Paper reports hexagonal ice phase above 200 GPa and 2,000K
Researchers led by Alexis Forestier used a diamond anvil cell and laser heating with synchrotron x-ray diffraction to study water ice at extreme conditions.
Researchers led by Alexis Forestier have published results in Physical Review Letters reporting a hexagonal close-packed (HCP) phase of water ice formed at around 2,000K and pressures above 200 GPa, according to hackaday.com.
The team used a diamond anvil cell with laser heating, combined with synchrotron x-ray diffraction, to study water ice under those conditions. At intermediate pressures they observed a mixed phase containing both face-centered cubic (FCC) and hexagonal close-packed structures.
Water ice is already known to adopt different structures as pressure rises. Above about 80 GPa, it forms ice X, which has a body-centered cubic oxygen sublattice, and the phases discovered after that were face-centered cubic.
What the measurements show
The reported HCP phase adds a hexagonal arrangement to the list of structures observed in water ice at high pressure and temperature. The experiments cover the pressure range where the FCC and HCP structures appear to coexist before giving way to the single hexagonal close-packed phase.
Quick answers
What phase of water ice was reported in the Physical Review Letters paper?
A hexagonal close-packed (HCP) phase, observed at around 2,000K and pressures over 200 GPa.
How did the researchers study the ice?
They used a diamond anvil cell and laser heating together with synchrotron x-ray diffraction.
What is ice X?
A known phase of water ice that forms above about 80 GPa and features a body-centered cubic oxygen sublattice.