There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Crystal structure of ice I h. Dashed lines represent hydrogen bonds. The accepted crystal structure of ordinary ice was first proposed by Linus Pauling in 1935.

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Ice-four (IV) and ice-twelve (XII) [82] are both metastable within the ice-five phase space. Cubic ice (I c) is metastable with respect to hexagonal ice (I h).

Ice IV, a wholly metastable ice phase, has a structure based on a framework of tetrahedrally hydrogen-bonded water molecules in a rhombohedral unit cell. The structure involves two non-equivalent types of water molecules and four non-equivalent types of hydrogen bonds.

Ice-four (ice IV) may be formed occasionally by the heating high-density amorphous ice at a slow (0.4 K ˣ min −1) rate from 145 K and at a constant pressure of 0.81 GPa [386] (a faster rate, for example, 15 K ˣ min −1, preferably produces ice-twelve).

Ice-four (ice IV) may be formed by the heating high-density amorphous ice at a slow (0.4 K min-1) rate from 145 K and at a constant pressure of 0.81 GPa [386] (a faster rate, for example, 15 K min - 1 , preferably produces ice-twelve).

Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral.

Ice-four (IV) and ice-twelve (XII) [82] are both metastable within the ice-five phase space. Cubic ice (Ic) is metastable with respect tohexagonal ice (Ih). It is worth emphasizing that liquid water is stable throughout its phase space above.

Nov 1, 1972 · The metastable phase ice IV can be made from ice VI on decreasing the pressure at temperatures from -13.6 to -14.6°C. The growth and the metastability region of ice IV are described. The liquid-ice IV-ice VI and liquid-ice V-ice VI triple points are located at 5567 bar, -6.62°C and at 6343 bar, +0.22°C, respectively.

Nov 21, 2023 · Ice IV is a metastable high-pressure phase of ice in which the water molecules exhibit orientational disorder. Although orientational ordering is commonly observed for other ice phases, it has not been reported for ice IV.