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

metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...

cubic

crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

variant of

ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaqu ...

. Hans König was the first to identify and deduce the structure of ice I_c. The

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...

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. Phase_diagram_of_water

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 Halo, halos or haloes usually refer to: * Halo (optical phenomenon) * Halo (religious iconography), a ring of light around the image of a head HALO, halo, halos or haloes may also refer to: Arts and entertainment Video games * ''Halo'' (franch ...

, 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.

References

Water ice {{inorganic-compound-stub

See also

References