View source for Earth:Ice XI

{{Short description|Alternative state of water ice}}
[[File:Ice XI View along c axis.png|thumb|250px|Crystal structure of Ice XI viewed along the c-axis]]
'''Ice XI''' is the hydrogen-ordered form of [[Earth:Ice Ih|I<sub>h</sub>]], the ordinary form of [[Earth:Ice|ice]]. Different [[Earth:Ice#Phases|phases of ice]], from [[Earth:Ice II|ice II]] to ice XIX, have been created in the laboratory at different temperatures and pressures. The total [[Physics:Internal energy|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> Water molecules in ice I<sub>h</sub> are surrounded by four semi-randomly directed [[Chemistry:Hydrogen|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 [[Chemistry:Triple point|triple point]] with hexagonal ice and gaseous water at (~72&nbsp;K, ~0&nbsp;Pa).

==Properties==
[[File:Ice XI side view.png|thumb|250px|Crystal structure of ice XI (c-axis in the vertical direction)]]
Ice XI has an [[Chemistry:Orthorhombic|orthorhombic]] structure with [[Space group|space group]] Cmc2<sub>1</sub> containing eight molecules per unit cell. Its lattice parameters are a=4.465(3) Å, b=7.859(4) Å, and c=7.292(2) Å at 5&nbsp;K.<ref>{{cite journal|last1=Line|first1=Christina M. B.|last2=Whitworth|first2= R. W.|title=A high resolution neutron powder diffraction study of D<sub>2</sub>O ice XI|journal=The Journal of Chemical Physics|date=1 January 1996|volume=104|issue=24|pages=10008–10013|doi=10.1063/1.471745|bibcode = 1996JChPh.10410008L }}</ref><ref>{{cite journal | last1 = Leadbetter | first1 = A. J. | last2 = Ward | first2 = R. C. | last3 = Clark | first3 = J. W. | last4 = Tucker | first4 = P. A. | last5 = Matsuo | first5 = T. | last6 = Suga | first6 = S. | year = 1985 | title = The equilibrium low-structure of ice | journal = The Journal of Chemical Physics | volume = 82 | issue = 1| pages = 424–428 | doi=10.1063/1.448763| bibcode = 1985JChPh..82..424L }}</ref> There are actually 16 crystallographically inequivalent hydrogen-ordered configurations of ice with an orthorhombic structure of eight atoms per unit cell, but electronic structure calculations show Cmc2<sub>1</sub> to be the most stable.<ref>{{cite journal | last1 = Kuo | first1 = J. L. | last2 = Singer | first2 = S. J. | year = 2003 | title = Graph invariants for periodic systems: Towards predicting physical properties from the hydrogen bond topology of ice | journal = Physical Review E | volume = 67 | issue = 1| page = 016114 | doi=10.1103/physreve.67.016114| pmid = 12636571 |bibcode = 2003PhRvE..67a6114K }}</ref><ref>{{cite journal | last1 = Hirsch | first1 = T. K. | last2 = Ojamae | first2 = L. | year = 2004 | title = Quantum-Chemical and Force-Field Investigations of Ice Ih: Computation of Proton-Ordered Structures and Prediction of Their Lattice Energies | journal = The Journal of Physical Chemistry B | volume = 108 | issue = 40| page = 15856 | doi=10.1021/jp048434u}}</ref> Another possible configuration, with space group Pna2<sub>1</sub> is also of interest, as it is an antiferroelectric crystal, which Davidson and Morokuma incorrectly suggested as the most stable structure in 1984.<ref>{{cite journal | last1 = Davidson | first1 = E. R. | last2 = Morokuma | first2 = K. J. | year = 1984 | title = A proposed antiferroelectric structure for proton ordered ice I<sub>h</sub>. | journal = The Journal of Chemical Physics | volume = 81 | issue = 8| page = 3741 | doi=10.1063/1.448101|bibcode = 1984JChPh..81.3741D }}</ref>

