Takashi Asaka

Preparation of LiFePO4 as Cathode Material for a Lithium Ion Battery by Microwave Processing

In the present study, we examined the use of microwave processing to prepare LiFePO4 cathode materials for lithium secondary batteries. Prepared samples were characterized by X-ray diffraction, SEM photographs, and electrochemical properties. Olivine-phase LiFePO4 was successfully prepared by microwave processing with the addition of iron or carbon powder. The initial discharge capacity of the LiFePO4 prepared with the addition of carbon powder was 134 mAh/g at 60 oC.

Effect of Pore Structures on the Humidity Sensitivity of TiO2-Based Ceramic Humidity Sensors

TiO2-based ceramic humidity sensors containing small amounts of Li2O and V2O5 were prepared by a solid-reaction method. The relationship between the pore structures of the sensors and one of the most important humidity properties, hysteresis in humidity sensitivity, was studied. The humidity sensitivity was investigated by measuring the impedance of the sensors under various conditions of humidity, and the pore-size distribution was measured by mercury-intrusion porosimetry and by the nitrogen-adsorption method. The hysteresis property of the sensors was shown to be significantly dependent on their microstructure, particularly the volume ratio of mesopores to all pores in the sensor elements. Nitrogen adsorption was found to be more useful than mercury porosimetry for determining the proportion of mesopores in the samples.

Sintering of Ba1-XSrXTiO3 Powders Prepared Using KOH-KNO3 Molten Salt Method

Barium strontium titanate (BST), which has a typical perovskite-type structure, shows excellent electrical properties. BST powders were synthesized by heating mixtures of commercial reagents with an excess of TiO2 in molten salts of KOH and KNO3, and the sintering behavior of the resulting powders was evaluated. The sample with the highest density of 95% was obtained by sintering of the BST powders.

Synthesis of Ba1-xSrxTiO3 Powders by KOH-KNO3 Molten Salt Method

The synthesis of Ba0.5Sr0.5TiO3 (BST) powders was attempted using KOH-KNO3 molten salt. Single-phase BST powders could not be obtained when stoichiometric powders were regardless of the molten salt composition. Only when powders with excessive TiO2 were used, single-phase BST powders were obtained. The shape and aggregation state of the single-phase BST powder changed according to the heating temperature and the molten salt composition.

Effect of Simultaneous Addition of Li2O and V2O5 on the Humidity Sensitivity of TiO2 Ceramics

Porous TiO2 ceramics containing Li2O and V2O5 were prepared by a solid-state reaction method and their humidity sensitivity was investigated. The types and amounts of additives determine the sinterability of TiO2 ceramics; simultaneous addition of Li2O and V2O5 resulted in significantly higher mechanical strength than that achieved by the separate addition of each additive. The additives also changed the microstructure of the ceramics, and relatively uniform grains and voids were observed with the simultaneous addition. The impedance of various samples was measured during changes in atmospheric humidity, and the results indicated that simultaneous addition decreased impedance and improved humidity sensitivity. Furthermore, we found that samples with almost no hysteresis in humidity sensitivity could be obtained by changing the ratio of Li2O toV2O5.

Three types of magnetic-field-operated shape memory effects

Three types of magnetic field operated shape memory ceramics have been developed. Namely, the shape memory movements can be operated by changes in magnetic flux density. The reversible shape memory effects are often induced by magnetostriction and magnetic field induced twin formation for Fe-Pd alloys. The former shows the precise shape change, whereas the later shows the large shape change expected. The strain value was about 182 ppm at 0.3 kOe at room temperature. The high magnetostrictive susceptibility was detected at low magnetic field. It was higher than that of Tb0.3Dy0.7Fe2 thin film developed. The other magnetic field operated shape change is recently found on softening near critical temperature of superconductors. The softening induced shape memory effect (SSME) has been found from 9.5 K to 20 K in pure metallic niobium.