This review highlights the critical issues and recent advances in developing highly volumetric-efficient and high capacitance MLCCs from the viewpoint of designing dielectric materials.

Dielectric aging of Mn and V-codoped BaTiO3 was investigated. The increase of V concentration had little influence on aging, whereas that of Mn increased it. Thermally stimulated depolarization current (TSDC) of low Mn concentration specimen showed one peak, whereas Mn-increased specimen showed two peaks. The first and second peak is supposed to be caused by the phase transition of the undoped core region and the defect dipole of Mn such as MnTi″-VO•• or MnTi′-VO••, respectively. High TSDC associated with the defect dipole of Mn and significant aging rate experimentally demonstrates that the dielectric aging is controlled by the defect dipole.

Heavily doped barium titanate (BaTiO3) powders, one with a donor‐rich and the other with an acceptor‐rich composition, were prepared. After sintering, the donor‐rich specimen exhibited a fine‐grained microstructure but significant grain growth occurred in the acceptor‐rich specimen. A stable dielectric behavior was observed only in the donor‐rich fine‐grained specimen over the temperature range studied. However, in both specimens, an undoped core region several hundred nanometers in size was detected. The core‐shell structure appeared to be maintained in BaTiO3 under the conventional sintering conditions.

The behaviors of the electrical resistance at room and high (200°C) temperatures of acceptor (Mg)-doped BaTiO3 ceramics with the increase of acceptor concentration were investigated. A series of coarse-grained specimens with different acceptor concentrations that were sintered at various oxygen partial pressures was prepared. The critical acceptor concentrations, beyond which the room temperature resistance increases abruptly, were experimentally evaluated and they were found to increase with a decrease in oxygen partial pressure during sintering. Each defect and electron concentrations at sintering and room temperature as a function of acceptor concentration were theoretically calculated. The results calculated could explain the experimentally observed behavior of the resistance versus acceptor concentration. The high (200°C) temperature resistances under high electric field showed resistance degradation critically depending on acceptor concentration in the very small concentration range below ∼0.1mol%, which occurred easily with the increase of acceptor concentration. It was explained that such behavior was caused by the variation of potential barrier of grain boundaries for the migration of oxygen vacancies as a function of acceptor concentration.

Changes in the microstructure and dielectric properties with the variation of the donor/acceptor ratio in BaTiO3 ceramics were investigated. In donor‐rich specimens, a liquid that appeared during sintering did not penetrate into grain boundaries. However, in the acceptor‐rich specimens, the grains were separated by a liquid film during sintering. The much higher mobility of the liquid film than that of the grain boundaries was suggested to cause extensive grain growth in acceptor‐rich BaTiO3. The macroscopic homogenization of dopants because of grain growth in acceptor‐rich specimens resulted in changes in the dielectric properties.