Ice Ic without stacking disorder by evacuating hydrogen from hydrogen hydrate
Kazuki Komatsu, Shinichi Machida, Fumiya Noritake, Takanori Hattori, Asami Sano-Furukawa, Ryo Yamane, Keishiro Yamashita, Hiroyuki Kagi
Abstract
Abstract Water freezes below 0 °C at ambient pressure ordinarily to ice I h , with hexagonal stacking sequence. Under certain conditions, ice with a cubic stacking sequence can also be formed, but ideal ice I c without stacking-disorder has never been formed until recently. Here we demonstrate a route to obtain ice I c without stacking-disorder by degassing hydrogen from the high-pressure form of hydrogen hydrate, C 2 , which has a host framework isostructural with ice I c . The stacking-disorder free ice I c is formed from C 2 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 c shows remarkable thermal stability, until the phase transition to ice I h at 250 K, originating from the lack of dislocations. This discovery of ideal ice I c will promote understanding of the role of stacking-disorder on the physical properties of ice as a counter end-member of ice I h .