Oxypnictide

In chemistry, oxypnictides are a class of materials including 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,^[1] interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006^[2] and 2008.^{[3] [4]} 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.^[5]

Structure

Many of the oxypnictides show a layered structure.^[6] For example LnFePO with layers of La³⁺O^2- and Fe²⁺P^3-.^[2] This structure is similar to that of ZrCuSiAs, which is now the parent structure for most of the oxypnictide.^[7]

Superconductivity

The first superconducting iron oxypnictide was discovered in 2006, based on phosphorus.^[2] A drastic increase in the critical temperature was achieved when phosphorus was substituted by arsenic.^[3] This discovery boosted the search for similar compounds, like the search for cuprate-based superconductors after their discovery in 1986.

The superconductvity 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.^[8]

oxypnictides

Material	Tc (K)
LaO0.89F0.11FeAs	26[9]
LaO0.9F0.2FeAs	28.5[10]
CeFeAsO0.84F0.16	41[9]
SmFeAsO0.9F0.1	43[9]
La0.5Y0.5FeAsO0.6	43.1[11]
NdFeAsO0.89F0.11	52[9]
PrFeAsO0.89F0.11	52[12]
GdFeAsO0.85	53.5[13]
SmFeAsO~0.85	55[14]

Tests in magnetic fields up to 45 teslas^[15][16] suggest the upper critical field of LaFeAsO_0.89F_0.11 may be around 64 T. A different lanthanum-based material tested at 6 K predicts an upper critical field of 122 T in La_0.8K_0.2FeAsO_0.8F_0.2.^[10]

Practical use

Because of the brittleness of the oxypnictides, superconducting wires are formed using the powder-in-tube process (using iron tubes).^[17]

See also

• Andreev reflection
• Charge transfer complex
• Color superconductivity in quarks
• Composite Reaction Texturing
• Conventional superconductor
• covalent superconductors
• Iron-based superconductor
• High-temperature superconductivity
• Homes's law
• Kondo effect
• Little-Parks effect
• Magnetic sail
• National Superconducting Cyclotron Laboratory
• Proximity effect
• Room temperature superconductor
• Rutherford cable
• Spallation Neutron Source
• Superconducting RF
• Superconductor classification
• Superfluid film
• Technological applications of superconductivity
• Timeline of low-temperature technology
• Type-I superconductor
• Type-II superconductor
• Unconventional superconductor

