Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 68 , Issue 6
Showing 1-35 articles out of 35 articles from the selected issue
Visions
Headline
  • Joachim MAIER
    2000 Volume 68 Issue 6 Pages 395-402
    Published: June 05, 2000
    Released: November 10, 2019
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    Point defect themodynamics is considered for macro- and nanocrystals. The first part reviews − for the equilibrium case − the way in which ionic and electronic carrier concentrations can be calculated in bulk and boundaries of macroscopic crystals as a function of the decisive control parameters. The includes pure and impure materials, complete and partial equilibria as well as different levels of concentrations (dilute case, interactions). In the second part trivial and non-trivial effects are discussed, occurring if the crystal size is continuously decreased towards and below the nano-range. Not only become core disorder and space charge effects increasingly important, but also will there be two characteristic scales defining mesoscopic effects. One is the Debye-length, the other the scale that characterises the transition from crystal chemistry to cluster chemistry. The situation is more complicated if pronounced elastic effects of long range are important. Simple estimates are given for a variety of simplified cases. The phenomena are discussed in terms of transport properties. The treatment includes boundary phase transitions and the effect of ionic heterostructures. Experimental examples are discussed which underline the conclusions.

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Comprehensive Paper
  • Kevin KENDALL, Caine M. FINNERIY, Geoff A. TOMPSEIT, Paul WINDIBANK, N ...
    2000 Volume 68 Issue 6 Pages 403-406
    Published: June 05, 2000
    Released: November 10, 2019
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    There are several possible applications for rapid heating SOFCs. One is vehicles which operate with dual fuel systems. For example, propane is widely used to provide cab heating for trucks whose main engines run on diesel fuel. Rapid heating SOFCs could be used with the propane/butane for auxiliary heat and power generation while diesel fuel drives the engine. Alternatively, rapid heating SOFCs could be used for domestic heat and power using natural gas as fuel. The background to the development of rapid heating zirconia SOFCs is described, especially the colloid process for producing high quality extruded electrolyte tubes. Then the study of individua1 cell tubes is outlined, with novel integrated fuel processing and total oxidation catalyst, together with the stacking of 1000 cells in a small reactor. The emphasis is on fuel processing and prevention of carbon deposition. It was demonstrated that 1% lithium doping of the nickel/zirconia anode reduced carbon deposition by 75%. Comparable electrochemical performance was obtained on hydrogen fuel and on hydrocarbon injected with air.

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Communications
Technical Papers
  • Han-Ill YOO, Chang-Rock SONG
    2000 Volume 68 Issue 6 Pages 415-422
    Published: June 05, 2000
    Released: November 10, 2019
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    Chemical diffusion coefficient of BaTiO3−δ was determined by a conductivity relaxation technique as afunction of oxygen partial pressure in the widest ever range of 10−15≤Po2/atm≤1 including an n/p mixed regime, at elevated temperatures of 800≤T/°C≤1100. The chemical diffusivity varies convex-upwardly in the range of 10−5/cm2 s−1 < 10−2 at al1 temperatures and its maximum falls approximately at the oxygen partial pressure where n-to-p transition occurs or δ≈0. This behavior of is analyzed on the basis of C. Wagner's classic theory of chemical diffusion in association with the defect structure of BaTiO3−δ. The measured total conductivity and chemical diffusivity combined leads, without using any assumptions, to the evaluation of the defect chemical parameters including carrier mobi1ities and defect equilibrium constants, and further to an insight into the nature of the inherent acceptors of “undoped’’ Ba-TiO3−δ.

