Scientists have announced the discovery of a new type of ice, designated as ice XXI, which forms under specific conditions at room temperature. This findings come from researchers at the Korea Research Institute of Standards and Science (KRISS), who used advanced technology to explore the behavior of super-compressed water.
Traditionally, ice is viewed simply as frozen water, yet it can adopt over 20 distinct forms, each with unique internal structures. While some ice types are familiar, like those found in freezers, others emerge only under extreme pressure, as observed in Earth”s mantle or on icy moons in the solar system. The new ice XXI challenges established concepts about ice formation.
The research team employed a sophisticated setup that combined diamond anvils and X-ray lasers to examine how water behaves when subjected to significant pressure at ambient temperatures. Surprisingly, they found that instead of transitioning to ice in a single step, the water underwent multiple freeze-melt cycles, leading to the formation of ice XXI within the pressure range typical for ice VI.
What sets ice XXI apart from the other known ice types is its distinctive atomic structure. This new form is classified as metastable, which means it can exist temporarily in an unstable state. This characteristic provides valuable insights into the processes that lead to ice formation under pressure, which is crucial for understanding conditions on icy planets and deep Earth environments.
“Rapid compression of water allows it to remain liquid at higher pressures, where it would typically crystallize into ice VI,” explained Geun Woo Lee, a scientist at KRISS. To create the high-pressure conditions necessary for the experiment, the researchers utilized diamond anvil cells, loading ultra-pure water into a tiny metal chamber.
Utilizing a combination of high-speed cameras, laser-based sensors, and real-time monitoring tools, the team meticulously tracked the transitions of water as it froze and melted at room temperature. By adjusting the pressure dynamically, they captured detailed snapshots of the transformation, observing changes in structure and volume with remarkable precision.
To determine the precise moment of transition from liquid water to the exotic ice form, the scientists leveraged powerful X-ray beams from a synchrotron facility. They analyzed the scattered X-ray signals using a specialized detection program, adjusting the pressure rhythm to align with the freezing process. This intricate setup allowed them to unveil the complex transformation pathways of water.
In their findings, the researchers also conducted molecular dynamics simulations employing two models: SPCfw and TIP4P/Ice. These simulations revealed that water does not freeze in a straightforward manner when subjected to super-compression; rather, it undergoes a series of freeze-melt loops before stabilizing into ice VI. Intriguingly, they discovered that within this pressure range, ice XXI emerges.
Ice XXI forms at approximately 1.6 gigapascals and features a body-centered tetragonal crystal structure. This new ice type possesses more energy than MS-ice VII at room temperature, indicating a lower stability, though the difference is minimal. Notably, ice XXI is unique in its ability to transform into MS-ice VII, a transition that ordinary water cannot achieve.
The implications of this research extend beyond ice formations on Earth. By revealing multiple crystallization pathways for water, the study, published in Nature Materials, enhances our understanding of the complex behaviors of ice and could provide new insights regarding the composition of icy moons, potentially shaping future explorations of extraterrestrial environments.
