Raman Scattering and X-ray Diffraction of Ice in the Megabar Range. Occurrence of a Symmetric Disordered Solid above 62 GPa

First results on a systematic study of ice by Raman scattering and X-ray diffraction in the megabar range are reported. Our discussion, which is based on the dynamical features of ice and its phase diagram, focuses on the possible occurrence of a symmetric state (ice X). It is concluded that above 62 GPa, delocalization of the proton occurs along O−O directions and ice may be symmetric from the statistical viewpoint.