Haruo Tominaga

Photorefractive effect of BaTiO 3 single crystals grown in inert atmospheres

BaTiO3 single crystals were grown by the top-seeded solution growth technique in inert atmospheres of nitrogen gas and of argon gas and in air. They were then annealed at 1200°C in air. These crystals, prepared from a mixture of 99.999% pure BaCO3 powder and 99.99% pure TiO2 powder, contained virtually equal amounts of transition-metal impurities (Fe, Co, Ni, etc.). The maximum beam-coupling gain of the two crystals grown in inert atmospheres was 6 cm−1, and that of the crystal grown in air was 3 cm−1; the sign of the beam-coupling gain of the crystals was positive. We found that the crystals grown in inert atmospheres exhibited high gains without having been doped with any transition-metal elements.

Superconducting Bi‐Sr‐Ca‐Cu‐O crystalline fibers prepared by the micro‐Czochralski method

Superconducting Bi‐Sr‐Ca‐Cu‐O crystalline fibers were successfully prepared by the micro‐Czochralski method from Bi2Sr2 CaCu2 Ox source ceramic rods. The maximum length of the fibers obtained was 55 mm (0.3 mm diameter). The fiber crystal grains were oriented with the current carrying a‐b basal planes parallel to the fiber axis. The values of Tc (zero) and Jc (77 K and zero magnetic field) for these fibers were ∼84 K and ∼3170 A/cm2 , respectively.

Influence of Poling Conditions on Properties of BaTiO3 Single Crystal

A BaTiO3 single crystal, whose dimensions were 3.9×3.9×3.6 mm3, was mechanically and electrically poled to remove its 90° and 180° ferroelectric domain walls, respectively. After mechanical poling, four-step electrical poling was applied to the crystal, which did not include 90° domain walls, with the aim of removing the 180° domains gradually. In each of these steps, the dielectric constant of the crystal was measured using an impedance analyzer. Prior to the electrical poling, the dielectric constant in the [001] direction was 137 at 100 kHz (unclamped) and 133 at 10 MHz (clamped). By applying four-step poling, these values varied gradually with the progress of poling, and became 130 and 58, respectively, after the final step, i.e., in a single-domain state.

Influence of 180° domains on ferroelectric properties of BaTiO3 single crystal

Mechanical poling was applied to a BaTiO3 single crystal grown by the top‐seeded solution growth (TSSG) method to remove its 90° domain walls, and then four‐step electrical poling was applied to rearrange the 180° domain configuration. In each of these steps, the dielectric constant (from 50 kHz to 10 MHz) was measured by using an impedance analyzer, and the 180° domains were observed by the etching method. The dielectric spectra were confirmed to vary with rearrangement in 180° domain configuration. Dielectric constant ec in the 〈001〉 direction was 130 at 100 kHz and 58 at 10 MHz. Dielectric constant ea in the 〈100〉 direction was 4700 at 100 kHz and 1900 at 10 MHz.

Dielectric and photorefractive dependence on 180° domain structure of BaTiO3 single crystal

Abstract Dielectric and photorefractive dependence on 180° domain was investigated by employing the BaTiO3 single crystal. Dielectric constant depends on the volume ratio between antiparalell domains. When the antiparalell domains were equal in volume, ϵ c and ϵ a were 130 and 2600 respectively. In the single-domain state, ϵ cunclamped and ϵ cclamped were 141 and 65, ϵ aunclamped and ϵ aclamped were 4300 and 2000, respectively.

Residual Resistance of Ultra High Purity Copper by Sulfate-Electrorefining and Zone-Refining

Ultra-high-purity (99.9999% or higher) copper rod having a RRR value of 5000 was prepared by a two-stage refining process, i.e., a combination of two processes, sulfate-electrorefining and zone-refining. In the first process, the potential of the cathode electrode was maintained at a level of 0.2V (vs NHE) at 25°C to prevent the deposition of more active metals than copper. In the second process, the width of the molten zone was made smaller than the diameter (16 mm) of the copper rod to obtain a higher refining efficiency. A wire of 0. 5 mm in diameter was drawn from the refined rod. The RRR value of the ultra-high-purity copper wire annealed in a N2 gas atmosphere at 500°C for two hours is as high as 4100, while that of conventional oxygen-free copper wire is usually 200. Ultra-high-purity copper will be suitable for applications in the superconducting field, electronic devices and so on.