Linear ordering of oxygen clusters in hyperstoicheiometric uranium dioxide

Abstract

The formation of hyperstoicheiometric oxides of UO₂ by the incorporation of additional oxygen atoms in the parent fluorite structure is described in terms of 2 : 2 : 2 oxygen clusters. A 2 : 2 : 2 cluster between two uranium atoms is treated as a co-ordination defect and consideration of electrostatic and polarisation effects together with X-ray photoelectron spectral data suggests that defect ordering is likely along 〈110〉 directions. The effect of chain-like linear ordering of oxygen clusters on structures in the oxide system UO₂–U₃O₈ is assessed and a crystal structure for U₄O₉ is postulated.