The microstructure of Y5V-1206 capacitor has been studied using X-ray diffractometry (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). Twinning occurs when a crystal undergoes a shear stress which produces a crystal structure which is a mirror image of itself. In BaTiO3, twinning occurs in (111) plane and the orientation relationships of it between two grains have been analyzed. We can define it for transformation matrices. We supply high-voltage, low-current pulses to capacitor for breakdown of it. We confer on reason for breakdown. We suspect the discrepancy is due to the change in the field distribution above and below Curie Temperature in core-shell structure. It differentiates dielectric constant (