Point defects and clustering in uranium dioxide by LSDA+U calculations

Abstract

A comprehensive investigation on point defects and their clustering behavior in nonstoichiometric uranium dioxide UO2+x is carried out using LSDA+U method based on density functional theory. Accurate energetic information and charge transfers available so far are obtained. With these energies that have improved more than 50% over that of pure GGA and LDA, we show the density functional theory predicts the predominance of oxygen defects over uranium ones at any compositions, which is possible only after treated the localized 5f electrons properly. Calculations also suggest an upper bound of x~0.03 for oxygen clusters to start off. The volume change induced by point uranium defects is monotonic but nonlinear, whereas for oxygen defects, increase x always reduces the system volume linearly, except dimers that require extra space for accommodation, which has been identified as meta-stable ionic molecule. Though oxygen dimers usually occupy Willis O'' sites and mimic a single oxygen in energetics and charge state, they are rare at ambient conditions. Its decomposition process and vibrational properties have been studied carefully. To obtain a general clustering mechanism in anion-excess fluorites systematically, we also analyze the local stabilities of possible basic clustering modes of oxygen defects. The result shows an unified way to understand the structure of Willis type and cuboctahedral clusters in UO2+x and beta-U4O9. Finally we generalize the point defect model to the independent clusters approximation to include clustering effects, the impact on defect populations is discussed.

20 pages, 12 figures

References in corpus (5)

• The physics of dynamical atomic charges: the case of ABO3 compounds
• Structural behavior of uranium dioxide under pressure by LSDA+U calculations
• First-principles equation of state and phase stability for the Ni-Al system under high pressures
• Hybrid expansions for local structural relaxations
• Order-disorder Effects on Equation of State in FCC Ni-Al Alloys

Cited by in corpus (16)

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• Ab initio investigation on oxygen defect clusters in UO2+x
• Importance of elastic finite-size effects: neutral defects in ionic compounds
• First-principles study on oxidation effects in uranium oxides and high-pressure high-temperature behavior of point defects in uranium dioxide
• Interatomic potentials for mixed oxide (MOX) nuclear fuels
• Chemisorption of a molecular oxygen on the UN (001) surface: ab initio calculations
• Ab Initio Construction of Interatomic Potentials for Uranium Dioxide Across all Interatomic Distances
• Prediction of novel ordered phases in U-X (X= Zr, Sc, Ti, V, Cr, Y, Nb, Mo, Hf, Ta, W) binary alloys under high pressure
• Anomalies in non-stoichiometric uranium dioxide induced by pseudo-phase transition of point defects
• He-Mg compounds and helium-driven nonmetal transition in metallic magnesium
• General linear correction method for DFT+X energy: application to U-M (M=Al, Ga, In) alloys under high pressure
• Theoretical assessment on the possibility of constraining point defect energetics by pseudo-phase transition pressures
• Theoretical Study on the Structural and Thermodynamic Properties of U-He compounds under High Pressure