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The first part of this paper presents a short survey on the phase diagram of ice in the pressure range from 2 to 100 GPa from 10 to 300 K. The description is mainly devoted to the problem of the symmetrization of the O -H· · ·O bond, that is, the transformation of ice VII or VIII to ice X. In connection with this introduction, in the second part of the paper new vibrational and structural data obtained from Raman scattering and x-ray diffraction in ice VIII are given and these properties are compared with those of ice VII. Specifically, below 100 K, solid VIII vanishes at 62 GPa to give birth to a state which is the first step to ice X. This transition is marked by a softening of the lowest Raman-active lattice mode and the disappearance of the Raman signal. During the compression of ice VIII the O-H stretching mode wavenumber shows soft mode behaviour. It is found that the expansivity of ice VIII is negative above 10 GPa.