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Journal Articles

CO adsorption and decomposition on Pd/Al$$_{2}$$O$$_{3}$$ studied by time-resolved XAFS using dispersive optics

Matsumura, Daiju; Okajima, Yuka*; Nishihata, Yasuo

Journal of Physics; Conference Series, 712(1), p.012042_1 - 012042_4, 2016/06

 Times Cited Count:0 Percentile:0.03

Journal Articles

Precise observation of growth of surface oxide layer for Pd and Cu nanoparticles during oxidative/reductive gases cyclic flow studied by real-time-resolved XAFS spectroscopy

Matsumura, Daiju; Nishihata, Yasuo; Okajima, Yuka*

e-Journal of Surface Science and Nanotechnology (Internet), 14, p.48 - 52, 2016/00

Journal Articles

Real-time-resolved X-ray absorption fine structure spectroscopy for cesium adsorption on some clay minerals

Matsumura, Daiju; Kobayashi, Toru; Miyazaki, Yuji; Okajima, Yuka*; Nishihata, Yasuo; Yaita, Tsuyoshi

Clay Science, 18(4), p.99 - 105, 2014/12

Journal Articles

200 Hz observation of hydrogenation reaction of Pd nanoparticles by using dispersive XAFS optics

Matsumura, Daiju; Okajima, Yuka*; Nishihata, Yasuo; Mizuki, Junichiro

Journal of Physics; Conference Series, 430, p.012024_1 - 012024_6, 2013/04

 Times Cited Count:3 Percentile:66.63

Journal Articles

Sagittal focusing of synchrotron radiation X-rays using a winged crystal

Nisawa, Atsushi*; Yoneda, Yasuhiro; Ueno, Go*; Murakami, Hironori*; Okajima, Yuka*; Yamamoto, Kenichiro*; Semba, Yasunori*; Uesugi, Kentaro*; Tanaka, Yoshihito*; Yamamoto, Masaki*; et al.

Journal of Synchrotron Radiation, 20(2), p.219 - 225, 2013/03

 Times Cited Count:12 Percentile:54.45(Instruments & Instrumentation)

A Si(111) winged crystal has been designed to minimize anticlastic bending and improve sagittal focusing efficiency. The crystal was thin with wide stiffening wings. The length-to-width ratio of the crystal was optimized by finite element analysis, and the optimal value was larger than the "golden value". The analysis showed that the slope error owing to anticlastic bending is less than the Darwin width. The X-rays were focused two-dimensionally using the crystal and a tangentially bent mirror. The observed profiles of the focal spot agreed well with the results of a ray-tracing calculation in the energy range from 8 to 17.5 keV. X-ray diffraction measurements with a high signal-to-noise ratio using this focusing system were demonstrated for a small protein crystal.

Journal Articles

Fast and real-time observation of hydrogen absorption kinetics for palladium nanoparticles

Matsumura, Daiju; Okajima, Yuka*; Nishihata, Yasuo; Mizuki, Junichiro

Journal of Alloys and Compounds, 509(Suppl.2), p.S849 - S852, 2011/09

 Times Cited Count:9 Percentile:47.15(Chemistry, Physical)

Dynamical structural change of Pd nanoparticles during hydrogen absorption was directly observed by X-ray absorption fine structure with dispersive optics. Hydrogen pressure dependence of the expansion of the interatomic distance in Pd nanoparticles was estimated by real-time-resolved observation with a rate of 50 Hz. It has been revealed that the Pd nanoparticles show strong hydrogen pressure dependence of the reaction rate. Determined reaction order implies that the surface dissociative adsorption process is the key issue for the hydrogen storage kinetics.

Journal Articles

${it In situ}$ X-ray diffraction measurements of aluminum pulverization prior to the hydrogenation reaction

Saito, Hiroyuki; Okajima, Yuka*; Yoneda, Yasuhiro; Machida, Akihiko; Katayama, Yoshinori; Aoki, Katsutoshi

Materials Transactions, 52(4), p.595 - 597, 2011/04

 Times Cited Count:3 Percentile:24.21(Materials Science, Multidisciplinary)

Journal Articles

Correlation between structure of titanium additives and dehydrogenation reaction of magnesium borohydride studied by continuous observation of X-ray absorption spectroscopy

Matsumura, Daiju; Oyama, Takahiro*; Okajima, Yuka*; Nishihata, Yasuo; Li, H.-W.*; Orimo, Shinichi*

