The accommodation of oxygen clusters in hyperstoicheiometric uranium dioxide and its effects on crystal structure

Abstract

Hyperstoicheiometric UO₂ is described in terms of chains of oxygen defect clusters parallel to the 〈110〉 direction within the parent fluorite lattice. The propagation of such cluster chains in more than one 〈110〉 direction is considered and the crystallographic properties of 4 : 3 : 2 clusters used to allow 2 : 2 : 2 cluster chains to cross. The compositional range over which interstitial clusters may be accommodated is assessed and the large tolerance of non-stoicheiometry in the fluorite lattice used to rationalise the overall structures in the uranium–oxygen system from UO₂ to UO₃.