Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 68 , Issue 1
Showing 1-20 articles out of 20 articles from the selected issue
  • Tomiya KISHI, Jin KAWAKITA, Takashi MIURA
    2000 Volume 68 Issue 1 Pages 2-7
    Published: January 05, 2000
    Released: November 10, 2019

    Lithium insertion behaviours of Li1+xV3O8 and its modified oxides were examined. Li4V3O8 phase was formed at x = 1.5 in Li1+xV3O8 and had smaller insertion rate of lithium. Modification of VO5 unit in the layer and neighboring octahedral Li+ ions in the interlayer affected the formation of Li4V3O8 phase. Lattice disorder and layer stacking of the mother oxide also influenced the insertion behavior of Li4V3O8 phase.

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Technical Papers
  • Xinge ZHANG, Satoshi OHARA, Kazuo MUKAI, Mitsue OGAWA, Takehisa FUKUI
    2000 Volume 68 Issue 1 Pages 11-16
    Published: January 05, 2000
    Released: November 10, 2019

    A chemical etching technique was used as a pretreatment of commercially available 8 mol % yittria stabilized zirconia (8YSZ) electrolyte to improve solid oxide fuel cell (SOFC) performance. It was found that the etching rate of the 8YSZ increased linearly with increases in hydrofluoric acid (HF) concentrations. Increasing the temperature of both a HF solution and a HF + HC1 (hydrochloric acid) solution accelerated the etching rate. Cell performance was improved not only by thinning the electrolyte but also by improved electrode performance, especially for the lanthanum strontium manganite (LSM) + YSZ composite cathode. An electrode kinetics analysis and scanning electron microscope (SEM) results suggest that this improved electrode performance was due to increases in three phase boundary (TPB) area.

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  • Wei WANG, Teruhisa KOMURA, Takahiro YAMAGUCHI, Kohshin TAKAHASHI
    2000 Volume 68 Issue 1 Pages 17-23
    Published: January 05, 2000
    Released: November 10, 2019

    The charge-transport properties of polythionine film were studied by cyclic voltammetry and ac impedance spectroscopy. The redox reaction of polythionine proceeded by a two-electron, two-proton transfer mechanism. Both the low-frequency resistance and the low-frequency capacitance obtained from the ac impedance response were proportional to the film thickness. The former showed a minimum, and the latter showed a maximum, at the half-wave potential. The coupled diffusion coefficient of electrons and protons also showed a maximum at the half-wave potential. This relationship between the oxidation level and the diffusion coefficient indicated that the rate of charge transport in the film may be controlled by electron transport. A decrease in the diffusion coefficient with increasing pH implied 1electron hopping accompanied with intermolecular proton exchange.

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  • Takeo HYODO, Eiichi KANAZAWA, Yuji TAKAO, Yasuhiro SHIMIZU, Makoto EGA ...
    2000 Volume 68 Issue 1 Pages 24-31
    Published: January 05, 2000
    Released: November 10, 2019

    Hydrogen sensing properties and mechanism of Nb2O5 varistors mixed with Bi2O3 (0-16.7 mol %) were investigated in the H2 concentration range of 0.2-2.0 % at 400-700 °C. Pure Nb2O5 showed higher breakdown voltage and higher sensitivity of 1,200 V mm−1 to 2.0 % H2 at 400 °C than the ZnO- and SnO2-based varistors reported before. The H2 sensitive properties of a Nb2O5 varistor were improved by the addition of Bi2O3 up to 5.0 mol % and the Nb2O5 varistor mixed with 1.0 mol % Bi2O3 exhibited the highest sensitivity at 400 °C among the varistors tested. However, further addition of Bi2O3 resulted in significant deterioration of the sensitivity. The addition of Bi2O3 1ed to a slight decrease in the grain size, a change in shape of Nb2O5 particles and formation of Bi2Nb10-O28 the surface of Nb2O5 particles. A.c. impedance measurement was performed to investigate the electric and electrochemical properties of the varistols. Resistances of the Nb2O5-Bi2O3 varistors were decomposed into four components, (i) bulk resistance (R0), (ii) grain boundary resistance (R1), (iii) resistance of oxide ion conduction (R2) and (iv) electrode-oxide interface resistance (R3). The R1, R2 and R3 decreased drastically with increasing H2 concentration, while R0 remained almost unchanged at 400 °C. Further studies have confirmed that R1 mainly dominated the breakdown voltage of the Nb2O5-Bi2O3 varistors, and then the change in the potential barrier height per grainboundary determined the magnitude of the H2-induced shift in the breakdown voltage.

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  • Sang Cheol NAM, Young Soo YOON, Won Il CHO, Byung Won CHO, Kyung Suk Y ...
    2000 Volume 68 Issue 1 Pages 32-37
    Published: January 05, 2000
    Released: November 10, 2019

    Electron beam deposited tin oxide thin films were studied for use as a negative electrode for lithium rechargeable battery. Tin oxide thin films prepared at different heat treatment conditions (temperature and time) were investigated by the implementation of X-ray diffraction analysis, Auger electron spectroscopy, and atomic force microscopy. Charge/discharge performance of these thin films, typically exhibiting capacities higher than 300 mAh/g lasting beyond 100 cycles, were found to depend on the heat treatment temperatures, which influence the structure, grain sizes, and adhesion to the substrate. Capacity was decreased as film thickness increased, but capacity loss was very small in accordance with increase of charge/discharge rate. Using AC impedance analysis, it was found that capacity loss was caused by resistance increase at cut off voltage under 0.1 V. Lithiated SnO2/PAN/V2O5 type full cell showed the capacity of 200 mAh/g, with active voltage of 2.0-2.7 V.

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20th and 21st Centuries as Seen by Our Past Presidents
Techniques in Electrochemical Measurement