Showing papers by "Masaki Takata published in 2007"
TL;DR: In this article, high-energy x-ray diffraction beamlines and a dedicated diffractometer for glass, liquid and amorphous materials at SPring-8 were introduced.
Abstract: High-energy x-rays from a synchrotron radiation source allow us to obtain high-quality diffraction data for disordered materials from ambient to extreme conditions, which is necessary for revealing the detailed structures of glass, liquid and amorphous materials. We introduced high-energy x-ray diffraction beamlines and a dedicated diffractometer for glass, liquid and amorphous materials at SPring-8 and report the recent developments of ancillary equipment. Furthermore, the structures of liquid and amorphous materials determined from the high-energy x-ray diffraction data obtained at SPring-8 are discussed.
228 citations
TL;DR: A metallic state in a nanostructured porous crystal 12CaO x 7Al2O3 is reported by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path.
Abstract: We report a metallic state in a nanostructured porous crystal 12CaO x 7Al2O3 by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path. High-density electron doping ( approximately 2 x 10(21) cm(-3)), which was achieved by a thermal treatment in Ti metal vapor at approximately 1100 degrees C, induces homogenization of the cage geometry to a symmetric state, resulting in an insulator-metal transition with a sharp enhancement of the electron drift mobility from approximately 0.1 to 4 cm(2) V(-1) s(-1). The results provide an approach for the realization of electroactive functions in materials composed only of environmentally benign elements by utilizing the appropriate nanostructures.
198 citations
122 citations
TL;DR: The present study proved that the powder diffraction at SPring-8 is a promising method for determination of experimental charge density for a wider range of materials.
Abstract: Accurate structure factors of silicon and diamond have been experimentally determined from powder diffraction data measured at the third-generation synchrotron-radiation source SPring-8, BL02B2. The accuracy of the obtained structure factors has been evaluated by comparing with structure factors in the literature measured by the Pendellosung method and with some from theoretical calculations. The results indicate that the structure factors from powder data are accurate enough to discuss the experimental charge-density distributions of these materials. The number of structure factors of silicon determined in the present study is 104, which is three times more than that of previous Pendellosung data. The experimental charge densities have been obtained by the maximum-entropy method from the present structure factors. The charge densities at bond mid-points for silicon and diamond show good agreement with different kinds of theoretical calculations. The present study proved that the powder diffraction at SPring-8 is a promising method for determination of experimental charge density for a wider range of materials.
77 citations
TL;DR: In this paper, the authors describe the direct observation of gas molecules adsorbed in the nanochannels of porous coordination polymers by the in situ synchrotron powder diffraction measurement of gas adsorption and the maximum entropy method (MEM)/Rietveld charge density analysis.
69 citations
TL;DR: Ge3Sb2Te6 was analyzed in detail using an x-ray diffraction method as discussed by the authors, where the crystal was characterized as a 33-layered cubic close-packed stacking structure.
Abstract: Ge3Sb2Te6 was analyzed in detail using an x-ray diffraction method. The crystal of this material in the space group R3¯m is characterized as a 33-layered cubic close-packed stacking structure. Te atoms fully occupy their specific layers, whereas Ge and Sb atoms are located in other layers thus causing partial atomic disordering. Te and Ge∕Sb layers are laminated alternately 11 times to form a NaCl block. Electron density distributions in the crystal were obtained using the maximum entropy method and band calculation, which showed very good agreement with each other. Ge3Sb2Te6 is a compound semiconductor with a very narrow band gap.
46 citations
TL;DR: The 3D coordination polymer [Fe(4ditz)3](PF6)2.solv], consisting of three interpenetrating infinite networks, consists of cavities between iron atoms of different networks, which are partly filled with solvent molecules.
Abstract: The 3D coordination polymer [Fe(4ditz)3](PF6)2.solv consists of three interpenetrating infinite networks. There are cavities between iron atoms of different networks, which are partly filled with solvent molecules. With a change of the solvent used during synthesis from methanol to ethanol, the magnetic behavior of the materials changes. Both show an abrupt two-step spin crossover from low spin (S = 0) to high spin (S = 2) with the methanolate curve lying 7 K higher and showing a small hysteresis. Single crystal and powder diffraction studies show that they both have the same structure, but in powder form, the methanolate slowly loses methanol to finally leave about 0.075 MeOH/Fe. In comparison, the bigger ethanol remains at 0.25 EtOH/Fe. These results, in conjunction with thermodynamic data, strongly suggest that the differences in magnetic behavior are largely entropic in nature. Possible reasons for this are discussed.
