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論文(リポジトリ)
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Sato, Mineo ; Ishigaki, Tadashi ; Uematsu, Kazuyoshi ; Toda, Kenji ; Okawa, Hirokazu
概要:
Crystals of dilithium manganese(II) silicate were grown under high-temperature hydrothermal conditions in the system Li
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OH—MnO2—SiO2. The title compound crystallizes in the βII-Li3PO4 structure type. The coordination polyhedra of all cations are slightly distorted tetrahedra (m symmetry for MnO4 and SiO4), which are linked by corner-sharing to each other. The vertices of the tetrahedra point to the same direction perpendicular to the distorted hexagonal close-packed (hcp) array of O atoms within which half of the tetrahedral voids are occupied by cations. In comparison with the previous refinement from powder X-ray data [Dominko et al. (2006 [triangle]). Electrochem. Commun. 8, 217–222], the present reinvestigation from single-crystal X-ray data allows a more precise determination of the distribution of the Li+ and Mn2+ cations, giving a perfectly site-ordered structure model for both Li+ and Mn2+.
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| 2.
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論文(リポジトリ)
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Ishigaki, Tadashi ; Madhusudan, Puttaswamy ; Inoue, Michiyo ; Kamei, Shinnosuke ; Uematsu, Kazuyoshi ; Toda, Kenji ; Sato, Mineo
概要:
Certain silicate materials with different crystal structures show excellent luminescence properties. Furthermore, these
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silicate compounds have high chemical and thermal stability and considered as an excellent phosphor host materials. In this study, we report (Gd1−xEux)3BSi2O10 as a novel ultraviolet (UV) excited white phosphors prepared under solid state reaction and their luminescence properties at 393 nm excitation were investigated in detail. The as prepared (Gd1−xEux)3BSi2O10 phosphors showed red emission with UV (around 580–630 nm) and near-UV light (around 250–410 nm). The chromaticity coordinates (0.60, 0.34) of the prepared borosilicate phosphor were very close to the NTSC standard value (0.67, 0.33) and its emission intensity was almost similar to commercial red phosphor Y2O2S:0.05Eu3+. Further, as prepared (Gd1−xEux)3BSi2O10 material is considered to be an efficient red-emitting phosphor for UV based light emitting diodes (LED).
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| 3.
論文(リポジトリ) |
論文(リポジトリ)
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Ishigaki, Tadashi ; Toda, Kenji ; Sakamoto, Tatsuya ; Uematsu, Kazuyoshi ; Sato, Mineo
概要:
Well-crystallized Ba2SiO4:Eu2+ powders were grown on a substrate by the vapor phase reaction between a mixed powder (bar
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ium carbonate and europium oxide) and SiO gas. The vaporization of SiO oc-curs at 1400–1600℃ from the SiO2 source (or SiO powder) in a reducing atmosphere. The formed SiO gas was transported by 95 vol% Ar - 5 vol% H2 gas and reacted with the raw material powders. The emission intensity of the Ba2SiO4:Eu2+ phosphor synthesized by the new vapor phase technique is about 2.6 times higher than that of a conventional solid-state reaction sample.
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| 4.
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論文(リポジトリ)
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Toda, Kenji ; Kawakami, Yoshitaka ; Kousaka, Shin-ichiro ; Ito, Yutaka ; Komeno, Akira ; Uematsu, Kazuyoshi ; Sato, Mineo
概要:
We focus on the development of new silicate phosphors for a white LED. In the europium doped silicate system, four LED phosphor candidates-Li_2SrSiO_4:Eu^<2+>, Ba_9Sc_2Si_6O_<24>:Eu^<2+>, Ca_3Si_2O_7:Eu^<2+>
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and Ba_2MgSi_2O_7:Eu^<2+> were found. Luminescent properties under near UV and visible excitation were investigated for the new Eu^<2+> doped LED silicate phosphors. These new phosphors have a relatively strong absorption band in a long wavelength region.
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| 5.
論文(リポジトリ) |
論文(リポジトリ)
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Ishigaki, Tadashi ; Toda, Kenji ; Yoshimura, Masahiro ; Uematsu, Kazuyoshi ; Sato, Mineo
概要:
We have applied a novel 'melt synthesis technique' rather than a conventional solid-state reaction to rapidly synthesize phosphor materials. During a synthesis, the mixture of oxides or their precursors is melted by light pulses
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(10?60?s) in an arc-imaging furnace on a water-cooled copper hearth to form a globule of 1?5?mm diameter, which is then rapidly cooled by turning off the light. Using this method, we synthesized several phosphor compounds including Y3Al5O12:Ce(YAG) and SrAl2O4:Eu,Dy. Complex phosphor oxides are difficult to produce by conventional solid-state reaction techniques because of the slow reaction rates among solid oxides; as a result, the oxides form homogeneous compounds or solid solutions. On the other hand, melt reactions are very fast (10?60?s) and result in homogeneous compounds owing to rapid diffusion and mixing in the liquid phase. Therefore, melt synthesis techniques are suitable for preparing multi component homogeneous compounds and solid solutions.
