Abstract
The effect of dopants and processing conditions on the dielectric properties of base-metal-electroded materials was investigated. BaTiO 3 materials simultaneously doped with MgO and Y 2 O 3 additives can achieve small capacitance variation (ΔC/C), which meets the X7R specification, when the proportion of additives is abundant enough and the materials are not over-fired. Presumably, small ΔC/C values of thus obtained materials are the result of the formation of core-shell structure, which requires stringent control of material processing conditions. In contrast, X7R-type materials can be obtained in a much wider processing window, when prepared by mixing two BaTiO 3 materials of suitable dielectric constant-temperature (K-T) characteristics. Duplexed materials prepared from these two end-point BaTiO 3 materials with ratios ranging from 3:1 to 1:2 exhibit K-T behavior within the X7R specification, provided that one of the components possesses flat K-T behavior. Moreover, the dielectric properties of these materials were simulated using a simplified microstructural model. Simulation results indicate that the effective dielectric constant of core-shell materials, (K e ) CS , varies significantly not only with the dielectric properties of cores and shells, but also with the shell-to-core thickness ratio, whereas the effective dielectric constant of duplexed materials, (K e ) D , can be maintained at a very small ΔC/C value for a wide range of end-point constituent ratios, which agrees very well with the measured K-T properties for the materials.