最新コンテンツ

Full Paper
published : vol. 127, no.12, December 2019
Yohei ONODERA, Shinji KOHARA, Shuta TAHARA, Atsunobu MASUNO, Hiroyuki INOUE, Motoki SHIGA, Akihiko HIRATA, Koichi TSUCHIYA, Yasuaki HIRAOKA, Ippei OBAYASHI, Koji OHARA, Akitoshi MIZUNO and Osami SAKATA
MORE
The structure of glassy, liquid, and amorphous materials is still not well understood, due to the insufficient structural information from diffraction data. In this article, attempts are made to understand the origin of diffraction peaks, particularly of the first sharp diffraction peak (FSDP, Q1), the principal peak (PP, Q2), and the third peak (Q3), observed in the measured diffraction patterns of disordered materials whose structure contains tetrahedral motifs. It is confirmed that the FSDP (Q1) is not a signature of the formation of a network, because an FSDP is observed in tetrahedral molecular liquids. It is found that the PP (Q2) reflects orientational correlations of tetrahedra. Q3, that can be observed in all disordered materials, even in common liquid metals, stems from simple pair correlations. Moreover, information on the topology of disordered materials was revealed by utilizing persistent homology analyses. The persistence diagram of silica (SiO2) glass suggests that the shape of rings in the glass is similar not only to those in the crystalline phase with comparable density (α-cristobalite), but also to rings present in crystalline phases with higher density (α-quartz and coesite); this is thought to be the signature of disorder. Furthermore, we have succeeded in revealing the differences, in terms of persistent homology, between tetrahedral networks and tetrahedral molecular liquids, and the difference/similarity between liquid and amorphous (glassy) states. Our series of analyses demonstrated that a combination of diffraction data and persistent homology analyses is a useful tool for allowing us to uncover structural features hidden in halo pattern of disordered materials.
Express Letter
published : vol. 127, no.12, December 2019
Rifki SEPTAWENDAR, Ahmad NURUDDIN, Lia Amelia TRESNA WULAN ASRI, Muhammad Rizqi ABDULLAH, Damar Rastri ADHIKA, Eneng MARYANI and Bambang Sunendar PURWASASMITA
MORE
Zirconia nanorods have been successfully synthesized from local zircon-based Zr(OH)4 precursors through a facile precursor-templating method assisted by sugarcane bagasse based-nano cellulose as the one-dimensional (1D) structure directing template. However, the 1D structure arrangement of the zirconia precursors by the cellulose template during synthesis undergoes at selective precursor pHs. The final products of zirconia consist of the t-metastable and the m-phases, exhibit microstructures of nanorods and elongated agglomerates, and reveal large specific surface areas.
Full Paper
published : vol. 127, no.12, December 2019
Xianrui ZHAO, Dunwen ZUO, Mengxian ZHANG, Yihang FANG, Qiangyong ZHANG, Zhengyu ZHU, Guixiang LIU and Feng XU
MORE
The phase formation mechanism of Ti(C,N)–TiB2–Co composite cermets during the reactive hot-pressing process was investigated by delicate microstructure and phase analysis of Co–Ti–C–BN powder compacts sintered at different temperatures. The results showed that Ti–BN and Co–Ti solid diffusion reactions occurred. As the sintering temperature was increased 1020°C, Co–Ti liquid was formed by the eutectic reaction between Ti and the preformed CoTi2. Subsequently, TiB combined with B to yield TiB2 through the mass transfer of liquid, whereas Ti0.3N and Ti2N gradually transformed into TiN. With increasing sintering temperature, Ti(C,N) was fabricated by the diffusion of C into TiN unit cell, and B reacted with Ti affording TiB2. High-density submicron Ti(C,N)-based cermets could be synthesized at low temperatures due to the formation of Co–Ti liquid at 1020°C and an applied pressure of 34 MPa. The Ti(C,N)–TiB2–Co composite cermets prepared at 1150°C possessed the optimum relative density, average particle size, hardness, and fracture toughness of 99.8%, 0.571 µm, 1947 HV10, and 6.6 MPa·m1/2, respectively. Moreover, the dry friction and wear resistance of Ti(C,N)–TiB2–Co composite cermets is 2.5 times higher than that of YT15 cemented carbide.
