View source for Phases of ice

{{Short description|States of matter for water as a solid}}
{{lead too short|date=May 2024}}
[[File:Phase diagram of water.svg|thumb|[[Semi-log plot|Log-lin]] pressure-temperature [[phase diagram]] of water. The [[Roman numeral]]s correspond to some ice phases listed below.]]

Variations in pressure and temperature give rise to different phases of [[ice]], which have varying properties and molecular geometries. Currently, twenty-one phases, including both crystalline and [[Amorphous solid|amorphous]] ices have been observed. In modern history, phases have been discovered through scientific research with various techniques including pressurization, force application, nucleation agents, and others.

On Earth, most ice is found in the hexagonal Ice I<sub>h</sub> phase. Less common phases may be found in the atmosphere and underground due to more extreme pressures and temperatures. Some phases are manufactured by humans for nano scale uses due to their properties. In space, amorphous ice is the most common form as confirmed by observation. Thus, it is theorized to be the most common phase in the universe. Various other phases could be found naturally in astronomical objects.

== Theory ==

Most liquids under increased pressure freeze at ''higher'' temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than {{convert|1|atm|MPa|abbr=on}}, water freezes at a temperature ''below'' 0&nbsp;°C. Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases. With care, at least fifteen of these phases (one of the known exceptions being ice X) can be recovered at ambient pressure and low temperature in [[metastable]] form.<ref>{{cite journal|last=La Placa|first=S. J.|author2=Hamilton, W. C.|author3=Kamb, B.|author4=Prakash, A.|year=1972|title=On a nearly proton ordered structure for ice IX|journal=Journal of Chemical Physics|volume=58|issue=2|pages=567–580|doi=10.1063/1.1679238|bibcode = 1973JChPh..58..567L }}</ref><ref>{{cite journal|last=Klotz|first=S.|author2=Besson, J. M.|author3=Hamel, G.|author4=Nelmes, R. J.|author5=Loveday, J. S.|author6=Marshall, W. G.|year=1999|title=Metastable ice VII at low temperature and ambient pressure|journal=Nature|volume=398|issue=6729|pages=681–684|doi=10.1038/19480|bibcode = 1999Natur.398..681K |s2cid=4382067}}</ref> The types are differentiated by their crystalline structure, proton ordering,<ref>{{cite web|url=https://www.uwgb.edu/dutchs/Petrology/Ice%20Structure.HTM|title=Ice Structure|last=Dutch|first=Stephen|publisher=University of Wisconsin Green Bay|access-date=12 July 2017|url-status=dead|archive-url=https://web.archive.org/web/20161016143124/http://www.uwgb.edu/dutchs/petrology/Ice%20Structure.HTM|archive-date=16 October 2016}}</ref> and density. There are also two [[metastable]] phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII.

== Crystal structure ==

[[Image:cryst struct ice.png|thumb|250px|Crystal structure of ice I<sub>h</sub>. Dashed lines represent hydrogen  bonds]]
[[File:Icexii-ru.jpg|thumb|250px|The crystal structure of ice XII]]
The accepted [[crystal structure]] of ordinary ice was first proposed by [[Linus Pauling]] in 1935. The structure of ice I<sub>h</sub> is the [[Wurtzite (crystal structure)|wurtzite lattice]], roughly one of crinkled planes composed of [[tessellation|tessellating]] hexagonal rings, with an [[oxygen]] atom on each vertex, and the edges of the rings formed by [[hydrogen bond]]s. The planes alternate in an ABAB pattern, with B planes being reflections of the A planes along the same axes as the planes themselves.<ref name=bjerrum>{{cite journal|last=Bjerrum|first=N|title=Structure and Properties of Ice|journal=Science|date=11 April 1952|volume=115|issue=2989|pages=385–390|doi=10.1126/science.115.2989.385|pmid=17741864|bibcode = 1952Sci...115..385B }}</ref> The distance between oxygen atoms along each bond is about 275&nbsp;[[picometre|pm]] and is the same between any two bonded oxygen atoms in the lattice. The angle between bonds in the crystal lattice is very close to the [[tetrahedral angle]] of 109.5°, which is also quite close to the angle between hydrogen atoms in the water molecule (in the gas phase), which is 105°.

This tetrahedral bonding angle of the water molecule essentially accounts for the unusually low density of the crystal lattice – it is beneficial for the lattice to be arranged with tetrahedral angles even though there is an energy penalty in the increased volume of the crystal lattice. As a result, the large hexagonal rings leave almost enough room for another water molecule to exist inside. This gives naturally occurring ice its rare property of being less dense than its liquid form. The tetrahedral-angled hydrogen-bonded hexagonal rings are also the mechanism that causes liquid water to be densest at 4&nbsp;°C. Close to 0&nbsp;°C, tiny hexagonal ice I<sub>h</sub>-like lattices form in liquid water, with greater frequency closer to 0&nbsp;°C.  This effect decreases the density of the water, causing it to be densest at 4&nbsp;°C when the structures form infrequently.

In the best-known form of ice, ice I<sub>h</sub>, the crystal structure is characterized by the oxygen atoms forming [[Hexagonal crystal family|hexagonal symmetry]] with near [[tetrahedral]] bonding angles. This structure is stable down to {{convert|-268|C|K F|0}}, as evidenced by x-ray diffraction<ref name=Rottger>{{cite journal|first1=K. |last1=Rottger |first2=A. |last2=Endriss |first3=J. |last3=Ihringer |first4=S. |last4=Doyle |first5=W. F. |last5=Kuhs|title=Lattice Constants and Thermal Expansion of H<sub>2</sub>O and D<sub>2</sub>O Ice I<sub>h</sub> Between 10 and 265 K |journal=Acta Crystallogr. |year=1994 |volume= B50 |issue=6 |pages=644–648 |doi=10.1107/S0108768194004933|bibcode=1994AcCrB..50..644R }}</ref> and extremely high resolution thermal expansion measurements.<ref name=Buckingham>{{cite journal|author=David T. W. Buckingham, J. J. Neumeier, S. H. Masunaga, and Yi-Kuo Yu|title=Thermal Expansion of Single-Crystal H<sub>2</sub>O and D<sub>2</sub>O Ice Ih|journal=Physical Review Letters |year=2018 |volume=121 |issue=18|pages=185505 |doi=10.1103/PhysRevLett.121.185505 |pmid=30444387|bibcode=2018PhRvL.121r5505B|doi-access=free}}</ref> Ice I<sub>h</sub> is also stable under applied pressures of up to about {{convert|210|MPa|atm}} where it transitions into ice III or ice II.<ref>{{cite journal|author=P. W. Bridgman|title=Water, in the Liquid and Five Solid Forms, under Pressure |journal=Proceedings of the American Academy of Arts and Sciences |year=1912 |volume=47 |issue=13 |pages=441–558 |doi=10.2307/20022754 |jstor=20022754 }}</ref>

=== Amorphous ice ===

While most forms of ice are crystalline, several amorphous (or "vitreous") forms of ice also exist. Such ice is an [[amorphous solid]] form of water, which lacks long-range order in its molecular arrangement. Amorphous ice is produced either by [[supercooling|rapid cooling]] of liquid water to its [[glass transition temperature]] (about 136&nbsp;K or −137&nbsp;°C) in milliseconds (so the molecules do not have enough time to form a [[Crystal structure|crystal lattice]]), or by compressing ordinary ice at low temperatures. The most common form on Earth, low-density ice, is usually formed in the laboratory by a slow accumulation of water vapor molecules ([[physical vapor deposition]]) onto a very smooth [[metal]] crystal surface under 120&nbsp;K. In [[outer space]] it is expected to be formed in a similar manner on a variety of cold substrates, such as dust particles.<ref>{{cite journal|doi=10.1126/science.1061757|pmid=11743196|title=Estimation of water-glass transition temperature based on hyperquenched glassy water experiments|first3=C. A.|last3=Angell|first2=S|year=2001|last2=Borick|last1=Velikov|first1=V.|journal=Science|volume=294|issue=5550|pages=2335–8|bibcode = 2001Sci...294.2335V |s2cid=43859537 }}</ref> By contrast, '''hyperquenched glassy water''' (HGW) is formed by spraying a fine mist of water droplets into a liquid such as propane around 80&nbsp;K, or by hyperquenching fine [[micrometer (unit)|micrometer]]-sized droplets on a sample-holder kept at [[liquid nitrogen]] temperature, 77&nbsp;K, in a vacuum. Cooling rates above 10<sup>4</sup>&nbsp;K/s are required to prevent crystallization of the droplets. At liquid nitrogen temperature, 77&nbsp;K, HGW is kinetically stable and can be stored for many years.

Amorphous ices have the property of suppressing long-range density fluctuations and are, therefore, nearly [[Hyperuniformity|hyperuniform]].<ref>{{Cite journal |last1=Martelli |first1=Fausto |last2=Torquato |first2=Salvatore |last3=Giovambattista |first3=Nicolas |last4=Car |first4=Roberto |date=2017-09-29 |title=Large-Scale Structure and Hyperuniformity of Amorphous Ices |url=https://link.aps.org/doi/10.1103/PhysRevLett.119.136002 |journal=Physical Review Letters |volume=119 |issue=13 |pages=136002 |doi=10.1103/PhysRevLett.119.136002|pmid=29341697 |s2cid=44864111 |arxiv=1705.09961 |bibcode=2017PhRvL.119m6002M }}</ref>  [[Statistical classification|Classification]] analysis  suggests that low and high density amorphous ices are [[glass]]es.<ref>{{Cite journal |last1=Martelli |first1=Fausto |last2=Leoni |first2=Fabio |last3=Sciortino |first3=Francesco |last4=Russo |first4=John |date=2020-09-14 |title=Connection between liquid and non-crystalline solid phases in water |url=https://aip.scitation.org/doi/10.1063/5.0018923 |journal=The Journal of Chemical Physics |volume=153 |issue=10 |pages=104503 |doi=10.1063/5.0018923 |pmid=32933306 |bibcode=2020JChPh.153j4503M |hdl=11573/1440448 |s2cid=221746507 |issn=0021-9606|hdl-access=free }}</ref>

== Pressure-dependent states ==

[[File:Water phase diagram extended to negative pressurs.png|thumb|Water phase diagram extended to negative pressures calculated with TIP4P/2005 model.<ref name="conde2009"/>]]

Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of {{convert|50|GPa|psi|abbr=on}} such ''superionic ice'' would take on a [[body-centered cubic]] structure. However, at pressures in excess of {{convert|100|GPa|psi|abbr=on}} the structure may shift to a more stable [[face-centered cubic]] lattice. Some estimates suggest that at an extremely high pressure of around {{convert|1.55|TPa|psi|abbr=on}}, ice would develop [[metal]]lic properties.<ref>{{cite journal |last1=Militzer |first1=Burkhard |last2=Wilson |first2=Hugh F. |title=New Phases of Water Ice Predicted at Megabar Pressures |journal=Physical Review Letters |date=2 November 2010 |volume=105 |issue=19 |page=195701 |doi=10.1103/PhysRevLett.105.195701 |pmid=21231184 |arxiv=1009.4722 |bibcode=2010PhRvL.105s5701M |s2cid=15761164 }}</ref>

== Heat and entropy ==
[[File:3D representation of several phases of water.jpg|thumb|An alternative formulation of the phase diagram for certain ices and other phases of water<ref>{{cite journal |last1=David |first1=Carl |title=Verwiebe's '3-D' Ice phase diagram reworked |journal=Chemistry Education Materials |date=8 August 2016 |url=https://opencommons.uconn.edu/chem_educ/94/ }}</ref>]]
Ice, water, and [[water vapour]] can coexist at the [[triple point]], which is exactly {{cvt|273.16|K|C}} at a pressure of 611.657&nbsp;[[Pascal (unit)|Pa]].<ref>{{cite journal |last1=Wagner |first1=Wolfgang |last2=Saul |first2=A. |last3=Pruss |first3=A. |title=International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance |journal=Journal of Physical and Chemical Reference Data |date=May 1994 |volume=23 |issue=3 |pages=515–527 |doi=10.1063/1.555947 |bibcode=1994JPCRD..23..515W }}</ref><ref>{{cite journal|doi=10.1256/qj.04.94 | volume=131 | issue=608 | title=Review of the vapour pressures of ice and supercooled water for atmospheric applications | year=2005 | journal=Quarterly Journal of the Royal Meteorological Society | pages=1539–1565 | last1 = Murphy | first1 = D. M.| bibcode=2005QJRMS.131.1539M | s2cid=122365938 | url=https://zenodo.org/record/1236243 | doi-access=free }}</ref> The [[kelvin]] was defined as {{sfrac|1|273.16}} of the difference between this triple point and [[absolute zero]],<ref>{{cite web|url=http://www1.bipm.org/en/si/base_units/|title=SI base units|publisher=Bureau International des Poids et Mesures|access-date=31 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120716202131/http://www.bipm.org/en/si/base_units/|archive-date=16 July 2012}}</ref> though this definition [[2019 revision of the SI|changed]] in May 2019.<ref>{{cite web |url=https://www.bipm.org/utils/common/pdf/SI-statement.pdf |title=Information for users about the proposed revision of the SI |publisher=Bureau International des Poids et Mesures |access-date=6 January 2019 |archive-date=21 January 2018 |archive-url=https://web.archive.org/web/20180121160000/https://www.bipm.org/utils/common/pdf/SI-statement.pdf |url-status=dead }}</ref> Unlike most other solids, ice is difficult to [[Superheating|superheat]]. In an experiment, ice at −3&nbsp;°C was superheated to about 17&nbsp;°C for about 250 [[picosecond]]s.<ref>{{cite journal|journal=Nature|volume=439|pages=183–186|year=2006| doi=10.1038/nature04415|pmid=16407948|title=Ultrafast superheating and melting of bulk ice|bibcode=2006Natur.439..183I|last1=Iglev|first1=H.|last2=Schmeisser|first2=M.|last3=Simeonidis|first3=K.|last4=Thaller|first4=A.|last5=Laubereau|first5=A.|issue=7073|s2cid=4404036}}</ref>
[[Image:Melting curve of water.svg|thumb|Pressure dependence of ice melting]]
The latent [[heat of melting]] is {{val|5987|u=J|up=mol}}, and its latent [[heat of sublimation]] is {{val|50911|u=J|up=mol}}. The high latent heat of sublimation is principally indicative of the strength of the [[hydrogen bond]]s in the crystal lattice. The latent heat of melting is much smaller, partly because liquid water near 0&nbsp;°C also contains a significant number of hydrogen bonds. By contrast, the structure of ice II is hydrogen-ordered, which helps to explain the entropy change of 3.22&nbsp;J/mol when the crystal structure changes to that of ice I. Also, ice XI, an orthorhombic, hydrogen-ordered form of ice I<sub>h</sub>, is considered the most stable form at low temperatures.

The transition entropy from ice XIV to ice XII is estimated to be 60% of Pauling entropy based on DSC measurements.<ref name="pmid29923547">{{cite journal| author=Köster KW, Fuentes-Landete V, Raidt A, Seidl M, Gainaru C, Loerting T | display-authors=etal| title=Author Correction: Dynamics enhanced by HCl doping triggers 60% Pauling entropy release at the ice XII-XIV transition. | journal=Nat Commun | year= 2018 | volume= 9 | issue=  | pages= 16189 | pmid=29923547 | doi=10.1038/ncomms16189 | pmc=6026910 | bibcode=2018NatCo...916189K}}</ref> The formation of ice XIV from ice XII is more favoured at high pressure.<ref name="pmid30101255">{{cite journal| author1=Fuentes-Landete V|author2= Köster KW|author3= Böhmer R|author4=Loerting T|author4-link=Thomas Loerting| title=Thermodynamic and kinetic isotope effects on the order-disorder transition of ice XIV to ice XII. | journal=Phys Chem Chem Phys | year= 2018 | volume= 20 | issue= 33 | pages= 21607–21616 | pmid=30101255 | doi=10.1039/c8cp03786h | pmc= |bibcode= 2018PCCP...2021607F|s2cid= 51969440| doi-access=free}}</ref>

When medium-density amorphous ice is compressed, released and then heated, it releases a large amount of heat energy, unlike other water ices which return to their normal form after getting similar treatment.<ref name="Nature2023" />

=== Hydrogen disorder ===
{{see also|Ice rules|Geometrical frustration#Water ice}}{{anchor|proton disorder}}
[[File:Wurtzite-boat-chair.png|thumb|The Wurtzite structure. In Ice I<sub>h</sub>, the oxygen atoms are arranged on the lattice points, and the hydrogen atoms are on the bonds between lattice points. Each oxygen atom has 4 neighboring ones. Note that the lattice bipartites into two subsets, here colored black and white.]]
The [[hydrogen]] atoms in the crystal lattice lie very nearly along the hydrogen bonds, and in such a way that each water molecule is preserved. This means that each oxygen atom in the lattice has two hydrogens adjacent to it: at about 101&nbsp;pm along the 275&nbsp;pm length of the bond for ice Ih. The crystal lattice allows a substantial amount of disorder in the positions of the hydrogen atoms frozen into the structure as it cools to absolute zero. As a result, the crystal structure contains some [[residual entropy]] inherent to the lattice and determined by the number of possible configurations of hydrogen positions that can be formed while still maintaining the requirement for each oxygen atom to have only two hydrogens in closest proximity, and each H-bond joining two oxygen atoms having only one hydrogen atom.<ref name=bernal>{{cite journal|last1=Bernal|first1=J. D.|last2=Fowler |first2=R. H.|title=A Theory of Water and Ionic Solution, with Particular Reference to Hydrogen and Hydroxyl Ions|journal=The Journal of Chemical Physics|date=1 January 1933|volume=1|issue=8|pages=515|doi=10.1063/1.1749327|bibcode=1933JChPh...1..515B}}</ref> This residual entropy {{math|{{var|S}}{{sub|0}}}} is equal to 3.4±0.1&nbsp;J&nbsp;mol<sup>−1</sup>&nbsp;K<sup>−1</sup> <math>=R\ln(1.50 \pm 0.02)</math>.<ref>{{Cite journal |last1=Berg |first1=Bernd A. |last2=Muguruma |first2=Chizuru |last3=Okamoto |first3=Yuko |date=2007-03-21 |title=Residual entropy of ordinary ice from multicanonical simulations |url=https://link.aps.org/doi/10.1103/PhysRevB.75.092202 |journal=Physical Review B |language=en |volume=75 |issue=9 |page=092202 |doi=10.1103/PhysRevB.75.092202 |issn=1098-0121|arxiv=cond-mat/0609211 |bibcode=2007PhRvB..75i2202B }}</ref>

=== Calculations ===
There are various ways of approximating this number from first principles. The following is the one used by [[Linus Pauling]].<ref>{{cite journal |last=Pauling |first=Linus |author-link=Linus Pauling |date=1 December 1935 |title=The Structure and Entropy of Ice and of Other Crystals with Some Randomness of Atomic Arrangement |journal=Journal of the American Chemical Society |volume=57 |issue=12 |pages=2680–2684 |doi=10.1021/ja01315a102|bibcode=1935JAChS..57.2680P }}</ref><ref>{{Cite book |last1=Petrenko |first1=Victor F. |url=http://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780198518945.001.0001/acprof-9780198518945 |title=Physics of Ice |last2=Whitworth |first2=Robert W. |date=2002-01-17 |publisher=Oxford University Press |isbn=978-0-19-851894-5 |chapter=2. Ice Ih |doi=10.1093/acprof:oso/9780198518945.003.0002}}</ref>

Suppose there are a given number {{mvar|N}} of water molecules in an ice lattice. To compute its residual entropy, we need to count the number of configurations that the lattice can assume. The oxygen atoms are fixed at the lattice points, but the hydrogen atoms are located on the lattice edges. The problem is to pick one end of each lattice edge for the hydrogen to bond to, in a way that still makes sure each oxygen atom is bond to two hydrogen atoms.

