{{short description|Class of materials containing oxygen and a group-V element}} In chemistry, '''oxypnictides''' are a class of materials composed of oxygen, a pnictogen (group-V, especially phosphorus and arsenic) and one or more other elements. Although this group of compounds has been recognized since 1995,<ref name=Jei1995>{{cite journal|title = The rate earth transition metal phosphide oxides LnFePO, LnRuPO and LnCoPO with ZrCuSiAs type structure|journal = Journal of Alloys and Compounds|volume = 229|issue = 2|pages = 238–242|year = 1995|doi = 10.1016/0925-8388(95)01672-4|last1 = Zimmer|first1 = Barbara I.|last2 = Jeitschko|first2 = Wolfgang|last3 = Albering|first3 = Jörg H.|last4 = Glaum|first4 = Robert|last5 = Reehuis|first5 = Manfred}}</ref> interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006<ref name=Hoso2006>{{cite journal|title = Iron-Based Layered Superconductor: LaOFeP|journal = J. Am. Chem. Soc.|volume = 128|issue = 31|pages = 10012–10013|year = 2006|doi = 10.1021/ja063355c|pmid = 16881620|author1 = Kamihara, Y|last2 = Hiramatsu|first2 = H|last3 = Hirano|first3 = M|last4 = Kawamura|first4 = R|last5 = Yanagi|first5 = H|last6 = Kamiya|first6 = T|last7 = Hosono|first7 = H}}</ref> and 2008.<ref name=Hoso2008>{{cite journal|title = Superconductivity at 43 K in an iron-based layered compound LaO<sub>1−x</sub>F<sub>x</sub>FeAs|journal = Nature|volume = 453|pages = 376–378|year = 2008|doi = 10.1038/nature06972|pmid = 18432191|issue = 7193|bibcode=2008Natur.453..376T|last1 = Takahashi|first1 = H|last2 = Igawa|first2 = K|last3 = Arii|first3 = K|last4 = Kamihara|first4 = Y|last5 = Hirano|first5 = M|last6 = Hosono|first6 = H| s2cid=498756 }}</ref><ref name=PysTo>{{cite journal|title = New family of quaternary iron-based compounds superconducts at tens of kelvin|author = Day, Charles |journal = Physics Today|volume = 61|issue = 5| pages = 11–12|year = 2008|doi = 10.1063/1.2930719|bibcode = 2008PhT....61e..11D }}</ref> In these experiments the oxide was partly replaced by fluoride.

These and related compounds (e.g. the 122 iron arsenides) form a new group of iron-based superconductors known as iron pnictides or ferropnictides since the oxygen is not essential but the iron seems to be.

Oxypnictides have been patented as magnetic semiconductors in early 2006.<ref>H. Hosono ''et al.'' (2006) [http://www.freepatentsonline.com/EP1868215.html Magnetic semiconductor material] European Patent Application EP1868215</ref>

The different subclasses of oxypnictides are oxynitrides, oxyphosphides, oxyarsenides, oxyantimonides, and oxybismuthides.

==Structure== Many of the oxypnictides show a layered structure.<ref>{{cite journal|title=Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors|pmc=5099654|journal=Sci. Technol. Adv. Mater.|volume=9|article-number=033003|year=2008|doi=10.1088/1468-6996/9/3/033003|bibcode = 2008STAdM...9c3003O|issue=3 |arxiv = 0808.1158 |last1=Ozawa|first1=T. C.|last2=Kauzlarich|first2=S. M.|pmid=27877997}}</ref> For example, LaFePO with layers of La<sup>3+</sup>O<sup>2−</sup> and Fe<sup>2+</sup>P<sup>3−</sup>.<ref name=Hoso2006/> This structure is similar to that of ZrCuSiAs, which is now the parent structure for most of the oxypnictide.<ref name=Johr>{{cite journal|title = Synthesis, crystal structure and superconductivity of LaNiPO|journal = Solid State Sciences|volume = 10|issue = 2|pages = 193–197|year = 2008|doi = 10.1016/j.solidstatesciences.2007.08.016|bibcode = 2008SSSci..10..193T |last1 = Tegel|first1 = Marcus|last2 = Bichler|first2 = Daniel|last3 = Johrendt|first3 = Dirk}}</ref>

==Superconductivity== The first superconducting iron oxypnictide was discovered in 2006, based on phosphorus.<ref name=Hoso2006/> A drastic increase in the critical temperature was achieved when phosphorus was substituted by arsenic.<ref name=Hoso2008/> This discovery boosted the search for similar compounds, like the search for cuprate-based superconductors after their discovery in 1986.

The superconductivity of the oxypnictides seems to depend on the iron-pnictogen layers.

