A transmission electron microscope study of commercial X7R-type multilayer ceramic capacitors

X7R-type multilayer ceramic capacitors produced by three commercial manufacturers (A, B and C) have been investigated by transmission electron microscopy. All the specimens contained grains with distinct core-shell structures, the cores were almost pure BaTiO3 and exhibited domain structures at room temperature. Specimens of type A had a grain size of 1-2 mu m, with 'wide' shells containing Pb, Bi, Nb, Ba and Ti. A bonding phase, rich in Si, Al, Ba and Ti was detected between the dielectric grains and Ag-Pd electrodes. Heating the samples to temperatures above 130 degrees C caused the ferroelectric domain structure to be lost and replaced by a dislocation network. Specimens of type B and C had a grain size of 0.5-1.0 mu m; the ferroelectric cores were surrounded by 'narrow' shells rich in Nb, Co, Ba and Ti. The Ag-Pd internal electrodes were twinned. Type I and type II core-shell structures were found in all three sets of multilayer ceramic capacitors. (C) 1998 Elsevier Science Limited. All rights reserved.