Direct Visualization of Energy-transferred Excited State in Eu Complex

Highly luminescent lanthanide (Ln) complexes have attracted much attention because Ln³⁺ ions show long-lived ff-emissions with narrow band shape. Their unique photo-optical properties are promising for the design of light-emitting materials and sensing devices. Although the ff-emissions are essentially weak because of Laporte forbidden, chelate ligands is effective to strengthen the intramolecular energy transfer from photo-excited organic ligands to Ln³⁺ ions. The direct evidence of energy transfer from ligands to Ln³⁺ and details of excited state, however, are still veiled. Here, we report direct visualization of energy-transferred excited state in Eu complex with a hexadentate ligand (L) consisting of two bipyridine moieties bridged by an ethylendiamine unit, [Eu³⁺(L)(NO₃)₂](PF₆) (Eu(L))[1] by Maximum Entropy Method (MEM) charge density[2] and electrostatic potential analysis[3] based on SR X-ray diffraction. First, we confirmed that the electron numbers of Eu and ligand L in the excited state are the same as those in the ground state, which is a direct evidence of energy transfer instead of charge transfer. Next, we observed charge re-distribution in the Eu ion and the ligand L. The electrostatic potential distributions calculated using MEM charge density give an experimental evidence for the existence of polarization of ligand L both in the ground and photo-excited states. The orientation polarization in the ground state changed during pumping at 315 nm, and the charge re-distribution are qualitatively consistent with a theoretical prediction. This characteristic luminescence behavior based on the energy relaxation process have not been detected by fundamental crystal structural analysis. We have succeeded in visualization of subtle but important change due to energy transfer in the mononuclear Europium complex with hexadentate ligand at the first time.

Structural Basis for Emergence of Superionic Conductivity by an Ion Exchange

Various superionic conductors have been examined in terms of the application to electrolytes for solid fuel cells [1]. Recently we demonstrated by impedance measurements that a simple two-step chemical reaction transformed an electronic conductor Na_xCoO₂ into a superionic one. In the present study, we performed in situ synchrotron X-ray diffraction experiments to investigate a structural mechanism for the superionic conductivity driven by the chemical treatment of the layered oxide Na_xCoO₂. We developed a temperature- and humidity-controllable capillary cell under hydrogen and helium gas flow to install in the Debye-Scherrer camera at BL44B2 of SPring-8. This cell allows us to explore a structural transformation process by reduction and humidification treatments. Structural identifications and refinements with in situ diffraction data proved that Co vacancies formed by a CoO separation suppressed the electronic conductivity. Meanwhile it turned out from charge estimation in the Na layers that the superionic conductor transition originated from an ion exchange of H₃O⁺ for Na⁺, which was confirmed by Raman spectroscopy measurements. In addition, charge densities clearly visualized the H₃O⁺ ions disordering around the Na original sites, suggesting that the H₃O⁺ behave as a carrier source. Finally it was found from electrostatic potentials that the disordering H₃O⁺ sites were coupled through shallow potential barriers to trace a honeycomb-like ion pathway. In the presentation, I will discuss what a carrier is for the superionic-conductive phase from different viewpoints such as activation energies, concentration cell tests, and molecular dynamics simulations using the experimental structure information.

Crystallization Behaviors of Linear Polymers in Spin-coating Processes Traced by GISWAXS Measurements

The purpose of this study is clarification of crystallization behaviors of linear polymers in spin-coating film-forming processes on the molecular scale by time-resolved measurements of grazing-incidence small-angle and wide-angle X-ray scattering (GISAXS and GIWAXS: GISWAXS) measurements using synchrotron radiation. A sample used in this study was a commercially-available poly(3-hydroxybutyrate) (P3HB) (Sigma-Aldrich, Mw=437,000, Mw/Mn=1.67, Tg= 276 K) which was a biobased and biocompatible polyester. By spin-coating at rotational speeds of 1000 - 4000 rpm with using 0.49, 1.0, and 2.1wt% chloroform solutions of the P3HB, P3HB thin films with thicknesses of ca. 30 -600 nm were formed on silicon substrates. In these spin-coating processes at 296K, GISAXS and GIWAXS patterns from the sample on the substrate were simultaneously detected at BL45XU of SPring-8 (Hyogo, Japan). At the beginning of spin-coating, an isotropic scattering pattern from the solution was observed. Next, anisotropic Bragg reflections from oriented orthorhombic crystals of P3HB appeared and increased in intensity for several tens seconds. This indicated that P3HB chains crystallized as chloroform evaporated from the sample. It was also found that P3HB orthorhombic crystal having edge-on orientation was preferentially formed in thinner films. When the rotational speed of the substrate increased, the apparent induction period of crystallization slightly increased and the crystal growth rate decreased. This implied that the chain mobility of P3HB for crystallization might reduce due to a reduction in quantity of the solvent molecules and an increase in magnitude of the centrifugal force. These results obtained in this research would be important knowledge to improve film processing technologies for biobased polymeric materials.