43 citations
TL;DR: In this paper, the electron charge density distributions in layered ferroelectrics Bi4Ti3O12 (BiT) and Bi3.25La 0.75Bi3O 12 (BLT) were investigated by analyzing high energy synchrotron-radiation powder diffraction data using the maximum entropy method/Rietveld method.
Abstract: Electron charge density distributions in layered ferroelectrics Bi4Ti3O12 (BiT) and Bi3.25La0.75Ti3O12 (BLT) are investigated by analyzing high-energy synchrotron-radiation powder diffraction data using the maximum entropy method/Rietveld method. BiT shows that chemical bonding resulting from orbital hybridization is established between Bi–O in the perovskite layer only along the a axis, whereas BLT exhibits isotropic chemical bonding of Bi∕La–O with a high electron density both along the a and b axes. High endurance to polarization fatigue reported for BLT films is suggested to originate from the stabilization of oxygen in the perovskite layer due to the isotropic chemical bonding of Bi∕La–O.
35 citations
TL;DR: In this article, a polycrystalline sample of the room-temperature ferromagnet was measured and analyzed for x-ray-diffraction patterns, and possible spin and orbital models for the magnetic order were proposed.
Abstract: Synchrotron x-ray-diffraction patterns were measured and analyzed for a polycrystalline sample of the room-temperature ferromagnet ${\mathrm{Sr}}_{3.12}{\mathrm{Er}}_{0.88}{\mathrm{Co}}_{4}{\mathrm{O}}_{10.5}$ from $300\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}650\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, from which two structural phase transitions were found to occur successively. The higher-temperature transition at $509\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is driven by ordering of the oxygen vacancies, which is closely related to the metallic state at high temperatures. The lower-temperature transition at $360\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is of first order, at which the ferromagnetic state suddenly appears exhibiting a jump in magnetization and resistivity. Based on the refined structure, possible spin and orbital models for the magnetic order are proposed.
32 citations
TL;DR: The structures of eight members of the series of double perovskites of the type Ba2LnB′O6 were examined both above and below room temperature using synchrotron X-ray powder diffraction.
TL;DR: GISAXS measurements under optimized geometry with quantitative calculations using DWBA revealed that the nanocells are spherical and aligned in a single layer of hexagonal lattice and are surrounded by CO(2)-philic block domains.
Abstract: Analysis of nanostructures is of increasing importance with advances of nanotechnology. Embedded nanostructures in thin films in particular are of recent interest. Grazing incident small angle x-ray scattering (GISAXS) has been recognized to be a powerful method to probe such embedded nanostructures; however, quantitative analysis of scattering pattern is not always trivial due to complex refraction and reflection at surface and interfaces. We prepared nanocellular thin films using block copolymer template with carbon dioxide (CO2); CO2 “bubbles” were formed in the CO2-philic block domains. Such nanocellular structures were analyzed by GISAXS and simulated using distorted wave Born approximation (DWBA). Unlike traditional transmission x-ray scattering, GISAXS requires a careful choice of incident angle to analyze the form factor of scatters embedded in a thin film. Nevertheless, the GISAXS measurements under optimized geometry with quantitative calculations using DWBA revealed that the nanocells are spher...
TL;DR: In this paper, the magnetic and structural properties of a spin-crossover complex, Fe(phen)2(NCS)2 (phen=1,10-phenanthroline), can be reversibly switched by the on-off action of the continuous photoexcitation at the same temperature.
Abstract: A photoexcitation is one of the promising external fields to control the material phases. Here, the authors have demonstrated that the magnetic and structural properties of a spin-crossover complex, Fe(phen)2(NCS)2 (phen=1,10-phenanthroline), can be reversibly switched by the on-off action of the continuous photoexcitation at the same temperature. The structural data suggest that the density of the high-spin Fe2+ in the photoinduced phase is about 0.88. Suppressed atomic vibrations of the photoinduced phase exclude the conventional heating effect as the origin for the observed optical switching.
TL;DR: In this article, the effects of O2− or OH− ion incorporation on the cage geometry in 12CaO·7Al2O3 (C12A7) crystals were examined by the maximum entropy method (MEM)/Rietveld analyses of synchrotron powder X-ray diffracting.
