Electroceramics in Japan X

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Authors: Kenji Yoshihara, Yoshinobu Saito, Morihiro Saito, Jun Kuwano, Hidenobu Shiroishi
Abstract: The activities of the pyrochlores Pb2Ru2-xMxO7-δ (M=Mn,Fe,Co,Ni)[PRM(0x)] toward electrochemical oxygen reduction (EOR) were examined in 0.1 M KOH and 0.05 M H2SO4 aqueous solutions. The onset voltage (Vo) and the efficiency (E4) of 4-electron reduction of oxygen for PRM(0x) were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In PRM01, the order of the EOR activities was PRMn01 > PRCo01 > PRNi01 > PRFe01 in both solutions. This was consistent with the variation of the lattice parameters, i.e. PRM01 with a smaller lattice parameter showed higher EOR activity. In addition, PRMn05 showed higher EOR activity than PRMn01. The onset voltages Vo were 0.95 and 0.50 V vs. reversible hydrogen electrode in 0.1 M KOH and 0.05 M H2SO4, respectively, while E4 was almost 100 % in both solutions. These results indicate that the EOR activity of PRM(0x) depends on the incorporated metal ions on the B-sites and their contents.
Authors: Satoshi Nakayama, Masaru Miyayama
Abstract: Electrolyte films of Ce0.8Sm0.2O1.9 (SDC) were prepared on NiO-SDC anode substrates by electrophoretic deposition (EPD) for intermediate-temperature solid oxide fuel cells (SOFCs). Dense and crack-free films were fabricated by cofiring the films and substrates. A cell using an SDC electrolyte film with a La0.6Sr0.4CoO3-δ cathode exhibited a power density of 281 mW/cm2 and an electrolyte resistance of 0.064 cm2 at 600°C. The film formation of SDC by EPD was found effective in decreasing the electrolyte resistance.
Authors: Jun Kikuchi, Seiji Koga, Katsuyuki Kishi, Morihiro Saito, Jun Kuwano
Authors: Haruhiko Toda, Takeshi Chuma, Morihiro Saito, Jun Kuwano, Hidenobu Shiroishi
Abstract: Two series of compositions, BaCe0.8-xGd0.2RuxO3-δ (BCGRx, x=0-0.8) and BaGd1-yRuyO3-δ (BGRy, y=0.5-1.0), were synthesized and their crystal phases were examined. The BCGR0.15 and BGR0.5 oxides were a single phase of perovskite solid solution, while BCGR0.67 and BGR0.67 were a perovskite-related superstructure phase. The onset voltage (Vo) of the reduction current and the efficiency (E4) of the 4-electron reduction of oxygen were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In the BCGRx series, the activities for electrochemical oxygen reduction (EOR) increased with increasing Ru content. In the BGRy series, the BGR0.67 superstructure phase showed a higher EOR activity than the perovskite BGR0.5 and the hexagonal(4H) BaRuO3. This indicates that the EOR activity depends on the crystal phase. The BGR0.67 exhibited the best EOR activity of all the samples. The Vo value was 0.80 V vs. reversible hydrogen electrode and the E4 value was almost 100 %.
Authors: Shinya Suzuki, Akira Ogawa, Masaru Miyayama
Abstract: The lithium intercalation properties of anatase TiO2 electrodes with a bimodal pore size distribution were examined. Porous anatase TiO2 was prepared by hydrolyzing titanium tetrabutoxide using polyoxietylene cetyl ether as a surfactant and its subsequent calcination at 500°C for 4 hours. A porous anatase TiO2 electrode with a relatively large pore volume and 50-nm-diamater pores showed a discharge capacity of approximately 150 mAh g-1. It maintained a relatively large discharge capacity of 125 mAh g-1 at a current density of 1 A g-1, and exhibited a good high-rate capability.
Authors: Izumi Mukoyama, Kenichi Myoujin, Takahiro Nakamura, Hironori Ozawa, Takashi Ogihara, Masao Uede
Abstract: Spherical LiNi0.5Mn1.5O4 powders were prepared by internal combustion type spray pyrolysis apparatus using gas burner. The powder production capacity was 1 kg/h by this equipment. After calcinations of as-prepared powders contained Ni at different temperatures from 800 to 1200 °C in air for 10h, LiNi0.5Mn1.5O4 powders were obtained. As-prepared particles have a porous microstructure with an average diameter of about 5 μm with narrow size distribution. XRD showed that LiNi0.5Mn1.5O4 powders were well crystallized to a spinel structure with Fd3m space group. LiNi0.5Mn1.5O4 powders calcined at 1000°C show good cycle performance with after 30 cycles discharge capacity of 112mAh/g and 95% retention after 400 cycles between 3.5 V and 5 V.
