We finally have experimental evidence for superionic conduction in water ice, verifying a prediction made in 1946 by scientist Percy Bridgman.
A team of physicists from the Lawrence Livermore National Laboratory in California (USA) believes they have finally discovered a totally new type of water ice called superionic ice, water that is both solid and liquid, which can teach us much more on this versatile substance and lead to the development of new materials.
The idea of super-ionic ice has been around for several decades and is believed to exist within the mantles of planets like Uranus and Neptune, but no one had managed to prove its existence in an experiment. Up to now.
The researchers were able to produce super ionic water from a type of high-pressure ice and a series of powerful laser pulses. That combination provided types of temperatures and pressures that we don’t naturally get here on Earth, giving us our first real glimpse of this mysterious water.
“These are very challenging experiments, so it was really exciting to see that we could learn a lot from the data. We spent about two years doing the measurements and two more years developing the methods to analyze the data,” says Marius Millot, co-author of the work publishes Nature Physics.
Water molecules are made of two hydrogen atoms connected to a V-shaped oxygen atom. The weak forces between the molecules become more obvious as they cool, causing them to separate when the water freezes. In superionic water, intense heat breaks the bonds between the atoms of a water molecule , leaving a solid crystalline structure of oxygen atoms and a flow of nuclei or hydrogen ions between them, creating a solid and a liquid at the same time. .
The experiment
To begin, scientists created a special type of ice called h ielo VII, an ice cube structure that occurs at high temperature and pressure and remains solid at room temperature.
In a separate laboratory, laser shock waves lasting between 10 and 20 billionths of a second were sent through the ice, resulting in conditions extreme enough to generate super ionic water. The initial precompression of the ice allowed the researchers to push the ice to very high temperatures before everything vaporized.
By capturing the optical appearance of the ice, the scientists were able to determine that ions rather than electrons were moving in the material due to its opaque rather than shiny appearance.
We now know that superionic ice actually exists and could help explain the rather off-center magnetic fields of Uranus and Neptune, a discrepancy that scientists have narrowed down to the superionic ice sheets within their mantles.
It is also another valuable example of how molecules act under extreme conditions of temperature and pressure and, in the future, we could even design new materials with specific properties by being able to manipulate how molecules react.
It is undoubtedly a turning point in physics.
Reference: Experimental evidence for superionic water ice using shock compression. Nature Physics (2018) doi: 10.1038 / s41567-017-0017-4
Image credit: S. Hamel / M. Millot / J.Wickboldt / LLNL / NI
Visualization of super ionic ice
