CaFeO<inf>2</inf>: A new type of layered structure with iron in a distorted square planar coordination

Cédric Tassel, José Miguel Pruneda, Naoaki Hayashi, Takashi Watanabe, Atsushi Kitada, Yoshihiro Tsujimoto, Hiroshi Kageyama, Kazuyoshi Yoshimura, Mikio Takano, Masakazu Nishi, Kenji Ohoyama, Masaichiro Mizumaki, Naomi Kawamura, Jorge Fniguez, Enric Canadell

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    79 Citations (Scopus)


    CaFeO2, a material exhibiting an unprecedented layered structure containing 3d6 iron in a high-spin distorted square-planar coordination, is reported. The new phase, obtained through a low-temperature reduction procedure using calcium hydride, has been characterized through powder neutron diffraction, synchrotron X-ray diffraction, Mössbauer spectroscopy, XAS experiments as well as first-principles DFT calculations. The XAS spectra near the Fe-K edge for the whole solid solution (Sr 1-xCax)FeO2 supports that iron is in a square-planar coordination for 0 ≤ x ≤ 0.8 but clearly suggests a change of coordination for x = 1. The new structure contains infinite FeO2 layers in which the FeO4 units unprecedentedly distort from square-planar toward tetrahedra and rotate along the c-axis, in marked contrast to the well-studied and accepted concept that octahedral rotation in perovskite oxides occurs but the octahedral shape is kept almost regular. The new phase exhibits high-spin configuration and G-type antiferromagnetic ordering as in SrFeO2. However, the distortion of the FeO2 layers leads to only a slight decrease of the Néel temperature with respect to SrFeOx. First-principles DFT calculations provide a clear rationalization of the structural and physical observations for CaFeO 2 and highlight how the nature of the cation influences the structural details of the AFeO2 family of compounds (A = Ca, Sr, Ba). On the basis of these calculations the driving force for the distortion of the FeO2 layers in CaFeO2 is discussed. © 2009 American Chemical Society.
    Original languageEnglish
    Pages (from-to)221-229
    JournalJournal of the American Chemical Society
    Issue number1
    Publication statusPublished - 14 Jan 2009


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