Ryosei Uno

Crystallization Process from Amorphous PbTiO3

Investigation has been made of the crystallization from the rapidly quenched amorphous state of PbTiO3 utilizing DTA and Raman spectroscopy. The DTA curves reveal sharp exothermic peaks between 500 and 600°C on heating the as-quenched samples. Essential differences between the Raman spectra from the as-quenched state and those from the crystalline state have been recognized: the soft mode observed in the crystalline state is found not to exist in the as-quenched state. By annealing samples, a dramatic change in the Raman spectra due to the structural relaxation is clearly visible.

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.

Dielectric Constant of Amorphous PbTiO3

Investigations have been made on the temperature dependence of dielectric constant in rapidly quenched amorphous samples of PbTiO3. In the first heating process, discontinuous change in dielectric constant has been observed when the sample crystallizes. Near the crystallization temperature it shows remarkable low frequency dispersion. By annealing samples above the crystallization temperature, the change in dielectric constant caused by the structural realxation toward the perfect crystalline state have been observed.

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.

“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.

EXAFS Studies on Amorphous PbTiO3

The Fourier transform of EXAFS curve of PbTiO 3 in an amorphous state has been determined. That of crystalline state has also been obtained and the effect of annealing the amorphous specimen has been studied.

Structure determination of amorphous PbTiO3 by Fourier analysis of exafs

Abstract The local structure of amorphous states in PbTiO3 has been determined by the Fourier transform of EXAFS function. The effect of annealing the amorphous specimen has also been studied.

The electrical properties of β-rhombohedral boron

Abstract Transient photoconduction induced by light flashes, and high field conduction by the use of a pulsed voltage, were measured on β-rhombohedral boron, at room temperature. From the former, it was observed that the sample used had many traps for photocarriers and the traps consist of two or more kinds. From the latter, it seems that the trapped carriers are not so numerous when a pulsed high voltage is applied, and a hot carrier behavior was observed at high field.

The high field electrical conduction of β rhombohedral boron measured by a single voltage pulse

Abstract The current-voltage characteristics of a β rhombohedral boron crystal (Wacker-Chemie) were measured between 96 and 294 K with a single voltage pulse. It seems that the measurement with a single pulse can reduce the build-up of space charge, because switching phenomena were not observed until 60 kV cm −1 , at which field a discharge along the surface took place. From 1 to 60 kV cm −1 only non-ohmic currents were observed over the whole temperature range. At low temperatures the conduction may be explained by an activationless hopping mechanism at high electric fields.

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.