Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Infinite-layer iron oxide with a square-planar coordination


Conventional high-temperature reactions limit the control of coordination polyhedra in transition-metal oxides to those obtainable within the bounds of known coordination geometries for a given transition metal1. For example, iron atoms are almost exclusively coordinated by three-dimensional polyhedra such as tetrahedra and octahedra. However, recent works have shown that binary metal hydrides act as reducing agents at low temperatures, allowing access to unprecedented structures2,3,4. Here we show the reaction of a perovskite SrFeO3 with CaH2 to yield SrFeO2, a new compound bearing a square-planar oxygen coordination around Fe2+. SrFeO2 is isostructural with ‘infinite layer’ cupric oxides5,6,7,8, and exhibits a magnetic order far above room temperature in spite of the two-dimensional structure, indicating strong in-layer magnetic interactions due to strong Fe d to O p hybridization. Surprisingly, SrFeO2 remains free from the structural instability that might well be expected at low temperatures owing to twofold orbital degeneracy in the Fe2+ ground state with D4h point symmetry. The reduction and the oxidation between SrFeO2 and SrFeO3 proceed via the brownmillerite-type intermediate SrFeO2.5, and start at the relatively low temperature of 400 K, making the material appealing for a variety of applications, including oxygen ion conduction, oxygen gas absorption and catalysis.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Figure 1: Structural transformation via a topotactic route.
Figure 2: Structural characterization of SrFeO 2 by Rietveld refinement of high-resolution neutron diffraction at room temperature.
Figure 3: Temperature evolution of the magnetic order in SrFeO2.

Accession codes

Data deposits

Atomic coordinates and structure factors for the crystal structure of SrFeO2 have been deposited with the ICSD database under accession codes 418603, 418605 and 418606.


  1. Wells, A. F. Structural Inorganic Chemistry 3rd edn (Oxford Univ. Press, Oxford, UK, 1962)

    Google Scholar 

  2. Hayward, M. A. & Rosseinsky, M. J. Anion vacancy distribution and magnetism in the new reduced layered Co(II)/Co(I) phase LaSrCoO3. 5-x . Chem. Mater. 12, 2182–2195 (2000)

    Article  CAS  Google Scholar 

  3. Hayward, M. A. et al. The hydride anion in an extended transition metal oxide array: LaSrCoO3H0. 7 . Science 295, 1882–1884 (2002)

    Article  CAS  ADS  Google Scholar 

  4. Blundred, G. D., Bridges, A. B. & Rosseinsky, M. J. New oxidation states and defect chemistry in the pyrochlore structure. Angew. Chem. Intl Edn 43, 3562–3565 (2004)

    Article  CAS  Google Scholar 

  5. Siegrist, T., Zahurak, S. M., Murphy, D. W. & Roth, R. S. The parent structure of the layered high-temperature superconductors. Nature 334, 231–232 (1988)

    Article  CAS  ADS  Google Scholar 

  6. Takano, M., Takeda, Y., Okada, H., Miyamoto, M. & Kusaka, T. ACuO2 (A: alkaline earth) crystallizing in a layered structure. Physica C 159, 375–378 (1989)

    Article  CAS  ADS  Google Scholar 

  7. Smith, M. G., Manthiram, A., Zhou, J. & Goodenough, J. B. Electron-doped superconductivity at 40 K in the infinite-layer compound Sr1-y Nd y CuO2 . Nature 351, 549–551 (1991)

    Article  CAS  ADS  Google Scholar 

  8. Azuma, M., Hiroi, Z., Takano, M., Bando, Y. & Takeda, Y. Superconductivity at 110 K in the infinite-layer compound (Sr1-x Ca x )1-y CuO2 . Nature 356, 775–776 (1992)

    Article  CAS  ADS  Google Scholar 

  9. Crespin, M., Levitz, P. & Gatineau, L. Reduced forms of LaNiO3 perovskite. 1. Evidence for new phases: La2Ni2O5 and LaNiO2 . J. Chem. Soc. Faraday Trans. 2, 1181–1194 (1983)

    Article  Google Scholar 

  10. Hyde, B. G. & Andersson, S. Inorganic Crystal Structure Ch. 15 (John Wiley & Sons, New York, 1989)

    Google Scholar 

  11. Berry, J. F. et al. An octahedral coordination complex of iron(VI). Science 312, 1937–1941 (2006)

    Article  CAS  ADS  Google Scholar 

  12. Bouwkamp, M. W., Bowman, A. C., Lobkovsky, E. & Chirik, P. J. Iron-catalyzed [2π + 2π] cycloaddition of α,ω-dienes: the importance of redox-active supporting ligands. J. Am. Chem. Soc. 128, 13340–13341 (2006)

    Article  CAS  Google Scholar 

  13. Hazen, R. M. & Burnham, C. W. The crystal structures of gillespite I and II: a structural determination at high pressure. Am. Mineral. 59, 1166–1176 (1974)

    CAS  Google Scholar 

  14. Leinenweber, K., Linton, J., Navrotsky, A., Fei, Y. & Parise, J. B. High-pressure perovskites on the join CaTiO3-FeTiO3 . Phys. Chem. Mineral. 22, 251–258 (1995)

    Article  CAS  ADS  Google Scholar 

  15. Takeda, Y. et al. Phase relation in the oxygen nonstoichiometric system SrFeO x (2.5 ≤ x ≤ 3). J. Solid-State Chem. 63, 237–249 (1986)

    Article  CAS  ADS  Google Scholar 

  16. Hodges, J. P. et al. Evolution of oxygen-vacancy ordered crystal structures in the perovskite series Sr n Fe n O3n-1 (n = 2, 4, 8, and ∞), and the relationship to electronic and magnetic properties. J. Solid-State Chem. 151, 190–209 (2000)

