Electroceramics in Japan IX

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Authors: Kiyotaka Tanaka, Kenichi Kakimoto, Hitoshi Ohsato
Abstract: The development of lead-free piezoelectric materials has been required from the viewpoint of environmental preservation. We focused the lead-free KNbO3-based systems, and used a chemical solution deposition (CSD) process to obtain their precursor. (Na1-xKx)NbO3 precursor solutions were prepared from metal alkoxides and solvents such as absolute ethanol and 2-methoxyethanol. Crystallization behavior of the precursor gels obtained from the above solutions was investigated by the thermogravimetry differential thermal analysis (TG-DTA) measurement.
Authors: Fuyuki Kano, Hiroshi Uchida, Kazuko Sugimoto, Seiichiro Koda
Abstract: Thin films of titanium oxide (TiO2) were synthesized from Titanium diisopropoxide bis(dipivaloylmethanate) [Ti(O-i-Pr)2(dpm)2] as a source material using supercritical carbon dioxide (CO2) fluid. Flat films with a uniform microstructure were fabricated on SiO2/(100)Si substrates at a fluid pressure of 8.0 MPa, while granular particles were deposited on the film surface at a fluid pressure of 10.0 MPa. TiO2 films fabricated in supercritical CO2 atmosphere at 10.0 MPa were crystalline at the reaction temperature of 100°C, which was significantly lower than those in the conventional film-deposition techniques.
Authors: Yuki Itoh, Kenichi Wakisaka, Masashi Satoh, Shinzo Yoshikado
Abstract: Thin-film heaters made of molybdenum silicide (MoSi2) were fabricated by RF magnetron sputtering, and the heating characteristics of these heaters in a high vacuum were evaluated. The crystal structure of thin-film was hexagonal contrary to the tetragonal one of the target. MoSi2 thin-film heaters deposited outside an alumina crucible showed almost linear resistance-temperature (R-T ) characteristics. However, resistance decreased due to repeated heatings. The heaters generated almost no contamination in vacuum. The temperature of the crucible reached 1000°C at an electric power of 190 W.
Authors: Kazuki Tajima, Woosuck Shin, Maiko Nishibori, Norimitsu Murayama, Toshio Itoh, Noriya Izu, Ichiro Matsubara
Abstract: Micro-thermoelectric hydrogen sensor (micro-THS) with the combination of the thermoelectric effect of Si0.8Ge0.2 thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation was prepared by microfabrication process. In the viewpoint of high sensitivity of micro-THS, the thermoelectric properties of the Si0.8Ge0.2 thin film could be improved by optimizing carrier concentration using helicon sputtering with an advantage of easy doping control, and sensitivity of the device with this thin film was investigated. As the result, the boron-doped Si0.8Ge0.2 thin film is considered to be the better choice ensuring the reliable monitoring of hydrogen concentration down to ppm level.
Authors: Haruki Ryoken, Isao Sakaguchi, Naoki Ohashi, Yutaka Adachi, Takeshi Ohgaki, Shunichi Hishita, Hajime Haneda
Abstract: The defect structure of undoped ZnO and (Zn1-x,Mgx)O solid-solution films were deposited on YSZ substrate with pulsed laser deposition (PLD) to investigate defect equilibria in those films. In particular, the effects of thermal treatment on the structures and prosperities of (Zn1-x,Mgx)O solid-solution films were examined. The films with high MgO concentration (x>0.12) decomposed to the wurtzite-type and rock-salt-type phase after thermal treatment, indicating that the solubility limit of Mg was about x=0.12 and the wurtzite-type (Zn,Mg)O films with x>0.12 were indicated to be non-equilibrium ones. The subsequent analyses of oxygen diffusivity in those films revealed that the films under non-equilibrium state, i.e., wurtzite-type (Zn1-x,Mgx)O with x>0.12, contained significantly high concentration of anion defects.
Authors: Sayuki Sawa, Shinzo Yoshikado
Abstract: Planar-type thin film Bi-Mn-Co-doped ZnO varistors were fabricated on a silica glass substrate or a sintered alumina substrate using a visible light (532 nm) pulsed laser ablation method. The deposited thin films were annealed at 800°C or 900°C in air. For the thin films deposited on alumina substrates and then annealed, the contents of Bi and Mn decreased compared with those of the as-deposited films. Voltage-current (V-I) characteristics of the thin-film varistor fabricated on the alumina substrates and annealed showed nonlinearity. The nonlinearity index α was approximately 10 for the thin film deposited on the alumina substrate and annealed at 800°C in air using a target of ZnO doped with 2.5 mol% Bi2O3, 0.5 mol% MnO2 and 0.2 mol% Co3O4. Moreover, the current density of 20 A/cm3 was relatively high for safety use.
Authors: Shigeru Tanaka, Yukari Ishikawa, Naoki Ohashi, Junichi Niitsuma, Takashi Sekiguchi, Noriyoshi Shibata
Abstract: We have obtained Er-doped ZnO thin film in a micropattern of reverse trapezoids processed on Si substrate by sputtering and ultrafine polishing techniques. Near-infrared light emission was detected successfully from the thin film filling a single micropit with 10 μm square. Transmission electron microscopy (TEM) observation showed epitaxial growth of ZnO crystals along the curvature of the micropit.
Authors: Masayuki Takada, Shinzo Yoshikado
Abstract: The effects of the electrical degradation characteristics and microstructure of Sb2O3-doped ZnO varistors were investigated by optical microscopy, X-ray diffraction (XRD) analysis, and voltage-current (V-I) characteristics analysis. The nonlinearity index α of the V-I characteristics of the Bi-Mn-Co-Sb2O3-doped ZnO varistors decreased with increasing Sb2O3 content after electrical degradation. The twin crystal of ZnO was formed by doping with Sb2O3. The number of twin crystals, of which two c-axes are perpendicular to the twin plane, increased and the number of twin crystals, of which c-axes are parallel to the twin plane, decreased with increasing amount of Sb2O3 doped. It is suggested that electrical degradation is affected by the combination of the orientation of ZnO grains containing twin planes and a double Schottky barrier may not be formed in the twin plane.
Authors: Kenichi Suzuki, Yuichiro Kuroki, Tomoichiro Okamoto, Masasuke Takata
Abstract: Beta gallium oxide (β-Ga2O3) ceramics was coupled and reacted with zinc oxide (ZnO) ceramics at 1200oC for 24 h. Energy dispersive X-ray spectroscopy (EDS) analysis revealed the existence of diffusion layer near the interface between β-Ga2O3 and ZnO. Furthermore, the layer showed monochromatic and intense cathodoluminescence (CL) at 3.5 eV. On the other hand, very weak emissions were observed from the out of the layer. The compound in the layer is considered to be an attractive material for ultraviolet optoelectronics.
Authors: Aki Yazawa, Takuya Hoshina, Hirofumi Kakemoto, Takaaki Tsurumi, Satoshi Wada
Abstract: Barium titanate (BaTiO3) colloidal sphere array was prepared by meniscus method using capillary force between particles from slurry. To pack particles closely, well-dispersed slurry was obtained using electric double layer. From SEM observation, it was confirmed that the colloidal sphere array had point contact or plane contact. Dielectric permittivity of prepared colloidal sphere array was measured at 1 MHz by impedance analyzer. An obtained sample with point contact showed about the same dielectric permittivity as that of simulation by finite element method (FEM) using closed packed model. However, colloidal sphere arrays with plane contact showed lower permittivity than a sample with point contact. From XRD measurement of these samples, it was suggested that the low permittivity was originated from lattice strain or smallness of particle size.

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