Titanium substitution mechanisms in forsterite
Ti K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra, together with atomic scale calculations, indicate that Ti occupies the Si site in anhydrous forsterite. The energy and intensity of the 1s .3d transition in the XANES spectrum is diag...
| Main Authors: | , , , , , |
|---|---|
| Format: | Journal Article |
| Published: |
Elsevier Science BV
2007
|
| Subjects: | |
| Online Access: | http://hdl.handle.net/20.500.11937/33653 |
| _version_ | 1848754007030366208 |
|---|---|
| author | Berry, A. Walker, A. Herman, J. O'Neil, H. Foran, G. Gale, Julian |
| author_facet | Berry, A. Walker, A. Herman, J. O'Neil, H. Foran, G. Gale, Julian |
| author_sort | Berry, A. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Ti K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra, together with atomic scale calculations, indicate that Ti occupies the Si site in anhydrous forsterite. The energy and intensity of the 1s .3d transition in the XANES spectrum is diagnostic of Ti on a four-coordinate site. The EXAFS spectra determine a Ti-O bond length of 1.81 0.01 This value is in excellent agreement with that of 1.8 A determined computationally by periodic density functional theory and an embedded cluster approach for Ti on the Si site; the calculated bond length for Ti on a Mg site is 2.0 Both computational methods further find that the direct substitution of Ti for Si is energetically favoured relative to substitution of Ti for Mg, charge balanced by either a Mg vacancy or Mg on a Si site. Together the results provide unambiguous evidence for Ti occupying the Si site in anhydrous forsterite. Ti-bearing olivine synthesised at upper mantle conditions in the presence of water, however, exhibits a pre-edge feature corresponding to six-fold coordination. This is consistent with the identification of a Ti-clinohumite-like point defect in samples of olivine from upper-mantle spinel peridotite. The change in Ti site thus provides a mechanism for the incorporation of water in olivine. The total Ti content of olivine will comprise varying contributions from Mg2 [4]TiO4 and Ti-clinohumite-like Mg[6]TiO2(OH)2 substitutions. |
| first_indexed | 2025-11-14T08:33:33Z |
| format | Journal Article |
| id | curtin-20.500.11937-33653 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T08:33:33Z |
| publishDate | 2007 |
| publisher | Elsevier Science BV |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-336532018-03-29T09:08:14Z Titanium substitution mechanisms in forsterite Berry, A. Walker, A. Herman, J. O'Neil, H. Foran, G. Gale, Julian hydrous defects Nominally anhydrous minerals Density functional theory XANES EXAFS Forsterite Ti K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra, together with atomic scale calculations, indicate that Ti occupies the Si site in anhydrous forsterite. The energy and intensity of the 1s .3d transition in the XANES spectrum is diagnostic of Ti on a four-coordinate site. The EXAFS spectra determine a Ti-O bond length of 1.81 0.01 This value is in excellent agreement with that of 1.8 A determined computationally by periodic density functional theory and an embedded cluster approach for Ti on the Si site; the calculated bond length for Ti on a Mg site is 2.0 Both computational methods further find that the direct substitution of Ti for Si is energetically favoured relative to substitution of Ti for Mg, charge balanced by either a Mg vacancy or Mg on a Si site. Together the results provide unambiguous evidence for Ti occupying the Si site in anhydrous forsterite. Ti-bearing olivine synthesised at upper mantle conditions in the presence of water, however, exhibits a pre-edge feature corresponding to six-fold coordination. This is consistent with the identification of a Ti-clinohumite-like point defect in samples of olivine from upper-mantle spinel peridotite. The change in Ti site thus provides a mechanism for the incorporation of water in olivine. The total Ti content of olivine will comprise varying contributions from Mg2 [4]TiO4 and Ti-clinohumite-like Mg[6]TiO2(OH)2 substitutions. 2007 Journal Article http://hdl.handle.net/20.500.11937/33653 10.1016/j.chemgeo.2007.03.010 Elsevier Science BV restricted |
| spellingShingle | hydrous defects Nominally anhydrous minerals Density functional theory XANES EXAFS Forsterite Berry, A. Walker, A. Herman, J. O'Neil, H. Foran, G. Gale, Julian Titanium substitution mechanisms in forsterite |
| title | Titanium substitution mechanisms in forsterite |
| title_full | Titanium substitution mechanisms in forsterite |
| title_fullStr | Titanium substitution mechanisms in forsterite |
| title_full_unstemmed | Titanium substitution mechanisms in forsterite |
| title_short | Titanium substitution mechanisms in forsterite |
| title_sort | titanium substitution mechanisms in forsterite |
| topic | hydrous defects Nominally anhydrous minerals Density functional theory XANES EXAFS Forsterite |
| url | http://hdl.handle.net/20.500.11937/33653 |