Please use this identifier to cite or link to this item:
Title: Titanium substitution mechanisms in forsterite
Authors: Berry, AJ
Walker, AM
Hermann, J
O'Neill, HStC
Foran, GJ
Gale, JD
Keywords: Absorption
Fine structure
Issue Date: 30-Jul-2007
Publisher: Elsevier
Citation: Berry, A. J., Walker, A. M., Hermann, J., O'Neill, H. St. C., Foran, G. J., & Gale, J. D. (2007). Titanium substitution mechanisms in forsterite. Chemical Geology, 242(1-2), 176-186. doi:10.1016/j.chemgeo.2007.03.010
Abstract: 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 Å. This value is in excellent agreement with that of 1.8 Å 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 Å. 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, Elsevier Ltd.
Gov't Doc #: 1122
ISSN: 0009-2541
Appears in Collections:Journal Articles

Files in This Item:
There are no files associated with this item.

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.