Influence of excess Ba concentration on the dielectric nonlinearity in Mn and V-doped BaTiO_3 multi layer ceramic capacitors

摘要

The effect of excess Ba concentration on the dielectric nonlinearity was investigated in Mn and V-doped BaTiO_3 multi layer ceramic capacitors (MLCC) under the same grain size condition, which was described by the Preisach model utilizing the first order reversal curve (FORC) distribution. The high-field dielectric constant and its ac field dependence dramatically changed increasing to a maximum and then decreasing with the increase of Ba concentration. The saturation polarization which scales to the magnitude of spontaneous polarization also showed similar behavior. These results indicate that the dependence of the dielectric constant on the Ba concentration is associated with the variation of both domain wall contribution and the magnitude of the spontaneous polarization, which could be correlated with the same dependence on the Ba concentration of the reversible FORC distribution at zero bias and the irreversible FORC distribution near origin. In the corresponding bulk specimens of the dielectrics of MLCC, almost the same amount of the Ba_2TiSi_2O_8 second phases were detected irrespective of Ba concentration, which shows that the excess Ba incorporate into BaTiO_3. Thus, low and high Ba concentration corresponds to Ba-deficient and Ba-rich or Ti-deficient BaTiO_3, respectively, which results in a small spontaneous polarization and low domain wall density. The intermediate Ba concentration for the maximum dielectric constant is supposed to be near stoichiometric condition in the AB03 structure corresponding to large spontaneous polarization and high domain wall density. The excess Ba concentration and its resultant A/B stoichiometry is a crucial factor controlling dielectric properties.