How Pressure Generates New Ice Structures

While ice typically forms below 0 °C, extreme pressure can also induce crystallization. At sufficiently high pressures, water can solidify at room temperature—or even above its normal boiling point. For example, when water is compressed beyond 0.96 GPa at room temperature, it transforms into Ice VI.

As water freezes, its hydrogen bonds rearrange in intricate patterns shaped by both pressure and temperature. These molecular shifts give rise to many distinct ice phases.

Figure 1. New Ice XXI Emerges Under Extreme Compression.

Understanding these transitions—and learning to control them under extreme conditions—may eventually allow scientists to create novel materials that don’t naturally exist on Earth. Figure 1 shows New Ice XXI Emerges Under Extreme Compression.

A Century of Charting Ice Phases

Over the last hundred years, scientists have uncovered 20 crystalline forms of ice by tuning pressure and temperature. These phases span an enormous range—over 2,000 K in temperature and more than 100 GPa in pressure. The region between 0 and 2 GPa is especially complex, containing over ten tightly clustered ice phases.

Creating a Supercompressed Liquid

Researchers at the KRISS Space Metrology Group generated a liquid water state that stays stable above 2 GPa at room temperature—more than twice the pressure where crystallization would normally occur. They accomplished this using their custom-built dynamic diamond anvil cell (dDAC), a device engineered for precise, extreme-pressure experimentation.

Standard diamond anvil cells (DACs) raise pressure by tightening bolts, but this approach can introduce mechanical disturbances and uneven compression, often triggering premature crystallization. The KRISS dDAC minimizes mechanical shock and cuts the compression time from tens of seconds to just 10 milliseconds. This rapid, smooth pressurization let researchers push water into the Ice VI pressure range while keeping it in a liquid state.

Capturing the Birth of Ice XXI

Working with international collaborators, the KRISS team combined their dDAC with the European XFEL—the world’s largest X-ray free-electron laser—to track the crystallization of supercompressed water with microsecond precision. The data revealed previously unseen crystallization pathways at room temperature. Every pathway passed through a newly identified phase: Ice XXI, now recognized as the 21st crystalline form of ice.

KRISS scientists also resolved the internal structure of Ice XXI and mapped the pathways leading to its formation. Ice XXI features an unusually large and complex unit cell—the fundamental repeating pattern of its crystal lattice. Its geometry forms a flattened rectangular shape with two base edges of equal length.

A Global Scientific Effort

This breakthrough was made possible through the collaboration of 33 researchers from South Korea, Germany, Japan, the United States, and England, working alongside teams at the European XFEL and DESY. The project was proposed and led by KRISS under the direction of principal investigator Dr. Lee Geun Woo.

Implications for Planetary Science

According to Dr. Lee Yun-Hee, “The density of Ice XXI is comparable to the high-pressure ice layers inside the icy moons of Jupiter and Saturn. This discovery may offer new clues for understanding how life could originate and survive under extreme extraterrestrial conditions.”

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2025), Water Transforms into New Ice XXI Under Extreme Compression, AnaTechMaz, pp. 438