Powder X-ray diffraction study of the volume change of ice VIII under high pressure

Abstract

Low-temperature powder X-ray diffraction measurements have been carried out on H 2O ice VIII in the pressure range from 5 to 50 GPa. The volume change associated with the ice VII–VIII phase transition and the compression curves of ice VIII have been obtained experimentally. The slope of the VII–VIII phase-boundary is explained qualitatively by the volume change, namely, an almost zero volume-change in a pressure-insensitive flat region below 10 GPa, and a negative volume-change in a negative slope region above 10 GPa.