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Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Takahiko KAWAGUCHI, Mayu YOSHIDA, Naonori SAKAMOTO, Kazuo SHINOZAKI, Hisao SUZUKI and Naoki WAKIYA
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Pulsed laser deposition (PLD) with an electromagnet (dynamic aurora PLD) and reflection high-energy electron diffraction (RHEED) was developed by installing an 11-tuned solenoid coil in a vacuum chamber. This method achieved thin film deposition under a magnetic field of up to 120 mT using dc current of 1,200 A. The electromagnet is a solenoid coil, which produces a magnetic field that is proportional to an electric field without saturation of the magnetic field. This PLD method enables in situ observation of the crystal structure of the thin film surface after turning the electromagnet off, but without breaking vacuum. Many reports have described studies of PLD in a magnetic field. For most such studies, permanent magnets have been used to apply a magnetic field to the plume. Nevertheless, when doing so, carrying out in-situ observation using RHEED is difficult because the magnetic field deflects the electron beam. This case study examined effects of magnetic field application to the plume on the in-plane orientation and resistivity of a NiO thin film deposited on a MgO(001) single crystal at room temperature (25 °C). Results demonstrate that the in-plane orientation (epitaxial growth) is unchanged, whereas thin film resistivity decreases exponentially with the magnetic field intensity during deposition. These results suggest that the Ni3+ ion concentration can be expected to increase exponentially with the magnetic field during deposition. The room-temperature resistivity of the NiO thin film deposited under a 120 mT magnetic field was 112 Ω cm.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Keisuke ISHIHAMA, Masanori KODERA, Takao SHIMIZU, Wakiko YAMAOKA, Risako TSURUMARU, Shintaro YOSHIMURA, Yusuke SATO and Hiroshi FUNAKUBO
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0.1(Bi,Na)TiO3–0.9BaTiO3 thin films were deposited by pulsed laser deposition as a candidate of lead-free thin films with a positive temperature coefficient of resistance for micro-thermistor applications in microelectro mechanical system devices. (001)-oriented epitaxial tetragonal films with a unity (Bi + Na + Ba)/Ti ratio were grown at 675 °C under a total pressure of 50 mTorr. The obtained films showed improved insulating properties and clear ferroelectricity. The Curie temperature was estimated to be 200 °C by the high-temperature X-ray diffraction measurement, which was almost the same as the reported value for the ceramic.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Mana MIYACHI, Manabu HAGIWARA and Shinobu FUJIHARA
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NiCo2O4 is promising as one of the p-type oxide semiconductors for practical applications in optoelectronic devices. In this study, we have elaborated NiCo2O4 hexagonal nanoplatelet films and examined their photovoltaic properties. The film fabrication was actually achieved by four steps: the synthesis of hexagonal nanoplatelets of a Ni1/3Co2/3(OH)2 precursor, the dispersion of the nanoplatelets in liquid media, the self-assembly of the nanoplatelets on dipped substrates, and the topological conversion of the hydroxide to the oxide by the heat treatment. The resultant NiCo2O4 thin films had structural features such as the crystallographic (111) orientation, the high specific surface area, and the high light-scattering ability. As a result, the NiCo2O4 thin films loaded with an N749 dye could work effectively as photocathodes in the configuration of dye-sensitized solar cells.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Shunpei SUZUKI, Toshiaki FUJITA, Yusuke HOSOKAWA, Kazutaka FUJIWARA and Noriaki NAGATOMO
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We developed a thin-film nitride thermistor on a resin substrate with high heat resistance by focusing on the interface between the polyimide (PI) substrate and (Al,Ti)N film. Heat resistance properties of nitride thermistors are degraded by an amorphous oxynitride layer on the PI substrate that forms during the initial stage of sputtering. We propose the introduction of an inorganic insulating underlayer at the interface between (Al,Ti)N and the PI substrate to prevent the formation of the amorphous phase. As a result, highly crystalline (Al,Ti)N was grown directly on an inorganic insulating underlayer and high heat resistance was achieved.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Yue SHI, Eisuke YAMAMOTO, Makoto KOBAYASHI and Minoru OSADA
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Single droplet assembly is a new thin-film technology using drop casting of two-dimensional (2D) materials: controlled convection by a pipette and a hotplate causes a uniform deposition, suggesting new possibility of 2D nanosheet assembly. We extended this new assembly technique to titania nanocoating by including detailed investigations on fabrication procedure and characteristics as coating applications. The layer-by-layer approach using single droplet assembly is effective for the fabrication of atomically uniform and highly dense nanofilms. As a consequence of the effective tiling by controlled convection, the films appeared flat on the atomic scale and uniform over a large area. We also address characteristics of single droplet assembly in comparison with other deposition methods.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Shintaro SANO, Takahisa SHIRAISHI, Takanori KIGUCHI and Toyohiko. J. KONNO
