Related Experiment Video
Updated: Jun 13, 2026

Methane Hydrate Crystallization on Sessile Water Droplets
Published on: May 26, 2021
Discovery of a low-density filled-ice phase in nitrogen hydrate at high pressure
Selene Berni1,2,3,4, Sophie Espert5, Tomasz Poręba6
1LENS, European Laboratory for Non-Linear Spectroscopy, Sesto Fiorentino (Firenze), Italy. berni@lens.unifi.it.
Abstract:
Nitrogen, Earth's most abundant atmospheric component, in the presence of water, is known to form clathrate hydrates, that are relevant to model the evolution of water-rich planets and satellites. Here, we map the high-pressure phase diagram of nitrogen hydrate up to 16 GPa at room temperature by combining neutron diffraction, Raman spectroscopy, and crystal structure prediction. We reveal a rich sequence of structural transformations, from sI/sII clathrates to hexagonal (sH) and tetragonal (sT) phases, culminating in a previously unknown orthorhombic filled-ice structure above 1.8 GPa. This new phase cannot be indexed to any known ice frameworks and exhibits a density approximately 30% lower than that of stable ice VII, pointing to distinctive water-nitrogen interactions. Our results refine the understanding of nitrogen hydrate behavior under extreme conditions and demonstrate the propensity of N2 and H2O to form stable filled-ice structures up to 16 GPa, with important implications for planetary science.
Related Concept Videos
Phase Diagrams
Phase Transitions: Sublimation and Deposition
Phase Diagram
Phase Diagram
The Joule and Joule–Thomson Experiments
Aldehydes and Ketones with Water: Hydrate Formation
The formation of hydrates is a reversible reaction. Hydrate formation is influenced by steric and electronic factors accompanying the alkyl substituents on the carbonyl group: The rate of hydrate formation increases with a decrease in the number of alkyl groups attached to the carbonyl carbon. Hence,...

