Shoji Ajimura

Development of long Y-123 coated conductors by ion-beam-assisted-deposition and the pulsed-laser-deposition method

100 m class Y-123 coated conductors were produced by using reel-to-reel vacuum ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) apparatuses. 100 m long IBAD-Gd2Zr2O7 template films were uniformly and routinely obtained on non-textured Ni-alloy tapes, with FWHM of Δ below 10°. Y-123 films with FWHM of Δ below 7° were formed on them by PLD. End-to-end Ic of 38 A and Jc of 0.76 MA cm−2 (77 K, self-field) were obtained in a 100 m long sample. For further texture improvement, secondary buffer layers of CeO2 and Gd2Zr2O7 grown by PLD on IBAD-Gd2Zr2O7 template films were studied. Δ of 3° and Jc of 2.9 MA cm−2 were obtained in a 0.1 m long Y-123 film and Jc improved to 1.6 MA cm−2 for an 80 m long Y-123 tape by using the CeO2 buffer layers.

Development of long Y-123 coated conductors for coil-applications by IBAD/PLD method

Long length Y-123 superconducting tapes were produced by reel-to-reel continuous vacuum processing, by using Ion-Beam-Assisted Deposition (IBAD) and Pulsed-Laser-Deposition (PLD). Biaxially textured Gd/sub 2/Zr/sub 2/O/sub 7/ buffer layers up to 255-m long were fabricated by IBAD with production speed of 0.5-1.0 m/h. Y-123 films were formed on them by PLD with production speed of 1.0-4.0 m/h. A 105-m long Y-123 film was fabricated with uniform thickness of 1.0 /spl mu/m and /spl Delta//spl phi/ of 3-4/spl deg/. I/sub c/ of 126 A was obtained in end-to-end at 77 K, 0 T, whose I-V curve had n-value of 28.5. I/sub c/ times length reached 13,230 Am. Another 70-m long Y-123 tape with I/sub c/ over 90 A (77 K, 0 T) was wound into a Solenoid type magnet whose inner diameter was 60 mm. The central field of 0.27 T was obtained at 66 K, with operating current of 130 A.

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.

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.