Solid oxygen
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2008-06-23T21:16:27Z
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'''Solid oxygen''' forms at normal [[atmospheric pressure]] at a temperature below 54.36 K (−218.79 °C, −361.82 °F). Solid [[oxygen]] O<sub>2</sub>, like [[liquid oxygen]], is a clear substance with a light [[diffuse sky radiation|sky-blue]] color caused by [[absorption]] in the red (by contrast with the blue color of the sky, which is due to [[Rayleigh scattering]] of blue light).
Oxygen molecules have attracted attention because of the relationship between the [[molecular magnetization]] and [[crystal structure]]s, [[electronic structure]]s, and [[superconductivity]]. [[Oxygen]] is the only one of the simple [[diatomic molecule]]s (and one of the few molecules in general) to carry a [[magnetic moment]].<ref name=solid/> This makes solid oxygen particularly interesting, as it is considered a 'spin-controlled' [[crystal]]<ref name=solid>
{{citejournal|author=Freiman, Y. A. & Jodl, H. J.|title=Solid oxygen|journal=Phys. Rep.|volume=401|pages=1–228|year=2004|doi=10.1016/j.physrep.2004.06.002}}</ref> that displays unusual magnetic order.<ref>
{{citejournal|author=Goncharenko, I. N., Makarova, O. L. & Ulivi, L.|title=Direct determination of the magnetic structure of the delta phase of oxygen|journal=Phys. Rev. Lett.|volume=93|year=2004|doi=10.1103/PhysRevLett.93.055502|pages=055502}}</ref> At very high pressures, solid oxygen changes from an [[insulating]] to a [[metal]]lic state;<ref name=metallic>
{{citejournal|author=Desgreniers, S., Vohra, Y. K. & Ruoff, A. L.|title=Optical response of very high density solid oxygen to 132 GPa|journal=J. Phys. Chem.|volume=94|pages=1117–1122|year=1990|doi=10.1021/j100366a020}}</ref> and at very low temperatures, it even transforms to a [[superconductors|superconducting state]].<ref name=superconductivity>
{{citejournal|author=Shimizu, K., Suhara, K., Ikumo, M., Eremets, M. I. & Amaya, K.|title=Superconductivity in oxygen|journal=Nature|volume=393|pages=767–769|year=1998|doi=10.1038/31656}}</ref> Structural investigations of solid oxygen began in the 1920s and, at present, six distinct [[crystallographic phase]]s are established unambiguously.<ref name=solid/>
==Phase transitions==
A total of 6 different [[Phase (matter)|phase]]s of solid oxygen are known to exist:<ref name=solid/><ref name=epsilon>{{citeweb|url=http://www.azonano.com/details.asp?ArticleID=1797|title=Solid Oxygen ε-Phase Crystal Structure Determined Along With The Discovery of a Red Oxygen O8 Cluster|accessdate=2008-01-10}}</ref>
# α-phase: ''light sky-blue'' — forms at 1 atm
# β-phase: ''pink'' — forms at room temperature and high pressure
# γ-phase: only stable below room temperature
# δ-phase: ''orange'' — forms at room temperature by applying a pressure of [[Orders of magnitude (pressure)|9]] [[Pascal (unit)|GPa]]
# ε-phase: ''dark-red'' — forms at room temperature at pressures greater than 10 GPa
# ζ-phase: ''metallic'' — forms at pressures greater than [[Orders of magnitude (pressure)|96]] GPa
It has been known that oxygen is solidified into a state called the β-phase at room temperature by applying pressure, and with further increasing pressure, the β-phase undergoes [[phase transition]]s to the δ-phase at 9 GPa and the ε-phase at 10 GPa; and, due to the increase in [[molecular interaction]]s, the pink color of the β-phase changes into orange (δ-phase) and red (ε-phase), and the red color of the ε-phase further changes to black with increasing pressure. It was found that a ζ-phase appears at 96 GPa when ε-phase oxygen is further compressed.<ref name=epsilon/>
== Red oxygen ==
{{seealso|Tetraoxygen}}
As the pressure of oxygen at room temperature is increased through 10 GPa, it undergoes a dramatic [[phase transition]] to a different [[allotrope]]. Its volume decreases significantly,<ref name="Akahama">{{cite journal
| last = Akahama
| first = Yuichi
| coauthors = Haruki Kawamura, Daniel Häusermann, Michael Hanfland, and Osamu Shimomura
| year = 1995
| month = June
| title = New High-Pressure Structural Transition of Oxygen at 96 GPa Associated with Metallization in a Molecular Solid
| journal = Physical Review Letters
| volume = 74
| issue = 23
| pages = 4690–4694
| doi = 10.1103/PhysRevLett.74.4690
| url = http://link.aps.org/abstract/PRL/v74/p4690
| format = abstract
}}</ref> and it changes color from blue to deep red.<ref>{{cite journal
| last = Nicol
| first = Malcolm
| coauthors = K. R. Hirsch, and Wilfried B. Holzapfel
| year = 1979
| month = December
| title = Oxygen Phase Equilibria near 298 K
| journal = Chemical Physics Letters
| volume = 68
| issue = 1
| pages = 49–52
| doi = 10.1016/0009-2614(79)80066-4
}}</ref> This ε-phase was discovered in 1979, but the structure has been unclear. Based on its [[infrared]] [[absorption spectrum]], researchers assumed in 1999 that this phase consists of {{chem|O|4}} molecules in a crystal lattice.<ref name="Gorelli">{{cite journal
| last = Gorelli
| first = Federico A.
