Ken Yukino

Thermogravimetric and High-Temperature X-Ray Studies on the Orthorhombic-to-Tetragonal Transition of YBa2Cu3Oy

Thermogravimetric experiment was performed to determine oxygen content in the high Tc superconductor YBa2Cu3Oy. The y varies from 5.8 to 6.5 depending on temperature and oxygen fugacity, indicating that the average valence of copper ions is between 2 and 1. The oxygen content is strongly affected by quenching process of a sample. High-temperature X-ray diffraction study showed orthorhombic-to-tetragonal transition (second or possibly higher order) at around 900 K. Combining this fact with the thermogravimetric data, we concluded that the compound having y less than ~6.0 has a tetragonal symmetry.

Studies on the Thermal Behavior of Ba2YCu3O7-x by X-Ray Powder Diffraction Method

Thermal behavior of Ba2YCu3O7-x was investigated mainly by X-ray powder diffraction method between 70 K and 1173 K. Oxygen-rich(x~0.5) specimen is orthorhombic in symmetry in the temperature range between 70 K and 943 K. It undergoes a phase transition to tetragonal form at 943 K or 783 K in air or N2 gas, respectively. On the other hand, oxygen-poor specimen(x~1.0) semiconductive down to 4.2 k is tetragonal up to 1173 K in N2 gas. Thermal expansion coefficient of a cell parameter is about 1.1 × 10-5 K-1 and that of c cell parameter is 2.5 × 10,,5 K-1, in air.

Electron Distribution in GaAs as Revealed by the X-Ray Diffraction

An X-ray study with CuKα was carried out on a fine-powder sample of GaAs. Relative intensities of 11 lines from the 111 to the 620 were measured and the scale factor was determined from absolute intensities of the 111 and the 220. Form the three-dimensional difference Fourier synthesis on the (110) plane, two sorts of peaks were found in Δ ρ ( x , y , z ). One lies near (1/8, 1/8, 1/8), which is the midpoint of chemical bond between Ga and As. This peak seems to correspond to a covalent bond. The other lies near (1/2, 1/2, 1/2), which is the position of anions in the NaCl structure with a cation at the origin. It may be possible that this latter peak corresponds to the ionicity of the bond.

New powder diffractometer for the Photon Factory

A new powder diffractometer for the Photon Factory was designed and constructed in 1986. Its performance has been confirmed as follows: (1) it is capable of determining the wavelength of the Cu K edge as 1.380619±0.000012 A using NBS standard Si powder 640b, while the reported one is 1.38059 A; (2) the accuracy of monitoring the incident beam intensity was ±0.2%, which was estimated by the normalized integrated intensity; (3) the angle resolution of diffraction lines was comparable with that of SSRL; and (4) the sum of three Gaussians was the best profile function fitted for lines from NBS standard Si powder 640b.

X-ray Fluorescence Analysis of Rare-Earth Atoms in Materials by Use of Ultrashort Wavelength X-rays.

A new technique of X-ray fluorescence analysis using ultrashort-wavelength X-rays was tested to obtain the K-series of spectra for rare-earth elements in two different kinds of materials, i.e. powder samples of rare-earth oxides and single crystals of rare-earth hexaborides. This technique utilizes a solid-state detector and multichannel pulse-height analyzer, and satisfies the requirements for quantitative identification in samples containing heavy elements. This technique was applied to determine the composition of the mixed compound La1-xCexB6 (x=0.25, 0.50 and 0.75). There is good agreement, within the limits of experimental error, between the values thus obtained and the nominal values.

“ε-Scanning”–A Method of Evaluating the Dimensional and Orientational Distribution of Crystallites by X-Ray Powder Diffractometer

When a specimen is rocked about the θ axis of an X-ray powder diffractometer with the detector fixed at a given Bragg peak 2θB, the resulting diffraction pattern reflects both the dimensional and the orientational distribution features of the crystallites in the specimen. For instance, reproducible fluctuations in the pattern can be attributed to coarse crystallites in the specimen, and the magnitude of the fluctuations corresponds to that of the peak intensity obtained by the θ-2θ scanning method, whereas a systematic deviation of the averaged pattern from that estimated from the absorption factor gives the angular dependence of the preferred orientation of the specimen directly. This method of evaluating the specimen using the X-ray powder diffractometer is reliable and convenient because of its applicability under the same experimental conditions as in the usual θ-2θ scanning method.

Crystallizing Process of Amorphous Thick Films of Ferroelectric Lead Germanate Family

Real-time investigation of crystallizing processes of amorphous thick films of ferroelectric lead germanate (PGO) and silicon-doped PGO (PGSO) is carried out using a high-temperature X-ray diffraction system. Two irreversible phase transitions took place near 370? C and 530? C on heating: the first is the crystallization from the amorphous to a metastable crystal state, and the second is from the metastable to a ferroelectric stable state of Pb5Ge3O11. Both transitions were completed very quickly, i.e., within approximately 7 and 58?min, respectively. The optimum heat-treatment conditions for fabricating well-oriented polycrystalline films were discussed together with the results of quick heating and quenching experiments.

Bonding Electron Distribution of GaP, GaAs and GaSb

Bonding electron distribution in GaP, GaAs and GaSb was investigated by the difference Fourier synthesis using structure factors obtained by X-ray diffraction from powder samples. As the 5th group atom becomes larger, a de-like deformation becomes greater and a part of the deformed electron is added to the bonding electron, so that the number of covalent electrons becomes greater. This situation is supported by several linear relations obtained between a measure of the number of covalent electrons calculated from the difference Fourier maps and several material constants of the three crystals, such as effective charge obtained from infrared reflection, optical dielectric constants and polarizability of the 5th group atoms.

Preparation of Modified Lead Zinc Niobate Compound Thick Films by Rapid Quenching

The solid solution compound films of (1-x)PZN-xBZN system were synthesized by rapid quenching using a twin-roller system. These films have a thickness range 30-200 µm. The average grain size of thick films is 20-30 µm and the density is almost full. The phase of as-quenched thick films was slightly different from that in the crystalline powders before melting, but it was recovered after heat treatment. The chemical compositions were the same after quenching. The dielectric constant of the composition of 0.88PZN-0.12BZN thick films was 8000 at room temperature at 1 kHz. This result suggests a possibility of application of thick films made by rapid quenching to industrial use as high-permittivity multilayer capacitors.

Electron distribution in some zincblende-type crystals

Abstract The elctron density distribution in crystalline ZnSe and ZnTe has been measured by X-ray diffraction on powder samples and is compared with the results for other zincblende-type crystals. It is shown that the data for these two compounds corroborate the linear dependence on the bond charge that has been found earlier for the effective atomic charge from infrared reflection measurements, the optical dielectric constant and the ionicity estimated from pseudopotential band theory.