Akihito Kurosaka

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.

Transport properties of BaTiO3−δ under high pressure

Abstract We have measured the electrical resistivity of doped ferroelectric single crystal BaTiO3−δ under high pressure up to 8.0 GPa in the temperature range between 4.2 and 295 K. By applying pressure above 6.5 GPa metallic conduction was observed down to 4.2 K. A T2-dependence of resistivity was found in the pressure-induced metallic phase below 100 K, suggesting that electrons in the Ti 3d band of BaTiO3−δ have a nature similar to strongly correlated electron systems.

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.

Effect of Oxygen Concentration in Growth Atmosphere on the Superconductivity of Bi-Sr-Ca-Cu-O Fibers Prepared by the Micro-Czochralski Technique

Bi-Sr-Ca-Cu-O crystalline fibers were grown by melt-growth method, i.e. micro-Czochralski technique, under atmosphere pressure with oxygen concentrations of 1 to 50 vol.%. The fibers were prepared at the rare of 5mm/h, and these fibers were annealed at 1053 K for 72 h in air. The relation between oxygen concentration at growth atmosphere and superconductivity, as well as the effect of annealing, were investigated. The Tc(on) and Tc(zero) values depends on the oxygen concentration, and the annealed fibers grown in air exhibit the highest Tc(on)=86 K, Tc(zero)=84 K and Jc(77K, 0T)=3100 A/cm2.

Influence of recrystallization on the outgassing characteristics of copper

Disk specimens were prepared from high‐purity copper and oxygen‐free copper, which had a residual resistance ratio (RRR; p298 K/p4.2K) of 5450 and 207, respectively, and thermal desorption spectroscopy (TDS) measurement was applied for evaluating outgassing characteristics of those. For these types of pure copper, outgassing was encouraged by primary and secondary recrystallization. Particularly, the TDS spectra of H2, CO, CH4 and CO2, obtained from an as‐rolled specimen of the high‐purity copper, exhibited sharp peaks at the primary recrystallization stage. The outgassing characteristics of these pure copper depended on their recrystallized textures, so the amount of outgassing became lower with growing of recrystallized grains. With the high‐purity copper, whose recrystallized grains were grown even by low‐temperature annealing, secondary recrystallization progressed more rapidly than that with the oxygen‐free copper.

Influence of Starting Composition on Characteristics of Bi-Sr-Ca-Cu-O Fibers Prepared by the Micro-Czochralski Technique

Bi-Sr-Ca-Cu-O system crystalline fiber (0.4-mm-diam) was grown in the pulling up direction at the rate of 5 mm/h by the micro-Czochralski method, i.e. a melt-growth technique, from Bi2Sr2Ca1Cu2Ox source ceramic rod. Despite deviating from the composition of source rod, the Bi1. 9Sr1. 9Ca0. 57Cu2Ox fiber which was annealed at 1053 K for 72 h in air exhibited the Jc value of 3100 A/cm2 (77 K, 0 T). In addition, the compositions of the fibers, grown in pulling-down direction at rate of 50 mm/h from the same ceramic rods, were similar tendencies to Bi1. 9Sr1. 9Ca0. 57Cu2Ox. However, the Jc values of these fibers were less than 230 A/cm2 (77 K, 0 T). On the other hand, the fibers prepared from BiaSr2Ca1Cu2Ox (a=1, 1.5, 2.5, 3) and Bi2Sr2CabCu2Ox (b=1.5, 2) source rods, the calcium content was considerably lower than that of the source rods, and the Jc values were less than 840 A/cm2 (77 K, 0 T).