Papers by Author: Takayuki Kodera

Abstract: La-doped SrTiO₃ (LST) powders were synthesized by ultrasonic spray pyrolysis using an aqueous solution of a metal nitrate. SEM images showed that the as-prepared LST powders had a spherical morphology with a diameter of 1 μm. XRD patterns showed that the crystal phase of the as-prepared powders was amorphous and that the powders crystallized to the perovskite phase by calcination at 900 °C. The sintered LST body had the highest electrical conductivity at a La doping concentration (La_x) of 0.1 under a reducing atmosphere. A solid oxide fuel cell (SOFC) with La_0.1Sr_0.9TiO₃Sm-doped CeO₂ (1:9) as the anode exhibited a maximum power density of 137.8 mW/cm² and an open circuit voltage of 1.08 V at 880 °C.

Abstract: LiFePO₄/C powders were synthesized by ultrasonic spray pyrolysis using carbon powder instead of organic substances as the carbon source. LiFePO₄ (LFP) powders containing different types of carbon powders were prepared and used as cathode active materials in lithium ion batteries. The charge-discharge properties of lithium ion batteries with LFP, LFP/AB, and LFP/CNT powders as the cathode material were worse than those of the battery with LFP/sucrose powder as the cathode active material.

Abstract: BaTiO₃ precursor powders were synthesized by two types of pulse jet spray pyrolysis1000 and 2000 kcal/h typesusing an aqueous solution of metal salt. All as-prepared powders crystallized to the cubic and other phases. However, the powders almost reached the tetragonal phase through calcination at 900 °C in air for 2 h. The crystallinity of the powders obtained from 2000 kcal/h type pyrolysis was higher than those obtained from the 1000 kcal/h type. When Ba (NO₃)₂ was used, nanoparticle formation at an average particle size of approximately 150 nm, with a narrow size distribution, was observed. The relative density of the sintered body was 87 %. The relative dielectric constant of the BaTiO₃ body was 1450, and its tanδ value was 0.017 at room temperature.

Abstract: Spherical fine Ni particles were prepared by ultrasonic spray pyrolysis, and the effects of starting materials, carrier gas, and pyrolysis temperature on the crystal phase of the fine particles were investigated. When the mist of starting solution was pyrolyzed at 850 °C in a N₂ atmosphere, the crystal phase of fine particles obtained from Ni (CH₃COO)₂·4H₂O was in good agreement with that of Ni. Furthermore, the other phases were not observed. The average particle size of the spherical Ni fine particles was 0.45 μm.

Abstract: Spherical Li₂Ti₃O₇ precursor powders were successfully prepared by spray pyrolysis. X-ray diffraction analysis revealed that the ramsdellite phase was obtained by calcining at 1100 °C for 3 h under an argon/hydrogen (95/5 %) atmosphere. The Li₂Ti₃O₇ anode exhibited higher rechargeable capacity and excellent cycle stability. The rechargeable capacity of the Li₂Ti₃O₇ anode was approximately 168 mAh/g at 0.1 C. The discharge capacity of the Li₂Ti₃O₇ anode after 100 cycles was approximately 90% of the initial discharge capacity.

Abstract: BaTiO₃ nanopowders were prepared by salt-assisted spray pyrolysis using a flux of KNO₃ and NaNO₃. Compounds of metal sources are thermally decomposed in the melting flux. Some flux mixtures make a eutectic composition because of the reduced melting point of the flux. The optimum temperature for the preparation of BaTiO₃ nanoparticles was 700 °C. When both KNO₃ and NaNO₃ were used as the flux, the average particle size of the BaTiO₃ powders was 40 nm, and the particle distribution was broad. On the other hand, when only KNO₃ was used, the average size of BaTiO₃ powders was 60 nm, and the particle distribution was narrow. This suggested that the sodium ions in the BaTiO₃ nanoparticles led to a broad particle distribution. X-ray diffraction (XRD) revealed that all the diffraction peaks were in agreement with the crystal phase of BaTiO₃. The relative density of the sintered body of BaTiO₃ powders was 87 %. The relative dielectric constant of the sintered body was 1180, and the dielectric loss (tanδ) was 0.023 at room temperature. This suggested that the residual potassium ions in the BaTiO₃ nanoparticles led to a reduction in the relative density and dielectric constant.

Abstract: Ce_0.8Sm_0.2O_1.9 (Samaria-doped ceria: SDC) precursors were synthesized by carbon-assisted spray pyrolysis. SDC thin films were prepared by electrophoretic deposition using the SDC precursor particles. The as-prepared SDC thin films were sintered at 1600 °C for 10 h. Uniform films with a thickness of approximately 20 μm were obtained. A fuel cell using the prepared thin films showed a maximum power density of 60.6 mW/cm² and an open circuit voltage (OCV) of 0.63 V at 700 °C.

Abstract: Li₄Ti₅O₁₂ powders were synthesized via the solid state reaction of Li₂CO₃ and spherical composite powders of carbon and TiO₂ (denoted by C/TiO₂) with different microstructures. These C/TiO₂ powders were synthesized by spray pyrolysis using various organic acid aqueous solutions. The particle characteristics of the resulting carbon composite Li₄Ti₅O₁₂ (denoted by C/Li₄Ti₅O₁₂) powders were determined using SEM, XRD, and DTA-TG. DTA-TG showed that the carbon content of all Li₄Ti₅O₁₂ powders. was around 3 wt%. XRD revealed that the spinel structure (Fd3m) was obtained by heating at 750 °C under N₂ atmosphere. The initial rechargeable capacity of the C/Li₄Ti₅O₁₂ powders formed using citric acid was approximately 170 mAh/g at 1 C. The rechargeable capacity of the C/Li₄Ti₅O₁₂ powders decreased with an increase in the rechargeable rate. The anodes maintained over 90% of their initial discharge capacity after 200 cycles at 1 C. The C/Li₄Ti₅O₁₂ powders also demonstrated high cycle stability at 50 °C. It was found that rechargeable capacity was influenced by the particles microstructure, but cycle stability did not depend on the microstructure.

Abstract: Plate-like LiMnPO₄ particles were prepared by polyol method. The chemical and physical properties of plate-like LiMnPO₄ particles were characterized by XRD and SEM. The thickness of plate-like LiMnPO₄ particles was approximately 35 nm. XRD pattern of plate-like LiMnPO₄ was good agreement with orthorhombic olivine structure. The first discharge capacity of C/LiMnPO₄ cathode was approximately 95 mAh/g. 99.9 % of initial discharge capacity was maintained after 100 cycles.

Abstract: LiFePO₄/C powders were synthesized by ultrasonic spray pyrolysis using carbon powder instead of organic substances as the carbon source. LiFePO₄ (LFP) powders containing different types of carbon powders were prepared and used as cathode active materials in lithium ion batteries. The charge-discharge properties of lithium ion batteries with LFP, LFP/AB, and LFP/CNT powders as the cathode material were worse than those of the battery with LFP/sucrose powder as the cathode active material.