Freezing kinetics in overcompressed water

We report high-pressure dynamic compression experiments of liquid water along a quasiadiabatic path leading to the ice-VII region of the phase diagram. We observe dynamic features resembling van der Waals loops and find that liquid water is compacted to a metastable state close to the ice density before the onset of crystallization. By analyzing the characteristic kinetic time scale involved we estimate the nucleation barrier and conclude that liquid water has been compressed to a high-pressure state close to its thermodynamic stability limit.