By first-principles LSDA+U calculations, we revealed that the current physical picture of defective uranium dioxide suggested solely by neutron diffraction analysis is unsatisfactory. An understanding based on quantum theory has been established as a thermodynamical competition among point defects and cuboctahedral cluster, which naturally interprets the puzzled origin of the asymmetric O' and O'' interstitials. It also gives a clear and consistent agreement with most available experimental data. Unfortunately, the observed high occupation of O'' site cannot be accounted for in this picture and is still a challenge for theoretical simulations.
@article{arxiv.0806.1793,
title = {Ab initio investigation on oxygen defect clusters in UO2+x},
author = {Hua Y. Geng and Ying Chen and Yasunori Kaneta and Motoyasu Kinoshita},
journal= {arXiv preprint arXiv:0806.1793},
year = {2009}
}