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Interactions between bare and protonated Mg vacancies and dislocation cores in MgO

  • Richard SkeltonEmail author
  • Andrew M. Walker
Original Paper
  • 42 Downloads

Abstract

Water can be incorporated into the lattice of mantle minerals in the form of protons charge-balanced by the creation of cation vacancies. These protonated vacancies, when they interact with dislocations, influence strain rates by affecting dislocation climb, pinning the dislocation, and, potentially, by altering the Peierls barrier to glide. We use atomic scale simulations to investigate segregation of Mg vacancies to atomic sites within the core regions of dislocations in MgO. Energies are computed for bare and \(V_{{{\text{Mg}}}}^{\prime \prime }\) protonated Mg vacancies occupying atomic sites close to ½ 〈110〉 screw dislocations, and ½ 〈110〉 {100} and ½ 〈110〉 {110} edge dislocations. These are compared with energies for equivalent defects in the bulk lattice to determine segregation energies for each defect. Mg vacancies preferentially bind to ½ 〈110〉 {100} edge dislocations, with calculated minimum segregation energies of − 3.54 eV for and − 4.56 eV for \({\text{2H}}_{{{\text{Mg}}}}^{{\text{x}}}\). The magnitudes of the minimum segregation energies calculated for defects binding to ½ 〈110〉 {110} edge or ½ 〈110〉 screw dislocations are considerably lower. Interactions with the dislocation strain field lift the threefold energy degeneracy of the \({\text{2H}}_{{{\text{Mg}}}}^{{\text{x}}}\) defect in MgO. These calculations show that Mg vacancies interact strongly with dislocations in MgO, and may be present in sufficiently high concentrations to affect dislocation mobility in both the glide- and climb-controlled creep regimes.

Keywords

MgO Dislocation Cation vacancy Atomic-scale modeling 

Notes

Acknowledgements

AMW is grateful for support from the UK Natural Environment Research Council (NE/K008803/1 and NE/M000044/1). RS is supported by an Australian Government Research Training Program (RTP) Scholarship. Calculations were performed on the Terrawulf cluster, a computational facility supported through the AuScope initiative. AuScope Ltd is funded under the National Collaborative Research Infrastructure Strategy (NCRIS), an Australian Commonwealth Government Programme. Ian Jackson is thanked for helpful comments made during the preparation of the manuscript. The authors would like to thank Taku Tsuchiya for his editorial handling, and Sebastian Ritterbex and an anonymous reviewer for constructive comments which improved the quality of the manuscript.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Research School of Earth SciencesAustralian National UniversityCanberraAustralia
  2. 2.School of Earth and EnvironmentUniversity of LeedsLeedsUK

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