French-Led Team Reports Hexagonal Close-Packed Ice Made at 2,357 Degrees Celsius
A French-led team squeezed water between diamond tips at up to 230 gigapascals and laser-heated it to thousands of kelvins, producing hexagonal close-packed ice that showed signs of a superionic state.
In the experiments, the researchers squeezed their water samples between the tips of diamonds, reaching pressures 2.3 million times the atmospheric pressure at Earth's sea level. For comparison, the pressure at the center of Earth is around 360 gigapascals. Lasers were used to heat the compressed samples to thousands of degrees, conditions the team describes as matching those expected in the interiors of the ice giant planets.
The crystal structure of the ice was tracked with an extremely narrow beam of synchrotron X-rays, which probed the samples for changes as they were compressed and heated. What emerged was hexagonal close-packed ice, a configuration that theoretical work had anticipated but that experiments had not previously identified without ambiguity.
As the hexagonal close-packed crystal was heated, its expansion carried a signature of superionic behavior, indicating that it entered the superionic state at roughly 1,700 kelvins. In that state, the material's behavior departs from that of ordinary ice, and its properties are of interest because superionic ice is thought to exist deep inside Uranus and Neptune, where it may play a role in generating those planets' unusual magnetic fields.
The results were published in Physical Review Letters. The work was reported by ScienceAlert and shared on Slashdot on September 12.