ASTROCHEMISTRY: Capturing Ferroelectric Ice

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Science  05 Jan 2007:
Vol. 315, Issue 5808, pp. 18b
DOI: 10.1126/science.315.5808.18b

At low temperature and pressure, water crystallizes in two distinct morphologies, termed ice I and ice XI. Ice I exhibits the form of a hexagonal lattice of oxygen atoms, with attached protons distributed randomly around them. In ice XI, the protons become ordered and the resulting solid is ferroelectric. The inherent stability of ice XI is of particular interest because of its possible formation in space. However, researchers have accessed it only by doping of water samples with potassium hydroxide, and the influence of the dopant on long-range ordering was not well resolved.

Fukazawa et al. have succeeded in making large quantities of Ice XI in the laboratory by doping D2O (deuterated to raise the neutron scattering efficiency) with very small amounts of KOD, and then carefully maintaining the samples in a 60 to 70 K temperature range over tens of hours. Neutron diffraction experiments confirmed an extended ordered structure. The existence of ice XI in cold space environments is therefore likely; the electronic properties of the bulk ice may affect the formation mechanism of icy planets. — JB

Astrophys. J. 652, L57 (2006).

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