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Zhao X, Strzelecki AC, Dacheux N, Qi L, Guo X. Phonon softening induced phase transition of CeSiO 4: a density functional theory study. Dalton Trans 2024; 53:6224-6233. [PMID: 38488116 DOI: 10.1039/d4dt00179f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Density functional theory plus Hubbard U (DFT+U) methodology was used to calculate the structures and energetic landscapes of CeSiO4, including its stetindite and scheelite phases from ambient pressure to ∼24 GPa. To ensure accurate simulations of the high-pressure structures, assessments of strain-stress methods and stress-strain methods were conducted in prior, with the former found to have a better agreement with the experimental result. From DFT calculations the equation of states (EOS) of both stetindite and scheelite were further obtained, with the fitted bulk moduli being 182(2) GPa and 190.0(12) GPa, respectively. These results were found to be consistent with the experimental values of 177(5) GPa and 222(40) GPa. Furthermore, the calculated energetics suggest that the stetindite structure is more thermodynamically stable than the scheelite structure at a pressure lower than 8.35 GPa. However, the stetindite → scheelite phase transition was observed experimentally at a much higher pressure of ∼15 GPa. A further phonon spectra investigation by the density functional perturbation theory (DFPT) indicated the Eg1 mode is being softened with pressure and becomes imaginary after 12 GPa, which is a sign of the lattice instability. Consequently, it was concluded that the stetindite → scheelite transition is predominantly initiated by the lattice instability under high-pressure.
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Affiliation(s)
- Xiaodong Zhao
- Department of Chemistry, Washington State University, Pullman, Washington, 99164, USA.
| | - Andrew C Strzelecki
- School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, 99164, USA
- Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, USA
| | - Nicolas Dacheux
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Site de Marcoule, Bagnols sur Cèze, 30207, France
| | - Liang Qi
- Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, 48109, USA.
| | - Xiaofeng Guo
- Department of Chemistry, Washington State University, Pullman, Washington, 99164, USA.
- School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, 99164, USA
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Estevenon P, Dumas T, Solari PL, Welcomme E, Szenknect S, Mesbah A, Kvashnina KO, Moisy P, Poinssot C, Dacheux N. Formation of plutonium(IV) silicate species in very alkaline reactive media. Dalton Trans 2021; 50:12528-12536. [PMID: 34545888 DOI: 10.1039/d1dt02248b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Studying the speciation of Pu(IV) in very alkaline and silicate ion rich reactive media allowed identification of the formation of plutonium(IV)-silicate colloidal suspensions which were stable for months. These colloids were stabilized in aqueous solution for pH > 13 and for concentrations around 10-2 mol L-1. Successive filtration processes allowed evaluation of their size, which was found to be smaller than 6 nm. Their structural characterization by XAS evidenced that their structure was similar to those identified for the other tetravalent actinide-silicate colloidal systems like thorium, uranium and neptunium. Their formation could explain the increase of plutonium solubility usually observed in alkaline silicate-rich solutions and could affect the plutonium mobility as a result in contaminated sites or in other environmental permeable media.
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Affiliation(s)
- Paul Estevenon
- CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, France. .,ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Bagnols-sur-Cèze, France. .,The Rossendorf Beamline at the ESRF, CS40220, 38043 Grenoble Cedex 9, France.,Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, P.O. Box 510119, 01314, Dresden, Germany
| | - Thomas Dumas
- CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, France.
| | - Pier Lorenzo Solari
- Synchrotron Soleil, L'Orme des Merisiers, Saint-Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex, France
| | | | | | - Adel Mesbah
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Bagnols-sur-Cèze, France.
| | - Kristina O Kvashnina
- The Rossendorf Beamline at the ESRF, CS40220, 38043 Grenoble Cedex 9, France.,Helmholtz Zentrum Dresden-Rossendorf (HZDR), Institute of Resource Ecology, P.O. Box 510119, 01314, Dresden, Germany
| | - Philippe Moisy
- CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule, France.
| | | | - Nicolas Dacheux
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Bagnols-sur-Cèze, France.
