Pressure induced hydrogen bond symmetrization in a hydrous mineral

Sano, Asami   ; Hattori, Takanori   ; Komatsu, Kazuki*; Kagi, Hiroyuki*; Nagai, Takaya*

Hydrogen exists not only on the Earth's surface as liquid water but also incorporated into minerals in the deep mantle as hydroxyl ion. At ambient pressure on the surface of the Earth, hydrogen in minerals generally takes an asymmetric position between two oxygen atoms, which forms a short covalent bond on the one side and a long and relatively weak hydrogen bond on the other side. However, it was theoretically predicted in 1970' that the hydrogen in ice locates at the center between two oxygen atoms under high pressure, which is so-called symmetrization of hydrogen bond. To investigate how the symmetrization affects on the physical properties of minerals, we conducted neutron diffraction experiments on -AlOOH at high pressure. We observed that hydrogen reaches at the center between two oxygen atoms at 18.1 GPa. The present study revealed that even small change of hydrogen atomic position but the symmetrization can change the physical property of mineral.