Osamu Kohno

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.

Structural and transport properties of biaxially aligned YBa2Cu3O7−x films on polycrystalline Ni‐based alloy with ion‐beam‐modified buffer layers

Biaxially aligned YBa2Cu3O7−x (YBCO) thin films were produced on polycrystalline Ni‐based alloy, by using biaxial yttria‐stabilized‐zirconia (YSZ) intermediate layers formed by off‐normal ion‐beam‐assisted deposition. Most explicit in‐plane alignment was obtained when the YSZ layer formed with the beam‐incident angle of 55° from substrate normal. Jc‐B characteristics and angular dependence of Jc on the magnetic field were measured. 5.0×105 and 5.5×104 A/cm2 were obtained at 77 K with 0 and 8 T, respectively. The distribution of misorientation angles of in‐plane a and b axes between YBCO grains was evaluated by both x‐ray pole figure measurement and planar observations of transmission electron microscopy. 50% of the grains had the misorientation angles restricted within ±5°. From the image of dislocations, the elastic strains at grain boundaries were estimated to be relaxed with lower misorientation angle. The high‐Jc properties are understood to be obtained by the current paths through low‐angle grain bou...

Biaxial alignment control of YBa 2 Cu 3 O 7− x films on random Ni-based alloy with textured yttrium stabilized-zirconia films formed by ion-beam-assisted deposition

Biaxially aligned YBa 2 Cu 3 O 7− x (YBCO) films were fabricated on random Ni-based alloy tapes with yttrium stabilized-zirconia (YSZ) buffer layers deposited by ion-beam-assisted deposition (IBAD). Ar + ion bombardment was found to have two significant effects on the crystalline structure of the YSZ buffer layers: to align a [100] axis with the substrate normal and a [111] axis with the bombarding beam axis. The resulting YSZ films were biaxially aligned on the random polycrystalline tapes, and the azimuthal distribution of the a - and b -axes of YBCO films on the top of the YSZ films was restricted to 10° FWHM. A critical current density ( J c ) of 1.13 × 10 6 A/cm 2 (77 K, 0 T) was obtained, and 1.1 × 10 5 A/cm 2 was maintained at 5 T (77 K, B⊥c). The existence of both intrinsic and extrinsic pinning properties was clearly observed in the angular dependence of J c with B⊥I. The longitudinal field effect on J c was clearly observed, which indicated straight transport currents. This is evidence for strongly coupled current paths that demonstrate the bulk pinning properties of YBCO.

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.

In-plane texturing control of Y-Ba-Cu-O thin films on polycrystalline substrates by ion-beam-modified intermediate buffer layers

Biaxially aligned YBCO thin films were successfully formed on polycrystalline Ni-based alloy by using ion-beam-modified yttria-stabilized-zirconia (YSZ) intermediate layers. YSZ layers were deposited by ion-beam-assisted deposition (IBAD) with concurrent off-axis ion beam bombardment. The YSZ

GROWTH STRUCTURE OF YTTRIA-STABILIZED-ZIRCONIA FILMS DURING OFF-NORMAL ION-BEAM-ASSISTED DEPOSITION

Biaxially aligned YSZ thin films with strong [100] fiber texture were formed on a polycrystalline Ni-based alloy by off-normal ion-beam-assisted deposition. Growth structures were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), etc., and the alignment mechanism was discussed using a selective growth model. Peculiar structural evolution of the crystalline orientation was observed and its development was well described by an exponential equation. It was explained as a collaboration of an anisotropic growth condition and epitaxial crystallization. The [100] fiber texture was formed by columnar structures of diameter of 30–100 nm, which were composed of 5–10 nm diameter crystallites. Very smooth surfaces were observed by AFM imaging with a roughness of 2–3 nm and a peculiar ripple structure. The origin of the azimuthal alignment was discussed with emphasis on the surface structure of YSZ films produced using ion-beam-assisted deposition (IBAD) and the etching rate measurements of (100) surfaces of YSZ single crystals.

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.

Nb/sub 3/Sn multifilamentary wires with CuNb reinforcing stabilizer

A bronze processed multifilamentary Nb/sub 3/Sn superconducting wire with CuNb reinforcing stabilizer (CuNb/Nb/sub 3/Sn), which exhibits a residual resistance ratio of 20 and a magnetoresistance of 0.2 mu Omega -cm at 23 T and 4.2 K, has been developed. The yield stress at 4.2 K, was noticeably improved; a value of 22 kg/mm/sup 2/ was obtained even after heat treatment of Nb/sub 3/Sn formation at 700 degrees C for 200 h. The effect of strain on critical current density, J/sub c/, was described well by using the upper critical field in the prestrain state. It was verified that the CuNb/Nb/sub 3/Sn wire mechanical and superconducting properties need to perform under an enormous electromagnetic force in high magnetic fields.<<ETX>>

Highly strengthened multifilamentary (Nb,Ti)/sub 3/Sn wires stabilized with CuNb composite

Multifilamentary (Nb,Ti)/sub 3/Sn superconducting wires with reinforcing stabilizer of CuNb composite, CuNb/(Nb,Ti)/sub 3/Sn, were developed. The outstanding point is that the 0.2% proof stress at 4.2 K in CuNb/(Nb,Ti)/sub 3/Sn was extremely improved to 320 MPa even after the heat treatment at 670/spl deg/C for 192 hours, which is 1.8 times higher than that in ordinary Cu/(Nb,Ti)/sub 3/Sn. The overall J/sub c/ value in CuNb/(Nb,Ti)/sub 3/Sn was obtained to be 110 A/mm/sup 2/ at 16 T and 4.2 K. These results show that the bronze processed multifilamentary (Nb,Ti)/sub 3/Sn superconducting wire with CuNb reinforcing stabilizer is actually employable for a high field superconducting magnet. >