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

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).

and

CrystalMaker®.

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