| coauthors = Lorenzo Ulivi, Mario Santoro, and Roberto Bini
| year = 1999
| month = November
| title = The ε Phase of Solid Oxygen: Evidence of an O<sub>4</sub> Molecule Lattice
| journal = Physical Review Letters
| volume = 83
| issue = 20
| pages = 4093–4096
| doi = 10.1103/PhysRevLett.83.4093
| url = http://link.aps.org/abstract/PRL/v83/p4093
| format = abstract
}}</ref> However, in 2006, it was shown by [[X-ray crystallography]] that this stable [[phase (matter)|phase]] known as '''ε oxygen''' or '''red oxygen''' is in fact {{chem|O|8}}.<ref>{{citejournal|title=O8 Cluster Structure of the Epsilon Phase of Solid Oxygen|
journal=Phys. Rev. Lett.|volume=97|doi=10.1103/PhysRevLett.97.085503|year=2006|
url=http://link.aps.org/abstract/PRL/v97/e085503|date=2006-08-26|accessdate=2008-01-10|
author=Hiroshi Fujihisa, Yuichi Akahama, Haruki Kawamura, Yasuo Ohishi, Osamu Shimomura, Hiroshi Yamawaki, Mami Sakashita, Yoshito Gotoh, Satoshi Takeya, and Kazumasa Honda|pages=085503}}</ref><ref name=nature>{{citejournal|url=http://www.nature.com/nature/journal/v443/n7108/abs/nature05174.html|
title=Observation of an O8 molecular lattice in the phase of solid oxygen|
journal=Nature|volume=443|pages=201–204|publishdate=2006-09-14|doi=10.1038/nature05174|accessdate=2008-01-10|
author=Lars F. Lundegaard, Gunnar Weck, Malcolm I. McMahon, Serge Desgreniers and Paul Loubeyre|
year=2006}}</ref> Nobody had predicted the structure theoretically:<ref name=epsilon/> a rhomboid {{chem|O|8}} cluster<ref>{{citejournal|title=Dark-Red O8 Molecules in Solid Oxygen: Rhomboid Clusters, Not S8-Like Rings|url=http://www3.interscience.wiley.com/cgi-bin/abstract/114084366/ABSTRACT?CRETRY=1&SRETRY=0|journal=[[Angewandte Chemie International Edition]]|volume=46|issue=11|pages=1768–1771|published=2007-01-23|accessdate=2008-01-10|doi=10.1002/anie.200604410|year=2007|author=Steudel, Ralf}}</ref> consisting of four {{chem|O|2}} molecules.
Of all the phases of solid oxygen, this phase is particularly intriguing: it exhibits a dark-red colour, very strong [[infrared absorption]], and a [[magnetic collapse]].<ref name=solid/> It is also stable over a very large pressure domain and has been the subject of numerous X-ray diffraction, spectroscopic and theoretical studies. It has been shown to have a [[monoclinic]] C2/m symmetry and its infrared absorption behaviour was attributed to the association of oxygen molecules into larger units.
*[[Liquid oxygen]] is already used as an [[oxidant]] in [[rocket|rockets]], and it has been speculated that red oxygen could make an even better oxidant, because of its higher [[energy density]].<ref>{{cite news
| first = Phillip
| last = Ball
| url = http://www.nature.com/news/2001/011122/full/011122-3.html
| title = New form of oxygen found
| work = Nature News
| date = 16 November 2001
| accessdate = 2006-07-13
}}</ref>
*Researchers think that this structure may greatly influence the structural investigation of elements.<ref name=epsilon/>
*It is the phase that forms above 600 K at pressures greater than 17 GPa.<ref name=epsilon/>
*At 11 GPa, the intra-cluster bond length of the {{chem|O|8}} cluster is 0.234 nm, and the inter-cluster distance is 0.266 nm. (For comparison, the intra-molecular bond length of the oxygen molecule {{chem|O|2}} is 0.120 nm.)<ref name=epsilon/>
*The formation mechanism of the {{chem|O|8}} cluster found in the work is not clear yet, and the researchers think that the charge transfer between oxygen molecules or the magnetic moment of oxygen molecules has a significant role in the formation.<ref name=epsilon/>
==Metallic oxygen==
{{seealso|Metal}}
It was found that a ζ-phase appears at 96 GPa when ε-phase oxygen is further compressed.<ref name="Akahama" /> This phase was discovered in 1990 by pressurizing oxygen to 132 GPa.<ref name=metallic/> The ζ-phase with metallic luster<ref>{{citejournal|journal=ChemPhysChem|volume=3|issue=1|pages=53–56|published=2002-01-14|author=Peter P. Edwards, Friedrich Hensel|title=Metallic Oxygen|publisher=WILEY-VCH-Verlag|location=Weinheim, Germany|year=2002|url=http://www3.interscience.wiley.com/cgi-bin/abstract/89014409/ABSTRACT?CRETRY=1&SRETRY=0|accessdate=2008-01-08|doi=10.1002/1439-7641(20020118)3:1<53::AID-CPHC53>3.0.CO;2-2}}</ref> has been known to exhibit superconductivity at low temperature.<ref name=superconductivity/><ref name=epsilon/> Oxygen molecules are among the very few molecules having magnetic moments, and have attracted attention because of the relationship between the molecular magnetization and crystal structures, electronic structures, and superconductivity.
==See also==
*[[Liquid oxygen]]
*[[Tetraoxygen]]
*[[Oxygen]]
==References==
{{reflist}}
{{oxygenallotropes}}
[[Category:Oxygen]]
[[Category:Cryogenics]]