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Journal Articles

Structure of Mg$$_{2}$$SiO$$_{4}$$ glass made by a method for containerless supercooled-liquid-phase processing at high temperatures

Kohara, Shinji*; Suzuya, Kentaro; Takeuchi, Ken*

Mirai Zairyo, 5(4), p.28 - 33, 2005/04

http://ci.nii.ac.jp/naid/40006719359

We succeeded in producing highly pure glass made of "forsterite," contained in upper mantle of the Earth and meteorites. Although ordinary glass is made of silica network structure, this glass has an unsymmetrical network structure of magnesium oxide polyhedrons, which is deemed to destroy the silica network structure. We produced glass with extremely rare impurities by melting forsterite while floating it with inert gas and sound waves and then quenching it while holding it in an approximate microgravity condition equivalent to space. Development of a new optical fiber and improvement and cost reduction of operating equipment, such as operation laser, because high-purity glass can be produced using materials, which has been deemed to be appropriate.

Journal Articles

The Disordered 3-dimensional structure visualized by a combination of high-energy synchrotron X-rays and computer simulations

Kohara, Shinji*; Oishi, Yasuo*; Takata, Masaki*; Yoneda, Yasuhiro; Suzuya, Kentaro

Nihon Kessho Gakkai-Shi, 47(2), p.123 - 129, 2005/04

https://doi.org/10.5940/jcrsj.47.123

The use of high-energy (E $$>$$ 50 keV) X-rays from SPring-8 allows us to perform X-ray diffraction experiments on disordered materials with the following advantages: high resolution in real space due to the wide range of scattering vector, small correction terms (particularly the absorption correction), and fast diffraction measurement with small amount of samples. Recently, high-energy X-ray diffraction data have been combined with neutron diffraction data from a pulsed neutron source to provide more detailed and reliable structural information than has hitherto been available. Furthermore, the use of reverse Monte Carlo modelling and PDF (pair distribution function) simulation based on high-energy X-ray diffraction data have succeeded in illustrating 3-dimensional structure of disordered materials and disorder in crystalline materials.

Journal Articles

Unusual structure in vitreous forsterite synthesized by an aero-acoustic levitation technique

Kohara, Shinji*; Suzuya, Kentaro; Takeuchi, Ken*

Nihon Maikurogurabiti Oyo Gakkai-Shi, 22(2), p.100 - 104, 2005/04

Forsterite Mg$$_{2}$$SiO$$_{4}$$ exhibits an orthorhombic structure consisted of two kinds of MgO$$_{6}$$ octahedra. Given only 33.3 mol% of SiO$$_{2}$$ in the material, the SiO$$_{4}$$ tetrahedra are isolated within the framework, sharing the O-O bonds with the common edges of the MgO$$_{6}$$ octahedra. If forsterite can be vitrified, an interesting question concerning the glass structure arises because there is insufficient glass forming SiO$$_{2}$$ to establish the corner-sharing SiO$$_{4}$$ tetrahedral network needed in conventional silicate glasses. A bulk Mg$$_{2}$$SiO$$_{4}$$ glass was synthesized using an aero-acoustic levitation technique and to determine the short- to intermediate-range structure by a combined high-energy X-ray and neutron diffraction and reverse Monte Carlo computer simulation. Interestingly, we found that the role of network former is largely taken on by corner- and edge-sharing ionic magnesium species that adopt 4-, 5- and 6-coordination with oxygen.