The oxygen atoms can be divided into two sets in a checkerboard pattern, shown in the picture as black and white balls. Focus attention on the oxygen atoms in one set: there are {{math|{{var|N}}/2}} of them. Each has four hydrogen bonds, with two hydrogens close to it and two far away. This means there are <math display="inline">\tbinom 4 2 = 6</math> allowed configurations of hydrogens for this oxygen atom (see [[Binomial coefficient]]). Thus, there are {{math|6{{sup|{{var|N}}/2}}}} configurations that satisfy these {{math|{{var|N}}/2}} atoms. But now, consider the remaining {{math|{{var|N}}/2}} oxygen atoms: in general they won't be satisfied (i.e., they will not have precisely two hydrogen atoms near them). For each of those, there are {{math|2{{sup|4}} {{=}} 16}} possible placements of the hydrogen atoms along their hydrogen bonds, of which 6 are allowed.  So, naively, we would expect the total number of configurations to be
<math display="block">6^{N/2} (6/16)^{N/2} = (3/2)^N .</math>

Using [[Boltzmann's entropy formula]], we conclude that
<math display="block">S_0 = k\ln(3/2)^N = n R \ln(3/2),</math>where {{mvar|k}} is the [[Boltzmann constant]] and R is the [[molar gas constant]]. So, the molar residual entropy is <math>R \ln(3/2) = 3.37 \mathrm{J}\cdot\mathrm{mol}^{-1}\mathrm{K}^{-1}</math>.

The same answer can be found in another way. First orient each water molecule randomly in each of the 6 possible configurations, then check that each lattice edge contains exactly one hydrogen atom. Assuming that the lattice edges are independent, then the probability that a single edge contains exactly one hydrogen atom is 1/2, and since there are 2N edges in total, we obtain a total configuration count <math>6^N \times (1/2)^{2N} = (3/2)^N </math>, as before.

=== Refinements ===
[[File:Iceviiistructure-ru.gif|thumb|The crystal structure of ice VIII]]
This estimate is 'naive', as it assumes the six out of 16 hydrogen configurations for oxygen atoms in the second set can be independently chosen, which is false. More complex methods can be employed to better approximate the exact number of possible configurations, and achieve results closer to measured values. Nagle (1966) used a series summation to obtain <math>R\ln(1.50685 \pm 0.00015)</math>.<ref>{{Cite journal |last=Nagle |first=J. F. |date=1966-08-01 |title=Lattice Statistics of Hydrogen Bonded Crystals. I. The Residual Entropy of Ice |url=https://pubs.aip.org/jmp/article/7/8/1484/382171/Lattice-Statistics-of-Hydrogen-Bonded-Crystals-I |journal=Journal of Mathematical Physics |language=en |volume=7 |issue=8 |pages=1484–1491 |doi=10.1063/1.1705058 |bibcode=1966JMP.....7.1484N |issn=0022-2488}}</ref>

As an illustrative example of refinement, consider the following way to refine the second estimation method given above. According to it, six water molecules in a hexagonal ring would allow <math>6^6 \times (1/2)^6 = 729</math> configurations. However, by explicit enumeration, there are actually 730 configurations. Now in the lattice, each oxygen atom participates in 12 hexagonal rings, so there are 2N rings in total for N oxygen atoms, or 2 rings for each oxygen atom, giving a refined result of <math>R\ln(1.5\times (730/729)^2) = R\ln(1.504)</math>.<ref>{{Cite journal |last=Hollins |first=G. T. |date=December 1964 |title=Configurational statistics and the dielectric constant of ice |url=https://dx.doi.org/10.1088/0370-1328/84/6/318 |journal=Proceedings of the Physical Society |language=en |volume=84 |issue=6 |pages=1001–1016 |doi=10.1088/0370-1328/84/6/318 |bibcode=1964PPS....84.1001H |issn=0370-1328}}</ref>
{{clear}}

== Known phases ==
<!-- Other articles link here. -->
These phases are named according to the [[Percy Williams Bridgman|Bridgman]] nomenclature. The majority have only been created in the laboratory at different temperatures and pressures.<ref>{{Cite web|last1=Flatz|first1=Christian|last2=Hohenwarter|first2=Stefan|title=Neue kristalline Eisform aus Innsbruck|url=https://www.uibk.ac.at/newsroom/neue-kristalline-eisform-aus-innsbruck.html.de|access-date=2021-02-18|website=Universität Innsbruck|date=18 February 2021 |language=de}}</ref>

{| class="wikitable"
|-
! Phase
! Year of discovery
! Temperature thresholds
! Pressure thresholds
! Density
! Crystal form
! Other characteristics
|-
| Ice I{{sub|h}}
| NA
(natural ice)
| {{Convert|273.15|K|C|0|lk=on}} (freezing)
| NA (atmospheric)
| 0.9167 g/cm<sup>3</sup>
| Hexagonal
|  Virtually all ice in the [[biosphere]] is ice I{{sub|h}}, with the exception only of a small amount of ice I{{sub|c}}. Has a [[refractive index]] of 1.31. 
|-
| Ice I{{sub|c}}
| 1943/2020<ref name="delRosso2020" /><ref name="Salzmann2020" />
| {{convert|130|and|220|K|C}} (formation);
{{convert|240|K|C}} (conversion to Ice I{{sub|h}})<ref>{{Cite journal |last1=Murray |first1=B.J. |last2=Bertram |first2=A. K. |year=2006 |title=Formation and stability of cubic ice in water droplets |url=https://open.library.ubc.ca/media/download/pdf/52383/1.0041852/3 |journal=Phys. Chem. Chem. Phys. |volume=8 |issue=1 |pages=186–192 |bibcode=2006PCCP....8..186M |doi=10.1039/b513480c |pmid=16482260 |hdl-access=free |hdl=2429/33770}}</ref><ref>{{cite journal |last=Murray |first=B.J. |year=2008 |title=The Enhanced formation of cubic ice in aqueous organic acid droplets |pages=025008 |journal=Env. Res. Lett. |volume=3 |doi=10.1088/1748-9326/3/2/025008|bibcode = 2008ERL.....3b5008M |issue=2 |doi-access=free }}</ref>
| NA (atmospheric)
| Similar to Ice I<sub>h</sub>
| Diamond<ref name="DowellRinfret1960">{{Cite journal |last1=Dowell |first1=L. G. |last2=Rinfret |first2=A. P. |date=December 1960 |title=Low-Temperature Forms of Ice as Studied by X-Ray Diffraction |journal=Nature |language=en |volume=188 |issue=4757 |pages=1144–1148 |bibcode=1960Natur.188.1144D |doi=10.1038/1881144a0 |issn=0028-0836 |s2cid=4180631}}</ref>
| A metastable [[cubic crystal|cubic]] crystalline variant of ice. 
|-
| Low-density amorphous ice (LDA)
| 1930s<ref name="PappasLS2023" />
| 
| NA (atmospheric or lower)
| 0.94&nbsp;g/cm<sup>3</sup><ref name="adsabs.harvard.edu" />
| NA (amorphous)
| Likely the most common phase in the universe.<ref name="PappasLS2023" /> More [[viscous]] than normal water.<ref name="adsabs.harvard.edu">{{Cite journal|last1=Jenniskens |first1=Peter |last2=Blake |first2=David F. |year=1994 |title= Structural transitions in amorphous water ice and astrophysical implications |journal=Science |volume=265 |pages=753–6 | pmid = 11539186|issue=5173 |bibcode = 1994Sci...265..753J |doi=10.1126/science.11539186 |url= https://zenodo.org/record/1230888}}</ref><ref>{{cite journal|doi= 10.1086/178220|title= Crystallization of amorphous water ice in the solar system|author1=Jenniskens P. |author2=Blake D. F. |journal=Astrophysical Journal |volume=473|pages=1104–13|year= 1996 | pmid = 11539415 |bibcode=1996ApJ...473.1104J|issue= 2|s2cid= 33622340|doi-access=free}}</ref><ref>{{cite journal|pmid=11542399 | volume=107 | issue=4 |date=July 1997 | pages=1232–41 |author1=Jenniskens P. |author2=Banham S. F. |author3=Blake D. F. |author4=McCoustra M. R. |title=Liquid water in the domain of cubic crystalline ice Ic|journal=Journal of Chemical Physics|bibcode = 1997JChPh.107.1232J |doi = 10.1063/1.474468 }}</ref> 
|-
| Medium-density amorphous ice (MDA)
| 2023<ref name="Nature2023">{{Cite journal |last1=Rosu-Finsen |first1=Alexander |last2=Davies |first2=Michael B. |last3=Amon |first3=Alfred |last4=Wu |first4=Han |last5=Sella |first5=Andrea |last6=Michaelides |first6=Angelos |last7=Salzmann |first7=Christoph G. |date=3 February 2023 |title=Medium-density amorphous ice |journal=Science |language=en |volume=379 |issue=6631 |pages=474–478 |doi=10.1126/science.abq2105 |pmid=36730416 |bibcode=2023Sci...379..474R |s2cid=256504172 |issn=0036-8075|url=https://discovery.ucl.ac.uk/id/eprint/10165056/ }}</ref><ref>{{cite news|author=|newspaper=Nature|title=Scientists made a new kind of ice that might exist on distant moons|url=https://www.nature.com/articles/d41586-023-00293-w |date=4 February 2023}}</ref> 
| {{Convert|73.15|K|C|0}} (freezing)
| NA (requires [[shear force]])
| 1.06±0.06 g cm<sup>3</sup><ref name="SM-20230203">{{cite news |last=Sullivan |first=Will |title=Scientists Have Created a New Type of Ice – It looks like a white powder and has nearly the same density as liquid water |url=https://www.smithsonianmag.com/smart-news/scientists-have-created-a-new-type-of-ice-180981579/ |date=3 February 2023 |work=[[Smithsonian (magazine)|Smithsonian Magazine]] |accessdate=4 February 2023 }}</ref> 
| NA (amorphous)
| Experimental procedure generates shear force by crushing ice into powder with centimeter-wide stainless-steel balls added to its container.
|-
| High-density amorphous ice (HDA)
| 1984<ref name="Nature 310, 393 1984" /> 
| <{{convert|140|K|C}} (normal formation);<br><{{convert|30|K|C}} (vapor deposition);<ref name="adsabs.harvard.edu" /><ref name="auto1">{{cite journal|doi=10.1086/176585|title= High-density amorphous ice, the frost on insterstellar grains|author1=Jenniskens P. |author2=Blake D. F. |author3=Wilson M. A. |author4=Pohorille A. |journal=Astrophysical Journal |volume=455|page=389|year=1995|bibcode=1995ApJ...455..389J|hdl= 2060/19980018148|s2cid= 122950585|hdl-access=free}}</ref><br>{{convert|77|K|C}} (stability point)<ref name="Nature 310, 393 1984">{{cite journal|author1=Mishima O. |author2=Calvert L. D. |author3=Whalley E. |journal= Nature |volume=310|pages=393–395 |year=1984|bibcode = 1984Natur.310..393M |doi = 10.1038/310393a0 |issue=5976|title='Melting ice' I at 77 K and 10 kbar: a new method of making amorphous solids|s2cid=4265281 }}</ref>
| At {{convert|77|K|C}}: 1.6&nbsp;GPa (formation from I<sub>h</sub>);<ref name="Nature 310, 393 1984" /> 0.5&nbsp;GPa (formation from LDA)<ref>{{cite journal |last1=Mishima |first1=O. |title=An apparently 1st-order transition between two amorphous phases of ice induced by pressure|doi=10.1038/314076a0|journal=Nature |volume=314 |issue= 6006|year=1985 |pages=76–78 |last2=Calvert |first2=L. D. |last3=Whalley |first3=E.|bibcode = 1985Natur.314...76M |s2cid=4241205 }}</ref>
| 1.17&nbsp;g/cm<sup>3</sup> (ambient pressure)<ref name="Nature 310, 393 1984" />
| NA (amorphous)
| 
|-
| Very high-density amorphous ice (VHDA)
| 1996<ref>{{cite journal|author=O.Mishima|journal=Nature |volume=384 |pages=546–549 |year=1996|doi=10.1038/384546a0|title=Relationship between melting and amorphization of ice|issue=6609|bibcode = 1996Natur.384..546M |s2cid=4274283 }}</ref>
| {{convert|160|K|C}} (formation from HDA);
{{convert|77|K|C}} (stability point)
| 1 and 2&nbsp;GPa (formation at {{convert|160|K|C}}); ambient (at {{convert|77|K|C}})
| 1.26&nbsp;g/cm<sup>3</sup> ({{convert|77|K|C}}; ambient pressure)<ref>{{cite journal|doi=10.1039/b108676f|title=A second distinct structural "state" of high-density amorphous ice at 77 K and 1 bar|year=2001|author1-link=Thomas Loerting|last1=Loerting|first1=Thomas|last2=Salzmann|first2=Christoph|last3=Kohl|first3=Ingrid|last4=Mayer|first4=Erwin|last5=Hallbrucker|first5=Andreas|s2cid=59485355|journal=Physical Chemistry Chemical Physics |volume=3 |pages=5355–5357 |issue=24 |bibcode=2001PCCP....3.5355L }}</ref>
| NA (amorphous)
| 
|-
| Ice II 
| 1900<ref name="Hobbs">{{cite book |last=Hobbs |first=Peter V. |date=May 6, 2010 |title=Ice Physics |url=https://books.google.com/books?id=7Is6AwAAQBAJ&pg=PA61 |publisher=[[Oxford University Press]] |pages=61–70 |isbn=9780199587711 |access-date=December 6, 2014}}</ref> 
| {{convert|190|K|C}} - {{convert|210|K|C}} (formation from ice I{{sub|h}});
{{convert|77|K|C}} (stability point)<ref name="Hobbs" />
| 300 [[MPa]]<ref name="auto">{{cite web |url=https://water.lsbu.ac.uk/water/ice_ii.html |title=Ice-two (Ice II) |author=Chaplin, Martin |work=Water Structure and Science |publisher=[[London South Bank University]]}}</ref> 
| 
| [[Rhombohedral]] 
|
|-
| Ice III
| 1900<ref name="Hobbs" /> 
| {{cvt|250|K|C}} (formation from liquid water);
{{convert|77|K|C}} (stability point)<ref name="Hobbs" />
| 300&nbsp;MPa  (formation from liquid water)<ref name="auto"/> 
| {{nowrap|1.16 g/cm<sup>3</sup>}} (at 350 MPa)<ref>{{Cite web |url=https://water.lsbu.ac.uk/water/ice_iii.html |title=Ice-three (Ice III) |author=Chaplin, Martin |work=Water Structure and Science |publisher=[[London South Bank University]] }}</ref> 
| [[Tetragonal]] 
| Very high relative [[permittivity]] at 117. A [[specific gravity]] of 1.16 with respect to water.
|-
| Ice IV
| 1900<ref name="Hobbs"/> 
| {{convert|190|K|C}} – {{convert|210|K|C}} (formation from HDA);
{{convert|77|K|C}} (stability point)
| 810&nbsp;MPa (formation from HDA)
| 
| Rhombohedral 
| Typically requires a nucleating agent to form.<ref>{{cite web|url=https://water.lsbu.ac.uk/water/ice_iv.html|title=Ice-four (Ice IV) |author=Chaplin, Martin|work=Water Structure and Science|publisher=[[London South Bank University]]}}</ref>
|-
| Ice V  
| 1900s<ref name="Salzmann2021">{{cite journal |last1=Salzmann |first1=Christoph G. |last2=Rosu-Finsen | first2=Alexander |last3=Sharif |first3=Zainab |last4=Radaelli |first4=Paolo G. |last5=Finney |first5=John L. |date=1 April 2021  |title=Detailed crystallographic analysis of the ice V to ice XIII hydrogen-ordering phase transition |journal=The Journal of Chemical Physics |publisher=AIP Publishing |volume=154 |issue=13 |issn=0021-9606 |doi=10.1063/5.0045443 |pmid=33832256 |bibcode=2021JChPh.154m4504S }}</ref>
| {{convert|253|K|C}} (formation from liquid water);
| 500&nbsp;MPa (formation from liquid water)<ref name="auto2">{{cite web|url=https://water.lsbu.ac.uk/water/ice_v.html|title=Ice-five (Ice V) |author=Chaplin, Martin|work=Water Structure and Science|publisher=[[London South Bank University]]}}</ref>
| 1.24 g/cm<sup>3</sup> (at 350 MPa).<ref>{{Cite journal|last=Drost-Hansen|first=W.|date=1969-11-14|title=The Structure and Properties of Water. D. Eisenberg and W. Kauzmann. Oxford University Press, New York, 1969. xiv + 300 pp., illus. Cloth, $10; paper, $4.50|journal=Science|volume=166|issue=3907|pages=861|doi=10.1126/science.166.3907.861|issn=0036-8075}}</ref> 
| [[Monoclinic]]
| Most complicated structure of all the phases. Includes 4-membered, 5-membered, 6-membered, and 8-membered rings and a total of 28 [[molecule]]s in the unit cell.<ref name=chaplin>{{cite web |title=Ice-five (Ice V) |url=https://water.lsbu.ac.uk/water/ice_v.html |author=Chaplin, Martin |work=Water Structure and Science |publisher=[[London South Bank University]]}}</ref><ref name=kamb1967>{{cite journal |last1=Kamb |first1=B. |last2=Prakash |first2=A. |last3=Knobler |first3=C. |title=Structure of ice. V |journal=Acta Crystallographica |date=May 1967 |volume=22 |issue=5 |pages=706–715 |doi=10.1107/S0365110X67001409 |bibcode=1967AcCry..22..706K |url=https://resolver.caltech.edu/CaltechAUTHORS:20160913-124848654 }}</ref>
|-
| Ice VI
| 1912<ref>{{cite journal |last1=Bridgman |first1=P. W. |title=Water, in the Liquid and Five Solid Forms, under Pressure |journal=Proceedings of the American Academy of Arts and Sciences |date=1912 |volume=47 |issue=13 |pages=441–558 |doi=10.2307/20022754 |jstor=20022754 }}</ref>
| {{convert|270|K|C}} (formation from liquid water);
{{convert|130|K|C}} - {{convert|355|K|C}} (stability range)
| 1.1&nbsp;GPa (formation from liquid water)<ref name="auto2"/>
| 1.31 g/cm<sup>3</sup><ref>[https://www.science.org/doi/10.1126/science.150.3693.205 ''Reports: Structure of Ice VI''] science.sciencemag.org, B. Kamb, 8 October 1965.</ref>
| Tetragonal
| Exhibits [[Debye relaxation]].<ref>{{cite web|url=https://water.ac.uk/water/ice_vi.html|title=Ice-six (Ice VI) structure|author=Chaplin, Martin|work=Water Structure and Science|publisher=[[London South Bank University]]}}</ref> 
|-
| Ice VII  
| 1937<ref name="Yao2017">{{cite journal|last1=Yao |first1=Shu-Kai |last2=Zhang |first2=Peng |last3=Zhang |first3=Ying |last4=Lu |first4=Ying-Bo |last5=Yang |first5=Tian-Lin |last6=Suna |first6=Bai-Gong |last7=Yuan |first7=Zhen-Yu |last8=Luo |first8=Hui-Wen |date=21 June 2017 |title=Computing analysis of lattice vibrations of ice VIII |journal=RSC Advances |volume=7 |issue=51 |pages=31789–31794 |doi=10.1039/C7RA05563C |doi-access=free |bibcode=2017RSCAd...731789Y }}</ref><ref name="Kamb1964">{{cite journal|last1=Kamb |first1=Barclay |last2=Davis |first2=Briant L. |date=1 December 1964 |title=Ice Vii, the Densest Form of Ice |journal=Proceedings of the National Academy of Sciences |volume=52 |issue=6 |pages=1433–1439 |doi=10.1073/pnas.52.6.1433 |doi-access=free |pmid=16591242 |pmc=300465 |bibcode=1964PNAS...52.1433K }}</ref>
| {{convert|355|K|C}} (formation from ice VI)
| 2.2&nbsp;GPa (formation from ice VI)
| 1.65 g/cm<sup>3</sup><ref>{{cite web|title=Ice VII (ice-seven)|url=https://water.lsbu.ac.uk/water/ice_vii.html}}</ref>
| Cubic
| The hydrogen atoms' positions are disordered. Exhibits Debye relaxation. The hydrogen bonds form two interpenetrating lattices. Tetragonal form (contested) known as Ice VII{{sub|t}}.<ref name="viit">{{cite journal |last1=Grande |first1=Zachary M. |display-authors=etal |title=Pressure-driven symmetry transitions in dense H2O ice |journal=APS Physics |year=2022 |volume=105 |issue=10 |page=104109 |doi=10.1103/PhysRevB.105.104109|bibcode=2022PhRvB.105j4109G |osti=1989084 |s2cid=247530544 }}</ref>
|-
| Plastic 
Ice VII
| 2025<ref>{{Cite journal |last1=Rescigno |first1=Maria |last2=Toffano |first2=Alberto |last3=Ranieri |first3=Umbertoluca |last4=Andriambariarijaona |first4=Leon |last5=Gaal |first5=Richard |last6=Klotz |first6=Stefan |last7=Koza |first7=Michael Marek |last8=Ollivier |first8=Jacques |last9=Martelli |first9=Fausto |last10=Russo |first10=John |last11=Sciortino |first11=Francesco |last12=Teixeira |first12=Jose |last13=Bove |first13=Livia Eleonora |date=2025-02-12 |title=Observation of Plastic Ice VII by Quasi-Elastic Neutron Scattering |url=https://www.nature.com/articles/s41586-025-08750-4 |journal=Nature |language=en |doi=10.1038/s41586-025-08750-4 |pmid=39938568 |issn=0028-0836}}</ref>