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  • Jin Hyun HWANG, Young Ho HAN
    2000 Volume 68 Issue 6 Pages 423-426
    Published: June 05, 2000
    Released: November 10, 2019
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    The equilibrium electrical conductivity of polycrystalline BaTiO3 with nonstoichiometric Ba/Ti ratio was studied over the oxygen partial pressure of 10−15 to 1 atm, at temperatures higher than 1200°C. Conductivity results showed that more TiO2 was incorporated into BaTiO3 solid solution, resulting in the conductivity minimum shift. The oxygen vacancy content due to the extra TiO2 was about three times as high as that of the stoichiometric composition, estimating from the relative position of the conductivity minimum. In contrast, the conductivity minimum of BaO excess samples was not shifted, which implies that the solubility of extra BaO in BaTiO3 could not significantly exceed the background acceptor impurity (100 ppm). It is believed that the extrinsic oxygen vacancy due to the excess TiO2 in BaTiO3 could affect the microstructure development and dielectric degradation behavior.

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  • Jong-Heun LEE, Toshiyuki MORI, Ji-Guang LI, Takayasu IKEGAMI, Manabu K ...
    2000 Volume 68 Issue 6 Pages 427-432
    Published: June 05, 2000
    Released: November 10, 2019
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    The effect of concentration, size, and distribution of Al2O3 upon scavenging siliceous phase at grain boundary, was studied in 8 mol% yttria-stabilized zirconia (8YSZ) containing 0.2-1 mol% Al2O3 prepared from ball milling and ultrasonic dispersion. The grain-boundary resistivity at 400°C decreased prominently with adding Al2O3 to 8YSZ, which reflects the scavenging of siliceous grain-boundary phase. The uniform distribution of fine Al2O3 particles (0.3μm) was more beneficial than that of coarse one (4-10 μm). However, the difference was not significant when the density is high, that is, when the connectivity between grain boundaries is good enough. As density decreases, the uniform distribution of fine Al2O3 particles becomes more important to decrease the grain-boundary resistivity. It explains that the scavenging reaction is assisted by rapid grain-boundary diffusion. From the 28Si concentration map using imaging scanning secondary ion mass spectroscopy (SIMS), it was proved that the coarse Al2O3 scavenges the siliceous phase mainly by interfacial reaction.

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  • Teruhisa HORITA, Katsuhiko YAMAJI, Hideyuki NEGISHI, Natsuko SAKAI, Ha ...
    2000 Volume 68 Issue 6 Pages 433-438
    Published: June 05, 2000
    Released: November 10, 2019
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    Oxygen chemical diffusion at La0.92MnO3 film/YSZ interface was investigated under cathodic polarized condition. Secondary ion mass spectrometry (SIMS) analysis was performed for the samples with isotope oxygen exchange (16O/18O exchange at 1073K). The diffusion profiles of 18O in the La0.92MnO3 film showed that fast 18O diffusion under cathodic polarization. The active sites for oxygen incorporation were distributed in many spots on YSZ single crystal surface from the SIMS imaging analysis. Also, Mn diffusion from LaMnO3 to YSZ was observed in many spots on YSZ surface. Oxygen permeation current density through the La0.92MnO3 film was calculated by the defect model of LaMnO3 under cathodic polarization, which was a smaller than the observed value.

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  • Tetsuo SHIMURA, Guilin MA, Hiroshige MATSUMOTO, Hiroyasu IWAHARA
    2000 Volume 68 Issue 6 Pages 439-443
    Published: June 05, 2000
    Released: November 10, 2019
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    The influence of non-stoichiometry, deviation of Sr/Ce from unity, on conduction properties in SrCeO3 was investigated and compared with that in BaCeO3. In SrxCeO3-α, single phase of samples was confirmed for x=0.98, 1.00, 1.02, 1.05 and 1.10. At x≤1.0, conduction was electronic in hydrogen and ionic in air. On the other hand, at x> 1.0, the dominant conduction carriers were protons in hydrogen and electron holes in air. The dependence of conduction characteristic on x in SrxCeO3-α was similar to that in BaxCeO3-α, although there was small quantitative difference between two systems. This means that the A/Ce non-stoichiometry results in the similar type of defect structure in SrxCeO3-α and in BaxCeO3-α. In Sr- or Ba-poor region, the partial substitution of excess Ce for A-site in ABO3 perovskite may occur. At x> 1.0, the substitution of excess Sr or Ba for B-site may happen and this substitution leads to the introduction of the oxide ion vacancies in the lattice.

