(ORDO NEWS) — Using a new method for studying substances at high pressures, scientists have discovered a previously completely unknown transitional form of crystalline ice, called Ice-VIIt. Probably, water in this aggregate state can exist inside the crust and mantle of the Earth, as well as on other water-rich planets.
Ice, like other solids, is able to take different forms, which depend on the temperature and pressure of formation. For example, carbon can exist as diamond or graphite. Ice is unique due to the large number of its phases.
Today, at least 20 of its forms are known: three amorphous and 17 crystalline. Now scientists from the University of Nevada at Las Vegas (USA) have discovered a completely new form of ice and described it in an article published in the journal Physical Review B.
The authors of the work conducted an experiment in a cell with diamond anvils. This design consists of two cone-shaped diamonds facing each other, between which a sample of the test substance is placed.
Due to the exceptional hardness of diamonds, it is possible to create a pressure of several million atmospheres on a sample site with a diameter of less than a millimeter. At the same time, the transparency of diamonds makes it possible to study the sample by various methods.
However, scientists did not just compress the ice, but also heated it using laser radiation. First, a sample of water was placed between two diamonds and the pressure was increased until it froze into several mixed ice crystals.
This ice was then heated with a laser so that it had time to melt before turning back into a crystal. In this way, the researchers gradually increased the pressure in the cell by periodically firing a laser beam at the sample.
The scientists watched as the ice made the transition from the studied phase with a cubic crystal lattice Ice-VII to a previously unknown intermediate phase with a tetragonal lattice, called Ice-VIIt.
After that, the sample passed into another well-known and also cubic phase Ice-X, which is formed at higher pressures than Ice-VII.
However, the formation of Ice-X was already observed at a pressure of 300,000 atmospheres, which is well below a million atmospheres – it was this pressure that was previously considered the threshold for the formation of Ice-X.
According to the authors of the work, the probability of detecting Ice-VIIt on the Earth’s surface is extremely small, but it is quite possible that this form is present inside the crust and upper mantle of our planet. In addition, Ice-VIIt may exist on other water-rich planets and their large moons outside the solar system.
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