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Ta substituted (K,Na)NbO3 powders with K-rich composition across polymorphic phase boundary were synthesized at 200 °C by hydrothermal method. The amount of Ta content in the powders was controlled by changing the nominal composition of raw powders, C = [Ta2O5]/([Nb2O5] + [Ta2O5]). Elemental mappings using a transmission electron microscope showed all the elements (K, Na, Nb, and Ta) were contained in the powders. X-ray diffraction measurement showed that (K,Na)(Nb,Ta)O3 solid solution powders can be obtained for all nominal compositions (C = 0–1), and that the orthorhombic-tetragonal phase transition can be induced by controlling C value, yet the diffraction peaks arising from a secondary phase were also detected in the range of C = 0.5–1. Scanning electron microscopy (SEM) observation revealed that the morphology of powder changed from polymorphic to square, and the size of the square-shaped (K,Na)(Nb,Ta)O3 powder decreased, with increasing the nominal composition. Temporal evolution of the emerged phases revealed that the range of intermediate phase became shorter with increasing the nominal composition, allowing the perovskite phase to form from early stages. In addition, the cause of the secondary phase was unreacted raw powder. Observations on the powder synthesis with end-member composition (KOH–Nb2O5, NaOH–Nb2O5, KOH–Ta2O5, and NaOH–Ta2O5) has shown that perovskite single-phase was formed in KOH-Nb2O5, NaOH-Nb2O5, and KOH-Ta2O5, while that unreacted raw powder was detected in the combination of NaOH and Ta2O5. These results demonstrated that Ta substitution is an effective way to control the morphology of powder and that the synthesis behavior of (K,Na)(Nb,Ta)O3 is strongly dependent on the combination of alkaline solution and raw powder.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Ryo TANAKA, Kazuyoshi UEMATSU, Mineo SATO and Kenji TODA
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Melt quenching method was applied to prepare the long persistent phosphor SrAl2O4:Eu2+,Dy3+, and Dy3+ concentration dependence of afterglow property was investigated. Melt quenched SrAl2O4:Eu2+,Dy3+ phosphors exhibit brighter afterglow intensity compared with these synthesized by a conventional solid-state reaction method. The afterglow property was improved with increase of Dy3+ concentration, and 10 mol % Dy3+ co-doped sample exhibits approximately 1.3 times higher afterglow intensity than commercially available phosphor.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Takahiko KAWAGUCHI, Jumpei SUZUKI, Naonori SAKAMOTO, Hisao SUZUKI and Naoki WAKIYA
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Mn3CuN thin films were prepared using dynamic aurora pulsed laser deposition (PLD), which enables magnetic field application during film growth. The magnetic field can stabilize a plasma state of nitrogen in plume generated from a nitride target. Results show that Mn3CuN phase with high crystallinity is observed clearly and grown epitaxially on MgO(001) in the as-grown thin films. The as-grown thin films show ferromagnetic transition near 150 K without post-annealing, indicating almost no nitrogen deficiency. These results suggest that dynamic aurora PLD is effective for nitride thin films with high crystallinity.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Yuka TAKAGI, Kohtaro EGUCHI, Hajime NAGATA, Isao SAKAGUCHI and Tadashi TAKENAKA
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Lead-free ferroelectric and piezoelectric ceramics, (Bi0.5Na0.5)TiO3 (BNT), with Mg and Nb additives were prepared and the concentration of oxygen vacancies as the 18O tracer diffusion of these ceramics were clarified by secondary ion mass spectroscopy (SIMS). Moreover, the samples were quenched after sintering to examine the depolarization temperature Td, and then their electrical properties were investigated. As a result, the obtained values of volume diffusion coefficient D of BNT doped with 0.4 wt % Mg and 0.4 wt % Nb were determined to be 9.2 × 10−11 and 1.1 × 10−13 cm2/s, respectively. The oxygen vacancy concentration increased with the amount of Mg added and decreased with that of Nb added. Moreover, quenching increased Td by ∼50 °C in BNT with the Mg additive (Mg x) and ΔTd also increased. Thus, the effect of quenching was promoted by Mg x. On the other hand, the Td of BNT with the Nb additive (Nb y) also increased despite the low concentration of oxygen vacancies. This is because the D of pure BNT (no additives) was revealed found to be 2.5 × 10−11 cm2/s, that is, pure BNT originally contained a high concentration of oxygen vacancies. The concentration was maintained even after quenching, then D showed 1.8 × 10−11 cm2/s. In addition, the electromechanical coupling factor k33 of the quenched ceramics remained similar to that of the ordinarily fired samples of BNT with the Mg and Nb additives.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Takahiko KAWAGUCHI, Takeshi KAWAI, Takuma HIRAIWA, Naonori SAKAMOTO, Kazuo SHINOZAKI, Hisao SUZUKI and Naoki WAKIYA