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  • Stefan DIETHELM, Alexandre CLOSSET, Jan VAN HERLE, Kemal NISANCIOGLU
    2000 Volume 68 Issue 6 Pages 444-450
    Published: June 05, 2000
    Released: November 10, 2019
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    Chemical diffusion () and surface exchange (k) coefficients for SrFeO3-δ were measured using an electrochemical cell combined with electrochemical impedance spectroscopy (EIS) and potential step technique (PS) in the temperature range of 850-915°C. A value of ~ 4·10-5 cm2/s and a k value of ~ 8·10-5 cm/s were obtained at 900°C. Slow scan (0.5-3 μV/s) cyclic voltametry (CV) was performed in the same temperature range and using the same electrochemical cell to obtain oxygen nonstoichiometry data. The oxygen nonstoichiometry (δ) at 900°C in air was determined as 0.4. A plateau corresponding to δ = 0.5 was observed below an oxygen partial pressure (p (O2)) of 10-6 atm. These results were shown to be consistent with the literature data. Nonstoichiometry data were further analysed using the existing defect models, and the limits of the independent point defect approximation and the necessity of considering interactions between point defects and clusters were established.

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  • Takanori OTAKE, Hiroo YUGAMI, Kenichi KAWAMURA, Yutaka NIGARA, Tatsuya ...
    2000 Volume 68 Issue 6 Pages 451-454
    Published: June 05, 2000
    Released: November 10, 2019
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    Nonstoichiometry of fluorite-type oxide solid solutions Zr0.164Ce0.654Y0.182O1.91-δ was measured as a function of temperature (T = 973-1273 K) and oxygen partial pressure (P(O2) = 10−2-10−24 atm) using thermogravimetry. The experimental date was well reproduced by the regular solution model. From the δ-logP(O2)-T relationship, the partial molar enthalpy and the partial molar entropy of oxygen in Zr0.164Ce0.654Y0.l82O1.91-δ were also determined as a function of δ. The agrees well with theoretical calculation using the random configuration. The δ dependence of can be attributed to origin of the deviation from ideal solution behavior of this system.

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  • Hiroshi YAMAMURA, Eiji KATOH, Mina ICHIKAWA, Katsuyoshi KAKINUMA, Tosh ...
    2000 Volume 68 Issue 6 Pages 455-459
    Published: June 05, 2000
    Released: November 10, 2019
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    In order to clarify the co-doping effect on oxide-ion conductivity in the fluorite-type structure, electrical conductivity was measured for the solid-solution system, Ce1-x-yLaxMyO2-δ (M = Ca, Sr). The electrical conductivity in the Ce1-xLaxO2-x/2 system showed a maximum value at x = 0.15, and then decreased gradually due to an ordering of oxygen vacancy. The decreased conductivity at x = 0.34 increased again by partial substitution of M2+ in place of La3+. This phenomenon was named as ``multiple doping effect’’, which was understood to suppress the ordering of oxygen vacancy on a basis of the estimation of the configurational entropy.

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  • Dong SONG, Hiromasa IKUTA, Masataka WAKIHARA
    2000 Volume 68 Issue 6 Pages 460-464
    Published: June 05, 2000
    Released: November 10, 2019
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    The cyc1ability of substituted stoichiometric spinels LiM1/6Mn11/6O4 (M = AI, Co and Ni) has been investigated in the cell Li | 1 mol dm-3 LiClO4 + EC-DEC | LiM1/6Mn11/6O4 at 50°C. The amount of manganese dissolved into the electrolyte from the spinel was measured at different cycle intervals by ICP technique. It was found that the capacity loss was considerably reduced in the case of substituted spinel compared to the parent one even at elevated temperature. Among these substituted compounds, the Ni-substituted spinel exhibited good capacity retention behavior with minimum loss of capacity followed by Co-substituted one. Non-stoichiometric spinels with metal excess structure which written as Li[M'excess]16c[M1/6Mn11/6]16dO4 (M' = Li, Mn, M ; M = Al, Ni) were synthesized under reduced partial pressure conditions. These compounds were observed to possess higher capacity and good cyclability in spite of their higher manganese dissolution over their corresponding stoichiometric counterparts.

