Journal of the Ceramic Society of Japan
Online ISSN : 1348-6535
Print ISSN : 1882-0743
ISSN-L : 1348-6535
Current issue
(July)
Displaying 1-23 of 23 articles from this issue
Feature: Cutting edge research on electroceramics, 2021: Preface
Feature: Cutting edge research on electroceramics, 2021: Review
  • Sayuri Okunaka, Yugo Miseki, Kazuhiro Sayama
    2022 Volume 130 Issue 7 Pages 395-402
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Photoelectrochemical (PEC) production of H2 from saltwater over a semiconductor photoelectrode under solar-light irradiation is one of the effective technologies for developing a cost-effective sustainable energy conversion process. However, because saltwater such as seawater contains Cl, O2 and HClO are produced competitively during oxidation reactions by photogenerated holes from electrolytes containing Cl during the photo-electrolysis reaction. HClO is a high value-added chemical used for bleaching, etc., however, it is also an undesirable chemical that accelerates corrosion deterioration of large-scale water splitting systems. Therefore, it is necessary to control selectivity of oxidative O2/HClO production in electrolytes containing Cl over photoelectrodes. In this review, we summarized our recent innovations in selective O2 or HClO production over the visible-light driven BiVO4/WO3 photoanodes by simple modification of metal oxides. Modifications of metal oxides such as MnOx or CoOx via spin-coating onto a photoelectrode could control the selectivity on the O2/HClO production from an aqueous solution containing Cl effectively. In addition, controlling loading conditions such as the loading amount of metal oxides, and calcination temperatures after coating a metal precursor solution enabled us to prepare photoelectrodes that produce O2 or HClO with selectivity of almost 100 % using MnOx or CoOx, respectively, along with maintaining their PEC performance under solar-light irradiation.

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Feature: Cutting edge research on electroceramics, 2021: Full papers
  • Ryusei Ogawa, Shinobu Fujihara, Manabu Hagiwara
    2022 Volume 130 Issue 7 Pages 403-409
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    The effects of dual doping by trivalent and monovalent cations on the thermoelectric properties of CaMnO3−δ ceramics were investigated. Na+ was selected as the monovalent cation, while three rare-earth (R) trivalent cations of La3+, Gd3+, and Dy3+ were used to study the role of their size and mass in the electrical and thermal transport properties. Dense ceramic samples with a nominal composition Ca1−x(R1/2Na1/2)xMnO3 (x = 0.1, 0.2, and 0.3) were fabricated via the conventional solid-state reaction route. Due to the partial evaporation of Na during sintering, the electrical conductivity increased and the Seebeck coefficient decreased with the doping level. Additionally, the dual doping by Na and R ions effectively decreased the thermal conductivity. The comparison of the thermoelectric properties of the samples demonstrated that a smaller and heavier R ion is more effective to obtain a high thermoelectric power factor and a low thermal conductivity. As a result, the sample with R = Dy and x = 0.1 possessed a high dimensionless figure-of-merit (ZT) of 0.11 at 1000 K.

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  • Yukio Suga, Sou Yasuhara, Takaaki Tsurumi, Takuya Hoshina
    2022 Volume 130 Issue 7 Pages 410-415
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    The ferroelectric properties of AgxK1−xNbSi2O7 (x = 0–0.10) single crystals were evaluated to understand the effect of Ag substitution on ferroelectricity in KNbSi2O7. Millimeter-sized plate-like AgxK1−xNbSi2O7 single crystals were fabricated by crystallization of the glass phase. The remanent polarization of AgxK1−xNbSi2O7 decreased with increasing the amount of Ag, meaning that the ferroelectricity of KNbSi2O7 is reduced by Ag substitution. Such a tendency was also confirmed by first-principles calculations for KNbSi2O7 and AgNbSi2O7. The displacement of Nb from the center of gravity of the NbO6 octahedron and the rotation of the NbO6 octahedron around the c-axis were smaller in AgNbSi2O7 than in KNbSi2O7. These may be due to the larger electronegativity and smaller ionic radius of Ag. The similarities between the AgxK1−xNbSi2O7 and AgxK1−xNbO3 were also discussed.

