Abstract
Interfaces such as grain boundaries (GBs) and heterointerfaces (HIs) are known to play a crucial role in structure-property relationships of polycrystalline materials. While several methods have been used to characterize such interfaces, advanced transmission electron microscopy (TEM) and scanning TEM (STEM) techniques have proven to be uniquely powerful tools, enabling quantification of atomic structure, electronic structure, chemistry, order/disorder, and point defect distributions below the atomic scale. This review focuses on recent progress in characterization of polycrystalline oxide interfaces using S/TEM techniques including imaging, analytical spectroscopies such as energy dispersive X-ray spectroscopy (EDXS) and electron energy-loss spectroscopy (EELS) and scanning diffraction methods such as precession electron nano diffraction (PEND) and 4D-STEM. First, a brief introduction to interfaces, GBs, HIs, and relevant techniques is given. Then, experimental studies which directly correlate GB/HI S/TEM characterization with measured properties of polycrystalline oxides are presented to both strengthen our understanding of these interfaces, and to demonstrate the instrumental capabilities available in the S/TEM. Finally, existing challenges and future development opportunities are discussed. In summary, this article is prepared as a guide for scientists and engineers interested in learning about, and/or using advanced S/TEM techniques to characterize interfaces in polycrystalline materials, particularly ceramic oxides.
Highlights
While bicrystals can be used as models on for structure property analysis, they do not fully represent grain boundaries (GBs) and heterointerfaces in polycrystalline materials, which contain grains with many different orientations [57,60]
High resolution transmission electron microscopy (TEM) (HRTEM) images demonstrate the atomic arrangement at interfaces and enable observation of individual defects, which can be used to analyze secondary phases or impurities and can probe local crystallinity at the GBs [118]
This agrees with the energy-loss spectroscopy (EELS) results shown on the side, presenting an increase in Ca2+ concentration at and near GB core compared to the bulk, as Ca2+ is lighter than Ce4+ we expect lower signals where it segregates
Summary
Solid-solid interfaces are ubiquitous in materials science and engineering with wideranging properties and applications [1,2]. In polycrystalline bulk materials and thin films, interfaces directly impact mechanical, optical, thermal, magnetic, electrical and (electro)chemical properties due to existence of local heterogeneity in structure, composition, chemistry, and electronic structure down to the atomic scale [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] Ceramics such as oxides [4,17] are prone to GB effects as annealing the GBs out by coarsening the grains usually requires ≥1000 ◦C, which is energy-intensive, costly, and deteriorates device components.
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