Yoshimitsu Ikeno

In‐plane aligned YBa2Cu3O7−x thin films deposited on polycrystalline metallic substrates

C‐axis oriented YBa2Cu3O7−x thin films are conventionally obtained on polycrystalline substrates, but a‐ and b‐axes are randomly distributed. Due to the weak links at the high‐angle grain boundaries in the a–b plane, the critical current density (Jc) are comparatively low, from 103 to 104 A/cm2 (77 K, 0 T), and the Jc decreases in magnetic field in a manner similar to bulk YBa2Cu3 O7−x samples. To reduce weak links at the high‐angle grain boundaries, biaxially oriented buffer layers of yttrium stabilized zirconia (YSZ) were formed on polycrystalline, Ni‐based alloy by ion‐beam assisted deposition (IBAD), and subsequently the a–b plane aligned YBa2Cu3 O7−x film was deposited by laser ablation. Jc of 2.5×105 A/cm2 (77 K, 0 T) and 2.2×104 A/cm2 (77 K, 8.0 T) were obtained. A new method to prevent intergranular weak links has been developed for potential applications using practical polycrystalline substrates.

Biaxially aligned YBa2Cu3O7−x thin film tapes

Abstract We report the formation of biaxially oriented films of yttorium-stabilized ZrO2 (YSZ) on a polycrystalline, Ni-based alloy (Hastelloy c276) by Ion-Beam-Assisted Deposition (IBAD), and the subsequent a-b plane aligned YBa2Cu3O7−x (YBCO) films deposited by laser ablation. Jc of 6.0×104 A/cm2 (77 K, O T) and 1.4×104 A/cm2 (77 K, 0.6 T) were obtained. A new method to prevent intergranular-weak-links has been developed for application of oxide superconducting thin films, for tape-shaped cables, magnets, magnetic shields, microwave devices, etc.

Critical Current Density of Y–Ba–Cu Oxide Wires

We have prepared Y–Ba–Cu oxide superconducting wires with stainless-steel, Cu–Ni alloy or silver sheath by a powder metallurgy technique, and confirmed superconductivity in stainless-steel or silver-sheathed wires. During the hea-treatment, a dielectric layer was formed at the interface between the sheath and Y–Ba–Cu oxide in stainless-steel-sheathed and Cu–Ni alloy-sheathed wires. The diffusion of the sheath element into Y–Ba–Cu oxide was analyzed using EPMA. The highest critical current dernsity, 560 A/cm2, was obtained for a silver-sheathed wire which was heat-treated in oxygen flow. A multicored wire was produced.

High Critical Current Density of Y-Ba-Cu Oxide Wire without a Metal Sheath

A critical current density of around 1000 A cm-2 in Y-Ba-Cu oxide wire sheathed with silver has previously been reported. In order to obtain a higher critical current density, it has been found that the metal sheath of a wire must be dissolved and thereafter the core heat-treated in ambient flowing oxygen. The maximum critical current density of a 0.72 mm diameter wire was found to be 3900 A cm-2 at the nitrogen temperature.

Critical Temperature and Critical Current Density of La-Sr-Cu Oxide Wires

Superconducting wires with La-Sr-Cu oxide were successfully produced. The resistivity became zero at 32 K. No difference was observed in the critical temperatures of wire and disk-shaped specimens. The critical current density of the wire was 50 A/cm2 at 4.2 K and zero external field.

Fabrication and Superconducting Properties of High T c Oxide Wire

Since the discovery of high Tc superconducting oxide such as Ln-Ba-Cu-O system which shows superconductivity above liquid nitrogen temperature, intensive study has been carried out to investigate its intrinsic properties[l-4]. Superconducting wire which operates in liquid nitrogen is one of the emerging products among application, however, there are many factors to be investigated for practical use. Critical current density, Jc, is one of the most important characteristics of superconductor, although, only few report describing Jc measurement ever published[5]. In this paper, fabrication procedure of silver sheathed Y-Ba-Cu-O wire by powder metallurgical technique and its superconducting properties have been reported. Other factors which may influence superconductivity such as microstructure of the oxide, configuration of wires, etc. are also discussed.

Characteristics of high-Tc oxide wire

Abstract We have prepared an Y-Ba-Cu-O superconducting wire with silver sheath by a powder metallurgy technique. The crystal structure of the oxide core was orthorhombic and no structural change was found after cold-drawing. The wire showed superconductivity after heat-treatment at 890°C. Diffusion behavior of oxygen atoms through the sheath material is discussed. The highest critical current density of 640 A/cm2 was obtained for the sample heat-treated in oxygen flow.

A-b Plane Aligned YBa2Cu3O7-x Thin Film Tapes

A method to reduce intergranular weak links has been developed for application of oxide superconducting thin films, for tape-shaped conductors or other applications using polycrystalline metallic substrates. To avoid weaklinks at the large-angle grain boundaries in the a-b plane, we formed the biaxially oriented YSZ buffer layer on a polycrystal1ine Ni-based alloy by Ion-Beam-Assisted Deposition (IBAD), and subsequently the a-b plane aligned YBa2Cu3O7−x film was deposited by laser ablation. Jc of 2.5×105 A/cm2 (77 K, 0 T) and 2.2×104 A/cm2 (77 K, 8.0 T) were obtained on practical polycrystalline substrates.

Fabrication and test of a forced cooled Nb 3 Sn superconducting coil

The forced cooled Nb 3 Sn superconducting magnet has been manufactured and tested in a high field test facility(HFTF). It consists of 4 double pancake coils by wind & react process. The magnet has been successfully tested under 4T of the back up field of HFTF this August. The test results appear that the quench of the magnet has occurred under the conditions of 8,000A, 6T and 10.3K. Those results have proved the good performances of the conductor and its magnet.

Microstructures of Ag-sheated YBaCuO superconducting tapes

Abstract Two kinds of Ag-sheated YBaCuO tapes, prepared with the same starting composition but annealed under different conditions, showed prominently different superconducting properties. A scanning electron microscope equipped with an energy dispersive X-ray spectrometer, and a transmission electron microscope, were employed to observe the microstructure as well as the localized compositions of these tapes. For the specimen having a very small value of J c , many small precipitates of an impurity phase are formed in the matrix of (123) phase. The (123) phase in this tapedoes not include any stacking faults. On the other hand, for the specimen showing a rather high value of J c (∼ 700 A/cm 2 ), stacking faults due to fluctuations in the (001) lattice spacing are frequently formed. The (124) phase is found in small, local areas in this sample. The pinning sites of the magnetic flux are proposed.