Fig. 1: Phase diagram at high to ultrahigh pressure.
From: Open questions on the structures of crystalline water ices
Stable phases of ice and liquid water at temperatures up to 4000 K and to ultrahigh pressures of 400 GPa. Grey indicates molecular and ionic liquid water. Blue indicates H-ordered ice VIII, red indicates H-disordered ice VII. Purple indicates the atomic solid ice X, in which the H atoms are at the centre between two O atoms. The dotted line separates ice X from ice VII, in which the H atoms are centred in a time-average, but localised in a snapshot. Green indicates ice XVIII, in which the H atoms are mobile and delocalised in a fixed lattice of O atoms. Dashed lines are estimates. Predicted post ice X polymorphs as candidates for future experimental discovery are listed at the ultrahigh pressure end.
