Masashi Shoyama

Sol–gel synthesis of zircon–effect of addition of lithium ions

The sol–gel method was applied to the preparation of zircon, ZrSiO4 powders. The addition of lithium ions to the ZrO2·SiO2 gels was found to be very effective to produce zircon at temperatures as low as 800–900°C. The zircon formation process in the gels was followed by using X-ray diffraction and i.r. analysis methods. A possible mineralizing mechanism of lithium ions, which is essentially different from the previous ones for the solid-state reaction, was proposed. Namely, the formation of orthosilicate such as Li4SiO4 as an intermediate compound was considered to trigger the zircon formation at low heat-treatment temperatures.

Dielectric properties of alkoxy-derived Sr2Nb2O7 thin films crystallized via rapid thermal annealing

The low temperature crystallization of ferroelectric Sr2Nb2O7 thin films on the Pt/TiO2/SiO2/Si(100) substrate was attained by rapid thermal annealing followed by each coating step using Sr2Nb2O7 precursor solution. X-ray diffraction results indicated that the crystallization of the Sr2Nb2O7 phase was initiated at 550 °C, and the Sr2Nb2O7 films exhibited the (0k0) orientation. The dielectric constant and loss value of the films annealed at 650 and 750 °C are 48, 0.022 and 50, 0.007, respectively, at room temperature (100 kHz).

Bi-Pb-Sr-Ca-Cu-O High-Tc Superconducting Fibers Prepared by the Pyrolysis of Organic Acid Salts

Bi-Pb-Sr-Ca-Cu-O high-Tc superconducting solid fibers were successfully prepared from the viscous mixture of organic acid salts containing oxide powders followed by the pyrolysis of organic acid salts. The addition of Pb efficiently enhanced the formation of the (Bi, Pb):Sr:Ca:Cu=2:2:2:3 phase. The Tc(end) of fibers was constantly over 100 K, the maximum Tc(end) being 108 K. The tensile strength of fibers with a Tc(end) of 108 K was 18 MPa.

Low temperature synthesis of ferroelectric Sr2Nb2O7 thin films by rapid thermal annealing

Abstract Ferroelectric Sr2Nb2O7thin films were successfully prepared on Pt/TiO2/SiO2/Si(100) substrates at temperatures as low as 650°C using a sol-gel method with rapid thermal annealing (RTA). It was found that improvements in film crystallinity and microstructural evolution could be realized by using a RTA process after each coating step. The Sr2Nb2O7films annealed above 650°C exhibited an 0k0 preferred orientation. The dielectric constant, loss value and remanent polarization of thin films annealed at 700°C were 48, 0.01 and 0.5 μ C/cm2, respectively.

THE INFLUENCES OF AG ADDITION ON SUPERCONDUCTING PROPERTIES AND TENSILE STRENGTH FOR BI-SR-CA-CU-O FIBERS PREPARED BY PYROLYSIS OF ORGANIC ACID SALTS

The influences of Ag addition on superconducting properties and tensile strength for Bi-Sr-Ca-Cu-O fibers prepared from the mixture of organic acid salts and oxide powders were investigated. The value of Tc(end) of fibers considerably increased to 72 K from 58 K for fibers without Ag2O addition and the tensile strength slightly increased. These results are attributed to Ag addition enabling the annealing to 840°C.

Preparation of Bi-Sr-Ca-Cu-O high-Tc superconducting fibers by pyrolysis of organic acid salts

Bi-Sr-Ca-Cu-O high Tc superconducting solid fibers were successfully obtained by pyrolysis of organic acid salts. The addition of oxide powder and the covering of fibers with hydroxypropylcellulose were necessary to prevent the deformation of fibers drawn from the liquid. The Tc(end) of the fibers was 60 K and the strength was 7.5 MPa after the fibers were heated at 800°C for 24 h. X-ray diffraction patterns showed the formation of the Bi:Sr:Ca:Cu=2:2:1:2 phase.

