Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory

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Journal Title
Journal ISSN
Volume Title
School of Science | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2009
Major/Subject
Mcode
Degree programme
Language
en
Pages
115421/1-11
Series
Physical Review B, Volume 80, Issue 11
Abstract
Using periodic density functional theory, we calculate the structure and migration energies of fluorine vacancies and interstitials in the bulk and at the stoichiometric bulk-truncated surface of three alkali-earth fluorides: CaF2, SrF2, and BaF2. We then study the adsorption of water and hydrogen, in both molecular and dissociated form, at the ideal surface, and at neutral and charged vacancies in the surface and subsurface layers. The results demonstrate that in nearly all cases molecular adsorption is strongly favored. For the most probable configurations on the surfaces, we also studied the migration paths and barriers, and found that water is highly mobile on the surface, even when adsorbed at defects. In general, CaF2 and SrF2 show similar behavior with respect to water, while adsorption energies and migration barriers for BaF2 are smaller. Finally, we discuss our results in the context of recent experimental Atomic Force Microscopy studies on CaF2 and compare to calculations on other insulating surfaces.
Description
Keywords
adsorption, atomic force microscopy, barium compounds, calcium compounds, density functional theory, strontium compounds, interstitials, vacancies (crystal)
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Citation
Foster, Adam S. & Trevethan, T. & Shluger, A. L.. 2009. Structure and diffusion of intrinsic defects, adsorbed hydrogen, and water molecules at the surface of alkali-earth fluorides calculated using density functional theory. Physical Review B. Volume 80, Issue 11. 115421/1-11. ISSN 1550-235X (electronic). DOI: 10.1103/physrevb.80.115421.