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Epitaxial Sr-excess SrTiO3 (ST) thin film (Sr/Ti = 1.41) was grown on ST(001) and ST(101) single-crystal substrates using dynamic aurora pulsed laser deposition (PLD) under a 200 mT magnetic field. The films spontaneously formed a superlattice structure comprising two layers having different concentrations of Ruddlesden–Popper (RP) planar faults. The superlattice periods of Sr-excess ST thin films deposited on ST(001) and ST(101) substrate were, respectively, 35 and 23 nm. For thin film deposited on ST(001), the in-plane lattice parameter coincided with the substrate, showing coherent growth. For thin film deposited on ST(101), coherent growth occurred along a direction ±45° declined against the substrate. The spontaneously formed superlattice was brought about by “up-hill diffusion” of spinodal decomposition. The direction of propagation of the composition wave of spinodal decomposition was regarded as perpendicular to the substrate and ±45° declined against the substrate for thin films deposited respectively on ST(001) and ST(101). The superlattice period of the thin film deposited on ST(101) (23 nm) is smaller by a factor of 1/√2 than that deposited on ST(001). This relation is explainable by the difference of the propagation direction of the composition wave. The thin film deposited on ST(001) is distorted tetragonally, whereas that on ST(101) is cubic. The Sr-excess ST thin film was also deposited on La-doped ST(101) (La-ST(101)) and La-ST(101) substrates to measure electrical properties. No change was found in the crystal structure and microstructure, irrespective of La-doping. The thin film deposited on La-ST(001) showed ferroelectricity. However, the film deposited on La-ST(101) shows no ferroelectricity. The difference of electrical properties is brought about by differences of crystal symmetry. The difference is also explainable from the perspective of thermodynamic phenomenology.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Yuma TAKEBUCHI, Kenichi WATANABE, Daisuke NAKAUCHI, Hiroyuki FUKUSHIMA, Takumi KATO, Noriaki KAWAGUCHI and Takayuki YANAGIDA
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Undoped and Ce-doped LiAlO2 single crystals, a novel neutron scintillator, were synthesized by the floating zone method, and the photoluminescence and scintillation properties were investigated. Under X-ray irradiation, all the synthesized crystals showed luminescence due to oxygen vacancies with decay time constants of 250 ns and 2 µs, and Ce-doped LiAlO2 crystals showed luminescence due to the 5d–4f transition of Ce3+ with a decay time constant of 40 ns as well. In the pulse height spectra under neutron irradiation from 252Cf, the synthesized crystals exhibited thermal neutron peak, and scintillation light yields increased by doping of Ce. Furthermore, neutron and gamma-ray pulse shape discrimination was examined, and 0.5 and 1.0 % Ce-doped ones showed a distinction of neutron and gamma-ray events.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Noriaki KAWAGUCHI, Hiromi KIMURA, Daisuke NAKAUCHI, Takumi KATO and Takayuki YANAGIDA
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We have developed a LiF/CaF2:Tb eutectic composite as a novel thermoluminescence (TL) dosimetric material. The LiF/CaF2:Tb eutectic composite was obtained using a melt-solidification method with a lower melting temperature than that of LiF and CaF2. The results of the PL emission and excitation spectra, the X-ray induced radioluminescence decay curve, and the TL emission spectrum indicate that the emissions of LiF/CaF2:Tb eutectic composite are due to 4f-4f transitions of the Tb3+ ion. The integrated TL intensity of the LiF/CaF2:Tb eutectic composite was 3.6 times higher than that of the commercial CaSO4:Tm dosimetric material that is known to show a relatively high TL intensity. The dose response curve of the LiF/CaF2:Tb eutectic composite was measured and the lower detection limit was 0.01 mGy which is the lowest value among the LiF/CaF2 based composites.
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Kohei MIZOI, Miki ARAI, Yutaka FUJIMOTO, Daisuke NAKAUCHI, Masanori KOSHIMIZU, Takayuki YANAGIDA and Keisuke ASAI
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Photoluminescence and scintillation properties are reported for SrCl2−xBrx:Yb2+ (x = 0, 0.3, 1.4, 1.6, and 2.0) crystals grown by a self-seeding solidification method. SrCl2−xBrx have been reported to crystallize in some structural types with different local site symmetries depending on the Cl/Br ratio. Taking advantage of this property, we can control the crystal structure and the local Yb2+ site symmetry of SrCl2−xBrx:Yb2+ by changing the compositions and investigate the behaviors of the spin-allowed and spin-forbidden transitions dependent on the local site symmetry. For photoluminescence and scintillation, both spin-allowed and spin-forbidden Yb2+ 5d–4f transitions were observed for SrCl2:Yb2+ with local Oh symmetry and SrCl0.4Br1.6:Yb2+ and SrBr2:Yb2+ with local C4h symmetry, whereas only spin-forbidden Yb2+ 5d–4f transition was observed for SrCl1.7Br0.3:Yb2+ and SrCl0.6Br1.4:Yb2+ with local D2h symmetry. The spin-allowed transitions were observed in crystals with higher local site symmetry. Light yields of SrCl2−xBrx:Yb2+ (x = 0, 0.3, 1.4, 1.6, and 2.0) were (21000 to 71000) photons/MeV. Crystals with higher local site symmetry, which showed the spin-allowed transitions, had relatively high light yields. Among them, SrCl0.4Br1.6:Yb2+ showed a light yield of 71000 photons/MeV, which is higher than those of previously reported Yb2+-doped scintillators, for example, SrI2:Yb2+ (56000 photons/MeV) and CsBa2I5:Yb2+ (54000 photons/MeV).
