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Nineteen Phases of Ice and Counting
Published in Fausto Martelli, Properties of Water from Numerical and Experimental Perspectives, 2022
Alfred Amon, Bharvi Chikani, Siriney O. Halukeerthi, Carissa Ponan, Alexander Rosu-Finsen, Zainab Sharif, Rachael L. Smith, Sukhpreet K. Talewar, Christoph G. Salzmann
Ice VII is a stable phase of ice above 2.1 GPa (Bridgman 1937, Pistorius et al. 1968). Like ice VI, it contains two interpenetrating networks that are isostructural with ice Ic (Kuhs et al. 1984, Jorgensen and Worlton 1985). Its cubic unit cell with Pn-3m space group symmetry contains two water molecules, one distinct oxygen site, and one type of hydrogen bond (cf. Fig. 3). The Pn-3m space group requires ice VII to be completely hydrogen disordered. In addition to ice Ih, ice VII is the second phase of ice considered to be a mineral following its discovery as an inclusion compound inside diamonds (Tschauner et al. 2018). Due to its simple structure, ice VII has been a testbed for probing the positional disorder of the oxygen atoms induced by the hydrogen-disorder (Kuhs et al. 1984, Jorgensen and Worlton 1985, Nelmes et al. 1998, Knight and Singer 2009, Bellin et al. 2011). In a recent neutron diffraction study, ice VII has been compressed beyond 60 GPa (Guthrie et al. 2019). In contrast to ice Ih, ice VII can accommodate lithium chloride and bromide at ~ 1:6 LiX:H2O molar ratios (Klotz et al. 2016, Klotz et al. 2009). The unit cell volume of ‘salty’ ice VII is strongly increased and the concomitant positional disorder of H2O makes it a “plastic” phase of ice. Compared to the lithium halides, the solubility of NaCl in ice VII is much smaller (Ludl et al. 2017).
Theoretical Consideration Of Solubility
Published in A. L. Horvath, Halogenated Hydrocarbons, 2020
Our information is most complete for the hexagonal structure of Ice Ih. Another form of ice is the cubic structure, which is metastable. A phase diagram of water, showing the pressure effect upon temperature, has been presented by, for example, Kamb (1965), Ross et al. (1977). The various modifications of ice have been determined by x-ray, electron, or neutron diffraction or x-ray powder study, or by infrared and Raman spectroscopy (Fox and Martin, 1940). Ice II has a rhombohedral structure, whereas Ices III, V, and VI have tetrahedrally coordinated structures. In Ice VII the oxygen atoms are arranged in a body-centered-cubic form. In contrast to the hydrogen-bonded organic substances, in ice the stronger hydrogen bonds lead to a decrease in the density of the structure (Fletcher, 1970).
Theoretical analyses of pressure induced glass transition in water: Signatures of surprising diffusion-entropy scaling across the transition
Published in Molecular Physics, 2021
Saumyak Mukherjee, Biman Bagchi
Two new peaks start to emerge at ∼4.7 Å and ∼5.4 Å under the influence of pressure. These are signatures of crystalline order. Our results are in good agreement with the reports of Tse et al. [1]. These two peaks are reminiscent of the structures of ice VII.