Hydrogen sites in the dense hydrous magnesian silicate phase E: a pulsed neutron powder diffraction study

Naotaka Tomioka, Takuo Okuchi, Narangoo Purevjav, Jun Abe, Stefanus Harjo

    Research output: Contribution to journalArticlepeer-review

    7 Citations (Scopus)

    Abstract

    Hydrogen site positions and occupancy in the crystal structure of dense hydrous magnesium silicate (DHMS) phase E were determined for the first time by pulsed neutron powder diffraction. A fully deuterated pure phase E powder sample, which had space group (Formula presented.) and lattice parameters of a = 2.97065(8) Å and c = 13.9033(4) Å, was synthesized at 15 GPa and 1100 °C. Through quantitative evaluation of refined structure parameters obtained with sufficient spatial resolution and very high signal-to-background ratio, we conclude that the O–D dipoles in the refined phase E structure are tilted by 24° from the direction normal to the layers of edge-shared MgO6 octahedra (octahedral layers). The tilted dipole structure of phase E is in remarkable contrast to that of brucite, Mg(OH)2, which has dipoles exactly normal to the octahedral layer. This contrast exists because the O–Si–O bonding unique in the phase E structure connects two adjacent octahedral layers and thereby reduces the interlayer O···O distance. This shrinkage of the interlayer distance induces the tilting of the O–D dipole and also generates unique O–D···O hydrogen bonding connecting all the layers in the phase E structure.

    Original languageEnglish
    Pages (from-to)267-275
    Number of pages9
    JournalPhysics and Chemistry of Minerals
    Volume43
    Issue number4
    DOIs
    Publication statusPublished - Apr 1 2016

    Keywords

    • DHMS phase
    • High pressure
    • Hydrogen sites
    • Neutron diffraction
    • Phase E

    ASJC Scopus subject areas

    • Materials Science(all)
    • Geochemistry and Petrology

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