Papers by Author: Kenkichiro Kobayashi

Abstract: Composites of mesoporous SiO₂ and LiAlCl₄ were synthesized, and the change in ionic conductivity due to the formation of the composites was investigated. The electrical conductivity of the composite with the SiO₂ : LiAlCl₄ of 2 : 3 was the highest with a value of 2 x 10^-6 S/cm at room temperature. A higher order of conductivity was observed for the composite compared to the non-composite LiAlCl₄. In addition, it was found that the conductivity of the composites depends on the pore size of the mesoporous SiO₂.

Abstract: Films containing ZnO quantum dots (ZnO QDs) with ca.5 nm in size were grown at 125°C by chemical vapor deposition. An emission is seen at a wavelength of 367 nm in photoluminescence spectra of the ZnO QDs, and its intensity is enhanced after the deposition of a Ga₂ZnO₄ film on the ZnO QDs. Using the films of ZnO QDs, we fabricated PIN devices constructed from In_1.8Zn_0.2O₃ / InGaZnO₄ / ZnO QDs / Ga₂ZnO₄ / Ni_0.7Zn_0.3O / Ni. The PIN devices exhibit good rectification characteristics.

Abstract: Films of hexagonal BN (h-BN) codoped with Mg and O atoms were grown on n-type Si and quartz substrates heated at 500 °C by sputtering targets consisting of h-BN and MgO powders. An absorption is seen at a wavelength < 400 nm for h-BN films prepared in an Ar atmosphere. In contrast, films prepared from the target containing 0.25 mol% MgO in an atmosphere of Ar + 1% O₂ shows an absorption at a wavelength < 260 nm and an electron field emission at a lower electric field of 3.6 V/μm.

Abstract: ron fluoride (III) anhydrate fine particle was prepared by drying in vacuum from FeF₃·3H₂O, a mechanical milling process and a calcination at 473 773 K. Particle size of FeF₃·3H₂O was ca. 3 5 μm and that of FeF₃ anhydrate was 100 500 nm after drying and milling. FeF₃ sample only after drying and milling was hygroscopic and became FeF₃·3H₂O under atmosphere. FeF₃ became stable under atmosphere after oxidation at 673 K for more than 20 minutes. It was found that Fe₂O₃ was produced by calcination and covered the surface of FeF₃ particles. In Charge-discharge measurements, the discharge capacity of these FeF₃ samples was 150 - 200 mAh/g at a discharge rate of 0.1 C. The oxidation could improve the discharge properties of FeF₃ cathode.

Abstract: Crystalline ZnO films were grown on Y-stabilized ZrO2 substrates heated at 300 - 600 °C in NH3 atmosphere. It is clarified from Fourier transform infrared measurements that N-doped ZnO films grown at 350 and 400 °C contain N-C and Zn-H bonds. In the devices of n-type ZnO/N-doped ZnO/Au, a good rectification characteristic is attained for an N-doped ZnO film deposited at 300°C, whereas a linear current vs. voltage characteristic is seen for a film deposited at 500 °C.

Abstract: ZnO films doped with Li and Cl atoms have been prepared by organometallic chemical vapor deposition method. In photoluminescence spectra of the doped ZnO films, strong emission appears at 376 nm which is slightly longer than that of free-excitons. As excitation intensity increases, a peak wavelength of the emission is shifted toward a shorter value. The emission near band-gap edge is assigned to radiative recombination via Li-Cl pairs.

Abstract: Li3-2xMxInBr6 (M=Mg, Ca, Sr and Ba) and Li3In1-xMxBr6 was synthesized, and thier substitution effect was investigated by means of 7Li and 115In NMR, X-ray diffraction and AC conductivity measurements. Phase transition was observed at 314 K in Li3InBr6 and fast Li+ diffusion was observed in the high temperature phase. Li3InBr6 has high Li+ ion conductivity and showed a little difference in X-ray diffraction patterns between the low-temperature phase and the high-temperature phase. These indicate that the sub-lattice for Li+ ions changed largely at the phase transition point and this change makes Li+ diffusion easily. In the high temperature phase of substituted compounds, the conductivity decreased with the amounts of substitution. and defects produced by the substitution with divalent cation did not contribute to the Li+ ion conduction. In the LT phase for Mg compound, the ionic conductivity increases up to x = 0.4 due to the introduction of the extrinsic vacancies.