Water under inner pressure: a dielectric spectroscopy study.

Water is the most studied substance on Earth. However, it is not completely understood why its structural and dynamical properties give rise to some anomalous behaviors. Some of them emerge when experiments at low temperatures and/or high pressures are performed. Here we report dielectric measurements on cold water under macroscopically constrained conditions, i.e., water in a large container at constant volume that cannot freeze below the melting point. The inner pressure in these conditions shifts the α relaxation peak to similar frequencies as seen in ice Ih. At 267 K we observe a peculiar response possibly due to the Grotthuss mechanism. At 251 K (the triple point) ice III forms.