X7R‐type BaTiO3 materials were analyzed using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Powder XRD indicated that the materials had pseudocubic lattices, but core–shell grain structures predominated in bright‐field (BF) TEM images. Electron diffraction patterns across the core–shell boundaries and convergent beam electron diffraction patterns of cores and shells indicated that coherent grain boundaries existed between cores and shells. The flat dielectric constant–temperature curves obtained from these materials can be interpreted in terms of the internal stress states in individual grains. The stress states were observed using weak‐beam dark‐field (WBDF) microscopy, and strain contours formed by distorted crystal planes were visible in the WBDF images. The contours observed were dependent on the stress state of the crystal instead of crystal symmetry and the stress distribution in individual grains was determined by both the thickness ratio of shell and core, and the geometrical relationship of the core and the shell. Twins observed in this material were determined to be growth rather than mechanical twins, through observation of the strain contour distribution.

The dielectric properties, dopant distributions, and microstructures of BaTiO 3 -based multilayer ceramic capacitors (MLCCs) sintered in H 2 -N 2 -H 2 O atmospheres with P O 2 5 10 À7.5 Pa (BMX-7.5) and P O2 5 10 À9.5 Pa (BMX-9.5) were studied, and the effects of oxygen partial pressures were analyzed. Dielectric measurements showed that BMX-7.5 had a lower dielectric constant at temperatures above 201C, but a higher dielectric constant at temperatures below 101C when compared with BMX-9.5. The coexistence of core-shell and core grains was observed in bright field (BF) transmission electron microscopy images in both types of capacitors. Triple-point and grain boundary phases were observed more frequently in BMX-9.5 than in BMX-7.5, and energy-dispersive X-ray spectrometer point-by-point analysis revealed that these second phases contained high concentrations of dopants such as Si, Y, and Ca. The dopant concentration in the shell regions in BMX-7.5 was higher than that in similar regions in BMX-9.5. Smeared and twisted grain boundaries with fringes observed in both types of MLCCs indicated that the shell regions in both samples were formed either by diffusion of foreign ions into BaTiO 3 or by crystallization of grain boundary and triple-point liquid phases. It was deduced that the partial pressure of oxygen in the sintering atmosphere influenced the microstructures, dopant distributions, and coreshell ratios of the grains in these materials. J ournal