Ice XV Discovered

Freeze water and you’ll get ice. But not all ice is created equal.

Ice can form a surprising number of crystalline and noncrystalline structures, depending on the temperature and pressure at which it forms and the way that conditions change after it has frozen.

Over the years, ice scientists have created and characterized some 15 different kinds of crystalline ice and three different kinds of amorphous noncrystalline ice. Almost all the ice on Earth is of type Phase lh (hexagonal crystalline), although there is a small amount of Phase lc (cubic crystalline) lying around here and there.

The others come in crystals of all shapes and sizes, such as rhombic, tetragonal, monoclinic, etc., but have only ever been seen in the laboratory, although they may well play a role in the geochemistry of comets and icy planets and moons.

But in all this time, one phase of ice has eluded everybody. Ice XV has long been predicted to exist at temperatures of between 108 and 180 kelvins and at a pressure of 1.1 gigapascals.

Now Christoph Salzmann at the University of Oxford and acquaintances have created the stuff for the first time and say that its properties differ significantly from those predicted. In particular, ice XV is antiferroelectric rather than ferroelectric, as had been predicted.

I guess that makes it slightly less interesting than had been hoped. Ferroelectric materials usually have interesting electrical properties, such as the ability to form capacitors. That would have given planetary geologists something to think about, but now they can rest easy.

Ref: http://arxiv.org/abs/0906.2489: Ice XV: A New Thermodynamically Stable Phase of Ice