We report the properties of CsCaCl₃, storage phosphors doped with Eu, Ce, or Cu. Both doped and undoped CsCaCl₃ samples were synthesized as ceramics. For undoped CsCaCl₃, thermally stimulated luminescence (TSL) spectrum showed a broad band around 360–390 nm, and optically stimulated luminescence (OSL) spectrum exhibited the same band with a shoulder near 320 nm. These bands were attributed to different kinds of defects or impurities. The OSL and TSL spectra of Eu-doped CsCaCl₃ showed a band around 440 nm arising from the 5d–4f transition of Eu²⁺. The Ce-doped CsCaCl₃ showed the OSL and TSL bands originating from the 5d–4f transition of Ce³⁺. An intense band at 345 nm appeared in the OSL spectrum of Cu-doped CsCaCl₃ due to Cu⁺, and an additional peak at 430 nm was ascribed to Cu⁺ ion perturbed by OH⁻ ion. On the other hand, the TSL spectrum of Cu-doped CsCaCl₃ had a peak around 470 nm and it was assigned to Cu²⁺. The TSL glow curves of the undoped, Eu-doped, Ce-doped, and Cu-doped CsCaCl₃ were different from each other. This suggested that the dopant ions influenced the trapping process of electron–hole pairs, which were formed upon irradiation.

View full abstract

Improving the conductivity of 8 mol % yttria-stabilized zirconia (8YSZ) electrolyte has enabled a lowering of the operating temperature of solid oxide fuel cells. We previously reported that millimeter-wave irradiation heating increases the ionic conductivity of ceramics. The ionic conductivity of 8YSZ under millimeter-wave irradiation heating had been up to 20 times higher than that with conventional heating. In the present study, we investigated the optimal thermal environment for millimeter-wave irradiation heating. We also investigated the thermal profile of samples under millimeter-wave irradiation heating to elucidate the rate of the non-thermal effect.

View full abstract

Uniaxial-compression creep test and dynamic viscoelastic measurement were performed on binary sodium- and lithium-silicate glasses at around their deformation temperature. The derived creep function was converted into a relaxation modulus using the Laplace transformation and its inversion. Shear relaxation modulus G(t) was expressed by a 1-term Maxwell model for both glass systems. In the sodium system, the viscous term in the model decreased with increasing modifying oxide. In contrast, the lithium system showed a higher value in the elastic term and a lower value in the viscous term than the sodium system. The storage elastic modulus E′(ω) observed in the dynamic measurement started to decrease at the glass transition temperatures, and complicated fluctuation of the modulus was observed at around the deformation temperatures for frequencies larger than a few Hz. The decrease in the modulus at the transition temperature has been suggested to originate from slipping between silicate clusters which were separated by non-bridging oxygen with the modifying cations similar to polymer materials. The master curve of the loss elastic modulus E′′(ω) showed unique frequency dependence in all sodium-silicate glasses, while the data at high frequencies at around the deformation temperature deviated from the curve. This suggested that slipping between silicate clusters is the main process of structural relaxation, and anomalies in the dynamic modulus at around the deformation temperature could be related to other relaxation. The E′(ω) of the lithium-silicate glass showed similar temperature dependence and the master curve of E′′(ω) had a narrower frequency distribution. The contribution to E′′(ω) below 10⁻² Hz was smaller than in the sodium system. This lack of slow relaxation was well consistent with the comparably lower viscous term of G(t) in the Maxwell model. Injection testing into a narrow pore showed a faster saturation of the injected volume for the lithium-silicate glass.

View full abstract

In this study, we report on the optical and thermolumienscence (TL) properties of newly developed (30 − x)Li₂O–20Al₂O₃–50B₂O₃–2xCeO₂ (values are in mol %) glass dosimeters prepared by a conventional melt quenching method. The optical absorption spectra showed broad absorption band in the 200–370 nm wavelength with Ce-doping. The photoluminescence (PL) band appeared near the wavelength of 365 nm under excitation at 240, 270, and 315 nm, which is due to the transition from 5d excited states to 4f (²F_5/2, ²F_7/2) ground states of Ce³⁺. In the TL glow curve measurements, the Ce-doped glasses exhibited a dominant glow peak in the 370–425 K temperature range. The 0.5 cat% Ce-doped glass (x = 0.5) showed the highest TL intensities in our prepared glasses. The 5d–4f (²F_5/2, ²F_7/2) emission band of Ce³⁺ also appeared in the 365 nm wavelength range in the TL spectrum. TL response in the dynamic range was confirmed using the 0.5 cat% Ce-doped glass over 10⁻³–10² Gy X-ray dose.

View full abstract

Mesoporous silica-phosphate hybrids were successfully prepared by three processes: hybridization post synthesis by H₃PO₄, hybridizations during synthesis by Na₂HPO₄ and by PO(OC₂H₅). X-ray diffraction patterns confirm that the hexagonal pore structure was maintained after the hybridization process. The maximum phosphate amount was 2.9 mol % in the sample prepared by hybridization during synthesis from Na₂SiO₃ and PO(OC₂H₅)₃. The specific surface area showed a large value of approximately 1000 m²/g despite the hybridization. The Si–O–P bonds were confirmed by nuclear magnetic resonance and X-ray photoelectron spectroscopy. The maximum adsorption amount of rare earth metal cations into the hybrid was approximately 70% of the initial concentration (50 mg/L) for each rare earth metal cation in coexistence with 13 rare earth metal cations.