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  • Ken Watanabe, Ayumu Tashiro, Yoshihiro Ichinose, Shinichi Takeno, Koic ...
    2022 Volume 130 Issue 7 Pages 416-423
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Li7La3Zr2O12 (LLZ) has great potential as a solid electrolyte for co-fired all-solid-state Li-ion secondary batteries. However, to realise a solid-state battery using LLZ, the sintering temperature of LLZ should be reduced to one that can suppress the formation of a high-resistance reaction layer at the interface between LLZ and the electrode. In this study, we demonstrate an effective method for reducing the sintering temperature of Li6La3ZrTaO12 by combining partial Bi-substitution for Ta and precise control of the compositional deviation. The intentional tuning of the La deficiency in Li6La3ZrTa0.8Bi0.2O12 (LLZTB0.2) promoted the formation of a liquid phase based on Li2O–Bi2O3 at the grain boundary, resulting in its densification at 775 °C. Furthermore, we fabricated a co-fired all-solid-state half-cell based on an LLZTB0.2 electrolyte attached to a LiCoO2 + LLZTB0.2 composite electrode and a half-cell operated at 60 °C. From these results, it was found that the proposed concept is effective in reducing the sintering temperature of LLZ and is applicable for co-firing an all-solid-state battery.

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  • Yuji Sakurai, Xueyou Yuan, Shinya Kondo, Masahito Yoshino, Takanori Na ...
    2022 Volume 130 Issue 7 Pages 424-428
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Deposition condition of (001)-epitaxial K(Ta0.6Nb0.4)O3 (KTN) films on SrRuO3/SrTiO3 substrates by pulsed laser deposition was optimized. The optimized KTN film showed a saturated ferroelectric hysteresis loop with large withstand electric field, and the paraelectric to ferroelectric phase transition at room temperature (RT). Electro-optic (EO) property was characterized by modulation ellipsometry at RT, showing the maximum EO coefficient rc of 42 pm/V, which is larger than the previously reported value for KTN thin films having the same composition. Our findings show the importance of the precise tuning of deposition condition to achieve the large EO response in KTN films, promoting the potential application as a light modulator in EO devices at ambient temperature in the future.

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  • Tsukasa Katayama, Akira Chikamatsu, Tetsuya Hasegawa
    2022 Volume 130 Issue 7 Pages 429-431
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Double-perovskite GdBaCo2O5.5 epitaxial films were fabricated on SrTiO3(001) substrates. X-ray diffraction and scanning transmission electron microscopy measurements of a 37 nm thick film confirmed the ionic order of Gd and Ba along the out-of-plane direction. The Gd/Ba order was absent within the region 1 nm from the film/substrate interface owing to the migration of Sr ions from the substrate. Unlike the 37 nm thick film, a thin film with a thickness of 10 nm did not show a distinct antiferromagnetic to ferromagnetic (FM) transition, whereas large magnetization was observed at low temperature. This was proposed to be because the cation-disordered phase near the interface was FM, even at low temperatures.

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  • Takanori Mimura, Takao Shimizu, Hiroshi Funakubo
    2022 Volume 130 Issue 7 Pages 432-435
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS
    Supplementary material

    Y-doped TaON films were grown on (001)YSZ and (012)Al2O3 substrates by radio frequency (RF) magnetron reactive sputtering deposition from Ta metal target and Y metal chips under the mixture gases of N2, O2 and Ar gases. Films with various Y content were prepared by changing area ratio of Y/(Y + Ta) of the target. The pure monoclinic phase was obtained for TaON films on both substrates by controlling the partial pressure of N2 and O2 gasses. Crystal structure changed from the monoclinic phase to the orthorhombic one with the lattice parameters of a = 0.518 nm, b = 0.488 nm, and c = 0.504 nm with the increase in Y content in the films. Our results reveal that TaON could be used as a novel mother fluorite-like monoclinic structure to prepare orthorhombic phase.

