Brillouin scattering of H2O ice to megabar pressures.

The sound velocity in polycrystalline ice was measured as a function of pressure at room temperature to 100 GPa, through the phase field of ice VII and crossing the ice X transition, by Brillouin scattering in order to examine the elasticity, compression mechanism, and structural transitions in this pressure range. In particular, we focused on previously proposed phase transitions below 60 GPa. Throughout this pressure range, we find no evidence for anomalous changes in compressibility, and the sound velocities and elastic moduli do not exhibit measurable discontinuous shifts with pressure. Subtle changes in the pressure dependence of the bulk modulus at intermediate pressures can be attributed to high shear stresses at these compressions. The C(11) and C(12) moduli are consistent with previously reported results to 40 GPa and increase monotonically at higher pressures.