Ice XII
Ice XII is a metastable, dense, crystalline phase of solid water, a type of ice. 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. Later research showed that ice XII could be created outside that range. Pure ice XII can be created from ice Ih at by rapid compression or by warming high density amorphous ice at pressures between. The proton-ordered form of ice XII is ice XIV.
While it is similar in density to ice IV it exists as a tetragonal crystal. Topologically it is a mix of seven- and eight-membered rings, a 4-connected net —the densest possible arrangement without hydrogen bond interpenetration.
Ordinary water ice is known as ice Ih,. Different types of ice, from ice II to ice XVI, have been created in the laboratory at different temperatures and pressures.