Feature: Cutting edge research on electroceramics, 2020
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published : vol. 129, no. 7, July 2021
Sou YASUHARA, Shintaro YASUI, Takashi TERANISHI, Takuya HOSHINA, Takaaki TSURUMI and Mitsuru ITOH
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High-speed rechargeable Li ion batteries are in strong demand. Two methods have been reported to improve the high-speed rechargeability of electrodes: reducing particle size and introducing a surface support. However, the effectiveness of the latter could not be directly compared among reports due particle size differences from study to study. Our previous report revealed that Li+ motion under high-speed charge–discharge conditions is accelerated around a surface-supporting material, an electrode, and an electrolyte interface. In this study, we prepared epitaxial LiCoO2 thin films with micropads of various kinds of materials and evaluated the high-speed rechargeability of each.
The 75th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 7, July 2021
Go OKADA
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Radio-photoluminescence (RPL) is a phenomenon whereby a new luminescent centre is generated in a material by the interaction of an ionizing radiation with the medium. Despite the usefulness of RPL, e.g. in radiation measurements, there are only a limited number of RPL materials available today, which limits our understanding of the phenomenon as well as extending its use for new applications. In recent investigations, a large number of new RPL material systems have been proposed for radiation measurements. In particular, Sm-based RPL is one of the most intensively studied alternative systems, which shows RPL properties owing to the intravalence reduction of the Sm ion (Sm3+ → Sm2+) induced by ionizing radiation. The generated Sm2+, as well as Sm3+, acts as a luminescent centre and shows photoluminescence, typically around 700 nm. This approach has enabled us to explore a wider range of material choices and to find a new application of RPL. An example is microbeam radiation therapy (MRT), which requires the measurement of extremely large radiation dose distributions at a microscopic scale. Such a new class of RPL is not only limited to Sm-based materials but also to those doped with other rare earth ions (e.g., Eu and Yb) and undoped materials.
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published : vol. 129, no. 7, July 2021
Teruaki FUCHIGAMI, Yuta SUMIYA and Ken-ichi KAKIMOTO
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Present study showed synthesis of novel type of porous alkali niobate piezoelectric ceramics, and the formation of domains and photocatalytic activity for the porous piezoelectric ceramics were investigated while comparing with dense ceramics to confirm enhancement of domain orientation and photocatalytic activity around pores. Porous Li0.06Na0.47K0.47NbO3 piezoelectric ceramics were synthesized by a template method using polymethylmethacrylate as a pore former agent. Uniform pores with 6 µm in diameter were dispersed in the porous ceramics. Porous ceramics synthesized with 10 vol % of the pore former agent showed piezoelectric voltage coefficient, 29 mVm/N, which is same as that of the dense ceramics. Smaller striped domains formed at an edge of pores on the porous ceramics, indicating that orientation of domains was promoted by electric field concentration around the pores. Through photoreduction reaction of Ag+ ion, local precipitation of Ag was shown around the pores on the poled porous ceramics, whereas Ag was located over an entire surface of unpoled porous ceramics. Highest photocatalytic activity was shown for the poled porous ceramics in photodecomposition test of methylene blue. These results clearly indicated photocatalytic activity was enhanced on ferroelectric domains around pores of porous piezoelectric ceramics.
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published : vol. 129, no. 7, July 2021
Masanori HIRANO, Miki SAKURAI and Hirohide MAKINO
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Aeschynite-type fine crystals of YTiTaO6 and Er3+– and Yb3+-co-doped YTiTaO6 (YTiTaO6:Er3+/Yb3+) were synthesized for the first time using hydrothermal method at 240 °C. The effects of Yb3+ and Er3+ concentrations and heating temperature in air on their crystalline phases were investigated. The images of transmission electron microscope (TEM) and energy dispersive X-ray spectrometry (EDS) elemental mapping showed that their metal cations were dispersed homogeneously in the cube-like crystals in the range of 200–300 nm. A single phase of aeschynite appeared in all of the as-prepared YTiTaO6 and YTiTaO6:Er3+/Yb3+ samples synthesized hydrothermally at 240 °C and samples after heating at 1100 and 1200 °C in air although YTiTaO6 is known to possess euxenite-type structure. The lattice constants of the orthorhombic aeschynite phase decreased slightly according to the Vegard’s law as the concentration of Yb3+ was increased from y = 0 to 0.30 in the Er0.10YbyY0.90−yTiTaO6 system. Under excitation at 270 nm the pure YTiTaO6 showed light blue green and broadband photoluminescence centered at 520 nm. The aeschynite-to-euxenite phase transition occurred completely in the whole Yb3+ concentration range, y = 0–0.30 in Er0.10YbyY0.90−yTiTaO6 and pure YTiTaO6 as a consequence of heating at 1400 °C for 1 h in air.
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published : vol. 129, no. 7, July 2021
Shingo MACHIDA, Ryoya UEDA, Kentaro HIRAYAMA, Toshimichi SHIBUE, Ken-ichi KATSUMATA and Atsuo YASUMORI
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A glass fiber cloth (GFC) with microporosity was prepared upon the suppression of crack generations. After the prepared GFC was heat-treated, it was slowly cooled to room temperature and then subsequently treated with hydrochloric acid. The experimental data through complementary techniques including scanning electron microscopy, nitrogen adsorption/desorption isotherm, solid-state 29Si nuclear magnetic resonance spectroscopy, and elemental analysis revealed the conversion of the slowly-cooled GFC into a microporous solid with no cracks in each glass fiber upon the alkaline leaching by hydrochloric acid. These results clearly indicated the formation of microporous GFC without cracking.
