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Hydrogen site analysis of hydrous ringwoodite in mantle transition zone by pulsed neutron diffraction
Author(s) -
Purevjav Narangoo,
Okuchi Takuo,
Tomioka Naotaka,
Abe Jun,
Harjo Stefanus
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl061448
Subject(s) - ringwoodite , neutron diffraction , transition zone , octahedron , hydrogen , mantle (geology) , materials science , crystallography , geology , crystal structure , mineralogy , chemistry , geochemistry , organic chemistry
Hydrogen site positions and occupancies in the crystal structure of synthetic hydrous ringwoodite have been determined for the first time by high‐resolution neutron powder diffraction conducted at the pulsed neutron source at Japan Proton Accelerator Research Complex (J‐PARC). It is demonstrated that hydrogen exchanges not only with Mg or Fe but also with Si cations to form hydroxyl and hydrogen bonding, both within the relevant octahedra or tetrahedra created by their surrounding oxygen anions. The hydrated octahedra shrink, whereas the hydrated tetrahedra expand. The occurrence of simultaneous hydration of octahedra and tetraheda is thus unambiguously confirmed, whereby the latter plays an especially unique role in reducing seismic velocity and for enhancing the electrical conductivity of ringwoodite at high pressures and temperatures. These results provide distinctive implications for discussing the physical properties of hydrous ringwoodite occurring in the mantle transition zone and evaluating the actual water content in the zone.