| >470 K (formation from Ice VII or liquid water)
| >4 GPa (formation from Ice VII or liquid water)
| 
| Cubic
| Plastic equivalent to Ice VII.
|-
| Ice VIII
| 1966<ref>{{Cite journal |last1=Whalley |first1=E. |last2=Davidson |first2=D. W. |last3=Heath |first3=J. B. R. |date=1 December 1966 |title=Dielectric Properties of Ice VII. Ice VIII: A New Phase of Ice |journal=The Journal of Chemical Physics |volume=45 |issue=11 |pages=3976–3982 |doi=10.1063/1.1727447 |bibcode=1966JChPh..45.3976W }}</ref>

| <{{convert|278|K|C|abbr=on}} (formation from ice VII)
| 2.1&nbsp;GPa (formation from ice VII)
| 
| Tetragonal
| Proton-ordered equivalent to Ice VII.
|-
| Ice IX
| 1968<ref name="Whalley1968">{{Cite journal |last1=Whalley |first1=E. |last2=Heath |first2=J. B. R. |last3=Davidson |first3=D. W. |date=1 March 1968 |title=Ice IX: An Antiferroelectric Phase Related to Ice III |journal=The Journal of Chemical Physics |volume=48 |issue=5 |pages=2362–2370 |doi=10.1063/1.1669438 |bibcode=1968JChPh..48.2362W }}</ref>
| {{convert|165|K|C}}  (formation from ice III);<br><{{convert|140|K|C}} (stability point)
| 200–400&nbsp;MPa (stability range)
| 1.16&nbsp;g/cm{{sup|3}}
| Tetragonal
| Proton-ordered equivalent to Ice III.<ref>{{Cite journal |last1=La Placa |first1=Sam J. |last2=Hamilton |first2=Walter C. |last3=Kamb |first3=Barclay |last4=Prakash |first4=Anand |date=1973-01-15 |title=On a nearly proton-ordered structure for ice IX |journal=The Journal of Chemical Physics |volume=58 |issue=2 |pages=567–580 |doi=10.1063/1.1679238 |bibcode=1973JChPh..58..567L |issn=0021-9606}}</ref> Antiferroelectric.<ref name="Whalley1968" /> 
|-
| Ice X 
| 2022 (contested)<ref>{{cite news|last1=Kim |first1=Shi En |date=24 March 2022 |title=Inside the hotly contested creation of 'ice X'|language=en|work=Popular Science|url=https://www.popsci.com/science/ice-x-discovery/ }}</ref> 
| {{convert|165|K|C}}  (formation from ice III);<br><{{convert|140|K|C}} (stability point)
| 30–70&nbsp;GPa (from ice VII)<ref name="auto4">{{cite web|url=https://water.lsbu.ac.uk/water/ice_vii.html|title=Ice-seven (Ice VII) |author=Chaplin, Martinwork=Water Structure and Science|publisher=[[London South Bank University]]}}</ref><ref name="viit"/>
| 
| Cubic
| Has symmetrized hydrogen bonds – a hydrogen atom is found at the center of two oxygen atoms. 
|-
| Ice XI
| 1972<ref>{{cite journal |last1=Hansen |first1=Thomas C. |date=26 May 2021 |title=The everlasting hunt for new ice phases  |journal=Nature Communications |volume=12 |issue=1 |page=3161 |doi=10.1038/s41467-021-23403-6 |doi-access=free |pmid=34039991 |pmc=8154907 |bibcode=2021NatCo..12.3161H }}</ref> 
| {{convert|72|K|C}}  (formation from ice I<sub>c</sub>) 
| 
| 
| [[Orthorhombic]]
| [[Ferroelectric]]. The most stable configuration of ice I{{sub|h}}.<ref>{{cite web|url=https://water.lsbu.ac.uk/water/ice_xi.html|title=Ice-eleven (ice XI)|author=Chaplin, Martin|work=Water Structure and Science|publisher=[[London South Bank University]]}}</ref>
|-
| Ice XII
| 1996<ref>C. Lobban, J.L. Finney and W.F. Kuhs, The structure of a new phase of ice, Nature 391, 268–270, 1998</ref>
| {{convert|260|K|C}} (formation from liquid water);
{{convert|77|K|C}} (formation from ice I<sub>h</sub>); {{convert|183|K|C}}  (formation from HDA ice)
| 0.55 GPa (formation from liquid water);<br>0.81–1.00 GPa/min (from ice I<sub>h</sub>);<br>810&nbsp;MPa (formation from HDA ice)
|  1.3 g/cm{{sup|−3}} (at {{convert|127|K|C}})
| Tetragonal
| Metastable. Observed in the phase space of ice V and ice VI. A topological mix of seven- and eight-membered rings, a 4-connected net (4-coordinate [[sphere]] packing)—the densest possible arrangement without [[hydrogen bond interpenetration]].
|-
| Ice XIII
| 2006<ref name="Salzmann2006">{{cite journal |last1=Salzmann |first1=Christoph G. |last2=Radaelli |first2=Paolo G. |last3=Hallbrucker |first3=Andreas |last4=Mayer |first4=Erwin |last5=Finney |first5=John L. |title=The Preparation and Structures of Hydrogen Ordered Phases of Ice |journal=Science |date=24 March 2006 |volume=311 |issue=5768 |pages=1758–1761 |doi=10.1126/science.1123896 |pmid=16556840 |bibcode=2006Sci...311.1758S |s2cid=44522271 }}</ref>
| {{convert|130|K|C}} (formation from liquid water)<ref name="Ice XII" />
| 500&nbsp;MPa (formation from liquid water)<ref name="Ice XII" />
| 
| Monoclinic
| The proton-ordered form of ice V.<ref name="Ice XII">{{cite web|url=https://water.lsbu.ac.uk/water/ice_xii.html|title=Ice-twelve (Ice XII) |author=Chaplin, Martin|work=Water Structure and Science|publisher=[[London South Bank University]]}}</ref>
|-
| Ice XIV
| 2006<ref name="Salzmann2006" />
| <{{convert|118|K|C}}  (formation from ice XII); <{{convert|140|K|C}} (stability point) 
| 1.2 GPa (formation from ice XII)<ref name="Ice XII"/>
| 
| Orthorhombic
| The proton-ordered form of ice XII.<ref name="Ice XII"/> Formation requires [[HCl]] doping.<ref name="pmid16556840">{{cite journal| author=Salzmann CG, Radaelli PG, Hallbrucker A, Mayer E, Finney JL| title=The preparation and structures of hydrogen ordered phases of ice. | journal=Science | year= 2006 | volume= 311 | issue= 5768 | pages= 1758–61 | pmid=16556840 | doi=10.1126/science.1123896 | pmc= | bibcode=2006Sci...311.1758S | s2cid=44522271 | url=https://pubmed.ncbi.nlm.nih.gov/16556840  }}</ref>
|-
| Ice XV
| 2009<ref>{{cite magazine|url=http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|title=A Very Special Snowball|author=Sanders, Laura|magazine=Science News|date=11 September 2009|access-date=11 September 2009|url-status=live|archive-url=https://web.archive.org/web/20090914174027/http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|archive-date=14 September 2009}}</ref>
| {{convert|80|K|C}} – {{convert|108|K|C|abbr=}} (formation from liquid water) 
| 1.1GPa (formation from liquid water)
| 
| 
| A proton-ordered form of ice VI formed by cooling water to around 80–108&nbsp;K at 1.1&nbsp;GPa.
|-
| Ice XVI
| 2014<ref name="Falenty2014" />
| <{{convert|118|K|C}}  (formation from ice III);
<{{convert|140|K|C}} (stability point)
| 1.2GPa (from ice VII)<ref name="Ice XII"/>
| 0.81 g/cm{{sup|3}}<ref name="Falenty2014">{{Cite journal | doi = 10.1038/nature14014| pmid = 25503235| title = Formation and properties of ice XVI obtained by emptying a type sII clathrate hydrate| journal = Nature| volume = 516| issue = 7530| pages = 231–233| year = 2014| last1 = Falenty | first1 = A. | last2 = Hansen | first2 = T. C. | last3 = Kuhs | first3 = W. F. | bibcode = 2014Natur.516..231F| s2cid = 4464711}}{{closed access}}</ref> 
| 
| The least dense crystalline form of water, topologically equivalent to the empty structure of sII [[clathrate hydrates]]. Transforms into the stacking-faulty ice I<sub>c</sub> and further into ordinary ice I<sub>h</sub> when above 145–147 K at positive pressures. Theoretical studies predict ice XVI to be thermodynamically stable at negative pressures (that is under [[tension (physics)|tension]]).<ref name="conde2009">{{cite journal|last1=Conde|first1=M.M.|last2=Vega|first2=C.|last3=Tribello|first3=G.A.|last4=Slater|first4=B.|title=The phase diagram of water at negative pressures: Virtual ices|journal=[[J. Chem. Phys.|The Journal of Chemical Physics]]|date=2009|volume=131|issue=34510|pages=034510|doi=10.1063/1.3182727|bibcode=2009JChPh.131c4510C|pmid=19624212}}{{closed access}}</ref><ref name="jacobson2009">{{cite journal|last1=Jacobson|first1=Liam C.|last2=Hujo|first2=Waldemar|last3=Molinero|first3=Valeria|title=Thermodynamic Stability and Growth of Guest-Free Clathrate Hydrates: A Low-Density Crystal Phase of Water|journal=[[J. Phys. Chem. B|Journal of Physical Chemistry B]]|date=2009|volume=113|issue=30|pages=10298–10307|doi=10.1021/jp903439a|pmid=19585976|doi-access=free}}{{closed access}}</ref> 
|-
| Square ice
| 2014<ref name=Algara-Siller2015>{{cite journal |title=Square ice in graphene nanocapillaries |first1=G. |last1=Algara-Siller |first2=O. |last2=Lehtinen |first3=F. C. |last3=Wang |first4=R. R. |last4=Nair |first5= U. |last5=Kaiser |first6=H. A. |last6=Wu |first7=A. K. |last7=Geim |first8=I. V. |last8=Grigorieva |journal=Nature |volume=519 |issue=7544 |pages=443–445 |date=2015-03-26 |doi=10.1038/nature14295|pmid=25810206 |arxiv=1412.7498 |bibcode=2015Natur.519..443A |s2cid=4462633 }}</ref>
| Room temperature (in the presence of [[graphene]]) 
| 10GPa<ref name=graphene>{{cite web |url=http://www.zmescience.com/science/chemistry/graphene-square-ice-0534534 |title=Sandwiching water between graphene makes square ice crystals at room temperature |date=2015-03-27 |work=ZME Science |access-date=2018-05-02}}</ref>
| 
| Square
| Formation likely driven by the [[van der Waals force]], which allows [[water vapor]] and liquid water to pass through laminated sheets of [[graphene oxide]], unlike smaller molecules such as [[helium]].<ref name=graphene />
|-
| Ice XVII
| 2016<ref name="delRosso2016">{{cite journal |last1=del Rosso |first1=Leonardo |last2=Celli |first2=Milva |last3=Ulivi |first3=Lorenzo |title=New porous water ice metastable at atmospheric pressure obtained by emptying a hydrogen-filled ice |journal=Nature Communications |date=7 November 2016 |volume=7 |issue=1 |pages=13394 |doi=10.1038/ncomms13394 |pmid=27819265 |pmc=5103070 |arxiv=1607.07617 |bibcode=2016NatCo...713394D }}</ref>
| <{{convert|118|K|C}}  (formation from ice III);<br><{{convert|140|K|C}} (stability point)
| 1.2 GPa (from ice III)
| Near that of ice XVI.<ref name="delRosso2016" /><ref name="xvii.lsbu">{{cite web |url=https://water.lsbu.ac.uk/water/ice_xvii.html |title=Ice-seventeen (Ice XVII) |author=Chaplin, Martin |work=Water Structure and Science |publisher=[[London South Bank University]]}}</ref>
| Hexagonal
| A porous crystalline phase with helical channels. Formed by placing hydrogen-filled ice in a vacuum and increasing the temperature until the hydrogen molecules escape.<ref name="delRosso2016" />
|-
| Ice XVIII
| 2019<ref name="Millot2019" />
| <{{convert|118|K|C}} (formation from ice III);<br><{{convert|140|K|C}} (stability point) 
| 1.2 GPa (from ice VII)<ref name="Ice XII"/>
| 
| 
| A form of water also known as superionic water or superionic ice in which oxygen ions develop a crystalline structure while hydrogen ions move freely.
|-
| Ice XIX
| 2018<ref name="pmid29780552">{{cite journal |last1=Gasser|first1=TM|last2=Thoeny|first2=AV|last3= Plaga|first3= LJ|last4= Köster|first4= KW|last5= Etter|first5= M|last6= Böhmer|first6= R |display-authors=etal |year=2018 |title=Experiments indicating a second hydrogen ordered phase of ice VI. |journal=Chem Sci |volume=9 |issue=18 |pages=4224–4234 |doi=10.1039/c8sc00135a |pmc=5942039 |pmid=29780552}}</ref>
| <{{convert|100|K|C}}  (formation from ice VI{{sub|h}});<ref name="Metcalfe-2021">{{cite news|last1=Metcalfe|first1=Tom|date=9 March 2021|title=Exotic crystals of 'ice 19' discovered|language=en|work=Live Science|url=https://www.livescience.com/exotic-ice-19-discovered.html}}</ref>
| 2 GPa (formation from ice VI{{sub|h}})<ref name="Metcalfe-2021" />
| 
| 
| Formation requires HCl doping.<ref name="pmid29780552" /><ref name="Metcalfe-2021" /><ref name="pmid33602936">{{cite journal |author=Yamane R, Komatsu K, Gouchi J, Uwatoko Y, Machida S, Hattori T, Kagi H |display-authors=etal |year=2021 |title=Experimental evidence for the existence of a second partially-ordered phase of ice VI. |journal=Nat Commun |volume=12 |issue=1 |pages=1129 |doi=10.1038/s41467-021-21351-9 |pmc=7893076 |pmid=33602936|bibcode=2021NatCo..12.1129Y }}</ref> 
|}

== History of research ==
[[File:Ice III phase diagram.svg|thumb|Phase diagram of water, showing the region where ice III is stable.]]

