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The influence of tetragonality (c/a) of the dielectrics of BaTiO3-based multi-layer ceramic capacitors (MLCC) on the direct current (dc) bias characteristics was investigated. The tetragonality can be reduced by decreasing the grain size, and it can be further decreased for the same grain size condition by increasing the measurement temperature or the A/B ratio in the ABO3 structure. Fine grain samples showed higher dielectric constants than those of coarse grain samples under a high dc-bias field over the entire temperature range below Curie temperature (TC), and they became similar to each other above TC. Whereas the dielectric constants under a high dc-bias field increase slightly with the increase of temperature for the fine grain samples, those of coarse grain samples systematically increase, of which the tetragonality is also supposed to change more distinctly. In fine grain samples, the dielectric constants under a high dc-bias field can be further enhanced by increasing the A/B ratio in ABO3 structures through the excess Ba addition that results in a decrease of tetragonality. All these results demonstrate that the reduction of tetragonality increases the intrinsic dielectric constants along the c-axis direction, and thus is a crucial factor for the enhancement of dielectric constant under a high dc-bias field condition where the domain alignment with the c-axis parallel to the dc-bias field occurs. [ABSTRACT FROM AUTHOR]

The multilayered ceramic capacitor (MLCC) is a key component of electronic equipment, such as smartphones, portable PCs and electric vehicles, which contain a number of MLCCs. As MLCCs distribute and control the amount of current flowing through circuits, remove noise, and prevent malfunction, MLCCs play a key role in enabling electronic devices to have high performance, multi-functionality, and high integration. This review highlights the critical issues and recent progress in developing highly volumetric-efficient and high capacitance MLCCs from the viewpoint of designing a BaTiO3-based dielectric layer. After a brief introduction of MLCCs and dielectric materials, we summarize the current issues in developing BaTiO3-based dielectric materials for MLCCs with high performance and reliability and describe the strategies to optimize dielectric properties through nano/microstructure control, chemical modification and doping. Finally, we provide an outlook on the development and future application of MLCCs. It is anticipated that this review can serve as an overview and evaluation of state-of-the-art synthesis and design of BaTiO3-based dielectric materials for MLCC applications. [ABSTRACT FROM AUTHOR]