Materials Transactions, 52(4), p.635 - 640, 2011/04

 Times Cited Count:12 Percentile:54.72(Materials Science, Multidisciplinary)

Local structure of Ti-based additives in Mg(BH$$_{4}$$)$$_{2}$$ was studied by X-ray absorption fine structure spectroscopy with conventional and dispersive mode in order to understand the correlation between the structure of the additives and dehydrogenation property of Mg(BH$$_{4}$$)$$_{2}$$. Simultaneous measurement of the dehydrogenation curve and the X-ray absorption spectroscopy by the dispersive optics revealed that a part of TiCl$$_{3}$$ additive is converted to Ti$$_{x}$$Mg$$_{1-3x/2}$$(BH$$_{4}$$)$$_{2}$$ ($$x$$ = 0$$sim$$0.67) just after ball milling mixture and then promptly resolved to TiB$$_{2}$$ at 100-150$$^{circ}$$C with the first dehydrogenation peak. TiO$$_{2}$$ additive is slowly converted to lower oxidation state in wide temperature range around the second dehydrogenation peak at 350$$^{circ}$$C where the main dehydrogenation reaction of Mg(BH$$_{4}$$)$$_{2}$$ occurs.

Journal Articles

Magnetic and dielectric study of R$$_{0.5}$$Sr$$_{0.5}$$MnO$$_{3}$$ (R = Gd, Tb and Dy)

Yoshii, Kenji; Hiramitsu, Yusuke*; Okajima, Yuka*; Yoneda, Yasuhiro; Nishihata, Yasuo; Mizuki, Junichiro; Nakamura, Akio; Shimojo, Yutaka; Ishii, Yoshinobu*; Morii, Yukio; et al.

Materials Research Bulletin, 45(11), p.1574 - 1580, 2010/10

 Times Cited Count:12 Percentile:37.35(Materials Science, Multidisciplinary)

Magnetic and dielectric properties of perovskite manganites R$$_{0.5}$$Sr$$_{0.5}$$MnO$$_{3}$$ (R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at Tg about 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R$$^{3+}$$ and Sr$$^{3+}$$ settled randomly at the same crystallographic site. Dielectric constants for each material were about 1000-10000 between about 50 K and 300 K and showed broad maximums above Tg. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan$$delta$$ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons.

Journal Articles

Real-time and direct observation of hydrogen absorption dynamics for Pd nanoparticles

Matsumura, Daiju; Okajima, Yuka; Nishihata, Yasuo; Mizuki, Junichiro

Materials Research Society Symposium Proceedings, Vol.1262, 6 Pages, 2010/05

Dynamic local structural change of Pd nanoparticles on alumina surface during hydrogen absorption process was directly observed by X-ray absorption fine structure spectroscopy with dispersive mode. Main four parameters of X-ray absorption spectroscopy were determined even in the case of 50 Hz observation. It is clearly revealed that Pd nanoparticles directly change to the hydride phase in 50 ms at 200 kPa of hydrogen pressure. Significant structural distortion was not investigated in the results of the Debye-Waller factor.

Journal Articles

Formation and crystal growth process of AlH$$_{3}$$ in Al-H system

Saito, Hiroyuki; Okajima, Yuka; Yoneda, Yasuhiro; Machida, Akihiko; Kawana, Daichi; Watanuki, Tetsu; Katayama, Yoshinori; Aoki, Katsutoshi

Journal of Alloys and Compounds, 496(1-2), p.L25 - L28, 2010/04

 Times Cited Count:21 Percentile:68.92(Chemistry, Physical)

JAEA Reports

A Guide to dispersive XAFS measurements at BL14B1 in SPring-8

Okajima, Yuka; Matsumura, Daiju; Nishihata, Yasuo; Konishi, Hiroyuki; Mizuki, Junichiro

JAEA-Technology 2009-058, 45 Pages, 2009/12

JAEA-Technology-2009-058.pdf:5.95MB

From 2004 to 2006, the Dispersive XAFS system was constructed at JAEA beamline BL14B1 in SPring-8, and has been developed. Recently, the application of this system to materials science started. We report on the outline of this Dispersive XAFS system and explain its operations.

