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First-principles study on oxidation effects in uranium oxides and high-pressure high-temperature behavior of point defects in uranium dioxide
- Source :
- Physical Review B. 84
- Publication Year :
- 2011
- Publisher :
- American Physical Society (APS), 2011.
-
Abstract
- Formation Gibbs free energy of point defects and oxygen clusters in uranium dioxide at high-pressure high-temperature conditions are calculated from first principles, using the LSDA+U approach for the electronic structure and the Debye model for the lattice vibrations. The phonon contribution on Frenkel pairs is found to be notable, whereas it is negligible for the Schottky defect. Hydrostatic compression changes the formation energies drastically, making defect concentrations depend more sensitively on pressure. Calculations show that, if no oxygen clusters are considered, uranium vacancy becomes predominant in overstoichiometric UO2 with the aid of the contribution from lattice vibrations, while compression favors oxygen defects and suppresses uranium vacancy greatly. At ambient pressure, however, the experimental observation of predominant oxygen defects in this regime can be reproduced only in a form of cuboctahedral clusters, underlining the importance of defect clustering in UO2+x. Making use of the point defect model, an equation of state for non-stoichiometric oxides is established, which is then applied to describe the shock Hugoniot of UO2+x. Furthermore, the oxidization and compression behavior of uranium monoxide, triuranium octoxide, uranium trioxide, and a series of defective UO2 at zero Kelvin are investigated. The evolution of mechanical properties and electronic structures with an increase of the oxidation degree are analyzed, revealing the transition of the groundstate of uranium oxides from metallic to Mott insulator and then to charge-transfer insulator due to the interplay of strongly correlated effects of 5f orbitals and the shift of electrons from uranium to oxygen atoms.<br />16 pages, 10 figures
- Subjects :
- Condensed Matter - Materials Science
Materials science
Strongly Correlated Electrons (cond-mat.str-el)
Condensed matter physics
Schottky defect
Uranium dioxide
Materials Science (cond-mat.mtrl-sci)
FOS: Physical sciences
chemistry.chemical_element
Computational Physics (physics.comp-ph)
Uranium
Condensed Matter Physics
Crystallographic defect
Electronic, Optical and Magnetic Materials
Condensed Matter - Strongly Correlated Electrons
symbols.namesake
chemistry.chemical_compound
chemistry
Uranium trioxide
Vacancy defect
symbols
Triuranium octoxide
Physics::Chemical Physics
Physics - Computational Physics
Debye model
Subjects
Details
- ISSN :
- 1550235X and 10980121
- Volume :
- 84
- Database :
- OpenAIRE
- Journal :
- Physical Review B
- Accession number :
- edsair.doi.dedup.....5ccff60b2bdc89d4e7d7242c77b7688b