Local electronic structure analysis for brownmillerite Ca(Sr)FeO2.5 using site-resolved energy-loss near-edge structures
Local electronic structure analysis for brownmillerite Ca(Sr)FeO2.5 using site-resolved energy-loss near-edge structures
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DOI：
10.1063/1.3610526
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发表时间：
2011-08-01
影响因子：
3.2
通讯作者：
Isoda, S.
中科院分区：
文献类型：
--
作者：
Haruta, M.;Kurata, H.;Isoda, S.
利用扫描透射电子显微镜结合电子能量损失谱，测量了钙钛矿Ca（Sr）FeO_（2.5）中Fe_6八面体和Fe_4四面体的氧K边和Fe L-2，L-3边电子能量损失近边结构（ELNES）。所观察到的现场分辨氧K-ELNES表现出不同的功能，反映了当地的化学键周围的FeO 6八面体和FeO 4四面体。在O K-边光谱，这是由于过渡到一个未占用的O 2 p带与Fe-3d带杂交的预峰，显示分裂的FeO 6八面体网站的光谱。此外，氧连接的八面体和四面体的铁网站在CaFeO 2.5，电荷转移被发现优先发生向四面体的铁离子。在SrFeO2.5的情况下，从位于ac平面的氧的电荷转移偏向四面体Fe原子。基于对O K-ELNES的预峰强度的分析，得出结论，在四面体位点处的氧原子和铁原子之间的键合比在八面体位点处的键合更共价。四面体位置的强共价特征将是Ca（Sr）FeO 2.5中的FeO 6八面体中的畸变的原因之一，如通过沿b轴的沿着延伸所展示的。(C)2011年美国物理学会。[doi：10.1063/1.3610526]
Oxygen K-edge and Fe L-2,L-3-edge electron energy-loss near-edge structures (ELNES) were measured for FeO6 octahedra and FeO4 tetrahedra in the brownmillerite Ca(Sr)FeO2.5 by focusing an electron probe at individual Fe sites using scanning transmission electron microscopy combined with electron energy-loss spectroscopy. The observed site-resolved oxygen K-ELNES showed different features reflecting the local chemical bonding around the FeO6 octahedra and FeO4 tetrahedra. A pre-peak in the O K-edge spectra, which is attributed to a transition to an unoccupied O 2p band hybridized with the Fe-3d band, shows splitting in the spectrum of the FeO6 octahedral site. Additionally, for the oxygen linking the octahedral and tetrahedral Fe sites in CaFeO2.5, charge transfer was found to preferentially occur toward the tetrahedral Fe ions. In the case of SrFeO2.5, charge transfer from the oxygen located in the ac plane was biased toward the tetrahedral Fe atoms. Based upon an analysis of the pre-peak intensity of the O K-ELNES, it was concluded that bonding between the oxygen and iron atoms at the tetrahedral site was more covalent in character than at the octahedral site. The strong covalent character of the tetrahedral sites would be one of the reasons for distortion in the FeO6 octahedra in Ca(Sr)FeO2.5, as exhibited by an extension along the b-axis. (C) 2011 American Institute of Physics. [doi:10.1063/1.3610526]