Kunisaburo Tomono

Synthesis and Characterization of Bi4Ti3O12 Thin Films by Sol-Gel Processing

Stoichiometric Bi4Ti3O12 thin films were prepared by sol-gel processing. This paper discusses the synthesis of polymerizable solutions containing Bi and Ti, and characterization of the resulting Bi4Ti3O12 thin films. The formation of metallic alkoxide and acetate alkoxide are indispensable, soluble precursors for these multicomponent systems. The double alkoxide was prepared by allowing Bi acetate to react with Ti alkoxides. The development of the polymerizable solution system containing Bi and Ti required choosing appropriate solvents and metallo-organic sources for the two components. Bismuth acetate, titanium methoxyethoxide and the solvents 2-methoxyethanol and glacial acetic acid were selected based on their successful use in a number of related systems. Thin films of Bi4Ti3O12 were obtained onto platinized Si substrates by spin casting, followed by heat-treated at 700°C. These films were later characterized by X-ray diffraction and SEM. The measured dielectric and ferroelectric properties of Bi4Ti3O12 were as follows: dielectric constant 120, dielectric loss 0.5%, remanent polarization Pr=4 µC/cm2, coercive field Ec=1.8 kV/cm.

GROWTH OF (BA,SR)TIO3 THIN FILMS BY THE HYDROTHERMAL-ELECTROCHEMICAL METHOD AND EFFECT OF OXYGEN EVOLUTION ON THEIR MICROSTRUCTURE

Thin films in the system BaTiO 3 –SrTiO 3 have been grown on Ti electrodes with control of the Ba/Sr composition in aqueous solutions of (Ba, Sr) (OH) 2 by the hydrothermal-electrochemical method. Barium contents of the solid-solution films were always lower than those of the synthesis solutions used. The BaTiO 3 and the (Ba, Sr)TiO 3 solid-solution films included “crater-shape” defects that resulted from the breakaway of the growing film, whereas no such defects were observed in the SrTiO 3 film. This dependence of the defect generation on the film composition was interpreted to be caused by differences of anodically evolved oxygen gas pressure in “short-circuiting paths” that exists characteristically in the films grown by this method.

Preparation of Lead Magnesium Niobate Titanate Thin Films by Chemical Vapor Deposition

Lead magnesium niobate titanate (PMN-PT) thin films were prepared on Pt-coated magnesium oxide single-crystal substrate (Pt(100)/MgO(100)) and Pt- and Ti-coated oxidized Si wafer (Pt(111)/Ti/SiO 2 /Si(100)) at 680-780°C by metalorganic chemical vapor deposition (MOCVD). The PMN-PT thin films comprising perovskite structure as a main phase were obtained in the composition of Ti/(Mg+Nb+Ti)≥25 mol%. Their room-temperature dielectric constant was 1000-1500 measured at 100 mV and 1 kHz.

CONTRIBUTION OF ELECTROLYSIS CURRENT TO GROWTH OF SRTIO3 THIN FILM BY THE HYDROTHERMAL-ELECTROCHEMICAL METHOD

The electrolysis treatment of the hydrothermal-electrochemical method has been modified so that it permits SrTiO 3 thin films to be grown on Ti electrodes being oxidized anodically in Sr(OH) 2 solutions far beyond a thickness limit of several tens of nanometers hitherto attained. The relation between the total current passed through the Ti anode and the amount of the resulting SrTiO 3 film was analyzed on the basis of a reaction model that interprets the anodic current to be compensated with electrons generated partly by oxidation of Ti and partly by decomposition of H 2 O. Current efficiency for the film growth was estimated to be in the range from 0.8 to 3% depending on the Ti electrode potential.

Ferroelectric properties and fatigue characteristics of Bi4Ti3O12 thin films by sol-gel processing

Stoichiometric Bi4Ti3O12 thin films were prepared by sol-gel processing. This paper discusses the synthesis of polymerizable solutions containing Bi and Ti, ferroelectric properties and fatigue characteristics of the resulting Bi4Ti3O12 thin films. The complex alkoxide was prepared by allowing Bi acetate to react with Ti alkoxides. Bismuth acetate and titanium methoxyethoxide, the solvents 2-methoxyethanol and glacial acetic acid were selected based on their successful use in a number of related systems. Thin films of Bi4Ti3O12 were obtained onto platinized Si substrates by spin casting, followed by heat treated at 700° C. The value of the dielectric constant and loss at 400 Hz, 100 mVrms, 25° C of this virgin films were 132 and 0.8%, respectively. This thin films with single phase layerd perovskite-like structure had very good D-E hysteresis characteristics. The remnant polarization, P r, and coercive field, E c, of this virgin films were 5.5 µ C/cm2 and 6.2 kV/cm, respectively. The remnant polarization of this thin films, P r+, P r-, and 2P r, were nearly constant up to 108 cycles. At 4×108 cycles, the decay in remnant polarization, P r+, P r-, and 2P r, was observed to be about 35% of the initial values, respectively. The coercive field was drastically increased after 108 cycles. The D-E hysteresis loop after 108 cycles was not completely saturated. After 108 cycles, leakage current was typically increased. We considered that the fatigue characteristics observed in our study are resulted from increasing of leakage current.