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  • Masakazu TAKEMATSU, Hitoshi KAWAJI, Tooru ATAKE, Tatsuya SHIRAKAMI, At ...
    2000 Volume 68 Issue 6 Pages 465-468
    Published: June 05, 2000
    Released: November 10, 2019
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    High quality sample of Li1-xNi1+xO2 (x ≈ 0.03) was synthesized. The de and ae magnetic susceptibilities and the field dependence of magnetization were measured by SQUID magnetometer between 4.5 and 300 K The results were compared with those obtained previously for the samples of x≈0.01 and 0.05. The magnetic properties were found to be strongly dependent upon the nonstoichiometry x. The spin glass-like behavior was detected in the sample of x≈0.03. The properties of the sample of x≈0.03 were found to be intermediate between those of x≈0.01 (typical spin glass) and x≈0.05 (mictomagnet).

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  • Yasushi IDEMOTO, Syuhei OGAWA, Nobuyuki KOURA, Kazuo UDAGAWA
    2000 Volume 68 Issue 6 Pages 469-473
    Published: June 05, 2000
    Released: November 10, 2019
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    To improve the cycle performance of the 4 V class lithium manganese oxide positive electrode material for the lithium secondary battery, we have been investigated the partial substitution of an another metal for Mn. In this study, the quaternary spinel, LiMn2-xMgxO4, in which a part of the Mn is replaced by Mg is prepared. The Mn valence was determined by chemical analysis. The heats of dissolution of the samples were measured by the solution calorimetry method. The standard enthalpy of formation, ΔfH0, and the change in the enthalpy of the reaction, Δ H, were calculated from the heat of dissolution. The ΔfH0 and Δ H decreased and the Mn valence increased with increasing Mg content. The effect of the electrode characteristics on these properties of the positive electrode active materials was investigated in the 4 V range. The discharge capacity decreased with increasing Mg content. On the other hand, the cycle performance was improved by increasing the Mg content. We investigated the relation between the cathode performance and the thermodynamic stability of the quaternary spinel, LiMn2-xMgxO4 (x = 0-0.2).

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  • Mika ECUCHI, Fumihiko MAKI, Hatomi KIMURA, Kazuhiro TAKAHASHI, Yoshihi ...
    2000 Volume 68 Issue 6 Pages 474-477
    Published: June 05, 2000
    Released: November 10, 2019
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    Effects of structural modification caused by substitution of Mo for a part of V in V2O5 on structural changes upon lithium insertion were investigated. For this purpose (V1-yMoy)2O5 (y = 0.1, 0.25) was synthesized, and their insertion behaviours and structural changes upon lithium insertion were analysed by XRD and ESR methods. The oxide with y = 0.1 behaved like as V2O5, and irreversible phase change from δ- to γ-phase occurred at a larger litnium content of x by about 0.3. Reversible lithium insertion range was expanded by Mo substitution. The oxide with y = 0.25 did not have any evident structural changes at x< 1.5 in (V1-yMoy)2O5.

