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Acta Cryst. (2014). A70, C99
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We are searching for intermediate-valence (IV) quasicrystals where IV ions are quasi-periodically arranged. Our previous study revealed that an icosahedral Au-Al-Yb quasicrystal forms an IV system [1]. X-ray absorption spectroscopy near the Yb L_3 edge indicated that the Yb ions in the quasicrystal assume a mean valence of 2.61, between a divalent state (4f^14, J = 0) and a trivalent one (4f^13, J = 7/2). Additionally we found that non-Fermi-liquid behaviour appears at low temperatures without doping, pressure, or field tuning. In this study we examined Au-M-Yb system, where M = Sn, Ge, and Ga. X-ray absorption spectroscopy measurements at SPring-8 (BL22XU) showed that each compounds forms IV system. The Yb valence values are respectively 2.27 for a Au-Sn-Yb 2/1 crystalline approximant, 2.24 for a Au-Ge-Yb 1/1 approximant, and 2.36 for a Au-Ga-Yb 1/1 approximant. By following the trend of Yb-based IV compounds, these valence values close to divalent suggest that the Yb 4f character in these compounds would be itinerant rather than localized one.

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Acta Cryst. (2014). A70, C360
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"To improve performance of hydrogen storage materials, it is essential to understand detailed mechanism of hydrogenation and dehydrogenation reactions. In-situ powder diffraction measurements provide direct information about structural changes accompanying the reactions. We therefore installed a time-resolved x-ray diffraction (XRD) system at a beamline BL22XU at the SPrign-8, a synchrotron radiation facility in Japan. The system was equipped with two area detectors, a flat panel sensor for precise structural analyses and a high speed video camera connected to an x-ray image intensifier for observation of rapid phase changes. Maximum frame rate for the flat panel sensor and high-speed video camera was 2 fps and 125 fps (effective), respectively. A sample cell was connected to a hydrogen supply system. Opening of upstream valve of the sample cell or a change of the pressure at the sample triggered the recording of the diffraction patterns. The pressure of hydrogen gas was limited to 1 MPa. To demonstrate the performance of the system, we have performed time-resolved XRD experiments for LaNi4.5Al0.5. LaNi5 exhibits the significant broadening of the diffraction peaks by hydrogen absorption; however, LaNi4.5Al0.5 shows the no significant broadening. We have succeeded in the measurements of the structural change from the solid solution phase to the hydride phase and have found the formation of the transient intermediate phase on this reaction process. The system is currently used to study several materials. This work was partly supported by New Energy and Industrial Technology Development Organization (NEDO) under ""Advanced Fundamental Research Project on Hydrogen Storage Materials""."

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Acta Cryst. (2014). A70, C868
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Hydrogen has been considered as a promising alternative fuel for transportation, provided we can find a way to store a large amount of hydrogen in a compact way. The realization of such a storage system can be achieved by developing materials that can easily absorb, safely store, and rapidly release hydrogen repeatedly. However, there is currently no material to meet all the requirements for on board storage. Great efforts have been made to understand hydrogenation properties of currently available materials to look for a way to improve properties or to prepare new materials. However, investigating the structure of some of these materials is challenging since their hydrides are only available under hydrogen gas pressure. Furthermore, many novel materials with improved properties often show heavily disordered or nanoscale structural features which are difficult to characterize using conventional crystallographic technique alone (crystallographically challenged hydrogen storage materials). In order to investigate the structural change in crystallographically challenged hydrogen storage materials during hydrogenation or dehydrogenation processes we have developed in-situ hydrogen gas loading setup for synchrotron X-ray total scattering experiments at the Japan Atomic Energy Agency (JAEA) beamline of BL22XU [1] at SPring-8. Coupled to an area detector [1,2], this setup allows us to obtain the atomic pair distribution function (PDF) [3] of metal hydrides either in equilibrium or in non-equilibrium state with hydrogen. In this poster, we will introduce our in-situ setup and present some preliminary results on AB5-type intermetallic compounds and Pd nanoparticles.

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Acta Cryst. (2014). A70, C1661
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Time-resolved visualization of the soaking process of tetragonal lysozyme crystal was performed by synchrotron radiation microtomography. Mother liquor containing hexachloroplatinate was introduced into a capillary bearing lysozyme crystals to visualize crystals undergoing soaking. The platinum distribution was first observed in the superficial layer of crystal and then gradually penetrated into the crystal core. The crystal structure of the platinum derivative in each soaking period was determined by time-resolved crystallography. A total of five platinum sites were identified in Bijvoet difference maps. These sites were classified into two groups on the basis of the time dependence of electron density development. A soaking process model consisting of binding-rate-driven and equilibrium-driven layers is proposed to describe the results. This study suggests that the structures of soaked crystals vary depending on the crystal position from which diffractions were taken.
Keywords: micro-CT; lysozyme.
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