Ab initio investigation on oxygen defect clusters in UO2+x

TL;DR

This study uses first-principles calculations to analyze oxygen defect clusters in UO2+x, challenging previous models and providing a quantum-theoretical understanding that aligns with experimental data.

Contribution

It introduces a thermodynamical model based on quantum theory to explain defect structures in UO2+x, improving upon previous neutron diffraction interpretations.

Findings

Reveals the inadequacy of current physical models for defects in UO2+x

Establishes a thermodynamical competition model for point defects and clusters

Aligns well with most experimental data, except for high O'' site occupation

Abstract

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.