Papers by Author: Mineo Sato

Abstract: Photochemical splitting of water into H2 and O2 using solar energy is process of great economic and environmental interest. In this study, we investigated novel photocatalytic compound, Na16Ti10O28, for water splitting. Na16Ti10O28 was prepared by solid-state reaction at 900 oC for 1 h. Prepared sample was characterized using powder X-ray diffraction, diffuse reflectance spectrum, and scanning electron microscopy. As-prepared Na16Ti10O28 sample is easily hydrated in water. Hydrous Na16Ti10O28 showed H2 evolution without co-catalyst.

Abstract: Fine TiO2 particles were synthesized from titanate precursor, Na16Ti10O28, dissolved in aqueous HNO3 solution. Crystalline rutile TiO2 powders were prepared by reflux of dissolved powders in the aqueous HNO3 solution under 100 °C. Prepared TiO2 powders were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy and BET specific surface area analysis.

Abstract: New red phosphors Na3YSi2O7:Eu3+ was prepared by a conventional solid-state reaction. This silicate phosphor can be efficiently excited by near UV light, yielding an intense red emission. Under the excitation of near UV light, the emission intensity is higher than that of a commercial red phosphor Y2O2S:Eu3+.

Abstract: Eu3+ doped and undoped Y(P,V)O4 phosphors were prepared using multi-mode and single-mode microwave oven operated at 2.45 GHz. In the case of the microwave heating method, the phosphor particles were non-aggregated. A homogeneous distribution of Eu ion was observed in the microwave synthesis. No sintering behavior found in the microwave heating may be attributed to a quite shorter heating time. The Eu3+ doped sample synthesized by microwave heating showed intense red emission under UV excitation.

Abstract: A white long persistence phosphor was synthesized in a single-phase of Mg2SnO4 which was synthesized by a solid-state reaction. This phosphor crystallized in an inverse spinel structure and showed a broad-band emission from 350nm to 700nm. The afterglow was observed upon the excitation by 254nm. A Li-doped Mg2SnO4 sample showed a higher photoluminescence intensity and a longer lifetime than the non-doped one.

Abstract: We report synthesis of well-grown blue phosphor powder, CaMgSi2O6:Eu2+, from new vapor phase method (Flash creation method) derived nanopowder precursor. Single phase phosphor sample was obtained by post-annealing at 1100 oC. Luminescence properties were compared with that of the sample synthesized by a conventional solid state reaction. The post-annealed sample showed intense blue emission under UV excitation.

Abstract: Reduced niobates, MLixCa2Nb3O10 (M = Rb, K and Na) and KNaxCa2Nb3O10 were synthesized by intercalation reaction with n-butyllithium or sodium azide. Ruddlesden-Popper type structure of sodium intercalation compound, KNaCa2Nb3O10, differ from that of the parent compound and lithium intercalation compound, KLiCa2Nb3O10. The magnetic susceptibility measurements showed that the sodium intercalation compound became superconductor with transition temperatures below 3.5 K. New lithium intercalation compound Na0.1Li0.8Ca2.45Nb3O10, for an ion exchange compound, Na0.1Ca2.45Nb3O10, with KCa2Nb3O10 type structure show the diamagnetic signals below 5 K.

Abstract: Nanoparticles and thin films of potassium niobate KNbO3 were prepared using a unique solution reaction at room temperature. Precursor solutions and as-prepared samples were characterized by Raman spectroscopy. The data demonstrated that the niobate nanosheets consist of distorted Nb-O polyhedra.

Abstract: Compositionally uniform nitride powders were synthesized from metal oxide powders using a fluidized bed in NH3 or NH3-N2 flows. GaN was synthesized by a two-step heating ; the first step was done at 700°C for 1 h; the second step was done at 900°C for 4 h. GaN-ZnO solid solution was synthesized at 900°C for 4 h. The grain sizes of the products were smaller than those of the starting materials.

Abstract: We present a new method for soft chemical synthesis of perovskite materials. Perovskite K1-xLixNbO3 powders are produced by an ion-exchange reaction of layered perovskite precursor, K2NbO3F, with lithium chloride in water at room temperature. X-ray diffraction and X-ray fluorescent spectroscopic studies show that a mechanism of the ion-exchange reaction is a self-assembly between the perovskite nanosheets in aqueous solution.