periodicity and uranium in three oxidation states: IV, V, and VI. This oscillatory diffusion profile is driven by the nature of the electron transfer process, and has implications for understanding the initial stages of oxidative corrosion in materials at the atomistic level.