Full Paper
published : vol. 127, no.12, December 2019
Qilong GUO, Caio V. JUVENCIO DA SILVA, Mei LIN, Sijun LUO, Junjun PEI, Xiaoqing WANG, Junguo LI and Lianmeng ZHANG
MORE
ZrB2/ZrAlC composite ceramics were successfully synthesized from Zr, Al, graphite and ZrB2 powders by using a spark plasma sintering method. The volume content of ZrAlC has a major impact on the fracture toughness. ZrAlC-rich (≥70 vol.%) composite ceramics exhibit much higher fracture toughness than do ZrB2-rich (≥60 vol.%) composite ceramics. The evidently larger ZrAlC grains in the ZrAlC-rich composite ceramics lead to a longer crack propagation path for toughening. Both the Vickers hardness and Young’s modulus of composite ceramics increase slightly with an increase in the ZrB2 volume content. The evident oxidation of composite ceramics at 1000°C results in the formation of Al18B4O33 and Al4B2O9. At 1200°C, the composite ceramics exhibit a fluffy and porous top oxidized layer composed of whiskers of Al18B4O33 and Al4B2O9 grains, and the thickness of the oxidized layer and oxidation mass gain increase with an increase in the ZrAlC volume content. The ZrB2-rich composite ceramics with less than 40 vol.% ZrAlC content do not exhibit apparently larger oxidation mass gain than does the pure ZrB2 ceramic after oxidation at 1200°C and higher temperatures. The composition-dependent microstructure and properties provide a comprehensive insight for the development of high-temperature composite ceramics based on ZrAlC and ZrB2.
Full Paper
published : vol. 127, no.12, December 2019
Yuuki ONO, Tomohiro HARADA, Hiroyuki SHIMIZU, Yutaka DOSHIDA, Tsuyoshi HONMA and Satoshi TANAKA
MORE
Crystal orientation is a strategy for the improvement of piezoelectric properties of lead-free piezoelectric materials. [101]-Oriented Li-modified (Na,K) NbO3 ceramics (LNKN) were fabricated using a colloidal method under a strong magnetic field, sintering, and subsequent electrical poling. For the Li0.06Na0.52K0.42NbO3 powder compact, which has a monoclinic phase at room temperature, the (-101) planes were oriented perpendicular to the magnetic field. Although the monoclinic phase transitioned to tetragonal and cubic phases above the Curie temperature during sintering, the crystal-oriented structure was maintained and developed even after phase transitions and grain growth during sintering. Furthermore, crystal reorientation was enhanced by domain switching under an electric field. Thus, [101]-oriented LNKN ceramics with a tetragonal crystal system were obtained. The piezoelectric d33 constant was improved to 208 pC/N from 112 pC/N due to the effects of electromechanical coupling coefficient and specific dielectric coefficient by the texturing process with magnetic field assisted shaping, sintering, and electrical poling.
Full Paper
published : vol. 127, no.12, December 2019
Mizuki ITO and Tomoaki WATANABE
MORE
CuFeO2 is a prospective photocathode material for water or CO2 reduction, but satisfactory performance has not been achieved yet. This has been ascribed to the large size of the CuFeO2 particles obtained by growing a CuFeO2 film on an Fe substrate when using hydrothermal method for enhanced adhesion between film and substrate. This study evaluates the effect of adding oleic acid or acetic acid as surfactants in the hydrothermal fabrication process with the expectation of controlling the crystal growth. The investigation of the shape and the size of the obtained CuFeO2 particles by scanning electron microscopy and X-ray diffraction and the evaluation of the photoelectrochemical performance of the CuFeO2 photoelectrodes by electrical conductivity and photoelectrochemical measurements demonstrate that, although an increase in the particle surface area can be achieved, the performance is highly affected by the grain boundary resistance.
Full Paper
published : vol. 127, no.12, December 2019
Shuichi FUNAHASHI, Eigo KOBAYASHI, Masahiko KIMURA, Kosuke SHIRATSUYU and Clive A. RANDALL
MORE
A new chemical strategy using a specific chelate complex for the recently introduced “Cold Sintering Process” (CSP) shows the ability to obtain high densification in spinel-based ceramics. CSP is the technique for sintering many kinds of ceramics at low temperatures, no more than 300°C, enabled with a transient solvent. However, spinel ceramics are one of the most difficult materials, in which CSP typically does not achieve high densities. The chelating agent was introduced to aid the sintering of spinel-based ceramics that include important spinel materials, such as Ni–Cu–Zn ferrite and Ni–Mn thermistor. Chelate complex assisted CSP aids our basic tool box for enabling the CSP mechanism, and points to the potential of applying this approach to an even broader group of ceramic structures and chemistries.
