Katsuya Teshima

Shinshu University, Shonai, Nagano, Japan

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Publications (108)316.51 Total impact

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    ABSTRACT: Dye-dispersing allophane–titania composite electrodes were prepared from titanium alkoxide sols containing dye and allophane. The photoelectric conversion properties of the electrodes were investigated by photoelectrochemical measurements. The photocurrent values in the UV range decreased with an increase in the allophane content, whereas those in the visible range were increased by adding 1.0% (Al/Ti ratio) allophane. As a small amount of allophane nanoparticles were highly dispersed in the titania electrodes, the dye molecules were dispersed in the electrodes without decreasing the efficiency of the electron injection from the dye to the titania conduction band. The dye molecules dispersed on the titania nanoparticle surface were capped with allophane nanoparticles which prevented desorption. The dye molecules strongly interacted with the titania nanoparticle surface and efficiently injected the excited electrons into the titania conduction band.
    Applied Clay Science 04/2015; 107. DOI:10.1016/j.clay.2015.01.015 · 2.70 Impact Factor
  • CrystEngComm 03/2015; DOI:10.1039/C5CE00386E · 3.86 Impact Factor
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    ABSTRACT: Flux growth is a promising method that allows to control both crystalline phase and crystal shape through the selection of a suitable flux. In this work, lanthanum titanate (La2Ti2O7) crystals with different morphologies were grown using the Na2MoO4, K2MoO4, NaCl, and mixed NaCl+K2MoO4 (molar ratio = 3:7) fluxes and their nitridability to form the LaTiO2N crystals under a high-temperature NH3 atmosphere was also investigated. The effects of solute concentration and cooling rate on the growth of the La2Ti2O7 crystals were also studied. The XRD results revealed that the {100} plane was dominant in the La2Ti2O7 platelet crystals grown using the alkali metal molybdate fluxes. By increasing the solute concentration from 1 to 20 mol%, an average size of the crystals decreased without considerably altering the overall crystal morphology. The La2Ti2O7 crystals with the preferred <010> and <001> growth directions along the b and c axes were grown using the Na2MoO4 and K2MoO4 fluxes, respectively. Compared to the Na2MoO4 flux, the K2MoO4 flux did not show a cooling rate-dependent effect on the growth of the La2Ti2O7 crystals. It was found that the conversion of the La2Ti2O7 crystals into the LaTiO2N crystals was strongly dependent on the flux used to grow the precursor La2Ti2O7 crystals. That is, the La2Ti2O7 crystals grown using the K2MoO4 and NaCl fluxes were nearly completely converted into the LaTiO2N crystals, while the conversion of the La2Ti2O7 crystals grown using the Na2MoO4 and mixed NaCl+K2MoO4 fluxes into the LaTiO2N crystals seemed to be not completed yet even after nitridation at 950°C for 15 h using NH3 due to the larger crystal size and the presence of unintentional impurities (Na and Mo from the flux) in the La2Ti2O7 crystal lattice. Nevertheless, the LaTiO2N crystals fabricated by nitriding the La2Ti2O7 crystals grown using the K2MoO4 and NaCl fluxes should be suitable for the direct solar water splitting.
    Inorganic Chemistry 03/2015; DOI:10.1021/ic502862t · 4.79 Impact Factor
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    ABSTRACT: Layered double hydroxide (LDH) is an environmentally benign anion exchanger that can adsorb various toxic anions. In this work, we demonstrate the fabrication of plate-like Mg-Al-type LDH crystals on in situ formed alumina particles using a flux method at a relatively low temperature (∼350 °C). At or below 300 °C, the melted Al source crystallized to form AlOOH or γ-alumina particles in KNO3-NaNO3 flux. However, LDH crystals did not form due to the inferior crystallization properties of the Mg precursor. Increasing the holding temperature up to 350 °C and above facilitated crystallization of the dissolved Mg and Al species in flux to yield plate-like LDH crystals on the preformed alumina particles. Top-surface and cross-sectional FE-SEM and EPMA analyses revealed the vertical alignment of the crystalline LDH plates on the surface of the alumina particles. On the other hand, solid-state reactions did not yield these well-grown, plate-like LDH crystals. The TG-DTA profile of the LDH precursors with flux depicted the decomposition and crystallization events that the Al and Mg precursors undergo. On the basis of the results from these characterization studies, we propose a mechanism in which LDH crystals sequentially form on the surface of the alumina particles.