=== Ice II ===
The properties of ice II were first described and recorded by [[Gustav Heinrich Johann Apollon 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 {{convert|-70|and|-80|C|K F}} under {{convert|200|MPa|atm|abbr=on|comma=}} 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 I<sub>h</sub>.<ref name="Hobbs"/>

In later experiments by Bridgman in 1912, it was shown that the difference in volume between ice II and ice III was in the range of {{convert|0.0001|m3/kg|cuin/lb|abbr=on|comma=gaps}}. This difference had not been discovered by Tammann due to the small change and was why he had been unable to determine an [[Vapor–liquid equilibrium|equilibrium curve]] between the two. The curve showed that the structural change from ice III to ice II was more likely to happen if the medium had previously been in the structural conformation of ice II. However, if a sample of ice III that had never been in the ice II state was obtained, it could be supercooled even below −70&nbsp;°C without it changing into ice II. Conversely, however, any superheating of ice II was not possible in regards to retaining the same form. Bridgman found that the equilibrium curve between ice II and ice IV was much the same as with ice III, having the same stability properties and small volume change. The curve between ice II and ice V was extremely different, however, with the curve's bubble being essentially a straight line and the volume difference being almost always {{convert|0.0000545|m3/kg|cuin/lb|abbr=on|comma=gaps}}.<ref name="Hobbs"/>

==== Search for a hydrogen-disordered counterpart ====

As ice II is completely hydrogen ordered, the presence of its disordered counterpart is a great matter of interest. Shephard et al.<ref>{{Citation | vauthors=((Shephard, J. J.)), ((Slater, B.)), ((Harvey, P.)), ((Hart, M.)), ((Bull, C. L.)), ((Bramwell, S. T.)), ((Salzmann, C. G.)) | year=2018 | title=Doping-induced disappearance of ice II from water's phase diagram | journal=Nature Physics | volume=14 | issue=6 | pages=569–572 | publisher=Springer Science and Business Media LLC | doi=10.1038/s41567-018-0094-z | bibcode=2018NatPh..14..569S | s2cid=54544973 | url=http://dx.doi.org/10.1038/s41567-018-0094-z}}</ref> investigated the phase boundaries of NH<sub>4</sub>F-doped ices because NH<sub>4</sub>F has been reported to be a hydrogen disordering reagent. However, adding 2.5 mol% of NH<sub>4</sub>F 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.,<ref>{{Citation | vauthors=((Nakamura, T.)), ((Matsumoto, M.)), ((Yagasaki, T.)), ((Tanaka, H.)) | year=2015 | title=Thermodynamic Stability of Ice II and Its Hydrogen-Disordered Counterpart: Role of Zero-Point Energy | journal=The Journal of Physical Chemistry B | volume=120 | issue=8 | pages=1843–1848 | publisher=American Chemical Society (ACS) | doi=10.1021/acs.jpcb.5b09544 | pmid=26595233 | url=http://dx.doi.org/10.1021/acs.jpcb.5b09544}}</ref> 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.<ref>{{Citation | vauthors=((Engelhardt, H.)), ((Kamb, B.)) | year=1981 | title=Structure of ice IV, a metastable high-pressure phase | journal=The Journal of Chemical Physics | volume=75 | issue=12 | pages=5887–5899 | publisher=AIP Publishing | doi=10.1063/1.442040 | bibcode=1981JChPh..75.5887E | url=http://dx.doi.org/10.1063/1.442040}}</ref> 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.<ref>{{Citation | vauthors=((Shephard, J. J.)), ((Ling, S.)), ((Sosso, G. C.)), ((Michaelides, A.)), ((Slater, B.)), ((Salzmann, C. G.)) | year=2017 | title=Is High-Density Amorphous Ice Simply a "Derailed" State along the Ice I to Ice IV Pathway? | journal=The Journal of Physical Chemistry Letters | volume=8 | issue=7 | pages=1645–1650 | publisher=American Chemical Society (ACS) | doi=10.1021/acs.jpclett.7b00492 | pmid=28323429 | s2cid=13662778 | url=http://dx.doi.org/10.1021/acs.jpclett.7b00492| arxiv=1701.05398 }}</ref> compressed the ambient phase of NH<sub>4</sub>F, an isostructural material of ice, to obtain NH<sub>4</sub>F 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.<ref>{{Citation | vauthors=((Engelhardt, H.)), ((Whalley, E.)) | year=1979 | title=The infrared spectrum of ice IV in the range 4000–400 cm−1 | journal=The Journal of Chemical Physics | volume=71 | issue=10 | pages=4050–4051 | publisher=AIP Publishing | doi=10.1063/1.438173 | url=http://dx.doi.org/10.1063/1.438173}}</ref> and Raman <ref>{{Citation | vauthors=((Salzmann, C. G.)), ((Kohl, I.)), ((Loerting, T.)), ((Mayer, E.)), ((Hallbrucker, A.)) | year=2003 | title=Raman Spectroscopic Study on Hydrogen Bonding in Recovered Ice IV | journal=The Journal of Physical Chemistry B | volume=107 | issue=12 | pages=2802–2807 | publisher=American Chemical Society (ACS) | doi=10.1021/jp021534k | url=http://dx.doi.org/10.1021/jp021534k}}</ref>

The disordered nature of Ice IV was confirmed by neutron powder diffraction studies by Lobban (1998) <ref>{{Citation | vauthors=((Colin Lobban)) | year=1998 | title=Neutron diffraction studies of ices | publisher=University College London | url=https://www.proquest.com/docview/1752797359| id={{ProQuest|1752797359}} }}</ref> and Klotz et al. (2003).<ref>{{Citation | vauthors=((Klotz, S.)), ((Hamel, G.)), ((Loveday, J. S.)), ((Nelmes, R. J.)), ((Guthrie, M.)) | year=2003 | title=Recrystallisation of HDA ice under pressure by in-situ neutron diffraction to 3.9 GPa | journal=Zeitschrift für Kristallographie – Crystalline Materials | volume=218 | issue=2 | pages=117–122 | publisher=Walter de Gruyter GmbH | doi=10.1524/zkri.218.2.117.20669 | bibcode=2003ZK....218..117K | s2cid=96109290 | url=http://dx.doi.org/10.1524/zkri.218.2.117.20669}}</ref> In addition, the entropy difference between ice VI (disordered phase) and ice IV is very small, according to Bridgman's measurement.<ref>{{Citation | vauthors=((Bridgman, P. W.)) | year=1935 | title=The Pressure-Volume-Temperature Relations of the Liquid, and the Phase Diagram of Heavy Water | journal=The Journal of Chemical Physics | volume=3 | issue=10 | pages=597–605 | publisher=AIP Publishing | doi=10.1063/1.1749561 | bibcode=1935JChPh...3..597B | url=http://dx.doi.org/10.1063/1.1749561}}</ref>

Several organic nucleating reagents had been proposed to selectively crystallize ice IV from liquid water,<ref>{{Citation | vauthors=((Evans, L. F.)) | year=1967 | title=Selective Nucleation of the High-Pressure Ices | journal=Journal of Applied Physics | volume=38 | issue=12 | pages=4930–4932 | publisher=AIP Publishing | doi=10.1063/1.1709255 | bibcode=1967JAP....38.4930E | url=http://dx.doi.org/10.1063/1.1709255}}</ref> 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'';<ref>{{Citation | vauthors=((Salzmann, C. G.)), ((Loerting, T.)), ((Kohl, I.)), ((Mayer, E.)), ((Hallbrucker, A.)) |author2-link=Thomas Loerting| year=2002 | title=Pure Ice IV from High-Density Amorphous Ice |journal=The Journal of Physical Chemistry B |volume=106 |issue=22 |pages=5587–5590 | publisher=American Chemical Society (ACS) |doi=10.1021/jp014391v | url=http://dx.doi.org/10.1021/jp014391v}}</ref> when [[High density amorphous ice|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 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.<ref name="pmid21946782">{{citation| last1=Salzmann|first1= CG|last2= Radaelli|first2= PG|last3= Slater|first3= B|last4= Finney|first4= JL| title=The polymorphism of ice: five unresolved questions. | journal=Phys Chem Chem Phys | year= 2011 | volume= 13 | issue= 41 | pages= 18468–80 | pmid=21946782 | doi=10.1039/c1cp21712g | pmc= |bibcode= 2011PCCP...1318468S| url=https://pubmed.ncbi.nlm.nih.gov/21946782  }}</ref> 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.<ref>{{Citation | vauthors=((Rosu-Finsen, A.)), ((Salzmann, C. G.)) | year=2022 | title=Is pressure the key to hydrogen ordering ice IV? | journal=Chemical Physics Letters | volume=789 | page=139325 | publisher=Elsevier BV | doi=10.1016/j.cplett.2021.139325 | bibcode=2022CPL...78939325R | s2cid=245597764 | url=http://dx.doi.org/10.1016/j.cplett.2021.139325}}
</ref>

=== Ice VII ===
Ice VII is the only disordered phase of ice that can be ordered by simple cooling. (While ice I<sub>h</sub> 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.<ref name="Pruzan1993">{{Cite journal |first1=Ph. |last1=Pruzan |first2=J. C. |last2=Chervin |first3=B. |last3=Canny |name-list-style=amp |journal=Journal of Chemical Physics |volume=99 |issue=12 |pages=9842–9846 |year=1993 |title=Stability domain of the ice VIII proton-ordered phase at very high pressure and low temperature |doi=10.1063/1.465467 |bibcode = 1993JChPh..99.9842P }}.</ref> 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;<ref name="Hemley1987">{{Citation |first1=R. J. |last1=Hemley |first2=A. P. |last2=Jephcoat |first3=H. K. |last3=Mao |journal=[[Nature (journal)|Nature]] |issue=6150 |volume=330 |pages=737–740 |year=1987 |title=Static compression of H<sub>2</sub>O-ice to 128 GPa (1.28 Mbar) |doi=10.1038/330737a0 |bibcode = 1987Natur.330..737H |s2cid=4265919 |url=https://zenodo.org/record/1233067 |display-authors=etal}}.</ref> 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.<ref>{{cite journal|last=Katoh|first=E.|s2cid=38999963|title=Protonic Diffusion in High-Pressure Ice VII|journal=Science|date=15 February 2002 |volume=29=5558|issue=5558|pages=1264–1266|doi=10.1126/science.1067746|bibcode = 2002Sci...295.1264K|pmid=11847334}}</ref>

=== Ice XI ===
[[File:Ice XI View along c axis.png|thumb|250px|Crystal structure of Ice XI viewed along the c-axis]]
[[File:Ice XI side view.png|thumb|250px|Crystal structure of ice XI (c-axis in the vertical direction)]]
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 I<sub>h</sub>, so in principle it should naturally form when ice I<sub>h</sub> is cooled to below 72&nbsp;[[Kelvin|K]]. The low temperature required to achieve this transition is correlated with the relatively low energy difference between the two structures.<ref>{{cite journal|last1=Fan|first1=Xiaofeng|last2=Bing|first2=Dan|last3=Zhang|first3=Jingyun|last4=Shen|first4=Zexiang|last5=Kuo|first5=Jer-Lai|title=Predicting the hydrogen bond ordered structures of ice I<sub>h</sub>, II, III, VI and ice VII: DFT methods with localized based set|journal=Computational Materials Science|date=1 October 2010|volume=49|issue=4|pages=S170–S175|doi=10.1016/j.commatsci.2010.04.004|url=http://jlk.iams.sinica.edu.tw/paper/2010/ComMateSci49S170.pdf|access-date=24 April 2012|archive-url=https://web.archive.org/web/20140714192340/http://jlk.iams.sinica.edu.tw/paper/2010/ComMateSci49S170.pdf|archive-date=14 July 2014|url-status=dead}}</ref> 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.<ref>{{cite journal|last1=Dengel|first1=O.|last2=Eckener|first2=U.|last3=Plitz |first3=H. |last4=Riehl|first4= N.|title=Ferroelectric behavior of ice|journal=Physics Letters|date=1 May 1964|volume=9|issue=4|pages=291–292|doi=10.1016/0031-9163(64)90366-X|bibcode = 1964PhL.....9..291D }}</ref> 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.<ref>{{cite journal|last=Kawada|first=Shuji|title=Dielectric Dispersion and Phase Transition of KOH Doped Ice|journal=Journal of the Physical Society of Japan|date=1 May 1972|volume=32|issue=5|pages=1442|doi=10.1143/JPSJ.32.1442|bibcode = 1972JPSJ...32.1442K }}</ref><ref>{{cite journal|last1=Tajima|first1=Yoshimitsu|last2=Matsuo|first2= Takasuke|last3= Suga|first3= Hiroshi|title=Calorimetric study of phase transition in hexagonal ice doped with alkali hydroxides|journal=Journal of Physics and Chemistry of Solids|year=1984|volume=45|issue=11–12|pages=1135–1144|doi=10.1016/0022-3697(84)90008-8|bibcode = 1984JPCS...45.1135T }}</ref><ref>{{cite journal|last1=Matsuo|first1=Takasuke|last2=Tajima|first2= Yoshimitsu|last3=Suga|first3=Hiroshi|title=Calorimetric study of a phase transition in D<sub>2</sub>O ice I<sub>h</sub> doped with KOD: Ice XI|journal=Journal of Physics and Chemistry of Solids|year=1986|volume=47 |issue=2|pages=165–173 |doi=10.1016/0022-3697(86)90126-5|bibcode = 1986JPCS...47..165M }}</ref>

Water molecules in ice I<sub>h</sub> 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.<ref>{{cite journal|last1=Castro Neto|first1=A.|last2=Pujol|first2= P. |last3=Fradkin|first3= E.|title=Ice: A strongly correlated proton system|journal=Physical Review B|year=2006|volume=74|issue=2|doi=10.1103/PhysRevB.74.024302|arxiv=cond-mat/0511092|page=024302|bibcode = 2006PhRvB..74b4302C |s2cid=102581583}}</ref> Correspondingly, ice XI is believed to have a [[triple point]] with hexagonal ice and gaseous water at (~72&nbsp;K, ~0&nbsp;Pa). Ice I<sub>h</sub> that has been transformed to ice XI and then back to ice I<sub>h</sub>, on raising the temperature, retains some hydrogen-ordered domains and more easily transforms back to ice XI again.<ref>{{cite journal |doi=10.1016/j.molstruc.2010.02.016 |title=Annealing effects on hydrogen ordering in KOD-doped ice observed using neutron diffraction |journal=Journal of Molecular Structure |volume=972 |issue=1–3 |pages=111–114 |year=2010 |last1=Arakawa |first1=Masashi |last2=Kagi |first2=Hiroyuki |last3=Fukazawa |first3=Hiroshi |bibcode=2010JMoSt.972..111A }}</ref> A neutron powder diffraction study found that small hydrogen-ordered domains can exist up to 111&nbsp;K.<ref name=astro-ordering>{{cite journal|last=Arakawa|first=Masashi|author2=Kagi, Hiroyuki|author3=Fernandez-Baca, Jaime A.|author4=Chakoumakos, Bryan C.|author5=Fukazawa, Hiroshi|title=The existence of memory effect on hydrogen ordering in ice: The effect makes ice attractive|journal=Geophysical Research Letters|date=17 August 2011|volume=38|issue=16|pages=n/a|doi=10.1029/2011GL048217|bibcode=2011GeoRL..3816101A|doi-access=free}}</ref>

There are distinct differences in the Raman spectra between ices  I<sub>h</sub> and XI, with ice XI showing much stronger peaks in the translational (~230&nbsp;cm<sup>−1</sup>), librational (~630&nbsp;cm<sup>−1</sup>) and in-phase asymmetric stretch (~3200&nbsp;cm<sup>−1</sup>) regions.<ref>K. Abe, Y. Ootake and T. Shigenari, ''Raman scattering study of proton ordered ice XI single crystal'', in Physics and Chemistry of Ice, ed. W. Kuhs (Royal Society of Chemistry, Cambridge, 2007) pp 101–108</ref><ref>{{cite journal | last1 = Abe | first1 = K. | last2 = Shigenari | first2 = T. | year = 2011 | title = Raman spectra of proton ordered phase XI of ICE I. Translational vibrations below 350 cm-1, J | journal = The Journal of Chemical Physics | volume = 134 | issue = 10| page = 104506 | doi=10.1063/1.3551620| pmid = 21405174 | bibcode = 2011JChPh.134j4506A }}</ref>