Abstract: Effects of O2− or OH− ion incorporation on the cage geometry in 12CaO·7Al2O3 (C12A7) crystals are examined by the maximum entropy method (MEM)/Rietveld analyses of synchrotron powder X-ray diffract...
TL;DR: In this article, a combination of the maximum entropy method (MEM) and Rietveld refinement for powder X-ray diffraction (XRD) data was used to visualize the peculiar bonds in these two derivative crystals.
Abstract: Boron carbide (B 12 C 3 ) and boron phosphide (B 12 P 2 ) have the similar structures to α-rhombohedral boron (α-B 12 ) and are considered to be derivative crystals of it. The peculiar bonds in these two derivative crystals are visualized by MEM/Rietveld analysis, which involves a combination of the maximum entropy method (MEM) and Rietveld refinement for powder X-ray diffraction (XRD) data. The distinctive bending of bonds observed in α-B 12 is reversed by an insertion of other atoms. This bending arises from the conflict between the crystal structure of the rhombohedral lattice and the icosahedral structure of the B 12 cluster. Bond strength and interatomic distances are also varied by the insertion. In order to estimate the bond strength, we obtained the electron density height at each bond critical point, and compared it with the force constant, which is derived from the Raman shift.
TL;DR: The N-isotope effect has been investigated for a series of layered superconductors with small carrier density as discussed by the authors, where the N-vibration phonon mode around $615\phantom{\rule{0.3em}{0ex}}{cm}}^{\ensuremath{-}1}$ interacting most strongly with electronic system has shown softening by about $20
Abstract: The N-isotope effect has been investigated for a series of layered superconductors ${\mathrm{Li}}_{x}\mathrm{ZrNCl}$ with small carrier density. The N-vibration phonon mode around $615\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ interacting most strongly with electronic system has shown softening by about $20\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $(=3.3%)$ upon $^{15}\mathrm{N}$ substitution. On the other hand, the decrease in the superconducting critical temperature $({T}_{c})$ upon $^{15}\mathrm{N}$ substitution has been found to be only $0.06\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ $(=0.5\ifmmode\pm\else\textpm\fi{}0.3%)$. This small change in ${T}_{c}$ corresponds to an isotope shift coefficient $\ensuremath{\alpha}=0.07\ifmmode\pm\else\textpm\fi{}0.04$, which is much smaller than the conventional value of 0.5, implying the relevance of other fluctuations than the phonon to the pairing interaction.
TL;DR: At low temperatures, the crystal is a paramagnet and the magnetic susceptibility decreases from 150 K with evidence of antiferromagnetic-like interactions by slow cooling, and a magnetic metastable state that can be controlled by the cooling rate is found.
Abstract: Magnetic properties of solvent-free crystals of the endohedral Sc@C82 are investigated by SQUID and X-ray powder diffraction. We find that the crystal is a paramagnet and the magnetic susceptibility decreases from 150 K with evidence of antiferromagnetic-like interactions by slow cooling. X-ray crystal analysis reveals the presence of a phase transition at 150 K, which is attributed to an orientational ordering transition of the fullerene molecules. At low temperatures we find a magnetic metastable state that can be controlled by the cooling rate. The metastable state can be formed by rapid cooling. The direction of Sc@C82 molecular axis in the crystals is disordered in the metastable state, and the susceptibility is higher than that in the slow cooling case at low temperature.
TL;DR: In this article, a new system of rapidly-scanning DSC/WAXD/SAXS simultaneous measurements has been successfully developed at the BL40B2 in SPring-8, Japan.
Abstract: A new system of rapidly-scanning DSC/WAXD/SAXS simultaneous measurements has been successfully developed at the BL40B2 in SPring-8, Japan. The combination of the ultra-bright and highly-directional X-ray beams with the highly-sensitive two-dimensional (2D) detectors such as an imaging plate (IP), a CCD detector and a flat panel (FP) detector has made it possible to perform the rapidly-scanning time-resolved measurements of WAXD and SAXS for the polymeric materials subjected to the various kinds of external field like temperature, tensile force, magnetic field, hydrostatic pressure, and so on. The experimental data about the phase transitions of vinylidene fluoride-trifluoroethylene copolymer with VDF 82 mol % content and poly(vinylidene fluoride) form I have been presented as actual examples, where the phase transitions of the polar crystal consisting of planar-zigzag chains to the gauche-type high-temperature phase have been confirmed definitely and the remarkable change in lamellar stacking structure could be detected in the temperature region immediately below the melting point.
