Shin'ya Aoki

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.

Superconducting properties of Ba2YCu3O7−x thin films prepared by chemical vapor deposition on SrTiO3 and a metal substrate

Superconducting Ba2 YCu3 O7−x thin films were prepared by chemical vapor deposition using β‐diketonate chelates on SrTiO3 single crystalline substrates, metal substrates, and metal substrates with a polycrystalline SrTiO3 buffer. The temperatures of complete superconducting transitions were observed at 89, 81, and 84 K, respectively. Reduced critical current density of the film on a single crystalline substrate in magnetic fields up to 600 mT at 77 K remained one or two orders of magnitude higher than that of powder metallurgical processed specimens. According to x‐ray diffraction patterns, the existence of a well‐oriented orthorhombic Ba2 YCu3 O7−x structure has been confirmed in all specimens.

Superconducting properties of Ba sub 2 YCu sub 3 O sub 7 minus x thin films prepared by chemical vapor deposition on SrTiO sub 3 and a metal substrate

Superconducting Ba2 YCu3 O7−x thin films were prepared by chemical vapor deposition using β‐diketonate chelates on SrTiO3 single crystalline substrates, metal substrates, and metal substrates with a polycrystalline SrTiO3 buffer. The temperatures of complete superconducting transitions were observed at 89, 81, and 84 K, respectively. Reduced critical current density of the film on a single crystalline substrate in magnetic fields up to 600 mT at 77 K remained one or two orders of magnitude higher than that of powder metallurgical processed specimens. According to x‐ray diffraction patterns, the existence of a well‐oriented orthorhombic Ba2 YCu3 O7−x structure has been confirmed in all specimens.

Rapid Synthesis of the YBa2Cu3Ox Film on Metal Substrate by Chemical Vapor Deposition Technique

A new chemical vapor deposition technique has been developed for rapid (max. 24 µm/h) formation of the oxide superconductor film on a metal substrate. In this system, blended β-diketonate chelates of source materials were slowly fed to the vaporizer with carrier gas. The source gas from the vaporizer and O2 gas were introduced into the reactor. We realized a superconducting YBCO thin film that had a Tc=87 K on a Hastelloy C-276 substrate.

Characteristics of high J/sub c/ Y-Ba-Cu-O tape on metal substrate prepared by chemical vapor deposition

With the goal of utilizing oxide superconductors as long wires in electric power applications, high-critical current density (J/sub c/) YBaCuO (YBCO) thin film was prepared on metal substrate with a good buffer at 700 degrees C by chemical vapor deposition (CVD). The best YBCO film on in-plane-aligned yttria-stabilized zirconia (YSZ

High Jc Y-Ba-Cu-O thin film on metal substrates prepared by chemical vapor deposition

High Jc superconducting Y-Ba-Cu-O (YBCO) thin films were prepared on metal substrates at 700°C under low oxygen partial pressure by chemical vapor deposition (CVD). Two kinds of substrates were used. One is a polycrystalline Hi-based alloy (Hastelloy C-276) with YSZ and Ag buffers, and another is the same alloy with a biaxially aligned YSZ(100) buffer. The biaxially aligned YSZ(100) buffer layer was formed by ion-beam-assisted deposition (IBAD). According to X-ray diffraction (XRD) analysis, these films were c-axis oriented. The YBCO film on Hastelloy C-276 with YSZ and Ag buffers had a critical temperature (Tc) with zero resistivity at 84.5 K and a critical current density (Jc) of 5.7×103 A/cm2 (77.3 K, 0 T). YBCO film on Hastelloy C-276 with a biaxially aligned YSZ(100) buffer had a Tc at 87.5 K and Jc of 7.1×104 A/cm2 (77.3 K, 0 T) and 3.0×103 A/cm2 (77.3 K, 7 T).

Characteristics of high T/sub c/ superconducting thin films prepared by chemical vapor deposition

Superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films were prepared at 750-840 degrees C by chemical vapor deposition (CVD) using beta-diketonate chelates on single-crystal SrTiO/sub 3/, MgO substrates, and metal substrates. The best films on single-crystal MgO had zero-resistance T/sub c/ at 89 K and J/sub c/ above 3.6*10/sup 4/ A/cm/sup 2/ (at 77.3 K, 0 T). On SrTiO/sub 3/, the best films had T/sub c/ at 92.5 K and J/sub c/ above 2.0*10/sup 5/ A/cm/sup 2/. X-ray diffraction confirmed the existence of orthorhombic crystal structures having c-axis orientation. The magnetic field dependence of J/sub c/ of the YBCO film was measured at 77.3 K. J/sub c/ depends on the angle between the direction of the applied field and that of the c-axis of YBCO. Superconducting tapes that are 10-cm long were obtained by CVD using Ni-based alloy as a substrate. These tapes had the crystal structures of YBa/sub 2/Cu/sub 3/O/sub 7-x/ [110]-oriented and T/sub c/ at 84.5 K. The strain dependence of J/sub c/ was measured. Bending strain of up to 0.08% did not reduce J/sub c/.

Rapid synthesis of Y-Ba-Cu-O tape on metal substrate by chemical vapor deposition technique

Abstract An advanced chemical vapor deposition (CVD) system has been developed for rapid formation of a superconducting oxide tape on long metal substrates. In this system, a mixed fine powder of source materials was slowly fed to a vaporizer with a carrier gas by a fine powder feeder, and the source gas from the vaporizer was continuously introduced to the reactor with oxygen gas. This system has a long substrate conveying equipment. By this system, using Hastelloy C-276 tapes with YSZ buffer as substrates, 1 meter long superconducting Y-Ba-Cu-O (YBCO) tapes could be obtained. These tapes had a critical temperature (Tc) with zero resistivity above 77.3 K and the best part of the tape had a Tc at 84 K and a critical current density (Jc) of 330 A/cm2 (77.3 K, 0 T).

Anisotropy of the critical current density in YBa2Cu3Ox films

Abstract The critical current density J c ( B, T , θ) of ab -axis oriented YBa 2 Cu 3 O x films was measured at 77 K as a function of the angle θ between the applied magnetic field and the film surface. The critical current density in a c -axis oriented film was fairly sensitive to the angle θ and the magnitude of the external magnetic field.

Characteristics of Superconducting YBa2Cu3O7-x Tapes Prepared by Chemical Vapor Deposition

Superconducting YBa2Cu3O7-x thin films were prepared by chemical vapor deposition using beta-diketonate chelates of Y, Ba and Cu on single-crystalline SrTiO3 substrates and metal substrates. We obtained superconducting YBa2Cu3O7-x thin films oriented c-axis on SrTiO3 (100) substrates at temperature above 840°C. The best film has the zero-resistivity temperature of 92K and the critical current density of 1.0x105A/cm2. On the other hand, the superconducting films on metal substrates at 750°C have Tc of 84. 5K and those with poly crystalline SrTiO3 buffer on metal substrates have Tc of 85K.