Papers by Author: Takashi Asaka

Abstract: 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.

Abstract: 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.

Abstract: 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.