Is pressure the key to hydrogen ordering ice IV?

Slightly Hydrogen-Ordered State of Ice IV Evidenced by In Situ Neutron Diffraction

“…#3, o 1 showed the largest deviation from 0.5 at 58 K among Exps. #1–3 (Figure ), which is consistent with the previous ex-situ DSC studies suggesting that the low-temperature state is more favored at high pressures; our neutron diffraction results also suggest the hydrogen ordering in ice IV is more pronounced at high pressures.…”

“…It is interesting to investigate the hydrogen-ordering behavior of ice IV not only because it may lead to the discovery of a new phase but also because the hydrogen-disordered structures of ices I and IV have been suggested to be related to the pressure-induced amorphization mechanism of ice I h into high-density amorphous ice (HDA); it was suggested that the local structure of HDA is similar to the structure of ice IV , and HDA is a “derailed” state of the ice I–IV transformation pathway due to hydrogen disorder in these crystalline phases . Quests for a hydrogen-ordered counterpart of ice IV have been made based on ex situ experiments using Raman spectroscopy, differential scanning calorimetry (DSC), , and powder X-ray diffraction techniques by Salzmann and co-workers. They prepared ice IV samples by heating HDA, quenched the samples to liquid nitrogen temperature, and released the pressure to recover them for analyses at ambient pressure.…”

“…These results suggest that there is a low-temperature state related to ice IV that (i) can be obtained only when HCl is doped, (ii) is more favored at higher pressures, and (iii) is not obtained by cooling doped ice IV at ambient pressure. The origin of the endotherms remains unclear as Rosu-Finsen and Salzmann (2021) listed three possible causes to explain the results: hydrogen ordering, orientational glass transition, and release of strain . To better understand the pressure–temperature response of doped ice IV and to corroborate a novel ordered phase if it exists, in situ experiments with high sensitivity to hydrogen ordering are desired.…”

Thermodynamically Stable Intermediate in the Course of Hydrogen Ordering from Ice V to Ice XIII

“…We focus on the limit of long times, i.e., equilibrated conditions, at ambient pressure avoiding the common uncertainty of ex-situ experiments whether or not the observed ice is transient or thermodynamically stable. Such distinguishments were hampered in many studies on ice polymorphs, especially those that include irreversible changes, due to several factors such as pT -dependency in high-pressure preparation (e.g., see refs , , and ).…”

Searching for a hydrogen-ordered counterpart of ice IV through in situ high-pressure powder neutron diffraction experiments

“…Ice IV is a high-pressure metastable phase with a completely hydrogen-disordered crystal structure, but its ordered counterpart has never been reported so far. According to Rosu-Finsen and Salzmann (2021), HCl-doped ice IV produces a weak endotherm in differential scanning calorimetry (DSC) as is quench-recovered to ambient pressure under liquid nitrogen and thereafter heated in a calorimeter [5]. Although this endothermic feature may originate from the order-to-disorder phase transition, other phenomena, such as unfreezing orientational glasses, could also produce such weak endotherms.…”