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  • Shinnosuke Yasuoka, Ryoichi Mizutani, Reika Ota, Takahisa Shiraishi, T ...
    2022 Volume 130 Issue 7 Pages 436-441
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    The thickness dependences of crystal structures and ferroelectric properties were investigated for (Al0.8Sc0.2)N films with thicknesses of 12 to 130 nm deposited on (111)Pt/TiOx/SiO2/(100)Si substrates. The internal structural parameter u, representing the crystal anisotropy of the wurtzite structure, decreased with decreasing film thickness. This was attributable mainly to the in-plane compressive strain originating from the larger atomic distance of (Al0.8Sc0.2)N film compared to that of the underlying Pt layer. Well-saturated Pr values were obtained at room temperature for the films down to 20 nm in thickness. The Pr value of the 12-nm-thick film tended to saturate against the electric field when the measurement temperature increased to 150 °C. These Pr values are considerably higher than those of conventional ferroelectric materials such as Pb(Zr,Ti)O3 and HfO2-based films in the thickness region below 20 nm. The Pr value tended to increase for film thicknesses below 50 nm. This originated from the increase in crystal anisotropy with decreasing film thickness due to the strain from the underlying Pt layers. Moreover, the significantly large Pr values of these strained films were larger than the expected values of pure AlN and were in good agreement with the theoretically calculated predictions based on the crystal anisotropy, u parameter. This suggests that the Pr values of (Al,Sc)N can be controlled mainly by the u parameter.

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  • Yuichi Sakuda, James R. Hester, Masatomo Yashima
    2022 Volume 130 Issue 7 Pages 442-447
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS
    Supplementary material

    Oxide-ion conductors based on hexagonal perovskite-related oxide Ba7Nb4MoO20 have attracted much attention due to high oxide-ion and proton conductivities and potential applications in many electrochemical devices such as solid oxide fuel cells (SOFCs). Herein, we report simultaneous improvement of oxide-ion conductivity and suppression of proton conductivity by Cr6+ doping in Ba7Nb4MoO20. New materials Ba7Nb4−xCrxMoO20+x/2 (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5) were synthesized. It was found that Ba7Nb3.8Cr0.2MoO20.1−δ (δ is the amount of oxygen deficiency in Ba7Nb3.8Cr0.2MoO20.1−δ) exhibits high oxide-ion conductivity of 1.6 × 10−3 S cm−1 at 508 °C and 1.1 × 10−2 S cm−1 at 904 °C in static air and low proton transport number under wet conditions. Ba7Nb3.8Cr0.2MoO20.1−δ also shows wide electrolyte domain in the oxygen partial pressure P(O2) regions from 1 to 2.2 × 10−27 atm (304 °C) and 1 to 1.5 × 10−26 atm (604 °C), indicating extremely high chemical and electrical stability. The structure analyses have shown that Ba7Nb3.8Cr0.2MoO20.1−δ is a hexagonal perovskite related oxide at 22 and 800 °C. The refined crystal structure of Ba7Nb3.8Cr0.2MoO20.1−δ has oxygen-deficient cubic (c′) close-packed Ba(O1)2−y(O5)z layer where y is the amount of oxygen vacancy at the tetrahedral O1 site and z is the amount of interstitial octahedral oxygen at the O5 site. The Cr bond valence sum indicates an oxidation number of +6: Cr6+. The Cr6+ cation is located at a crystallographic site near the c′ layer, which leads to the excess oxygen and high conductivity, and is likely to suppress the proton conduction. Maximum-entropy method (MEM) analyses have demonstrated that oxide ions two-dimensionally migrate through the lattice O1 and interstitial O5 sites in the c′ layer via the interstitialcy diffusion mechanism at 800 °C, which enables the high oxide-ion conduction. Cr6+ doping in various hexagonal perovskite-related oxides would be a new strategy for the simultaneous improvement of oxide-ion conductivity and suppression of proton conduction.

