Electroceramics in Japan IX

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Authors: Jun Ichi Hamagami, Kazuhiro Hasegawa, Kiyoshi Kanamura
Abstract: A novel micropatterning process for a particle assembly has been performed by using an electrophoretic deposition (EPD) method with a local electric field in a colloidal suspension generated by a three-electrode system. Monodisperse silica colloidal spheres with a diameter of 300 nm were used to fabricate micropattern of colloidal crystal. An interdigitated gold-microarray electrode with a 10 μm of width and a gold plate electrode were used as the working and the counter electrodes, respectively. After optimization of the EPD processing parameters, a micropattern was constructed from silica colloidal spheres. It had a relatively close-packed structure formed onto the interdigitated microarray electrode. This micropattern showed a characteristic optical reflectance peak due to Bragg’s law.
Authors: Kaori Nishizawa, Haruhiko Fukaya, Takeshi Miki, Kazuyuki Suzuki, Kazumi Kato
Abstract: A new photochromic ZrO2 precursor solution was prepared using zirconium tetra-n-butoxide, 4-(phenylazo)benzoic acid and ethyleneglycol monomethylether. The ZrO2 precursor solution was irradiated with ultraviolet light (UV) at room temperature. After that, UV-irradiated precursor solution was irradiated with visible light (Vis) at room temperature. UV-Vis spectra were measured before irradiation, after UV irradiation and Vis irradiation. Changes of UV-Vis spectra indicated that the new ZrO2 precursor including 4-(phenylazo)benzoic acid shows photochromism. The phenomena have synchronized with reversible photoisomerization of 4-(phenylazo)benzoic acid in the precursor. In addition, the difference of peak position originated from Zr-O CT transition between before UV irradiation and after UV irradiation increased with increasing the concentration of 4-(phenylazo)benzoic acid. Furthermore, the optimized structure of the new ZrO2 precursor was derived by density functional theory (DFT) calculation.
Authors: Koichi Shigeno, Hidenori Katsumura, Hiroshi Kagata, Hiroshi Asano, Osamu Inoue
Abstract: We examined sintering additives for alumina. When using CuO-TiO2-Nb2O5 additive, dense sintered alumina was obtained by firing at 1000°C or below, even though additive content was at most 10 mass%. It is considered that the formation of mixed oxide consists of CuO, TiO2 and Nb2O5 has an important role for low temperature sintering of alumina. Thermal conductivity of the above sample was 15 W/mK, which was the highest value yet reported within LTCC (Low Temperature Co-fired Ceramics) materials.
Authors: Katsufumi Ehata, Shenglei Che, Norimasa Sakamoto
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.
Authors: Hirofumi Kakemoto, Song Min Nam, Satoshi Wada, Takaaki Tsurumi
Abstract: The microwave reflection intensity was measured at room temperature for Cu-plate, Al2O3 and SrTiO3 single crystals using a un-contact probe as a function of distance between sample and probe. The difference of reflection intensity for Cu-plate, Al2O3 and SrTiO3 single crystals was observed in the region where the distance of 0.2mm between sample and probe, and it was caused from dielectric permittivities of samples. The reflection coefficient of sample was estimated in comparison with results of electromagnetic simulation using finite differential time domain method. The reflection intensity for Cu-plate, Al2O3 and SrTiO3 single crystals was transformed to dielectric permittivity at reflection intensity minimum point. The dielectric permittivity mapping was also examined at reflection intensity minimum point.
Authors: Kenji Sakai, Kiyohiro Hiraki, Hiroki Kusunoki, Takatoshi Kondo, Shinzo Yoshikado
Abstract: It is found through simulation that composite electromagnetic wave absorbers made of Ni-Zn ferrite and SiO2 particles, which are isolated in the continuous medium of Ni-Zn ferrite, show good absorption. In particular, absorbers show absorption in the frequency regions both below and above 1 GHz for the mixing ratio of SiO2 of 80 mol%. To simulate the complex permeability of the composite materials, we considered some arrangements of SiO2 in the Ni-Zn ferrite medium. Measured values of complex permeability are close to simulated ones above 1 GHz.
Authors: Shoichi Kume, Masaki Yasuoka, Koji Watari
Abstract: The effect of sintering additives on dielectric loss tangent and microstructure of AlN ceramics have been investigated. Different amounts of Y2O3 and La2O3 were added as sintering additives to AlN powder and pressureless sintering was performed at 1900 °C for 2 h in a flowing nitrogen atmosphere. Bulk densities of sintered AlN were found to be 3.27 and 3.32 Mg·m-3 when Y2O3 contents were 0.5 and 1 mol%, respectively. The bulk densities of AlN-Y2O3 increased with increasing La2O3 content. Densities of 3.41 and 3.42 Mg·m-3 were obtained for 0.5 mol%Y2O3-1 mol%La2O3-AlN and 1 mol%Y2O3-1 mol%La2O3-AlN ceramics respectively. A decrease in tan δ was observed with increase in La2O3 content and a minimum value of 1.3 x 10-3 was obtained for 0.5 mol%La2O3-1 mol%Y2O3-AlN ceramic in the present study.
Authors: Shenglei Che, Norimasa Sakamoto
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.
Authors: Isao Kanada, 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.
Authors: Shigeru Fujino, Makoto Kuwabara
Abstract: Dielectric constants were measured for phosphate and silica glass systems in the frequency region of 1 to 10 GHz using the resonance cavity method. Compositional dependence of dielectric constant and tangent loss were discussed. The effect of the cations on the ε indicates that ε increases in the order, R:Mg

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