# UNLV physicists find ice-X distorts into a less symmetric structure above 222 GPa in a diamond anvil cell

- Published: 2026-11-05 21:15 UTC
- Section: Science › Physics
- Tags: ice-X, water under high pressure, 222 GPa, synchrotron X-ray diffraction, diamond anvil cell, Pbcm symmetry, icy giants Uranus Neptune, University of Nevada Las Vegas, Communications Chemistry
- URL: https://realtech.media/news/rt-379e2ed633acd6be3ad57963_unlv_physicists_find/

**In diamond-anvil experiments with X-ray diffraction, water ice-X lost its cubic symmetry at 222(12) GPa, which redefines the upper stability limit of this phase.**

![UNLV physicists find ice-X distorts into a less symmetric structure above 222 GPa in a diamond anvil cell](https://sgzwpqqelzmajkcubgkl.supabase.co/storage/v1/object/public/rt-media/2026/11/cab4ada00f652d25.jpg)
*José A. Flores-Livas, Lilia Boeri, Antonio Sanna, Gianni Profeta, Ryotaro Arita, Mikhail E, Wikimedia Commons, CC BY 4.0*

Physicists from the University of Nevada, Las Vegas, compressed water between diamond anvils and recorded a change in its atomic structure above 222(12) GPa, about 2.2 million times standard atmospheric pressure at sea level. The work was published in Communications Chemistry. According to the authors, ice-X transforms into a less symmetric structure at this pressure [1].

Water governs the structure and dynamics of icy planets and, through the pressure-induced transition from hydrogen to ionic bonding, changes markedly across the pressure range of planetary interiors [1]. Researchers therefore study its state under conditions found in the interiors of bodies such as Uranus and Neptune.

## Experiment and diffraction data

The structure was probed with synchrotron X-ray diffraction. Many materials are expected to favour simple, densely packed lattices under growing compression, and ice-X follows this pattern in the form of a cubic lattice with hydrogen atoms positioned symmetrically between oxygen atoms. In this experiment, however, the cubic lattice became distorted [1].

The diffraction data are consistent with either Pbcm or P4₂/nnm symmetry. Ab initio calculations strongly favour the Pbcm variant, according to the report [1]. The diffraction data alone do not choose between the two candidates.

## Upper limit of ice-X stability

The authors state that the transition marks the onset of a new regime of structural complexity in high-pressure H₂O and redefines the upper stability limit of ice-X [1]. Such behaviour has been seen in other elements: the complex hP4 phase of sodium is cited as an example of unexpected structural complexity at extreme pressures [1].

The NV Techno account of the study adds that the lattice stretched and became asymmetric instead of forming a denser, more symmetric arrangement. The outlet links such a deformation to properties of planetary matter, including thermal conductivity and density. These links are the outlet's interpretation and are not part of the original abstract.

The result comes from a laboratory experiment on a small sample of water under static compression. The reported transition pressure is 222 GPa with an uncertainty of 12 GPa [1].

## Sources

1. [Communications Chemistry](https://doi.org/10.1038/s42004-026-02241-x)
2. [NV Техно](https://techno.nv.ua/ukr/popscience/voda-pid-visokim-tiskom-novu-strukturu-atomiv-vidkrili-amerikanski-vcheni-50656540.html)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-379e2ed633acd6be3ad57963_unlv_physicists_find/