Ice I<sub>c</sub> also has a proton-ordered form. The total internal energy of ice XI<sub>c</sub> was predicted as similar as ice XI<sub>h</sub>.<ref>{{cite journal|last1=Raza|first1=Zamaan|last2=Alfè|first2=Dario|title=Proton ordering in cubic ice and hexagonal ice; a potential new ice phase—XIc.|journal=Physical Chemistry Chemical Physics|date=28 Nov 2011|volume=13|issue=44|pages=19788–95|doi=10.1039/c1cp22506e|pmid=22009223|bibcode =  2011PCCP...1319788R|s2cid=31673433}}</ref>

==== 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.<ref>{{cite journal|last=Bramwell|first=Steven T.|journal=Nature|date=21 January 1999|title=Ferroelectric ice|volume=397|issue=6716|pages=212–213|doi=10.1038/16594|bibcode = 1999Natur.397..212B |s2cid=204990667|doi-access=free}}</ref> Cubic ice also has a ferrolectric phase and in this case the ferroelectric properties of the ice have been experimentally demonstrated on monolayer thin films.<ref>{{cite journal|last=Iedema|first=M. J.|author2=Dresser, M. J. |author3=Doering, D. L. |author4=Rowland, J. B. |author5=Hess, W. P. |author6=Tsekouras, A. A. |author7=Cowin, J. P. |title=Ferroelectricity in Water Ice|journal=The Journal of Physical Chemistry B|date=1 November 1998|volume=102|issue=46|pages=9203–9214|doi=10.1021/jp982549e|s2cid=97894870}}</ref> 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.<ref>{{cite journal|last=Su|first=Xingcai|author2=Lianos, L. |author3=Shen, Y. |author4= Somorjai, Gabor |title=Surface-Induced Ferroelectric Ice on Pt(111)|journal=Physical Review Letters|volume=80|issue=7|pages=1533–1536|doi=10.1103/PhysRevLett.80.1533|bibcode = 1998PhRvL..80.1533S |year=1998|s2cid=121266617}}</ref>  One-dimensional nano-confined ferroelectric ice XI was created in 2010.<ref name=onedim1>{{cite journal|last=Zhao|first=H.-X. |author2=Kong, X.-J. |author3=Li, H. |author4=Jin, Y.-C. |author5=Long, L.-S. |author6=Zeng, X. C. |author7=Huang, R.-B. |author8=Zheng, L.-S. |title=Transition from one-dimensional water to ferroelectric ice within a supramolecular architecture|journal=Proceedings of the National Academy of Sciences|date=14 February 2011|volume=108|issue=9|pages=3481–3486|doi=10.1073/pnas.1010310108|bibcode = 2011PNAS..108.3481Z |pmid=21321232 |pmc=3048133|doi-access=free }}</ref>

=== 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 ''P''2<sub>1</sub>2<sub>1</sub>2<sub>1</sub> structure were found 4 K per water molecule higher in energy.<ref name="Knight Singer 2005 pp. 21040–21046">{{cite journal | last1=Knight | first1=Chris | last2=Singer | first2=Sherwin J. | title=Prediction of a Phase Transition to a Hydrogen Bond Ordered Form of Ice VI | journal=The Journal of Physical Chemistry B | publisher=American Chemical Society (ACS) | volume=109 | issue=44 | date=2005-10-19 | issn=1520-6106 | doi=10.1021/jp0540609 | pages=21040–21046| pmid=16853726 }}</ref>

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 [[Antiferroelectricity|antiferroelectric]] rather than [[Ferroelectricity|ferroelectric]] as had been predicted.<ref name="Wired">{{cite magazine |first= Laura |last= Sanders |title= Super-Dense Frozen Water Breaks Final Ice Frontier |url= https://www.wired.com/wiredscience/2009/09/sn_icexv/ |magazine= [[Wired (magazine)|Wired]] |publisher= [[Condé Nast Publications|Condé Nast]] |date= 11 September 2009 |access-date= 13 September 2009 }}</ref><ref>{{Cite journal|arxiv = 0906.2489|doi = 10.1103/PhysRevLett.103.105701|title = Ice XV: A New Thermodynamically Stable Phase of Ice|year = 2009|last1 = Salzmann|first1 = Christoph G.|last2 = Radaelli|first2 = Paolo G.|last3 = Mayer|first3 = Erwin|last4 = Finney|first4 = John L.|journal = Physical Review Letters|volume = 103|issue = 10|page = 105701|pmid = 19792330|bibcode = 2009PhRvL.103j5701S|s2cid = 13999983}}</ref>

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.<ref name="Shephard Salzmann 2015 pp. 63–66">{{cite journal | last1=Shephard | first1=Jacob J. | last2=Salzmann | first2=Christoph G. | title=The complex kinetics of the ice VI to ice XV hydrogen ordering phase transition | journal=Chemical Physics Letters | publisher=Elsevier BV | volume=637 | year=2015 | issn=0009-2614 | doi=10.1016/j.cplett.2015.07.064 | pages=63–66| arxiv=1507.02665 | bibcode=2015CPL...637...63S }}</ref> It was also shown that HCl-doping is selectively effective in producing ice XV while other acids and bases (HF, LiOH, HClO<sub>4</sub>, HBr) do not significantly enhance ice XV formations.<ref name="Rosu-Finsen Salzmann 2018 p. 244507">{{cite journal | last1=Rosu-Finsen | first1=Alexander | last2=Salzmann | first2=Christoph G. | title=Benchmarking acid and base dopants with respect to enabling the ice V to XIII and ice VI to XV hydrogen-ordering phase transitions | journal=The Journal of Chemical Physics | publisher=AIP Publishing | volume=148 | issue=24 | date=2018-06-28 | issn=0021-9606 | doi=10.1063/1.5022159 | page=244507| pmid=29960300 | arxiv=1801.03812 | bibcode=2018JChPh.148x4507R }}</ref>

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.<ref name="Komatsu2016">{{cite journal | last1=Komatsu | first1=K. | last2=Noritake | first2=F. | last3=Machida | first3=S. | last4=Sano-Furukawa | first4=A. | last5=Hattori | first5=T. | last6=Yamane | first6=R. | last7=Kagi | first7=H. | title=Partially ordered state of ice XV | journal=Scientific Reports | publisher=Springer Science and Business Media LLC | volume=6 | issue=1 | date=2016-07-04 | issn=2045-2322 | doi=10.1038/srep28920 | page=28920| pmid=27375120 | pmc=4931510 | bibcode=2016NatSR...628920K }}</ref>
Other researchers argued that ''P''-1 model is still the best (with the second best candidate of ''P''2<sub>1</sub>), 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.<ref name="Salzmann2016">{{cite journal | last1=Salzmann | first1=Christoph G. | last2=Slater | first2=Ben | last3=Radaelli | first3=Paolo G. | last4=Finney | first4=John L. | last5=Shephard | first5=Jacob J. | last6=Rosillo-Lopez | first6=Martin | last7=Hindley | first7=James | title=Detailed crystallographic analysis of the ice VI to ice XV hydrogen ordering phase transition | journal=The Journal of Chemical Physics | publisher=AIP Publishing | volume=145 | issue=20 | date=2016-11-22 | issn=0021-9606 | doi=10.1063/1.4967167 | page=| pmid=27908115 | arxiv=1607.04794 | bibcode=2016JChPh.145t4501S }}</ref> -->

===Ice XVII===
[[File:IceXVII wiki.jpg|thumb|400px|Crystal structure of ice XVII]]
In 2016, the discovery of a new form of ice was announced.<ref name="delRosso2016" /> Characterized as a "porous water ice metastable at atmospheric temperatures", this new form was discovered by taking a filled ice and removing the non-water components, leaving the crystal structure behind, similar to how ice&nbsp;XVI, another porous form of ice, was synthesized from a [[clathrate hydrate]].
<ref name="Liu2019">{{cite journal |last1=Liu |first1=Yuan |last2=Huang |first2=Yingying |last3=Zhu |first3=Chongqin |last4=Li |first4=Hui |last5=Zhao |first5=Jijun |last6=Wang |first6=Lu |last7=Ojamäe |first7=Lars |last8=Francisco |first8=Joseph S. |last9=Zeng |first9=Xiao Cheng |title=An ultralow-density porous ice with the largest internal cavity identified in the water phase diagram |journal=Proceedings of the National Academy of Sciences |date=25 June 2019 |volume=116 |issue=26 |pages=12684–12691 |doi=10.1073/pnas.1900739116 |pmid=31182582 |pmc=6600908 |bibcode=2019PNAS..11612684L |doi-access=free }}</ref><ref name="cnr">{{cite web | url=http://www.ifac.cnr.it/~ulivi/IceXVII.htm | title=Ice-seventeen (Ice XVII) | first1=Martin | last1=Chaplin | access-date=2022-09-11 | archive-date=2022-09-11 | archive-url=https://archive.today/20220911222749/http://www.ifac.cnr.it/~ulivi/IceXVII.htm | url-status=bot: unknown }}{{self-published inline|date=September 2022}}</ref>

To create ice&nbsp;XVII, the researchers first produced filled ice in a stable phase named C{{sub|0}} from a mixture of hydrogen (H{{sub|2}}) and water (H{{sub|2}}O), using temperatures from {{cvt|100|to|270|K|C F}} and pressures from {{cvt|360|to|700|MPa|psi atm}}, and C{{sub|2}} are all stable solid phases of a mixture of H{{sub|2}} and H{{sub|2}}O molecules, formed at high pressures.<ref name="Liu2019"/><ref name="xvii.lsbu" /> Although sometimes referred to as [[clathrate hydrate]]s (or clathrates), they lack the cagelike structure generally found in clathrate hydrates, and are more properly referred to as filled ices.<ref name="Liu2019" /> The filled ice is then placed in a vacuum, and the temperature gradually increased until the hydrogen frees itself from the crystal structure.<ref name="xvii.lsbu" /> If kept at a temperature range between {{cvt|110|and|120|K|C F}}, after about two hours, the structure will have emptied itself of any detectable hydrogen molecules.<ref name="delRosso2016" /> The resulting form is [[metastable]] at room pressure while under {{cvt|120|K|C F}}, but collapses into ice&nbsp;I{{sub|h}} (ordinary ice) when brought above {{cvt|130|K|C F}}.<ref name="xvii.lsbu" /> The crystal structure is hexagonal in nature, and the pores are [[Helix|helical]] channels with a diameter of about {{cvt|6.10|Å|m in|lk=in}}.<ref name="delRosso2016" /><ref name="xvii.lsbu" />

=== Cubic ice ===
It was reported in 2020 that cubic ice based on [[heavy water]] (D{{sub|2}}O) can be formed from ice&nbsp;XVII.<ref name="delRosso2020">{{cite journal |last1=del Rosso |first1=Leonardo |last2=Celli |first2=Milva |last3=Grazzi |first3=Francesco |last4=Catti |first4=Michele |last5=Hansen |first5=Thomas C. |last6=Fortes |first6=A. Dominic |last7=Ulivi |first7=Lorenzo |title=Cubic ice Ic without stacking defects obtained from ice XVII |journal=Nature Materials |date=June 2020 |volume=19 |issue=6 |pages=663–668 |doi=10.1038/s41563-020-0606-y |pmid=32015533 |arxiv=1907.02915 |bibcode=2020NatMa..19..663D |s2cid=195820566 }}</ref> This was done by heating specifically prepared D{{sub|2}}O ice&nbsp;XVII powder.<ref name="delRosso2020" /> The result was free of structural deformities compared to standard cubic ice, or ice&nbsp;I{{sub|sd}}.<ref name="delRosso2020" /> This discovery was reported around the same time another research group announced that they were able to obtain pure D{{sub|2}}O cubic ice by first synthesizing filled ice in the C{{sub|2}} phase, and then decompressing it.<ref name="Komatsu2020">{{cite journal |last1=Komatsu |first1=Kazuki |last2=Machida |first2=Shinichi |last3=Noritake |first3=Fumiya |last4=Hattori |first4=Takanori |last5=Sano-Furukawa |first5=Asami |last6=Yamane |first6=Ryo |last7=Yamashita |first7=Keishiro |last8=Kagi |first8=Hiroyuki |title=Ice Ic without stacking disorder by evacuating hydrogen from hydrogen hydrate |journal=Nature Communications |date=3 February 2020 |volume=11 |issue=1 |pages=464 |doi=10.1038/s41467-020-14346-5 |pmid=32015342 |pmc=6997176 |arxiv=1909.03400 |bibcode=2020NatCo..11..464K }}</ref>

=== Ice XVIII (superionic water) ===
{{multiple image
 | align = right
 | total_width = 320

 | image1 = Superionic ice rest.svg
 | alt1 = Superionic ice at rest
 | caption1 = In the absence of an applied [[electric field]], H<sup>+</sup> ions [[Atomic diffusion|diffuse]] in the O<sup>2−</sup> lattice.

 | image2 = Superionic ice conducting.svg
 | alt2 = Superionic ice conducting protons in an electric field
 | caption2 = When an electric field is applied, H<sup>+</sup> ions migrate towards the [[anode]].

 | footer = A remarkable characteristic of superionic ice is its ability to act as a [[Electrical conductor|conductor]].
}}
In 1988, predictions of the so-called superionic water state were made.<ref name="Demontis">{{cite journal |doi=10.1103/PhysRevLett.60.2284 |pmid=10038311 |title=New high-pressure phases of ice |first1=P. |last1=Demontis |first2=R. |last2=LeSar |first3=M. L. |last3=Klein |display-authors=1 |journal=Phys. Rev. Lett. |volume=60 |issue=22 |pages=2284–2287 |year=1988 |bibcode=1988PhRvL..60.2284D |url=http://eprints.uniss.it/377/1/Demontis_P_Articolo_1988_New.pdf }}</ref> In superionic water, water molecules break apart and the oxygen ions [[crystallization|crystallize]] into an evenly spaced lattice while the [[hydrogen ions]] float around freely within the oxygen lattice.<ref name="newscientist.com">[https://www.newscientist.com/article/mg20727764.500-weird-water-lurking-inside-giant-planets.html Weird water lurking inside giant planets], New Scientist,01 September 2010, Magazine issue 2776.</ref> The freely mobile hydrogen ions make superionic water almost as [[electrical resistivity and conductivity|conductive]] as typical metals, making it a [[Fast ion conductor|superionic conductor]].<ref name="Millot2019">{{cite journal |last1=Millot |first1=Marius |last2=Coppari |first2=Federica |last3=Rygg |first3=J. Ryan |last4=Correa Barrios |first4=Antonio |last5=Hamel |first5=Sebastien |last6=Swift |first6=Damian C. |last7=Eggert |first7=Jon H. |title=Nanosecond X-ray diffraction of shock-compressed superionic water ice |journal=Nature |date=8 May 2019 |volume=569 |issue=7755 |pages=251–255 |doi=10.1038/s41586-019-1114-6|pmid=31068720 |bibcode=2019Natur.569..251M |osti=1568026 |s2cid=256768272 |url=https://www.osti.gov/biblio/1568026 }}</ref> The ice appears black in color.<ref name="NP-20180205"/><ref name="auto3"/> It is distinct from [[Self-ionization of water|ionic water]], which is a hypothetical liquid state characterized by a disordered soup of hydrogen and oxygen ions.

