Raman spectroscopic study of hydrous γ-Mg2SiO4 to 56.5 GPa

A. K. Kleppe, A. P. Jephcoat, J. R. Smyth

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    27 Citations (Scopus)

    Abstract

    Raman spectra of a single-crystal fragment of hydrous γ-Mg2SiO4, synthesized in a multianvil press, have been measured in a diamond-anvil cell with helium as pressure-transmitting medium to 56.5 GPa at room temperature. All five characteristic spinel Raman modes shift continuously up to the highest pressure, showing no evidence for a major change in the crystal structure despite compression well beyond the stability field of ringwoodite in terms of pressure. At pressures above ~30 GPa a new mode on the low-frequency site of the two silicate-stretching modes is clearly identifiable, indicating a modification in the spinel structure which is reversible on pressure release. The frequency of the new mode (802 cm-1 extrapolated to 1 bar) suggests the presence of Si-O-Si linkages and/or a partial increase in the coordination of Si. Direct determination of the subtle structural change causing the new Raman mode would require high-pressure, single-crystal synchrotron X-ray diffraction experiments. The Raman modes of hydrous and anhydrous Mg-end-member ringwoodite are nearly identical up to 20 GPa, suggesting that protonation has only minor effect on the lattice dynamics over the entire pressure stability range for ringwoodite in the mantle.

    Original languageEnglish
    Pages (from-to)473-476
    Number of pages4
    JournalPhysics and Chemistry of Minerals
    Volume29
    Issue number7
    DOIs
    Publication statusPublished - Aug 1 2002

    Keywords

    • Diamond-anvil cell
    • High-pressure
    • Hydrous minerals
    • Raman spectroscopy
    • Ringwoodite

    ASJC Scopus subject areas

    • Materials Science(all)
    • Geochemistry and Petrology

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