Correlating structure and energy landscape of perovskite oxide grain boundaries

对晶体结构、点缺陷和扩展缺陷如何影响离子迁移的能量景观的基本理解的发展对于钙钛矿氧化物的许多应用是非常重要的。然而，晶界的原子结构，它们的空间电荷区域，占据和迁移的离子的网站能量，以及它们随浓度的变化之间的关系仍然没有得到很好的理解。因此，在计划研究小组的该项目中，将通过分析和高分辨率透射（扫描）电子显微镜（HR（S）TEM）研究沿沿着和跨晶界以及具有选定倾斜晶界的双晶体体积中的各向异性扩散。最初，我们选择作为一个模型系统的碱金属离子扩散在立方钙钛矿SrTiO 3具有明确的小角度和大角度晶界的不同倾斜角。在项目开发过程中，研究将扩展到与固体氧化物燃料电池相关的双晶外延钙钛矿薄膜。晶界的原子和化学结构将通过使用HR（S）TEM结合空间分辨光谱技术（EDX，EELS）进行研究。这也允许局部扩散分布的确定和它们的二次离子质谱（西姆斯，AG Weitzel，P1）和3D浓度分布的断层原子探针（APT，AG Weitzel，P3）的结果进行比较。另一个中心目标是通过离轴电子全息术确定晶界的电势以及空间电荷区域。光谱和漫电子散射方法被用来检测点缺陷的体积和周围的晶界的影响。晶界的原子，化学和电学结构的结果是中心的网站能量的理论测定（从头算方法，AG雅各布，P6），以及从扩散实验的能量景观的确定。在研究小组中，拟议的项目与其非常先进的TEM方法相结合，可以为理解场地景观和人口密集的场地能量及其对当地电位的依赖做出重要贡献。

The development of a fundamental understanding of how crystal structure, point defects and extended defects influence the energy landscape for ion migration is of great importance for many applications of perovskite oxides. However, the relationship between the atomic structure of grain boundaries, their space charge regions, the site energies for occupation and migration of ions, and their changes with concentration is still not very well understood. In this project of the planned research group, therefore, anisotropic diffusion along and across grain boundaries as well as in the volume of bicrystals with selected tilt grain boundaries will be investigated by means of analytical and high-resolution transmission (scanning) electron microscopy (HR(S)TEM). Initially, we select as a model system the alkali ion diffusion in the cubic perovskite SrTiO3 with well-defined small and large angle grain boundaries of different tilt angles. In the course of the project development, the investigations will be extended to bicrystalline epitaxial manganate perovskite films that are relevant for solid oxide fuel cells. The atomic and chemical structure of the grain boundaries will be investigated by using HR(S)TEM in combination with spatially resolved spectroscopic techniques (EDX, EELS). This also allows the determination of local diffusion profiles and their comparison with the results of secondary ion mass spectroscopy (SIMS, AG Weitzel, P1) and 3D concentration distributions from tomographic atom probe (APT, AG Volkert, P3). A further central goal is the determination of the electric potentials as well as the space charge regions of the grain boundaries by off-axis electron holography. Spectroscopy and diffuse electron scattering methods are used to detect the influence of point defects in the volume and in the surrounding of grain boundaries. The results on the atomic, chemical and electrical structure of grain boundaries are central for the theoretical determination of the site energies (ab initio methods, AG Jacob, P6) as well as for the determination of the energy landscape from diffusion experiments. In the research group, the proposed project with its combination of very advanced TEM methods can make a central contribution to the understanding of the landscape of site and populated site energies and their dependence on local electrical potentials .