01 Jan 2007
TL;DR: In this paper, a new system of rapidly-scanning DSC/WAXD/SAXS simultaneous measurements has been developed at the BL40B2 in SPring-8, Japan.
Abstract: A new system of rapidly-scanning DSC/WAXD/SAXS simultaneous measurements has been suc- cessfully developed at the BL40B2 in SPring-8, Japan. The combination of the ultra-bright and highly-directional X-ray beams with the highly-sensitive two-dimensional (2D) detectors such as an imaging plate (IP), a CCD detector and a flat panel (FP) detector has made it possible to perform the rapidly-scanning time-resolved measurements of WAXD and SAXS for the polymeric materials subjected to the various kinds of external field like temperature, tensile force, magnetic field, hydrostatic pressure, and so on. The experimental data about the phase transitions of vinylidene fluoride- trifluoroethylene copolymer with VDF 82 mol % content and poly(vinylidene fluoride) form I have been presented as actual examples, where the phase transitions of the polar crystal consisting of planar-zigzag chains to the gauche-type high-temperature phase have been confirmed definitely and the remarkable change in lamellar stacking structure could be detected in the temperature region immediately below the melting point. (doi:10.1295/polymj.PJ2007105)
TL;DR: It is clarified that the external heavy metal effect of Pr(III) on melem is much stronger in the film than in the bulk solid state, resulting in producing an unusual triplet state of melem.
Abstract: A novel emissive molecular system is constructed by the intercalation of the fluorophore melem (triamino-tri-s-triazine) within a Langmuir–Blodgett (LB) film of stearic acid with the periodic arrangement of lanthanides (Ln(III)), mainly Pr(III) with supporting of Eu(III). From emission spectra, decay curves, quantum yields and XPS measurements, it is clarified that the external heavy metal effect of Pr(III) on melem is much stronger in the film than in the bulk solid state, resulting in producing an unusual triplet state of melem. The triplet state of melem in the LB film donates the excitation energy to Pr(III) in the LB film, which is completely different from the energy transfer pathway of Pr–melem complex in the solid state through the singlet state of melem.
TL;DR: In this paper, the stacking structure of high-density polyethylene (HDPE) thin films was investigated using synchrotron grazing-incidence small-angle and wide-angle X-ray scattering (GISWAXS) measurements at the BL40B2 beamline in SPring-8.
Abstract: We have investigated lamellar stacking structure of melt-crystallized and annealed high-density polyethylene (HDPE) thin films, with a thickness of ca 400 nm prepared on silicon wafers, using synchrotron grazing-incidence small-angle and wide-angle X-ray scattering (GISWAXS) measurements at the BL40B2 beamline in SPring-8. In-situ measurements of GISWAXS were carried out for the films in a stepwise annealing process under vacuum. Scattering peaks relating to the long period, the average distance between stacked crystalline lamellae, were measured only in the in-plane direction near the Yoneda peak of the grazing-incidence small-angle X-ray scattering patterns. On the other hand, the orthorhombic (110) and (200) reflections of oriented HDPE crystals were measured in the out-of-plane direction of the grazing-incidence wide-angle X-ray scattering patterns. It was revealed that crystalline lamellae were stacked in a parallel direction to the film surface and the long period increased from ca 25 nm to ca 32 nm in a stepwise annealing process. Within a lamella, molecular chains were found to be packed regularly and the chain axis (the c axis) was relatively oriented parallel to the film surface.
TL;DR: The structure of the double perovskite Ba2HoTaO6 was examined using synchrotron X-ray powder diffraction at fine temperature intervals over the range of 90-300 K as mentioned in this paper.
07 Feb 2007
TL;DR: In this paper, the x-ray pinpoint structural measurement (XSTM) technique was developed at SPring-8 to explore the novel concept and new phenomena for nanomaterials and/or devices.