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  • Oliver TELLER, Manfred MARTIN
    2000 Volume 68 Issue 6 Pages 478-481
    Published: June 05, 2000
    Released: November 10, 2019
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    The steady state demixing of an initially homogeneous oxide solid solution in an electrical potential gradient is studied theoretically and experimentally. Experiments were performed with single crystalline (CoxNi1-x)1-δO exposed to electrical potential gradients of different strength. With respect to the oxide sublattice one can observe a crystal drift towards the cathode, where an enrichment of Co is found, due to its higher mobility compared to Ni (DCo > DNi > > Do). The demixing increases with increasing strength of the electrical potential gradient. For the steady state conditions a formal treatment is given, which considers the diagonal elements LAA and LBB of the transport coefficient matrix. The predicted demixing profile corresponds well to the experimental one.

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  • Jong-Ho LEE, Manfred MARTIN, Han-Ill YOO
    2000 Volume 68 Issue 6 Pages 482-485
    Published: June 05, 2000
    Released: November 10, 2019
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    We have performed a Chemla-type electrotransport experiment on magnetite, Fe3O4, from which the tracer diffusion coefficient of iron and its effective charge can be determined simultaneously. The experiment was conducted with radiotracer 59Fe by measuring the spread and drift of the tracer source in a constant electric field at a temperature of 1200°C and an oxygen activity of log(aO2,) = −4. The tracer diffusion coefficient and the effective charge of Fe in magnetite were determined from the tracer profiles using both the residual activity and the tracer sectioning method. While the tracer diffusion coefficient agrees well with the values reported in literature, the effective charge number of Fe was found to be + 2, in contrast to the average, formal charge number 8/3 of Fe in magnetite. This result can be explained either due to the interaction between ionic and electronic charge carriers which has been observed in other semiconducting oxides or due to a much higher mobility of Fe2+ compared to Fe3+.

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  • Hisakazu OKAMURA, Morihiro YASUDA, Masatoshi OHTA
    2000 Volume 68 Issue 6 Pages 486-488
    Published: June 05, 2000
    Released: November 10, 2019
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    A single phase of hydroxyapatite was produced at electrolytic voltage more than 10.0 V in CaHPO4·2H2O (DCPD) and Ca(H2PO4)2·nH2O (MCP) acidic electrolytic aqueous solutions. Ca/P molar ratio of single phase of hydroxyapatite increased from 1.42 to 1.54 with an increase in the applied electrolytic voltage, but it was remarkably lower than that of the stoichiometric hydroxyapatite (1.67). The effects of phosphoric acid concentration on produced weight and Ca/P molar ratio of calcium-deficient hydroxyapatite (Ca10-x(HPO4)x(PO4)6-x(OH)2-x·nH2O, (0<x≦1.5); DAp), and electrolytic current were investigated in DCPD and MCP electrolytic solutions at electrolytic voltage of 35.0 V. The electrolytic current increased with an increase in the amount added of H3PO4, however, Ca/P molar ratio was not affected by pH value. DAp was dissolved at pH region less than 3. These results suggests that DAp was electrochemically produced on the cathode, but was not chemically done. Furthermore, DAp-collagen composite was synthesized by means of the electrolytic deposition method in DCPD and MCP acidic electrolytic solution added with collagen aqueous solution.

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  • Yong-Chae CHUNG
    2000 Volume 68 Issue 6 Pages 489-493
    Published: June 05, 2000
    Released: November 10, 2019
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    In this study, polarization of ionic species in the ionic solids under the electric field was simulated by a numerical method, the finite difference method (FDM). In adapting FDM to the polarization problem, many aspects of the FDM were investigated to adequately accommodate the steep change of the concentration near the electrode. Several interesting observations about the behavior of the ion concentration and the electric field in ionic solids were reported from this simulation.