Full Paper
published : vol. 127, no.12, December 2019
Ichiro FUJII, Kentaro HIRAI, Takahito IMAI and Takahiro WADA
MORE
The effect of Bi2O3 content on the crystal structure, microstructure, and optical and electric properties of [Li0.05(K0.5Na0.5)0.95]NbO3 + x wt %Bi2O3 ceramics was investigated. These ceramics were fabricated using a conventional pressure-less sintering, and were observed to be opaque at x = 0 and 3 but transparent at x = 5 and 7. The transmittance at an infrared wavelength of 1310 nm was 68 and 62% at x = 5 and 7, respectively. At x = 5, a high Curie temperature of 365°C, a ferroelectric polarization–electric field loop with a reduced remanent polarization, and a quadratic electro-optic effect of 3.1 × 10−17 m2/V2 were observed. The effective linear electro-optic effect (Δn/Eπ) was calculated by the birefringence (Δn) divided by a half-wave electric field (Eπ) of 43.2 kV/cm. This value was equal to 146 pm/V, which was higher than the linear electro-optic effect of previously reported (K,Na)NbO3-based transparent ceramics and a LiNbO3 single crystal. However, it was lower than that of a K(Ta,Nb)O3 single crystal and (Pb,La)(Zr,Ti)O3 transparent ceramics.
Full Paper
published : vol. 127, no.12, December 2019
Yoshiko HIGASHI and Eiichi KOGA
MORE
Nonlinear electrical properties of individual grain boundaries in SrCoO3-doped ZnO varistor ceramics are investigated using a nano-prober system. In particular, the effect of post-annealing is clarified for them after sintering in a reducing atmosphere is studied. The nonlinear characteristics are enhanced by annealing in air at above 600°C. The resulting characteristics attributed to an increase of p-type carrier concentration in SrCoO3 phase at grain boundaries. By annealing at a higher temperature (e.g., 800°C), the grain boundaries possess nonlinear characteristics similar to conventional Bi-doped ZnO varistors, as well as bulk-bodies.
Full Paper
published : vol. 127, no.12, December 2019
Hoang Tuan TONG, Nobuhiko NISHIHARAGUCHI, Takenobu SUZUKI and Yasutake OHISHI
MORE
We experimentally demonstrate for the first time a successful fabrication of a new tellurite hollow core optical fiber which has 6 non-touching air holes in the cladding. This is because it is known from the simulation that when the two nearby cladding air-holes connect to each other, the confinement loss in the core will be high. New tellurite glass is developed to improve the optical and thermal properties and the light transmission properties from 0.4 to 2.4 µm are studied experimentally. In addition, the calculation shows that high transmission bands and low transmission bands which locate alternately in the measured transmission spectrum correspond to the effects of resonant reflection and anti-resonant reflection.
Full Paper
published : vol. 127, no.12, December 2019
Hirokazu MASAI, Masanori KOSHIMIZU, Hiroki KAWAMOTO, Takahiro OHKUBO, Akitoshi KOREEDA, Yasuhiro FUJII, Koji OHARA, Hironori OFUCHI and Hiroyuki SETOYAMA
MORE
X-ray absorption near-edge structure (XANES) spectroscopy is one of the most effective techniques for determining the valence states of cations. Since K- and L-edge transition processes are different, the validity of X-ray irradiation to evaluate these excitation processes must be determined. In this study, we focus on the valence states of silver cations in aluminophosphate glasses, whose compositions have been used as radiophotoluminescence (RPL) glass detectors for personal monitoring. Slight difference was observed between the Ag K-edge XANES spectra of reference materials and those of experimental samples. It is also challenging to detect spectral changes due to the coloration of Ag-doped glass. However, absorption edge shifts depending on the valence state were observed in Ag L3-edge XANES spectra. We found that additional absorption bands, whose peak intensities increase with increasing irradiation doses, were generated at lower absorption energies during the measurement. The degrees of change in absorption intensities depend on the chemical composition of the sample. Considering the nature of the RPL glass detector, we assumed that the species generated are related to the Ag2+ species, which is an activator after irradiation.
Full Paper
published : vol. 127, no.12, December 2019
Jiangfeng LI, Baijun YAN, Zijia CHENG and Tengfei DENG
MORE
The solid wastes Red mud and fly ash were used as the raw materials in the production of thermal storage ceramics. Red mud was used to lower the firing temperature and fly ash powders were introduced to improve the mechanical properties. The physical properties of samples, including firing behavior, thermal storage properties and thermal shock resistance were evaluated. Also, the effects of fly ash and red mud on the properties of ceramics were investigated. The results showed that the thermal shock resistance of the sample improved by the addition of fly ash powders in the preparation of thermal storage ceramics. Besides, the addition of red mud promoted the formation of liquid phase. In particularly, sample R3 (40 wt % fly ash, 15 wt % clay shale, 20 wt % feldspar, 25 wt % quartz and addition of 15 wt % red mud) fired at 1140°C exhibited the best performance, in which the open porosity, bulk density, bending strength, thermal conductivity at 500°C and theoretical heat storage density (room temperature-500°C) were 0.37%, 2.54 g/cm3, 89.81 MPa, 3.62 W/(m·K), 1.56 KJ/cm3, respectively. Despite the bending strength of R3 sample fired at 1140°C decreased by 20.29% after 30 thermal shock cycles, it still maintained a flexural strength of 73.78 MPa.
