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Report No.

Hydrogen sites in the dense hydrous magnesian silicate phase E; A Pulsed neutron powder diffraction study

Tomioka, Naotaka*; Okuchi, Takuo*; Purevjav, N.*; Abe, Jun*; Harjo, S.  

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 $$R$$$$overline{3}$$m and lattice parameters of $$a$$ = 2.97065(8) ${AA}$ and $$c$$ = 13.9033(4) ${AA}$, was synthesized at 15 GPa and 1100$$^{circ}$$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$$^{circ}$$ from the direction normal to the layers of edge-shared MgO$$_{6}$$ 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.



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Category:Materials Science, Multidisciplinary



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