Papers by Author: Norimasa Sakamoto

Abstract: Effects of powder properties of the filler, including the particle size, the specific surface area and the lattice strain on the dielectric permittivity and Q of the ceramics-polymer composites were investigated in order to achieve composites with high dielectric permittivity and Q. The dielectric properties of the composites were strongly influenced by the powder properties of the filler, despite that the fillers have the same composition. Generally, lower specific surface area and lower lattice strain of the filler lead to higher Q of the composites.

Abstract: Micrometer-sized spherical single crystal particles of a perovskite oxide based on Ca0.40Sr0.60Ti0.95Zr0.05O3 were prepared from a pulverized powder by flame fusion method. The obtained particles are polyhedrons exhibiting 6 quadrate planes, 8 octagonal planes and 8 triangular planes. Semplice electron diffraction patterns corresponding to orthorhombic structure were obtained for the whole thin section of a particle from different radiation directions, indicating that the particle is single crystal. Changes of the morphology, structure and crystallinity of particles were observed by SEM and TEM to investigate the formation mechanism of the particles. It is revealed that a pulverized particle melts in the flame and solidifies to form an as-fused spherical particle which is composed of an amorphous shell and a crystal core. The crystal core acts as a crystal nucleus in the sequential heat-treating process and finally grows to a single crystal above 1150°C.

Abstract: Details of a new technique for the permittivity measurement of ceramic powders at microwave frequencies are described. Permittivity of a powder is calculated from the permittivity of liquid medium and that of the slurry made from the liquid medium and the powder. Measured permittivities of BaNd2Ti4O12 ceramic powders vary by processing conditions of the powders. This result is consistent with permittivities of composite substrates made from these powders and a thermosetting resin.

Abstract: BaNd2Ti4O12 dielectric oxide particles were spheroidized by melting them with a LPG-O2 flame to improve packing and fluidity of the powder. Changes in the particle morphology, structure and crystallinity during the process were investigated. It is revealed that most of the as-melted particles are dense, spherical and amorphous with smooth surfaces, which crystallize in the annealing process to form polycrystalline spherical particles with uneven surfaces. Annealing at above 1100°C is necessary for the spheroidized powder to recover its crystallinity and dielectric properties.