Papers by Author: Nobuo Ogata

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: 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.

Abstract: Spherical Li
Ni1/3Mn1/3Co1/3O2 precursor powders were synthesized by aerosol plasma pyrolysis using aqueous solution of metal nitrate. XRD, SEM, TEM and BET analysis were used for determi- nation of the composition, morphology, particle size and surface area. SEM observation showed that the size of as-prepared particles were about 200 nm. The value of geometrical standard deviation (σg) calculated from the particle size distribution was 1.20, suggesting that the particle size distribution was narrow. The crystal phase of Li
Ni1/3Mn1/3Co1/3O2 was resulted in layered rock salt structure with R3m space group. The rechargeable capacity of Li
Ni1/3Mn1/3Co1/3O2 was about 142-175 mAh/g. The discharge capacity of Li
Ni1/3Mn1/3Co1/3O2 decreased with increasing cycle number. However, the cycling stability of Li(Ni1/3Mn1/3Co1/3)O2 powders that aerosol plasma pyrolysis process offered superior performance to ultrasonic spray pyrolysis process.

Abstract: Titania nanocrystals were prepared by hydrolysis of titanium alkoxide in ethanol solution. The preparation of titania / alumina thin film was performed on ITO coated glass substrate by dip coating method using ethanol of titania nanocrystal and boemite sol. The crystal structures, microstructure and thickness of titania / alumina thin film were examined by XRD and SEM. The adsorption of dye was influenced by the surface structure of thin film. The adsorption of dye on the films was improved by the immersion into acid as HNO3. Ruthenium polypyridyl complex and triarylmethylium salt were used as dye. Electrode using titania / alumina thin film for dye-sensitized solar cell was constructed.

Abstract: Homogeneous BaTiO3 nano-sized powders were successfully prepared by spray pyrolysis using multiphase plasma under the air atmosphere. Particle size, morphology, crystal phase and crystallinity of as-prepared powders were characterized by SEM and XRD. The effect of starting precursor solution on the formation of nanoparticles was investigated. The use of Ba/Ti aqueous solution derived from malic acid led to formation of cubic BaTiO3 nanoparticles with 50 nm size.

Abstract: LiM(M=Fe,Al,Mg)XMn2-XO4 fine powders were synthesized by the ultrasonic spray pyrolysis using metal nitrate solution. LiMn2O4 powders obtained by this method have a spherical morphology with a submicron size. XRD revealed that as-prepared powders were crystallized to spinel structure with Fd3m space group. LiM(M=Fe,Al,Mg)XMn2-XO4 showed enhanced cycling performance at room temperature. Reduced Jahn-Teller distortion of LiMn2O4 by metal doping was responsible for enhanced cycle performance of LiMn2O4.

Abstract: Spherical La0.8Sr0.2Ga0.8Mg0.2O2.8 precursor powders were synthesized by ultrasonic spray pyrolysis using aqueous solution of citric acid and of metal nitrate. As-prepared powders obtained by this method have a spherical morphology with a submicron size. The calcination behavior of the precursor powders of the above phases were examined in the temperature range of 1073 –1773 K in an air atmosphere. XRD, SEM, DTA-TG and BET analysis were used for determination of the composition, morphology, particle size and surface area. XRD revealed that as-prepared powders were crystallized to perovskite structure after the sintering at 1573 K for 10 h.