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Lopez-Bezanilla A, Selim FA, Oskar Liedke M, Uberuaga BP. The role of defect charge, crystal chemistry, and crystal structure on positron lifetimes of vacancies in oxides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:445701. [PMID: 39047766 DOI: 10.1088/1361-648x/ad673b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Accepted: 07/24/2024] [Indexed: 07/27/2024]
Abstract
Density functional theory based positron lifetime (PL) calculations for cation and oxygen monovacancies in a range of oxides-hematite, magnetite, hercynite, and alumina-have been conducted to compare the impact of defect chemistry and crystal structure on the predicted lifetimes. The role of defect charge state has also been examined. A comparison across the same type of crystalline structure but different composition shows that oxygen vacancies only induce a slight increase in the positron-electron overlap and thus barely modify the PL as compared to the bulk. A much more substantial increase of PL is observed for cation monovacancies, regardless of crystal structure or the elemental nature of the vacancy, which we ascribe to an enhanced localization of charge density around the vacant site. The structural and compositional richness of the oxide leads to longer defect PLs, with defected hercynite exhibiting the longest PLs. The charge state of cation monovacancies modifies only by a small percentage the positron localization, relegating to secondary importance the metal defect's oxidation state in modifying the lifetime of positrons within vacancy traps.
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Affiliation(s)
- Alejandro Lopez-Bezanilla
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, United States of America
| | - Farida A Selim
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287, United States of America
| | - Maciej Oskar Liedke
- Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany
| | - Blas P Uberuaga
- Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, United States of America
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Morris IM, Klink K, Singh JT, Mendoza-Cortes JL, Nicley SS, Becker JN. Rare isotope-containing diamond colour centres for fundamental symmetry tests. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2024; 382:20230169. [PMID: 38043574 PMCID: PMC10693981 DOI: 10.1098/rsta.2023.0169] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2023] [Accepted: 06/30/2023] [Indexed: 12/05/2023]
Abstract
Detecting a non-zero electric dipole moment in a particle would unambiguously signify physics beyond the Standard Model. A potential pathway towards this is the detection of a nuclear Schiff moment, the magnitude of which is enhanced by the presence of nuclear octupole deformation. However, due to the low production rate of isotopes featuring such 'pear-shaped' nuclei, capturing, detecting and manipulating them efficiently is a crucial prerequisite. Incorporating them into synthetic diamond optical crystals can produce defects with defined, molecule-like structures and isolated electronic states within the diamond band gap, increasing capture efficiency, enabling repeated probing of even a single atom and producing narrow optical linewidths. In this study, we used density functional theory to investigate the formation, structure and electronic properties of crystal defects in diamond containing [Formula: see text], a rare isotope that is predicted to have an exceptionally strong nuclear octupole deformation. In addition, we identified and studied stable lanthanide-containing defects with similar electronic structures as non-radioactive proxies to aid in experimental methods. Our findings hold promise for the existence of such defects and can contribute to the development of a quantum information processing-inspired toolbox of techniques for studying rare isotopes. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.
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Affiliation(s)
- Ian M. Morris
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
| | - Kai Klink
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
| | - Jaideep T. Singh
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
| | - Jose L. Mendoza-Cortes
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI, USA
| | - Shannon S. Nicley
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI, USA
- Department of Electrical and Computer Engineering, Michigan State University, East Lansing, MI, USA
- Coatings and Diamond Technologies Division, Center Midwest (CMW), Fraunhofer USA Inc., 1449 Engineering Research Court,East Lansing, MI 48824, USA
| | - Jonas N. Becker
- Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
- Coatings and Diamond Technologies Division, Center Midwest (CMW), Fraunhofer USA Inc., 1449 Engineering Research Court,East Lansing, MI 48824, USA
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Goswami K, Murphy ST. Influence of Lithium Vacancy Defects on Tritium Diffusion in β-Li 2TiO 3. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2020; 124:12286-12294. [PMID: 33133328 PMCID: PMC7590524 DOI: 10.1021/acs.jpcc.0c02551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 05/10/2020] [Indexed: 06/11/2023]
Abstract
Lithium metatitanate, Li2TiO3, is a leading candidate for application as a tritium breeding material in a future fusion reactor. Following transmutation of lithium, the tritium must escape the crystal in order to be extracted for use in the fusion plasma. The rate-limiting step to release tritium from the Li2TiO3 pebbles is diffusion through the crystal grains. In this work, the activation barriers for tritium diffusion have been calculated using density functional theory. The results show that tritium can diffuse as an interstitial with a barrier of 0.52 eV. However, when a tritium ion becomes bound to a lithium vacancy defect, the energy required to either detrap the tritium from the vacancy or for the cluster to diffuse increases to >1 eV. Overall, these results suggest that the introduction of lithium vacancies due to Li burn-up may lead to an increase in tritium retention in the pebbles.
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