Takeharu Mori

Internal distortion in ZrO2–CeO2 solid solutions: Neutron and high-resolution synchrotron x-ray diffraction study

Neutron and high-resolution synchrotron x-ray diffraction measurements have indicated a tetragonal zirconia phase with both an axial ratio of unity and internal shear deformation: The oxygen displacements from ideal fluorite positions of 0.088 and 0.078 A are observed for 65 and 70 mol % CeO2–ZrO2 samples, respectively, although both c/a values are 1.000±0.001. The c/a ratio decreases with increasing of CeO2 content and decreases discontinuously to unity around a 60 mol % CeO2 composition, while the oxygen displacement decreases continuously up to about 90 mol % CeO2.

Developing 100 ps-resolved X-ray structural analysis capabilities on beamline NW14A at the Photon Factory Advanced Ring

NW14A is a newly constructed undulator beamline for 100 ps time-resolved X-ray experiments at the Photon Factory Advanced Ring. This beamline was designed to conduct a wide variety of time-resolved X-ray measurements, such as time-resolved diffraction, scattering and X-ray absorption fine structure. Its versatility is allowed by various instruments, including two undulators, three diffractometers, two pulse laser systems and an X-ray chopper. The potential for the detection of structural changes on the 100 ps time scale at NW14A is demonstrated by two examples of photo-induced structural changes in an organic crystal and photodissociation in solution.

Cubic-tetragonal phase change of yttria-doped hafnia solid solution : high-resolution X-ray diffraction and Raman scattering

Abstract High-resolution synchrotron X-ray powder diffraction and Raman scattering have demonstrated the existence of tetragonal yttria-doped hafnia solid solution with an axial ratio, c f / a f , of unity, but having displacements along the c f -axis from the ideal fluorite position in the oxygen sublattice. The values of c f / a f ratio in HfO 2 – X mol%YO 1.5 samples ( X =13, 14, and 16) are estimated to be unity with the precision of ±0.00003 from the estimated standard deviation of the peak position and less than ±0.001 from the full-width at the half-maximum of the 400 f reflection peak. However, the Raman spectra of the samples of X =13, 14, and 16 clearly demonstrate the tetragonal phase.

Vertically and horizontally focusing beam line BL‐3A of the Photon Factory

An x‐ray beam line BL‐3A at the Photon Factory has been designed and constructed to have optical components of a collimating paraboloidal mirror, a sagittal‐focusing double‐crystal monochromator, and a focusing paraboloidal mirror. The evaluation at the (+,−,−) setting of Si (111) showed that the vertical angular divergence was reduced from 13.4 to 9.5 (arcsec) by the collimating mirror. The vertical focusing with two mirrors gave the beam size of 0.2 mm (1/50). The horizontal beam size was reduced to 1/60 by sagittal focusing.

Upgrade of the small angle X-ray scattering beamlines at the Photon Factory

BL-10C and BL-15A at the Photon Factory, which became operational in 1982, are some of the oldest small angle X-ray scattering beamlines in the world. Recently, both beamlines were upgraded for two-dimensional (2D) SAXS-WAXS experiments. A wide-area imaging plate (IP) detector and a fast-readout flat panel (FP) detector were installed at BL-10C and BL-15A, respectively. Preliminary experiments of both systems showed promising results.

X-ray polarization anomaly of forbidden reflections of iron pyrite, FeS2, near the Fe K-absorption edge

X-ray polarization analysis of allowed and forbidden reflections from iron pyrite, FeS 2 , was carried out using synchrotron radiation. Since the incident beam was σ-polarized, the polarization of allowed reflections was also σ. However, the polarization of the forbidden reflections showed complex structure. From investigating the polarization and its azimuthal angle dependence, it was concluded that the reflections were caused by the ATS (Anisotropy of the Tensor of Susceptibility) scattering.

X-ray fluorescence hologram data collection with a cooled avalanche photodiode

A high counting rate X-ray detector with an appropriate energy resolution is desired for high quality X-ray fluorescence hologram measurements because a holographic pattern is detected as extremely small intensity variations of X-ray fluorescence on a large intensity background. A cooled avalanche photodiode (APD), which has about 10% energy resolution and is designed for a high counting rate, fits the above requirements. Reconstructed atomic images from experimental holograms using the APD system provide us a clear view of the first and second neighbor atoms around an emitter. The present result proved that a combination of this APD system and a synchrotron X-ray source enables us to measure a high quality hologram for a reasonable measurement time.

Site-Specific Studies on X-Ray Magnetic Circular Dichroism at Fe K Edge for Transition-Metal Ferrites

Experiments on X-ray magnetic circular dichroism (XMCD) were performed with synchrotron radiation for Zn and Mn–Zn ferrites (normal-spinel structure) and Ni, Co and Cu ferrites and magnetite (inverse-spinel structure). The inverse-spinel ferrites have positive-to-negative dispersion-type XMCD signals in the pre-edge region of the Fe K edge, which originate from Fe3+ ions in the A sites. There are no such signals for normal-spinel ferrites. Two kinds of negative-to-positive dispersion-type XMCD signals were observed in 7.119–7.125 keV and 7.122–7.129 keV regions of the main edge, which are caused by a mixture of Fe3+ and Fe2+ ions of the B sites in magnetite and Fe3+ ions of the B sites in the other inverse-spinel ferrites, respectively. The B-site origin of the XMCD main-edge spectra was also confirmed by observation of X-ray resonant magnetic scattering for the 222 reflection of Ni ferrite.

High-temperature synchrotron X-ray powder diffraction study of the orthorhombic–tetragonal phase transition in lanthanum titanate perovskite La0.68(Ti0.95,Al0.05)O3

Abstract We have investigated in situ an orthorhombic ( o )–tetragonal ( t ) phase transition of double perovskite-structured La 0.68 (Ti 0.95 ,Al 0.05 )O 3 by high-resolution ( Δd / d ≈0.0002) synchrotron powder diffraction technique. The unit-cell parameters increased continuously with temperature also near the o – t transition point. Good agreement was obtained in the unit-cell parameter values between heating and cooling. These results indicate that the o – t phase transition occurs reversibly and continuously at T c =350±2 °C. We demonstrate that the present synchrotron X-ray powder diffraction technique is very powerful to determine both the transition temperature of a continuous transformation and precise unit-cell parameters even near the continuous transition point.

Compositional Dependence of X-Ray Absorption Spectra on Magnetic Circular Dichroism and Near-Edge Structure at Co K Edge in La1-xSrxCoO3 (0≤x≤0.6)

We have studied the effect of Sr doping on the magnetic structure of La1-xSrxCoO3 (x=0, 0.2, 0.3, 0.4, 0.5 and 0.6) by X-ray magnetic circular dichroism (XMCD) at Co K absorption edges. A negative XMCD peak was clearly observed for pure LaCoO3 at E=7.719 keV within the threshold region of the main edge, suggesting the existence of the intermediate-spin state of Co3+. A positive XMCD peak appeared at E=7.723 keV by Sr substitution of La in LaCoO3 (x≥0.2) in accordance with the low-spin state of Co4+ and X-ray absorption near-edge-structure (XANES) spectra. A negative XMCD peak was also observed at the pre-edge, which can be explained as the hybridization with the neighboring Co4+ in the dipole transition. The dispersion-type XMCD signals at the main edge may be rationalized with the hypothetical double-exchange interaction between Co3+ and Co4+.