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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,^[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]

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

Structure

Many of the oxypnictides show a layered structure.^[6] For example, LaFePO with layers of La³⁺O²⁻ and Fe²⁺P³⁻.^[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 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.^[8]

oxypnictides
Material	T_c (K)
LaO_0.89F_0.11FeAs	26^[9]
LaO_0.9F_0.2FeAs	28.5^[10]
CeFeAsO_0.84F_0.16	41^[9]
SmFeAsO_0.9F_0.1	43^[9]
La_0.5Y_0.5FeAsO_0.6	43.1^[11]
NdFeAsO_0.89F_0.11	52^[9]
PrFeAsO_0.89F_0.11	52^[12]
GdFeAsO_0.85	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]

References

^ Zimmer, Barbara I.; Jeitschko, Wolfgang; Albering, Jörg H.; Glaum, Robert; Reehuis, Manfred (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.
^ ^a ^b ^c Kamihara, Y; Hiramatsu, H; Hirano, M; Kawamura, R; Yanagi, H; Kamiya, T; Hosono, H (2006). "Iron-Based Layered Superconductor: LaOFeP". J. Am. Chem. Soc. 128 (31): 10012–10013. doi:10.1021/ja063355c. PMID 16881620.
^ ^a ^b Takahashi, H; Igawa, K; Arii, K; Kamihara, Y; Hirano, M; Hosono, H (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. S2CID 498756.
^ Day, Charles (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.
^ H. Hosono et al. (2006) Magnetic semiconductor material European Patent Application EP1868215
^ Ozawa, T. C.; Kauzlarich, S. M. (2008). "Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors". Sci. Technol. Adv. Mater. 9 (3): 033003. arXiv:0808.1158. Bibcode:2008STAdM...9c3003O. doi:10.1088/1468-6996/9/3/033003. PMC 5099654. PMID 27877997.
^ Tegel, Marcus; Bichler, Daniel; Johrendt, Dirk (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.
^ Ren, Z. A.; Yang, J.; Lu, W.; Yi, W.; Che, G. C.; Dong, X. L.; Sun, L. L.; Zhao, Z. X. (2008). "Samarium based SmFeAsO_1−xF_x". Materials Research Innovations. 12 (3): 105. arXiv:0803.4283. Bibcode:2008MatRI..12..105R. doi:10.1179/143307508X333686. S2CID 55488705.
^ ^a ^b ^c ^d Ishida, Kenji; Nakai, Yusuke; Hosono, Hideo (2009). "To What Extent Iron-Pnictide New Superconductors Have Been Clarified: A Progress Report". J. Phys. Soc. Jpn. 78 (6): 062001. arXiv:0906.2045. Bibcode:2009JPSJ...78f2001I. doi:10.1143/JPSJ.78.062001. S2CID 119295430.
^ ^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. 84 (5): 57003. Bibcode:2008EL.....8457003P. doi:10.1209/0295-5075/84/57003. S2CID 119254951.
^ 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 La_1‑xY_xFeAsO_y". Physical Review B. 78 (17): 172503. Bibcode:2008PhRvB..78q2503S. doi:10.1103/PhysRevB.78.172503.
^ 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. arXiv:0803.4283. Bibcode:2008MatRI..12..105R. doi:10.1179/143307508X333686. S2CID 55488705.
^ Yang, Jie; Li, Zheng-Cai; Lu, Wei; Yi, Wei; Shen, Xiao-Li; Ren, Zhi-An; Che, Guang-Can; Dong, Xiao-Li; Sun, Li-Ling; et al. (2008). "Superconductivity at 53.5 K in GdFeAsO_1−δ". Superconductor Science and Technology. 21 (8): 082001. arXiv:0804.3727. Bibcode:2008SuScT..21h2001Y. doi:10.1088/0953-2048/21/8/082001. S2CID 121990600.
^ Ren, Zhi-An; Che, Guang-Can; Dong, Xiao-Li; Yang, Jie; Lu, Wei; Yi, Wei; Shen, Xiao-Li; Li, Zheng-Cai; Sun, Li-Ling; Zhou, Fang; Zhao, Zhong-Xian (2008). "Superconductivity and phase diagram in iron-based arsenic-oxides ReFeAsO_1−δ (Re = rare-earth metal) without fluorine doping". EPL. 83 (1): 17002. arXiv:0804.2582. Bibcode:2008EL.....8317002R. doi:10.1209/0295-5075/83/17002. S2CID 96240327.
^ "High-temp superconductors pave way for 'supermagnets'". planetanalog. May 29, 2008.^{[permanent dead link‍]}
^ Hunte, F; Jaroszynski, J; Gurevich, A; Larbalestier, D. C.; Jin, R; Sefat, A. S.; McGuire, M. A.; Sales, B. C.; Christen, D. K.; Mandrus, D (2008). "Two-band superconductivity in LaFeAsO_0.89F_0.11 at very high magnetic fields". Nature. 453 (7197): 903–905. arXiv:0804.0485. Bibcode:2008Natur.453..903H. doi:10.1038/nature07058. PMID 18509332. S2CID 115211939.
^ 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. S2CID 122471407.