World’s largest X-ray laser discovers never-before-seen type of ice that is solid at room temperature

Scientists squeezed water between two diamonds and created an entirely new form of ice that is solid at room temperature.

The ice, named Ice XXI, forms when water is exposed to extreme pressure and becomes metastable, an unstable state that becomes physically unstable with the slightest disturbance.

The researchers created Ice XXI by hypercompressing water between two diamonds and detected it with the world’s largest X-ray laser, the European X-ray Free Electron Laser (XFEL). The research team discovered that supercompressed water undergoes a structural change from a dense state to an ultra-dense state.

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The discovery could have implications for space exploration, opening up new ways in which ice could form on other worlds, according to a study published Oct. 10 in the journal Nature Materials.

“Our findings suggest the possible existence of more high-temperature metastable ice phases and associated transition paths, and may provide new insights into the composition of icy satellites,” study co-author Rachel Husband, a postdoctoral fellow at the German Center for Electron Synchrotron Research, said in a statement.

Ice XXI, Roman numeral 21, is the 21st known ice phase. Others include tetrahedral crystals of ice XIX and star-hot superionic ice. Water can exist in different solid state forms thanks to its molecular structure, in which bifurcated hydrogen atoms solidify into different crystalline and amorphous structures.

Scientists have discovered many water-ice transition pathways by applying pressure to water at low temperatures, where molecules are slower, but expect ice diversity to decrease at higher temperatures, where molecules have more kinetic energy.

In the new study, researchers investigated the path of ice transition at room temperature, around 72 degrees Fahrenheit (22 degrees Celsius). The researchers used a diamond anvil cell, a device that takes advantage of diamond’s extreme hardness to apply enormous pressure to the material. In this case, the water was subjected to about 20,000 times more pressure than normal air on Earth, forcing the H2O molecules to bond together until they became very compact and formed a solid structure. XFEL scanned the sample every millionth of a second (1 microsecond) and tracked how its structure changed.

“Europe’s XFEL’s unique X-ray pulses revealed multiple crystallization pathways in H2O that was rapidly compressed and depressurized over 1,000 times using a dynamic diamond anvil cell,” study co-author Geun Woo Lee, a researcher at the Korea Institute of Standards and Science (KRISS), said in a statement.