What is this recently discovered “XIX ice”?

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Using X-ray diffraction, Austrian researchers have unraveled the secret behind the structure of a new form of ice. Forming at ultra-low temperatures and incredible pressures, this “XIX ice” exists only in laboratory experiments.

An umpteenth variant of ice form

It’s not a scoop, the ice cream is none other than the solid form of water (H2O). In contrast, the public is much less aware that ice exists in different forms. Science has known this since researchers carried out work on its structure, using X-ray diffractometry. This is an analysis technique based on the diffraction of X-rays by matter. , especially when it is crystalline.

Scientists call the various forms of ice “crystalline polymorphs”. However, there were 18 before researchers at the University of Innsbruck (Austria) identified a new one: ice cream XIX. This one finds at its base the ice VI, forming at high pressure. The point is that this VI ice does not have perfect crystals, these are even rather messy. More than a decade ago, researchers already had got a variant (ice XV) by arranging periodically – and therefore in an orderly manner – the hydrogen atoms.

Credits: University of Innsbruck

Austrian researchers explained via a publication in the journal Nature communications on February 18, 2021 having obtained XIX ice cream by modifying the manufacturing process ice cream XV. It is about slowing down the cooling process and increasing the pressure to about 20 kbar.

“Twin ice creams”

You should know that this discovery was made three years ago. However, this expectation at the level of the publication of results concerning the crystalline structure of ice XIX is not the result of chance. Indeed, neutron diffraction is the responsibility of replace light hydrogen in water by deuterium (2H), in other words heavy hydrogen. However, this has the effect of slowing down the process of formation of this same ice. Finally, the researchers found the solution: mix a few percent normal water with heavy water.

The point is that Ice XV and Ice XIX are the only known “twin ice creams”. It turns out that these have the same arrangements of their oxygen atoms. On the other hand, the arrangements of their hydrogen atoms differ. This feature therefore shows that it is quite possible to make the transition between two forms of ice in the laboratory.

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