Hideyuki Kanai

A high-resolution transmission electron microscope study of a zinc oxide varistor

Investigations were made of varistor microstructure, the morphology of Bi2O3 at multiple ZnO grain junctions, Bi2O3/ZnO grain boundaries and ZnO/ZnO grain boundaries (especially whether Bi2O3 is present or not at the ZnO/ZnO grain boundary) by means of high-resolution transmission electron microscopy and X-ray microanalysis in the scanning transmission electron microscope. Bi2O3 at multiple ZnO grain junctions consists of small particles of 0.1μm in diameter, and they are vitrified to some extent. It is suggested that bismuth ions dissolve into ZnO grains over a 30 nm range from a Bi2O3/ZnO grain boundary; however, there is no bismuth at ZnO/ZnO grain boundaries.

Effect of Heat Treatment on Dielectric Properties of X7R Designated MLCs with Ni Internal Electrodes

The heat treatment of base-metal Ni electrode multilayer capacitors (MLCs) in air was investigated with a view to reducing manufacturing costs. This treatment was found to recover the insulation resistance in the same way as heat treatment under low oxygen partial pressure. At temperatures above 800°C, heat treatment in air was associated with cracking as a result of volumetric expansion of Ni through oxidation. TG-DTA analysis revealed that the oxidation behavior of Ni electrodes in MLCs differs from that of Ni plates or Ni fine powder. The capacitance of 1.2 μF MLCs in EIA 1206 size was successfully manufactured by the novel process.

Grain Size Dependence of Dielectric Constant for Modified (Pb0.63Ba0.37)(Zr0.7Ti0.3)O3 Ceramic Material

The grain size dependence of the dielectric constant for a modified (Pb0.63Ba0.37)(Zr0.7Ti0.3)O3 material from -55° C to 150° C has been studied. Grain sizes in the range of 1.2 µ m to 7.0 µ m were prepared by varying the sintering temperature and time. The maximum dielectric constant decreased monotonously as the grain size decreased. The dielectric constant at a lower temperature for the ferroelectric phase (-55° C) also decreased monotonously. However, at a high temperature for the cubic phase (150° C), the dielectric constant was almost constant. This monotonous decrease of the dielectric constant at a lower temperature is the same phenomenon as for the Pb(Mg1/3Nb2/3)O3 material. The Curie temperature of the ceramic shifted toward a higher temperature as the grain size was reduced. However, the aging rate was almost independent of the grain size.

Effects of SiO2 and Cr2O3 on the formation process of ZnO varistors

The effects of SiO2 and Cr2O3 on the formation process of ZnO varistors were investigated. Prior to formation of the Zn2.33Sb0.67O4 spinel phase (Sp-phase), a spinel-like phase forms. However, this phase does not control the varistor microstructure. The Sp-phase and the Bi2O3-phase which were formed by the decomposition of the Bi2(Zn4/3Sb2/3)O6 pyrochlore phase played important parts in the control of the varistor microstructure. That is, the Bi2O3 phase produced in the reaction promotes the initial sintering of the varistor and the Sp-phase inhibits the ZnO grain growth. In this reaction, SiO2 and Cr2O3 play a role in decreasing the decomposition temperature of the pyrochlore phase. Decreasing the decomposition temperature below 900° C (where ZnO grain growth begins) leads to the inhibition of ZnO grain growth.

Hydrothermal Crystal Growth of Lanthanum-Modified Lead Zirconate Titanate

Single crystals of lanthanum-modified lead zirconate titanate (PLZT) were grown under hydrothermal conditions. The starting nutrient at the bottom of the capsule dissolved in KF solution at 640° C, and recrystallized at the top of the capsule at 600° C. The basic shape of the grown crystals was cubic and they were black in color. The content of Zr in the crystals was markedly reduced in comparison with that of starting PLZT nutrient.

