Bulk modulus of H 2 O across the ice VII–ice X transition measured by time-resolved x-ray diffraction in dynamic diamond anvil cell experiments

We have studied the ${\mathrm{H}}_{2}\mathrm{O}$ ice VII--ice X phase transition at room temperature by performing three quasicontinuous synchrotron time-resolved x-ray-diffraction experiments in a dynamic diamond anvil cell, reaching pressures of 180 GPa. The dense pressure coverage of our volume data allows us to directly derive the bulk modulus for ${\mathrm{H}}_{2}\mathrm{O}$ over the entire pressure range. Our data document three major changes in compression behavior in the ranges of 35--40, 50--55, and 90--110 GPa, likely corresponding to the formation of pretransition dynamically disordered ice VII and ice X, and static ice X, respectively. Our results confirm that ice X has a very high bulk modulus.