Impact of microstructure and crystallinity on surface exchange kinetics of strontium titanium iron oxide perovskite by in situ optical transmission relaxation approach
Impact of microstructure and crystallinity on surface exchange kinetics of strontium titanium iron oxide perovskite by in situ optical transmission relaxation approach
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DOI：
10.1039/c7ta04940d
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发表时间：
2017-11-28
影响因子：
11.9
通讯作者：
Perry, Nicola H.
中科院分区：
文献类型：
--
作者：
Chen, Ting;Harrington, George F.;Perry, Nicola H.
混合导体表面的氧交换速率是影响高温能量转换/存储装置性能的关键特性。微观结构特征，如晶界密度和晶体质量，预计会影响表面交换动力学，但其影响尚未得到广泛研究。在这项工作中，采用脉冲激光沉积生长的混合导电钙钛矿SrTi0.65Fe0.35O3（δ）d（STF35）薄膜作为模型系统，系统地研究了微观结构对氧表面交换动力学的影响。通过 X 射线衍射、扫描探针显微镜、透射电子显微镜和角分辨 X 射线光电子能谱 (AR-XPS) 评估了生长温度对晶体质量、取向、晶粒尺寸、表面粗糙度和表面化学的影响。然后采用无接触、连续、原位光学传输弛豫方法来量化薄膜的天然表面氧交换系数（k（chem））。在低温（25 摄氏度）下生长的非晶薄膜没有表现出可测量的氧交换能力。在高温（800 摄氏度）下生长的高度结晶薄膜表现出合理但不是最佳的 k(chem)。发现最快的 k(chem) 是在中间生长条件下，即对于在较高温度（550 摄氏度）下结晶后的非晶生长薄膜或在接近（580 摄氏度）结晶温度下生长的薄膜。结合 AR-XPS 结果显示，在较高温度下生长的薄膜中表面 Sr 浓度更高，结果表明快速 kchem 是作为良好晶体质量和低 Sr 表面浓度之间的权衡而获得的。随着时间的推移，k(chem) 的降解与 Sr 表面浓度的增加相关。此外，具有优异结晶质量的（100）取向外延薄膜与纳米柱状晶粒（110）取向薄膜表现出非常相似的 k（化学）和老化行为，表明晶界和薄膜取向都不会导致该组合物中表面交换动力学的可观察到的变化。
The rate of oxygen exchange at the surface of mixed conductors is a critical property impacting the performance of elevated temperature energy conversion/storage devices. Microstructural features, such as grain boundary density and crystalline quality, are expected to impact the surface exchange kinetics, but their effect has not yet been widely studied. In this work, mixed conducting perovskite SrTi0.65Fe0.35O3 (delta) d (STF35) thin films grown by pulsed laser deposition were applied as a model system to systematically study the effect of microstructure on oxygen surface exchange kinetics. The impact of growth temperature on crystalline quality, orientation, grain size, surface roughness, and surface chemistry was evaluated by X-ray diffraction, scanning probe microscopy, transmission electron microscopy, and angle-resolved X-ray photoelectron spectroscopy (AR-XPS). A contact-free, continuous, in situ optical transmission relaxation approach was then applied to quantify the films' native surface oxygen exchange coefficients (k(chem)). Amorphous films, grown at low temperatures (25 degrees C), did not exhibit measurable oxygen exchange ability. Highly crystalline films, grown at high temperatures (800 degrees C), exhibited reasonable, but not optimal k(chem). The most rapid k(chem) was found for intermediate growth conditions, i.e., for amorphous-grown thin films just after crystallization at higher temperatures (550 degrees C) or for films grown near (580 degrees C) the crystallization temperature. Combined with the AR-XPS results showing greater surface Sr concentrations in films grown at higher temperatures, results suggest rapid kchem is obtained as a trade-off between good crystalline quality and low Sr surface concentration. Degradation of k(chem) over time was correlated to increased Sr surface concentration. Additionally, (100)-oriented epitaxial vs. nano-columnar grained (110)-oriented thin films with excellent crystalline quality exhibited very similar k(chem) and aging behavior, suggesting that neither grain boundaries nor film orientation cause observable changes in surface exchange kinetics in this composition.