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Strzelecki AC, Bourgeois C, Kriegsman KW, Estevenon P, Wei N, Szenknect S, Mesbah A, Wu D, Ewing RC, Dacheux N, Guo X. Thermodynamics of CeSiO 4: Implications for Actinide Orthosilicates. Inorg Chem 2020; 59:13174-13183. [PMID: 32871073 DOI: 10.1021/acs.inorgchem.0c01476] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Zircon (ZrSiO4, I41/amd) can accommodate actinides, such as thorium, uranium, and plutonium. The zircon structure has been determined for several of the end-member compositions of other actinides, such as plutonium and neptunium. However, the thermodynamic properties of these actinide zircon structure types are largely unknown due to the difficulties in synthesizing these materials and handling transuranium actinides. Thus, we have completed a thermodynamic study of cerium orthosilicate, stetindite (CeSiO4), a surrogate of PuSiO4. For the first time, the standard enthalpy of formation of CeSiO4 was obtained by high temperature oxide melt solution calorimetry to be -1971.9 ± 3.6 kJ/mol. Stetindite is energetically metastable with respect to CeO2 and SiO2 by 27.5 ± 3.1 kJ/mol. The metastability explains the rarity of the natural occurrence of stetindite and the difficulty of its synthesis. Applying the obtained enthalpy of formation of CeSiO4 from this work, along with those previously reported for USiO4 and ThSiO4, we developed an empirical energetic relation for actinide orthosilicates. The predicted enthalpies of formation of AnSiO4 are then determined with a discussion of future strategies for efficiently immobilizing Pu or minor actinides in the zircon structure.
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Affiliation(s)
- Andrew C Strzelecki
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.,Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, United States.,Materials Science and Engineering, Washington State University, Pullman, Washington 99164, United States
| | - Clement Bourgeois
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.,Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, United States
| | - Kyle W Kriegsman
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.,Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, United States
| | - Paul Estevenon
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Site de Marcoule, Bagnols sur Cèze 30207, France.,CEA, DES, ISEC, DMRC, Univ Montpellier, Site de Marcoule 30207, France
| | - Nian Wei
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.,College of Physical Science and Technology, Sichuan University, Chengdu 610065, People's Republic of China
| | - Stephanie Szenknect
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Site de Marcoule, Bagnols sur Cèze 30207, France
| | - Adel Mesbah
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Site de Marcoule, Bagnols sur Cèze 30207, France
| | - Di Wu
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.,Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, United States.,Materials Science and Engineering, Washington State University, Pullman, Washington 99164, United States.,The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington 99164, United States
| | - Rodney C Ewing
- Department of Geological Sciences, Stanford University, Stanford, California 94305, United States
| | - Nicolas Dacheux
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Site de Marcoule, Bagnols sur Cèze 30207, France
| | - Xiaofeng Guo
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States.,Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman, Washington 99164, United States.,Materials Science and Engineering, Washington State University, Pullman, Washington 99164, United States
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Abstract
Most of the highly radioactive spent nuclear fuel (SNF) around the world is destined for final disposal in deep-mined geological repositories. At the end of the fuel's useful life in a reactor, about 96% of the SNF is still UO2. Thus, the behaviour of UO2 in SNF must be understood and evaluated under the weathering conditions of geologic disposal, which extend to periods of hundreds of thousands of years. There is ample evidence from nature that many uranium deposits have experienced conditions for which the formation of coffinite, USiO4, has been favoured over uraninite, UO2+x, during subsequent alteration events. Thus, coffinite is an important alteration product of the UO2 in SNF. Here, we present the first evidence of the formation of coffinite on the surface of UO2 at the time scale of laboratory experiments in a solution saturated with respect to amorphous silica at pH = 9, room temperature and under anoxic conditions.
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