(Sr1鈥?i>xBax)FeO2 (0.4 鈮?x 鈮?1): A New Oxygen-Deficient Perovskite Structure

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• 作者：Takafumi Yamamoto ; Yoji Kobayashi ; Naoaki Hayashi ; C茅dric Tassel ; Takashi Saito ; Shoji Yamanaka ; Mikio Takano ; Kenji Ohoyama ; Yuichi Shimakawa ; Kazuyoshi Yoshimura ; Hiroshi Kageyama
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：July 18, 2012
• 年：2012
• 卷：134
• 期：28
• 页码：11444-11454
• 全文大小：588K
• 年卷期：v.134,no.28(July 18, 2012)
• ISSN：1520-5126

文摘

Topochemical reduction of (layered) perovskite iron oxides with metal hydrides has so far yielded stoichiometric compositions with ordered oxygen defects with iron solely in FeO₄ square planar coordination. Using this method, we have successfully obtained a new oxygen-deficient perovskite, (Sr_1鈥?i>xBa_x)FeO₂ (0.4 鈮?x 鈮?1.0), revealing that square planar coordination can coexist with other 3鈥?-fold coordination geometries. This BaFeO₂ structure is analogous to the LaNiO_2.5 structure in that one-dimensional octahedral chains are linked by planar units, but differs in that one of the octahedral chains contains a significant amount of oxygen vacancies and that all the iron ions are exclusively divalent in the high-spin state. M枚ssbauer spectroscopy demonstrates, despite the presence of partial oxygen occupations and structural disorders, that the planar-coordinate Fe²⁺ ions are bonded highly covalently, which accounts for the formation of the unique structure. At the same time, a rigid 3D Fe鈥揙鈥揊e framework contributes to structural stabilization. Powder neutron diffraction measurements revealed a G-type magnetic order with a drastic decrease of the N茅el temperature compared to that of SrFeO₂, presumably due to the effect of oxygen disorder/defects. We also performed La substitution at the Ba site and found that the oxygen vacancies act as a flexible sink to accommodate heterovalent doping without changing the Fe oxidation and spin state, demonstrating the robustness of this new structure against cation substitution.