Titanium substitution mechanisms in forsterite

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dc.contributor.authorBerry, AJen_AU
dc.contributor.authorWalker, AMen_AU
dc.contributor.authorHermann, Jen_AU
dc.contributor.authorO'Neill, HSCen_AU
dc.contributor.authorForan, GJen_AU
dc.contributor.authorGale, JDen_AU
dc.date.accessioned2008-03-03T05:09:44Zen_AU
dc.date.accessioned2010-04-30T05:02:01Zen_AU
dc.date.available2008-03-03T05:09:44Zen_AU
dc.date.available2010-04-30T05:02:01Zen_AU
dc.date.issued2007-07-30en_AU
dc.date.statistics2007-07en_AU
dc.description.abstractTi 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.en_AU
dc.identifier.citationBerry, A. J., Walker, A. M., Hermann, J., O'Neill, H. S. 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.2007.03.010en_AU
dc.identifier.govdoc1122en_AU
dc.identifier.issn0009-2541en_AU
dc.identifier.issue1-2en_AU
dc.identifier.journaltitleChemical Geologyen_AU
dc.identifier.pagination176-186en_AU
dc.identifier.urihttp://dx.doi.org/10.1016/j.chemgeo.2007.03.010en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/1007en_AU
dc.identifier.volume242en_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectAbsorptionen_AU
dc.subjectEnergyen_AU
dc.subjectOlivineen_AU
dc.subjectWateren_AU
dc.subjectPeridotitesen_AU
dc.subjectFine structureen_AU
dc.titleTitanium substitution mechanisms in forsteriteen_AU
dc.typeJournal Articleen_AU
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