The initial evidence came from optical measurements of laser-heated water in a [[diamond anvil cell]],<ref name="Goncharov">{{cite journal |doi=10.1103/PhysRevLett.94.125508 |pmid=15903935 |title=Dynamic Ionization of Water under Extreme Conditions |first1=Alexander F. |last1=Goncharov |first2=Nir |last2=Goldman |first3=Laurence E. |last3=Fried |first4=Jonathan C. |last4=Crowhurst |first5=I-Feng W. |last5=Kuo |first6=Christopher J. |last6=Mundy |first7=Joseph M. |last7=Zaug |display-authors=1 |journal=Phys. Rev. Lett. |volume=94 |issue=12 |pages=125508 |year=2005 |bibcode=2005PhRvL..94l5508G |url=https://digital.library.unt.edu/ark:/67531/metadc1417703/m2/1/high_res_d/15015926.pdf }}</ref> and from optical measurements of water shocked by extremely powerful lasers.<ref name="NP-20180205">{{cite journal |author=Millot, Marius |display-authors=etal |title=Experimental evidence for superionic water ice using shock compression |date=5 February 2018 |journal=[[Nature Physics]] |volume=14 |issue=3 |pages=297–302 |doi=10.1038/s41567-017-0017-4 |bibcode=2018NatPh..14..297M |osti=1542614 |s2cid=256703104 |url=https://www.osti.gov/biblio/1542614 }}</ref> 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.<ref name="Millot2019" /> In 2005 Laurence Fried led a team at [[Lawrence Livermore National Laboratory]] (LLNL) to recreate the formative conditions of superionic water. Using a technique involving smashing water molecules between [[diamond]]s and super heating it with [[laser]]s they observed frequency shifts which indicated that a [[phase transition]] had taken place.  The team also created [[computer model]]s which indicated that they had indeed created superionic water.<ref name="nature.com" />  In 2013 Hugh F. Wilson, Michael L. Wong, and Burkhard Militzer at the University of California, Berkeley published a paper predicting the [[face-centered cubic]] lattice structure that would emerge at higher pressures.<ref name=Phys.org-2013-04-25/> Additional experimental evidence was found by Marius Millot and colleagues in 2018 by inducing high pressure on water between diamonds and then shocking the water using a laser pulse.<ref name="NP-20180205"/><ref name="auto3">{{Cite magazine|url=https://www.wired.com/story/a-bizarre-form-of-water-may-exist-all-over-the-universe/|title=A Bizarre Form of Water May Exist All Over the Universe|last=Sokol|first=Joshua|date=2019-05-12|magazine=Wired|access-date=2019-05-13|issn=1059-1028}}</ref>

{{As of|2013}}, it is theorized that superionic ice can possess two crystalline structures.  At pressures in excess of {{convert|50|GPa|psi|lk=in|abbr=on}} 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.<ref name=Phys.org-2013-04-25/>

In 2018, the existence of superionic ice was confirmed in a laboratory setting. To create the required pressure, LLNL researchers compressed small amounts of water between pieces of diamond. At {{convert|360000|psi|MPa|order=flip|abbr=on|lk=in}}, the water became ice VII, a form that is solid at room temperature. This ice, trapped within [[diamond anvil cell]]s, was taken to the [[University of Rochester]] to be blasted with a laser. For less than a billionth of a second, the ice was subjected to conditions similar to those within the mantle of an [[ice giant]]. The temperature in the diamond cells rose thousands of degrees, and the pressure increased to over a million times that of Earth's atmosphere.<ref name=":0">{{Cite news|url=https://www.nytimes.com/2018/02/05/science/superionic-water-neptune-uranus.html|title=New Form of Water, Both Liquid and Solid, Is 'Really Strange'|last=Chang|first=Kenneth|date=2018-02-05|work=The New York Times|access-date=2018-02-13|language=en-US|issn=0362-4331}}</ref><ref>{{cite web |last1=Langin |first1=Katie |title=Scientists create a new form of matter—superionic water ice |url=https://www.science.org/content/article/scientists-create-new-form-matter-superionic-water-ice |website=Science |access-date=17 May 2024}}</ref> 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.<ref name=":0" /> More recent experiments from the same LLNL team used x-ray crystallography on laser-shocked water droplets to determine that the oxygen ions enter a face-centered-cubic phase, which was dubbed ice XVIII and reported in the journal ''Nature'' in May 2019.<ref name="Millot2019" />

=== Ice XIX ===
The first report regarding ice XIX was published in 2018 by Thomas Loerting's group from Austria.<ref name="pmid29780552"/> They quenched HCl-doped ice VI to 77 K at different pressures between 1.0 and 1.8 GPa to collect [[differential scanning calorimetry]] (DSC) thermograms, [[Dielectric spectroscopy|dielectric spectrum]], [[Raman spectroscopy|Raman spectrum]], and [[X-ray diffraction]] patterns. In the DSC signals, there was an endothermic feature at about 110 K in addition to the endotherm corresponding to the ice XV-VI transition. Additionally, the Raman spectra, dielectric properties, and the ratio of the lattice parameters differed from those of ice XV. Based on these observations, they proposed the existence of a second hydrogen-ordered phase of ice VI, naming it ice beta-XV.

In 2019, Alexander Rosu-Finsen and Christoph Salzman argued that there was no need to consider this to be a new phase of ice, and proposed a "deep-glassy" state scenario.<ref name="pmid30713649">{{cite journal |last1=Rosu-Finsen |first1=A|last2= Salzmann |first2=CG |year=2019 |title=Origin of the low-temperature endotherm of acid-doped ice VI: new hydrogen-ordered phase of ice or deep glassy states? |journal=Chem Sci |volume=10 |issue=2 |pages=515–523 |doi=10.1039/c8sc03647k |pmc=6334492 |pmid=30713649}}</ref> 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, D<sub>2</sub>O 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) <ref name="pmid31257365">{{cite journal |author1=Thoeny AV|author2= Gasser TM|author3= Loerting T|author3-link=Thomas Loerting |year=2019 |title=Distinguishing ice β-XV from deep glassy ice VI: Raman spectroscopy. |journal=Phys Chem Chem Phys |volume=21 |issue=28 |pages=15452–15462 |doi=10.1039/c9cp02147g |pmc= |pmid=31257365|bibcode= 2019PCCP...2115452T|s2cid= 195764029|doi-access=free }}</ref> 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.<ref name="pmid31972078">{{cite journal |author=Rosu-Finsen A, Amon A, Armstrong J, Fernandez-Alonso F, Salzmann CG |year=2020 |title=Deep-Glassy Ice VI Revealed with a Combination of Neutron Spectroscopy and Diffraction. |journal=J Phys Chem Lett |volume=11 |issue=3 |pages=1106–1111 |doi=10.1021/acs.jpclett.0c00125 |pmc=7008458 |pmid=31972078}}</ref> 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.<ref name="pmid33602936"/> collected neutron diffraction profiles ''in situ'' (''i.e.'' under high pressure) and found new Bragg features completely different from both ice VI and ice XV. They performed [[Rietveld refinement]] of the profiles based on the <math>\sqrt{2} \times \sqrt{2} \times 1</math> supercell of ice XV and proposed some leading candidates for the space group of ice XIX: P-4, Pca21, Pcc2, P21/a, and P21/c. They also measured dielectric spectra ''in situ'' and determined phase boundaries of ices VI/XV/XIX. They found that the sign of the slope of the boundary turns negative from positive at 1.6 GPa indicating the existence of two different phases by the [[Clausius–Clapeyron relation]].

Gasser et al.<ref name="pmid33602946">{{cite journal| author=Gasser TM, Thoeny AV, Fortes AD, Loerting T| title=Structural characterization of ice XIX as the second polymorph related to ice VI. | journal=Nat Commun | year= 2021 | volume= 12 | issue= 1 | pages= 1128 | pmid=33602946 | doi=10.1038/s41467-021-21161-z | pmc=7892819 | bibcode=2021NatCo..12.1128G }}</ref> 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 D<sub>2</sub>O ice XIX was significantly smaller than that of HCl-doped H<sub>2</sub>O ice XIX, and that doping of 0.5% of H<sub>2</sub>O into D<sub>2</sub>O 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.<ref name="pmid34039987">{{cite journal| author=Salzmann CG, Loveday JS, Rosu-Finsen A, Bull CL| title=Structure and nature of ice XIX. | journal=Nat Commun | year= 2021 | volume= 12 | issue= 1 | pages= 3162 | pmid=34039987 | doi=10.1038/s41467-021-23399-z | pmc=8155070 | bibcode=2021NatCo..12.3162S }}</ref> 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.

== Practical implications ==
=== Earth's natural environment ===
[[image:Icecube-detail.jpg|thumb|Photograph showing details of an ice cube under magnification.  Ice I<sub>h</sub> is the form of ice commonly seen on Earth.]]
[[image:Phase Space of Ice Ih.png|thumb|Phase space of ice I<sub>h</sub> with respect to other ice phases.]]
Virtually all ice in the [[biosphere]] is ice I<sub>h</sub> (pronounced: '''ice one h''', also known as '''ice-phase-one'''). Ice I<sub>h</sub> exhibits many peculiar properties that are relevant to the existence of life and regulation of [[Climatology|global climate]].<ref>{{cite web |type=Physics 511 paper |url=http://atom.me.gatech.edu/zhut/Courses/Courses_HarvardCollection/caiwei/phasesofice.pdf|title=The Many Phases of Ice|author=Norman Anderson|publisher=Iowa State University|archive-url=https://web.archive.org/web/20091007073915/http://atom.me.gatech.edu/zhut/Courses/Courses_HarvardCollection/caiwei/phasesofice.pdf|archive-date=7 October 2009}}</ref> For instance, its density is lower than that of [[Properties of water|liquid water]]. This is attributed to the presence of [[hydrogen bonds]] which causes atoms to become closer in the liquid phase.<ref>{{cite book|url=https://books.google.com/books?id=BV6cAQAAQBAJ&pg=PA144 |first1=Peter |last1=Atkins |first2=Julio |last2=de Paula |page=144 |title=Physical chemistry.|date=2010|publisher=W. H. Freeman and Co.|location=New York|isbn=978-1429218122|edition=9th}}</ref> Because of this, ice I<sub>h</sub> floats on water, which is highly unusual when compared to other materials. The solid phase of materials is usually more closely and neatly packed and has a higher density than the liquid phase. When lakes freeze, they do so only at the surface, while the bottom of the lake remains near {{convert|4|C|K F|0}} because water is densest at this temperature. This anomalous behavior of water and ice is what allows fish to survive harsh winters. The density of ice I<sub>h</sub> increases when cooled, down to about {{convert|-211|C|K F|0}}; below that temperature, the ice expands again ([[negative thermal expansion]]).<ref name=Rottger /><ref name=Buckingham />

Besides ice I<sub>h</sub>, a small amount of ice I<sub>c</sub> may occasionally present in the upper atmosphere clouds.<ref>{{cite journal |last=Murray |first=Benjamin J.|author2=Knopf, Daniel A. |author3=Bertram, Allan K. |year=2005|title=The formation of cubic ice under conditions relevant to Earth's atmosphere|journal=Nature|volume=434|pages=202–205|doi=10.1038/nature03403|pmid=15758996|issue=7030|bibcode=2005Natur.434..202M|s2cid=4427815}}</ref> It is believed to be responsible for the observation of Scheiner's [[Halo (optical phenomenon)|halo]], a rare ring that occurs near 28 degrees from the Sun or the Moon.<ref>{{Cite journal |last=Whalley |first=E. |year=1981 |title=Scheiner's Halo: Evidence for Ice I{{sub|c}} in the Atmosphere |journal=Science |volume=211 |issue=4480 |pages=389–390 |bibcode=1981Sci...211..389W |doi=10.1126/science.211.4480.389 |pmid=17748273}}</ref> However, many atmospheric samples which were previously described as cubic ice were later shown to be stacking disordered ice with trigonal symmetry,<ref>{{Cite journal |last1=Murray |first1=Benjamin J. |last2=Salzmann |first2=Christoph G. |last3=Heymsfield |first3=Andrew J. |last4=Dobbie |first4=Steven |last5=Neely |first5=Ryan R. |last6=Cox |first6=Christopher J. |year=2015 |title=Trigonal Ice Crystals in Earth's Atmosphere |url=http://eprints.whiterose.ac.uk/86859/8/MurrayTrigonalIceCrystals.pdf |journal=Bulletin of the American Meteorological Society |volume=96 |issue=9 |pages=1519–1531 |bibcode=2015BAMS...96.1519M |doi=10.1175/BAMS-D-13-00128.1}}</ref><ref>{{Cite web |url=https://water.lsbu.ac.uk/water/ice1h1c.html |title=Stacking disordered ice; Ice I{{sub|sd}} |author=Chaplin, Martin |work=Water Structure and Science |publisher=[[London South Bank University]]}}</ref><ref>{{cite journal |last1=Malkin |first1=Tamsin L. |last2=Murray |first2=Benjamin J. |last3=Salzmann |first3=Christoph G. |last4=Molinero |first4=Valeria |last5=Pickering |first5=Steven J. |last6=Whale |first6=Thomas F. |title=Stacking disorder in ice I |journal=Physical Chemistry Chemical Physics |date=2015 |volume=17 |issue=1 |pages=60–76 |doi=10.1039/c4cp02893g|pmid=25380218 |doi-access=free }}</ref> and it has been dubbed the ″most faceted ice phase in a literal and a more general sense.″<ref>{{Cite journal |last1=Kuhs |first1=W. F. |last2=Sippel |first2=C. |last3=Falenty |first3=A. |last4=Hansen |first4=T. C. |year=2012 |title=Extent and relevance of stacking disorder in "ice I{{sub|c}}" |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=52 |pages=21259–21264 |bibcode=2012PNAS..10921259K |doi=10.1073/pnas.1210331110 |pmc=3535660 |pmid=23236184 |doi-access=free }}</ref> The first true samples of cubic ice were only reported in 2020.<ref name="Salzmann2020">{{cite journal |last1=Salzmann |first1=Christoph G. |last2=Murray |first2=Benjamin J. |title=Ice goes fully cubic |journal=Nature Materials |date=June 2020 |volume=19 |issue=6 |pages=586–587 |doi=10.1038/s41563-020-0696-6|pmid=32461682 |bibcode=2020NatMa..19..586S |s2cid=218913209 }}</ref><ref name="Komatsu2020" />

Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for [[noctilucent clouds]] on Earth and is usually formed by [[vapor deposition|deposition]] of water vapor in cold or vacuum conditions. Ice clouds form at and below the Earth's high latitude mesopause (~90&nbsp;km) where temperatures have been observed to fall as to below 100 K.<ref>{{cite journal |last1=Lübken |first1=F.-J. |last2=Lautenbach |first2=J. |last3=Höffner |first3=J. |last4=Rapp |first4=M. |last5=Zecha |first5=M. |title=First continuous temperature measurements within polar mesosphere summer echoes |journal=Journal of Atmospheric and Solar-Terrestrial Physics |date=March 2009 |volume=71 |issue=3–4 |pages=453–463 |doi=10.1016/j.jastp.2008.06.001|bibcode=2009JASTP..71..453L }}</ref> It has been suggested that homogeneous nucleation of ice particles results in low density amorphous ice.<ref>{{cite journal |last1=Murray |first1=Benjamin J. |last2=Jensen |first2=Eric J. |title=Homogeneous nucleation of amorphous solid water particles in the upper mesosphere |journal=Journal of Atmospheric and Solar-Terrestrial Physics |date=January 2010 |volume=72 |issue=1 |pages=51–61 |doi=10.1016/j.jastp.2009.10.007|bibcode=2010JASTP..72...51M }}</ref> Amorphous ice is likely confined to the coldest parts of the clouds and stacking disordered ice I is thought to dominate elsewhere in these [[polar mesospheric clouds]].<ref>{{cite journal |last1=Murray |first1=Benjamin J. |last2=Malkin |first2=Tamsin L. |last3=Salzmann |first3=Christoph G. |title=The crystal structure of ice under mesospheric conditions |journal=Journal of Atmospheric and Solar-Terrestrial Physics |date=May 2015 |volume=127 |pages=78–82 |doi=10.1016/j.jastp.2014.12.005 |bibcode=2015JASTP.127...78M |doi-access=free }}</ref>

In 2018, ice VII was identified among [[Inclusion (mineral)|inclusions]] found in natural [[diamonds]].<ref>{{cite journal |author=O. Tschauner |author2=S Huang |author3=E. Greenberg |author4=V.B. Prakapenka |author5=C. Ma |author6=G.R. Rossman |author7=A.H. Shen |author8=D. Zhang |author9=M. Newville |author10=A. Lanzirotti |author11=K. Tait |title = Ice-VII inclusions in diamonds: Evidence for aqueous fluid in Earth's deep mantle | journal = Science |year = 2018 |volume=359 |issue = 6380 |pages=1136–1139 |doi = 10.1126/science.aao3030 |pmid = 29590042 |bibcode = 2018Sci...359.1136T |s2cid = 206662912 |doi-access = free }}</ref>  Due to this demonstration that ice VII exists in nature, the [[International Mineralogical Association]] duly classified ice VII as a distinct [[mineral]].<ref>{{cite journal|url=https://www.science.org/content/article/pockets-water-may-lay-deep-below-earth-s-surface|title=Pockets of water may lay deep below Earth's surface|author=Sid Perkins|journal=Science|date=2018-03-08|access-date=March 8, 2018|url-status=live|archive-url=https://web.archive.org/web/20180308220310/http://www.sciencemag.org/news/2018/03/pockets-water-may-lay-deep-below-earth-s-surface|archive-date=March 8, 2018}}</ref> The ice VII was presumably formed when water trapped inside the diamonds retained the high pressure of the deep [[mantle (geology)|mantle]] due to the strength and rigidity of the diamond lattice, but cooled down to surface temperatures, producing the required environment of high pressure without high temperature.<ref>{{cite news|last1=Netburn|first1=Deborah|title=What scientists found trapped in a diamond: a type of ice not known on Earth|url=http://www.latimes.com/science/sciencenow/la-sci-sn-water-in-diamonds-20180308-story.html|access-date=12 March 2018|work=Los Angeles Times|url-status=live|archive-url=https://web.archive.org/web/20180312003000/http://www.latimes.com/science/sciencenow/la-sci-sn-water-in-diamonds-20180308-story.html|archive-date=12 March 2018}}</ref>

Ice XI is thought to be a more stable conformation than ice I<sub>h</sub>, and so it may form on Earth. However, the transformation is very slow. According to one report, in Antarctic conditions it is estimated to take at least 100,000 years to form without the assistance of catalysts.{{citation needed|date=August 2017}} Ice XI was sought and found in Antarctic ice that was about 100 years old in 1998.<ref>{{cite journal |doi=10.1016/S0009-2614(98)00908-7 |title=Proton ordering in Antarctic ice observed by Raman and neutron scattering |journal=Chemical Physics Letters |volume=294 |issue=6 |pages=554–558 |year=1998 |last1=Fukazawa |first1=Hiroshi |last2=Mae |first2=Shinji |last3=Ikeda |first3=Susumu |last4=Watanabe |first4=Okitsugu |bibcode=1998CPL...294..554F }}</ref> A further study in 2004 was not able to reproduce this finding, however, after studying Antarctic ice which was around 3000 years old.<ref>{{cite journal|last=Fortes|first=A. D.|author2=Wood, I. G.|author3=Grigoriev, D.|author4=Alfredsson, M.|author5=Kipfstuhl, S.|author6=Knight, K. S.|author7=Smith, R. I.|title=No evidence for large-scale proton ordering in Antarctic ice from powder neutron diffraction|journal=The Journal of Chemical Physics|date=1 January 2004|volume=120|issue=24|pages=11376–9|doi=10.1063/1.1765099|url=http://jcp.aip.org/resource/1/jcpsa6/v120/i24/p11376_s1?isAuthorized=no|pmid=15268170|bibcode=2004JChPh.12011376F|access-date=22 April 2012|archive-url=https://archive.today/20120729031327/http://jcp.aip.org/resource/1/jcpsa6/v120/i24/p11376_s1?isAuthorized=no|archive-date=29 July 2012|url-status=dead}}</ref> The 1998 Antarctic study also claimed that the transformation temperature (ice XI => ice I<sub>h</sub>) is {{convert|-36|°C|K}}, which is far higher than the temperature of the expected triple point mentioned above  (72&nbsp;K, ~0&nbsp;Pa). Ice XI was also found in experiments using pure water at very low temperature (~10&nbsp;K) and low pressure&nbsp;– conditions thought to be present in the upper atmosphere.<ref>{{cite journal | last1 = Furić | first1 = K. | last2 = Volovšek | first2 = V. | year = 2010 | title = Water ice at low temperatures and pressures; new Raman results | journal = J. Mol. Structure | volume = 976 | issue = 1–3| pages = 174–180 | doi=10.1016/j.molstruc.2010.03.024| bibcode = 2010JMoSt.976..174F }}</ref> Recently,{{Recently|date=May 2024}} small domains of ice XI were found to form in pure water; its phase transition back to ice I<sub>h</sub> occurred at 72 K while under hydrostatic pressure conditions of up to 70 MPa.<ref>{{cite journal|last1=Yen|first1=Fei|last2=Chi|first2=Zhenhua|title=Proton ordering dynamics of H<sub>2</sub>O ice|journal=Physical Chemistry Chemical Physics|date=16 Apr 2015|volume=17|issue=19|pages=12458–12461|doi=10.1039/C5CP01529D|pmid=25912948|arxiv = 1503.01830 |bibcode = 2015PCCP...1712458Y |s2cid=7736338}}</ref>

=== Human industry ===
Amorphous ice is used in some scientific experiments, especially in [[cryo-electron microscopy]] of biomolecules.<ref>{{cite journal|last1=Dubochet|first1=J.|last2=Adrian|first2=M.|last3=Chang|first3=J. .J|last4=Homo|first4=J. C.|last5=Lepault|first5=J-|last6=McDowall|first6=A. W.|last7=Schultz |first7=P. |year=1988 |title=Cryo-electron microscopy of vitrified specimens |journal=Quarterly Reviews of Biophysics |volume=21 |issue=2 |pages=129–228 |s2cid=2741633 |doi=10.1017/S0033583500004297 |pmid=3043536 |url=https://serval.unil.ch/resource/serval:BIB_D6E6989A1815.P001/REF.pdf }}</ref> The individual molecules can be preserved for imaging in a state close to what they are in liquid water.

