Ice Ic

Ice I_c (pronounced "ice one c" or "ice I see") is a metastable cubic crystalline variant of ice. Hans König was the first to identify and deduce the structure of ice I_c. The oxygen atoms in ice I_c are arranged in a diamond structure; it is extremely similar to ice I_h having nearly identical densities and the same lattice constant along the hexagonal puckered-planes. It forms at temperatures between upon cooling, and can exist up to upon warming, when it transforms into ice I_h.

Apart from forming from supercooled water, ice I_c has also been reported to form from amorphous ice as well as from the high-pressure ices II, III and V. It can form in and is occasionally present in the upper atmosphere and is believed to be responsible for the observation of Scheiner's halo, a rare ring that occurs near 28 degrees from the Sun or the Moon.

Ordinary water ice is known as ice I_h (in the Bridgman nomenclature). Different types of ice, from ice II to ice XIX, have been created in the laboratory at different temperatures and pressures.

Some authors have expressed doubts whether ice I_c really has a cubic crystal system, claiming that it is merely ''stacking-disordered ice I'' (“ice I_sd”), and it has been dubbed the ″most faceted ice phase in a literal and a more general sense.″ However, in 2020, two research groups individually prepared ice I_c without stacking disorder; Komatsu et al. prepared C₂ hydrate at high pressure and decompressed it at 100 K to make hydrogen molecules extracted from the structure, resulting in ice I_c without stacking disorder; del Rosso et al. prepared ice XVII from C₀ hydrate and heated it at 0 GPa to obtain pure ice I_c without stacking disorder.

See also

* Ice I, for the other crystalline form of ice

References

Water ice

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