Mystery of Uranium Oxidation Configuration in Hexagonal U3O8

Uranium oxides are important materials in the nuclear fuel cycle. Triuranium octoxide (U3O8) is the most stable of these compounds, and it happens to display a peculiar effect: the uranium atoms are separated into two sites: two U(V) and one U(VI) oxidation state. But at elevated temperature the crystal structure has only one U site. How are 16 electrons distributed across the three identical uranium sites? The mystery may involve the subtle rearrangement of oxygen atoms, the influence of lattice vibrations, and a fast "electron-hopping" mechanism. Using high-resolution neutron diffraction, we hope to track subtle movements of oxygen atoms in U3O8, which we hope will provide some guidance about the interplay of these effects.