Ice Ic without stacking disorder by evacuating hydrogen from hydrogen hydrate

Kazuki Komatsu, Shinichi Machida, Fumiya Noritake, Takanori Hattori, Asami SanoFurukawa, Ryo Yamane, Keishiro Yamashita & Hiroyuki Kagi

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Oct 02, 2019
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Received Date: 23rd September 19

Water freezes below 0 °C at ambient pressure, ordinarily to ice Ih with an ABAB… hexagonal stacking sequence. However, it is also known to produce “ice Ic” nominally with an ABCABC… cubic stacking sequence under certain conditions1, and its existence in Earth’s atmosphere2-4, or in comets<sup5,6 is debated. “Ice Ic”, or called as cubic ice, was first identified in 1943 by König7, who used electron microscopy to study the condensation of ice from water vapor to a cold substrate. Subsequently, many different routes to “ice Ic” have been established, such as the dissociation of gas hydrates, warming amorphous ices or annealing high-pressure ices recovered at ambient pressure, freezing of μ- or nano-confined water (see refs in 1). Despite the numerous studies on “ice Ic”, its structure has not been fully verified, because the diffraction patterns of “ice Ic” show signatures of stacking-disorder1,8, and ideal ice Ic without stacking-disorder had not been formed until very recently9. Here we demonstrate a route to obtain ice Ic without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C2, which has a host framework that is isostructural with ice Ic10. Surprisingly, the stacking-disorder free ice Ic is formed from C2 via an intermediate amorphous or nano-crystalline form under decompression, unlike the direct transformations that occur in the cases of recently discovered ice XVI11 from neon hydrate, or ice XVII12 from hydrogen hydrate. The obtained ice Ic shows remarkable thermal stability until the phase transition to ice Ih at 250 K; this thermal stability originates from the lack of dislocations, which promote changes in the stacking sequence13. This discovery of ideal ice Ic will promote understanding of the role of stacking-disorder14 on the physical properties of ice as a counter end-member of ice Ih.

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This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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