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

高密度含水マグネシア珪酸塩相E中の水素サイト; パルス中性子粉末回折研究

富岡 尚敬*; 奥地 拓生*; Purevjav, N.*; 阿部 淳*; Harjo, S.   

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 m and lattice parameters of = 2.97065(8) and = 13.9033(4) , was synthesized at 15 GPa and 1100C. 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 MgO octahedra (octahedral layers). The tilted dipole structure of phase E is in remarkable contrast to that of brucite, Mg(OH), which has dipoles exactly normal to the octahedral layer.