A groundbreaking discovery has reshaped our understanding of water ice under extreme conditions. Scientists led by Livia Bove from Sorbonne University have confirmed the existence of “plastic ice VII’.
Initially predicted in 2008, this peculiar phase of ice in which water molecules rotate freely within a body-centered cubic (BCC) structure. This new discovery was made possible through advanced neutron-scattering experiments at the Institut Laue-Langevin in France.
Plastic ice VII forms under extreme pressures exceeding three gigapascals (GPa) and temperatures above 450 Kelvin. While most water ice phases remain fixed, plastic ice VII exhibits molecular rotations, giving it unique properties.
The research team utilized powerful neutron beams and diamond-anvil cells to overcome the challenges of observing this phase in such small, high-pressure samples.
By analyzing neutron diffraction patterns and detecting the energy shifts from scattered neutrons, the researchers observed that plastic ice VII retains a crystalline structure but allows water molecules to rotate.
M. Rescigno et al. [1]; adapted by APS
Interestingly, molecular dynamics simulations confirmed that these rotations are not entirely random but occur between a few favored directions, resembling behaviors seen in certain organic crystals like neopentyl glycol.
This exotic phase, however, occupies a narrow range of temperature and pressure conditions, much more constrained than the broader-known ice VII.
Ice VII is believed to exist between their rocky cores and vast oceans on icy moons such as Jupiter’s Callisto, Ganymede, and Saturn’s Titan.
While the influence of plastic ice VII on the formation or structure of these moons remains uncertain, this discovery opens exciting avenues for understanding extreme planetary environments.
This confirmation of plastic ice VII represents a remarkable leap in studying high-pressure water phases, with implications for planetary science, materials research, and our broader understanding of molecular behavior under intense conditions.
Journal Reference
- Rescigno, M., Toffano, A., Ranieri, U. et al. Observation of Plastic Ice VII by Quasi-Elastic Neutron Scattering. Nature (2025). DOI: 10.1038/s41586-025-08750-4
Source: Tech Explorist
