Ice XII 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 ...

dense Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematically ...

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 ...

phase of

solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...

water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...

, a type 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 ...

. Ice XII was first reported in 1996 by C. Lobban, J.L. Finney and W.F. Kuhs and, after initial caution, was properly identified in 1998. It was first obtained by cooling liquid water to at a pressure of . Ice XII was discovered existing within the phase stability region of

ice V Ice V, pronounced "ice five", is a monoclinic crystalline phase of water, formed by cooling water to 253 K at 500 MPa. It has a density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The s ...

. Later research showed that ice XII could be created outside that range. Pure ice XII can be created from ice I_h at by rapid compression (0.81-1.00 GPa/min) or by warming

high density amorphous ice Amorphous ice (non-crystalline or "vitreous" ice) is an amorphous solid form of water. Common ice is a crystalline material wherein the molecules are regularly arranged in a hexagonal lattice, whereas amorphous ice has a lack of long-range order ...

at pressures between . While it is similar in density (1.29 g/cm³ at ) to

ice IV Ice IV is a metastable high-pressure phase of ice. It is formed when liquid water is compressed with an immense force. Preparation Several organic nucleating reagents had been proposed to selectively crystallize ice IV from liquid water, but e ...

(also found in the

space) it exists as a

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...

crystal 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, macro ...

. Topologically it is a mix of seven- and eight-membered rings, a 4-connected net (4-coordinate

sphere A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is th ...

packing)—the densest possible arrangement without hydrogen bond interpenetration. Ordinary water ice is known as ice I_h, (in the Bridgman nomenclature). Different types of ice, from

ice II Ice II is a rhombohedral crystalline form of ice with a highly ordered structure. It is formed from ice Ih by compressing it at a temperature of 198 K at 300 MPa or by decompressing ice V. When heated it undergoes transformation to ice III. ...

ice XVI Ice XVI is the least dense (0.81 g/cm) experimentally obtained crystalline form of ice. It is topologically equivalent to the empty structure of sII clathrate hydrates. It was first obtained in 2014 by removing gas molecules from a neon clathra ...

, have been created in the laboratory at different temperatures and pressures.

Ice XIV

When hydrochloric-acid-doped ice XII is cooled down to about 110 K, it undergoes a phase transition into a partially hydrogen-ordered phase, namely ice XIV. The transition entropy from ice XIV to ice XII is estimated to be 60% of Pauling entropy based on DSC measurements. The formation of ice XIV from ice XII is more favoured at high pressure.

References

* C. Lobban, J.L. Finney and W.F. Kuhs, The structure of a new phase of ice, Nature 391, 268–270, 1998 * Water ice {{inorganic-compound-stub

Ice XIV

See also

References