View full abstract

Rare earth hydroxide nitrates are prepared from rare earth nitrates by hydrothermal treatment. Three crystal phases, M(OH)₃ (M1), M₂(OH)_5.14(NO₃)_0.86·H₂O (M2), and M₄O(OH)₉NO₃ (M4) are identified. The crystal phase systematically changes from M1 to M4 through M2 with decreasing radius of rare earth cation. Morphology of nanocrystal depends on the crystal phase. M1 and M4 phases grow to be nanorod, and M2 to nanoplate.

View full abstract

Bimodal porous alumina was prepared from the solution with aluminum chloride and 1,2-propylene oxide by adding propylene glycol oligomers (PPG). Because of hydrophobic nature of PPG, the addition of PPG induces phase separation during sol–gel reaction, and macroporous morphologies are formed by fixing transitional structure of phase separation. Since ethanol works as a co-solvent, the macropore size of the obtained gel can be increased by decreasing ethanol content. Change in the concentration of other constituents such as PPG has also an effect to control morphologies through changing the timing of phase separation and sol–gel transition.

View full abstract

Cr-based layered double hydroxides (LDHs) containing Ni, Zn, or Cu as the divalent cation were prepared with a divalent-to-trivalent cation molar ratio of 3. Then, LDH hybrids intercalated with polyanions ([PMo₁₂O₄₀]³⁻(PMoO) or [H₂W₁₂O₄₂]¹⁰⁻ (HWO)) were prepared by ion exchange and hydrothermal processes. The shift of the diffraction line indicating interlayer space in the X-ray diffraction patterns confirmed the intercalation in the LDH. The fraction of PMoO and HWO anions incorporated was 30–70 or 60–90% of ion exchange capacity, respectively, by charge compensation for Cr³⁺. In the conversion of styrene by epoxidation and oxidation, the hybrid of the LDH composed of Zn and Cr with PMoO showed the maximum catalytic activity, with 70% conversion. For the LDH composed of Ni and Cr, hybridization with a polyanion enhanced the catalytic behavior by a synergistic effect resulting from the basicity of the LDH phase.

View full abstract

The electronic and structural characteristics of the octahedral molybdenum cluster-based ternary compound, Cs₂[Mo₆Cl₁₄], were investigated based on density functional theory (DFT) and subsequent comparisons with experimentally observed results. The geometry optimization and band structure calculations of Cs₂[Mo₆Cl₁₄] were performed using three standard functionals: local density approximation, Perdew-Burke-Ernzerhof (PBE) as a generalized gradient approximation, and PBE revised for solid compounds (PBEsol). The validity of the calculated results was experimentally examined via X-ray powder diffraction, ultraviolet–visible (UV–vis) diffuse reflection, and X-ray photoemission spectra (XPS) measurements. PBEsol was found to show the best performance in terms of reproducing the experimentally refined lattice structure of the compound. The calculated band gap energy (E_g) was consistent with the value evaluated from the UV–vis measurement. Furthermore, the XPS valence spectrum of the compound was well reproduced by the calculated projected density of state weighted with the photoionization probabilities of Al K_α. Although the spectral shapes simulated using the three functionals were similar, PBEsol reproduced the energy levels of the electronic states of both [Mo₆Cl₁₄]²⁻ and Cs⁺ ion with greater consistency. Therefore, it was concluded that PBEsol is the most appropriate functional for DFT calculations of the metal cluster-based lattice system.

View full abstract

Structural analyses of niobium oxide (NbO_x) amorphous film prepared with a sputtering method have been performed by using synchrotron X-ray radiation at SPring-8. The composition was determined as Nb₂O₅·0.8H₂O from the measurements of Rutherford back scattering, X-ray fluorescence, X-ray absorption near edge structure, and thermal desorption spectroscopy. Structural information was obtained by extended X-ray absorption fine structure and high energy X-ray diffraction measurements. It was supposed from the experimental data that NbO_x consisted of distorted NbO_n polyhedra connected by corner- and edge-sharing. Structural models were constructed with reverse Monte Carlo (RMC) simulations. In the RMC models, the structural characteristics were successfully reproduced, and H atoms were, however, randomly distributed. Then, bond valence sum (BVS) constraint was introduced to the RMC simulation. As the results, narrower distribution in BVS was achieved for all the constituent atoms, and distinct OH bonds were effectively generated in the RMC model.

