Phase transition and equation of state of dense hydrous silica up to 63 GPa

C. Nisr, Kurt Leinenweber, V. Prakapenka, C. Prescher, S. Tkachev, Sang-Heon Shim

    Research output: Contribution to journalArticle

    2 Citations (Scopus)

    Abstract

    Although it has previously been considered to be essentially anhydrous, Al-free stishovite can contain up to ∼1.3 wt % of H2O, perhaps through the direct substitution ((Formula presented.)), according to recent studies. Yet the stability of such substitution and its impact on the properties of silica and rutile-structured hydrous phases (such as δ-AlOOH and phase H) are unknown at the conditions of the deeper mantle. We have synthesized hydrous and anhydrous Al-free stishovite samples at 723 K and 9 GPa, and 1473 K and 10 GPa, respectively. Synchrotron X-ray diffraction patterns show that the unit cell volume of hydrous stishovite is 1.3% greater than that of anhydrous stishovite at 1 bar, suggesting significant incorporation of OH in the crystal structure (3.2 ± 0.5 wt % H2O). At 300 K, we found a lower and broader transition pressure from rutile type to CaCl2 type (28–42 GPa) in hydrous dense silica. We also found that hydrous silica polymorphs are more compressible than their anhydrous counterparts. After the phase transition, the unit cell volume of hydrous silica becomes the same as that of anhydrous silica, showing that the proton incorporation through a direct substitution can be further stabilized at high pressure. The lower pressure transition and the pressure stabilization of the proton incorporation in silica would provide ways to transport and store water in the lower mantle in silica-rich heterogeneities, such as subducted oceanic crust.

    Original languageEnglish (US)
    Pages (from-to)6972-6983
    Number of pages12
    JournalJournal of Geophysical Research: Solid Earth
    Volume122
    Issue number9
    DOIs
    StatePublished - Sep 1 2017

    Fingerprint

    phase transition
    Equations of state
    equation of state
    Silicon Dioxide
    silica
    equations of state
    stishovite
    Phase transitions
    Silica
    silicon dioxide
    substitution
    Substitution reactions
    transition pressure
    substitutes
    rutile
    protons
    Protons
    Earth mantle
    lower mantle
    crystal structure

    Keywords

    • direct proton substitution
    • equation of state
    • hydrous stishovite
    • phase transition
    • water in the lower mantle

    ASJC Scopus subject areas

    • Geophysics
    • Oceanography
    • Forestry
    • Aquatic Science
    • Ecology
    • Condensed Matter Physics
    • Water Science and Technology
    • Soil Science
    • Geochemistry and Petrology
    • Earth-Surface Processes
    • Physical and Theoretical Chemistry
    • Polymers and Plastics
    • Atmospheric Science
    • Earth and Planetary Sciences (miscellaneous)
    • Space and Planetary Science
    • Materials Chemistry
    • Palaeontology

    Cite this

    Phase transition and equation of state of dense hydrous silica up to 63 GPa. / Nisr, C.; Leinenweber, Kurt; Prakapenka, V.; Prescher, C.; Tkachev, S.; Shim, Sang-Heon.

    In: Journal of Geophysical Research: Solid Earth, Vol. 122, No. 9, 01.09.2017, p. 6972-6983.

    Research output: Contribution to journalArticle

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