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 journalArticle

6 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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