Application of Electron Energy-loss Spectroscopy to BaTiO3 Multi-layer Ceramic Capacitors

BaTiO3 multi-layer ceramic capacitors (MLCCs) are meeting the growing performance demands in consumer electronics, aerospace and defense research. Distribution and segregation of elements during complex fabrication process of MLCCs significantly affect the phase composition, microstructures and hence the performance, which necessitates an effective analytical means capable of accurately resolving elements of MLCCs at microscopic scales. Elemental analysis techniques integrated with modern transmission electron microscope (TEM) have unique advantages due to their ultra-high spatial resolution, reaching the sub-angstrom scale. Among them, energy dispersive X-ray spectroscopy (EDS) provides a simple and fast way for qualitative analysis of metallic elements. However, their limitations, such as low sensitivity for detecting the light element O, and more critically, low energy resolution (similar to 130 eV), which results in the severe overlap of spectral peaks of Ba and Ti elements, hinder accurate quantitative analysis of BaTiO3. In contrast, electron energy-loss spectroscopy (EELS) possesses ultra-high energy resolution (<1.0 eV), and can provide additional information regarding chemical valence, thus demonstrating enhanced potentials and advantages in the micro-scale elemental analysis of MLCC. In this work, EELS is employed to address the limitation of EDS in distinguishing between Ba and Ti elements due to the overlap of spectral peaks. In addition, EELS reveals that proportion of Ti3+ ions is higher in smaller BaTiO3 grains. Meanwhile, EELS line-scan analysis of individual grains indicates that Ba element diffuses more easily than Ti during sintering process of ceramics. Given its high spatial resolution, EELS offers more accurate and comprehensive information on the elements and valence states, thereby providing potential support for the process improvement and performance optimization of MLCC.