Authors: Sang Wook Woo, Hiroyuki Nakano, Kaoru Dokko, Kiyoshi Kanamura
Abstract: Macroporous LiCoO2 was prepared by a colloidal crystal templating method. Colloidal crystal consisting of monodisperse polystyrene particles was used as the template for the synthesis of macroporous LiCoO2. A Li-Co-O sol was injected into the template, and it was calcined at high temperatures. A porous membrane of LiCoO2 with three dimensionally ordered macroporous (3DOM) structure was obtained. The prepared material had a rock-salt type crystallographic structure with R3m space group. The interconnected macropores with relative uniform size (0.8~0.9 ;m) were observed on entire part of the membrane. The electrochemical properties of the 3DOM LiCoO2 were characterized with galvanostatic charge-discharge measurements in an organic electrolyte containing a lithium salt. The 3DOM LiCoO2 exhibited charge and discharge capacities of 136 and 107 mA h g-1, respectively, at around 3.9 V vs. Li/Li+, indicating that 3DOM LiCoO2 electrode had solid state redox reaction accompanying with Li+ ion insertion and extraction to CoO2 frameworks.
Authors: Hideyuki Morimoto, Kenji Kurita, Tetsuya Matsuda, Shinichi Tobishima
Abstract: Anatase-type TiO2-based oxide gel /carbon composites were treated chemically with LiOH aqueous solution at 60 °C. The crystalline phase of treated powder was examined by powder x-ray diffraction using CuKα radiation. The main diffraction peaks may be detected as belonging to cubic LiTiO2. High-rate lithium intercalation properties of the samples were estimated in nonaqueous electrolyte including lithium ions. The composite electrodes exhibited high coulombic efficiency over 90% at first cycle and high capacities over 200 mAh g-1 after 200 cycle at large charge-discharge current density of 5.0 mA cm-2 (3.7 A g-1). The composite materials are one of the promising candidates as electrode materials for energy storage devices, such as hybrid capacitor, that require high-power operations.
Authors: Kenichi Myoujin, Takashi Ogihara, Koji Nakane, Nobuo Ogata
Abstract: Spherical Li[Ni(1/3-x)Mn(1/3-x)Co(1/3-x)Mx]O2 (M=Fe, Mg, Al) precursor powders were synthesized by ultrasonic spray pyrolysis using aqueous solution of metal nitrate. X-ray diffraction (XRD), scanning electron microscope (SEM), BET method using N2 adsorption analysis and Battery tester were used for determination of the composition, morphology, particle size, surface area and electrochemical properties. SEM observation showed that the size of as-prepared particles were about 0.9 μ with narrow size distribution. The crystal phase of Li[Ni(1/3-x)Mn(1/3-x)Co(1/3-x)Mx]O2 (M=Fe, Mg, Al) was resulted in layered rock salt structure with R3m space group by calcinations at 1023 K for 10 h. No impurity-related peaks are observed from the XRD pattern with various doping metals. Mg and Al doped Li(Ni1/3Co1/3Mn1/3)O2 showed very good cycling stability. The Mg substitution for Ni led to the most excellent. On the other hand, the capacity degradation during cycling was observed by Fe substitution for Mn doped Li(Ni1/3Co1/3Mn1/3)O2.
Authors: Hiroshi Yoshida, Masayuki Takada, Shinzo Yoshikado
Abstract: The relationship between the crystal structure of Bi2O3 and the recovery of the electrical degradation of ZnO varistors was investigated. The evaluation methods used were analysis of the voltage-current (V-I) characteristics, scanning electron microscopy (SEM), energy-dispersion X-ray spectroscopy (EDX), and X-ray diffraction (XRD) measurements. The electrical degradation was estimated by the nonlinearity of the V-I characteristics. A marked recovery of the nonlinearity of the V-I characteristics was observed for a sample having the crystal structure of δ-type Bi2O3. It is speculated that the electrical degradation is markedly recovered for optimum conditions of both the amount and the crystal structure of the added Bi2O3, because, for samples sintered for a long time, the recovery speed is shorter than that for samples sintered for a shorter time. During long-time sintering, the amount of Bi2O3 decreased because of evaporation. No change of the crystal structure of Bi2O3 was observed upon repeated the electrical degradation and the recovery. It is suggested that another mechanism apart from the diffusion of oxygen ions through the grain boundaries of ZnO particles contributes to the electrical degradation and recovery of the nonlinearity of V-I characteristics.

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