Yasuo Uehara

Electrical Properties of Rapid Quenched Bi4Ti3O12 Amorphous Ribbons

The electrical properties before and after annealing for rapid quenched Bi4Ti3O12 amorphous ribbons have been studied. Before crystallization, its dielectric breakdown strength is very high, while its dielectric constant is rather low since it is non-ferroelectricity. After crystallization, its room temperature dielectric constant becomes higher than that for a sample prepared by ordinary firing method. For instance, the value for the sample annealed at 650°C is 300, which is about two times as large as that for the latter. Similar behaviors on the ferroelectric and breakdown properties of the annealed sample are also observed.

Grain orientation of SbSI ceramics

When SbSI ceramics is viewed as a piezoelectric material, since the direction of the spontaneous polarization is limited to one dimension, it is necessary to perform grain orientation. In this paper, as a method for grain orientation at room temperature, a rolling and an extrusion method are considered, and the fabrication method of SbSI grain-orientation ceramics is examined. Furthermore, the electrical characteristics of the obtained grain-orientation sample are examined.

Grain-Oriented Ceramics in Bismuth Layer-Structure Compounds for Capacitor Material

The systematic investigation of the composition of high-permittivity bismuth layer-structure oxides and the examination of the grain-oriented ceramics were carried out. Through investigation of the composition of high-permittivity materials, it was clarified that the dielectric constant e s of more than 1000 can be attained using Pb4Bi4Ti7O24 compound. Moreover, it was confirmed that favorable characteristics for use as dielectric ceramics for high-voltage capacitors (stability of e s on DC bias, high resistivity, etc.) can be attained using this compound. The examination of the characteristics of grain-oriented Pb4Bi4Ti7O24 ceramics clarified that the dielectric breakdown strength and the stability of e s on DC bias can be improved in the direction perpendicular to the polarization axis. As a result, grain-oriented ceramics are considered to be appropriate for use as capacitor materials.

Grain-Orientation of Bi4Ti3O12 Ceramics by Cold-Uniaxial Method

The purpose of this paper is to investigate processes of grain-orientation in Bi4Ti3O12 ceramics prepared by a cold-uniaxial method used press forging. This method is characterized by utilizing shape anisotropy of ceramic particles prepared by grinding after prefiring. Such particles are aligned by means of the uniaxial pressing process and high alignment of grains in the ceramics can be achieved by grain growth during sintering process. The maximum degree of grain-orientation in the obtained samples reaches 0.76 in terms of the method proposed by Lotgering, which is nearly equal to that obtained by hot-working methods.

Electrical and mechanical characteristics of PbnBi4Tin+3O3n+12 ceramics

The electrical and mechanical characteristics of Pb n Bi 1 Ti n+3 O 3n+12 ceramics were examined. With increasing n, the dielectric constant e y increased, and the temperature dependence of e s broadened. e s , at room temperature, reached a value of approximately 750 at n = 3 and n = 4 at 100 kHz. The dielectric breakdown strength E b and the three-point bending strength σ decreased with increasing n. For example, σ of the sample at n = 4 was approximately a 70% value of the sample at n = 0. On the other hand, the examination of the characteristics of grain-oriented samples clarified that E b and σ can be improved in the direction perpendicular to the polarization axis.

Preparation and Properties of Rapid Quenched (BaO)1-x·(TiO2)x Amorphous Ribbons

Amorphous ribbons of (BaO)1-x(TiO2)x are prepared by rapid quenching method using a twin-roller apparatus. Transparent ribbon-like thin samples are obtained for the composition range 0.60x0.75. For as-quenched samples with composition 0.55x0.80, exothermic peaks in DTA curves are clearly observed at 600–820°C. The dielectric constant for each amorphous sample is about 25 at room temperature, and independent of compositional change. Changes in dielectric behavior of quenched samples with x=0.68 by heat treatment are also discussed.

Grain orientation and properties of SrBi2Ta2O9 ceramics with excess Bi2O3

Abstract The purpose of this paper is to investigate the grain orientation and properties of SrBi2Ta2O9 (SBT) ceramics with excess Bi2O3. Ordinarily fired (OF) ceramics were prepared by conventional ceramic techniques at 900–1300°C for 2 h. The grain-oriented (GO) ceramics were prepared using the hot-forging method. With addition of Bi2O3 in the amount of 0 – 1.5 wt% to the SBT of stoichiometric composition, the optimum firing temperature in OF ceramic samples gradually lowered with increasing Bi2O3 addition, and was about 1100°C in the case of 0.5 wt% of excess Bi2O3. Plastic deformation is easily accomplished using the hot forging method where Bi2O3 exists as a state of liquid phase within the sample. In fact, the GO sample with 0.5 wt% of excess Bi2O3 showed a highly structured orientation f=0.97 in the case of hot-forging at 1100°C.

Dielectric Breakdown Strength of Grain-Oriented Bi4Ti3O12 Ceramics

DC dielectric breakdown strength Eb of grain-oriented Bi4Ti3O12 ceramics fabricated by the hot-forging method and the cold-uniaxial pressing method has been studied. In the hot-forging sample with the X-ray orientation factor of 0.84, Eb was about 22 MV/m, when electric field was applied parallel to the pressing axis of the grain-oriented ceramics. On the other hand, Eb was about 16 MV/m, when the field was perpendicular to the pressing axis. It was found that grain orientation is effective in increasing Eb parallel to the pressing axis.

Preparation and Properties of Ceramics Prepared from Bi4Ti3O12 Amorphous Material

We attempted to prepare a low-temperature-fired Bi4Ti3O12 ceramics from an amorphous substance as a basic material and Bi2O3 as a liquid phase material. When Bi2O3 was added in the amount of 10% by weight to the basic material, and then the mixture was fired under the conditions of 870° C–5 h, ceramic samples having a relative density of about 90% were prepared. The grain sizes of the sample were 2 µ m or less, that is, about one-tenth that of a sample fired under standard conditions. The electric properties of the samples were also examined. Results showed that the electrostatic capacitance change (ΔC/C) of the sample caused by the DC bias was relatively low. The DC dielectric breakdown strength was 1.4 times higher, and the remanent polarization was about one-third, as compared with a sample fired under standard conditions.