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published : vol. 129, no. 7, July 2021
Haoran WANG, Lichen ZHAO, Xiao YU, Shichang LEI, Yumin QI and Chunxiang CUI
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In order to impart nano hydroxyapatite (HA) more biological functions and develop its potential application in biomedical field, silver modified hydroxyapatite (Ag-HA) nanoparticles were synthesized via sol–gel method. The powders were sintered at 600 °C for 1 h. The microstructures, morphologies and chemical compositions of HA and Ag-HA were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), High resolution transmission electron microscopy (HR-TEM), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). The results indicate that Ag modification has a certain effect on the microstructure, morphology and Zeta potential of HA. The hemocompatibility of HA and Ag-HA with different doses were evaluated by lots of hemolytic tests. The results indicate that pure HA performs non-hemolytic activity at the dose range of 20–2000 µg/cm3. Due to the appearance of Ag, the hemocompatibility of Ag-HA with different Ag concentration show obvious differences. The Ag-HA with concentration of 0.5 mol % Ag (0.5Ag-HA) has better hemocompatibility, its hemolytic ratio is less than 5 % when its usage dose is up to 1000 µg/cm3. But Ag-HA with concentration of 1.0 mol % and 1.5 mol % Ag (1.0Ag-HA and 1.5Ag-HA) show non-hemolytic property only lower doses. The antibacterial ratio of 0.5Ag-HA against Streptococcus mutans is up to 99 % only the dose of 400 µg/cm3. The biological evaluation further confirmed the safe dose of the antibacterial HA nanoparticles for its application in biomedical field.
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published : vol. 129, no. 7, July 2021
Hiroshi IRIE, Masaomi YODA, Toshihiro TAKASHIMA and Junya OSAKI
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Platinum (Pt) was selectively photodeposited onto zinc rhodium oxide (ZnRh2O4) to serve as a hydrogen (H2)-evolution photocatalyst in a silver (Ag)-inserted ZnRh2O4 and bismuth vanadium oxide (Bi4V2O11) solid-state photocatalyst (ZnRh2O4/Ag/Bi4V2O11). The amount of deposited Pt was controlled by the photodeposition time to generate Pt-loaded ZnRh2O4/Ag/Bi4V2O11 (Pt/ZnRh2O4/Ag/Bi4V2O11) containing up to 0.17 wt % of Pt cocatalyst. The prepared Pt/ZnRh2O4/Ag/Bi4V2O11 photocatalysts were able to catalyze the overall pure-water splitting reaction under irradiation with red light at a wavelength of 700 nm and enhanced the stoichiometric evolution of H2 and O2 from water at Pt amounts exceeding 0.12 wt % of Pt. The apparent quantum efficiency of the water-splitting reaction was highest at 0.17 wt % of Pt. In addition to the loading amount of Pt, the loading of Pt as Pt0 (metallic Pt) is crucial for enhancing the water-splitting activity of Pt/ZnRh2O4/Ag/Bi4V2O11.
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published : vol. 129, no. 7, July 2021
Yohei YONEDA, Chie HOTEHAMA, Atsushi SAKUDA, Masahiro TATSUMISAGO and Akitoshi HAYASHI
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All-solid-state batteries using oxide electrolytes are regarded as safe batteries. However, most crystalline oxide solid electrolytes require high-temperature sintering for densification. Oxide electrolytes with high formability, which enable the construction of high-performance batteries, are thus required. In this study, Li4SiO4–Li2SO4 glasses and glass-ceramics were prepared by mechanochemical treatment and subsequent heat treatment at 270 °C to achieve electrolytes with high formability. As the Li2SO4 content was increased, the formability of the electrolyte increased. The 90Li4SiO4·10Li2SO4 glass-ceramic electrolyte with a hexagonal structure (a P63/mmc space group) showed the highest ionic conductivity of 2.2 × 10−6 S cm−1 at 25 °C. In this crystal structure, oxygen anions form a hexagonal close-packed structure, and silicon and sulfur cations randomly occupy the tetrahedral sites formed by oxygen anions. An all-solid-state Li–In/LiNi1/3Mn1/3Co1/3O2 cell using a 90Li4SiO4·10Li2SO4 glass-ceramic electrolyte operated at 100 °C as a secondary battery without high-temperature sintering. These oxide materials are promising solid electrolytes for oxide-type all-solid-state batteries.
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published : vol. 129, no. 7, July 2021
Shingo HIRATA, Aya INOUE, Miki INADA and Junichi HOJO
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Gaseous volatile organic pollutants may be removed from the environment through photocatalysts combined with adsorbents. Herein, a mesoporous SiO2–TiO2/WO3 composite was fabricated by the sol–gel method in order to remove acetaldehyde in the gas phase. TiO2 and WO3 were well-dispersed in the SiO2 matrix. The adsorption-photodecomposition properties of mesoporous SiO2–TiO2/WO3 were evaluated through a three-step kinetic analysis, including direct-decomposition, adsorption, and adsorption-decomposition. The composition of WO3 in the SiO2–TiO2 increased the acidity and improved the affinity between the photocatalyst and acetaldehyde. This effectively enhanced the initial removal rate of acetaldehyde. The atomization of WO3 further improved the affinity between the photocatalyst and acetaldehyde and enhancing the photodecomposition rate constant.
