Ice I<sub>c</sub> without stacking disorder by evacuating hydrogen from hydrogen hydrate.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 32015342.
- Also identified by DOI 10.1038/s41467-020-14346-5 and PMC identifier 6997176.
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Abstract
Water freezes below 0 °C at ambient pressure ordinarily to ice I<sub>h</sub>, with hexagonal stacking sequence. Under certain conditions, ice with a cubic stacking sequence can also be formed, but ideal ice I<sub>c</sub> without stacking-disorder has never been formed until recently. Here we demonstrate a route to obtain ice I<sub>c</sub> without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C<sub>2</sub>, which has a host framework isostructural with ice I<sub>c</sub>. The stacking-disorder free ice I<sub>c</sub> is formed from C<sub>2</sub> via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations occurring in ice XVI from neon hydrate, or ice XVII from hydrogen hydrate. The obtained ice I<sub>c</sub> shows remarkable thermal stability, until the phase transition to ice I<sub>h</sub> at 250 K, originating from the lack of dislocations. This discovery of ideal ice I<sub>c</sub> will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice I<sub>h</sub>.