Ice-ten (Ice X)

Ice-ten cubic structure consisting of 8 unit cells of two water molecules plus extra atoms found within the basic cubic structure

As the pressure is raised and the O···O distance contracts, ice-seven appears to undergo a continuous transition into cubic ice-ten (ice X) (still space group, a, b, c = 2.78 Å at 62 GPa, 300 K [719 ]) where the ice protons are equispaced (and equally bonded) between the oxygen atoms in a molecular crystal [1621 ]. The oxygen atoms are arranged in a body-centered cubic arrangement (8 neighbors) and the hydrogen atoms in a body-centered truncated cubic arrangement (12 neighbors).

The melting curve for ice-ten has been proposed at high temperatures (1000-2400 K) [612a]. As ice X is approached with increasing pressure from very hot liquid water and the O-H energy minima draw near to each other, the protons rapidly swap positions giving many short-lived OH^- and H₃O⁺ ions [612b]. In the ice X, however, protons are less mobile than in ice VII as there is only one energy minimum for each O-H-O bond,

Ice-ten looks identical as seen from the x, y or z direction.

Ice-ten has triple points with ice-seven and ice-eight (100 K, 62 GPa) and ice-seven and water (~1000 K, ~47 GPa) [612b].

Interactive Jmol structures are given.