Water exhibits unusual properties under normal conditions, but its behavior becomes even more complex under extreme pressures and temperatures. A recent study has revealed a new form of superionic ice, created at pressures exceeding 2 million atmospheres and temperatures above 2,000 degrees Celsius. This state of ice is characterized by oxygen atoms arranged in a hexagonal close-packed (hcp) lattice, with hydrogen ions moving freely through the structure, combining solid and liquid properties.
The research team, led by physicist Alexis Forestier from the French Alternative Energies and Atomic Energy Commission, simulated conditions found deep within ice giant planets like Uranus and Neptune. Using diamond anvils to generate pressures up to 230 gigapascals and lasers to heat water samples, they probed the crystal structure with synchrotron X-rays. The experiments confirmed the existence of the hcp phase, distinct from the previously known face-centered cubic (fcc) superionic ice.
As pressure and temperature increased, the ice transitioned from a mixture of fcc and hcp phases to predominantly hcp. This phase shift could influence the electrical conductivity and mechanical properties of superionic ice, factors that are important for understanding the unusual magnetic fields of ice giants. The discovery opens new avenues for theoretical and experimental research to explore the properties of hcp superionic ice and its role in planetary interiors.
These findings, published in Physical Review Letters, enhance our knowledge of water's behavior under extreme conditions and contribute to planetary science by providing insights into the materials composing distant worlds.