Plasticky ice

Abstract

Discrepancies between previous experimental and simulation results had led researchers to question the existence of this phase. The main difficulty lay in detecting this distinct phase transition, which is primarily governed by changes in hydrogen dynamics rather than by structural transformation. To circumvent this issue, the team investigated the dynamics of water using quasi-elastic neutron scattering measurements, which link the broadening in the incident neutron spectrum to the molecular motion in the sample. Rescigno and colleagues performed these experiments in the temperature range 450–600 K and at pressures of up to 6 GPa.

The results demonstrated that, under these conditions, water ice adopts a body-centred cubic structure. Furthermore, the team showed that water molecules exhibit liquid-like rotational motion on the picosecond timescale while maintaining their crystalline structure. Therefore, the overall signal revealed a crystalline structure combined with active molecular motion, which are the key characteristics of the plastic ice VII phase.