    Crystal Growth & Design 02/2015; 15(2):732-736. DOI:10.1021/cg501534f · 4.56 Impact Factor
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    ABSTRACT: Highly crystalline, platelike La(2)Ti(2)O7 were grown from a NaCl flux, and LaTiO2N crystals were obtained by subsequent nitridation under NH3 flow. The TEM analysis indicated that the flux-grown platelike La2Ti2O7 crystals are single-crystalline growing along the a axis. The shapes and sizes of the LaTiO2N crystals were almost unchanged from the La2Ti2O7 precursor. In addition, LaTiO2N crystals remained single-crystalline with a porous nanostructure. The optical absorption edges of the La2Ti2O7 and LaTiO2N crystals were approximately 320 and 600 nm.
    Crystal Growth & Design 01/2015; 15(1):124-128. DOI:10.1021/cg5010006 · 4.56 Impact Factor
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    ABSTRACT: Oxynitride perovskites and related phases have received considerable attention due to their potential application for visible-light-responsive photocatalyst and nontoxic inorganic pigments. The changes in bonding and structure by a partial replacement of O2– by N3– give rise to interesting dielectric behavior. Here, we report on the fabrication of highly crystalline La2TiO5 crystals by chloride flux growth method and their subsequent nitridation to form the LaTiO2N crystals using NH3 gas. The flux-grown La2TiO5 crystals had a columnar structure grown in the ⟨001⟩ direction. Using the NaCl flux, larger columnar La2TiO5 crystals were grown compared to those grown using the KCl flux. With increasing solute concentration, the aspect ratio of columnar La2TiO5 crystals decreased significantly. The columnar La2TiO5 crystals with smooth surface were readily converted by nitridation at 950 °C for 45 h followed by acid treatment into the LaTiO2N crystals with a highly porous structure that formed from the strong segregation of nanocrystals, leading to the largest specific surface area (16.5–18.4 m2·g–1). For the La2TiO5 crystals grown using the chloride fluxes, the wavelength of the absorption edges was approximately 320 nm (Eg = 3.87 eV), whereas the absorption edges exhibited by the LaTiO2N crystals obtained by nitridation were approximately 600 nm (Eg = 2.06 eV). Particularly, the LaTiO2N crystals prepared in this study by nitriding the precursor La2TiO5 crystals did not show a noticeable absorption in the near-infrared region above 600 nm, which is generally attributable to some reduced Ti3+ species and nitrogen deficiency, even after a long nitridation process. The fabricated LaTiO2N crystals with low defect density will be advantageous for various applications that specially require higher specific surface area.
    Crystal Growth & Design 01/2015; 15(1):333−339. DOI:10.1021/cg501397x · 4.56 Impact Factor
  • Kunio Yubuta, Katsuya Teshima, Shuji Oishi
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    ABSTRACT: The structure of Nb2O5 nanotubes was studied by electron diffraction and high-resolution transmission electron microscopy (HRTEM). The nanotubes were prepared from highly crystalline-layered K4Nb6O17 crystals grown from a KCl flux using the intercalating and exfoliating techniques. Nanotubes have a length of about 200 nm and a diameter of 20 nm. The observed electron diffraction patterns revealed that the nanotubes have a helical structure with the basal plane of (010) and the tube-axis parallel to the [201] direction. Their basal plane corresponds to the (010) plane of the layered K4Nb6O17 crystals. The helical lattice plane was directly observed by a Fourier filtered HRTEM image. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 10/2014; 46(10-11). DOI:10.1002/sia.5478 · 1.39 Impact Factor
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    ABSTRACT: Graphene monoliths made from graphene oxide colloids by unidirectional freeze-drying method were activated by typical activation processes of CO2 activation, chemical activation using ZnCl2 or H3PO4, and KOH activation. The porosity development of graphene monolith markedly depends on the activation method. The monoliths with highest surface area are obtained by the KOH activation method; only the KOH activation is effective for production of the graphene monolith of which surface area is in the range of 1760–2150 m2 g−1. The mechanism of the porosity development by KOH activation method is proposed. This work provides a promising route for the bottom-up design of pore width-tunable nanoporous carbons.
