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Growth and surface modification of LaFeO3 thin films induced by reductive annealing

机译：还原退火诱导LaFeO3薄膜的生长和表面改性

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The mixed electronic and ionic conductivity of perovskite oxides has enabled their use in diverse applications such as automotive exhaust catalysts, solid oxide fuel cell cathodes, and visible light photocatalysts. The redox chemistry at the surface of perovskite oxides is largely dependent on the oxidation state of the metal cations as well as the oxide surface stoichiometry. In this study, LaFeO3 (LFO) thin films grown on yttria-stabilized zirconia (YSZ) was characterized using both bulk and surface sensitive techniques. A combination of in situ reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) demonstrated that the film is primarily textured in the [1 0 0] direction and is stoichiometric. High-resolution transmission electron microscopy measurements show regions that are dominated by [1 0 0] oriented LFO grains that are oriented with respect to the substrates lattice. However, selected regions of the film show multiple domains of grains that are not [1 0 0] oriented. The film was annealed in an ultra-high vacuum chamber to simulate reducing conditions and studied by angle-resolved X-ray photoelectron spectroscopy (XPS). Iron was found to exist as Fe(0), Fe(II), and Fe(III) depending on the annealing conditions and the depth within the film. A decrease in the concentration of surface oxygen species was correlated with iron reduction. These results should help guide and enhance the design of LFO materials for catalytic applications. (C) 2015 Elsevier B.V. All rights reserved.
机译：钙钛矿氧化物的混合的电子和离子电导率使其能够用于多种应用中，例如汽车尾气催化剂，固体氧化物燃料电池阴极和可见光光催化剂。钙钛矿氧化物表面的氧化还原化学很大程度上取决于金属阳离子的氧化态以及氧化物表面化学计量。在这项研究中，使用体感和表面敏感技术对在氧化钇稳定的氧化锆（YSZ）上生长的LaFeO3（LFO）薄膜进行了表征。原位反射高能电子衍射（RHEED），X射线衍射（XRD）和卢瑟福背散射光谱（RBS）的组合表明，该膜主要在[1 0 0]方向上织构化并且是化学计量的。高分辨率透射电子显微镜测量显示区域由相对于基底晶格定向的[1 0 0]定向LFO晶粒占主导。但是，薄膜的选定区域显示出晶粒的多个区域不是[1 0 0]取向的。该膜在超高真空室内退火以模拟还原条件，并通过角分辨X射线光电子能谱（XPS）进行研究。发现铁以Fe（0），Fe（II）和Fe（III）的形式存在，这取决于退火条件和膜中的深度。表面氧种类浓度的降低与铁的还原有关。这些结果应有助于指导和增强用于催化应用的LFO材料的设计。 （C）2015 Elsevier B.V.保留所有权利。

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