Kazunori Onabe

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...

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

Superconducting property of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ films formed on silver substrates by continuous chemical vapor deposition technique

A new CVD system equipped with a triple-reactor was developed to improve the forming rate of the superconducting tape. Three-layered Y123 films with good crystallinity covering the total thickness were obtained directly on roll milled non-textured Ag tapes by using this triple-stage CVD system. 11 m long Y123 tape with a uniform J/sub c/ of 3.0/spl times/10/sup 4/ A/cm/sup 2/ at 77 K, 0 T was successfully prepared on roll milled non-textured Ag tape at a forming rate of 3.0 m/h, Y123 films formed directly on the cube-textured Ag[100] tapes showed two types of orientation, cube-on-cube and diagonal-on-cube, between Y123 and Ag. On the other hand, Sm123 and Nd123 films showed the simple orientation, cube-on-cube, so these films were expected to improve the in-plane alignment of Y123 film by inserting them as the intermediate layer.

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.

{110}〈110〉 textured Ag tapes for biaxially oriented YBa2Cu3O7 coated conductors

Textured Ag tape is one of the most ideal substrates for the next generation high-Tc wires operable in liquid nitrogen, because Ag is the only metal on which we can grow high-Tc superconducting films without any chemical reactions. The {110} plane was reported to be the most suitable one for obtaining the biaxially aligned YBa2Cu3O7 films among the various crystal planes of Ag. We obtained {110}〈112〉 and {110}〈110〉 textured Ag tapes by cold rolling and subsequent heat treatments. The texture of the tape after cold rolling was typical “brass type”, and the 800 °C annealing in Ar gave {110}〈112〉 texture, while {110}〈110〉 texture was obtained by the 800 °C annealing in dry air. Careful control of the cold rolling and the heat treatment conditions gave the very smooth surfaces and the shallow grooves at grain boundaries.Textured Ag tape is one of the most ideal substrates for the next generation high-Tc wires operable in liquid nitrogen, because Ag is the only metal on which we can grow high-Tc superconducting films without any chemical reactions. The {110} plane was reported to be the most suitable one for obtaining the biaxially aligned YBa2Cu3O7 films among the various crystal planes of Ag. We obtained {110}〈112〉 and {110}〈110〉 textured Ag tapes by cold rolling and subsequent heat treatments. The texture of the tape after cold rolling was typical “brass type”, and the 800 °C annealing in Ar gave {110}〈112〉 texture, while {110}〈110〉 texture was obtained by the 800 °C annealing in dry air. Careful control of the cold rolling and the heat treatment conditions gave the very smooth surfaces and the shallow grooves at grain boundaries.

Superconducting Property of Y1Ba2Cu3Ox Films Formed on Silver Substrates by Continuous Chemical Vapor Deposition

Good c-axis oriented YBCO films were formed directly on both non-textured and cube- textured Ag tapes. 11m long YBCO tape with Jc (lμV/cm) of 3.0x104A/cm2 at 77K, 0T was prepared on roll milled non-textured Ag tape at a forming rate of 3.0m/h. YBCO films formed on cube-textured Ag{100} tapes showed two types of the location, cube-on-cube and diagonal- on-cube between YBCO and Ag, however, no inter-diffusion between YBCO and Ag was analyzed by TEM-EDS study, and also the epitaxial growth of YBCO layer grew on Ag{l00} was observed.

Improvement of Jc-B characteristics in biaxially aligned Y-Ba-Cu-O thin films on metallic substrate

Abstract Biaxially aligned (triaxially aligned) YSZ thin films were formed on polycrystalline substrates by ionbeam assisted deposition (IBAD). The biaxial aligning of YSZ was much affected by the incident angle of the assisting ion-beam toward the substrate. In-plane aligned YBCO thin films were deposited by laser ablation on polycrystalline substrates, Hastelloy alloy, with biaxially aligned YSZ thin films as the buffer layers. Jc-B characteristics of these YBCO thin films were improved in one order of magnitude, compared with ones buffered with conventionally sputtered YSZ, and high Jc values of 10 5 A/cm 2 (77K, OT) range stable for many times were obtained. The small mis-orientation angles at grain boundaries of in-plane aligned YBCO thin film along a- and b-axes were observed by TEM.

Long length {110} textured Ag tapes for biaxially oriented YBa/sub 2/Cu/sub 3/O/sub 7/ coated conductors

A good {110} texture was successfully obtained by the only 3 minutes post-roll annealing by the careful control of the cold-roll process. Such a short annealing time will enable to skip the final annealing process of the Ag tape for the recrystallization and to save the cost of the furnace, energy and the time. We could obtain 20 m long cold-rolled Ag tape with enough uniformity, which can be converted to the {110} textured Ag tape by the only short time annealing. The 3 cm samples, cut from both end and from the middle part of the 20 m long cold-rolled tape and then annealed at 800 /spl deg/C for 5 minutes, were confirmed to have smooth surfaces and the shallow grooves at grain boundaries, as well as good {110} textures from the X-ray {100} pole figures and the SEM photographs.

Fabrication of YBa2Cu3Ox, Superconducting Tape by Continuous MOCVD Technique

YBCO superconducting tapes formed by a continuous CVD technique on 30cm long Hastelloy with biaxially aligned YSZ buffer layer showed high Jc of larger than 5×104A/cm2 (77K, 0T) covering the full length of the tapes that included the maximum value of 5.9×105A/cm2 (Ic=10.4A). The structure of high Jc YBCO tapes have been studied using by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). Good c-axis oriented growth of YBCO layer normal to the flat surface of YSZ buffer layer was shown in the cross-sectional TEM view, in addition the intermediate layer as barium zirconate (BZO) with 15–20nm in the thickness was formed on the top of YSZ layer. The precipitates with the size of 1–3 µ m and 0.1–0.5 µ m were observed in the SEM and TEM images of YBCO tapes, and these were characterized as the gathering of Cu-O and Y-Ba-Cu-O grains by the EDS analysis. But these second phase grew from a part of 0.3 µ m in the thickness from the bottom of YBCO layer, so the effective volume of the current path within these region were not completely blocked.

High-Current Laser-Ablated YBCO Tape with Biaxially Aligned Structure

High Current YBCO thin film tapes were fabricated using flexible tapes of Ni-based alloy (15 cm length, 1.0 cm width, 0.2 mm thick). In order to avoid Jc degradation by intergranular weak-links, biaxially aligned structure (c-axis aligned normal, and a-b basal plane also aligned) was formed by using ion-beam-modified YSZ buffer layers. A tape sample of YBCO thickness of 2.0 µm was obtained that had Ic values of 52 A (Jc = 2.6×105 A/cm2), and 103 A (Jc = 5.2×105 A/cm2) at 77K, 0T, measured with length of 10 cm, and 1 cm, respectively. Jc values of 6.2×105 A/cm2 (Ic=93A), and 2.6×105 A/cm2 (Ic=39A) were obtained at 77 K, with 0 T, and 0.6T (B⊥c, B⊥I), respectively, in a part of a tape sample with the YBCO thickness of 1.5µm.