    Carbon 09/2014; 76:220–231. DOI:10.1016/j.carbon.2014.04.071 · 6.16 Impact Factor
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    ABSTRACT: Higher performance active materials containing cathodes have been strongly required for the achievement of advanced lithium-ion rechargeable batteries. We report the formation of a densely packed and idiomorphic LiCoO2 crystal layer directly on a substrate surface using flux coating with a LiNO3–LiOH mixed flux and their applications as an additive-free cathode to enhance gravimetric energy density per single cell as well as durability. The formation mechanism of LiCoO2 nanocrystals from high temperature melt of the mixed flux was controlled under evolution selection growth, driven by supersaturation. The as-grown crystals formed a petal-shape with well-developed {001} faces. After annealing treatment, the crystal shape transformed into hexagonal plates with vertical orientation. The hexagonal plate-shaped crystal arrays were identified to be homogeneous LiCoO2 having a rhombohedral crystal system. Their lattice parameters were a = 0.2784 and c = 1.4248 nm, and the Li/Co ratio in the crystals was 1.00. Furthermore, transmission electron microscopic images and selected area electron diffraction patterns revealed that the interface between the crystal layer and the substrate was smoothly connected and free of impurities. In fact, the LiCoO2 nanoplate layer exhibited desirable properties such as a large discharge capacity close to its theoretical value, higher rate performance, and high cyclability over 500 cycles with no assistance of additional electroconductive materials and binders, meaning that the interfaces provide seamless charge transportation pathways.
    Crystal Growth & Design 03/2014; 14(4):1882–1887. DOI:10.1021/cg5000217 · 4.56 Impact Factor
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    ABSTRACT: Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol-gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e., the dye-titania complex. This result indicated that the dianion form was the most favorable for formation of the dye-titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band. This article is protected by copyright. All rights reserved.
    Photochemistry and Photobiology 02/2014; 90(4). DOI:10.1111/php.12254 · 2.68 Impact Factor
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    ABSTRACT: Low-temperature growth of idiomorphic spinel-type Li1+xMn2−xO4 (x = 0.09, 0.14) crystals was achieved by using a LiCl-KCl flux. The flux growth driven by rapid cooling resulted in truncated octahedral Li1+xMn2−xO4 crystals surrounded by both dominating {111} and minor {100} faces. The chemical compositions, sizes, and shapes of the Li1+xMn2−xO4 crystals could be tuned by simply changing the growth conditions. Among the various products, the crystals grown at a low temperature of 600 °C showed a small average size of 0.2 μm. The small Li1+xMn2−xO4 crystals grown at 600 °C showed better rate properties than the large crystals grown at 900 °C, when used as a positive active material in lithium-ion rechargeable batteries.
    CrystEngComm 01/2014; 16(6):1157. DOI:10.1039/c3ce41682h · 3.86 Impact Factor
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    ABSTRACT: Dye-dispersing ZnO precursor gel films were prepared on indium tin oxide electrodes from a zinc acetate solution containing eosin Y by dip-coating, steam treatment, and then heating at a low temperature. The electronic interaction between the dye and zinc in the dye-dispersing gel films were investigated by spectroscopic and electrochemical measurements. A photocurrent was observed in the dye-dispersing gel electrodes before the steam treatment. The photocurrent value increased by the steam treatment and heating due to crystallization of the gel and removal of organic impurities. The dye molecules existed between the interlayers of the layered zinc hydroxide coexisting with the ZnO. The photoexcited electron in the dye should be injected into the ZnO conduction band via the layered zinc hydroxide. The value increased with an increase in the dye content even though the ZnO crystallinity decreased. The dye–zinc interaction, i.e., the complex formation and photoinduced electron injection, played an important role in the electron transport and photoelectric conversion.
    Research on Chemical Intermediates 01/2014; DOI:10.1007/s11164-014-1761-z · 1.54 Impact Factor
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    ABSTRACT: Photocatalytic Nb2O5 nanocrystal layers were successfully synthesized using NbOx nanosheets obtained from layered K4Nb6O17 crystals. First, idiomorphic K4Nb6O17 crystals were grown using the KCl flux method, and then a two-step process involving proton exchange and exfoliation was carried out in order to make the nanosheets. Next, the rectangular nanosheets were mixed with polyethylene glycol, water and ethanol to prepare a nanosheet paste, and the paste was then evenly spin-cast on silica glass. Upon heating, decomposition and evaporation of the solvents yielded transparent, colorless nanocrystal layers with good adhesion. During the heating process, some nanosheets rolled up into nanotubes; therefore, nanocrystal layers consisting of both nanosheets and nanotubes were fabricated. The nanocrystal layers exhibited photocatalytic activity for the photodegradation of organosilane thin films under UV light irradiation. The organosilane thin films were photocatalytically decomposed and that the surfaces were converted from hydrophobic to ultrahydrophilic. Furthermore, micropatterned nanocrystal layer was readily fabricated using hydrophobic/hydrophilic template.