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  • Naohiro Tomiyama, Sou Yasuhara, Takaaki Tsurumi, Takuya Hoshina
    2022 Volume 130 Issue 7 Pages 448-451
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    An oxide solid electrolyte with high Li-ion conductivity is in strong demand to improve the safety of all-solid-state Li-ion batteries. However, only a limited number of crystal structures have been reported as solid electrolytes due to the difficulty of exploring superior solid electrolytes. In this study, we focused on a corundum-related structure of a LiNbO3-type one in LiNbO3 because a corundum-type structure was previously reported as an anode material. A LiNbO3–Al2O3 system was synthesized via a conventional solid-state reaction, and its crystal structure and ionic conductivities were evaluated. The substitution of Al2O3 into LiNbO3 was revealed by X-ray diffraction results, and the substitution limit of Al2O3 was 40 mol % to LiNbO3. AC impedance measurements showed an enhancement of ionic conductivity of LiNbO3, with 1.5 × 10−5 S/cm as the highest value.

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  • Kota Hasegawa, Takao Shimizu, Naoki Ohashi
    2022 Volume 130 Issue 7 Pages 452-457
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS
    Supplementary material

    The density functional theory (DFT) was employed to understand the ferroelectric behaviors of wurtzite (WZ)-type aluminum nitride (AlN). To explain the decrease in the coercive field (Ec) due to lattice deformation, the total energy and enthalpy of the strained WZ phase were compared to those of the non-polar (NP) phase, which acted as a transition state during polarity switching. The shrinkage of the c-axis length and elongation of the a-axis length were favorable for reducing Ec. In addition, the calculated residual stress in the transient NP phase was as high as 30 GPa, suggesting that such a high residual stress may be related to the polarity switching behavior under a very high electric field.

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  • Mizuki Watanabe, Honoka Takahashi, Kazuyoshi Uematsu, Mineo Sato, Taka ...
    2022 Volume 130 Issue 7 Pages 458-463
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    All-inorganic halides exhibit excellent optical as well as luminescence properties. Among them, non-toxic copper-doped halide Cs2ZnCl4 with high stability is a promising material. However, the conventional method for preparing these materials, using the hot injection technique, is unsuitable for mass production. Therefore, herein, we suggest a simple and low-temperature (below 100 °C) method without using special equipment, regents, and treatments. Cu-doped Cs2ZnCl4 was successfully synthesized using the water-assisted solid-state reaction (WASSR) method, and the oxidation state of Cu in the samples was estimated through the iodometric titration technique. The optical and luminescence properties were investigated using the absorption and photoluminescence excitation/emission spectra. Significantly, Cu-doped Cs2ZnCl4 exhibited unique green emission centered at ∼520 nm under ultraviolet irradiation. Moreover, the oxidation of Cu in the Cs2ZnCl4 lattice was suppressed owing to the low-temperature conditions in the WASSR.

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  • Haruki Zayasu, Takahiko Kawaguchi, Hiroki Nakane, Nobuyoshi Koshida, K ...
    2022 Volume 130 Issue 7 Pages 464-470
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Epitaxial growth of yttria-stabilized zirconia (YSZ) thin film on through-hole-type porous silicon [tht-PSi(001)] with vertical pores penetrating from the surface to the back side of the Si(001) substrate was achieved. The in-plane and out-of-plane lattice parameters of YSZ thin film deposited on the tht-PSi(001) were, respectively 0.5167 and 0.5124 nm. Therefore, 0.54 % tensile strain was applied to the YSZ thin film. Also for this work, an all epitaxially grown thin film of YSZ/La0.7Sr0.3MnO3(LSMO)/CeO2/YSZ/Si(001) was prepared. The out-of-plane lattice parameter of YSZ was 0.5145 nm. Therefore, the YSZ thin film of YSZ/LSMO/CeO2/YSZ/Si(001) is almost relaxed, with a small amount of tensile strain (0.12 %). In-plane and out-of-plane electrical properties were measured respectively for YSZ/tht-PSi(001) and YSZ/LSMO/CeO2/YSZ/Si(001) thin films. Results show that ionic conduction was confirmed at 400 °C through constant electric conductivity against the change of oxygen partial pressure (pO2). Enhanced ionic conduction was observed for epitaxial YSZ/tht-PSi(001) thin films measured along the in-plane direction. Such enhanced ionic conduction was not observed for epitaxial YSZ/LSMO/CeO2/YSZ/Si(001) thin films measured along the out-of-plane direction. These findings suggest that enhanced ionic conduction is correlated with tensile strain in YSZ thin films.

