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Ice VII is a cubic crystalline form of ice formed when liquid water freezes at pressures above 2.2 GPa.[1] It can also be reached in the solid state by increasing the pressure on ice VI at ambient temperature.[2] Like the majority of ice phases (including ice Ih), the hydrogen atom positions are disordered.[3] In addition, the oxygen atoms are disordered over multiple sites.[4][5][6] The structure of ice VII comprises a hydrogen bond framework in the form of two interpenetrating (but non-bonded) sub-lattices.[4]
Ice VII is the only disordered phase of ice that can be ordered by simple cooling,[2] and it forms (ordered) ice VIII below 273 K up to ~ 8 GPa. Above this pressure, the VII-VIII transition temperature drops rapidly, reaching 0 K at ~60 GPa.[7] Thus, ice VII has the largest stability field of all of the molecular phases of ice. The cubic oxygen sub-lattices that form the backbone of the ice VII structure persist to pressures of at least 128 GPa;[8] this pressure is substantially higher than that at which water loses its molecular character entirely, forming ice X.
Ordinary water ice is known as ice Ih, (in the Bridgman nomenclature). Different types of ice, from ice II to ice XIV, have been created in the laboratory at different temperatures and pressures.
The crystal structure of ice VII
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[edit] References
- ^ IAPWS, Release on the pressure along the melting and the sublimation curves of ordinary water substance, 1993. Retrieved on 2008-02-22.
- ^ a b G.P. Johari, A.Lavergne and E.Whalley, Journal of Chemical Physics Vol 61 p4292 (1974)
- ^ V.F. Petrenko and R.W. Whitworth, The Physics of Ice, Oxford University Press, New York (2002).
- ^ a b W.F. Kuhs, J.L. Finney, C. Vettier and D.V. Bliss, J. Chem. Phys. Vol. 81 (8) 3612-3623 (1984).
- ^ J.D. Jorgensen and T.G. Worlton, J. Chem. Phys. Vol 83 (1) 329-333 (1985).
- ^ R.J. Nelmes, J.S. Loveday, W.G. Marshall et al, Phys. Rev. Lett. Vol 81 (13) 2719-2722 (1998).
- ^ Ph. Pruzan, J.C. Chervin and B. Canny, J. Chem. Phys. Vol 99 (12) 9842-9846 (1993).
- ^ R.J. Hemley, A.P. Jephcoat, H.K. Mao et al, Nature, Vol. 330, 737-740 (1987).
