High dielectric constant can be reached in a reductive-sintered SrBaTiO₃ barrier-layer capacitor with core‒rim structures as dominant microstructural features. By SEM and aberration-corrected TEM observations, an interfacial zone between the core and rim, named as white-rim (w-rim), was found always enriched with Ba, while the core was free of Ba solution. The reductive liquid-phase sintering resulted in three times the concentrations of oxygen vacancies (V_O) into cores and rims compared to their A-site vacancies (V_A), while enabling the highest concentration of V_O (~17%) without V_A in w-rim. The strained core/w-rim interfaces, with obvious interfacial polarizations, which can effectively raise the dielectric constant, were expected to be created from a temporary equilibrium between the cores and the liquid-phase. The synergetic evolution of core‒rim structures, Sr–O vacancies, multiple internal polarized structures can be utilized to better control and optimize dielectric behaviors and other functionalities for perovskite capacitors and other multi-functional ceramics.