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  • Tetsuro KOBAYASHI, Katsushi ABE, Yoshio UKYO, Hiroyasu IWAHARA
    2000 Volume 68 Issue 6 Pages 494-498
    Published: June 05, 2000
    Released: November 10, 2019
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    A steam electrolysis cell was constructed with a perovskite-type protonic conductor, SrZr0.9Yb0.1O3-α, as an electrolyte. The steam electrolysis cell efficiently produced hydrogen in the temperature range from 400 to 600°C. The application of this cell to reduce nitrogen oxide (NO) by the hydrogen was examined. When Pt/Ba/Al2O3 catalyst was employed on the cathode, the cell could reduce NO even in Oz-rich atmosphere. The cathode potential of the cell revealed that the reduction of O2 might be inhibited due to the absorption of NO and O2 into Ba, and that NO absorbed in Ba might be reduced to N2 by atomic hydrogen.

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  • Natsuko SAKAI, Katsuhiko YAMAJI, Hideyuki NEGISHI, Teruhisa HORITA, Ha ...
    2000 Volume 68 Issue 6 Pages 499-503
    Published: June 05, 2000
    Released: November 10, 2019
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    A significant interaction was observed between water vapor and ionic or mixed conducting oxides as that found in proton conducting ceramics. For the case of yttrium substituted zirconium oxide (YSZ), the oxygen exchange on the surface is found to be governed by the interaction of water molecule and oxygen vacancy of YSZ in a humid atmosphere. This reaction rate was found to be much faster than the reaction between oxygen gas and vacancy, which was observed as very large values of rate constant for oxygen tracer exchange reaction on YSZ in H218O + 18O2 atmospheres at T = 773 K The interfacial resistance of platinum electrode/YSZ electrolyte significantly decreased in humid atmospheres at T = 761 K.

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  • Naoya SAKAI, Kenji TODA, Mineo SATO
    2000 Volume 68 Issue 6 Pages 504-506
    Published: June 05, 2000
    Released: November 10, 2019
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    Solid solutions of Yx(Ta3xW1-3x)O3 (0≦x≦0.33) with a highly A-site deficient perovskite structure were prepared by a solid state reaction and were found to show a high trivalent ionic conductivity. The crystal structure of Yx(Ta3xW1-3x)O3 (0≦x≦0.33) was changed from a Y-ordered super-structure to a disordered structure with decreasing x. The high trivalent ionic conductivity of Yx(Ta3xW1-3x)O3 was observed in the disordered structure. The solid solution with x = 0.06 in Yx(Ta3xW1-3x)O3 exhibited the highest conductivity 2.58×10-5 Scm-1 at 635 K. The polarization data suggested strongly that Y3 + ions are the main mobile species in Yx(Ta3xW1-3x)O3. From the DC polarization measurement, the ionic transfer number of Yx(Ta3xW1-3x)O3 (x = 0.06) was found to be over 98%.

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  • Hideki KANAI, Takuya HASHIMOTO, Hiroaki TAGAWA, Junichiro MIZUSAKI
    2000 Volume 68 Issue 6 Pages 507-514
    Published: June 05, 2000
    Released: November 10, 2019
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    The electrical conductivity and Seebeck coefficient of La2-xSrxCuO4-δ with x = 0~0.30 were measured as a function of temperature between room temperature and 100°C and oxygen partial pressure of 1 ~ 1×10-4.5 atm. From the analysis of the relationship between the electrical conductivity and Seebeck coefficient, it was suggested that a hopping conduction model and a degenerated band conduction one are applicable to electrical conduction of La2-xSrxCuO4-δ when electrical conductivity is less than 30 S cm-1 and more than 60 S cm-1, respectively. Combining oxygen nonstoichiometry data with the electrical conductivity and the Seebeck coefficient, it was revealed that the electrical properties of La2-xSrxCuO4-δ at high temperatures are determined only by the Cu mean valence. The concentration of hole carrier is determined by the Cu mean valence and carrier mobility is not dependent of the oxygen nonstoichiometry nor the Sr content. Also revealed was that the Seebeck coefficient of La2-xSrxCuO4-δ is determined only by the Cu mean valence. Although apparent continuous relationship was observed between electrical conductivity, Seebeck coefficient and the Cu mean valence, indicated was that the conduction mechanism changes continuously from hopping conduction to degenerated band conduction at the Cu mean valence of around 2.05 +.

