Atsuo Imai

MICROSTRUCTURE AND CRYSTALLIZATION BEHAVIOUR OF TIO2 PRECURSOR PREPARED BY THE SOL-GEL METHOD USING METAL ALKOXIDE

TiO2 precursors were prepared by the sol-gel method using titanium tetraisopropoxide. The effects of water and hydrochloric acid addition for the hydrolysis and polymerization reaction on the crystal lattice or the molecular structure, and on the crystallization behaviour of prepared precursors, were examined by using Raman, and infrared spectroscopy, X-ray diffraction, DTA-TG and carbon analysis. The quantity of unhydrolysed alkyls in precursors decreased with increasing amounts of H2O and HCl addition, but the alkyls always remained. Raman spectroscopy revealed that the molecular structure of prepared amorphous precursors resembled that of the anatase phase with increased H2O and HCl addition. On the crystallization process of these precursors, the ratio of anatase formed at 310 °C was influenced by residual unhydrolysed alkyls. Steric hindrance by the residual alkyls preventing crystallization to crystalline anatase was observed, and there was estimated to be 2.5 mol of octahedral coordination of Ti-O per 1 mol of residual alkyls. It is noted that crystallization of the anatase phase and the transformation from anatase to the rutile phase were also observed on long-term ageing of precursors at room temperature.

Electronic conduction of tin oxide thin films prepared by chemical vapor deposition

SnO2 thin films having low resistivity were prepared by chemical vapor deposition. Conductivity, its dependence on temperature, and Hall effect of films were measured. Examination of the surface morphology by scanning electron microscope showed that the SnO2 thin films are made up of many grains. Experimental results were discussed by the grain‐boundary model. The carrier transport mechanism across a grain boundary is the tunnel effect rather than the thermionic emission.

Formation and crystallization of beta-alumina from precursor prepared by sol-gel method using metal alkoxides

Abstract Preparation of uniform gels by the sol-gel method using metal alkoxides has been examined to prepare bulk Na2Oue5f8Al2O3 crystalline phases in a wide range of composition. Subsequent crystallization reaction from the precursor was studied by X-ray and TG/DTA analysis, and a non-equilibrium phase diagram at 10 h anneal was estimated. By the present method, the beta-alumina phase was synthesized between 960 and 1090°C for 10 h anneal between 0.82 and 0.9 mole fraction of Na2O, and the beta′-alumina phase was not crystallized.

Ionic conduction in Sr hexa-aluminate with β-alumina structure

Abstract A new type of strontium β-alumina was developed by a single solid state reaction. Polycrystals of Sr β-alumina with the chemical formula of SrMgAl10O17 were prepared and examined by a conductivity. The values of ionic conductivity in the Sr β-alumina were 5 to 3 orders of magnitude lower than those of polycrystalline Na β-alumina between 773 and 1273 K. The ion exchange of Sr β-alumina for sodium was also examined, and the values of conductivity for the partially ion-exchanged samples increased with the increase of the excess amount of Na+ up to 0.5–0.6 in comparison with that of the ideal Na β-alumina.

High-temperature resistivity measurements of YBa2Cu3O7−x

The high-temperature resistivity of YBa2Cu3O7-x was measured by a DC four-probe technique at partial oxygen pressures (pO2 ) of 1.0, 0.2, 0.053, 0.013 and 0.006 atm. The determined resistivity values increased with increasing temperature and decreasing pO2 in accordance with the increase of the oxygen deficiency. The discontinuous change of the slopes d(log ρ)/d(1/T) was observed at temperatures 20–95°C lower than those reported for the orthorhombic-to-tetragonal transition.

PmP111. Effects of dopant Nb+5 on lead zirconate-titanate

Abstract Impurity effects of Nb+5 dopants were investigated on optimum calcination temperatures and grain growth in sintering process. As the amount of Nb+5 dopant increased, optimum calcination temperatures increased. Grain sizes in sintered ceramics decreased in inverse proportion to the amount of Nb+5. Experimental results were expressed in terms of the volume ratio between grain boundary region and grain. Thickness of grain boundary region is estimated to be about 40 A, that corresponds to about 10 lattice layer.

Ionic conduction in partially ion exchanged Sr β-alumina; Sr1−xNa2xMgAl10O17

Abstract Polycrystals of Sr β-alumina with the chemical formula of SrMgAl 10 O 17 were subjected to the ion exchange for sodium in a molten salt mixture of Na 2 CO 3 and SrCl 2 , and partially ion-exchanged samples, Sr 1− x Na 2 x MgAl 10 O 17 with x between 0.0 and 0.964 were prepared. Conductivities were determined by an ac impedance method for partially ion substituted samples, increased with the increase of the extent of ion exchange up to those in a polychrystalline Na β-alumina with the exception at x values lower than 0.20. Anomalies of both conductivity and activation energy for samples of x =0.6 were observed, and suggested the possible order-disorder transition as reported in K 1.875 Ba 0.022 Mg 0.919 Al 10.08 O 17 .

Ionic conduction in divalent hexa-aluminates and gallates with β-alumina structure

Abstract Hexagonal aluminates and gallates having β″-alumina structure with the chemical formula, RMs(Al/Ga) 10 O 17 (R=large divalent cation, and Ms=spinel forming elements), were synthesized by a solid state reaction. In addition, β″-alumina phase, RMs 3 (Al/Ga) 14 O 25 , was found to be stable in Sr. Pb, and Ba gallate systems with Ms=Zn. The stability limits of magnetoplumbite, β- and β″-aluminas were empirically elucidated using the relation between critical R 2+ ion radius for the stability of each phase and dimensions of the spinel unit for aluminates and gallates. The ionic conductivities of β″-alumina phases showed the similar values regardless of spinel constituents, showing 3 to 5 orders of magnitude lower than that of N β″-alumina between 600 and 1000°C. The ion exchange was made on Sr β″-alumina phase, SrMgAl 10 O 17 .

Critical current densities of hot pressed YBa2Cu3O7−δAg thick film

Abstract Composite thick films of YBa 2 Cu 3 O 7−δ (YBCO) containing 15wt% Ag have been prepared on partially stabilized zirconia substrates using screen printing and uniaxially pressured sintering. The increase of the sintering pressure decreases the electrical resistance in the normal conductive region and increases the critical current density in the superconductive region. The critical current density was 4.2×10 4 A/cm 2 at 50K. The YBCO grain size decreased as the sintering pressure increased, The c-axes of YBCO grains oriented preferentially in parallel to the pressure direction.

ac transport in amorphous silicon‐nitrogen alloys

The frequency‐dependent conductivity of sputtered (with and without hydrogen) and glow‐discharge amorphous silicon‐nitrogen alloy films has been measured in the temperature range 15–330 K. The ac loss decreases with the introduction of hydrogen. The origin of the ac loss is interpreted in terms of electron transfer between dangling‐bond states of silicon and nitrogen‐related two‐level systems.