Preparation
Several organic nucleating reagents had been proposed to selectively crystallize ice IV from liquid water, but even with such reagents, the crystallization of ice IV from liquid water was very difficult and seemed to be a random event. In 2001, Salzmann and his coworkers reported a whole new method to prepare ice IV ''reproducibly''; when high-density amorphous ice (HDA) is heated at a rate of 0.4 K/min and a pressure of 0.81 GPa, ice IV is crystallized at about 165 K. What governs the crystallization products is the heating rate; fast heating (over 10 K/min) results in the formation of single-phaseCrystal structure
The crystal structure of ice IV was elucidated by Engelhardt and Kamb in 1981 by low-temperature single-crystal X-ray diffraction. Its structure is described by a rhombohedral unit cell with a space group of R-3c. The hydrogen geometry had been suggested to be completely disordered as IR and Raman spectra consist only of broad peaks, and the disordered nature was confirmed by neutron powder diffraction studies by Lobban (1998) and Klotz et al. (2003).. In addition, the entropy difference between ice VI (disordered phase) and ice IV is very small according to Bridgman's measurement.Engelhardt-Kamb Collapse (EKC)
Engelhardt and Kamb mentioned in the paper in 1981 that the structure of ice IV could be derived from the structure ofQuest for hydrogen ordering
As discussed above, ice IV is a hydrogen-disordered phase. Its ordered counterpart, however, has never been reported yet. Salzmann et al. (2011) reported the DSC thermograms of HCl-doped ice IV finding an endothermic feature at about 120 K. Ten years later, Rosu-Finsen and Salzmann (2021) reported more detailed DSC data where the endothermic feature becomes larger as the sample is quench-recovered at higher pressure. They proposed three scenarios to explain the experimental results: weak hydrogen-ordering, orientational glass transition, and mechanical distortions.References
{{Ice , expanded Water ice