Water can form various types of structures, such as ice, liquid, and vapor. Now, a new study added one more phase to the list.
Scientists at UChicago and Carnegie have discovered a new state of matter: supersonic ice.
Supersonic ice forms at extremely high temperatures and pressures. It is black and hot, unlike the normal ice found in the freezer or north pole. A cube of it would weigh four times as much as a normal one.
The supersonic ice was first theoretically predicted more than 30 years ago. In 2019, scientists had only been glimpsed in a brief instant as scientists sent a shockwave through a droplet of water. In this new study, scientists have found a way to create, sustain, and examine the ice.
Co-author Vitali Prakapenka, a University of Chicago research professor and beamline scientist at the Advanced Photon Source at Argonne National Laboratory, said, “It was a surprise—everyone thought this phase wouldn’t appear until you are at much higher pressures than where we first find it. But we were able to very accurately map the properties of this new ice, which constitutes a new phase of matter, thanks to several powerful tools.”
Using the Advanced Photon Source, scientists drive electrons to extremely high speeds close to the speed of light to generate brilliant beams of X-rays. By squeezing their samples between two pieces of diamond, scientists simulated the intense pressures and then shot lasers through the diamonds to heat the sample.
At last, they sent an x-ray beam through the sample and piece together the arrangement of the atoms inside based on how the X-rays scatter off the sample.
During experiments, the readings of the structure were much different than expected.
After seeing the reading, the authors thought something had gone wrong, and there had been an unwanted chemical reaction, which often happens with water in such experiments.
Prakapenka said, “But when I turned off the laser, and the sample returned to room temperature, the ice went back to its original state. That means it was a reversible, structural change, not a chemical reaction.”
“Looking at the structure of the ice, we realized it had a new phase on its hands. They were able to map its structure and properties precisely.”
“Imagine a cube, a lattice with oxygen atoms at the corners connected by hydrogen. When it transforms into this new superionic phase, the lattice expands, allowing the hydrogen atoms to migrate around while the oxygen atoms remain steady in their positions. It’s kind of like a solid oxygen lattice sitting in an ocean of floating hydrogen atoms.”
“This has consequences for how the ice behaves: It becomes less dense but significantly darker because it interacts differently with light. But the full range of the chemical and physical properties of superionic ice has yet to be explored. It’s a new state of matter, so it acts as a new material, and it may be different from what we thought.”
Mapping the exact conditions where different phases of ice occur is essential to know more about planet formation and even where to look for life on other planets. According to scientists, similar conditions exist at the interiors of Neptune and Uranus and other cold, rocky planets like them elsewhere in the universe.
Prakapenka said, “there are many more angles to explore, such as conductivity, viscosity, and chemical stability, which change when the water mixes with salts or other minerals, the way it often does deep beneath the Earth’s surface. This should stimulate a lot more studies.”
- Prakapenka, V.B., Holtgrewe, N., Lobanov, S.S. et al. Structure and properties of two superionic ice phases. Nat. Phys. (2021). DOI: 10.1038/s41567-021-01351-8