Ice II The properties of ice II were first described and recorded by
Gustav Tammann in 1900 during his experiments with ice under high pressure and low temperatures. Having produced ice III, Tammann then tried condensing the ice at a temperature between under of pressure. Tammann noted that in this state ice II was denser than he had observed ice III to be. He also found that both types of ice can be kept at normal
atmospheric pressure in a stable condition so long as the temperature is kept at that of
liquid air, which slows the change in conformation back to ice Ih. investigated the phase boundaries of NH4F-doped ices because NH4F has been reported to be a hydrogen disordering reagent. However, adding 2.5 mol% of NH4F resulted in the disappearance of ice II instead of the formation of a disordered ice II. According to the DFC calculation by Nakamura et al., the phase boundary between ice II and its disordered counterpart is estimated to be in the stability region of liquid water.
Ice IV 1981 research by Engelhardt and Kamb elucidated crystal structure of ice IV through a low-temperature single-crystal X-ray diffraction, describing it as a rhombohedral unit cell with a space group of R-3c. This research mentioned that the structure of ice IV could be derived from the structure of ice Ic by cutting and forming some hydrogen bondings and adding subtle structural distortions. Shephard et al. compressed the ambient phase of NH4F, an isostructural material of ice, to obtain NH4F II, whose hydrogen-bonded network is similar to ice IV. As the compression of ice Ih results in the formation of high-density amorphous ice (HDA), not ice IV, they claimed that the compression-induced conversion of ice I into ice IV is important, naming it "Engelhardt–Kamb collapse" (EKC). They suggested that the reason why we cannot obtain ice IV directly from ice Ih is that ice Ih is hydrogen-disordered; if oxygen atoms are arranged in the ice IV structure, hydrogen bonding may not be formed due to the donor-acceptor mismatch. and Raman The disordered nature of Ice IV 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. 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-phase ice XII.
Search for a hydrogen-ordered counterpart The ordered counterpart of ice IV has never been reported yet. 2011 research by Salzmann's group 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.
Ice VII Ice VII is the only disordered phase of ice that can be ordered by simple cooling. (While ice Ih theoretically transforms into proton-ordered ice XI on geologic timescales, in practice it is necessary to add small amounts of KOH catalyst.) It forms (ordered) ice VIII below 273 K up to ~8 GPa. Above this pressure, the VII–VIII transition temperature drops rapidly, reaching 0 K at ~60 GPa. Thus, ice VII has the largest stability field of all of the molecular phases of ice. The cubic oxygen sub-lattices that form the backbone of the ice VII structure persist to pressures of at least 128 GPa; this pressure is substantially higher than that at which water loses its molecular character entirely, forming ice X. In high pressure ices, protonic diffusion (movement of protons around the oxygen lattice) dominates molecular diffusion, an effect which has been measured directly.
Ice XI Ice XI is the hydrogen-ordered form of the ordinary form of ice. The total
internal energy of ice XI is about one sixth lower than ice Ih, so in principle it should naturally form when ice Ih is cooled to below 72
K. The low temperature required to achieve this transition is correlated with the relatively low energy difference between the two structures. Hints of hydrogen-ordering in ice had been observed as early as 1964, when Dengel et al. attributed a peak in thermo-stimulated depolarization (TSD) current to the existence of a proton-ordered ferroelectric phase. However, they could not conclusively prove that a phase transition had taken place, and Onsager pointed out that the peak could also arise from the movement of defects and lattice imperfections. Onsager suggested that experimentalists look for a dramatic change in heat capacity by performing a careful calorimetric experiment. A phase transition to ice XI was first identified experimentally in 1972 by Shuji Kawada and others. Water molecules in ice Ih are surrounded by four semi-randomly directed
hydrogen bonds. Such arrangements should change to the more ordered arrangement of hydrogen bonds found in ice XI at low temperatures, so long as localized proton hopping is sufficiently enabled; a process that becomes easier with increasing pressure. Correspondingly, ice XI is believed to have a
triple point with hexagonal ice and gaseous water at (~72 K, ~0 Pa). Ice Ih that has been transformed to ice XI and then back to ice Ih, on raising the temperature, retains some hydrogen-ordered domains and more easily transforms back to ice XI again. A neutron powder diffraction study found that small hydrogen-ordered domains can exist up to 111 K. There are distinct differences in the Raman spectra between ices Ih and XI, with ice XI showing much stronger peaks in the translational (~230 cm−1), librational (~630 cm−1) and in-phase asymmetric stretch (~3200 cm−1) regions. Ice Ic also has a proton-ordered form. The total internal energy of ice XIc was predicted as similar as ice XIh.
Ferroelectric properties Ice XI is
ferroelectric, meaning that it has an intrinsic polarization. To qualify as a ferroelectric it must also exhibit polarization switching under an electric field, which has not been conclusively demonstrated but which is implicitly assumed to be possible. Cubic ice also has a ferroelectric phase and in this case the ferroelectric properties of the ice have been experimentally demonstrated on monolayer thin films. In a similar experiment, ferroelectric layers of hexagonal ice were grown on a platinum (111) surface. The material had a polarization that had a decay length of 30 monolayers suggesting that thin layers of ice XI can be grown on substrates at low temperature without the use of dopants. One-dimensional nano-confined ferroelectric ice XI was created in 2010.
