Electroceramics in Japan IX

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Authors: Takuya Hoshina, Hirofumi Kakemoto, Takaaki Tsurumi, Masatomo Yashima, Yoshihiro Kuroiwa, Satoshi Wada
Abstract: Almost impurity-free, defect-free and dense barium titanate (BaTiO3) fine particles with various sizes from 20 to 430 nm were prepared by the 2-step thermal decomposition method and post-heating treatment. The crystal structures of these particles in the range from -150 to 150 °C were investigated using synchrotron radiation XRD measurement. The crystal structure refinement using Rietveld method revealed that BaTiO3 particles with the size over 40 nm were composed of two parts; (a) cubic shell and (b) core with successive phase transitions. The crystal structure of the core component can be related to the dielectric properties at room temperature. Moreover, it was revealed that the phase transition behavior of BaTiO3 nanoparticles was different from that of the BaTiO3 single crystal.
Authors: Takayuki Kodera, Hajime Horikawa, Takashi Ogihara, Nobuo Ogata, Koji Nakane, Suetaka Omura, Masao Uede, Kazuya Higeta, Susumu Hiyama
Abstract: Homogeneous BaTiO3 nano-sized powders were successfully prepared by spray pyrolysis using multiphase plasma under the air atmosphere. Particle size, morphology, crystal phase and crystallinity of as-prepared powders were characterized by SEM and XRD. The effect of starting precursor solution on the formation of nanoparticles was investigated. The use of Ba/Ti aqueous solution derived from malic acid led to formation of cubic BaTiO3 nanoparticles with 50 nm size.
Authors: Satoshi Wada, Masanori Ohishi, Kayo Takizawa, Takuya Hoshina, Hirofumi Kakemoto, Takaaki Tsurumi
Abstract: Barium titanate (BaTiO3) fine particles were prepared using the 3-step thermal decomposition method of barium titanyl oxalate under various vacuum atmospheres. In this method, the first two steps prepared BaTiO3 nanoparticles with 30 nm, and at the 3rd step, BaTiO3 nanoparticles were heat-treated at various temperature and degree of vacuum. As a result, as degree of vacuum is high, particle size of BaTiO3 fine particles decreased. Moreover, the dielectric constant of BaTiO3 fine particles was measured using the powder dielectric measurement method with slurry. The dielectric constant of these particles showed the dielectric maximum of 4,320 at 200 nm despite degree of vacuum. This result revealed that degree of vacuum during particle growth of BaTiO3 particles had no relation about dielectric constant.
Authors: Kouji Tokita, Shigeki Sato
Abstract: Barium titanate (BaTiO3) particles with average size of smaller than 100 nm were synthesized by a hydrothermal process at 100°C to 300°C. The c- to a-axis ratios of the particles increased as the synthesis temperature increased. Disk capacitors were fabricated with as-synthesized particles and some additives to obtain X7R capacitors. The temperature coefficient of capacitance with particles synthesized at 100°C was much larger than that for 300°C, indicating that the former had uniform composition in the grain while the latter had a core-shell structure. This data show that barium titanate particles hydrothermally synthesized at high temperature are useful when creating the X7R capacitors with small grain size.
Authors: Keisuke Yokoh, Song Min Nam, Hirofumi Kakemoto, Takaaki Tsurumi, Hirohiko Kumagai, Satoshi Wada
Abstract: For potassium niobate (KNbO3) single crystal, the 31 resonators with the highest piezoelectric constant d31 were designed using transformation of axis. We confirmed that the engineered domain configurations with maximum d31 of –55.1 pC/N was caused by a combination between two polarization with polar directions along [101]c and [-101]c directions. Moreover, if there are larger piezoelectric constants from domain wall region, we can expect the much higher piezoelectric properties. To induce the above domain configuration, a new poling method using patterning electrode was investigated. In this study, the two methods on the basis of temperature-induced phase transition at 207 °C and electric-field-induced phase transition at room temperature were investigated.
Authors: Satoshi Wada, Koichi Yako, Tomomitsu Muraishi, Hirofumi Kakemoto, Takaaki Tsurumi
Abstract: For the [111] oriented barium titanate (BaTiO3) single crystals, the patterning electrode was applied to induce the finer engineered domain configurations with domain size of 3 2m. The poling treatment was performed at 134 °C under electric fields below 6 kV/cm to inhibit the burning of the patterning electrode with photoresist. As the results, the gradient domain sizes from 3 to 8-9 2m were induced into the 31 resonator. The d31 was measured at -243.2 pC/N, and this value was almost 70 % of the expected d31 of –337.7 pC/N for the resonator with domain size of 3 2m. This difference was originated from lower applied electric field below 6 kV/cm. However, this study was revealed that the patterning electrode was very powerful tool to induce much finer domain sizes below 5 2m.
Authors: Junko Yahiro, Hiroaki Imai
Abstract: The morphology of wurtzite-type zinc oxide (ZnO) grown from an aqueous solution was successfully controlled by addition of phosphate ions and various organic molecules having carboxy groups. Basically, array of hexagonal needles with a diameter of 50–100 nm was grown on a substrate in the absence of the additives. Hexagonal plates were perpendicularly arranged on the substrate by the adsorption of citric, tartaric and maleic acids. The presence of phosphate ions induced an open cellular structures consisting of zinc oxide nanosheets. Densely packed columns and bundles consisting of nanoscale fibrous crystals were produced by the addition of bulky dye molecules, such as phenolphthalein. The influence of the dye molecules depended on pH of the solution. The morphological variation of ZnO films was ascribed to the selective adsorption of the anionic species on the basal and prism planes of the wurtzite structure.
Authors: Takeshi Miki, Kaori Nishizawa, Kazuyuki Suzuki, Kazumi Kato
Abstract: To obtain porous alumina films, the precursor sol was prepared by hydrolysis of Al isopropoxide and then mixing with poly(ethylene glycol) (PEG). The porous alumina films were fabricated by dip-coating technique on glass substrates and heating at 500 °C. The film was composed of nano sized particles (30-50 nm). The maximum thickness of the film prepared by one-run dip-coating was ca. 1000 nm. The film had humidity-sensitive electrical resistance at room temperature.
Authors: Koji Yamada, Kentaro Abe, Masafumi Mikami, Morihiro Saito, Jun Kuwano
Abstract: Multi-walled carbon nanotubes (MWCNTs) were synthesized from camphor by a chemical vapor deposition (CVD) method in a range of 750-900. The catalyst was fed in three ways: (a) a sputtered Fe-film on a quartz substrate (b) vaporized ferrocene in an Ar flow; (c) both of (a) and (b). In the case (c), highly pure, dense and aligned MWCNT arrays formed on the quartz substrate at 850, whereas nonaligned MWCNTs formed in the cases (a) and (b).
Authors: Minoru Osada, Masato Kakihana, H. Yasuoka, M. Käll, L. Börjesson
Abstract: We report a fabrication of high-density nanodots by photodoping in overdoped Bi2Sr2CaCu2O8+d thin film (Tc = 80 K). A scanning near-field optical microscope probe is used to locally excite carrier, and photodoped region is associated with lower Tc phase (Tc = 75 K) via overdoping. Nanoscale characterizations with optical reflectivity reveal that nanodots (30-nm diameter) are regularly distributed in 50-nm step. The resultant films with photoinduced nanodots enhance Jc, a situation being similar to strong pinning effects observed in films modified by either ion irradiation or sputtered nanoparticles. These results suggest that photoinduced nanodots with lower Tc act as effective pinning centers.

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