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  • Atsushi MINESHIGE, Junko IZUTSU, Maiko NAKAMURA, Kengo NIGAKI, Masafum ...
    2000 Volume 68 Issue 6 Pages 515-518
    Published: June 05, 2000
    Released: November 10, 2019
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    Electrical conductivity of mixed conducting perovskite-type oxide, La1-xSrxCo0.2Fe0.8O3-δ (LSCF, 0.4≤x≤0.7) was determined as functions of Sr-content (x), temperature (T) and oxygen partial pressure [P (O2)]. Crystal structure and oxygen nonstoichiometry (δ) of LSCF was evaluated and correlated with its electrical property. The electrical conductivity (σ) in LSCF was greatly affected by oxygen nonstoichiometry and B-O-B angle (B; B-site elements) in the crystal.

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  • Geoffrey A. TOMPSETT, Caine FINNERIY, Kevin KENDALL, Nigel M. SAMMES
    2000 Volume 68 Issue 6 Pages 519-521
    Published: June 05, 2000
    Released: November 10, 2019
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    In order to combine internal pre-reforming, heat for SOFC operation and clean combustion, a triple catalyst micro-SOFC unit was designed. The unit consisted of retrofitting a Camping Gaz® catalytic burner with a micro-SOFC stack and a Ru pre-reformer. The butane gas is jetted over the surface of the Pt honeycomb catalyst, where it is burnt to release heat. In order to utilise the gas for the co-generation of heat and electricity in the camping gas burner, the retrofitting of a 28 fuel cell stack above the combustion catalyst was investigated. In this case, the Ni/YSZ/CeO2 anode electrode layer is applied to the exterior of the electrolyte tube for the impinging fuel gas, and the dopedlanthanum manganite cathode layer is applied to the inside of the tubes. A pre-reforming catalyst comprising of Ru metal on Saffil® coamic wool, was used to partially reform the butane gas prior to the fuel cell, greatly improving the OCV and power output. The 28-cell stack micro-fuel cell system with the Ru pre-reformer was successfully retrofitted to the Camping Gaz® burner and initial performance results were obtained.

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  • Masaki HIROTA, Masaji ARAI, Takashi SAKUMA, Yoshinobu ISHII
    2000 Volume 68 Issue 6 Pages 522-525
    Published: June 05, 2000
    Released: November 10, 2019
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    The crystal structure of CuClTe has been analyzed by the Rietveld method with neutron powder diffraction data at 10 K, 290 K, 473 K and 633 K. The high temperature tetragonal phase including a statistical distribution of Cu atoms can be maintained in CuClTe even at 10 K. As the temperature increases, the inter atomic distances between Cu 4(b) and Cu 16(h) sites, Cu 16(h) and the first nearest Cu 16(h) sites, and Cu 16(h) and second nearest Cu 16(h) sites have a tendency to decrease. At high temperature Cu atoms would primarily diffuse through the route 4(b)→16(h)→4(a)→16(h)→4(b) sites along the c-axis.

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Technological Report
  • Isamu YASUDA, Masakazu HISHINUMA
    2000 Volume 68 Issue 6 Pages 526-530
    Published: June 05, 2000
    Released: November 10, 2019
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    The dimensional changes of doped lanthanum chromites (LaCrO3) upon reduction were investigated by thermal expansion measurements in oxidizing and reducing atmospheres. Judging from the crack formation in these experiments, an empirical guideline for materials selection of LaCrO3-based interconnectors in solid oxide fuel cells has been identified that materials showing relative linear expansions of less than 0.1% are to be used. It was also found that the lattice expansion increased with decrease of oxygen partial pressure (P (O2)) and showed a trend to saturate at very low P(O2). This trend has successfully been elucidated by a simple model derived by using Vegard's law.

