Impact of Surface Oxidation on the Morphology of Uranium Dioxide Nanoparticles

The undeniable importance of nanoparticles has led to vast efforts, in many fields of science, to understand their chemical and physical properties. In this paper, the morphology dependence of f-element nanoparticles is correlated to the oxygen environment and the type and coverage of capping ligands. This dependence was evaluated by first-principles calculations of the surface energies of different crystallographic planes (001, 110, and 111) as a function of the relative oxygen chemical potential and under the influence of different ligands. Uranium dioxide nanoparticles were the focus of this study due to their high sensitivity to oxidation compared to thorium dioxide nanoparticles, a homoleptic material but insensitive to oxidation. To fully explain the experimental observations of uranium dioxide nanocrystals, theoretical modeling shows that the consideration of surfaces with different oxidation conditions is necessary. It is shown that, for materials with low oxidation potential, such as uranium dioxide, the oxygen environment and capping ligand concentration are competing factors in determining the nanoparticle morphology.