Stability and single crystal growth of dielectric materials containing lead under hydrothermal conditions

Abstract Stability of lead magnesium niobate (PMN; Pb(Mg 1/3 Nb 2/3 )O 3 ), lead scandium niobate (PSN; Pb(Sc 0·5 Nb 0·5 )O 3 ), a solid solution in the PSN–lead titanate system (PSNT), and lead zirconate titanate (PZT; Pb(Zr 0·53 Ti 0·47 )O 3 ) were all examined in a platinum capsule under hydrothermal conditions. The perovskite PMN was formed from the low crystalline pyrochlore PMN at 600°C by the hydrothermal treatment in pure water. However, the perovskite was decomposed to the pyrochlore by further hydrothermal treatment in pure water for a longer time or at higher temperature. In KF solutions, single crystals of PMN, PSN and PSNT with a pyrochlore structure were grown at the top of the capsule by hydrothermal treatments at 600°C with a temperature gradient of 40°C. In the case of PZT, single crystals of the tetragonal PZT were grown, but the content of Zr in the grown crystals decreased in comparison with that of the starting material.

Crystal Growth of Lead Zirconate Titanate with Additives under Hydrothermal Conditions

Single crystals of lead zirconate titanate (PZT) with an additive such as La2O3, Nb2O3 or MnO were grown under hydrothermal conditions with the starting nutrient of PZT ceramic powder based on Pb(Zr0.53Ti0.47)O3. The powder placed at the bottom of the capsule was dissolved in the KF solution at 640° C, and recrystallized at the top of the capsule at 600° C. Large crystals up to 1.8 mm in length were grown in 45 wt% KF solution, but a decrease in the concentration resulted in the reduction of the volume and size of the grown crystals. The addition of Nb to PZT ceramics inhibited the growth of the crystals. The additives in the starting materials were incorporated into the grown crystals, but the concentration of Zr in the crystals was markedly reduced in comparison with that of the starting materials.

A new relaxor dielectric for high voltage multilayer ceramic capacitors with large capacitance

A new ceramic dielectric, based on (Pb0.65Ba0.35)(Zr0.7Ti0.3)O3 has been developed. This dielectric, fired at low temperature of 1080°C, showed a high dielectric constant of 4500, a less than 0.3% dissipation factor and flat temperature characteristics of capacitance satisfying Y5P specifications in the EIA (Electronic Industries Association) Standard. Evaluation as a multilayer ceramic capacitor (MLC) revealed an excellent capacitance dependence under a high DC field. Thus, this dielectric is one of the promising candidates for high voltage MLCs with large capacitance.

Effects of B2O3 and SiO2 on dielectric properties and reliability of a lead-based relaxor dielectric ceramic

The effects of B2O3 and SiO2 which are major constituents of vitreous low-firing agents on the dielectric properties and reliability of ceramic dielectrics were elucidated for the case of the lead-based relaxor dielectric ceramic [(Pb0.875Ba0.125)][Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]O3. Boron oxide (B2O3) led to a decrease in dielectric constant and degraded reliability under a humidity load condition at 85°C and 95% RH. Although SiO2 also caused a decrease in dielectric constant, it did not result in a reliability degradation. Analysis of the microstructure using TEM and STEM revealed that a water-soluble secondary phase consisting of B2O3 and PbO was present at the grain boundaries and triple points in specimens with added B2O3. In contrast, no secondary phase existed in SiO2-doped specimens, but Si segregated at the grain boundaries. The existence of a water-soluble grain boundary phase was shown to degrade lifetime under humidity load conditions.

Characterization of grain boundary phase of a lead-based relaxor by raman scattering spectroscopy

Abstract The grain boundary phase of a lead-based relaxor was identified by Raman scattering spectroscopy using standard specimens including PbO, PbO 2 , and Pb 3 O 4 , as well as standard specimens synthesized from the compositions of the grain boundary phase analyzed by a scanning transmission electron microscope. It was revealed that the grain boundary phase contains the PbO phase along with the main perovskite phase in addition to the pyrochlore phase. This result agrees well with the results of X-ray photoelectron spectroscopy studies and strongly supports a previously described degradation mechanism for insulation resistance under humid loading conditions: dissolution of PbO in the grain boundary phase into water is the trigger phenomenon leading to degradation.