Journal Articles

Dynamic structural change of Pd particles on LaFeO$$_{3}$$ under redox atmosphere and CO/NO catalytic reaction studied by dispersive XAFS

Matsumura, Daiju; Okajima, Yuka; Nishihata, Yasuo; Mizuki, Junichiro; Taniguchi, Masashi*; Uenishi, Mari*; Tanaka, Hirohisa*

Journal of Physics; Conference Series, 190, p.012154_1 - 012154_6, 2009/11

 Times Cited Count:10 Percentile:89.88

Pd/LaFeO$$_{3}$$ is known to keep the metal particle size small even after the long time redox processes because Pd atoms make complex oxide with LaFeO$$_{3}$$ perovskite-type crystal under the oxidative atmosphere. We observed the local structure of Pd atoms by dispersive optics from the viewpoint of dynamical structure change of Pd during metal-oxide change and CO-NO catalytic reaction. It was recognized that, under the reductive atmosphere, Pd atoms show similar speed of movement from oxide to metal state both on LaFeO$$_{3}$$ and Al$$_{2}$$O$$_{3}$$. However, under the oxidative atmosphere, Pd atoms on LaFeO$$_{3}$$ show faster movement from metal to oxide state with single reaction step than those on Al$$_{2}$$O$$_{3}$$ with two-step oxidation. In addition, many differences in structure and shape between Pd particles on LaFeO$$_{3}$$ and Al$$_{2}$$O$$_{3}$$ are observed.

Journal Articles

Magnetic and dielectric properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$ (0$$underline{<}$$x$$underline{<}$$1)

Yoshii, Kenji; Ikeda, Naoshi*; Michiuchi, Takamasa*; Yokota, Yusuke*; Okajima, Yuka; Yoneda, Yasuhiro; Matsuo, Yoji*; Horibe, Yoichi*; Mori, Shigeo*

Journal of Solid State Chemistry, 182(7), p.1611 - 1618, 2009/06

 Times Cited Count:15 Percentile:51.51(Chemistry, Inorganic & Nuclear)

We have investigated the magnetic and dielectric properties of YbFe$$_{2-x}$$Mn$$_{x}$$O$$_{4}$$ (0$$underline{<}$$x$$underline{<}$$1), which is an Fe-site-substituted system of new multiferroic oxides RFe$$_{2}$$O$$_{4}$$ (R=Y, Ho-Lu). X-ray diffraction measurements show that a solid solution is formed between YbFe$$_{2}$$O$$_{4}$$ (x=0) and YbFeMnO$$_{4}$$ (x=1) for 0$$underline{<}$$x$$underline{<}$$1. The valence of the Mn ion is determined to be $$sim$$2+, consistently with the suppression of low-temperature magnetization by the Mn substitution. The magnetic transition temperature and the dielectric constant decrease monotonically with increasing x. This result plausibly confirms that the magnetic and dielectric properties in oxides isostructural with RFe$$_{2}$$O$$_{4}$$ are governed by the electron transfer between Fe-site ions, unlike ordinary ferroelectrics and dielectrics, in which the ionic displacement plays a key role. The possibility for application is briefly discussed.

Journal Articles

Magnetic and dielectric properties of R$$_{0.5}$$Ca$$_{0.5}$$MnO$$_{3}$$ (R=Eu-Lu)

Yoshii, Kenji; Hiramitsu, Yusuke*; Yoneda, Yasuhiro; Okajima, Yuka; Nishihata, Yasuo; Mizuki, Junichiro; Ikeda, Naoshi*

Ferroelectrics, 379(1), p.183 - 190, 2009/05

 Times Cited Count:8 Percentile:39.9(Materials Science, Multidisciplinary)

The magnetic and dielectric properties of perovskite manganites R$$_{0.5}$$Ca$$_{0.5}$$MnO$$_{3}$$ (R=Eu-Lu) have been investigated. Their dielectric constants were about 1000 at around room temperature. Inflections or peaks of temperature dependences of the dielectric constants were observed at around the charge-ordering temperatures determined from the magnetic measurements. Analyses of tan and EXAFS spectra suggested that the dielectric properties of this system are due to a spatial arrangement and transfer of the Mn-3d electrons. The observation of a two-peak structure of tan indicates that dielectric measurement can be used to observe homogeneity or in homogeneity of sample, as mentioned in our previous paper.