In situ synchrotron powder diffraction for an ionic conductor transition

In situ synchrotron X-ray powder diffraction can be one of the most powerful probes to investigate the structure evolution by a chemical reaction thanks to simultaneity of data collection. It is not, however, with ease to produce a homogeneous chemical reaction in the limited spaces, which is essential to see an atomic-scale structure evolution. We have developed an in situ capillary cell for both high-temperature H₂ reduction and precise humidity control at the SPring-8 BL44B2. We successfully applied this in situ system to an electronic conductor LaSr₃Fe₃O₁₀, which is transformed into an ionic conductor by the two-step chemical treatments [1]. LaSr₃Fe₃O₁₀ has a triple-layer structure with a FeO₆ octahedral unit. One triple layer is bonded with another layer through van der Waals interaction. Structure refinements with in situ synchrotron powder diffraction data revealed that the H₂ reduction at 613 K produced in-plane oxygen vacancies, which resulted in suppression of the interlayer interaction. We found from charge density studies and Raman spectroscopy measurements that the following humidification intercalated H₂O and OH^- into the interlayer and intralayer, respectively. That means that H₂O plays a role for suppression of three-dimensional electronic conductivity, stabilizing the intercalation structure. On the other hand, the OH^- ions behave as carriers for ionic conductivity, maintaining the charge neutrality in the intralayer. Finally we determined the composition of the ionic conductor to be LaSr₃Fe₃O_8.0 (OH) _1.2·2H₂O, which indicates a transformation of LaSr₃Fe₃O₁₀ into an OH^- ionic conductor. In the presentation, I will discuss the OH^- ionic conduction channel based on electrostatic potentials obtained from charge densities.

The 100 Years History of Crystallography in Japan

A century ago, crystallogtaphy ushered in the era of modern science & technology in Japan. The beginning of modern crystallography in Japan dates back to 1913. Torahiko Terada (Tokyo Imperial University) demonstrated X-ray diffraction[1] and Shoji Nishikawa (Tokyo Imperial University) reported on X-ray patterns of fibrous, lamellar and granular substances[2]. In 1936, Ukichiro Nakaya (Hokkaido University) successfully classified natural snow crystals and made the first artificial snow crystals. In the last half-century, developments in crystallography helped form thriving manufacturing sectors such as the semiconductor industry, the iron and steel industries, the pharmaceutical industry, the electronics industry, the textile industry, and the polymer industry, as well as a wide array of academic research.

Japanese Crystallography in Culture and Art

"We can find many seeds of crystallography in Japanese culture. Most of the family crests have symmetry elements such as rotation axes and mirror symmetry elements. Sekka-zue, a picture book of 86 kinds of crystals of snow, was made by Toshitura Doi, who is a feudal lord in Edo-period and he observed snow using a microscope in nineteenth century. In recent years, people enjoy to make crystal structures, polyhedrons, carbon nanotube, quasicrystal etc. by origami, the art of folding paper [1]. In the field of science, the Japanese crystallography has contributed to explore culture and art. An excellent example is unveiling the original color of Japanese painting "Red and White Plum Blossoms" by Korin Ogata [2]. Prof. Izumi Nakai (Tokyo University of Science) developed an X-ray fluorescence analyzer and an X-ray powder diffractometer designated to the investigation of cultural and art works and had succeeded in reproducing the silver-colored waves through computer graphics after X-ray analyses of crystals on the painting. The scientific approach by Prof. Nakai et al. unveiled the mystery of cultural heritage of ancient near east, ancient Egypt etc. and is being to contribute to insight into the history of human culture. [1] An event to enjoy making crystals by origami is under contemplation. [2] The symposium ""Crystallography which revives heritages"" was held on February 16, 2014 at Atami in Japan."

Japanese Science & Technology with Crystallography

Divers Japanese Science and Technology has advanced together with the progress of crystallography in biology, chemistry, physics, materials science, metallurgy, electronics, engineering, geoscience, etc. Based on the highly scientific and crystallographic technology, Japan has been a great contributor in developing of high-end X-ray generator, electron microscope as well as large scale Photon Science facilities, such as Photon Factory (SR), SPring-8 (SR), J-PARC (Neutron) and SACLA (XFEL). Under such background, we promote IYCr2014 with the partnership of 36 academic societies in the field of pure and applied sciences. In the last half-century, developments in crystallography have also helped thriving manufacturing sectors such as the semiconductor, the iron and steel, the pharmaceuticals, the electronics, the textile, and the chemical industries. Some of the recent impressive outcomes in Japan are fundamental findings of photosynthesis [1] and pristine asteroid [2]. Crystallography in Japan keeps promoting our nationwide projects grappling with global problems such as environment and food, and will contribute to realize a sustainable society.

