Imaging of the Core–Shell Structure of Doped BaTiO3 Ceramics by Energy Filtering TEM

Abstract

Energy-filtering transmission electron microscopy (EFTEM) was applied to investigate the core-shell structure of a X7R-dielectrics. The investigations were performed with a Philips CM20 equipped with a GATAN imaging filter at 200 kV acceleration voltage. The BaTiO 3 ceramics, of grain sizes 0.1 to 0.5 μm, was doped with low concentrations of the elements Zr, Yb, Sr and Mg. The cores contained ferroelectric domains whilst the shells were completely free of domains. EDXS and EELS analyses revealed that the cores were pure BaTiO 3 whilst the shells contained the doping elements. EFTEM was used to visualize the small concentration differences between the core and the shell within the BaTiO 3 grains. The core-shell structure can be visualized by recording jump-ratio images at the Ti-L 2,3 ionization edge under rocking beam illumination. The distribution of the doping elements can be shown by recording jump-ratio images with the Zr-M 4,5 and Yb-N 4,5 ionization edges. The jump-ratio images recorded under rocking beam illumination have the advantage, that the elemental distributions are not disturbed by diffraction effects such as in case of EFTEM elemental maps measured with the three-window method. Therefore, the core-shell structure could not be detected in the EFTEM elemental maps. This new method allows the rapid and unequivocal visualization of the core-shell structure of BaTiO 3 grains down to nanometer resolution. The methodology presented in this work can be applied to all X7R-dielectrics and is easily useable for rapid routine characterization of these materials.