Fabrication of PbTiO3 Ceramic Fibers by Sol-Gel Processing

The sol-gel processing was applied to the fabrication of PbTiO3 fibers. Pb(CH3COO)2·3H2O and Ti(OC3H7i)4 were refluxed with stirring in 2-methoxyethanol to form Pb-methoxyethoxide and Ti-methoxyethoxide, respectively, followed by mixing with stirring in 2-methoxyethanol to form Pb−Ti double alkoxide. The hydrolysis and polycondensation reaction of this double alkoxide gave polymerized products, and as a result the viscosity of the solution increased, suggesting that linear polymers were produced through the hydrolysis and polycondensation reaction. Homogeneous PbTiO3 gel fibers were drawn from the spinnable viscous solutions, which were wellcrystallized into perovskite type PbTiO3 at 650°C. The heat-treated fibers were a few centimeters long and from 10 to 100 μm in diameter. The fiber was made up of extremely uniform grains. Electron diffraction revealed a preferred growth of (101) planes along the fiber axis, which might be due to the linear molecular characteristics of the alkoxide.

BATIO3-BASED NON-REDUCIBLE LOW-LOSS DIELECTRIC CERAMICS

Dielectrics composed of BaTiO3-rare earth oxide-MgO have been studied to design a non-reducible low-loss dielectric material. Curie temperatures of dielectrics composed of BaTiO3–Gd2O3–MgO were lowered by Gd2O3, which provided the dielectrics with low power loss. It was found that the addition of BaZrO3 to BaTiO3–Gd2O3–MgO decreased the capacitance change with temperature. Gd2O3 diffused easily into BaTiO3, but, it could not easily diffuse into BaTiO3 to which BaZrO3 had been added. It was considered that BaZrO3 prevented the Gd2O3 diffusion into BaTiO3, resulting the remains of ferroelectricity and reduced capacitance change. Thus non-reducible and low power loss X7R dielectric ceramics were developed.

Electrical and Mechanical Properties of Pb(Zr, Ti)O3 Ceramics Related to Mn Ion Diffusion

The electrical and mechanical properties of Pb(Zr, Ti)O3 (PZT) ceramics with Mn ions injected by diffusion at high temperature were studied. The rise of mechanical quality factor (Qm) and the change of fracture mechanism from intergranular fracture to transgranular fracture was observed with increased diffusion temperature. These changes are related to the diffusion of Mn ions from the grain boundaries into the grains.

Effect of Microstructure on Reliability of Ca(TiZr)O3-Based Multilayer Ceramic Capacitors

We examined the reliability of Ca(TiZr)O3 (CTZ)-based Ni-electrode multilayer ceramic capacitors (MLCs) prepared by two different processes with particular interest in the microstructure. One process was to calcine the mixture of CaCO3 and TiO2 to prepare CaTiO3 (CT) powder and the mixture of CaCO3 and ZrO2 to prepare CaZrO3 (CZ) powder, and then mix these calcined powders and sinter them to synthesize the CTZ-based ceramics. The other was to calcine the mixture of CaCO3, TiO2 and ZrO2 powders together to prepare CTZ powder and then sinter them. These two processes of CTZ ceramic preparation resulted in a different crystallinity and distribution of the elements. We found that these factors influenced the reliability of CTZ-based MLCs.

Energy trapping characteristics for thickness extensional vibration of preferentially orientated ZnO ceramics

The energy trapping characteristics for thickness extensional (TE) mode vibration were studied for preferentially orientated zinc oxide (ZnO) ceramics fabricated by the chemical transfer method. The results of both the dispersion curve analysis and the finite-element method (FEM) simulation indicate that frequency-lowering-type energy trapping is possible for ZnO ceramics. The number of generating mode in the ZnO ceramic plate decreases with decreasing diameter of the electrode in the experiment. This means that the energy trapping characteristics were obtained on the ZnO ceramics. However single-mode energy trapping was not realized in this study.