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Scientists Propose 18th Known Crystalline Form of Water

A research team from the department of chemistry at the University of Nebraska-Lincoln is ready to introduce to the world the 18th known crystalline form of water that is 25 percent less dense than the last recorded form which was revealed by a European team in 2014.

Xiao Cheng Zeng, an emeritus University Professor of chemistry stated that their team had performed repetitive calculations to confirm whether it is indeed the lowest density form of ice discovered till date. “Ice”, one of the three physical states of water exhibits exceptionally rich and complicated phase diagrams consisting of 17 known crystalline polymorphs. Water itself displays a complex configuration known as ‘clathrate’- an interconnecting cage like structure attributed to the presence of a large number of water molecules and foreign substances such as methane.

The research team

Until now, the inclusion of an external source was highly appreciated while attempting to assemble a stable form of water. However, the UNL team managed to build a clathrate which was able to retain its structure even after removal of the external source. Researchers revealed that construction of the newest ice form requires extensive outward expanding pressure with consistent negative temperature.

It is also essential for the molecules to be in close proximity with each other. At minus-10 Fahrenheit, the system would be subjected to a pressure four times greater than what is experienced inside the Pacific Ocean's deepest trench and at -460 Fahrenheit it would increase to a much greater extent. This would be followed by extracting the guest molecules with the help of a vacuuming process.

Ice's molecular configuration
The team conveyed that their research is relevant to the world as water is the key ingredient for our existence. Manipulating the properties might either have an adverse effect or could be proven beneficial to the society, as claimed by the researchers.

Named as “Ice XVII”, the Monte Carlo packing algorithm and dispersion-corrected density functional theory optimization technique confirmed that the structure consists of two large icosihexahedral cavities (8sup(6)6sup(8)4sup(12)) and six small decahedral cavities (8sup(2)4sup(8)) per unit cell. The group confirmed that their next work will be to take a deeper look inside the molecular structure.

The research was funded and supported by the National Science Foundation and UNL's Holland Computing Center. The complete report of the research was published in the Science Advances journal.

Source: University of Nebraska–Lincoln |Science Advances

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