Ice III and IX (Ice three and Ice nine)
- Ice III can be formed from liquid water at 300 MPa (3000 bar) by lowering the temperature to approx. 250 K.
- The relative permittivity is very high (~ 117)
- Density: 1.16 g/cm3
- Ice III is also called Keatite Ice, because the oxygen atoms are located at analogous positions of the silicon atoms in the SiO2 phase Keatite.
- Ice IX is the proton-ordered form of Ice III.
- The tetrahedral environment of the water molecules are considerably distorted.
- Interestingly, there are no 6-membered rings present anymore, but 5, 7, and 8 –membered rings instead. The 5-membered rings can be best seen if you look along the a or b direction:
- Two-third of the water molecules are forming 41 helices/screws running along the c axis, which means that Ice III is chiral! The other water molecules connect these helices and are forming a 21 helix.
- Space group: P41212 (No. 92)
- Crystal system: tetragonal
- Lattice parameters:
- a = b = 6.73(1) Å, c = 6.83(1) Å
- α = β = γ = 90°
Here, you can download the CIF.
[Atomic structure figures created with
K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).