Ice I_c

Ice I_c (pronounced "ice one c" or "ice I c") is a

Apart from forming from supercooled water,^[5] ice I_c has also been reported to form from amorphous ice^[2] as well as from the high-pressure ices II, III and V.^[6] It can form in and is occasionally present in the upper atmosphere^[7] 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.^[8]

Ordinary water ice is known as ice I_h (in the Bridgman nomenclature). Different types of ice, from ice II to ice XIX,^[9] 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”),^[10][11][12] and it has been dubbed the ″most faceted ice phase in a literal and a more general sense.″^[13]

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.^[14] 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.^[15] Pure ice I_c prepared in the latter method transforms into ice I_h at 226 K with an enthalpy change of -37.7 J/mol.^[16]

See also

• Ice I
  , for the other crystalline form of ice

References

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