View full abstract

We demonstrated that a moth-eye surface pattern on the luminous inorganic glass could enhance the photoluminescence (PL) intensity notably. A moth-eye pattern of a square array of cones at pitch of 250 nm was fabricated on Eu³⁺-doped MgF₂–MgO–BaO–B₂O₃ glass by thermal nanoimprinting at 520°C. A simulation with rigorous coupled-wave analysis demonstrated that the surface structure could reduce the surface reflectance in the optical input for the excitation wavelength λ of 405 nm, i.e., −1.1% for p-polarized light, 10.6% for s-polarized light, and 4.1% for non-polarized light in total of a half round angle for the irradiation from a surface light source. The angularly dependent PL of the excitation angle on the nanoimprinted glass was measured by an excitation of UV laser diode (λ = 405 nm). The enhancements of ∼0% for p-polarized light and ∼9% for s-polarized light were observed at the incident angle = 5°.

View full abstract

Local structures around copper oxides (CuO_x) supported on aluminum oxide borates (10A2B) during the NH₃ combustion reaction were studied by operando XAFS. Although CuO_x in as-prepared CuO_x/10A2B at room temperature can be assigned to CuO, the CuO was partly reduced to Cu₂O during NH₃ combustion at 400°C. In contrast, CuAl₂O₄ was formed after thermal aging of CuO_x/10A2B at 900°C for 100 h in air, local structures of which were preserved during NH₃ combustion at 600°C.

View full abstract

A novel PdO/La₁₀Si₆O₂₇/γ-Al₂O₃ catalyst was developed in order to decompose methane. In this catalyst, we selected the oxide-ion-conducting La₁₀Si₆O₂₇ solid with an apatite-type structure as a promoter to facilitate the supply of active oxygen to the PdO activator. For the comparison with PdO/La₂O₃/γ-Al₂O₃, where La₂O₃ is a simple rare earth sesquioxide, the catalytic activity of PdO/La₁₀Si₆O₂₇/γ-Al₂O₃ was higher than that of PdO/La₂O₃/γ-Al₂O₃, regardless of their same surface area. Since La₁₀Si₆O₂₇ exhibited two orders of magnitude higher conductivity than La₂O₃, the high oxide-ion-conducting property of La₁₀Si₆O₂₇ might facilitate the oxidation of methane by supplying active oxygen from inside the lattice.

View full abstract

Pyrochlore-type (K_0.73H_0.27)NbO₃·1.72H₂O and (K_0.56H_0.44)TaO₃·1.14H₂O were synthesized by a hydrothermal reaction. The K⁺ ions in these compounds were reacted with Ag⁺ ions in excess molten AgNO₃ at 300°C. This reaction produced fluorite-type Ag_0.41Nb_0.59O_1.68 and pyrochlore-type Ag_0.93TaO_2.97·0.94H₂O. Their crystal structures were refined by the Rietveld method using synchrotron X-ray powder diffraction data. Only the pyrochlore-type Ag_0.93TaO_2.97·0.94H₂O exhibited photocatalytic activity toward phenol degradation under UV light irradiation.

View full abstract

One dimensional rod-shaped and two dimensional twin-crystal shaped ZnO crystals were fabricated by thermal evaporation of a mixture of ZnS and graphite powders in air at atmospheric pressure. Twin-crystal shaped ZnO crystals were formed at 1050°C, while rod-shaped ZnO crystals were synthesized at 1150°C. The morphology of ZnO crystals was drastically changed according to the growth temperature. It is particularly interesting that two hexagonal plates formed a twin crystal, in which hexagonal shaped ZnO plates were symmetrically grown on both sides of a mirror-like plane. The twin crystal looked like a yo-yo. X-ray diffraction analysis showed that the rod and twin-crystal shaped ZnO crystals exhibited a wurtzite crystallographic structure. A strong green emission peak at 500 nm was observed in the cathodoluminescence spectra of the ZnO crystals at room temperature.

View full abstract

Suspension spraying is a promising surface modification technique, because finer particles can be used in contrast to the case of conventional thermal spraying. However, the optimal conditions for preparing suitable suspensions have not yet been established. Thus, the effects of particle dispersion and flocculation states on the properties of suspension-sprayed coatings were examined in the present study. Y₂O₃ suspensions were prepared using various quantities of the dispersant. The flow curves and gravitational settling behaviors of the prepared suspensions were investigated. The amounts of the dispersant adsorbed on the particles were also determined. In addition, Y₂O₃ coatings were fabricated using suspension spraying, and the properties of the obtained coatings were investigated. The addition of the dispersant affected the suspension flow characteristics, because the amount of the dispersant adsorbed increased with increasing dispersant concentration. Furthermore, the coating characteristics improved as the apparent viscosity of the suspension decreased.

View full abstract

Usually, the synthetic process of hafnium carbide (HfC) by using hafnium dioxide as hafnium source requires high reaction temperature. In this study, we have successfully synthesized HfC nanoparticles by a solid state reaction of hafnium dioxide, lithium carbonate and metallic magnesium in a stainless-steel autoclave at 700°C for 10 h. The X-ray powder diffraction pattern reveals that the obtained sample is cubic phase HfC with lattice constant of a = 4.633 Å. Scanning electron microscope images show that the obtained HfC sample is composed of uniform particles with an average size of about 10 nm. Furthermore, the formation mechanism and oxidation resistance of the HfC nanoparticles have been investigated.

View full abstract