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Regular Issue: Special Article-Academic Achievements: The 76th CerSJ Awards for Academic Achievements in Ceramic Science and Technology: Review
  • Hiromichi Ohta
    2022 Volume 130 Issue 7 Pages 471-476
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Thermoelectric energy conversion attracts increasing attention as a technology for effectively reusing waste heat. Although thermoelectric materials that show a good thermoelectric figure of merit (ZT) have been proposed thus far, they are not practical at all because they are thermally and chemically unstable and composed of toxic elements. In order to address this issue, the author focused on metal oxides as thermoelectric materials that are thermally and chemically stable and non-toxic, and succeeded in significantly improving thermoelectric ZT by using two-dimensional electron gas and elemental substitution. In 2007, the author focused on Prof. Dresselhaus’s theory that “by confining carriers in a quantum well thinner than the thermal de Broglie wavelength, the thermoelectric power can be greatly enhanced without lowering the conductivity”, and the oxide superlattice was introduced. In 2010, the author demonstrated a field-effect transistor structure on an insulator SrTiO3 crystal and measured thermopower while inducing 2DEG with a thickness of 2 nm by applying a voltage, similar to an artificial superlattice. It was discovered that the thermoelectric field can be increased 5 times as much as the bulk ratio. Furthermore, in 2020, the author found that the Ba1/3CoO2 thin film with a layered crystal structure had the highest room temperature ZT of 0.11 among metal oxides.

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Regular Issue: Full papers
  • Chang Fa, Zhang Jungui, Lu Shijia, Guo Keke, Dai Pinqiang, Liu Chao, Z ...
    2022 Volume 130 Issue 7 Pages 477-486
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    Advance online publication: June 22, 2022
    JOURNAL FREE ACCESS

    High-entropy alloys (HEAs) hold promise for achieving excellence performance due to unconventional composition and structure. In this paper, the effect of FeCoCrNiAl HEAs as binder instead of Co on the microstructure of WC cemented carbide was investigated. The isothermal oxidation resistance of the WC-HEAs cemented carbides with 6, 10, 15 % was studies at 700, 800, 900 and 1000 °C. The results revealed that the microstrcture of WC-HEAs cemented carbides was dense, and the average grain sizes of WC decreased with the increase of HEAs binder content. The oxide layers containing WO3, NiWO4, and a small amounts of MWO4 (M = Co, Cr) were formed after high-temperature oxidation of WC-HEAs cemented carbides, the ratio of MWO4-to-WO3 in the WC-HEAs oxide layer increases gradually as oxidation temperature increase. The oxide films thickness of WC-10HEAs cemented carbides became thinner than that of WC-10Co at 900 °C. The oxidation kinetic curves also demonstrated that the oxidation resistance of the WC-HEAs cemented carbides was better than that of WC-Co cemented carbide except that the binder content was 6 %, and the oxidation resistance of the WC-HEAs cemented carbide was superior to WC-Co cemented carbide, which was attributed to the formation of protective oxides and MWO4 tungstate.