    Applied Surface Science 09/2013; 280:539-544. DOI:10.1016/j.apsusc.2013.05.023 · 2.54 Impact Factor
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    ABSTRACT: Well-aligned honeycomb-designed layers of potassium tungstate (K0.33WO3.165) were successfully fabricated by spray deposition and microsphere lithography using polystyrene (PS) colloidal crystals as templates. A densely packed monolayer of monodisperse PS microspheres was formed on a silica glass surface, using the Langmuir–Blodgett thin film technique. Subsequently, a (NH4)10W12O41·5H2O-KCl aqueous solution was sprayed as a micromist on the PS templates. While the K0.33WO3.165 crystal layers were synthesized by chemical reaction between W and K sources during the heating, the PS templates were thermally decomposed, generating an inverse opal surface structure where the interstitial space of the densely hexagonal packed PS microspheres had been. Numerous hexagonal rodlike crystals were grown on the honeycomb-designed layer of K0.33WO3.165. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy analyses, and X-ray photoelectron spectroscopy were performed to analyze the combined one-dimensional and three-dimensional honeycomb-designed structure.
    Crystal Growth & Design 07/2013; 13(8):3294–3298. DOI:10.1021/cg400714e · 4.56 Impact Factor
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    ABSTRACT: Dye-dispersing titania electrodes were prepared from the dye-containing titanium alkoxide sols by a room temperature sol–gel process and steam treatment at 110 °C. The spectroscopic and photoelectric conversion properties of the electrodes were investigated in order to clarify the influences of the dye dispersion and the co-dispersion of the two dyes on the electron transfer process. The fluorescein and eosin Y molecules were dispersed into the titania as their monomers. The shapes of the photocurrent action spectra of the fluorescein and/or eosin Y-dispersing titania electrodes corresponded well to those of their absorption spectra because the excited electrons in the dyes were directly injected into the titania conduction band without any interaction between the dye molecules, such as energy transfer. This result indicated that the dye molecules were separately encapsulated in the pores between the titania nanoparticles and tightly adsorbed or bonded to the titania particle surface. The internal quantum efficiency of the photoelectric conversion was higher than that of the conventional dye-adsorbing titania electrodes in which the dye molecules were easily aggregated and thus deactivated by the energy transfer. The co-dispersion of the two dyes on the titania surface allowed effective extension of the visible light region for the photoelectric conversion.
    05/2013; 3(6):1512-1519. DOI:10.1039/C3CY00007A
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    ABSTRACT: The growth of NaTaO3 crystals through the reaction between NaNO3 and a Ta substrate was directly observed using in-situ laser microscopy and in-situ X-ray diffraction. Voids and creases were first produced at 430 °C and then NaTaO3 crystals grew at 440 °C in a moment. Because the NaTaO3 crystals had formed during heating, the driving force for crystal growth was concluded to be the evaporation of NaNO3.