References

1. ^ Barbara I. Zimmer, Wolfgang Jeitschko, Jörg H. Albering, Robert Glaum and Manfred Reehuis (1995). "The rate earth transition metal phosphide oxides LnFePO, LnRuPO and LnCoPO with ZrCuSiAs type structure". Journal of Alloys and Compounds 229 (2): 238–242. doi:10.1016/0925-8388(95)01672-4. 
2. ^ ^{a b c} Yoichi Kamihara, Hidenori Hiramatsu, Masahiro Hirano, Ryuto Kawamura, Hiroshi Yanagi, Toshio Kamiya, and Hideo Hosono (2006). "Iron-Based Layered Superconductor: LaOFeP". J. Am. Chem. Soc. 128 (31): 10012–10013. doi:10.1021/ja063355c. PMID 16881620. 
3. ^ ^{a b} Hiroki Takahashi, Kazumi Igawa, Kazunobu Arii, Yoichi Kamihara, Masahiro Hirano, Hideo Hosono (2008). "Superconductivity at 43 K in an iron-based layered compound LaO_1-xF_xFeAs". Nature 453 (7193): 376–378. Bibcode 2008Natur.453..376T. doi:10.1038/nature06972. PMID 18432191. 
4. ^ Charles Day (2008). "New family of quaternary iron-based compounds superconducts at tens of kelvin". Physics Today 61 (5): 11–12. Bibcode 2008PhT....61e..11D. doi:10.1063/1.2930719. http://ptonline.aip.org/journals/doc/PHTOAD-ft/vol_61/iss_5/11_1.shtml. 
5. ^ H. Hosono et al. (2006) Magnetic semiconductor material European Patent Application EP1868215
6. ^ T C Ozawa and S M Kauzlarich (2008). "Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors" (free-download review). Sci. Technol. Adv. Mater. 9 (3): 033003. Bibcode 2008STAdM...9c3003O. doi:10.1088/1468-6996/9/3/033003. 
7. ^ Marcus Tegel, Daniel Bichler and Dirk Johrendt (2008). "Synthesis, crystal structure and superconductivity of LaNiPO". Solid State Sciences 10 (2): 193–197. Bibcode 2008SSSci..10..193T. doi:10.1016/j.solidstatesciences.2007.08.016. 
8. ^ X. H. Chen, T. Wu, G. Wu, R. H. Liu, H. Chen and D. F. Fang (2008). "Samarium based SmFeAsO_1−xF_x". Materials Research Innovations 12 (3): 105. doi:10.1179/143307508X333686. 
9. ^ ^{a b c d} K. Ishida et al (2009). "To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report". J. Phys. Soc. Jpn. 78 (6): 062001. Bibcode 2009JPSJ...78f2001I. doi:10.1143/JPSJ.78.062001. 
10. ^ ^{a b} Prakash, J.; Singh, S. J.; Samal, S. L.; Patnaik, S.; Ganguli, A. K. (2008). "Potassium fluoride doped LaOFeAs multi-band superconductor: Evidence of extremely high upper critical field". EPL (Europhysics Letters) 84 (5): 57003. Bibcode 2008EL.....8457003P. doi:10.1209/0295-5075/84/57003. 
11. ^ Shirage, Parasharam M.; Miyazawa, Kiichi; Kito, Hijiri; Eisaki, Hiroshi; Iyo, Akira (2008). "Superconductivity at 43 K at ambient pressure in the iron-based layered compound La1‑xYxFeAsOy". Physical Review B 78 (17): 172503. Bibcode 2008PhRvB..78q2503S. doi:10.1103/PhysRevB.78.172503. 
12. ^ Ren, Z. A.; Yang, J.; Lu, W.; Yi, W.; Che, G. C.; Dong, X. L.; Sun, L. L.; Zhao, Z. X. (2008). "Superconductivity at 52 K in iron based F doped layered quaternary compound Pr[O_1–xF_x]FeAs". Materials Research Innovations 12 (3): 105. doi:10.1179/143307508X333686. 
13. ^ Yang, Jie; Li, Zheng-Cai; Lu, Wei; Yi, Wei; Shen, Xiao-Li; Ren, Zhi-An; Che, Guang-Can; Dong, Xiao-Li et al. (2008). "Superconductivity at 53.5 K in GdFeAsO1−δ". Superconductor Science and Technology 21 (8): 082001. Bibcode 2008SuScT..21h2001Y. doi:10.1088/0953-2048/21/8/082001. 
14. ^ Ren, Zhi-An; Che, Guang-Can; Dong, Xiao-Li; Yang, Jie; Lu, Wei; Yi, Wei; Shen, Xiao-Li; Li, Zheng-Cai et al. (2008). "Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO1−δ (Re = rare-earth metal) without fluorine doping". EPL (Europhysics Letters) 83: 17002. Bibcode 2008EL.....8317002R. doi:10.1209/0295-5075/83/17002. 
15. ^ R. Colin Johnson (Mai 29, 2008). "High-temp superconductors pave way for 'supermagnets'". planetanalog. http://www.planetanalog.com/news/showArticle.jhtml?articleID=208401297. 
16. ^ F. Hunte, J. Jaroszynski, A. Gurevich, D. C. Larbalestier, R. Jin, A. S. Sefat, M. A. McGuire, B. C. Sales, D. K. Christen & D. Mandrus (2008). "Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields". Nature 453 (7197): 903–905. Bibcode 2008Natur.453..903H. doi:10.1038/nature07058. PMID 18509332. 
17. ^ Gao, Zhaoshun; Wang, Lei; Qi, Yanpeng; Wang, Dongliang; Zhang, Xianping; Ma, Yanwei (2008). "Preparation of LaFeAsO_0.9F_0.1 wires by the powder-in-tube method". Superconductor Science and Technology 21 (10): 105024. Bibcode 2008SuScT..21j5024G. doi:10.1088/0953-2048/21/10/105024. 

Further reading

• A selection of free-download papers on iron-based superconductors in New Journal of Physics
• T C Ozawa and S M Kauzlarich (2008). "Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors" (free-download review). Sci. Technol. Adv. Mater. 9 (3): 033003. Bibcode 2008STAdM...9c3003O. doi:10.1088/1468-6996/9/3/033003. 
• P. M. Shirage et. al (2009). "High-pressure synthesis and physical properties of new iron (nickel)-based superconductors". Physica C: 469 (9–12): 355. Bibcode 2009PhyC..469..355S. doi:10.1016/j.physc.2009.03.027. </ref>

External links

• Hosono at JST Has diagram of LaO & FeAs layers in LaOFeAs