Ice&nbsp;XVII can repeatedly [[adsorb]] and release hydrogen molecules without degrading its structure.<ref name="delRosso2016" />  The total amount of hydrogen that ice&nbsp;XVII can adsorb depends on the amount of pressure applied, but hydrogen molecules can be adsorbed by ice&nbsp;XVII even at pressures as low as a few millibars{{efn|One millibar is equivalent to {{cvt|100|Pa|psi atm}}.<!-- 1 bar is defined as 100000 pa -->}} if the temperature is under {{cvt|40|K|C F}}.<ref name="delRosso2016" /> The adsorbed hydrogen molecules can then be released, or [[desorbed]], through the application of heat.<ref name="DelRosso2017">{{cite journal |last1=Del Rosso |first1=Leonardo |last2=Celli |first2=Milva |last3=Ulivi |first3=Lorenzo |title=Ice XVII as a Novel Material for Hydrogen Storage |journal=Challenges |date=June 2017 |volume=8 |issue=1 |pages=3 |doi=10.3390/challe8010003 |doi-access=free }}</ref> This was an unexpected property of ice&nbsp;XVII, and could allow it to be used for [[hydrogen storage]], an issue often mentioned in [[environmental technology]].
<ref name="DelRosso2017" />

Aside from storing hydrogen via [[compressed hydrogen|compression]] or [[liquid hydrogen|liquification]], it can also be stored within a solid substance, either via a reversible chemical process ([[chemisorption]]) or by having the hydrogen molecules attach to the substance via the [[van der Waals force]] ([[physisorption]]). The latter process can occur within ice&nbsp;XVII.<ref name="DelRosso2017" /> In physisorption, there is no chemical reaction, and the chemical bond between the two atoms within a hydrogen molecule remains intact. Because of this, the number of adsorption&ndash;desorption cycles ice&nbsp;XVII can withstand is "theoretically infinite".<ref name="DelRosso2017" />

One significant advantage of using ice&nbsp;XVII as a hydrogen storage medium is the low cost of the only two chemicals involved: hydrogen and water.<ref name="DelRosso2017" /> In addition, ice&nbsp;XVII has shown the ability to store hydrogen at an H{{sub|2}} to H{{sub|2}}O [[molar ratio]] above 40%<!-- using '%' as this is a technical article, as per mos:% -->, higher than the theoretical maximum ratio for [[Clathrate hydrate#Structure|sII]] clathrate hydrates, another potential storage medium.<ref name="delRosso2016" />  However, if ice&nbsp;XVII is used as a storage medium, it must be kept under a temperature of {{cvt|130|K|C F}} or risk being destabilized.<ref name="DelRosso2017" />

=== Outer space ===
In outer space, hexagonal crystalline ice (the predominant form found on Earth) is extremely rare. Known examples are typically associated with volcanic action.<ref>{{cite news|url=https://www.nytimes.com/2004/12/09/science/09ice.html|title=Astronomers Contemplate Icy Volcanoes in Far Places|author=Chang, Kenneth|work=The New York Times|date=9 December 2004|access-date=30 July 2012|url-status=live|archive-url=https://web.archive.org/web/20150509123243/http://www.nytimes.com/2004/12/09/science/09ice.html|archive-date=9 May 2015}}</ref> Water in the [[interstellar medium]] is instead dominated by amorphous ice, making it likely the most common form of water in the universe.<ref name="stanley">{{cite journal|last1=Debennetti|first1=Pablo G. |last2=Stanley |first2=H. Eugene |year=2003 |title=Supercooled and Glassy Water |journal=Physics Today |volume=56 |issue=6 |pages=40–46 |bibcode=2003PhT....56f..40D|doi=10.1063/1.1595053 |url=http://polymer.bu.edu/hes/articles/ds03.pdf |access-date=19 September 2012 }}</ref><ref name="PappasLS2023">{{cite news|last1=Pappas|first1=Stephanie|date=2 February 2023|title=Scientists created a weird new type of ice that is almost exactly as dense as water|language=en|work=Live Science|url=https://www.livescience.com/new-medium-density-amorphous-ice}}</ref>

Amorphous ice can be separated from crystalline ice based on its [[Near-infrared spectroscopy|near-infrared]] and infrared spectrum. At near-IR wavelengths, the characteristics of the 1.65, 3.1, and 4.53&nbsp;[[μm]] water absorption lines are dependent on the ice temperature and crystal order.<ref name="NewmanBuratti2008">{{cite journal |title=Photometric and spectral analysis of the distribution of crystalline and amorphous ices on Enceladus as seen by Cassini |last1=Newman |first1=Sarah F. |last2=Buratti |first2=B. J. |last3=Brown |first3=R. H. |last4=Jaumann |first4=R. |last5=Bauer |first5=J. |last6=Momary |first6=T. |journal=Icarus |volume=193 |issue=2 |pages=397–406 |year=2008 |bibcode=2008Icar..193..397N |doi=10.1016/j.icarus.2007.04.019|url=https://dspace.mit.edu/bitstream/1721.1/114323/1/1028747523-MIT.pdf |hdl=1721.1/114323 |hdl-access=free }}</ref> The peak strength of the 1.65&nbsp;μm band as well as the structure of the 3.1&nbsp;μm band are particularly useful in identifying the crystallinity of water ice.<ref>{{cite journal|title=The temperature-dependent near-infrared absorption spectrum of hexagonal H<sub>2</sub>O ice|author1=Grundy, W. M. |author2=Schmitt, B. |journal=Journal of Geophysical Research|volume=103|issue=E11 |page=25809|year=1998|bibcode=1998JGR...10325809G|doi=10.1029/98je00738}}</ref><ref>{{cite journal|last1=Hagen |first1=W. |last2=ielens |first2=A.G.G.M. |last3=Greenberg |first3=J. M. |year=1981 |title=The Infrared Spectra of Amorphous Solid Water and Ice Between 10 and 140 K |journal=Chemical Physics |volume=56 |issue=3 |pages=367–379 |doi=10.1016/0301-0104(81)80158-9 |bibcode = 1981CP.....56..367H }}</ref>

At longer IR wavelengths, amorphous and crystalline ice have characteristically different absorption bands at 44 and 62&nbsp;μm in that the crystalline ice has significant absorption at 62&nbsp;μm while amorphous ice does not.<ref name="Moore, Marla H.; Hudson, Reggie L. 1992 353"/> In addition, these bands can be used as a temperature indicator at very low temperatures where other indicators (such as the 3.1 and 12&nbsp;μm bands) fail.<ref>{{cite journal|title=Molecular ices as temperature indicators for interstellar dust: the 44- and 62-μm lattice features of H2O ice.|author1=Smith, R. G. |author2=Robinson, G. |author3=Hyland, A. R. |author4=Carpenter, G. L. |journal=Monthly Notices of the Royal Astronomical Society|volume=271|issue=2 |pages=481–489|year=1994|bibcode=1994MNRAS.271..481S|doi=10.1093/mnras/271.2.481|doi-access=free}}</ref> This is useful studying ice in the interstellar medium and circumstellar disks. However, observing these features is difficult because the atmosphere is opaque at these wavelengths, requiring the use of space-based infrared observatories.

==== Properties of the amorphous ice in the Solar System ====
In general, amorphous ice can form below ~130&nbsp;K.<ref>{{cite journal|doi=10.1007/BF00651770|title=The heterogeneous condensation of interstellar ice grains|author=Seki, J. |author2=Hasegawa, H.|journal=Astrophysics and Space Science |volume=94|issue=1|pages=177–189|year=1983|bibcode=1983Ap&SS..94..177S|s2cid=121008219 }}</ref> At this temperature, water molecules are unable to form the crystalline structure commonly found on Earth. Amorphous ice may also form in the coldest region of the Earth's atmosphere, the summer polar mesosphere, where [[noctilucent clouds]] exist.<ref>{{cite journal |last=Murray |first=B. J.|author2=Jensen, E. J.|year=2010 |title=Homogeneous nucleation of amorphous solid water particles in the upper mesosphere|journal=J. Atmos. Sol.-Terr. Phys.|volume=72 |issue=1|pages=51–61 |doi=10.1016/j.jastp.2009.10.007|bibcode = 2010JASTP..72...51M }}</ref> These low temperatures are readily achieved in astrophysical environments such as molecular clouds, circumstellar disks, and the surfaces of objects in the outer Solar System. In the laboratory, amorphous ice transforms into crystalline ice if it is heated above 130&nbsp;K, although the exact temperature of this conversion is dependent on the environment and ice growth conditions.<ref name="SolarSystemIces">{{cite book |last1=Jenniskens |last2=Blake |last3=Kouchi |title=Solar System Ices |year=1998 |publisher=Dordrecht Kluwer Academic Publishers |pages=139–155}}</ref> The reaction is irreversible and exothermic, releasing 1.26–1.6&nbsp;kJ/mol.<ref name="SolarSystemIces" />

An additional factor in determining the structure of water ice is deposition rate. Even if it is cold enough to form amorphous ice, crystalline ice will form if the flux of water vapor onto the substrate is less than a temperature-dependent critical flux.<ref name="Kouchi, A., Yamamoto, T., Kozasa, T., Kuroda, T., Greenberg, J. M. H. 1994 1009">{{cite journal|last1=Kouchi |first1=A. |last2=Yamamoto |first2=T. |last3=Kozasa |first3=T. |last4=Kuroda |first4=T. |last5=Greenberg |first5=J. M. |year=1994 |title=Conditions for condensation and preservation of amorphous ice and crystallinity of astrophysical ices |journal=Astronomy and Astrophysics |volume=290 |page=1009 |bibcode=1994A&A...290.1009K |url=https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/42838/1/59kozasa_AA290.pdf |archive-url=https://web.archive.org/web/20200322062604/https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/42838/1/59kozasa_AA290.pdf |archive-date=22 March 2020 |url-status=live }}</ref> This effect is important to consider in astrophysical environments where the water flux can be low. Conversely, amorphous ice can be formed at temperatures higher than expected if the water flux is high, such as flash-freezing events associated with [[cryovolcanism]].

At temperatures less than 77&nbsp;K, irradiation from ultraviolet photons as well as high-energy electrons and ions can damage the structure of crystalline ice, transforming it into amorphous ice.<ref>{{cite journal|title=Amorphization of cubic ice by ultraviolet irradiation|author1=Kouchi, Akira |author2=Kuroda, Toshio |journal=Nature |volume=344|pages=134–135|year=1990|bibcode=1990Natur.344..134K|doi=10.1038/344134a0|issue=6262|s2cid=4306842 }}</ref><ref name="Moore, Marla H.; Hudson, Reggie L. 1992 353">{{cite journal|title=Far-infrared spectral studies of phase changes in water ice induced by proton irradiation|author1=Moore, Marla H. |author2=Hudson, Reggie L. |journal=Astrophysical Journal|volume=401|page=353|year=1992|bibcode=1992ApJ...401..353M|doi=10.1086/172065}}</ref> Amorphous ice does not appear to be significantly affected by radiation at temperatures less than 110&nbsp;K, though some experiments suggest that radiation might lower the temperature at which amorphous ice begins to crystallize.<ref name="Moore, Marla H.; Hudson, Reggie L. 1992 353"/>

[[Peter Jenniskens]] and David F. Blake demonstrated in 1994 that a form of high-density amorphous ice is also created during vapor deposition of water on low-temperature (<&nbsp;30&nbsp;K) surfaces such as interstellar grains. The water molecules do not fully align to create the open cage structure of low-density amorphous ice. Many water molecules end up at interstitial positions. When warmed above 30&nbsp;K, the structure re-aligns and transforms into the low-density form.<ref name="adsabs.harvard.edu"/><ref name="auto1"/>

====Molecular clouds, circumstellar disks, and the primordial solar nebula====
[[Molecular cloud]]s have extremely low temperatures (~10&nbsp;K), falling well within the amorphous ice regime. The presence of amorphous ice in molecular clouds has been observationally confirmed.<ref>{{cite journal|title=High-Density Amorphous Ice, the Frost on Interstellar Grains|author1=Jenniskens, P. |author2=Blake, D. F. |author3=Wilson, M. A. |author4=Pohorille, A. |journal=Astrophysical Journal|volume=401|page=389|year=1995|bibcode=1995ApJ...455..389J|doi = 10.1086/176585 |hdl=2060/19980018148 |s2cid=122950585 |hdl-access=free}}</ref> When molecular clouds collapse to form stars, the temperature of the resulting [[circumstellar disk]] isn't expected to rise above 120&nbsp;K, indicating that the majority of the ice should remain in an amorphous state.<ref name="Kouchi, A., Yamamoto, T., Kozasa, T., Kuroda, T., Greenberg, J. M. H. 1994 1009"/> However, if the temperature rises high enough to sublimate the ice, then it can re-condense into a crystalline form since the water flux rate is so low. This is expected to be the case in the circumstellar disk of IRAS 09371+1212, where signatures of crystallized ice were observed despite a low temperature of 30–70&nbsp;K.<ref>
{{citation
 |bibcode = 1990ApJ...355L..27O 
 | last1 = Omont | first1 = Alain | last2 = Forveille | first2 = Thierry
 | last3 = Moseley | first3 = S. Harvey | last4 = Glaccum | first4 = William J.
 | last5 = Harvey | first5 = Paul M. | last6 = Likkel | first6 = Lauren Jones
 | last7 = Loewenstein | first7 = Robert F. | last8 = Lisse | first8 = Casey M.
 | title = Observations of 40–70 micron bands of ice in IRAS 09371 + 1212 and other stars
 | journal = Astrophysical Journal Letters
 | issn=0004-637X
 | date = May 20, 1990 | volume=355 | pages = L27–L30
 |doi = 10.1086/185730 | doi-access = free
}}</ref>

For the primordial solar nebula, there is much uncertainty as to the crystallinity of water ice during the circumstellar disk and planet formation phases. If the original amorphous ice survived the molecular cloud collapse, then it should have been preserved at heliocentric distances beyond Saturn's orbit (~12&nbsp;AU).<ref name="Kouchi, A., Yamamoto, T., Kozasa, T., Kuroda, T., Greenberg, J. M. H. 1994 1009"/>

==== Comets ====
The possibility of the presence of amorphous water ice in comets and the release of energy during the phase transition to a crystalline state was first proposed as a mechanism for comet outbursts.<ref>Patashnick, et.al., Nature Vol.250, No. 5464, July 1974, pp. 313–314.</ref> Evidence of amorphous ice in comets is found in the high levels of activity observed in long-period, Centaur, and Jupiter Family comets at heliocentric distances beyond ~6&nbsp;AU.<ref>{{cite journal|title=Activity of comets at large heliocentric distances pre-perihelion|author1=Meech, K. J. |author2=Pittichová, J. |author3=Bar-Nun, A. |author4=Notesco, G. |author5=Laufer, D. |author6=Hainaut, O. R. |author7=Lowry, S. C. |author8=Yeomans, D. K. |author9=Pitts, M. |journal=Icarus |volume=201|issue=2 |pages=719–739|year=2009|bibcode=2009Icar..201..719M|doi=10.1016/j.icarus.2008.12.045}}</ref> These objects are too cold for the sublimation of water ice, which drives comet activity closer to the Sun, to have much of an effect. Thermodynamic models show that the surface temperatures of those comets are near the amorphous/crystalline ice transition temperature of ~130&nbsp;K, supporting this as a likely source of the activity.<ref>{{cite journal|title=Thermochemistry of cometary nuclei 1: The Jupiter family case|author1=Tancredi, G. |author2=Rickman, H. |author3=Greenberg, J. M. |journal=Astronomy and Astrophysics|volume=286|page=659|year=1994|bibcode=1994A&A...286..659T}}</ref> The runaway crystallization of amorphous ice can produce the energy needed to power outbursts such as those observed for Centaur Comet [[29P/Schwassmann–Wachmann]] 1.<ref>{{cite journal|title=The search for a cometary outbursts mechanism: a comparison of various theories|author=Gronkowski, P.|journal=Astronomische Nachrichten|volume=328|issue=2|pages=126–136|year=2007|bibcode= 2007AN....328..126G|doi=10.1002/asna.200510657|doi-access=free}}</ref><ref>{{cite journal|title=Outburst Dust Production of Comet 29P/Schwassmann-Wachmann 1|author1=Hosek, Matthew W. Jr. |author2=Blaauw, Rhiannon C. |author3=Cooke, William J. |author4=Suggs, Robert M. |journal=The Astronomical Journal|volume=145|issue=5 |page=122|year=2013|bibcode=2013AJ....145..122H|doi=10.1088/0004-6256/145/5/122|doi-access=free}}</ref>

