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Ghosh PS, Arya A. Evidence of vacancy ordered structures in PuO 2-x and AmO 2-x from first-principles calculations. Phys Chem Chem Phys 2023; 25:14117-14125. [PMID: 37161928 DOI: 10.1039/d3cp00971h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
A combination of first-principles calculations and cluster expansion method is used to study ordering of oxygen vacancies in PuO2-x and AmO2-x. Vacancy ordered stable/metastable structures of composition Pu8O15 (PuO1.875), Pu6O11 (PuO1.833), Pu8O14 (PuO1.75) and Am10O19 (AmO1.90), Am8O15 (AmO1.875), Am10O18 (AmO1.80), Am8O13 (AmO1.625) are identified in PuO2-x and AmO2-x, respectively, from cluster expansion calculations. A comparison of formation enthalpies of vacancy ordered and vacancy disordered structures shows that Am8O15 (AmO1.875) and Am8O13 (AmO1.625) are more stable by 52 and 55 meV per atom, respectively, compared to their disordered counterparts. Similarly, vacancy ordered Pu8O15 (PuO1.875) and Pu8O14 (PuO1.75) structures are more stable compared to the disordered structures by 10 and 8 meV per atom, respectively. In contrast, the disordered PuO1.625 structure is more stable compared to the cluster expansion generated structures. The vacancy ordered structures are mechanically stable and their bulk modulus, Young's modulus, shear modulus and Poisson's ratio are reported.
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Affiliation(s)
- P S Ghosh
- Glass and Advanced Materials Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094, India
| | - A Arya
- Glass and Advanced Materials Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094, India
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Cheng JX, Yang F, Wang QB, He YY, Liu YN, Hu ZY, Wen WW, Wu YP, Zheng CY, Yu A, Lu X, Zhang Y. First-Principles Study on Mechanical and Optical Behavior of Plutonium Oxide under Typical Structural Phases and Vacancy Defects. MATERIALS (BASEL, SWITZERLAND) 2022; 15:7785. [PMID: 36363381 PMCID: PMC9656257 DOI: 10.3390/ma15217785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 10/29/2022] [Accepted: 11/02/2022] [Indexed: 06/16/2023]
Abstract
The chemical corrosion aging of plutonium is a very important topic. It is easy to be corroded and produces oxidation products of various valence states because of its 5f electron orbit between local and non-local. On the one hand, the phase diagram of plutonium and oxygen is complex, so there is still not enough research on typical structural phases. On the other hand, most of the studies on plutonium oxide focus on PuO2 and Pu2O3 with stoichiometric ratio, while the understanding of non-stoichiometric ratio, especially for Pu2O3-x, is not deep enough. Based on this, using the DFT + U theoretical scheme of density functional theory, we have systematically studied the structural stability, lattice parameters, electronic structure, mechanical and optical properties of six typical high temperature phases of β-Pu2O3, α-Pu2O3,γ-Pu2O3, PuO, α-PuO2,γ-PuO2. Further, the mechanical properties and optical behavior of Pu2O3-x under different oxygen vacancy concentrations are analyzed and discussed in detail. The result shows that the elasticity modulus of single crystal in mechanical properties is directly related to the oxygen/plutonium ratio and crystal system. As the number of oxygen vacancies increases, the mechanical constants continue to increase. In terms of optical properties, PuO has the best optical properties, and the light absorption rate decreases with the increase of oxygen vacancy concentration.