Full Paper
published : vol. 127, no.12, December 2019
Hirosuke SONOMURA, Tomoatsu OZAKI, Kazuaki KATAGIRI, Yasunori HASEGAWA, Tsutomu TANAKA and Atsushi KAKITSUJI
MORE
Dissimilar welds between Al2O3 and AZX612-Mg alloy were obtained easily by a friction stir spot welding method with a machining center and a drilling machine. We analyzed the interface with scanning transmission electron microscopy energy dispersive X-ray spectrometry. The results suggested that the rotating tool induced the diffusion of Mg and Ca from the AZX612-Mg alloy, which reacted with Al2O3, forming Mg, Al, and Ca compounds and creating a strong welding interface at low temperatures.
Full Paper
published : vol. 127, no.12, December 2019
Michito KISHI, Masaki TANAKA and Takamasa MORI
MORE
The effect of slurry preparation for polymer electrolyte fuel cells on the electrode performance has been investigated in this work. The amount of ionomer adsorbed onto Pt–C powder increases when water is used as a solvent; however, the size of non-adsorbed ionomer particles increases as well, resulting in a larger gas permeation resistance. Meanwhile, increasing the ethanol-to-water mass ratio in a mixed solvent decreases the ionomer size. Therefore, an improved two-step slurry preparation procedure utilizing the irreversibility of the ionomer adsorption onto Pt–C powder has been investigated. In this method, (1) Pt–C powder is mixed with ionomer in water to maximize its adsorbed fraction, after which (2) ethanol is added to the prepared slurry to minimize the size of non-adsorbed ionomer. As compared with the conventional one-step synthesis method, the developed two-step preparation procedure enhances the electrode performance without changing its composition.
Full Paper
published : vol. 127, no.12, December 2019
Md SAIDUZZAMAN, Shuto WANI, Takahiro TAKEI, Sayaka YANAGIDA, Nobuhiro KUMADA, Ichiro FUJII, Satoshi WADA, Chikako MORIYOSHI and Yoshihiro KUROIWA
MORE
A pyrochlore-type compound, Sn0.34Bi1.52Ti1.86Sn0.14O6.62, was synthesized using a solid-state reaction in a N2 atmosphere. The crystal structure was refined using the synchrotron powder X-ray diffraction data. This compound comprised mixed-valence states Sn2+ and Sn4+. The morphology of this compound was irregular shapes with particle size approximately 1–5 µm. The band gap of this compound was estimated to be 2.83 eV from the ultraviolet–visible spectrum. The dielectric constant of this compound was 78 under 100 Hz frequency and weak photocatalytic activity for methylene blue degradation under visible light irradiation.
Note
published : vol. 127, no.12, December 2019
Yuki OBUKURO, Toru OKAWARA and Tetsuya OKUYAMA
MORE
The electronic structure of Er-doped monoclinic ZrO2 was investigated by the generalized gradient approximation (GGA), GGA plus on-site Coulomb interaction (GGA + U) calculation, and modified Becke-Johnson (MBJ) exchange potential calculation. In the GGA calculation, the minimum bandgap energy of ZrO2 was estimated to be 3.74 eV. The valence band was mainly composed of O 2p states, which strongly hybridized with the Zr 4d states. The conduction band was composed of Zr 4d and O 2p states. When an Er atom replaced one of the Zr atoms, seven-fold Er 4f states appeared in the forbidden gap of ZrO2. Considering the spin–orbit coupling, the energy positions of the seven-fold Er 4f states in the forbidden gap hardly changed. Based on the GGA + U calculation, the Er 4f states shifted to the lower energy direction and entered into the valence band of ZrO2 with an increase in the U parameter. In addition, the MBJ calculation gave similar results using a small U parameter in the valence band energy region, while the conduction band region is similar to the GGA + U calculation result with a large U parameter. Based on these results, we concluded that the GGA calculation is the most appropriate to describe the position of Er 4f states in the bandgap of Er-doped ZrO2 phosphors among the three kinds of calculation methods examined in the present study.
Note
published : vol. 127, no.12, December 2019
Masayoshi OHASHI, Yumiko MIYAKE, Junzaburou ONO and Fukue NAGATA
MORE
Tantalum(V) nitride (Ta3N5) pigment have attracted considerable attention as an alternative candidate for the colors of the cadmium base. The improvement of chroma of the pigment is necessary to raise the charm as the color. In this study, the Ta3N5 pigment was prepared by heat-treatment for mixed powders of Ta(V) oxide, aluminum nitride and potassium fluoride in nitrogen gas which kept supplied during the synthesis until it got cooled to room temperature. The pigment prepared in such completely inert atmosphere had slightly dull color. However, the chroma of the pigment was largely improved by a subsequent low-temperature oxidation treatment.