Electric conduction of thin-layer Ni-multilayer ceramic capacitors with core-shell structure BaTiO₃

The electric conduction mechanism for multilayer ceramic capacitors with Ni internal electrodes (Ni-MLCCs) was investigated, utilizing impedance spectroscopy (IS) and thermally stimulated current (TSC) measurement techniques. A modified 4RC equivalent circuit model was proposed to analyze the IS data for the Ni-MLCCs. This model revealed that electrode/ceramics interfaces (E/C-I) and grain boundaries (GBs) have a Schottky type conduction mechanism controlling the leakage behavior at low electric field. The Schottky barrier height at E/C-I and surface level height at GB were calculated being 1.43 and 1.06 eV, respectively. The Ni-MLCCs showed a tunneling conduction occurs with high dc electric fields of more than 10 V/μm. The onset electric field for the tunneling conduction shifted toward high electric fields as the Mn content of the capacitors increased. TSC measurements revealed that a low Mn content resulted in high mobile oxygen vacancies concentration in the Ni-MLCCs. Mn also played a role in preventing oxygen vacancies from migrating to cathode electrodes, which resulted in a long lifetime for the Ni-MLCCs.