An X-ray absorption spectroscopic study on mixed conductive La0.6Sr0.4Co0.8Fe0.2O(3-δ) cathodes. I. Electrical conductivity and electronic structure.
An X-ray absorption spectroscopic study on mixed conductive La0.6Sr0.4Co0.8Fe0.2O(3-δ) cathodes. I. Electrical conductivity and electronic structure.
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DOI：
10.1039/c1cp20982e
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发表时间：
2011-09
期刊：
影响因子：
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通讯作者：
Y. Orikasa;T. Ina;Takayuki Nakao;A. Mineshige;K. Amezawa;Masatsugu Oishi;H. Arai;Z. Ogumi;Y. Uchimoto
中科院分区：
文献类型：
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作者：
Y. Orikasa;T. Ina;Takayuki Nakao;A. Mineshige;K. Amezawa;Masatsugu Oishi;H. Arai;Z. Ogumi;Y. Uchimoto
本文从氧空位形成过程中的电子结构变化出发，研究了钙钛矿型混合导电氧化物La（0.6）Sr（0.4）Co（0.8）Fe（0.2）O（3-δ）作为固体氧化物燃料电池阴极材料的导电机理。La（0.6）Sr（0.4）Co（0.8）Fe（0.2）O（3-δ）在不同氧分压p（O（2））s下于1073 K退火并淬火。碘量滴定表明，La（0.6）Sr（0.4）Co（0.8）Fe（0.2）O（3-δ）的氧非化学计量比与退火p（O（2））有关，p（O（2））s越低，引入的氧空位越多。在O K-、Co L-、Fe L-、Co K-和Fe K-边缘处进行X射线吸收光谱测量。通过X射线吸收近边结构（XANES）研究了Co和Fe L（III）边的价态。而Fe的平均价态几乎是恒定的，Co离子的价态随着氧空位的引入而降低。O-K边XANES谱表明，氧空位的引入使电子进入Co3d/O2p杂化态.在Co和Fe的K-边XANES的吸收边向较低的能量与氧空位的引入。在Co K-边缘的移动导致的Co平均价态的降低，而在Fe K-边缘出现的Fe离子周围的配位环境的变化所造成的。La（0.6）Sr（0.4）Co（0.8）Fe（0.2）O（3-δ）的总电导率随着p（O（2））的减小而减小，这是由于空穴浓度的减小。
The electrical conduction mechanism of mixed conductive perovskite oxides, La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ), for cathode materials of solid oxide fuel cells has been investigated from electronic structural changes during oxygen vacancy formation. La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) was annealed under various oxygen partial pressures p(O(2))s at 1073 K and quenched. Iodometric titration indicated that the oxygen nonstoichiometry of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) depended on the annealing p(O(2)), with more oxygen vacancies introduced at lower than at higher p(O(2))s. X-Ray absorption spectroscopic measurements were performed at the O K-, Co L-, Fe L-, Co K-, and Fe K-edges. The valence states of the Co and Fe ions were investigated by the X-ray absorption near edge structure (XANES) at the Co and Fe L(III)-edges. While the Fe average valence was almost constant, the valence of the Co ions decreased with oxygen vacancy introduction. The O K-edge XANES spectra indicated that electrons were injected into the Co 3d/O 2p hybridization state with oxygen vacancy introduction. Both absorption edges at the Co and Fe K-edge XANES shifted towards lower energies with oxygen vacancy introduction. The shift at the Co K-edge resulted from the decrease in the Co average valence and that at the Fe K-edge appeared to be caused by changes in the coordination environment around the Fe ions. The total conductivity of La(0.6)Sr(0.4)Co(0.8)Fe(0.2)O(3-δ) decreased with decreasing p(O(2)), due to a decreasing hole concentration.