Structure of water under high pressure and high temperature

Katayama, Yoshinori; Hattori, Takanori   ; Fukui, Hiroshi*; Nozawa, Akifumi*; Funakoshi, Kenichi*

Liquid water shows anomalous properties and these properties are attributed to a network structure formed by hydogen-bonded water molecules. To study the structure of water under high pressure, we have carried out in-situ high-pressure high-temperature X-ray diffraction experiments in SPring-8. In addition to the previous X-ray diffraction measurements using a cubic-type multianvil press installed on BL14B1, measurements up to about 17 GPa were successfully carried out using a Kawai-type double-stage press installed on BL04B1. The stcuture factor, , at ambient pressure has two maxima at 2A and 3A. With increasing pressure, these maxima merged and formed a sharp peak which is resembles that for a simple liquid. Futher compression shifted the peak to larger-Q direction. The increase of density is attributed to an increase of coordination number up to a few GPa and then it is attributed to a decrease of inter-molecular distance at higher pressures.