Some found in 2008 to be high-temperature superconductors (up to 55 K) of composition ReOTmPn, where Re is a rare earth, Tm is a transition metal and Pn is from group V e.g. As.<ref>{{cite journal|doi = 10.1179/143307508X333686| title = Samarium based SmFeAsO<sub>1−x</sub>F<sub>x</sub>|year = 2008|journal = Materials Research Innovations|volume = 12|page = 105|issue = 3| last1 = Ren| first1 = Z. A.| last2 = Yang| first2 = J.| last3 = Lu| first3 = W.| last4 = Yi| first4 = W.| last5 = Che| first5 = G. C.| last6 = Dong| first6 = X. L.| last7 = Sun| first7 = L. L.| last8 = Zhao| first8 = Z. X.|arxiv = 0803.4283| bibcode = 2008MatRI..12..105R| s2cid = 55488705}}</ref>

{|class="wikitable" |+ oxypnictides !Material !''T''<sub>c</sub> (K) <!-- could add columns for pressure, Hc2(UCF) --> |- |LaO<sub>0.89</sub>F<sub>0.11</sub>FeAs | 26<ref name=r1>{{cite journal|title=To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report|journal=J. Phys. Soc. Jpn.|volume=78|year=2009|article-number=062001|doi=10.1143/JPSJ.78.062001|bibcode = 2009JPSJ...78f2001I|issue=6 |arxiv = 0906.2045 |last1=Ishida|first1=Kenji|last2=Nakai|first2=Yusuke|last3=Hosono|first3=Hideo|s2cid=119295430 }}</ref> |- |LaO<sub>0.9</sub>F<sub>0.2</sub>FeAs | 28.5<ref name=prakash>{{cite journal|doi = 10.1209/0295-5075/84/57003|title = Potassium fluoride doped LaOFeAs multi-band superconductor: Evidence of extremely high upper critical field|year = 2008|author = Prakash, J.|journal = EPL|volume = 84|article-number = 57003|first2 = S. J.|first3 = S. L.|first4 = S.|first5 = A. K.|last2 = Singh|last3 = Samal|last4 = Patnaik|last5 = Ganguli|bibcode = 2008EL.....8457003P|issue = 5 | s2cid=119254951 }}</ref> |- |CeFeAsO<sub>0.84</sub>F<sub>0.16</sub> | 41<ref name=r1/> |- |SmFeAsO<sub>0.9</sub>F<sub>0.1</sub> | 43<ref name=r1/> |- |La<sub>0.5</sub>Y<sub>0.5</sub>FeAsO<sub>0.6</sub> | 43.1<ref>{{cite journal|bibcode = 2008PhRvB..78q2503S|doi = 10.1103/PhysRevB.78.172503|title = Superconductivity at 43 K at ambient pressure in the iron-based layered compound La<sub>1‑x</sub>Y<sub>x</sub>FeAsO<sub>y</sub>|year = 2008|author = Shirage, Parasharam M.|journal = Physical Review B|volume = 78|article-number = 172503|first2 = Kiichi|first3 = Hijiri|first4 = Hiroshi|first5 = Akira|last2 = Miyazawa|last3 = Kito|last4 = Eisaki|last5 = Iyo|issue = 17}}</ref> |- |NdFeAsO<sub>0.89</sub>F<sub>0.11</sub> | 52<ref name=r1/> |- |PrFeAsO<sub>0.89</sub>F<sub>0.11</sub> | 52<ref>{{cite journal|doi = 10.1179/143307508X333686|title = Superconductivity at 52 K in iron based F doped layered quaternary compound Pr[O<sub>1–x</sub>F<sub>x</sub>]FeAs|year = 2008|author = Ren, Z. A.|journal = Materials Research Innovations|volume = 12|page = 105|first2 = J.|first3 = W.|first4 = W.|first5 = G. C.|first6 = X. L.|first7 = L. L.|first8 = Z. X.|last2 = Yang|last3 = Lu|last4 = Yi|last5 = Che|last6 = Dong|last7 = Sun|last8 = Zhao|issue = 3|arxiv = 0803.4283| bibcode=2008MatRI..12..105R | s2cid=55488705 }}</ref> |- |GdFeAsO<sub>0.85</sub> | 53.5<ref>{{cite journal|doi = 10.1088/0953-2048/21/8/082001|title = Superconductivity at 53.5 K in GdFeAsO<sub>1−δ</sub>|year = 2008|author = Yang, Jie|journal = Superconductor Science and Technology|volume = 21|article-number = 082001|first2 = Zheng-Cai|first3 = Wei|first4 = Wei|first5 = Xiao-Li|first6 = Zhi-An|first7 = Guang-Can|first8 = Xiao-Li|first9 = Li-Ling|last2 = Li|last3 = Lu|last4 = Yi|last5 = Shen|last6 = Ren|last7 = Che|last8 = Dong|last9 = Sun|bibcode = 2008SuScT..21h2001Y|issue = 8 |display-authors = 9|last10 = Zhou|first10 = Fang|last11 = Zhao|first11 = Zhong-Xian|arxiv = 0804.3727| s2cid=121990600 }}</ref> |- |SmFeAsO<sub>~0.85</sub> | 55<ref>{{cite journal|doi = 10.1209/0295-5075/83/17002|title = Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO<sub>1−δ</sub> (Re = rare-earth metal) without fluorine doping|year = 2008|author = Ren, Zhi-An|journal = EPL|volume = 83|article-number = 17002|first2 = Guang-Can|first3 = Xiao-Li|first4 = Jie|first5 = Wei|first6 = Wei|first7 = Xiao-Li|first8 = Zheng-Cai|first9 = Li-Ling|last2 = Che|last3 = Dong|last4 = Yang|last5 = Lu|last6 = Yi|last7 = Shen|last8 = Li|last9 = Sun|bibcode=2008EL.....8317002R|arxiv = 0804.2582 |last10 = Zhou|first10 = Fang|last11 = Zhao|first11 = Zhong-Xian| issue=1 | s2cid=96240327 }}</ref> |}