Instrumentation of SAXS for the Analysis of Heterogeneous Structure in Polymer

Polymer materials have hierarchal structure in the very wide range of scale. It is well known that the property is dependent on the hierarchical structure. In order to improve the performance of the materials, clarifying the hierarchical structure in a wide range and the feed back to the manufacturing process are important. However, it is difficult to clarify the hierarchical heterogeneous structure of polymer materials using only single method. Therefore the combination of microbeam small- and wide- angle X-ray scattering (SAXS/WAXS) is useful for evaluation of the hierarchical heterogeneous structural of polymer materials. The BL03XU, in alias, FSBL, in SPring-8 was constructed by consortium of industrial and academic groups and has been used from 20101),2). Structure characterization of advanced materials in the industrial field has been carried out using microbeam SAXS/WAXS method. In addition to the description of the SAXS/WAXS measurement system at BL03XU, we will report on the local structural evaluation of carbon fiber (CF). A hierarchal heterogeneous structure of CFs was visualized in the space resolution of 1 μm using a microbeam and an X-ray imaging technique. The image contrasts were identified by the difference in peak positions corresponding to the void size, the peak width corresponding to the crystallite size, and intensities corresponding to the amount of crystallites and voids. The X-ray scattering images of high-modulus CF are shown in a figure. Nanometer-size voids estimated by SAXS are abundant in the center of a fiber, on the other hand, the crystallite is abundant in the vicinity of a surface was revealed. It is suggested that the voids were generated near the center of the fiber to relax the strain during the crystallization process from the surface during the graphitization of fibers. We succeeded in visualizing the distribution of voids and crystallite of a few nanometers, which cannot be observed by an X-ray transmission imaging method.

Orbital Order and Structural Phase Transitions in Vanadium Spinel FeV₂O₄

Orbital degrees of freedom plays an important role in condensed matter physics because it is strongly related with phase transitions and induces the fascinating physical properties. A spinel oxide FeV₂O₄ is one of the peculiar examples because this compound has double orbital degrees of freedom at both Fe²⁺ and V³⁺ ions. Furthermore, this material represents exotic physical properties [1,2], i.e.; multiferroic, large magnetostriction, and successive structural transitions with decreasing temperature: cubic - tetragonal (c < a: tetraHT, 138K) - orthorhombic (orthoHT, 108 K) - tetragonal (c > a: tetraLT, 68 K). However, the origin of structural transitions and physical properties is controversial until now. In order to clarify the origin, we have performed synchrotron x-ray diffraction experiments at low temperatures at beamline BL02B2 (for the powder samples) in SPring-8 and BL-4C (for the single crystal) of the Photon Factory, KEK. Furthermore, we have carried out the magnetization and the specific heat measurements using polycrystalline samples and single crystal of FeV₂O₄. We have firstly found another orthorhombic phase (orthoLT) below 30 K in the polycrystalline sample of FeV₂O₄, shown in figure 1. The Rietveld analysis was performed, and the overall qualities of fittings were fairly good. In order to investigate the details of the orbital state of Fe²⁺ and V³⁺ in FeV₂O₄, we have performed the normal mode analysis, which is based on static displacements of the tetrahedron of FeO₄ and octahedron of VO₆. In the orthoLT phase, we found the orbital order of Fe²⁺ ions, which is mixture of 3z²-r² and y²-z² orbitals, without change of orbital order of V³⁺ ions. This result indicates that the origin of the orthoLT phase is derived from the competition between cooperative Jahn-Teller effect and relativistic spin-orbit coupling of Fe²⁺ ions. We also discuss the origins of the other phase transitions considering the orbital state of V³⁺ and Fe²⁺ ions, and then the orbital dilution effect, where the structural and magnetic properties are investigated by using powder samples substituted for Fe²⁺ and V³⁺ ions by other ions (Mn²⁺ and Fe³⁺) with no orbital degrees of freedom.

Nanoporous Structural Science Developed by the MEM/Rietveld Method

Wide-spread functionalization research of Metal Organic Frameworks(MOFs) has brought rapid increase in variety of materials since the beginning of structural study in nanoporous of MOFs were made by SR(Synchrotron Radiation) powder diffraction using the MEM(Maximum Entropy Method)/Rietveld Method(Kitaura et al, 2002). The MEM/Rietveld method has successfully applied to refine the structural position of absorbed molecules and to investigate a bonding nature between the molecules and MOF's pore walls. Noise-resistance electron density mapping with incomplete data set was a key advantage of MEM to visualize unmodeled feature of molecules in nanoporous. Since then, the charge density studies by the MEM/Rietveld Method have uncovered various ordering structure of absorbed molecules into nanoporous more and more(Takata, 2008). Those findings ignited trends to design the nanoporous as the space to be functionalized. Recently, the MEM/Rietveld method has been further developed as the method to map an electrostatic potential and electric field(Tanaka 2006). This technique is making a progress in structural science of MOFs since the visualized electrostatic potential in the nanoporous ought to provide information of interplay between the molecule and the pore walls. The talk will present the recent progress and challenges of the MEM/Rietveld method to the structural science of the MOFs.