In practice, ice XI is most easily prepared from a dilute (10 mM) [[Chemistry:Potassium hydroxide|KOH]] solution kept just below 72&nbsp;K for about a week (for [[Chemistry:Heavy water|D<sub>2</sub>O]] a temperature just below 76&nbsp;K will suffice).<ref>{{cite journal|last=Kawada|first=Syuji|title=Dielectric properties of KOH-doped D<sub>2</sub>O ice.|journal=Journal of the Physical Society of Japan|date=1989|volume=58|issue=1|page=295|url=https://www.jstage.jst.go.jp/article/jpsj1946/58/1/58_1_295/_article|access-date=12 May 2014|bibcode = 1989JPSJ...58..295K |doi = 10.1143/JPSJ.58.295 }}</ref><ref>{{cite journal|last1=Fukazawa|first1=Hiroshi|last2=Ikeda|first2= Susumu|last3=Mae|first3= Shinji|title=Incoherent inelastic neutron scattering measurements on ice XI; the proton-ordered phase of ice I<sub>h</sub> doped with KOH|journal=Chemical Physics Letters|year=1998|volume=282|issue=2|pages=215–218|doi=10.1016/S0009-2614(97)01266-9|bibcode = 1998CPL...282..215F }}</ref> The hydroxide ions create defects in the hexagonal ice, allowing protons to jump more freely between the oxygen atoms (and so this structure of ice XI breaks the '[[Earth:Ice rules|ice rules]]'). More specifically, each hydroxide ion creates a [[Chemistry:Bjerrum defect|Bjerrum L defect]] and an ionized vertex. Both the defect and the ion can move throughout the lattice and 'assist' with proton reordering. The positive K<sup>+</sup> ion may also play a role because it is found that KOH works better than other [[Chemistry:Alkali hydroxide|alkali hydroxide]]s.<ref name = "suga">{{cite journal|last=Suga|first=Hiroshi|title=A facet of recent ice sciences|journal=Thermochimica Acta|date=1 October 1997|volume=300|issue=1–2|pages=117–126|doi=10.1016/S0040-6031(96)03121-8}}</ref> The exact details of these ordering mechanisms are still poorly understood and under question because experimentally the mobility of the hydroxide and K<sup>+</sup> ions appear to be very low around 72&nbsp;K.<ref>Chris Knight and Sherwin J. Singer, ''Theoretical study of a hydroxide ion within the ice-Ih lattice'', Physics and Chemistry of Ice (Proceedings of the 11th International Conference on the Physics and Chemistry of Ice), ed., Werner F. Kuhs (Royal Soc. of Chemistry, 2007), p. 339.</ref><ref>{{cite book |url=https://books.google.com/books?id=anEoDwAAQBAJ&pg=PA329 |first1=Chris |last1=Knight |first2=Sherwin J. |last2=Singer |title=Tackling the problem of hydrogen bond order and disorder |work=Physics and Chemistry of Ice (Proceedings of the 11th International Conference on the Physics and Chemistry of Ice) |editor-first=Werner F. |editor-last=Kuhs |publisher=Royal Soc. of Chemistry |date=2007 |page=329 |isbn=9781847557773 }}</ref> The current belief is that KOH acts only to assist with the hydrogen reordering and is not required for the lower-energy stability of ice XI. However, calculations by Toshiaki Iitaka in 2010 call this into question.<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> Iitaka argues that the KOH ions compensate for the large net electric dipole moment of the crystal lattice along the c-axis. The aforementioned electronic structure calculations are done assuming an infinite lattice and ignore the effects of macroscopic electric fields created by surface charges. Because such fields are present in any finite size crystal, in non-doped ice XI, domains of alternating dipole moment should form as in conventional ferroelectrics.<ref name=stability/> It has also been suggested that the ice I<sub>h</sub> => ice XI transition is enabled by the [[Physics:Proton tunneling|tunneling of protons]].<ref>{{cite journal|last1=Castro-Neto|first1=A. H.|last2=Pujol|first2=P|last3=Fradkin|first3=Eduardo|title=Ice: A strongly correlated proton system|journal=Physical Review Letters|date=21 Jul 2006|volume=74|issue=2|pages=024302–12|doi=10.1103/PhysRevB.74.024302|arxiv = cond-mat/0511092 |bibcode = 2006PhRvB..74b4302C |s2cid=102581583}}</ref>

Although ice XI is thought to be a more stable conformation than ice I<sub>h</sub>, 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, 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>

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>

[[Earth:Ice Ic|Ice I<sub>c</sub>]] also has a proton-ordered form. The total internal energy of ice XIc was predicted as similar as ice XIh 
<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>

==History==
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>

==Ferroelectric properties==
Ice XI is [[Physics:Ferroelectric|ferroelectric]], meaning that it has an intrinsic polarization. To qualify as a ferroelectric it must also exhibit polarization switching under an electric field, which has not been conclusively demonstrated but which is implicitly assumed to be possible. Cubic ice also has a 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>

==Astrophysical implications==
As was mentioned, 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 [[Astronomy:Uranus|Uranus]] and [[Astronomy:Neptune|Neptune]]<ref name=astro-ordering /> and on [[Astronomy:Pluto|Pluto]] and [[Astronomy: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>

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 [[Earth:Ice-nine|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"/> 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>

==References==
{{reflist|30em}}

==External links==
*{{cite web| url=http://www.lsbu.ac.uk/water/ice_xi.html| title=Ice-eleven (ice XI)| access-date=2012-04-02| author=Chaplin, Martin| date=2007-11-11| work=Water Structure and Science}}
*{{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}}

{{ice}}

[[Category:Water ice]]
[[Category:Ferroelectric materials]]

{{Sourceattribution|Ice XI}}