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Topotactic Synthesis and Crystal Structure of a Highly Fluorinated Ruddlesden–Popper-Type Iron Oxide, Sr3Fe2O5+xF2–x (x ≈ 0.44)

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posted on 23.08.2011, 00:00 authored by Yoshihiro Tsujimoto, Kazunari Yamaura, Naoaki Hayashi, Katsuaki Kodama, Naoki Igawa, Yoshitaka Matsushita, Yoshio Katsuya, Yuichi Shirako, Masaki Akaogi, Eiji Takayama-Muromachi
Topotactic reaction of the n = 2 Ruddlesden–Popper phase Sr3Fe2O7−δ (δ ≈ 0.18) with polytetrafluoroethylene (PTFE) yields a highly fluorinated phase Sr3Fe2O5+xF2–x (x ≈ 0.44), compared with Sr3Fe2O6F0.87 prepared by the reaction of Sr3Fe2O6 and F2 gas. Structure analyses based on powder neutron diffraction, synchrotron powder diffraction, and 57Fe Mössbauer spectroscopy measurements demonstrate that the new oxyfluoride perovskite has no anion deficiencies and adopts the tetragonal structure (space group I4/mmm) with the lattice constants a = 3.87264(6) Å and c = 21.3465(6) Å at room temperature. The fluoride ions preferentially occupy the terminal apical anion sites with oxide ions in a disordered manner, which results in square pyramidal coordination around iron. The present compound also shows an antiferromagnetic order with a Néel temperature (TN) of 390 K, in sharply contrast to Sr3Fe2O6F0.87, which has a TN value that is lower than room temperature.

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