Papers by Author: Takashi Ogihara

Abstract: Several types of Ag powder were used as electrode paste for a multilayer ceramic substrate. The shrinkage behavior of the silver powders was investigated during the sintering. Bending and cracking were frequently observed on the substrate when coarse powders that show a broad size distribution and aggregation were used. The shrinkage curve of the Ag paste obtained by spray pyrolysis agreed well with that of the substrate. Furthermore, the electrical properties of the Ag paste were also determined. The resistivity of a silver electrode sintered at 900°C was about 2.00×10-6 Ω･cm.

Abstract: Silica, silica/polymethylmethacrylate (PMMA) hybrid, and silica-particle blend silica films were successfully prepared on polybutylene terephtalate (PBT) substrate by dip coating using perhydropolysilazane (PHPS) as a silica source. The effect of thermal treatment on conversion from PHPS to silica was investigated in detail by scanning electron microscopy and Fourier transform infrared spectroscopy. Mechanical properties of silica and silica/PMMA hybrid thin films also were examined by the pencil scratch hardness tests.

Abstract: TiO2 powder was synthesized hydrothermally from titanium alkoxide ethanol solution in supercritical state and obtained anatase type crystalline powder sized ca. 20 nm. Dye-sensitized solar cells were fabricated with the powders and evaluated the power generation efficiencies.

Abstract: Ba(Mg1/3Ta2/3)O3 (BMT) powders were successfully prepared by ultrasonic spray pyrolysis from an aqueous solution of Ba, Mg and Ta. The particles characteristics of BMT nano-sized powders were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). As-prepared powder particles had a sub-micrometer size with a narrow distribution. Transmission electron microscopy (TEM) observation revealed that the average size of the BMT nano-particles was around 20 nm, and that these particles were aggregated. The dielectric constant (r) of 23.2 and the Q・f of 98,300 were obtained at 1550°C by a spray pyrolysis.

Abstract: LiNi1/3Co1/3Mn1/3O2 precursor powders were successfully prepared by internal combustion type spray pyrolysis. The production capacity of precursor powders was about 1 kg/h when the solution concentration was 0.5 mol/dm3. Particle size, morphology and crystal phase of LiNi1/3Co1/3Mn1/3O2 powders were characterized by XRD and SEM. XRD showed that a layered rock salt structure with a R3m space group was formed by calcination at 750 °C for 10 h. SEM showed that hollow powders with a particle size of 6 μm and irregular morphology were obtained. The discharge capacity of LiNi1/3Co1/3Mn1/3O2 was 130 mAh/g, which showed good cycle performance.

Abstract: Internal combustion type spray pyrolysis apparatus was used to prepare cathode materials for lithium ion batteries. Spherical LiNi0.5Mn1.5O4 precursor powders with an average size of about 2 m were successfully produced by this technique. After calcination at 800°C, LiNi0.5Mn1.5O4 precursor powders crystallized to a spinel structure. The spherical morphology changed to an irregular morphology at temperatures higher than 900°C. The discharge capacity of the LiNi0.5Mn1.5O4 cathode was 130 mAh/g at 1C. After 300 cycles at 1C, 90% of the initial discharge capacity was maintained, and after 100 cycles at 6C, 70% of the discharge capacity at 1C was maintained.

Abstract: Carbon doped LiFePO4 precursor particles were successfully prepared by spray pyrolysis. The saccharides such as monosaccharide and disaccharide or organic acid were used as carbon source. SEM observation showed that as-prepared particles had spherical morphology with narrow size distribution. XRD analysis revealed that olivine phase was obtained by heating at 700°C under the atmosphere of argon/hydrogen (5%). Electrochemical measurement revealed that the discharge capacity of LiFePO4 was improved by the addition of carbon. The addition of citric acid was most effective for the stabilization of cycle life.

Abstract: Spherical Li[Ni(1/3-x)Mn(1/3-x)Co(1/3-x)Mx]O2 (M=Fe, Mg, Al) precursor powders were synthesized by ultrasonic spray pyrolysis using aqueous solution of metal nitrate. X-ray diffraction (XRD), scanning electron microscope (SEM), BET method using N2 adsorption analysis and Battery tester were used for determination of the composition, morphology, particle size, surface area and electrochemical properties. SEM observation showed that the size of as-prepared particles were about 0.9 μ with narrow size distribution. The crystal phase of Li[Ni(1/3-x)Mn(1/3-x)Co(1/3-x)Mx]O2 (M=Fe, Mg, Al) was resulted in layered rock salt structure with R3m space group by calcinations at 1023 K for 10 h. No impurity-related peaks are observed from the XRD pattern with various doping metals. Mg and Al doped Li(Ni1/3Co1/3Mn1/3)O2 showed very good cycling stability. The Mg substitution for Ni led to the most excellent. On the other hand, the capacity degradation during cycling was observed by Fe substitution for Mn doped Li(Ni1/3Co1/3Mn1/3)O2.

Abstract: Spherical LiNi0.5Mn1.5O4 powders were prepared by internal combustion type spray pyrolysis apparatus using gas burner. The powder production capacity was 1 kg/h by this equipment. After calcinations of as-prepared powders contained Ni at different temperatures from 800 to 1200 °C in air for 10h, LiNi0.5Mn1.5O4 powders were obtained. As-prepared particles have a porous microstructure with an average diameter of about 5 μm with narrow size distribution. XRD showed that LiNi0.5Mn1.5O4 powders were well crystallized to a spinel structure with Fd3m space group. LiNi0.5Mn1.5O4 powders calcined at 1000°C show good cycle performance with after 30 cycles discharge capacity of 112mAh/g and 95% retention after 400 cycles between 3.5 V and 5 V.

Abstract: BaTiO3 nano-sized powders were successfully prepared by spray pyrolysis using multiphase plasma under the air atmosphere. The particles characteristics of BaTiO3 nano-sized powders were studied by SEM and XRD. The effect of volume of arc plasma and precursor solution on the formation of BaTiO3 nano-sized powders was investigated. The use of Ba-Ti complex precursor solution derived from lactic acid led to formation of tetragonal BaTiO3 nano-sized powders with 140 nm size. As for BaTiO3 ceramics, the effect of sintering temperature on relative density and the temperature dependence of dielectric properties were investigated.