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Affiliation(s)
- Jin-Xing Cheng
- Beijing Institute of High Technology, Beijing 100094, China
| | - Fei Yang
- College of Mathematics and Physics, Beijing University of Chemical Technology, Beijing 100029, China
| | - Qing-Bo Wang
- Beijing Institute of High Technology, Beijing 100094, China
| | - Yuan-Yuan He
- College of Mathematics and Physics, Beijing University of Chemical Technology, Beijing 100029, China
| | - Yi-Nuo Liu
- College of Mathematics and Physics, Beijing University of Chemical Technology, Beijing 100029, China
| | - Zi-Yu Hu
- College of Mathematics and Physics, Beijing University of Chemical Technology, Beijing 100029, China
| | - Wei-Wei Wen
- Beijing Institute of High Technology, Beijing 100094, China
| | - You-Peng Wu
- Beijing Institute of High Technology, Beijing 100094, China
| | | | - Ai Yu
- Beijing Institute of High Technology, Beijing 100094, China
| | - Xin Lu
- Beijing Institute of High Technology, Beijing 100094, China
| | - Yue Zhang
- Beijing Institute of High Technology, Beijing 100094, China
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Neilson W, Steele H, Murphy ST. Evolving Defect Chemistry of (Pu,Am)O 2±x. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:15560-15568. [PMID: 34476035 PMCID: PMC8392350 DOI: 10.1021/acs.jpcc.1c03274] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 06/25/2021] [Indexed: 06/01/2023]
Abstract
The β decay of 241Pu to 241Am results in a significant ingrowth of Am during the interim storage of PuO2. Consequently, the safe storage of the large stockpiles of separated Pu requires an understanding of how this ingrowth affects the chemistry of PuO2. This work combines density functional theory (DFT) defect energies and empirical potential calculations of vibrational entropies to create a point defect model to predict how the defect chemistry of PuO2 evolves due to the incorporation of Am. The model predicts that Am occupies Pu sites in (Pu,Am)O2±x in either the +III or +IV oxidation state. High temperatures, low oxygen-to-metal (O/M) ratios, or low Am concentrations favor Am in the +III oxidation state. Am (+III) exists in (Pu,Am)O2±x as the negatively charged (AmPu 1-) defect, requiring charge compensation from holes in the valence band, thereby increasing the conductivity of the material compared to Am-free PuO2. Oxygen vacancies take over as the charge compensation mechanism at low O/M ratios. In (Pu,Am)O2±x , hypo- and (negligible) hyperstoichiometry is found to be provided by the doubly charged oxygen vacancy (VO 2+) and singly charged oxygen interstitial (Oi 1-), respectively.
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Affiliation(s)
- William
D. Neilson
- Engineering
Department, Lancaster University, Bailrigg, Lancaster LA1
4YW, U.K.
| | - Helen Steele
- Sellafield
Ltd., Sellafield, Cumbria CA20 1PG, U.K.
| | - Samuel T. Murphy
- Engineering
Department, Lancaster University, Bailrigg, Lancaster LA1
4YW, U.K.
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Neilson WD, Pegg JT, Steele H, Murphy ST. The defect chemistry of non-stoichiometric PuO 2±x. Phys Chem Chem Phys 2021; 23:4544-4554. [PMID: 33599636 DOI: 10.1039/d0cp06497a] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An increased knowledge of the chemistry of PuO2 is imperative for the design of procedures to store, dispose, or make use of PuO2. In this work, point defect concentrations in PuO2 are determined by combining density functional theory (DFT) defect energies and empirical potential calculations of vibrational entropies. The obtained defect concentrations are expressed as a function of temperature and oxygen partial pressure and used to calculate non-stoichiometry in PuO2±x. The results show that the defect chemistry of PuO2 is dominated by oxygen vacancies and interstitials. Hypo-stoichiometric PuO2-x is accommodated by both the uncharged oxygen vacancy and positively charged oxygen vacancy at small values of x, with increasingly dominant with increasing x. The negatively charged oxygen interstitial (O2-i) is found to accommodate hyper-stoichiometry (PuO2+x), but reluctance to form hyper-stoichiometric PuO2+x is observed, with oxygen interstitials present only in very low concentrations irrespective of conditions. The small degree of hyper-stoichiometry found is favoured by low temperatures.
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Affiliation(s)
- William D Neilson
- Engineering Department, Lancaster University, Lancaster, LA1 4YW, UK.
| | - James T Pegg
- 1QB Information Technologies (1QBit), Vancouver, British Columbia V6E 4B1, Canada and Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Helen Steele
- Sellafield Ltd, Sellafield, Cumbria, CA20 1PG, UK
| | - Samuel T Murphy
- Engineering Department, Lancaster University, Lancaster, LA1 4YW, UK.