Ice XV Although the parent phase ice VI was discovered in 1935, corresponding proton-ordered forms (ice XV) had not been observed until 2009. Theoretically, the proton ordering in ice VI was predicted several times; for example,
density functional theory calculations predicted the phase transition temperature is 108 K and the most stable ordered structure is antiferroelectric in the space group
Cc, while an antiferroelectric
P212121 structure were found 4 K per water molecule higher in energy. On 14 June 2009, Christoph Salzmann and colleagues at the University of Oxford reported having experimentally reported an ordered phase of ice VI, named ice XV, and say that its properties differ significantly from those predicted. In particular, ice XV is
antiferroelectric rather than
ferroelectric as had been predicted. In detail, ice XV has a smaller density (larger unit-cell volume) than ice VI. This makes the VI-to-XV disorder-to-order transition much favoured at low pressures. Indeed,
differential scanning calorimetry by Shephard and Salzmann revealed that reheating quench-recovered HCl-doped ice XV at ambient pressure even produces exotherms originating from transient ordering,
i.e. more ordered ice XV is obtained at ambient pressure. Being consistent with this, the ice VI-XV transition is reversible at ambient pressure. It was also shown that HCl-doping is selectively effective in producing ice XV while other acids and bases (HF, LiOH, HClO4, HBr) do not significantly enhance ice XV formations. Based on powder neutron diffraction, the crystal structure of ice XV has been investigated in detail. Some researchers suggested that, in combination with density functional theory calculations, none of the possible perfectly ordered orientational configurations are energetically favoured. This implies that there are several energetically close configurations that coexist in ice XV. They proposed 'the orthorhombic
Pmmn space group as a plausible space group to describe the time-space averaged structure of ice XV. Other researchers argued that
P-1 model is still the best (with the second best candidate of
P21), whereas Rietveld refinement using the Pmmn space group only works well for poorly ordered samples. The lattice parameters, in particular
b and
c, are good indicators of the ice XV formation. Combining density functional theory calculations, they successfully constructed fully ordered model in
P-1 and showed that experimental diffraction data should be analysed using space groups that permit full hydrogen order while the Pmmn model only accepts partially ordered structures.
Ice XVII In 2016, the discovery of a new form of ice was announced. To create ice XVII, the researchers first produced filled ice in a stable phase named C from a mixture of hydrogen (H) and water (HO), using temperatures from and pressures from , and C are all stable solid phases of a mixture of H and HO molecules, formed at high pressures. This was done by heating specifically prepared DO ice XVII powder.
Ice XVIII (superionic water) In 1988, predictions of the so-called superionic water state were made. In superionic water, water molecules break apart and the oxygen ions
crystallize into an evenly spaced lattice while the
hydrogen ions float around freely within the oxygen lattice. The freely mobile hydrogen ions make superionic water almost as
conductive as typical metals, making it a
superionic conductor. The ice appears black in color. and from optical measurements of water shocked by extremely powerful lasers. The first definitive evidence for the crystal structure of the oxygen lattice in superionic water came from x-ray measurements on laser-shocked water which were reported in 2019. , it is theorized that superionic ice can possess two crystalline structures. At pressures in excess of it is predicted that superionic ice would take on a
body-centered cubic structure. However, at pressures in excess of 100 GPa, and temperatures above 2000 K, it is predicted that the structure would shift to a more stable
face-centered cubic lattice. The experiment concluded that the current in the conductive water was indeed carried by ions rather than electrons and thus pointed to the water being superionic. According to their DSC data, the size of the endothermic feature depends not only on quench-recovery pressure but also on the heating rate and annealing duration at 93 K. They also collected neutron diffraction profiles of quench-recovered
deuterium chloride-doped, D2O ice VI/XV prepared at different pressures of 1.0, 1.4 and 1.8 GPa, to show that there were no significant differences among them. They concluded that the low-temperature endotherm originated from kinetic features related to glass transitions of deep glassy states of
disordered ice VI. Distinguishing between the two scenarios (new hydrogen-ordered phase vs. deep-glassy disordered ice VI) became an open question and the debate between the two groups has continued. Thoeny et al. (Loerting's group) collected another series of Raman spectra of ice beta-XV, and reported that (i) ice XV prepared by the protocol reported previously contains both ice XV and ice beta-XV domains; (ii) upon heating, Raman spectra of ice beta-XV showed loss of H-order. In contrast, Salzmann's group again argued for the plausibility of a 'deep-glassy state' scenario based on neutron diffraction and neutron inelastic scattering experiments. Based on their experimental results, ice VI and deep-glassy ice VI share very similar features based on both elastic (diffraction) scattering and inelastic scattering experiments, and are different from the properties of ice XV. In 2021, further crystallographic evidence for a new phase (ice XIX) was individually reported by three groups: Yamane et al. (Hiroyuki Kagi and Kazuki Komatsu's group from Japan), Gasser et al. (Loerting's group), and Salzmann's group. Yamane et al. also collected powder neutron diffractograms of quench-recovered ices VI, XV, and XIX and found similar crystallographic features to those reported by Yamane et al., concluding that P-4 and Pcc2 are the plausible space group candidates. Both Yamane et al.'s and Gasser et al.'s results suggested a partially hydrogen-ordered structure. Gasser et al. also found an isotope effect using DSC; the low-temperature endotherm for DCl-doped D2O ice XIX was significantly smaller than that of HCl-doped H2O ice XIX, and that doping of 0.5% of H2O into D2O is sufficient for the ordering transition. Several months later, Salzmann et al. published a paper based on
in-situ powder neutron diffraction experiments of ice XIX. In a change from their previous reports, they accepted the idea of the new phase (ice XIX) as they observed similar features to the previous two reports. However, they refined their diffraction profiles based on a disordered structural model (Pbcn) and argued that new Bragg reflections can be explained by distortions of ice VI, so ice XIX may still be regarded as a deep-glassy state of ice VI. The crystal structure of ice XIX including hydrogen order/disorder is still under debate as of 2022.
Plastic ice VII Plastic ice VII and suggests potential implications for the internal dynamics and differentiation of icy planets and moons. == Practical implications ==