Journal Articles

Intermediate-range order in vitreous SiO$$_{2}$$ and GeO$$_{2}$$

Kohara, Shinji*; Suzuya, Kentaro

Journal of Physics; Condensed Matter, 17(5), p.S77 - S86, 2005/02

https://doi.org/10.1088/0953-8984/17/5/009
 Times Cited Count：82 Percentile：90.9(Physics, Condensed Matter)

The total structure factors, S(Q), obtained from high-energy X-ray and neutron diffraction measurements on vitreous SiO$$_{2}$$ (v-SiO$$_{2}$$) and vitreous GeO$$_{2}$$ (v-GeO$$_{2}$$) have been analysed by the reverse Monte Carlo (RMC) modelling technique to generate a three-dimensional structural model. The bond angle distributions and the ring size distributions from the model indicated that the sixfold ring and six- and sevenfold rings are dominant in v-SiO$$_{2}$$ and v-GeO$$_{2}$$, respectively. However, the fraction of threefold rings of Ge in v-GeO$$_{2}$$ is larger than that of Si in v-SiO$$_{2}$$ glass. These features are consistent with the published neutron diffraction and Raman scattering studies.

Journal Articles

Structure of oxide glasses by synchrotron X-ray and neutron diffraction

Suzuya, Kentaro

Hamon, 13(1), p.51 - 55, 2003/01

https://doi.org/10.5611/hamon.13.51

With the arrival of the latest generation of synchrotron sources and the introduction of advanced insertion devices, the high-energy (E $$>$$ 30 keV) X-ray diffraction technique has become feasible, leading to new approaches in the quantitative study of the structure of disordered materials. Recently, the high-energy X-ray diffraction data have been combined with neutron diffraction data from a pulsed source to provide more detailed and reliable structural information than that hitherto available. We have developed a two-axis diffractometer for glass, liquid and amorphous materials at the SPring-8 high-energy X-ray diffraction beamline BL04B2. Furthermore, we have succeeded to analyze the intermediate-range order of network forming glasses, SiO$$_{2}$$, B$$_{2}$$O$$_{3}$$, and GeO$$_{2}$$ by the reverse Monte Carlo (RMC) modelling technique with special focused on the ring structures using both high-energy X-ray and neutron diffraction data.

Journal Articles

Structural analysis of 1-ethyl-3-methylimidazolium bifluoride melt

Matsumoto, Kazuhiko*; Hagiwara, Rika*; Ito, Yasuhiko*; Kohara, Shinji*; Suzuya, Kentaro

Nuclear Instruments and Methods in Physics Research B, 199, p.29 - 33, 2003/01

https://doi.org/10.1016/S0168-583X(02)01400-3
 Times Cited Count：34 Percentile：88.67(Instruments & Instrumentation)

The structure of 1-ethyl-3-methylimidazolium bifluoride (EMImF$$cdot$$HF) melt has been analyzed at 333 K by a high-energy synchrotron X-ray diffraction method. The total correlation function of the EMImF$$cdot$$HF melt was similar to that of the solid state, indicating that not only the short-range but also the intermediate-range ordering in the solid are partially preserved in the liquid state. The intra-molecular F-F correlation in the anions clearly appears in the total correlation function of the EMImF$$cdot$$HF melt, whereas prominent peaks are not observed in the case of a room temperature molten salt, 1-ethyl-3-methylimidazolium fluorohydrogenate (EMImF$$cdot$$2.3HF).

Journal Articles

High-energy X-ray diffraction studies of disordered materials

Kohara, Shinji*; Suzuya, Kentaro

Nuclear Instruments and Methods in Physics Research B, 199, p.23 - 28, 2003/01

https://doi.org/10.1016/S0168-583X(02)01554-9
 Times Cited Count：34 Percentile：88.67(Instruments & Instrumentation)

With the arrival of the latest generation of synchrotron sources and the introduction of advanced insertion devices (wigglers and undulators), the high-energy (E $$>$$ 30 keV) X-ray diffraction technique has become feasible, leading to new approaches in the quantitative study of the structure of disordered materials. High-energy X-ray diffraction has several advantages: higher resolution in real space due to a wide range of scattering vector Q, smaller correction terms (especially the absorption correction), reduction of truncation errors, the feasibility of running under extreme environments, including high-temperatures and high-pressures, and the ability to make direct comparisons between X-ray and neutron diffraction data. Recently, high-energy X-ray diffraction data have been combined with neutron diffraction data from a pulsed source to provide more detailed and reliable structural information than that hitherto available.

