Yutaka Shimizugawa

Anomalous scattering and EXAFS study of GeO2 P2O5 glass system

Abstract Analyses of the local atomic arrangements around Ge atoms were carried out on GeO 2 P 2 O 5 glasses with three different P 2 O 5 contents (11.4, 20.5 and 24.4 mol%) with the anomalous X-ray scattering method and the Ge K-edge EXAFS spectroscopy using synchrotron radiation. The average nearest-neighbor GeO interatomic distances ranged between 0.173 and 0.178 nm depending on the P 2 O 5 content. The interatomic distances and coordination numbers obtained by the anomalous scattering method and by the EXAFS analysis are in agreement. EXAFS results based on two-shell fitting indicate that some Ge atoms change their coordination numbers from four to six depending on the P 2 O 5 content. The fractions of six-coordinate Ge atoms ( N 6 ) were estimated on the basis of the observed GeO distances and ionic radii, and the observed results support the partial change of coordination numbers from four to six.

Diffractometer for synchrotron radiation structural studies of high temperature melts

A diffractometer has been constructed for structural studies of high‐temperature melt with synchrotron radiation. It was designed to measure diffracted intensities from the free surface of a molten sample by scanning a scintillation counter with a fixed glancing angle of the incident beam. In order to heat samples up to 1500 °C, a small electric furnace is attached to the diffractometer. It carries a hemicircular (100 mm in diameter) cover, which has a window for the passage of x rays. The window is covered with a Kapton film. The sample container made of 30 Rh‐Pt is mounted at the center of the furnace. A test measurement was performed on GeO2. Monochromatic beams with λ=1.32 A and its second harmonics were taken out of synchrotron radiation by a β‐alumina crystal (d002=11.3 A) and used as incident beams. To partial scattering curves obtained with λ and λ/2 were combined to a single curve after correction for absorption. The radial distribution function obtained from these data is in good agreement with ...

RDF studies of GexSe1−x glasses employing anomalous scattering

Structural studies of Ge x Se 1−x (x=0.15 and 0.25) glasses have been done by RDF Ge(Se) employing anomalous scattering at Ge and Se edges. A peak at about 1 A − in interference function may probably due to local arrangements of Selenium. Glasses of Selenium-rich compositions are consistent basically with four-fold coordination around Ge atom and two-fold coordination around Se atom. A contribution of Ge-Ge pair to the first peak at the RDF is rather small.

An EXAFS study of coordination of Mn atoms in synthetic manganoan fluoromicas.

Mn K EXAFS analyses were carried out on synthetic manganoan fluoromicas and glasses. These glasses were quenched from the melts of the respective starting mixtures used for syntheses of the mica crystals. The crystals showed inverse pleochroism compared with ordinary micas. Sr2MnGe2O7 and MnCO3 were used as reference materials to Mn2+ ions coordinated by four oxygens and by six oxygens, respectively, in the EXAFS analyses. The average Mn-O distances were estimated by the curve-fitting method to be 2.11-2.13 A in the micas and 2.06-2.10 A in the glasses. These values indicate that a port of Mn2+ ions are in tetrahedral coordinations. The inverse pleochroism is supposed to be due to the existence of Mn2+ ions at the tetrahedral sites in the mica structures. The obtained Mn-O distances suggest that the coordination number of Mn2+ ions is greater in mica crystals than in the melts, from which micas crystallize out.

Characterization of Fe80P16C4 amorphous alloy powders made by rapid quenching water atomization process

Amorphous Fe80P16C4 powders were prepared by the rapid quenching water atomization method. The structure of the amorphous powder was determined by the X-ray radial distribution method and Fe EXAFS spectroscopy. The D(r) curve was in good agreement with the previous reports on the amorphous ribbons. The first-neighbor interatomic distance was estimated to be 2.56 A by the methods of the radial distribution and the EXAFS spectroscopy. A W3O-type structure model was proposed for this amorphous alloy. The crystallization process of the powder was determined by X-ray diffraction and EXAFS spectroscopy. The crystallization products after the first DTA peak were bcc (a = 2.93 A), fcc (a = 3.59 A) and W3O (a = 4.18 A) type phases, and the average first neighbor interatomic distance became 2.61 A by the re-arrangement of the initial amorphous structure to relax the stress due to rapid quenching. The crystallization products after the second DTA peak were the stable phases of Fe3P, Fe3C and α-Fe.