Tag Archives: crystalline Ice

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).



Ice Ih

Ice Ih (Ice one hexagonal)

Structural features:

  • single molecule and molecular arrangement

  • Ice Ih is a proton-disordered phase

  • every water molecule is involved in 4 H-bonds (2 acceptors, 2 donors)
  • tetrahedrally coordinated
  • O-H bond length approx. 99 pm
  • H …. O-H distance approx. 175 pm
  • O … O distance approx. 275 pm
  • H-bond strength: approx. 21 kJ/mol
  • 6-membered rings
    • chair-like conformation in the (a,b) plane
    • boat-like conformation along the c direction

(graphic created with VESTA:
K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr.44, 1272-1276 (2011).

  • sometimes called “tridymite ice” because the oxygen atoms occupy the Si analogeous positions in the SiO2 phase tridymite
  • Space group P63/mmc
    • a = b = 4.4975 Å, c = 7.3224 Å
    • α = β = 90°, γ = 120°

 Here, you can download the CIF.