Kohei Kodaira

Preparation of ferroelectric PZT films by thermal decomposition of organometallic compounds

Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C. The films deposited on platinum substrates were smooth and uniform, but microcrackings were observed in the films deposited on fused silica substrates. The ratio of metal composition in the PZT film agreed with that in the mixture of starting materials. Films obtained at 700° C on platinum substrate showed a hysteresis loop. A spontaneous polarization was 35.65μC cm−2, a saturation remanent polarization was 30.56μC cm−2 and a coercive field was 45 kV cm−1. Dielectric constant and dielectric loss angle were about 300 and 0.05, respectively.

Preparation and properties of antimony-doped SnO2 films by thermal decomposition of tin 2-ethylhexanoate

Transparent Sb-doped SnO2 films were prepared at 600° C on glass substrates by thermal decomposition of tin 2-ethylhexanoate and antimony tributoxide. The films 100 to 300 nm thick, which are composed of fine particles, were very smooth. The films showed no preferred orientation. The minimum resistivity (2.1×10−2Ω cm) was attained at a concentration of 8 at% Sb on the substrate precoated with SiO2. The transmission of these films was about 80% over a wavelength range from 0.4 to 2.0 μm.

Preparation of transparent amorphous tungsten trioxide thin films by a dip-coating method

The amorphous tungsten trioxide (a-WO3) thin film is one of the most promising materials for electrochromic display (ECD). There are many methods for preparing a-WO 3 films; vacuum vapour deposition [1, 2], sputtering [3], spraying [4], anodization [5], decomposition of a complex compound [6] or polymerization of tungstoic acid [7]. However, large-scale and complicated equipment is needed in vacuum vapour deposition and sputtering, and large energy consumption or long duration are also required in other methods. The dip-coating method, which has recently been reviewed by some authors [8, 9], has possibilities to overcome such drawbacks. Thin films with a large section can also be obtained by this method. Yamanaka [10] prepared a W O 3 film from toluene solution of hexaphenoxy-tungsten by spin coating and thermal decomposition, but the film was coloured brown because of incomplete decomposition of organic matter. In the present report, we describe the preparation of colourless and transparent a-WO 3 thin films from tungsten hexaethoxide by adopting suitable heat-treatment Resultant properties, such as electrochromism of the films, are also discussed. 1.0 g tungsten hexaethoxide (Rare Metallic Co, Ltd, 99.99%) was dissolved into a mixed solvent of 15 ml butanol and 0.2ml acetylacetone by refluxing at

Crystal growth of bismuth titanates and titanium oxide from melts in the system Bi2O3-V2O5-TiO2

Abstract Single crystals of Bi 4 Ti 3 O 12 , Bi 2 Ti 2 O 7 , Bi 2 Ti 4 O 11 and TiO 2 were grown from the melt with various compositions in the system Bi 2 O 3 -V 2 O 5 -TiO 2 . The crystal growth regions can be divided into three parts designated I, II, and III in the ternary diagram of the system: Bi 4 Ti 3 O 12 growth in the region I, Bi 2 Ti 4 O 11 in II, Bi 2 Ti 2 O 7 on the boundary between I and II and TiO 2 in region III. The V 2 O 5 content in the Bi 2 O 3 , V 2 O 5 and TiO 2 mixture was increased according to the sequence I → II → III. The increase in V 2 O 5 content reduced the Bi content in the grown crystal to 0% in the case of the Bi-free crystal of TiO 2 . It was concluded that the increase in V 2 O 5 content leads to complexing between bismuth oxide and vanadium oxide in the melt and thus reduces the Bi content in the grown crystal.

Efficient laser performance of N:dGdVO 4 crystals grown by the floating zone method

Efficient laser performance is demonstrated with Nd:GdVO4 crystals grown by the floating zone method. With a 2-at. % Nd-doped crystal a slope efficiency of 67% is achieved with pumping at 808 nm. We also find that pumping at 879 nm with a bandwidth of 1.8 nm is practical for laser diode pumping. With this pumping level the slope efficiency reaches 78%. High-quality Nd:GdVO4 crystals are successfully grown with as much as 15-at.% Nd concentration by the floating zone method without inclusions or macroscopic defects. Homogeneity and high reproducibility of crystal growth are confirmed.