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Notes
  • Yoshiharu UCHIMOTO, Takeshi YAO, Hiromitsu TAKAGI, Toru INAGAKI, Hiroy ...
    2000 Volume 68 Issue 6 Pages 531-533
    Published: June 05, 2000
    Released: November 10, 2019
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    Crystal structures of (Ba1-xLax)2In2O5+x (x = 0.00, 0.20, 0.30, 0.40, 0.50) were analyzed and electrical conductivity were measured. The Rietveld results for (Ba1-xLax)2In2O5+x (x = 0.20, 0.40) revealed that these oxides belonging to cubic Pm3m space group. This result indicated that the oxide ion vacancies distribute randomly in the cubic perovskite type structure. The electrical conductivities of (Ba1-xLax)2In2O5+x (x = 0.20, 0.40, 0.50) did not show a sharp discontinuity because the disorder phase of defective perovskite type structure was stabilized at low temperature by doping La3+ cations. The oxide ion transference number of the (Ba1-xLax)2In2O5+x determined by blocking method is 1.00.

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  • Yoshiyuki INAGUMA, Tetsuhiro KATSUMATA, Mitsuru ITOH
    2000 Volume 68 Issue 6 Pages 534-536
    Published: June 05, 2000
    Released: November 10, 2019
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    A-site deficient perovskites Sr0.5La0.05Li0.350.1Ti0.5Ta0.5O3 and Sr0.35La0.15Li0.350.15Ti0.5Ta0.5O3 were synthesized, and their structures and lithium ion conductivities were investigated. Both compounds have cubic symmetry (space group; Pm3m) and the A- and B-site ions are randomly distributed. The ionic conductivities for the bulk part at 300 K are 6.8×10-4 S em-1 for Sr0.5La0.05Li0.350.1Ti0.5Ta0.5O3 and 7.2×10-4 S cm-1 for Sr0.35La0.15Li0.350.15Ti0.5Ta0.5O3, respectively, which are higher than that of Sr0.5Li0.5Ti0.5Ta0.5O3 (5.5×10-4 S em-1). The ionic conduction of their compounds was found to be based on the vacancy process as was observed for other perovskite-type lithium ion conductors.

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  • Shigenori MATSUSHIMA, Kenkichiro KOBAYASHI
    2000 Volume 68 Issue 6 Pages 537-539
    Published: June 05, 2000
    Released: November 10, 2019
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    The electronic structures of ZnO, Li-doped ZnO and N-doped ZnO are calculated using the discrete variational Xα method on model clusters. For ZnO, it is found that the Zn-O bonding is not perfectly ionic but partially covalent because of the hybridization between Zn 3d and O 2p orbitals in the valence band. When a Zn atom of the cluster is replaced with a Li atom, the width of the valence band is expanded than that of the ZnO cluster, and at the same time the energy gap between HOMO and LUMO decreases. On the other hand, the new energy states originating from N 2p orbitals in the energy gap are formed for N-doped ZnO.

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  • Kai KAMADA, Yumi YANARU, Yasumichi MATSUMOTO
    2000 Volume 68 Issue 6 Pages 540-542
    Published: June 05, 2000
    Released: November 10, 2019
    JOURNALS OPEN ACCESS

    Electrochemical cation doping into the bismuth oxide superconductor (Bi2Sr2CaCu2Oy, BSCCO) was carried out using the solid oxide electrochemical doping (SOED) method, where electrolysis system consists of Anode(Ag)/M-β"-Al2O3/BSCCO/Na-β"-Al2O3/Cathode(Ag). Various cations (Ag+, K+, Zn2+) were doped together with substitution for Sr2+ in BSCCO. The doping occurred only in the grain boundaries of the ceramics when the monovalent cations were used as the dopant. On the other hand, Zn2+ was doped in the grain bulk as well as the grain boundaries under the same electrolysis condition. This doping mechanism is briefly discussed.

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