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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


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 Pn bar3 m 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]. Thus each oxygen atom has four equidistantly tetrahedrally placed nearest neighbor hydrogen atoms. The oxygen atoms are arranged in a body-centered cubic arrangement (each has eight oxygen atoms nearest neighbors arranged as a cube). The hydrogen atoms have 12 nearest neighbor hydrogen atoms arranged in a body-centered truncated cube. Likely, ice-ten is at least partially ionized with both hydrogen atoms and oxygen atoms fully ionized. Also, some protons are likely to occupy the octahedral cavities as this behavior has been seen to develop in ice-seven at lower pressures [2027]. These dissociations have not been shown in the cartoons here


Ice-ten lattice


Ice-ten lattice



The ice VII - ice X phase line has been described by an equation of state covering pressures up to 450 GPa [3860] but varies between studies [4223]. 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 each other, the protons rapidly swap positions giving many short-lived OH and H3O+ ions [612b]. In ice X, however, protons are less mobile than in ice VII as there is only one energy minimum for each O-H-O bond. The bulk modulus of ice X has been established as about 600 GPa at a pressure of 120 GPa [4225].


Ice-ten looks identical as seen from the x-, y- or z-direction. Using a first-principles DFT code, ideal crystals of ice X have been shown to have a Raman peak at 998 cm−1 and two infrared absorption peaks at 450 cm−1 and 1507 cm−1 [3481].


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].


It has been theoretically determined that doping ice-ten with NH2 gives rise to a superconductor with a critical temperature of about 60 K at 150 GPa [2990].



Interactive Jmol structures are given.



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This page was established in 2003 and last updated by Martin Chaplin on 4 October, 2021

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