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Theoretical analysis of X-ray absorption near-edge structure in forsterite, Mg2SiO4-Pbnm, and fayalite, Fe2SiO4-Pbnm, at room temperature and extreme conditions |
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| Authors: | Ziyu Wu Annibale Mottana Augusto Marcelli Calogero Rino Natoli Eleonora Paris |
| Institution: | 1. Institut des Matériaux de Nantes, CNRS UMR 110, 2 rue de la Houssinière, 44072, Nantes Cedex 03, France 2. Dipartimento di Scienze Geologiche, Terza Universita' di Roma, Via Ostiense 169, 00154, Roma, Italy 3. INFN — Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati, Italy 4. Dipartimento di Scienze della Terra, Universita' di Camerino, Via Gentile III da Varano, 62032, Camerino, MC, Italy |
| Abstract: | We calculated the forsterite Mg K-edge and the fayalite Fe K-edge X-ray absorption spectra both for the M 1 and M 2 sites and for the overall edge by using the one-electron multiple-scattering theory. The validity of the theoretical model is well illustrated by comparison of calculations with experimental data at the Mg K-edge of MgO (periclase) and at the Mg and Fe K-edges spectra of forsterite and fayalite. Starting from these results at room conditions, we calculated the Mg and Fe K-edges X-ray absorption spectra of forsterite and fayalite at low and high temperatures and at high pressures as well. Variations of fine structures occur mostly in the intermediate multiple scattering (IMS) regions and as a result of the applied pressure. In order to demonstrate the capability of XAS to lead to deeper knowledge of structure relevant to Earth's upper mantle we also attempted calcuating the high-P edge for Fe 2+ in low-spin using a different occupation of valence electrons. If a change in spin state really occurs in fayalite, our simple model shows that XAS would evidence it easily even with low resolution. |
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