==== Kuiper Belt objects ====
With radiation equilibrium temperatures of 40–50&nbsp;K,<ref>{{cite journal|title=Colors and Spectra of Kuiper Belt Objects|author1=Jewitt, David C. |author2=Luu, Jane X. |journal=The Astronomical Journal|volume=122|issue=4 |pages=2099–2114|year=2001|bibcode=2001AJ....122.2099J|doi=10.1086/323304|arxiv = astro-ph/0107277 |s2cid=35561353 }}</ref> the objects in the Kuiper Belt are expected to have amorphous water ice. While water ice has been observed on several objects,<ref>{{cite journal|title=Water Ice on Kuiper Belt Object 1996 TO_66|author1=Brown, Robert H. |author2=Cruikshank, Dale P. |author3=Pendleton, Yvonne |journal=The Astrophysical Journal|volume=519|issue=1 |page=L101|year=1999|bibcode=1999ApJ...519L.101B|doi=10.1086/312098|doi-access=free}}</ref><ref>{{cite journal|title=Water ice on the surface of the large TNO 2004 DW|author1=Fornasier, S. |author2=Dotto, E. |author3=Barucci, M. A. |author4=Barbieri, C. |journal=Astronomy and Astrophysics|volume=422|issue=2 |page=L43|year=2004|bibcode=2004A&A...422L..43F|doi=10.1051/0004-6361:20048004|doi-access=free}}</ref> the extreme faintness of these objects makes it difficult to determine the structure of the ices. The signatures of crystalline water ice was observed on [[50000 Quaoar]], perhaps due to resurfacing events such as impacts or cryovolcanism.<ref>{{cite journal|title=Crystalline water ice on the Kuiper belt object (50000) Quaoar|author1=Jewitt, David C. |author2=Luu, Jane |journal=Nature|volume=432|pages=731–3|year=2004|bibcode=2004Natur.432..731J|doi=10.1038/nature03111|pmid=15592406|issue=7018|s2cid=4334385 }}</ref>

==== Icy moons ====
The Near-Infrared Mapping Spectrometer (NIMS) on NASA's Galileo spacecraft spectroscopically mapped the surface ice of the Jovian satellites [[Europa (moon)|Europa]], [[Ganymede (moon)|Ganymede]], and [[Callisto (moon)|Callisto]]. The temperatures of these moons range from 90 to 160&nbsp;K,<ref>{{cite journal|title=Temperatures on Europa from Galileo Photopolarimeter-Radiometer: Nighttime Thermal Anomalies|author1=Spencer, John R. |author2=Tamppari, Leslie K. |author3=Martin, Terry Z. |author4=Travis, Larry D. |journal=Science|volume=284|pages=1514–1516|year=1999|bibcode=1999Sci...284.1514S|doi=10.1126/science.284.5419.1514|pmid=10348736 |issue=5419}}</ref> warm enough that amorphous ice is expected to crystallize on relatively short timescales. However, it was found that Europa has primarily amorphous ice, Ganymede has both amorphous and crystalline ice, and Callisto is primarily crystalline.<ref name="Hansen2004">{{cite journal|title=Amorphous and crystalline ice on the Galilean satellites: A balance between thermal and radiolytic processes|author1=Hansen, Gary B. |author2=McCord, Thomas B. |s2cid=140162310 |journal=Journal of Geophysical Research|volume=109|issue=E1 |pages=E01012 |year=2004|bibcode=2004JGRE..109.1012H|doi = 10.1029/2003JE002149 |doi-access= }}</ref> This is thought to be the result of competing forces: the thermal crystallization of amorphous ice versus the conversion of crystalline to amorphous ice by the flux of charged particles from Jupiter. Closer to Jupiter than the other three moons, Europa receives the highest level of radiation and thus through irradiation has the most amorphous ice. Callisto is the farthest from Jupiter, receiving the lowest radiation flux and therefore maintaining its crystalline ice. Ganymede, which lies between the two, exhibits amorphous ice at high latitudes and crystalline ice at the lower latitudes. This is thought to be the result of the moon's intrinsic magnetic field, which would funnel the charged particles to higher latitudes and protect the lower latitudes from irradiation.<ref name="Hansen2004"/>  Ganymede's interior probably includes a liquid water ocean with tens to hundreds of kilometers of ice V at its base.<ref name=showman1997>{{Cite journal | doi = 10.1006/icar.1997.5778| title = Coupled Orbital and Thermal Evolution of Ganymede| journal = Icarus| volume = 129| issue = 2| pages = 367–383| year = 1997| last1 = Showman | first1 = A. | bibcode = 1997Icar..129..367S| url = http://www.lpl.arizona.edu/~showman/publications/showman-etal-1997.pdf}}</ref>

The surface ice of Saturn's moon [[Enceladus]] was mapped by the Visual and Infrared Mapping Spectrometer (VIMS) on the NASA/ESA/ASI Cassini space probe. The probe found both crystalline and amorphous ice, with a higher degree of crystallinity at the "[[Tiger stripes (Enceladus)|tiger stripe]]" cracks on the surface and more amorphous ice between these regions.<ref name="NewmanBuratti2008" /> The crystalline ice near the tiger stripes could be explained by higher temperatures caused by geological activity that is the suspected cause of the cracks. The amorphous ice might be explained by flash freezing from cryovolcanism, rapid condensation of molecules from water geysers, or irradiation of high-energy particles from Saturn.<ref name="NewmanBuratti2008" /> Similarly, one of the inner layers of [[Titan (moon)|Titan]] is believed to contain ice VI.<ref>{{Cite web|url=https://science.nasa.gov/saturn/moons/titan/facts/|title=Titan: Facts – NASA Science|website=science.nasa.gov|date=2 May 2018 |accessdate=25 April 2024}}</ref>

Medium-density amorphous ice may be present on Europa, as the experimental conditions of its formation are expected to occur there as well. It is possible that the MDA ice's unique property of releasing a large amount of heat energy after being released from compression could be responsible for 'ice quakes' within the thick ice layers.<ref name="Nature2023" />

==== Planets ====
Because ice XI can theoretically form at low pressures at temperatures between 50–70&nbsp;K&nbsp;– temperatures present in astrophysical environments of the outer solar system and within permanently shaded polar craters on the Moon and Mercury. Ice XI forms most easily around 70&nbsp;K&nbsp;– paradoxically, it takes longer to form at lower temperatures. Extrapolating from experimental measurements, it is estimated to take ~50 years to form at 70&nbsp;K and ~300 million years at 50&nbsp;K.<ref name=astroice/> It is theorized to be present in places like the upper atmospheres of [[Uranus]] and [[Neptune]]<ref name=astro-ordering /> and on [[Pluto]] and [[Charon (moon)|Charon]].<ref name=astroice>{{cite journal|title=Ice XI on Pluto and Charon?|publisher= Division for Planetary Sciences Meeting, American Astronomical Society|issue=49.02|journal= Bulletin of the American Astronomical Society|date=August 2005|volume=37|pages=732|bibcode=2005DPS....37.4902M|last1=McKinnon|first1=W. B.|last2=Hofmeister|first2=A.M.}}</ref>

Ice VII may comprise the ocean floor of [[Europa (moon)|Europa]] as well as [[Exoplanet|extrasolar planets]] (such as [[Gliese 436 b|Awohali]], and [[Gliese 1214 b|Enaiposha]]) that are largely made of water.<ref>University of Liège (2007, May 16). Astronomers Detect Shadow Of Water World In Front Of Nearby Star. ScienceDaily. Retrieved Jan. 3, 2010, from {{cite web |url=https://www.sciencedaily.com/releases/2007/05/070516151053.htm |title=Astronomers Detect Shadow of Water World in Front of Nearby Star |access-date=2018-04-22 |url-status=live |archive-url=https://web.archive.org/web/20170821212607/https://www.sciencedaily.com/releases/2007/05/070516151053.htm |archive-date=2017-08-21 }}</ref><ref>{{cite web |url=http://www.cfa.harvard.edu/news/2009/pr200924.html |title=Astronomers Find Super-Earth Using Amateur, Off-the-Shelf Technology |author=David A. Aguilar |date=2009-12-16 |publisher=Harvard-Smithsonian Center for Astrophysics |access-date=January 23, 2010 |url-status=live |archive-url=https://web.archive.org/web/20120407045343/http://www.cfa.harvard.edu/news/2009/pr200924.html |archive-date=April 7, 2012 }}</ref>

Small domains of ice XI could exist in the atmospheres of Jupiter and Saturn as well.<ref name=astro-ordering />  The fact that small domains of ice XI can exist at temperatures up to 111&nbsp;K has some scientists speculating that it may be fairly common in interstellar space, with small 'nucleation seeds' spreading through space and converting regular ice, much like the fabled [[ice-nine]] mentioned in Vonnegut's ''[[Cat's Cradle]]''.<ref name=astro-ordering/><ref>{{cite web|last=Grossman|first=Lisa|title=Electric ice a shock to the solar system|url=https://www.newscientist.com/article/mg21128274.400-electric-ice-a-shock-to-the-solar-system.html|publisher=[[New Scientist]]|access-date=7 April 2012|date=25 August 2011}}</ref> The possible roles of ice XI in interstellar space<ref name=astroice/><ref>{{cite journal|last1=Fukazawa|first1=H.|last2=Hoshikawa|first2= A.|last3=Ishii|first3= Y.|last4= Chakoumakos|first4= B. C.|last5= Fernandez-Baca|first5= J. A.|title=Existence of Ferroelectric Ice in the Universe|journal=The Astrophysical Journal|date=20 November 2006|volume=652|issue=1|pages=L57–L60|doi=10.1086/510017|bibcode = 2006ApJ...652L..57F |doi-access=free}}</ref> and planet formation<ref>{{cite journal | last1=Iedema | first1=M. J. | last2=Dresser | first2=M. J. | last3=Doering | first3=D. L. | last4=Rowland | first4=J. B. | last5=Hess | first5=W. P. | last6=Tsekouras | first6=A. A. | last7=Cowin | first7=J. P. | title=Ferroelectricity in Water Ice | journal=The Journal of Physical Chemistry B | publisher=American Chemical Society (ACS) | volume=102 | issue=46 | year=1998 | issn=1520-6106 | doi=10.1021/jp982549e | pages=9203–9214}}</ref> have been the subject of several research papers. Until observational confirmation of ice XI in outer space is made, the presence of ice XI in space remains controversial owing to the aforementioned criticism raised by Iitaka.<ref name=stability>{{cite arXiv|last=Iitaka|first=Toshiaki|title=Stability of ferroelectric ice |date=13 July 2010|eprint=1007.1792|class=cond-mat.mtrl-sci}}</ref> The infrared absorption spectra of ice XI was studied in 2009 in preparation for searches for ice XI in space.<ref>{{cite journal|last=Arakawa|first=M.|author2=Kagi, H. |author3=Fukazawa, H. |title=Laboratory Measurements of Infrared Absorption Spectra of Hydrogen-Ordered Ice: a Step to the Exploration of Ice XI in Space|journal=The Astrophysical Journal Supplement Series|date=1 October 2009|volume=184|issue=2|pages=361–365|doi=10.1088/0067-0049/184/2/361|bibcode = 2009ApJS..184..361A |doi-access=free}}</ref>

It is theorized that the [[ice giant]] planets [[Uranus]] and [[Neptune]] hold a layer of superionic water.<ref name="NYT-20180205">{{cite news |last=Chang |first=Kenneth |title=Newly Discovered Form of Water Ice Is 'Really Strange' – Long theorized to be found in the mantles of Uranus and Neptune, the confirmation of the existence of superionic ice could lead to the development of new materials. |url=https://www.nytimes.com/2018/02/05/science/superionic-water-neptune-uranus.html |date=5 February 2018 |work=[[The New York Times]] |accessdate=5 February 2018 }}</ref><ref name="nature.com">{{cite journal |title=Giant planets may host superionic water |journal=Nature |date=22 March 2005 |doi=10.1038/news050321-4 |last1=Marris |first1=Emma }}</ref><ref name="Lawrence Livermore">{{cite web|author=Charlie Osolin |url=https://www.llnl.gov/news/newsreleases/2005/SF-05-04-01.html |title=Public Affairs Office: Recreating the Bizarre State of Water Found on Giant Planets |work=Lawrence Livermore National Laboratory |publisher=Llnl.gov |accessdate=24 December 2010}}</ref><ref name=Phys.org-2013-04-25>{{cite news |website=Phys.org |url=http://phys.org/news/2013-04-phase-dominate-interiors-uranus-neptune.html |title=New phase of water could dominate the interiors of Uranus and Neptune |first=Lisa |last=Zyga |date=25 April 2013}}</ref> [[Machine learning]] and free-energy methods predict [[close-packed]] superionic phases to be stable over a wide temperature and pressure range, and a [[body-centred cubic]] superionic phase to be kinetically favoured, but stable over a small window of parameters.<ref>{{cite journal | title = Phase behaviours of superionic water at planetary conditions | last1 = Cheng | first1 = Bingqing | last2 = Bethkenhagen | first2 = Mandy | last3 = Pickard | first3 = Chris J. | last4 = Hamel | first4 = Sebastien | journal = Nature Physics | volume = 17 | pages = 1228–1232 | year = 2021 | issue = 11 | doi  = 10.1038/s41567-021-01334-9| arxiv = 2103.09035 | bibcode = 2021NatPh..17.1228C | s2cid = 232240463 }}</ref> On the other hand, there are also studies that suggest that other elements present inside the interiors of these planets, particularly [[carbon]], may prevent the formation of superionic water.<ref>{{cite journal |title=Chemical processes in the deep interior of Uranus |first1=Ricky |last1=Chau |first2=Sebastien |last2=Hamel |first3=William J. |last3=Nellis |journal=[[Nature Communications]] |volume=2 |at=Article number: 203 |doi=10.1038/ncomms1198 |pmid=21343921 |year=2011 |doi-access=free |bibcode=2011NatCo...2..203C }}</ref><ref>{{cite journal |last1=Wang |first1=Yanchao |title=High pressure partially ionic phase of water ice |journal=Nature Communications |date=29 November 2011 |volume=2 |page=563 |doi=10.1038/ncomms1566 |pmid=22127059 |doi-access=free |bibcode=2011NatCo...2..563W }}</ref>

== Notes ==
{{notelist}}

== References ==
{{reflist}}

== Further reading ==
* [http://www.idc-online.com/technical_references/pdfs/chemical_engineering/Ice_phases.pdf Ice phases] (www.idc-online.com)
* {{cite book |url=https://books.google.com/books?id=botnPwAACAAJ |title = The Chemical Physics of Ice|isbn = 9780521112307|last1 = Fletcher|first1 = N. H.|date = 2009-06-04| publisher=Cambridge University Press }}
* {{cite book |url=https://books.google.com/books?id=oC941a8lXWIC |title = Physics of Ice|isbn = 9780191581342|last1 = Petrenko|first1 = Victor F.|last2 = Whitworth|first2 = Robert W.|date = 1999-08-19| publisher=OUP Oxford }}
* {{cite web |url=https://water.lsbu.ac.uk/water/ice1h.html |title=Hexagonal ice structure |author=Chaplin, Martin |work=Water Structure and Science |publisher=[[London South Bank University]]}}
* [https://water.lsbu.ac.uk/water/phase.html London South Bank University Report]
* [https://iktp.tu-dresden.de/IKTP/pub/11/XP_ln.pdf Physik des Eises] (PDF in German, iktp.tu-dresden.de)

== External links ==
* {{cite web |first=Maren |last=Hunsberger |title=A New State of Water Reveals a Hidden Ocean in Earth's Mantle |date=September 21, 2018 |work=[[Seeker (media company)|Seeker]] |url=https://www.youtube.com/watch?v=pgm4z8vJVVk  |archive-url=https://ghostarchive.org/varchive/youtube/20211221/pgm4z8vJVVk |archive-date=2021-12-21 |url-status=live|via=[[YouTube]] }}{{cbignore}}
* {{cite web |first=Marcus |last=Woo |date=July 11, 2018 |title=The Hunt for Earth's Deep Hidden Oceans |work=[[Quanta Magazine]] |url=https://www.quantamagazine.org/the-hunt-for-earths-deep-hidden-oceans-20180711 }}
* [https://water.lsbu.ac.uk/water/amorph.html Discussion of amorphous ice] at [[London South Bank University|LSBU]]'s website.
* [http://www.nature.com/nature/journal/v435/n7041/full/nature03708.html Glass transition in hyperquenched water] from [[Nature (journal)|Nature]] (requires registration)
* [http://www.sciencemag.org/cgi/content/summary/294/5550/2305?rbfvrToken=765f39b90461f7428be6054763df6aa5a115d711 Glassy Water] from [[Science (journal)|Science]], on [[phase diagram]]s of water (requires registration)
* [https://web.archive.org/web/20050904190945/http://www.aip.org/pnu/2002/split/612-3.html AIP accounting discovery of VHDA]
* [http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?1995ApJ%2E%2E%2E455%2E%2E389J HDA in space]
* [https://web.archive.org/web/20050828183818/http://exobiology.arc.nasa.gov/ice/high.html Computerized illustrations of molecular structure of HDA]

{{Ice |expanded}}

[[Category:Water ice| ]]
[[Category:Glaciology]]
[[Category:Cryosphere]]
[[Category:Hydrogen storage]]