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published : vol. 129, no. 7, July 2021
Sumio AISAWA, Jing SANG, Yuya NITANAI, Hidetoshi HIRAHARA and Eiichi NARITA
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To investigate a dynamic intercalation behavior of organic anions into layered double hydroxide (LDH) interlayer by ion-exchange, a quartz crystal microbalance (QCM) with the Mg–Al LDH thin film immobilized gold disc (LDH/QC) electrode has been used. A stable minute LDH film was prepared by using translucent aqueous sol of LDH containing OH ions and magnesium acetate molecule in the interlayer and immobilized on the gold disc after pretreatment of the surface of the supporting silica electrode with hydrophobic agent. In the kinetic analysis, alkyl sulfates having n-alkyl chain (CnH2n+1, n = 5–12; abbreviated as CnS) were used as guest anions. As the results, the time-dependence on CnS intercalation by ion-exchange with guest OH ions and magnesium acetate molecules was measured in the cases of CnS (n ≥ 7), and the data of C11S and C12S intercalation were successively analyzed using the rate equation based on the reversible pseud first-order reaction. Finally, the instrumental analyses of the LDH films before and after the intercalation of C12S revealed that the organic anions could be intercalated into the LDH interlayer of the LDH/QC electrode in each aqueous solutions.
Note
published : vol. 129, no. 7, July 2021
Hirosuke SONOMURA
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The stability of the LiC6/β-Li3PS4 interface was examined by performing calculations within the density functional theory framework. The calculated adhesion energy of the interface was 4.8 eV·nm−2, indicating that the LiC6(100) and β-Li3PS4(010) surfaces were joined the same strength as the interface with the cathode electrode. Lithium ions were periodically present near the LiC6/β-Li3PS4 interface.
Note
published : vol. 129, no. 7, July 2021
Koji KOYAMA, Seong-Woo KIM and Mamoru YOSHIMOTO
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We examined the influence of diamond-etching conditions on microneedles fabricated by a thermochemical reaction between a Ni film with pinholes and a diamond (100) wafer in an H2 atmosphere. The diamond microneedles fabricated by varying the annealing temperatures and thickness of the Ni film coated on the diamond were characterized by scanning electron microscopy. Relatively uniform and long diamond microneedles, with diameters of about 1 µm and heights of about 20 µm, were obtained by annealing for 6 h at 850 °C. For Ni films thicker than 1 µm, microneedles with inverted conical shape were obtained, whereas those fabricated with thinner Ni films exhibited a conical shape.
Note
published : vol. 129, no. 7, July 2021
Akira SARUWATARI, Kayano SUNADA, Toshihiro ISOBE, Sachiko MATSUSHITA, Takeshi NAGAI, Hitoshi ISHIGURO and Akira NAKAJIMA
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Thin La2Mo2O9 (LMO) films were prepared using wet processing with acetylacetonates as starting materials. After acetylacetonates of La and Mo were dissolved into a mixture of 2-methoxyethanol and acetylacetone, the obtained precursor solution was coated onto Pyrex glass plates by spin coating. Transparent porous LMO thin film was obtained after vacuum ultraviolet light illumination and firing at 500 °C for 1 h in ambient air. The film exhibited antibacterial and antiviral activities that were almost equivalent to those of LMO powder against Escherichia coli, Staphylococcus aureus, bacteriophage Qβ, and bacteriophage Φ6.
The 75th CerSJ Awards for Advancements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 5, May 2021
George HASEGAWA
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Preceramic polymer routes, which produce ceramic products called polymer-derived ceramics (PDCs) from molecular precursors, have been developed as a powerful tool to synthesize reduced ceramics in different morphologies (fibers, coatings and monoliths) for over half a century. In recent years, pore control of porous ceramic monoliths has attracted attention for improving their functionalities, which has driven the preceramic polymer routes to be integrated with other synthetic techniques for porous materials such as templating, foaming, emulsion and phase separation. This article briefly overviews porous PDC monoliths with a special emphasis on those derived from porous preceramic polymer gels which are prepared via the sol–gel process accompanied by spinodal decomposition. Ceramization behaviors of Si- and Ti-based preceramic polymers are highlighted in terms of crystal transition and variation of pore properties in different length scales.
The 75th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
Special Article
published : vol. 129, no. 5, May 2021
Masato MACHIDA
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Heat- and corrosion-resistant catalytic materials are essential in the field of environmental protection and energy production. In this article, recent progress in material research in this field is reviewed based on publications from the author’s research group. In an automotive three-way catalyst (TWC), thermal deactivation by sintering of platinum group metal (PGM) nanoparticles can be suppressed by controlling the interfacial bonding to the surface of the support, which provides an anchoring effect. A similar concept is useful in solar thermochemical cycles to produce clean fuels, which are conducted in a high-temperature and corrosive environment containing sulfuric acid vapor. A further challenge in both applications is the replacement of PGM catalysts by economically viable catalysts. Thermally stable multicomponent transition metal oxides were proposed as a possible candidate for PGM-free TWC. A positive synergy between the different functionalities of metal elements results in high catalytic performance. Molten phases of metal vanadates, which are used for solar thermochemical cycles of sulfur, are another example of PGM-free catalysts. These examples highlight the critical roles of each metal element and their combination for obtaining synergy, which are required to further understand the ways to simultaneously achieve catalytic activity and thermal/corrosion stability.