Preparation of thin Nd-doped YVO4 single crystal rods by the floating zone method

Thin neodymium-doped yttrium orthovanadate (Nd:YVO4) single crystal rods were successfully prepared by the floating zone method with an infrared convergence type heater. The minimum diameter obtained was about 0.8 mm. The double pass technique was used to keep a stable molten zone throughout the growth of thin single crystals. The as-grown crystals were violet and transparent, and did not have macroscopic defects such as cracks and inclusions. The growth in the pure oxygen flow suppressed the evaporation of the vanadium oxides effectively. Dislocation density was decreased with decreasing crystal diameters. No low-angle grain boundaries and no strains were observed for any crystals up to 3 mm in diameter.

Growth of apatite-type neodymium silicate single crystals by the floating-zone method

Apatite-type neodymium silicate single crystals, which show high oxide ionic conductivity, were successfully grown by the floating-zone method. At a growth rate of 5 mm/h, numerous tiny bubbles were easily incorporated into the crystal, whereas those grown at 2 mm/h contained no bubbles. The crystals were found to have sufficient quality for electrical measurements, that is, no low-angle grain boundaries nor twin structures were observed by polarizing microscopy.

Float zone growth and characterization of Pr9.33(SiO4)6O2 and Sm9.33(SiO4)6O2 single crystals with an apatite structure

Single crystals of apatite-type praseodymium silicate (Pr9.33(SiO4)6O2) and samarium silicate (Sm9.33(SiO4)6O2) with high oxide ionic conductivity have been grown by the floating zone method. The as-grown crystals of Pr9.33(SiO4)6O2 and Sm9.33(SiO4)6O2 are green and orange, respectively, and both crystals are transparent. The crystals do not contain inclusions, low-angle grain boundaries or twin structures but the samarium silicate crystals contain a few cracks perpendicular to the c-axis whereas the praseodymium silicate crystals are crack-free. Microcracks are also introduced in the samarium silicate crystals during the cutting and polishing processes. The oxide ionic conductivities of these crystals are comparable to that of neodymium silicate with the same structure.

Floating zone growth and characterization of aluminum-doped rutile single crystals

Abstract Transparent and grain-boundary-free rutile (TiO 2 ) single crystals, to which a small amount of Al 2 O 3 was added, were successfully grown by the floating zone method. The most effective Al addition was 0.4 at%. On the other hand Al-free, pure rutile crystals were dark-blue and comprised many low-angle grain boundaries. Al 3+ ions have two roles in rutile crystals. One is to pin down the migration of dislocations during cooling because of the difference in the ionic radii between Ti 4+ and Al 3+ , so that polygonization, namely formation of low-angle grain boundaries, does not occur. The other role is to form oxygen vacancies, via which oxygen ions can easily migrate in the rutile crystal during cooling to room temperature after the crystal growth. The conductivity of the Al-doped crystal was larger by one order of magnitude than that of the pure crystal at a temperature range of 600–900°C, which indicates that the diffusion rate of oxygen ions is much higher in the Al-doped crystal than in the pure crystal.

Catalytic activity of various iron sulphides in coal liquefaction

Abstract Iron sulphides with various S-Fe atomic ratios, such as pyrite, iron(III) sulphide, pyrrhotite and troilite, were used as catalysts for coal liquefaction. Catalytic activities were compared on the basis of the temperature of the exothermic peak due to coal hydrogenolysis. Effects of hydrogen sulphide on catalytic activity of iron sulphides were also investigated. It is concluded that: 1. 1. The catalytic activity of iron sulphides increases with increasing S-Fe ratio; 2. 2. pyrite, with the highest catalytic activity, is converted to pyrrhotite before the onset of exothermic reactions from coal hydrogenolysis, this evidently being the reason for the high catalytic activity; 3. 3. the catalytic activity of iron sulphides depends on the coal type; 4. 4. the high catalytic activity of pyrite may be due to the creation of fresh pyrite surface during the reaction rather than to the presence of high concentrations of hydrogen sulphide.