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Zhang L, Sun B, Zhang Q, Liu H, Liu K, Song H. First-Principles Study of the Hydrogen Resistance Mechanism of PuO 2. ACS OMEGA 2020; 5:7211-7218. [PMID: 32280861 PMCID: PMC7143429 DOI: 10.1021/acsomega.9b03790] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 03/12/2020] [Indexed: 06/11/2023]
Abstract
The in-depth investigation of hydrogen behaviors in Pu-oxide overlayers (mainly PuO2 and α-Pu2O3) is critical for modeling the complex induction period of Pu hydriding. Within density functional theory (DFT) + U + D3 schemes, our systematic first-principles calculations and ab initio thermodynamic evaluations reveal that the hydrogen incorporation, dissolution behaviors, and diffusion mechanism in PuO2 are quite different from those in α-Pu2O3, among which the highly endothermic incorporation and dissolution of hydrogen are the primary hydrogen resistance mechanism of PuO2. Since its difficult recombination, atomic H is the preferred existence state in PuO2, but H will recombine spontaneously in α-Pu2O3. In PuO2, H diffusion is always clinging to O anions, whereas in α-Pu2O3, H2 prefers to migrate along O vacancies with higher barriers. H dissolution in intact PuO2 is very difficult, which can only be driven by extremely high pressure PH2 and temperature. Based on a series of theoretical studies, we conclude that the main interactions between hydrogen and Pu-oxide overlayers are not involved with chemical reactions, and intact PuO2 can effectively inhibit hydrogen permeation.
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Affiliation(s)
- Le Zhang
- Institute
of Applied Physics and Computational Mathematics, No. 2 of Fenghao East Road, Beijing 100094, People’s Republic of China
| | - Bo Sun
- Institute
of Applied Physics and Computational Mathematics, No. 2 of Fenghao East Road, Beijing 100094, People’s Republic of China
| | - Qili Zhang
- Institute
of Applied Physics and Computational Mathematics, No. 2 of Fenghao East Road, Beijing 100094, People’s Republic of China
| | - Haifeng Liu
- Institute
of Applied Physics and Computational Mathematics, No. 2 of Fenghao East Road, Beijing 100094, People’s Republic of China
| | - Kezhao Liu
- Science
and Technology on Surface Physics and Chemistry Laboratory, Mianyang 621908, People’s Republic of China
| | - Haifeng Song
- Institute
of Applied Physics and Computational Mathematics, No. 2 of Fenghao East Road, Beijing 100094, People’s Republic of China
- CAEP
Software Center for High Performance Numerical Simulation, No. 6 of Huayuan Road, Beijing 100088, People’s Republic of China
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Ghosh PS, Arya A. Structural, thermodynamic, electronic and elastic properties of Th 1-xU xO 2 and Th 1-xPu xO 2 mixed oxides. Phys Chem Chem Phys 2020; 22:6406-6417. [PMID: 32149299 DOI: 10.1039/d0cp00220h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The structural, thermodynamic, electronic, and elastic properties of Th1-xUxO2 and Th1-xPuxO2 mixed oxides (MOX) have been calculated with Hubbard corrected density functional theory (DFT+U) to account for the strong 5f electron correlations. The ideal solid solution is approximated by special quasi-random structures and the U-ramping method is used to account for the presence of metastable states in the self-consistent field solution of the DFT+U approach. The mixing enthalpy (ΔHmix) is positive throughout the composition range of the Th1-xUxO2 MOX, consistent with a simple miscibility gap (at low temperature) phase diagram. The behavior of the Th1-xPuxO2 MOX is more complex, where ΔHmix is positive in the ThO2-rich region and negative in the PuO2-rich region. Electronic structure analysis shows that substitution of Th by U/Pu in ThO2 leads to a reduction of the average Th-O bond lengths, causing distortion in the crystal structure. The distortion in the crystal structure results in an increase in the conduction bandwidth and a reduction of the band-gap in the MOX. Good agreement of our DFT+U calculated elastic properties of ThO2, UO2 and PuO2 compounds with experiments leads to convincing prediction of these properties for Th1-xUxO2 and Th1-xPuxO2 MOX.
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Affiliation(s)
- P S Ghosh
- Glass & Advanced Materials Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
| | - A Arya
- Glass & Advanced Materials Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India.
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