A new form of water ice has been discovered.
It takes place as the substance slides between two already known, cubic arrangements of molecule.
We might think water is commonplace, but it is not. Depending on the conditions around it, the arrangement of water's frozen form can vary significantly.
We know of at least 19 solid phases of ice, some of which are naturally occurring, some of which have only been seen in laboratory conditions.
The most common natural ice on Earth is the ice you see in the freezer or in the sky. Oxygen atoms are arranged in a hexagonal grid. The structure is frustrated with the hydrogen atoms hanging about in a disorderly fashion.
When Ice-I is cooled and applied different pressures, the hydrogen and oxygen atoms within can periodically reach different arrangements. The various forms of water ice are not always stable, but we can explore them in the lab to see their strange structures.
Ice-X and Ice-VII are the two phases that have a symmetrical structure. These can be reached by subjecting ice to high pressures to hundreds of thousands greater than Earth's atmospheric pressure at sea level.
A team of physicists led by the University of Nevada, Las Vegas performed experiments on high pressure ice using a new technique to measure the properties of the ice as pressure was applied.
A sample of water was squeezed in a diamond anvil and forced to freeze. The researchers described the sample as a powder-like collection of crystals after using lasers to heat it.
The researchers created Ice-VII by gradually raising the pressure in the anvil, and observed the transition to Ice-X. The new intermediate phase, Ice-VII t, was observed thanks to their new measurement technique.
In this phase, the lattice of Ice-VII is stretched along one of its vectors so that it can be stretched into a rectangular arrangement with a cubic footprint. The arrangement is known as a quadrangular.
The team showed that Ice-X can form at lower pressures. 30,000 atmospheric pressures is how much ice-VII forms from 3 gigapascals. The transition to Ice-VIIt occurs at 5.1 gigapascals according to the team.
The transition pressure for Ice-X is between 40 and 120 gigapascals. Grande and his team observed the transition between Ice-VII t and Ice-X.
The debate about the Ice-X transition pressure should be resolved by this.
Physicist Ashkan Salamat of the University of Nevada, Las Vegas said that the transformation to an ionic state occurs at much lower pressures than thought before.
It is the missing piece, and the most precise measurements ever on water at these conditions.
This could have important implications for studying the interior conditions of other worlds. Water-rich planets outside the Solar System could have Ice-VII t in abundance, increasing the chance of conditions suitable for the emergence of life.
The research was published in Physical Review B.
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