Ice IX is a form of solid water stable at temperatures below 140 K and pressures between 200 and 400 MPa. It has a tetragonal crystal lattice and a density of 1.16 g/cm³, 26% higher than ordinary ice. It is formed by cooling ice III from 208 K to 165 K (rapidly—to avoid forming ice II). Its structure is identical to ice III other than being hydrogen-ordered.[clarification needed]
- Ice, for other crystalline forms of ice.
- Bridgman, P. W. (1937) J. Chem. Phys. 5, 964.
- Chaplin, Martin (2007-11-11). "Ice-three and ice-nine structures". Water Structure and Science. Retrieved 2008-01-02.