IMAGING OF THE CORE-SHELL STRUCTURE OF DOPED BATIO3 CERAMICS BY ENERGY-FILTERING TEM

Energy-filtering transmission electron microscopy (EFTEM) was applied to investigate the core-shell structure of a X7R-dielectrics, The inve stigations were performed with a Philips CM20 equipped with a GATAN im aging filter at 200 kV acceleration voltage. The BaTiO3 ceramics, of g rain sizes 0.1 to 0.5 mu m, was doped with low concentrations of the e lements Zr, Yb, Sr and Mg. The cores contained ferroelectric domains w hilst the shells were completely free of domains. EDXS and EELS analys es revealed that the cores were pure BaTiO3 whilst the shells containe d the doping elements. EFTEM was used to visualize the small concentra tion differences between the core and the shell within the BaTiO3 grai ns. The core-shell structure can be visualized by recording jump-ratio images at the Ti-L-2,L-3 ionization edge under rocking beam illuminat ion. The distribution of the doping elements can be shown by recording jump-ratio images with the Zr-M-4,M-5 and Yb-N-4,N-5 ionization edges . The jump-ratio images recorded under rocking beam illumination have the advantage, that the elemental distributions are not disturbed by d iffraction effects such as in case of EFTEM elemental maps measured wi th the three-window method. Therefore, the core-shell structure could not be detected in the EFTEM elemental maps. This new method allows th e rapid and unequivocal visualization of the core-shell structure of B aTiO3 grains down to nanometer resolution. The methodology presented i n this work can be applied to all X7R-dielectrics and is easily useabl e for rapid routine characterization of these materials.