Full Paper
published : vol. 129, no. 5, May 2021
Yoshihito SHIMABUKURO, Tetsuto WATANABE and Shiro KAMBE
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Although Pb2+ substitution for Bi3+ increases the hole concentration, p, in Pb-substituted Bi-based superconductors, the Pb substitution effect has yet to be studied in detail. Herein the Pb substitution effect on the electronic properties of Bi2201, 2212, and 2223 superconductors is investigated to elucidate the role of Pb on the correlation between p and formal valence, v. Consistent with Mott-Hubbard theory, p increases as v increases in the Pb-free Bi2201 and Pb-free Bi2212 phases. In contrast, p decreases with increasing v for the Pb-substituted Bi2201 phase, which contradicts Mott-Hubbard theory but can be explained by the increase in Pb4+. For the Pb-substituted Bi2212 phase, p increases with increasing v from 2.0 to 2.2, and then remains constant at p = 0.10–0.20 from v 2.2 to 2.63. When v increases from 2.0 to 2.2, the hole is doped at a Cu site, which is the same behavior as that of the Pb-free Bi2212 phase. As v increases from 2.2 to 2.63, the hole is doped in a Pb site and not a Cu one. For the Pb-substituted Bi2223 phase, p decreases with increasing v, and a mixed-valence state between Pb2+ and Pb4+ may coexist. As the v increases, the Pb valence increases and the Cu valence decreases. These results indicate two factors influence p. One is correlated with the substitution of Sr2+ for La3+ or Y3+ for Ca2+, which obeys Mott-Hubbard theory. The other is correlated with the substitution of Pb2+/4+ for Bi3+, which does not obey Mott-Hubbard theory. The results strongly suggest that Pb substitution for Bi does not necessarily dope a hole but decreases the hole concentration.
Full Paper
published : vol. 129, no. 5, May 2021
Hiroki ITO, Akira MIURA, Yosuke GOTO, Yoshikazu MIZUGUCHI, Chikako MORIYOSHI, Yoshihiro KUROIWA, Nataly Carolina ROSERO-NAVARRO and Kiyoharu TADANAGA
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The magnetic and electronic properties of CeOInS2 and their influence on phase transition were analyzed in this study. High-temperature XRD measurements of CeOInS2 revealed that orthorhombic CeOInS2 transformed into tetragonal CeOInS2 at a high temperature of 636 K. The transport properties of CeOInS2 showed semiconducting behavior, with a larger temperature dependence of electronic resistivity in the tetragonal phase compared to that in the orthorhombic phase. Unlike structurally similar Ce(O,F)BiS2 superconductors that show long-range magnetic ordering, CeOInS2 neither exhibited superconductive transition nor long-range magnetic ordering at temperatures between 2 and 300 K.
Full Paper
published : vol. 129, no. 5, May 2021
Yutaka OHYA, Hiroaki KANAOKA, Souma IWATA, Chika TAKAI-YAMASHITA and Takayuki BAN
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The electrical conductivity of porous and high-purity β-Ga2O3 ceramics was measured as a function of oxygen partial pressure, po2, at 700 to 900 °C. In the high po2 range, the conductivity was proportional to about −1/4th power of po2, while in the lower po2 range less than about 10−5 atm its exponent was −0.1 to −0.13. This suggests that different types of defects were formed at high and low po2. The point defect of doubly ionized interstitial gallium ion causes the exponent of −1/4, the same value of the experiment in high po2. When po2 was changed, the electrical conductivity first changed sharply, followed by a slow change, suggesting some migrations and/or formation of crystalline defects, and so on. In the Ga2O3 samples, many dislocations, with density of about 1012 cm−2, were observed. As the source of carriers, line defects, such as dislocations, should be considered as well as point defects.
Full Paper
published : vol. 129, no. 5, May 2021
Yuichi HAMAZAKI and Hiromichi TAKEBE
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The dissolution behavior of calcium aluminosilicate (CAS) glasses with various CaO and Al2O3 concentrations was investigated at 180 °C in NaOH aqueous solutions with an initial pH of 13.2–14.0. A CaO–Na2O–Al2O3–SiO2–H2O (C–N–A–S–H) layer was formed on the immersed glass surface due to the dissolution and penetration of the glass and solution constituents. An excellent alkali durability was achieved by the minimization of Al2O3 addition and a [CaO]/[SiO2] molar ratio of 1.10–1.20 for the glass composition design. The results of the infrared spectroscopy indicated that the C–N–A–S–H layer contained H2O and CO32− species from the ambient atmosphere and consisted of the network structure of SiO4–AlO4 tetrahedra. The hydrothermal reactions between the CAS glasses and NaOH solution promoted the formation of the C–N–A–S–H layer and precipitation of Ca(OH)2 with an immersion time. Stable Al-substituted tobermorite and hillebrandite phases were finally formed on the immersed glass surfaces due to the hydrothermal reactions.
