- At even higher pressures, ionic water will further condense into superionic water, where the oxygen lattice.
- Here O in the subscripts indicates that both the initially bonded oxygen and the vacancy that is produced lie on an oxygen lattice site, while the superscripts on the oxygen and vacancy indicate charge.
- There may be a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions move freely within the oxygen lattice.
- The cubic oxygen sub-lattices that form the backbone of the ice VII structure persist to pressures of at least 128 GPa; this pressure is substantially higher than that at which water loses its molecular character entirely, forming ice X . In high pressure ices, protonic diffusion ( movement of protons around the oxygen lattice ) dominates molecular diffusion, an effect which has been measured directly.