Moritaka Hida

Electronic structure of Eu@C60 studied by XANES and UV-VIS absorption spectra

Eu endohedral C60, Eu@C60, has been extracted with aniline from soot prepared by arc-heating of a graphite/Eu2O3 composite rod and obtained at high concentration by combining sublimation and repeated high-performance liquid chromatography. The laser desorption time-of-flight mass spectrum showed a pronounced peak of Eu@C60+. The UV–VIS absorption spectrum of this sample has a red-shift in the onset (>900 nm) in comparison with those for C60 and C70, as expected from electron transfer from the Eu atom to the C60 cage. The valence state of the Eu atom in Eu@C60 has been determined to be +2 by Eu LIII-edge XANES.

Development of a Laboratory EXAFS Facility and Its Application to Amorphous GeSe Semiconductors

A new type of X-ray spectrometer and detector system for performing extended X-ray absorption fine structure measurements in the laboratory has been developed. The spectrometer is equipped with an asymmetrically-cut flat crystal monochromator in the magnifying mode and converts the energy dispersion to position dispersion using a position-sensitive detector. Two advantages of this apparatus are that it has no moving parts and that it makes the X-ray path shorter. The application of the spectrometer to amorphous GeSe semiconductors is also presented to show its usefulness.

Stress induced products and ductility due to lattice instability of β phase single crystal of Ti-Mo alloys

Abstract Stress induced products — athermal ω phase, twin or martensite—in single crystals of Ti-14 and 20 wt.% Mo alloys were studied mainly with the X-ray precession method. Athermal ω phase was found in as-quenched and deformed 14 wt.% Mo alloys. The lattice constant of the matrix was contracted by the athermal ω phase. The deformation mode of the excellently ductile 14 wt.% Mo alloys was twin-like. In plastically unstable 20 wt.% Mo alloys, athermal ω phase and twin were not induced by tensile deformation, but α martensite was formed in the portion of necking which appeared just after yielding. The lattice constant of the matrix was extended by the martensite. The formation of α martensite seems to give rise to stress concentrations and the phenomena such as local softening which prevents the propagation of work-hardened region.

Structural stability and mechanochemical activity of titanium nitride prepared by mechanical alloying

Pure titanium nitride (TiN) was synthesized by mechanical alloying (MA). In order to prevent the contamination from the MA vial and atmospheric gas, the MA steel vial was replaced with a titanium vial and atmospheric gas was deoxidized using sponge titanium heated to 623 K. The mechanochemical activity during MA was estimated from the gas purification temperature. The investigation of thermal and pressure stability by thermal treatment and hot isostatic pressing (HIP) revealed that titanium nitride, TiN, was stable on heating to 1173 K under a vacuum, but became unstable under a high pressure, 100 MPa.

In situ observation of stress-induced martensitic transformation and plastic deformation in TiNi alloy

Stress-induced martensitic transformation and plastic deformation in TiNi alloy have been investigated using transmission electron microscope with an in situ deformation technique. It was found that martensite bands were formed and grew with increasing strain and shrank with decreasing strain in tension. In the second deformation stage, a high density of looped dislocations was formed in the reverse-transformed matrix, while in the first deformation stage dislocations were not formed in the reverse-transformed matrix. The formation of dislocation in the second deformation stage is considered as bearing a relation to reverse martensitic transformation and twinning dislocations lying inside the stress-induced martensite.

Study of the ω-Phase in Ti–Mo Alloys by Diffuse X-Ray Scattering

The X-ray diffraction profiles of the ω-phase in Ti 1- x Mo x , 0.07 ≤ x ≤0.20, are carefully examined for the first time. The intensity distribution near the wave vector q 0 =(2/3, 2/3, 2/3) is asymmetric. The ω-phase appears in rod shaped clusters along the direction in the body-centered-cubic lattice. The incommensurate diffuse scattering can be detected above the critical composition x c =0.10. The scattering profiles are almost independent of temperature over a temperature range -120°C to 50°C. The observed diffuse scattering is discussed in terms of the planar displacements described by a stacking soliton and the coherency of the ω-phase domains.

Nitriding of dilute Mo-Ti alloys at a low temperature of 1373 K

Abstract For Mo-0.5 mass% Ti and pure Mo alloy nitrided in a NH 3 gas at a relatively low temperature of 1373 K, microstructural observations through optical and transmission electron microscopes, X-ray diffraction analysis and hardness measurements were carried out. A surface nitriding layer with very high hardness of approximately Hv ~ 1800 consisted of two Mo-nitride regions: an outer one of γ-Mo 2 N and an inner one of β-Mo 2 N. The inward diffusion of nitrogen is a rate-controlling process in the growth of the surface nitriding layer. In Mo-Ti alloy additionally an internal nitriding layer with relatively high hardness of Hv ~ 800 was formed beneath the surface nitriding layer. Such high hardness in the internal nitriding layer was found to result from the uniform dispersion of extremely fine plate-like particles of titanium nitride. The particles are approximately 0.4 nm thick and have coherent strain field in the matrix.

EXAFS Study on the Local Structure of a New High-Tc Superconductor in the Bi-Sr-Ca-Cu-O System

X-ray absorption spectroscopy has been used to study a new superconducting phase in the Bi-Ca-Sr-Cu-O system. X-ray absorption measurements at the Cu K-edge indicate that a copper ion is surrounded by five coordinated oxygen atoms, and that the Cu-O distance is 1.91 A. Measurements at the Bi LIII-edge give the interatomic distance between bismuth and oxygen as 2.10 A.

Microscopic approaches to isothermal transformation of incommensurate omega phase zones in Ti-20wt%Mo alloy studied by XDS, HREM and EXAFS

Abstract The as-quenched omega zones in Ti-20%Mo alloy, showed incommensurate X-ray diffuse scattering (XDS). Dark field images obtained with a high resolution electron microscope (HREM) showed that the omega zone was a chain-like array of 3 ~ 5 white dots, and each dot (~6 nm in size) was considered to be a 3 atom molecule estimated from the results of EXAFS. The omega zones were observed as weak modulated fringes on lattice images micrographs. The variants (ω1 and ω3, 5 ~ 10 nm in size) of isothermal commensurate omega phase formed after an incubation period showed the lattice fringe spacings of 0.28 and 0.40 nm corresponding to (222) 3 and ( 1 1 2) 3 points, respectively. During the incubation period, we observed some morphologically unidentified products (5 ~ 20 nm in size), which were discerned as the precursors of omega variants (ω2 and ω4).

Heterogeneous Structure of Amorphous Materials

Heterogeneous structure with different electron density distribution has been proposed from the data of the extended X-ray absorption fine structure (EXAFS) and the small angle X-ray scattering (SAXS) in an amorphous Fe 0.9 Zr 0.1 alloy, an amorphous GeSe semiconductor and an amorphous PbTiO 3 dielectric quenched from the melts. The local structures and the density correlations in the above three materials were determined.