Mitsuo Harata

Dielectric Properties of Modified Lead Zinc Niobate Ceramic

Crystal structures, dielectric properties and electrical resistivities for partially substituted lead zinc niobate [Pb(Zn1/3Nb2/3)O3] ceramic were investigated. This ceramic, sintered at 1000–1050°C, was composed mainly of perovskite phase and showed a high dielectric constant (3500–5000) and a high resistivity (approximately 1013Ωcm) when partial substitutions of the Pb site by Ba or Sr and the (Zn1/3Nb2/3) site by Ti in the Pb(Zn1/3Nb2/3)O3 were carried out. The reason why the perovskite phase was stable in the sintered body is explained qualitatively by introducing the concepts of an electronegativity difference and a tolerance factor.

Low firing and high dielectric constant X7R ceramic dielectric for multilayer capacitors based on relaxor and barium titanate composite

A temperature stable ceramic dielectric with a low firing temperature (1130 °C) and a high dielectric constant (3700 to 2600) has been developed by sintering the mixture of precalcined lead-based relaxor and prefired modified barium titanate.This dielectric was confirmed to be a two-phase ceramic composite body, according to X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy and dielectric measurements.A shortcoming of the high dissipation factor in the dielectric has been reduced by incorporating MnO into the barium titanate constituent prior to mixed sintering.This ceramic dielectric meets X7R specifications in the EIA (Electronic Industries Association) standard.

High Volume Efficiency Multilayer Ceramic Capacitor

Multilayer ceramic (MLC) capacitor with small size, large capacitance and low cost are increasingly demanded as components for miniaturized electronic equipment. The conventional dielectric materials for MLC capacitors are mainly based on BaTiO3 . They are co-fired in air with internal electrodes at around 1,300 oC.) Therefore, the internal electrodes must be a precious metal, such as platinum or palladium, in order to prevent oxidation or reaction with dielectrics. In the case of large capacitance MLC capacitors, the precious metal cost constitutes large proportion of the selling price of the capacitor. So, large capacitance MLC capacitor is too expensive for consumer electronics applications.

Lead Perovskite Relaxor-Based Low-Loss Ceramic Dielectric for High-Voltage Ceramic Capacitors

A low-loss ceramic dielectric with a less than 0.1% dissipation factor at 100 kHz, based on a modified lead zinc niobate relaxor, has been fabricated by shifting the ferroelectric transition temperature (Tc) to below -55°C. This dielectric has a high dielectric constant (K), ranging from 250 to 2000. The temperature coefficient of capacitance (TCC) locates at the middle area between values for temperature compensation dielectric and values for high-K dielectric. Even at 150°C, high insulation resistance, more than 5×1013 Ωcm, was also retained. Moreover, a typical composition with K=530 revealed that the dielectric has a high breakdown voltage of 95 kV per 10 mm of thickness and a TCC value of -2900 ppm/°C. Accordingly, this dielectric has proven useful for high-voltage ceramic capacitors.

Effects of Specific Surface Area of Starting Pre-Calcined Dielectric Powders on Sintering Behavior and Dielectric Properties of Relaxor/Modified-BaTiO3 Composite

Sintering behavior and dielectric properties of relaxor/Zr-modified BaTiO3 (BTZ) dielectric composite have been investigated as functions of specific surface area (SSA) of starting pre-calcined dielectric powders, as well as firing temperature. Relative dielectric constant of the dielectric composite increased with the SSA of relaxor. However, this was not in the case with the BTZ powder. The relative dielectric constant decreased either when the SSA of BTZ was 2.0[m2/g] or when firing temperature was 1210°C. Optimization of the SSAs of relaxor and BTZ powders, as well as firing temperature made it possible to produce Multilayer Ceramic Capacitors (MLCs) which meet X7R specifications in the Electronic Industries Association (EIA) standard.