A metastable limit for compressed liquid water

The transformation of liquid water to solid ice is typically a slow process. To cool a sample below the melting point requires some time, as does nucleation from the metastable liquid1, so freezing usually occurs over many seconds2. Freezing conditions can be created much more quickly using isentropic compression techniques, which provide insight into the limiting timescales of the phase transition. Here, we show that water rapidly freezes without a nucleator under sufficient compression, establishing a practical limit for the metastable liquid phase. Above 7 GPa, compressed water completely transforms to a high-pressure phase within a few nanoseconds. The consistent observation of freezing with different samples and container materials suggests that the transition nucleates homogeneously. The observation of complete freezing on these timescales further implies that the liquid reaches a hypercooled state3.