Abstract: The pulse characteristic and high coherent x‐ray beam of SPring‐8 allow us to investigate dynamics of chemical reactions and phase transition of materials caused by applied field. In order to realize such direct investigation, “x‐ray pinpoint structural measurement”, which is the advanced x‐ray measurement technique in nanometer spatial scale and/or pico‐second time scale, is being developed at SPring‐8. The features of “x‐ray pinpoint structural measurement” technique are, 1) spatial resolution: ∼ 100 nm, 2) time resolution: ∼ 40 ps, and 3) measurement under the photo‐irradiation, electric field, magnetic field, high pressure and active devices. Using this technique, we will explore the novel concept and new phenomena for nanomaterials and/or devices, and also demonstrate their validity.
TL;DR: In this paper, the authors analyzed liquid structures of the Zr-Cu and Zr50Ni50 alloys with different compositions and found that the effect of concentration variation in the liquid ZrNi alloys was significantly different from that of the Liquid ZrCu alloys, and that a degree of the short-range correlation between the constituents in the liquids affects substantially the glass-forming ability of binary Zr alloys.
Abstract: In order to obtain an insight into the high glass-forming ability of bulk metallic glasses, we have analyzed liquid structures of the Zr-Cu and the Zr-Ni binary alloys with different compositions. High-energy (E = 113 keV) x-ray diffraction experiments were carried out for the liquid alloys levitated by a conical nozzle levitation (CNL) technique. While a peculiar shoulder on the second peak was observed in the structure factors of the Zr-Cu liquid alloys, those of the Zr70Ni30 and the Zr50Ni50 liquids exhibit an asymmetric shape of the second peak. In addition, it was found that the effect of concentration variation in the liquid Zr-Ni alloys was significantly different from that of the liquid Zr-Cu alloys. The liquid structure analyses using the reverse Monte Carlo (RMC) simulation have clarified that a degree of the short-range correlation between the constituents in the liquids affects substantially the glass-forming ability of the binary Zr alloys.
TL;DR: In this article, the structure of high-purity bulk forsterite (Mg2SiO4) glass synthesized by a conical nozzle levitation (CNL) technique and diffraction experiments was determined by a combination of high energy x-ray, neutron diffraction, and reverse Monte Carlo (RMC) modeling technique.
Abstract: Two topics are described for structure analyses of glass and liquid using a combination of conical nozzle levitation (CNL) technique and diffraction experiments. The structure of high-purity bulk forsterite (Mg2SiO4) glass synthesized by a CNL technique has been determined by a combination of high-energy x-ray, neutron diffraction, and reverse Monte Carlo (RMC) modeling technique. The 3-dimensional atomic configuration derived from RMC modeling revealed that unusual network structure. In order to study structures of high-temperature and undercooled liquids, a CNL system has been developed and integrated with the two-axis diffractometer for glass, liquid, and amorphous materials at SPring-8, which is one of the third-generation synchrotron source. High-energy x-ray diffraction experiments were performed to obtain reliable diffraction data for the liquid phase of metallic glass-forming Zr-Cu binary alloys.
TL;DR: Based on the maximum entropy method (MEM) charge density, the authors visualized the electrostatic potential of a charge transfer compound, RbMn[Fe(CN) 6 ], which shows the charge transfer transition from the nominal Mn 2+ -Fe 3+ configuration to the Mn 3+ −Fe 2+ one below 220 K.
Abstract: Based on the maximum entropy method (MEM) charge density, we have visualized the electrostatic potential of a charge-transfer compound, RbMn[Fe(CN) 6 ], which shows the charge-transfer transition from the nominal Mn 2+ –Fe 3+ configuration to the Mn 3+ –Fe 2+ one below 220 K. In the low-temperature phase, the transferred electron spreads over the hexacyanoferrate ([Fe(CN) 6 ]) via the strong Fe t 2 g -CNπ * hybridization. Such an extended charge-transfer state is responsible for the relatively strong ferromagnetic coupling between the neighbouring Mn 3+ spins.
07 Feb 2007
TL;DR: In this article, a new attachment for thin film x-ray measurements equipped with the large Debye-Scherrer camera at BL02B2 of the SPring‐8 was developed.
Abstract: We have developed a new attachment for thin film x‐ray measurements equipped with the large Debye‐Scherrer camera at BL02B2 of the SPring‐8. It is quite easy to handle and control the attachment using user‐friendly computer programs. It is also notable that the attachment realizes both low‐glancing‐angle incident beam condition and in‐plane measurement condition. The attachment enables us to measure high precision x‐ray diffraction data from many kinds of thin films with the Debye‐Scherrer camera. Using this attachment we try to analyze some dimensionally controlled thin film structures.