Journal Articles

The Structures of alkylimidazolium fluorohydrogenate molten salts studied by high-energy X-ray diffraction

Hagiwara, Rika*; Matsumoto, Kazuhiko*; Tsuda, Tetsuya*; Ito, Yasuhiko*; Kohara, Shinji*; Suzuya, Kentaro; Matsumoto, Hajime*; Miyazaki, Yoshinori*

Journal of Non-Crystalline Solids, 312-314, p.414 - 418, 2002/10

https://doi.org/10.1016/S0022-3093(02)01700-3
 Times Cited Count：32 Percentile：85.82(Materials Science, Ceramics)

The structures of a series of XF$$^{.}$$2.3HF (X= 1-methylimidazolium (MI), 1-ethyl-3-methylimidazolium (EMI), 1-butyl-3-methylimidazolium (BMI), 1-hexyl-3-methyl-imidazolium (HMI)) room temperature molten salts have been investigated by high-energy synchrotron X-ray diffraction technique. The correlation peaks appeared in the total correlation function are mainly ascribed to intra-molecular correlation of alkylimidazolium cations. However, it is suggested that the peak at around 3.6 $$AA$$ is ascribed not only to intra-molecular but also inter-molecular correlation of the cation. The contribution of the latter is also supported by the first sharp diffraction peak of the total structure factor found at almost the same position as that of a Bragg peak in the simulated X-ray diffraction pattern of solid EMIF$$^{.}$$HF with a layered structure, corresponding to the layer separation of

Journal Articles

High-energy X-ray diffraction studies of short- and intermediate-range structure in oxide glasses

Suzuya, Kentaro; Kohara, Shinji*

Materia, 41(3), p.206 - 215, 2002/03

http://ci.nii.ac.jp/naid/10008836947

With the arrival of the latest generation of synchrotron sources and the introduction of advanced insertion devices, the high-energy (E $$>$$ 30 keV) X-ray diffraction technique has become feasible, leading to new approaches in the quantitative study of the structure of disordered materials. Recently, the high-energy X-ray diffraction data have been combined with neutron diffraction data from a pulsed source to provide more detailed and reliable structural information than that hitherto available. We have developed a two-axis diffractometer for glass, liquid and amorphous materials at the SPring-8 high-energy X-ray diffraction beamline BL04B2. Furthermore, we have succeeded to analyze the intermediate-range order of network forming glasses, SiO$$_{2}$$, B$$_{2}$$O$$_{3}$$, and GeO$$_{2}$$ by the reverse Monte Carlo (RMC) modelling technique with special focused on the ring structures using both high-energy X-ray and neutron diffraction data.

Journal Articles

Intermediate range order of vitreous silica studied by high energy X-ray diffraction, neutron diffraction and reverse Monte Carlo modelling

Kohara, Shinji*; Suzuya, Kentaro

Physics and Chemistry of Glasses, Vol.43C 2002, p.51 - 54, 2002/00

With the arrival of the latest generation of synchrotron sources and the introduction of advanced insertion devices, the high-energy (E $$>$$ 30keV) X-ray diffraction technique has become feasible, leading to new approaches in the quantitative study of the structure of disordered materials. Recently, the high-energy X-ray diffraction data have been combined with neutron diffraction data from a pulsed source to provide more detailed and reliable structural information than that hitherto available. We have developed a two-axis diffractometer for glass, liquid and amorphous materials at the SPring-8 high-energy X-ray diffraction beamline BL04B2. Furthermore, we have succeeded to analyze the intermediate-range order of a typical network forming glass, silica (SiO$$_{2}$$), by reverse Monte Carlo (RMC) modelling technique with special focused on the ring structures using both high-energy X-ray and neutron diffraction data.

