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Shingo Ide, Hiroki Takahashi, Isamu Yashima, Koichi Suematsu, Ken Watanabe, Kengo Shimanoe, Effect of Boron Substitution on Oxide-Ion Conduction in c-Axis-Oriented Apatite-Type Lanthanum Silicate, Journal of Physical Chemistry C, 10.1021/acs.jpcc.9b11454, 124, 5, 2879-2885, 2020.02, Apatite-type lanthanum silicate (LSO) is a material with high oxide-ion conductivity in the low- and intermediateerature range (573-873 K) and is, therefore, a promising solid electrolyte for lowerature applications such as solid oxide fuel cells and oxygen sensors. Herein, the effect of B substitution at the Si site in a c-axis-oriented apatite-type lanthanum silicate (La9.7Si5.3B0.7O26.2, c-LSBO) polycrystal on oxide-ion conduction is investigated. A highly c-axis-oriented LSBO polycrystal is fabricated by a vapor-solid reaction in which a dense La2SiO5 disk is heated in B2O3 vapor at ≥1673 K. The oxide-ion conductivity of c-LSBO reaches 16 mS cm-1 at 678 K with an activation energy of 0.4 eV. The obtained oxide-ion conductivity of c-LSBO is approximately 190 times higher than that of yttria-stabilized zirconia and 5.8 times higher than that of the polycrystalline c-axis-oriented nondoped lanthanum silicate. Based on 11B nuclear magnetic resonance measurements, B is located at the SiO4 site as BO4, suggesting the formation of an oxygen vacancy at the O4 site located along the c-axis due to charge compensation. In addition, molecular dynamics simulations indicate that the oxide-ion diffusion coefficient of the B-doped LSO is higher than that of the nondoped LSO. The high oxide-ion conductivity of c-LSBO is likely attributable to the formation of an oxygen vacancy at the O4 site by B doping, which has a lower valency than Si. Therefore, c-LSBO is a promising candidate as a solid electrolyte in electrochemical devices operating at low and moderately high temperatures.. |
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Ken Watanabe, Isao Sakaguchi, Minako Hashiguchi, Noriko Saito, Emily M. Ross, Hajime Haneda, Takeo Ohsawa, Naoki Ohashi, Isotope tracer investigation and ab-initio simulation of anisotropic hydrogen transport and possible multi-hydrogen centers in tin dioxide, Journal of Applied Physics, 10.1063/1.4953387, 119, 22, 2016.06, Hydrogen as an impurity in single crystals of tin dioxide was investigated through diffusivity and vibrational-mode analyses performed using isotope tracers and density functional theory calculations. It was found that hydrogen diffusion along the 001 axis is very fast, even at relatively low temperatures (400 �C), but is considerably slower within the (001) plane. Using transitional state calculations, this diffusion behavior was determined to be the result of anisotropy in the migration barrier for interstitial hydrogen (Hi). In addition, the two distinct vibrational modes observed in the optical spectrum were identified as the O-H stretching modes of Hi and the substitutional hydrogen at the tin sites.. |
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Ken Watanabe, Takeo Ohsawa, Isao Sakaguchi, Oliver Bierwagen, Mark E. White, Min Ying Tsai, Ryosuke Takahashi, Emily M. Ross, Yutaka Adachi, James S. Speck, Hajime Haneda, Naoki Ohashi, Investigation of charge compensation in indium-doped tin dioxide by hydrogen insertion via annealing under humid conditions, Applied Physics Letters, 10.1063/1.4870425, 104, 13, 2014.03, The behavior of hydrogen (H) as an impurity in indium (In)-doped tin dioxide (SnO2) was investigated by mass spectrometry analyses, with the aim of understanding the charge compensation mechanism in SnO2. The H-concentration of the In-doped SnO2 films increased to (1-2)×1019cm-3 by annealing in a humid atmosphere (WET annealing). The electron concentration in the films also increased after WET annealing but was two orders of magnitude less than their H-concentrations. A self-compensation mechanism, based on the assumption that H sits at substitutional sites, is proposed to explain the mismatch between the electron- and H-concentrations.. |
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Ken Watanabe, Isao Sakaguchi, Shunichi Hishita, Naoki Ohashi, Hajime Haneda, Visualization of grain boundary as blocking layer for oxygen tracer diffusion and a proposed defect model in non doped BaTiO3 ceramics, Applied Physics Express, 10.1143/APEX.4.055801, 4, 5, 2011.05, We performed visualization of the oxygen diffusion path in oxidized and reduced BaTiO3 ceramics by utilizing an ion-imaging technique. The oxygen tracer diffused quickly from the surface up to the grain boundary, and then behaved as discontinuous steps at the grain boundary. The grain boundary acted as a blocking layer against oxygen diffusion. The reduction process enhanced the blocking effect. The blocking of oxygen diffusion at the grain boundary originated in the formation and distribution of complex defects between the charged oxygen vacancy and the reduced Ti near the grain boundary.. |
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Watenabe, Ken; Yuasa, Masayoshi; Kida, Tetsuya; Teraoka, Yasutake; Yamazoe, Noboru; Shimanoe, Kengo, High-Performance Oxygen-Permeable Membranes with an Asymmetric Structure Using Ba0.95La0.05FeO3-delta Perovskite-Type Oxide, ADVANCED MATERIALS, 10.1002/adma.200903953, 22, 21, 2367-2370, 2010.06. |
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Ken Watanabe, Masayoshi Yuasa, Tetsuya Kida, Kengo Shimanoe, Yasutake Teraoka, Noboru Yamazoe, Dense/porous asymmetric-structured oxygen permeable Membranes based on la0.6Ca0.4CoO3 perovskite-type oxide, Chemistry of Materials, 10.1021/cm8013144, 20, 22, 6965-6973, 2008.11, To achieve high-efficiency oxygen permeation using mixed (ionic and electronic) conducting perovskite-type oxides, we examined asymmetric-structured membranes of La0.6Ca0.4CoO3 in which a thin dense membrane was deposited on a porous support. The La0.6Ca 0.4CoO3 porous support was fabricated using irregular-shaped precursor particles prepared through an oxalate method. The fabricated support had good gas permeability and thermal stability, showing sufficient properties as a support for dense thin membranes. A dense membrane of 10 μm thickness was successfully formed on the porous support by coating a La0.6Ca0.4CoO3 slurry and subsequent densification by sintering. The deposited thin membrane was gastight and free from clacks, as revealed by gas permeation tests and SEM observations. The asymmetric membrane exhibited a high oxygen permeability of 1.66 cm3 (STP, standard temperature and pressure) min-1 cm-2 at 930 °C, which was four times higher than that of a typical sintered-disk type membrane with 1200 μm thickness, demonstrating its feasibility as a high-performance oxygen separation membrane.. |