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  • Qing Qin, Yoshio Hasegawa, Toshimitsu Tetsui
    2022 Volume 130 Issue 7 Pages 487-492
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    The development of a basic process for the mass production of continuous zirconia fibers with a tensile strength of more than 2 GPa is being extensively researched. It is expected that the use of oxide/oxide composites will improve the performance of jet engines. In this study, continuous zirconia fibers with diameters and crystal sizes below 10 µm and 10 nm, respectively, were synthesized using a dry-spinning method by employing molecular-designed precursor polymers. In addition, strength-enhancing fibers were developed by improving the precursors, solvents, and infusibilization/sintering conditions. The properties of the fibers were investigated via scanning electron microscopy, X-ray diffraction, and mechanical tensile tests. Furthermore, the application of the as-prepared materials as reinforcements for ceramic matrix composites is presented.

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  • Xiaofeng Yuan, Yixuan Wei, Hongliang Liu, Pengpeng Chang, Ying Zhou, Q ...
    2022 Volume 130 Issue 7 Pages 493-497
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    The high-k [(K0.5Bi0.5)xBi1−x](WxV1−x)O4 (0 ≤ x ≤ 0.1) ceramic was prepared via the modified solid-state reaction method. When x = 0.1, the monoclinic scheelite structure was obtained at low sintering temperature. However, when x = 0.2, the impurity phase was found. After being sintered at 650 °C for 6 h, the [(K0.5Bi0.5)0.1Bi0.9](W0.1V0.9)O4 ceramic possesses the best properties with a relative permittivity of 78.7, Q × f value of 7210 GHz and a temperature coefficient of +163 ppm/°C at the frequency of 4.11 GHz. Compared with the result of the pure BiVO4 ceramic, the sintering temperature dropped from 740 to 650 °C and the relative permittivity was increased from 67.8 to 78.7. Due to the high relative permittivity and the low sintering temperature, the [(K0.5Bi0.5)0.1Bi0.9](W0.1V0.9)O4 ceramic is potential to realize the miniaturization in communication application.

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  • Takuma Takayanagi, Akira Nasu, Fumika Tsuji, Kota Motohashi, Atsushi S ...
    2022 Volume 130 Issue 7 Pages 498-503
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS
    Supplementary material

    For the practical application of all-solid-state batteries, it is necessary to improve the performance of the solid electrolytes. We previously reported the fabrication of Na2.88Sb0.88W0.12S4, which showed the highest ionic conductivity among Na+ conducting sulfide solid electrolytes. In this study, we focused on the anion substitution of Na2.88Sb0.88W0.12S4 and evaluated oxygen substitution. Samples of Na2.88Sb0.88W0.12S4−xOx (0 ≤ x ≤ 0.5) were fabricated by a mechanochemical process and subsequent heat treatment, and structural analysis and electrochemical evaluation were performed. The solid solution of oxygen was found to proceed in the range of x ≤ 0.3. The oxygen substitution decreased the ionic conductivity, but it maintained a high ionic conductivity of more than 10−3 S cm−1. The reduction tolerance was improved by the oxygen substitution based on cyclic voltammetry measurements. An all-solid-state Na–Sn/TiS2 cell using the Na2.88Sb0.88W0.12S3.7O0.3 electrolyte operated at room temperature.

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  • Takuya Aoyagi, Yohei Onodera, Shinji Kohara, Takashi Naito, Toshiaki I ...
    2022 Volume 130 Issue 7 Pages 504-508
    Published: July 01, 2022
    Released on J-STAGE: July 01, 2022
    JOURNAL FREE ACCESS

    Achieving both high water durability and low glass transition temperature is crucial for the practical use of low-melting glass in hermetic sealing. In Ag2O–V2O5–TeO2 glass, we found that the increase in Ag2O content lowers glass transition temperature and improves water durability. Furthermore, the reason for the improvement of water durability is considered to be due to the increase in the coordination number of oxygen atoms around vanadium ions without the change in oxidation state, as shown by X-ray absorption fine structure measurements. We demonstrate that a Ag2O–V2O5–TeO2 glass is a key glass system for low-temperature hermetic sealing.

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