Superionic water

Superionic water, also called superionic ice or ice XVIII is a phase of water that exists at extremely high temperatures and pressures. In superionic water, water molecules break apart and the oxygen ions crystallize into an evenly spaced lattice while the hydrogen ions float around freely within the oxygen lattice. The freely mobile hydrogen ions make superionic water almost as conductive as typical metals, making it a superionic conductor. It is one of the 19 known crystalline phases of ice. Superionic water is distinct from ionic water, which is a hypothetical liquid state characterized by a disordered soup of hydrogen and oxygen ions. While theorized for decades, it was not until the 1990s that the first experimental evidence emerged for superionic water. Initial evidence came from optical measurements of laser-heated water in a diamond anvil cell, and from optical measurements of water shocked by extremely powerful lasers. The first definitive evidence for the crystal structure of the oxygen lattice in superionic water came from x-ray measurements on laser-shocked water which were reported in 2019. If it were present on the surface of the Earth, superionic ice would rapidly decompress. In May 2019, scientists at the Lawrence Livermore National Laboratory (LLNL) were able to synthesize superionic ice, confirming it to be almost four times as dense as normal ice and black in color. Superionic water is theorized to be present in the mantles of giant planets such as Uranus and Neptune. it is theorized that superionic ice can possess two crystalline structures. At pressures in excess of it is predicted that superionic ice would take on a body-centered cubic structure. However, at pressures in excess of , and temperatures above 3,140 degrees Fahrenheit, it is predicted that the structure would shift to a more stable face-centered cubic lattice. The ice appears black in color. Demontis et al. made the first prediction for superionic water using classical molecular dynamics simulations in 1988. In 1999, Cavazzoni et al.