Journal Articles

Magnetic and dielectric properties of InFe$$_{2}$$O$$_{4}$$, InFeCuO$$_{4}$$, and InGaCuO$$_{4}$$

Yoshii, Kenji; Ikeda, Naoshi*; Okajima, Yuka; Yoneda, Yasuhiro; Matsuo, Yoji*; Horibe, Yoichi*; Mori, Shigeo*

Inorganic Chemistry, 47(14), p.6493 - 6501, 2008/07

 Times Cited Count:28 Percentile:73.64(Chemistry, Inorganic & Nuclear)

The magnetic and dielectric properties of InFe$$_{2}$$O$$_{4}$$, InFeCuO$$_{4}$$and InGaCuO$$_{4}$$ have been investigated. All these materials areisostructural with RFe$$_{2}$$O$$_{4}$$ (R=Y, Ho-Lu), which shows ferroelectricity due to iron-valence ordering. InFe$$_{2}$$O$$_{4}$$ exhibits similar properties to those of RFe$$_{2}$$O$$_{4}$$; the origins of the magnetic and dielectric phenomena are likely common in InFe$$_{2}$$O$$_{4}$$ and RFe$$_{2}$$O$$_{4}$$. From measurements of the other two materials, we found that both the magnetic transition temperature and the dielectric constant are decreased in the order of InFe$$_{2}$$O$$_{4}$$, InFeCuO$$_{4}$$ and InGaCuO$$_{4}$$. This result strongly supports the previously reported explanation based on an electron transfer between the Fe-site ions for the corresponding rare-earth systems. Therefore, we propose that the dielectric properties of the oxides isostructural with RFe$$_{2}$$O$$_{4}$$ are plausibly governed by electron transfer; this situation is different from that of ordinary ferroelectrics and dielectrics, in which the displacement factions and anions is important. In addition, InFeCuO$$_{4}$$ and InGaCuO$$_{4}$$ exhibit large dielectric constants (larger than about 1500). Inconsideration of this property, the possible applications of these oxides are discussed.

Journal Articles

High-pressure structural study on amorphous materials using cBN anvils

Hattori, Takanori; Saito, Hiroyuki; Kaneko, Hiroshi; Okajima, Yuka; Aoki, Katsutoshi; Utsumi, Wataru

KEK Proceedings 2007-7, p.56 - 60, 2007/12

We introduce high-pressure study on amorphous materials using a multi-anvils press equipped with the X-ray transparent cBN anvils. First, we mention merits of the angle-dispersive X-ray diffraction system compared with the conventional energy-dispersive system. Next, we show the results of the verification of the high-pressure formation of the elemental bulk metallic glass as an example. Finally, the characteristics of X-ray absorption are shown both for the combinational sintered diamond anvils and the presently used cBN anvils.

Journal Articles

Does bulk metallic glass of elemental Zr and Ti exist ?; Verification of the high-pressure formation of amorphous Zr and Ti

Hattori, Takanori; Saito, Hiroyuki; Aoki, Katsutoshi; Kaneko, Hiroshi; Okajima, Yuka; Utsumi, Wataru

Nihon Kessho Gakkai-Shi, 49(3), p.179 - 185, 2007/06

The high-pressure formation of the bulk metallic glass of elemental Zr and Ti, which has been recently reported, is verified by a newly developed angle dispersive X-ray diffraction (ADX) system using a large volume multi-anvil apparatus equipped with X-ray transparent anvils. The ADX data revealed that Zr and Ti remain as a crystalline form at high-pressure and temperature condition where the amorphization has been reported. The misinterpretation in the previous papers is attributed to the anomalous rapid grain growth that is related to the characteristic lattice dynamic and the resulting anomalously fast self diffusion in the high-temperature phases of Zr and Ti.

Journal Articles

Energy dispersive XAFS in the high energy region at BL14B1, SPring-8

Okajima, Yuka; Matsumura, Daiju; Nishihata, Yasuo; Konishi, Hiroyuki; Mizuki, Junichiro

AIP Conference Proceedings 879, p.1234 - 1237, 2007/01

no abstracts in English

Journal Articles

Phantom of elemental bulk metallic glass; Verification of the amorphous formation of Zr and Ti under pressure

Hattori, Takanori; Saito, Hiroyuki; Utsumi, Wataru; Aoki, Katsutoshi; Kaneko, Hiroshi; Okajima, Yuka

SPring-8 Riyosha Joho, 12(1), p.45 - 50, 2007/01

no abstracts in English

62 (Records 1-20 displayed on this page)