Synthesis of Ta-oxide Based Nano-sized Cathode Catalyst on Highly Ordered Meso-porous Carbon for PEM Fuel Cells

Group 4 and 5 metal (Ta, Zr) oxide-based cathode catalysts for polymer electrolyte fuel cells have been reported by Ishihara et al. However, nano-sized non-precious metal oxide based cathode catalysts have never been reported. In this study, a new preparation process of nanosized non-precious metal catalyst is proposed. Ta-based nano-sized oxides supported on highly ordered mesoporous carbon (MPC) have been investigated as nonprecious metal cathode catalyst for polymer electrolyte fuel cell. Mesoporous carbon (MPC) was fabricated by using meso-porous silica (MPS) as a template. MPS powders were impregnated with sucrose as a carbon source, followed by SiO2 matrix was etched in hydrofluoric acid solution. Synthesized MPC powders show particular nano-pore structure with 3 to 4 nm in diameter and 1,200m/g in specific surface area. TaON/MPC hybrid catalyst was synthesized as follows. MPC powders were put into Ta-alkoxide solution to immerse metallic component into carobn nanopores, followed by Ta/MPC precursors which were calcined in ammonia flow to obtain TaON/MPC. Figure 1 shows the TEM image of TaON (6.6wt%) /MPC hybrid catalyst. As shown in the figure, Ta-based catalyst was successfully synthesized in carbon nanopores and its particle size was appeared 3 to 4 nm. According to the XRD analysis, Ta-based catalyst had Ta3N5 type crystal structure. Potential-current curves of the TaON/MPC hybrid catalysts under N2 and O2 in 0.1 M H2SO4 at 30C were shown in Figure 2. A carbon plate and RHE were applied as the counter electrode and reference electrode, respectively. The difference of the current between under N2 and O2 would be responsible for the oxygen reduction reaction (ORR). Onset potential for the ORR (EORR) was defined as the electrode potential at the ORR current of 0.2 μAcm. The onset potential for the ORR of TaON/MPC hybrid catalyst reached 0.85V vs. RHE. Therefore, the TaON/MPC hybrid catalyst showed sufficient electrical conductivity and the definite catalytic activity for the ORR as an electrocatalyst for PEM fuel cells. In conclusion, nano-sized TaON/MPC hybrid catalyst was successfully synthesized on highly ordered meso-porous carbon by using meso-porous silica(MPS) as a template. The TaON/MPC hybrid catalyst showed high surface area (~1,200m/g) and high onset potential for the oxygen reduction reaction (EORR~0.85V vs. RHE). Acknowledgements The authors thank the New Energy and Industrial Technology Development Organization (NEDO) for financial support.

Evaluation of the sintering properties of pottery bodies using terahertz time-domain spectroscopy

ABSTRACT Terahertz (THz) time-domain spectroscopy was applied to evaluate the sintering properties of pottery bodies. The transmittance, absorption coefficient, and refractive index of pottery bodies fired at various temperatures were evaluated over the THz frequency range of 0.3–1.3 THz, and the relationships between these properties and their sintering properties were examined. The absorption coefficient and refractive index at 0.5 THz were sensitive under sintering conditions. In particular, the sintering-temperature dependence of the refractive index in the THz region showed a similar trend to that shown by the bulk density. THz-wave two-dimensional imaging was used to visualize inhomogeneities inside the bodies. Our study demonstrated that THz-wave analysis can be used to manage the firing process of pottery and ceramics and to conduct nondestructive testing of products.

Fabrication and photoluminescence of (Zn,Mg) O solid solution powders

ZnO has a wide band gap of 3.37eV at room temperature and has attracted some interest because it is considered a promising green light-emitting phosphor for low-voltage luminescence in flat panel displays such as vacuum fluorescent displays (VFDs) and field emission displays (FEDs). It has been increasingly requested to develop blue cathode phosphors with high-efficiency and low-cost. The blue emission luminescence can be expected in Mg-doped ZnO because the band gap increases by partial substitution of MgO for ZnO. In this work, the fabrication for (Zn,Mg)O solid solution and the effect of Mg-doping on the photoluminescence were investigated.