Papers by Author: Satoshi Wada

Abstract: Barium titanate (BaTiO3) fine particles were prepared using the 3-step thermal decomposition method of barium titanyl oxalate under various vacuum atmospheres. In this method, the first two steps prepared BaTiO3 nanoparticles with 30 nm, and at the 3rd step, BaTiO3 nanoparticles were heat-treated at various temperature and degree of vacuum. As a result, as degree of vacuum is high, particle size of BaTiO3 fine particles decreased. Moreover, the dielectric constant of BaTiO3 fine particles was measured using the powder dielectric measurement method with slurry. The dielectric constant of these particles showed the dielectric maximum of 4,320 at 200 nm despite degree of vacuum. This result revealed that degree of vacuum during particle growth of BaTiO3 particles had no relation about dielectric constant.

Abstract: Almost impurity-free, defect-free and dense barium titanate (BaTiO3) fine particles with various sizes from 20 to 430 nm were prepared by the 2-step thermal decomposition method and post-heating treatment. The crystal structures of these particles in the range from -150 to 150 °C were investigated using synchrotron radiation XRD measurement. The crystal structure refinement using Rietveld method revealed that BaTiO3 particles with the size over 40 nm were composed of two parts; (a) cubic shell and (b) core with successive phase transitions. The crystal structure of the core component can be related to the dielectric properties at room temperature. Moreover, it was revealed that the phase transition behavior of BaTiO3 nanoparticles was different from that of the BaTiO3 single crystal.

Abstract: Barium titanate (BaTiO3) colloidal sphere array was prepared by meniscus method using capillary force between particles from slurry. To pack particles closely, well-dispersed slurry was obtained using electric double layer. From SEM observation, it was confirmed that the colloidal sphere array had point contact or plane contact. Dielectric permittivity of prepared colloidal sphere array was measured at 1 MHz by impedance analyzer. An obtained sample with point contact showed about the same dielectric permittivity as that of simulation by finite element method (FEM) using closed packed model. However, colloidal sphere arrays with plane contact showed lower permittivity than a sample with point contact. From XRD measurement of these samples, it was suggested that the low permittivity was originated from lattice strain or smallness of particle size.

Abstract: Dielectric permittivity of BaTiO3 powders was determined by measuring permittivity of slurries prepared from BaTiO3 powder and propylene carbonate as dispersion medium followed by analyzing with a finite element methods (FEM). The permittivity of powders depended on their characters such as tetragonality (c/a ratio), density, particle size and specific surface area. In order to extract the effect of each character, a statistical analysis was carried out to represent the permittivity of powders with an empirical equation where the c/a ratio, density and particle size were used as parameters. A fairly good agreement between observed data and those estimated from the relation was obtained and the contribution of each character to the permittivity could be determined.

Abstract: The crystal structures of barium titanate (BaTiO3) fine particles with a size around 140 nm were investigated using a synchrotron radiation X-ray diffraction method. The observed diffraction pattern was analyzed by Rietveld method assuming several models. As a result, it is found that the BaTiO3 fine particles have composite structures include (a) a tetragonal region with a constant c/a ratio, (b) a tetragonal region with gradient c/a ratios and (c) a cubic region. In order to estimate these structures, the partial profile relaxation technique was applied in the Rietveld refinement. It is considered that the composite structure is important for the size effect on BaTiO3 fine particles.

Abstract: A new method for ultrafine barium titanate (BaTiO3) particles with diameters of around 5 nm is proposed. In this method, barium titanyl oxalate aqua solution with low concentration below 10-3 mol/l was used as the starting material. The droplets with a size below 3 μm were atomized with an ultrasonic vibrator, dried and thermally decomposed at higher temperatures over 300°C. In the preparation of the BaTiO3 particles, there were two parameters such as thermal decomposition temperature and precursor solution concentration. Therefore, various particles were prepared by changing these parameters. Finally, non-aggregated nm-sized BaTiO3 particles with an average diameter of 5.2 nm, despite wide size distribution from 2 to 20 nm, were prepared by using the precursor solution with 10-6 mol/l.

Abstract: A new measuring method and analyzing procedure were proposed to determine the complex dielectric permittivity of materials with relatively high permittivity using an RF-impedance analyzer. Samples used for the measurement were (Ba0.6Sr0.4)TiO3 and Ba(Zr0.25Ti0.75)O3 ceramics. Micro planar electrodes were used for the measurement of complex admittance of these samples. Electromagnetic simulations were carried out for determining the relative dielectric permittivity and dielectric loss. The complex dielectric permittivity vs. frequency curves of Ba(Zr0.25Ti0.75)O3 showed a broad dielectric relaxation, while that of (Ba0.6Sr0.4)TiO3 was almost flat up to 3 GHz.

Abstract: Microwave reflection intensity for microwave absorber, Cu-plate and Al2O3 (0001) single crystal substrate was measured from 8GHz to11GHz as a function of distance between single probe and sample at room temperature. The minimum reflection intensity was observed in the distance of 0.2mm between single probe and sample at 9.4GHz, although the reflection intensity was decreased with increasing distance in other measurement frequencies. The electromagnetic field analysis was hence carried out for simulation model that is defined with coaxial cable, probe and sample using finite differential time domain method. The reflection coefficient and impedance for simulation model were calculated, and compared to the experimental data. From results of electromagnetic analysis, the minimum point of reflection intensity was caused from an impedance matching.

Abstract: In order to fabricate a microstrip band pass filter in GHz region as a passive component of RF modules, Al2O3 thick films were prepared on Cu metal substrates by AD (Aerosol Deposition) process. The dimensions of the filters were determined by the high frequency electromagnetic analysis. The filters were successfully fabricated on AD-derived Al2O3 thick films by employing sputtering, photolithography, electroplating and chemical etching processes. Their filtering characteristics were examined by a Network Analyzer. Through this work, we suggest that the AD process will be important the fabrication technology for integrated RF modules.