High-temperature and high-pressure plastic phase of ice at the boundary of liquid water and ice VII

Abstract

Simultaneous high-temperature and high-pressure studies reveal phase transformation of bulk liquid water to an ice-VII-like structure having an eight coordination. It was demonstrated through this numerical study that the observed high-temperature and high-pressure phase of water obtained upon shock compression and equilibration has high rotational diffusion and thereby the hydrogen dynamics of these crystal structures are significantly complex compared with ice VII. The current work provides new characterization methods for the numerically observed plastic crystal phase of ice at the boundary of the liquid water and ice VII phases in which the molecules have a defined lattice position but rotate freely. It is anticipated that the present work will provide important data and guide new theoretical and experimental investigations in the search for plastic crystal phases of water. The power spectra plots of bulk liquid water subjected to different temperature and pressure conditions have also been presented in this numerical study, demonstrating significant differences between these high-temperature and high-pressure shock-equilibrated phases and those of pure ice VII at 10 GPa and liquid water at ambient temperature and pressure, as well as at elevated pressures and temperatures.