Haruno Murayama

Direct Observation of a Metastable Crystal Phase of LixFePO4 under Electrochemical Phase Transition

The phase transition between LiFePO4 and FePO4 during nonequilibrium battery operation was tracked in real time using time-resolved X-ray diffraction. In conjunction with increasing current density, a metastable crystal phase appears in addition to the thermodynamically stable LiFePO4 and FePO4 phases. The metastable phase gradually diminishes under open-circuit conditions following electrochemical cycling. We propose a phase transition path that passes through the metastable phase and posit the new phases role in decreasing the nucleation energy, accounting for the excellent rate capability of LiFePO4. This study is the first to report the measurement of a metastable crystal phase during the electrochemical phase transition of LixFePO4.

Supramolecularly engineered perylene bisimide assemblies exhibiting thermal transition from columnar to multilamellar structures

Perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI) was functionalized with ditopic cyanuric acid to organize it into complex columnar architectures through the formation of hydrogen-bonded supermacrocycles (rosette) by complexing with ditopic melamines possessing solubilizing alkoxyphenyl substituents. The aggregation study in solution using UV-vis and NMR spectroscopies showed the formation of extended aggregates through hydrogen-bonding and π-π stacking interactions. The cylindrical fibrillar nanostructures were visualized by microscopic techniques (AFM, TEM), and the formation of lyotropic mesophase was confirmed by polarized optical microscopy and SEM. X-ray diffraction study revealed that a well-defined hexagonal columnar (Col(h)) structure was formed by solution-casting of fibrillar assemblies. All of these results are consistent with the formation of hydrogen-bonded PBI rosettes that spontaneously organize into the Col(h) structure. Upon heating the Col(h) structure in the bulk state, a structural transition to a highly ordered lamellar (Lam) structure was observed by variable-temperature X-ray diffraction, differential scanning calorimetry, and AFM studies. IR study showed that the rearrangement of the hydrogen-bonding motifs occurs during the structural transition. These results suggest that such a striking structural transition is aided by the reorganization in the lowest level of self-organization, i.e., the rearrangement of hydrogen-bonded motifs from rosette to linear tape. A remarkable increase in the transient photoconductivity was observed by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements upon converting the Col(h) structure to the Lam structure. Transient absorption spectroscopy revealed that electron transfer from electron-donating alkoxyphenyl groups of melamine components to electron-deficient PBI moieties takes place, resulting in a higher probability of charge carrier generation in the Lam structure compared to the Col(h) structure.

X-ray diffractometry for the structure determination of a submicrometre single powder grain.

A high-precision diffractometer with a synchrotron radiation microfocusing technique has been developed to investigate the crystal structure of a submicrometre-scale single grain of powder sample. The structure of a BaTiO3 single powder grain, of dimensions ∼600 × 600 × 300 nm, was determined.

EXAFS study on interfacial structure between Pd cluster and n-octadecanethiolate monolayer : Formation of mixed Pd-S interlayer

The geometrical structure of a Pd cluster (diameter of � 3.1 nm) protected by n-octadecanethiolate monolayer has been investigated by high-resolution TEM (HRTEM), XRD, and EXAFS spectroscopy. The HRTEM and XRD measurements have revealed that the cluster core is comprised of an fcc single crystal of Pd. The mean coordination numbers of the Pd–Pd and Pd–S shells determined by the Pd K-edge EXAFS analysis suggest that the surface of the Pd core is sulfurized to form a mixed Pd–S layer underneath the thiolate monolayer. 2003 Elsevier Science B.V. All rights reserved.

Time-Resolved Investigation of Nanosecond Crystal Growth in Rapid-Phase-Change Materials: Correlation with the Recording Speed of Digital Versatile Disc Media

The crystallization process in digital versatile disc (DVD) media was investigated using a time-resolved X-ray diffraction apparatus coupled with in situ photoreflectivity measurement. The time profiles of crystallization were found to be consistent with the changes in photoreflectivity. The phase changes were characterized by the start and end time; 90±1 and 273±1 ns for Ge2Sb2Te5, and 85±1 and 206±1 ns for Ag3.5In3.8Sb75.0Te17.7, respectively. The faster crystallization time in Ag3.5In3.8Sb75.0Te17.7 is ascribed to its characteristic crystallization process; its X-ray diffraction profile shows a significant sharpening during the crystallization process, whereas the peak width of Ge2Sb2Te5 remained unchanged. The present findings suggest that crystal growth control is another key for designing faster phase-change materials.

Formation of Pdn(SR)m clusters (n < 60) in the reactions of PdCl2 and RSH (R = n-C18H37, n-C12H25)

Abstract Mass spectroscopic analysis revealed that Pd clusters passivated by thiolates and the stoichiometric thiolate complexes, Pd n ( SR ) 2n (n=5,6) , are formed in the reactions between palladium chloride and n-alkanethiols (RSH: R=n-C18H37, n-C12H25) in toluene. The Pd clusters thus formed are formulated as Pdn(SR)m with m∼0.6n. The cluster sizes, distributed in the range of 5⩽n⩽60, are consistent with their core diameters of ∼1 nm observed by TEM. A gap of ∼2 eV was observed in the optical transition of the Pdn(SR)m clusters showing the emergence of non-metallic properties as a result of size reduction.

Structural and electronic properties of extremely long perylene bisimide nanofibers formed through a stoichiometrically mismatched, hydrogen-bonded complexation.

Extremely long nanofibers, whose lengths reach the millimeter regime, are generated via co-aggregation of a melamine-appended perylene bisimide semiconductor and a substituted cyanurate, both of which are ditopic triple-hydrogen-bonding building blocks; they co-aggregate in an unexpected stoichiometrically mismatched 1:2 ratio. Various microscopic and X-ray diffraction studies suggest that hydrogen-bonded polymeric chains are formed along the long axis of the nanofibers by the 1:2 complexation of the two components, which further stack along the short axis of the nanofibers. The photocarrier generation mechanism in the nanofibers is investigated by time-of-flight (TOF) experiments under electric and magnetic fields, revealing the birth and efficient recombination of singlet geminate electron-hole pairs. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements revealed intrinsic 1D electron mobilities up to 0.6 cm(2) V(-1) s(-1) within nanofibers.

RISING beamline (BL28XU) for rechargeable battery analysis

The BL28XU beamline, dedicated to rechargeable battery analysis, is described.

In situ two-dimensional imaging quick-scanning XAFS with pixel array detector

Two-dimensional imaging quick-scanning XAFS measurements were performed using a pixel array detector.

Ultra-high-precision time control system over any long time delay for laser pump and synchrotron x-ray probe experiment

An ultra-high-precision clock system for long time delay has been developed for picosecond time-resolved x-ray diffraction measurements using synchrotron radiation (SR) pulses and synchronized femtosecond laser pulses. The time delay control between pump laser pulse and the probe SR pulse was achieved by combining an in-phase quadrature modulator and a synchronous counter. This method allowed us to change the delay time by a nearly infinite amount while maintaining the precision of +/-8.40 ps. Time-resolved diffraction measurements using the delay control system were demonstrated for precise measurement of an acoustic velocity in a single crystal of gallium arsenide.