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| 6.
論文(リポジトリ) |
論文(リポジトリ)
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Uematsu, Kazuyoshi ; Ochiai, Ayumi ; Toda, Kenji ; Sato, Mineo
概要:
LiFePO_4 has been synthesized using FeC_2O_4・2H_2O, LiOH・H_2O and NH_4H_2PO_4 as raw materials by a temperature controll
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able microwave heating oven. The products were characterized by X-ray diffraction, scanning electron microscope and electrochemical methods. Measurement of dielectric properties of individual raw materials and products at a constant microwave frequency revealed that the starting mixture preheated at 320℃ as well as added acetylene black were well microwave absorbers. Single phase olivin-type LiFePO_4 with uniform and fine particle sizez was successfully synthesized by microwave heating at 350℃ in 15 min. The LiFePO_4 cathode materials thus obtained had a higher discharge capacity and better cycle performance than those of the LiFePO_4 sample by a conventional solid-state reaction.
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| 7.
論文(リポジトリ) |
論文(リポジトリ)
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Tokumitsu, Toshiaki ; Toda, Kenji ; Aoyagi, Tsukuru ; Sakuraba, Daiki ; Uematsu, Kazuyoshi ; Sato, Mineo
概要:
Crystal structure of a layered perovskite, KCa_2Nb_3O_10, was determined by the Rietveld refinement method for a powder
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neutron diffraction pattern. The compound crystallizes a monoclinic system with a space group P2_1/m (No.11) and lattice parameters of a=0.77418(6)nm, b=0.77073(6)nm, c=1.4859(1)nm, β=97.51(1)°.
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| 8.
論文(リポジトリ) |
論文(リポジトリ)
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Tokumitsu, Toshiaki ; Toda, Kenji ; Aoyagi, Tsukuru ; Sakuraba, Daiki ; Uematsu, Kazuyoshi ; Sato, Mineo
概要:
Crystal structure of a layered perovskite, KCa_2Nb_3O_<10>, was determined by the Rietveld refinement method for a powde
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r neutron diffraction pattern. The compound crystallizes a monoclinic system with a space group P2_1/m (No. 11) and lattice parameters of a=0.77418(6)nm, b=0.77073(6)nm, c=1.4859(1)nm, β=97.51(1)°.
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| 9.
論文(リポジトリ) |
論文(リポジトリ)
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Toda, Kenji ; Uematsu, Kazuyoshi ; Sato, Mineo
概要:
A new layered perovskite compound, NaLaTa2O7, was synthesized by ion-exchange reaction of the rubidium compound, RbLaTa2O7. The crystal structure of the compound was determined by the Rietveld analysis for powder X-ray diffraction
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pattern. The crystal structure is analogous to that of the corresponding niobate compound, NaLaNb2O7. This layered perovskite compound is a new member of the Dion-Jacobson series with n=2 for the general formula M[An-1BnO3n+1] (M=alkali metals).
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| 10.
論文(リポジトリ) |
論文(リポジトリ)
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Toda, Kenji ; Kurita, Satoru ; Sato, Mineo
概要:
New layered perovskite compounds, LiLnTiO4 (Ln=La and Eu), have been synthesized by an ion-ex-change reaction from parent sodium compounds, NaLnTiO4. The crystal structures of LiLaTiO4 and LiEuTiO4 were determined by Rietveld analysis of the
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powder X-ray diffraction (XRD) patterns. The lithium ion-exchanged compounds retain the crystal symmetry of the parent phases. Although the framework of the perovskite layer of these compounds is the same as that of the parent compounds, there exists a fundamental difference. The lithium ions within the interlayer have a tetrahedral coordination because of small ionic radius for a rock-salt coordination. The structure of LiLaTiO4 and LiEuTiO4 consist of intergrowths of the perovskite sheets with the layers of Li-O in a tetrahedral coordination and those of Ln-O in a distorted rock-salt coordination. These compounds exhibit new phases analogous to the Ruddlesden-Popper phase.
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