Journal Articles

High-energy X-ray diffraction of disordered materials in high-energy X-ray diffraction beamline BL04B2 at SPring-8

Kohara, Shinji*; Suzuya, Kentaro

Hoshako, 14(5), p.365 - 375, 2001/11

http://ci.nii.ac.jp/naid/10007157514

no abstracts in English

Journal Articles

A Horizontal two-axis diffractometer for high-energy X-ray diffraction using synchtoron radiation on bending magnet beamline BL04B2 at SPring-8

Kohara, Shinji*; Suzuya, Kentaro; Kashihara, Yasuharu*; Matsumoto, Norimasa; Umesaki, Norimasa*; Sakai, Ichiro*

Nuclear Instruments and Methods in Physics Research A, 467-468(Part.2), p.1030 - 1033, 2001/07

https://doi.org/10.1016/S0168-9002(01)00630-1
 Times Cited Count：138 Percentile：99.12(Instruments & Instrumentation)

no abstracts in English

Journal Articles

High energy X-ray study on the structure of vitreous B$$_{2}$$O$$_{3}$$

Yoneda, Yasuhiro*; Kohara, Shinji*; Suzuya, Kentaro; Umesaki, Norimasa*

Physics and Chemistry of Glasses, 41(5), p.282 - 285, 2000/10

no abstracts in English

Journal Articles

The Structures of disordered materials studied by high energy X-ray diffraction and reverse Monte Carlo modelling

Kohara, Shinji*; Suzuya, Kentaro; Ono, Hideo

Yoyuen Oyobi Koon Kogaku, 43(2), p.41 - 52, 2000/05

http://ci.nii.ac.jp/naid/40004799783

no abstracts in English

Oral presentation

Examining phase transitions by high-energy X-ray diffraction

Yoneda, Yasuhiro

no journal, , 

The bending magnet beamlines of SPring-8 can provide wide band X-rays, which critical energy is 28.9 keV. One can performs the high-energy X-ray diffraction measurements by combining X-ray focusing system of a crystal bender. We examined a coherence part in ceramics samples by using the large penetration depth of the high-energy X-rays. For example, we found structural phase transitions in (Na,K,Li)NbO$$_3$$ and (Bi$$_{0.5}$$Na$$_{0.5}$$)TiO$$_3$$. We also applied this technique to a surrogate materials for nitride fuel of (Dy,Zr)N.

Oral presentation

Short- and middle-range order structures of ferroelectric materials revealing by high-energy Synchrotron X-ray diffraction

Yoneda, Yasuhiro

no journal, , 

A lecture will be given on nano-scale structural analysis of ferroelectric materials using atomic pair-distribution function obtained by synchrotron high-energy X-rays. The results of local structure analyses to relaxor ferroelectrics and potassium niobate nanocrystals are discussed.

Oral presentation

Local structure analysis of (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$-based system with tetragonal structure

Yoneda, Yasuhiro; Takuwa, Chihaya*

no journal, , 

Oral presentation

High-energy X-ray diffraction study of (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ - Ca(Zr$$_{0.5}$$Ti$$_{0.5}$$)O$$_3$$

Yoneda, Yasuhiro; Takuwa, Chihaya*; Kobune, Masafumi*

no journal, , 

A two-body correlation distribution function obtained from high-energy X-ray diffraction experiments was applied to a niobium-based oxide ferroelectric (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ - Ca(Zr$$_{0.5}$$Ti$$_{0.5}$$)O$$_3$$ with excellent piezoelectric properties. The average structure of (Na$$_{0.5}$$K$$_{0.45}$$Li$$_{0.05}$$)NbO$$_3$$ - Ca(Zr$$_{0.5}$$Ti$$_{0.5}$$)O$$_3$$ changes with a small amount of Ta-additives. When the density and grain size of the sample were matched to determine whether the local structure changed with the change in the average structure, there was almost no difference in the local structure between 3${AA}$ and 10${AA}$. The difference was observed in the coherence of the nanoscale region, suggesting a difference in the ferroelectric domain size.

18 (Records 1-18 displayed on this page)
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