Haruo Ozawa

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.

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.

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.

Study of Cu Absorption Edge of YBCO Superconductor by X-Ray Powder Diffraction Method.

Using synchrotron radiation, we carried out X-ray powder diffraction of the YBa 2 Cu 3 O y compounds at the several points near the Cu K absorption edge. From the Rietveld analysis of these data, we obtained the anomalous X-ray atomic scattering factor of the Cu ions in the Cu(1) and Cu(2) sites in the superconductor ( y =6.90) and the nonsuperconductor ( y =6.07). In both compounds, the absorption edge of the Cu ions in the Cu(1) and Cu(2) sites is nearly equal to that of CuO. The results indicate that changes in the O content of YBa 2 Cu 3 O y produce no significant changes in the valence state of Cu ions in the Cu(1) and Cu(2) sites. Detailed inspection of the spectra, however, shows that the energy position of the edge of the Cu(1) sites in the nonsuperconductor is a little lower than in the superconductor, but the magnitude of the shift is not large as that expected from monovalent Cu ion.

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.

Transient photoconduction of β-rhombohedral boron(II)

Abstract The transient photoconduction of β-rhombohedral boron was observed using a Xenon flash lamp and a ruby-laser light source, in the temperature range between room temperature and about 373 K. The whole pattern of the photocurrent is simulated by a theory of trap-controlled transient photoconduction given by Schmidlin, on the assumption that carriers are active with two kinds of traps. The estimated activation energy of the release rate of traps is 0.60 eV from the data with the Xenon lamp and 0.29 eV from those with the ruby-laser.

Transient photoconduction of β‐rhombohedral bulk boron (III)

The transient, longitudinal photocurrent of β‐rhombohedral boron was measured and simulated by the theory of the trap‐controlled transient photoconduction given by Schmidlin, assuming that the sample has one kind of traps. An effect of the electric field gradient was taken into account which was built up by a space charge in the sample. The activation energy estimated from the temperature dependence of the capture rate of traps was about 0.25 eV and estimated mobility showed that an activation process such as hopping conduction plays a main role in the determination of the mobility of holes.