Technical Report
published : vol. 129, no. 5, May 2021
Takashi AKATSU, Masashi UNNO and Tomotsumi FUJISAWA
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Prestress in alumina-strengthened porcelain, caused by the mismatch in thermal shrinkage between the porcelain matrix and alumina particles during porcelain cooling, is estimated using Raman spectroscopy by monitoring the frequency shift of Raman band at 417 cm−1, which is assigned to the A1g vibrational mode of α-alumina. This spectroscopic estimation supports the validity of prestress which is expected to accumulate during porcelain cooling beginning at ∼850 °C.
Full Paper
published : vol. 129, no. 4, April 2021
Son Thanh NGUYEN, Tsuyoshi TAKAHASHI, Ayahisa OKAWA, Hisayuki SUEMATSU, Koichi NIIHARA and Tadachika NAKAYAMA
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In the emerging era of aircraft industry, silicon carbide (SiC) is regarded as an appropriate material for gas turbine engine blades. In order to protect this ceramic component against the oxidation and volatilization in hot steam environments, environmental barrier coating should be utilized. The composite of SiC/Yb2Si2O7–Yb2SiO5 with self-healing ability is a candidate for the top layer of this coating. In this study, the crack-healing behavior of SiC/Yb2Si2O7–Yb2SiO5 nanocomposites is investigated by pre-cracking followed by annealing in oxidizing environments. Comparing to previous studies, the healing time and healing temperature can be reduced to 15 min and 800 °C by increasing the volume fraction of SiC to 20 %. In addition, nanocomposites with both self-healing ability and superior strength were created in this research by combining two types of SiC filler (whiskers and nanoparticulates). The self-healing mechanism in these composites is the SiC oxidation and silicate transformation associated with their volume expansion, which is evidenced by X-ray diffraction and scanning electron microscope. According to the results, the best volume ratio between whisker and nanoparticulate is determined as 1/3.
Full Paper
published : vol. 129, no. 4, April 2021
Yoshihiro KAWAKAMI
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In this paper, the results of evaluating vibration power generation by increasing the area of the BaTiO3 (BT) film formed on a stainless-steel substrate by aerosol deposition (AD) is presented. Fe–Cr–Al-based heat-resistant stainless steel with a thickness of 0.1 mm was used as the substrate. BT films with a thickness of about 10 µm were formed on the substrate of six different shapes with different widths and lengths and BT films were annealed at 1000 °C. Electrodes were formed on the surface of these samples, and the poling process with a voltage of 60 V was applied to prepare samples for evaluation. A weight was attached to the tip of these samples and set up in a cantilever state. A damped vibration under the same stress condition was applied to the BT film by pushing and snapping the tip of samples one time. The generated voltage on the load resistance connected in parallel to the BT film was measured and the generation energy was evaluated. As a result, it was confirmed that the generation energies of the samples with areas of 15 × 3 and 30 × 40 mm2 were 0.17 and 39 µJ, respectively. About 230 times as much energy was obtained by increasing the film area about 20 times. This result indicates that increasing the film area using AD method effectively increases the generation energy.
Note
published : vol. 129, no. 4, April 2021
Susumu NAKAYAMA
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In this study, phosphors based on Srx(La9.2−xTb0.8)(SiO4)6Oα (x = 2, 3, 4, 5, and 6) ceramic powders were prepared and their photoluminescence (PL) spectra were investigated. The phosphors show green emission at approximately 545 nm when excited by 378 nm UV light. X-ray photoelectron spectroscopy suggests that Tb in the Tb3+ and Tb4+ valence states coexist in phosphors at a Tb3+/Tb4+ atomic ratio of unity. [Sr2−x(La,Tb)x]SiOα was confirmed to exist in addition to Srx(La9.2−xTb0.8)(SiO4)6Oα at x = 4, 5, and 6. The PL intensity increased with increasing Sr(x) content, which is considered to be due increasing Srx(La9.2−xTb0.8)(SiO4)6Oα particle size. The strongest PL intensity was observed at x = 6, where the absorptivity, internal quantum efficiency, and external quantum efficiency were 20, 50, and 10 %, respectively.
Note
published : vol. 128, no.11, November 2020
Hiroya OKAZAKI, Ryota KOBAYASHI, Rei HASHIMOTO, Emiko FUKUSHI and Junichi TATAMI
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We successfully fabricated dense aluminum nitride (AlN) ceramics containing AlN whiskers by low-temperature pressureless sintering and evaluated their microstructures, thermal conductivities, and mechanical strengths. Furthermore, the anisotropy of thermal conductivities caused by the orientation of AlN whiskers was also evaluated. The thermal conductivities of the samples measured in parallel and perpendicular to the longer direction of AlN whiskers were 98 and 67 W m−1 K−1, respectively. The bending strengths of the samples without and with AlN whiskers were 147 and 235 MPa, respectively. From the observation of the fracture surface of the samples, AlN whiskers in the samples probably withstand the fracture originating from weak grain boundaries.