Tests in magnetic fields up to 45 teslas<ref>{{cite web|url = http://www.planetanalog.com/news/showArticle.jhtml?articleID=208401297|title = High-temp superconductors pave way for 'supermagnets'|date = May 29, 2008|publisher = planetanalog|access-date = June 9, 2008|archive-date = September 10, 2012|archive-url = https://archive.today/20120910214530/http://eetimes.com/electronics-news/4077116/High-temp-superconductors-pave-way-for-supermagnets-|url-status = dead}}</ref><ref>{{cite journal|title = Two-band superconductivity in LaFeAsO<sub>0.89</sub>F<sub>0.11</sub> at very high magnetic fields|journal = Nature|volume = 453|pages = 903–905|year = 2008|doi = 10.1038/nature07058|pmid = 18509332|issue = 7197|bibcode = 2008Natur.453..903H|last1 = Hunte|first1 = F|last2 = Jaroszynski|first2 = J|last3 = Gurevich|first3 = A|last4 = Larbalestier|first4 = D. C.|last5 = Jin|first5 = R|last6 = Sefat|first6 = A. S.|last7 = McGuire|first7 = M. A.|last8 = Sales|first8 = B. C.|last9 = Christen|first9 = D. K.|last10 = Mandrus|first10 = D|arxiv = 0804.0485| s2cid=115211939 }}</ref> suggest the upper critical field of LaFeAsO<sub>0.89</sub>F<sub>0.11</sub> may be around 64 T. A different lanthanum-based material tested at 6 K predicts an upper critical field of 122 T in La<sub>0.8</sub>K<sub>0.2</sub>FeAsO<sub>0.8</sub>F<sub>0.2</sub>.<ref name=prakash/>

==Practical use== Because of the brittleness of the oxypnictides, superconducting wires are formed using the powder-in-tube process (using iron tubes).<ref>{{cite journal|doi = 10.1088/0953-2048/21/10/105024|title = Preparation of LaFeAsO<sub>0.9</sub>F<sub>0.1</sub> wires by the powder-in-tube method|year = 2008|author = Gao, Zhaoshun|journal = Superconductor Science and Technology|volume = 21|article-number = 105024|first2 = Lei|first3 = Yanpeng|first4 = Dongliang|first5 = Xianping|first6 = Yanwei|last2 = Wang|last3 = Qi|last4 = Wang|last5 = Zhang|last6 = Ma|bibcode = 2008SuScT..21j5024G|issue = 10 | s2cid=122471407 }}</ref>

==See also== {{commons category|Oxypnictides}} {{div col}} *{{annotated link|Charge-transfer complex}} *{{annotated link|Color superconductivity}} in quarks *{{annotated link|Kondo effect}} *{{annotated link|Magnetic sail}} *{{annotated link|National Superconducting Cyclotron Laboratory}} *{{annotated link|Spallation Neutron Source}} *{{annotated link|Superconducting radio frequency}} *{{annotated link|Superfluid film}} *{{annotated link|Timeline of low-temperature technology}}

{{div col end}}

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

==External links== *[http://www.jst.go.jp/EN/seika/01/seika16.html Hosono at JST] {{Webarchive|url=https://web.archive.org/web/20100106080403/http://www.jst.go.jp/EN/seika/01/seika16.html |date=2010-01-06 }} Has diagram of LaO & FeAs layers in LaOFeAs

{{Superconductivity}} Category:Superconductors Category:Pnictides