    CrystEngComm 04/2013; 15(20):4058-4061. DOI:10.1039/C3CE40330K · 3.86 Impact Factor
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    ABSTRACT: The International Conference on Thin Films is the most established conference for all researchers and persons interested in thin films and coatings. It is one of the tri-annual conference series endorsed and co-organized by the Thin Film Division of the International Union for Vacuum Science, Technique and Applications (IUVSTA), a union of national member societies whose role is to stimulate international collaboration in the fields of vacuum science, techniques and applications and related multi-disciplinary topics including solid-vacuum and other interfaces. The 15th International Conference on Thin Films (ICTF-15) is organized by The Vacuum Society of Japan (VSJ) and held at Kyoto TERRSA in Kyoto, Japan on 8-11 November 2011, following the 14th International Conference on Thin Films (ICTF-14), which was held in Ghent, Belgium in 2008. Thin films and coatings are daily becoming increasingly important in the fields of various industries. This International Conference provides a multi-disciplinary forum for recent advances in basic research, development and applications of thin films and coatings. This conference will present a unique opportunity for researchers, engineers and managers to acquire new knowledge of thin films and coatings. We hope that our understanding on thin films and coatings will be deepened through this conference. The conference site, 'Kyoto TERRSA' is located in the historical heart of the old capital Kyoto. Kyoto is an ancient city with a 1200-year history. It was established as Japan's capital under the name 'Heian-kyo' in the year 794. Although many transformations have taken place over the years, Kyoto has always embraced the most advanced standards of the times. It has greatly contributed to the nation's industrial, economic and cultural development. The dauntless spirit of leadership of Kyoto's past as a capital city is still felt here today. Kyoto also preserves the beloved examples of its culture as testimonials of time. This is shown in the ancient temples and shrines, as well as private houses, which are built in styles unique to Kyoto. Furthermore, many festivals, ceremonies and traditional activities reveal the will of this city to convey and develop its 1200-year-old culture. Participants of the conference will also be able to see many world heritage sites in the city. Moreover, November is the best time of year to visit Kyoto. We hope you will enjoy Kyoto very much. We would like to offer our thanks for all the contributions from the members of the International Advisory Committee and Organizing Committee, Symposium Chairs, the Secretary General, the Thin Film Division of IUVSTA (chair: Professor Dr Alberto Tagliaferro), IUVSTA, VSJ and other cooperating societies, and to all of the supporting organizations and enterprises. We would also like to express our thanks to all of the participants, secretariat members and members of the supporting staff. I am very pleased to welcome you to ICTF-15 and Kyoto! Director Professor Dr Osamu Takai Chairperson of ICTF-15 EcoTopia Science Institute, and Department of Materials, Physics and Energy Engineering Graduate School of Engineering Nagoya University Japan
    Journal of Physics Conference Series 03/2013; 417(1):1001-. DOI:10.1088/1742-6596/417/1/011001
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    ABSTRACT: High-quality upconversion YO1–xF1+2x:Ln (Ln = Yb, Er, Ho, and Tm) layers with good adhesion, comprising densely packed, plate-shaped idiomorphic crystals, were directly grown on stainless steel (SUS) substrates by flux coating. The LiNO3–KNO3 flux effectively promoted crystal growth. Additionally, the near-infrared-to-visible (NIR-vis) upconversion fluorescence properties of the YO1–xF1+2x:Ln crystal layers could be tuned by varying the type of dopant (Ln element). YO1–xF1+2x:Yb,Er, YO1–xF1+2x:Yb,Ho, and YO1–xF1+2x:Yb,Tm crystal layers showed red, green, and blue fluorescence, respectively, under 980 nm laser irradiation.
    Crystal Growth & Design 02/2013; 13(3):1187–1192. DOI:10.1021/cg301613k · 4.56 Impact Factor
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    ABSTRACT: Anticorrosive molybdate films composed mainly of Mg(OH)2, MoO2, MoO3, and MgF2 were formed on magnesium alloy AZ31 by chemical conversion. The film had relatively compact surfaces and a thickness of approximately 800 nm. The XPS studies revealed that the film contained Mg, Al, Mo, O, P, S, and F elements. The corrosion resistant performances of the films were investigated by electrochemical measurements. The potentiodynamic polarization curves showed that anodic current densities and corrosion potential of the Mo coated AZ31 were lower and more positive than those of bare AZ31. The EIS measurement and appropriate equivalent circuit models revealed that the corrosion resistance was improved.
    Surface and Coatings Technology 02/2013; 217:76–83. DOI:10.1016/j.surfcoat.2012.11.076 · 2.20 Impact Factor
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    ABSTRACT: High-quality, idiomorphic, single-phase Li5La3Nb2O12 crystals were successfully grown using a LiOH flux cooling method at the relatively low temperature of 500 °C at a solute concentration of 5 mol %. The grown Li5La3Nb2O12 crystals had polyhedral shapes with well-developed, flat {211} and {110} faces. Their shapes were relatively uniform, and the average crystal size was approximately 59.2 μm. No aggregation was observed in scanning electron microscopy images. The high crystallinity of the Li5La3Nb2O12 crystals was confirmed by transmission electron microscopy images. Their lattice parameter was determined from the X-ray diffraction pattern to be a = 1.281 nm, which is consistent with the literature value (a = 1.282 nm). Furthermore, the crystal phase, form, size, and crystallinity of the flux-grown Li5La3Nb2O12 crystals were obviously dependent on the growth conditions including the solute concentration and holding temperature.
    Crystal Growth & Design 01/2013; 13(2):479–484. DOI:10.1021/cg3012348 · 4.56 Impact Factor