    Article  CAS  ADS  Google Scholar 

  17. Grenier, J.-C. et al. Electrochemical oxygen intercalation into oxide networks. J. Solid-State Chem. 96, 20–30 (1992)

    Article  CAS  ADS  Google Scholar 

  18. Hayashi, N., Terashima, T. & Takano, M. Oxygen-holes creating different electronic phases in Fe4+-oxides: successful growth of single crystalline films of SrFeO3 and related perovskites at low oxygen pressure. J. Mater. Chem. 11, 2235–2237 (2001)

    Article  CAS  Google Scholar 

  19. Hayward, M. A. Structural and magnetic properties of topotactically reduced YSr2Mn2O7-x (0 < x < 1.5). Chem. Mater. 18, 321–327 (2006)

    Article  CAS  Google Scholar 

  20. Poltavets, V. V. et al. La3Ni2O6: a new double T’-type nickelate with infinite Ni1+/2+O2 layers. J. Am. Chem. Soc. 128, 9050–9051 (2006)

    Article  CAS  Google Scholar 

  21. Hayward, M. A. Phase separation during the topotactic reduction of the pyrocholore Y2Ti2O7 . Chem. Mater. 17, 670–675 (2005)

    Article  CAS  Google Scholar 

  22. Hayward, M. A., Green, M. A., Rosseinsky, M. J. & Sloan, J. Sodium hydride as a powerful reducing agent for topotactic oxide deintercalation: synthesis and characterization of the nickel(I) LaNiO2 . J. Am. Chem. Soc. 121, 8843–8854 (1999)

    Article  CAS  Google Scholar 

  23. Greenwood, N. N. & Gibb, T. C. Mössbauer Spectroscopy Ch. 3 & 5 (Chapman and Hall, London, 1971)

    Book  Google Scholar 

  24. Shao, Z. & Haile, S. M. A high-performance cathode for the next generation of solid-state fuel cells. Nature 431, 170–173 (2004)

    Article  CAS  ADS  Google Scholar 

  25. Sammells, A. F., Schwartz, M., Mackay, R. A., Barton, T. F. & Peterson, D. R. Catalytic membrane reactors for spontaneous synthesis gas production. Catal. Today 56, 325–328 (2000)

    Article  CAS  Google Scholar 

  26. Badwal, S. P. S. & Ciacchi, F. T. Ceramic membrane technologies for oxygen separation. Adv. Mater. 13, 993–996 (2001)

    Article  CAS  Google Scholar 

  27. Wang, Y., Chen, J. & Wu, X. Preparation and gas-sensing properties of perovskite-type SrFeO3 oxide. Mater. Lett. 49, 361–364 (2001)

    Article  CAS  Google Scholar 

  28. Takano, M. et al. Pressure-induced high-spin to low-spin transition in CaFeO3 . Phys. Rev. Lett. 67, 3267–3270 (1991)

    Article  CAS  ADS  Google Scholar 

  29. Battle, P. D. et al. Magnetoresistance in high oxidation state iron oxides. Chem. Commun. 767, 987–988 (1998)

    Article  Google Scholar 

  30. Mostovoy, M. Helicoidal ordering in iron perovskite. Phys. Rev. Lett. 94, 137205 (2005)

    Article  ADS  Google Scholar 

  31. Adler, P. et al. Structural phase transition in Sr2Fe2O5 under high pressure. J. Solid-State Chem. 155, 381–388 (2000)

    Article  CAS  ADS  Google Scholar 

  32. Izumi, F. & Ikeda, T. Rietveld-analysis program RIETAN-98 and its applications to zeolites. Mater. Sci. Forum 321–324, 198–203 (2000)

    Article  Google Scholar 

  33. Rodríguez-Carvajal, J. Recent advances in magnetic-structure determination by neutron powder diffraction. J. Phys. B 192, 55–69 (1993)

    Article  Google Scholar 

  34. Brown, I. D. & Altermatt, D. Bond-valence parameters obtained from a systematic analysis of the inorganic crystal structure database. Acta Crystallogr. B 41, 244–247 (1985)

    Article  Google Scholar 

Download references


We thank Y. Kiuchi, H. Ueda, M. Isobe and Y. Ueda for their help in EDS and thermogravimetric measurements and K. Kato for his help in the synchrotron X-ray experiments at SPring-8. This work was supported by Young Scientists A (H.K.), the Grant-in-Aid for Scientific Research on Priority Areas (H.K. and K.Y.) and Scientific Research S (M.T.) from MEXT. See the Supplementary Notes for more details.

Author Contributions H.K. designed the study in collaboration with W.P, with M.T.’s help; C.T. performed the initial synthesis and proposed the structural model; Y.T. and T.W. optimized the synthetic conditions, performed chemical characterizations, X-ray diffraction measurements and corresponding structural refinement; N.H. conducted the Mössbauer experiment, with M.T.’s help; M.C., C.R. and W.P. performed the neutron diffraction measurements and M.C. and W.P. performed the corresponding structural refinement; All the authors discussed the results; H.K. wrote the manuscript, with comments mainly from M.T. and W.P.

Author information

Authors and Affiliations


Corresponding author

Correspondence to H. Kageyama.

Supplementary information

Supplementary Information

This file contains Supplementary Figures S1-S4 with Legends, Supplementary Table S1 with Legend, and Supplementary Notes. (PDF 1324 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Tsujimoto, Y., Tassel, C., Hayashi, N. et al. Infinite-layer iron oxide with a square-planar coordination. Nature 450, 1062–1065 (2007).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing