Owing to the many different ways atoms can be arranged within the material, ice can exist in many more forms than what’s known as ice I, the type we’re all familiar with. Scientists have actually categorized 18 different types of the material, each with its own unique crystalline structure, and now have added another, called ice XIX, to the list.
Ice I is the ice we see forming in ice and snow here on Earth, and stands alone as the only type of ice you’ll find on the surface of our planet, with the exception of research laboratories. Other forms, such as ice VI and VII, have been discovered to have developed deep in the Earth’s mantle locked inside diamonds that were slowly pushed upward over time, while other types can be found on other planets and moons or in space.
These different types of ice form in response to different pressures and temperatures, which shapes the way the oxygen and hydrogen atoms and water molecules are arranged within them. Scientists at Austria’s University of Innsbruck have been experimenting with this process for years, making tweaks to the process that produces ice VI, which normally forms under high pressure, to see what eventuates.
By slowing down the cooling process and increasing the pressure even further, the scientists made a breakthrough several years ago. This method led to the formation of a different type of ice, which featured a different arrangement of hydrogen atoms.
"We found clear evidence at that time that it is a new ordered variant, but we were not able to elucidate the crystal structure,” explains study author Thomas Loerting.
Loerting and his colleagues have continued studying this new form of ice, dubbed ice XIX, and have now managed to confirm its crystal structure using a technique called neutron diffraction. The team likens this to finding a needle in a haystack, having to sort through thousands of candidates before landing on the correct crystal structure, which was confirmed by a different research group in Japan in separate experiments.
It might be the 19th type of ice scientists have confirmed, but the discovery does herald a significant first. Ice XIX was found to feature some striking similarities with XV, with the oxygen lattice found to be the same, although the hydrogen atoms were arranged differently. This makes ice XV and ice XIX the first sibling pair in ice physics, according to the researchers.
"This also means that for the first time it will now be possible to realize the transition between two ordered ice forms in experiments," says Loerting.
The research was published in the journal Nature Communications.
Source: University of Innsbruck