Ice III and IX

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

Structural features

  • 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).




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