Structure of water under high pressure

Katayama, Yoshinori; Hattori, Takanori   ; Saito, Hiroyuki; Fukui, Hiroshi*

Liquid water shows unique properties and they are related to a network structure formed by hydrogen bonds. Simulation studies predicted that pressure induced drastic structural change, such as weakening of the hydrogen-bond network and molecular dissociation, in a pressure range from several GPa to several tens GPa. We have measured X-ray diffraction of liquid water up to about 9 GPa and 420C using a cubic-type multi-anvil press on BL14B1 at SPring-8, a synchrotron radiation facility in Japan. The coordination number of water molecules increases rapidly to about 10 around 4 GPa while the intermolecular distance was almost constant. The structure of water evolves toward a simple structure which can be described by a hard sphere model with increasing pressure. This result is in agreement with that of a recent neutron scattering study.