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The effect of excess Ba concentration on the dielectric nonlinearity was investigated in Mn and V-doped BaTiO3 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 Ba2TiSi2O8 second phases were detected irrespective of Ba concentration, which shows that the excess Ba incorporate into BaTiO3. Thus, low and high Ba concentration corresponds to Ba-deficient and Ba-rich or Ti-deficient BaTiO3, 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 ABO3 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. [ABSTRACT FROM AUTHOR]

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 ∼0.1 mol %, 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. [ABSTRACT FROM AUTHOR]

The positive temperature coefficient of resistivity (PTCR) effect in ferroelectric Pb(Fe1/2Nb1/2)O3 (PFN) ceramics was examined to determine its physical meaning as the evidence of the ferroelectric domain structure. Monitoring of the temperature dependence of resistivity showed that its PTCR effect begins around the dielectric maximum temperature (Tm). The existence of the space charge region near the grain boundary was verified via impedance spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicated it to be due to Pb volatilization during the sintering process. In addition, well-development ferroelectric domain structure, which was expected to be found according to Jonker''s theory, was observed with transmission electron microscopy (TEM). [Copyright &y& Elsevier]