Nobuo Tanabe

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.

Solid-state dye-sensitized solar cells using polymerized ionic liquid electrolyte with platinum-free counter electrode

A polymerized ionic liquid electrolyte and platinum-free counter electrode are employed for solid-state DSSCs. We are able to prepare a thin polymer electrolyte layer on nanocrystalline TiO(2) in order to reduce the cell resistance. In addition, an electron conductive polymer (PEDOT/PSS) or a single-wall carbon nanotube gel is used with the cell as an inexpensive counter electrode instead of platinum. The overall photon-to-current conversion efficiency was 3.7% in this study.

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.

Durability of Dye-Sensitized Solar Cells and Modules

It was investigated that the intrusion of water into the electrolyte was the most critical reason for the low stability of a dye-sensitized solar cell. To prevent the water intrusion, robust solar cells and submodules with a novel protection layer of metal circuit and tightly sealing package was developed. The excellent stability of the cell with ionic liquid electrolyte at high temperature conditions was also reveled. The resulting cell employing noble construction and ionic liquid electrolyte showed an extremely high stability to pass several endurance tests standardized in JIS for the stability of the photovoltaic submodule.

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.

Biaxially Aligned YSZ Buffer Layer on Polycrystalline Substrates

Biaxially aligned YSZ thin films were deposited on polycrystalline metallic substrates by Ion- Beam-Assisted Deposition (IBAD), with inclined ion beam bombardment. In-plane ordered YSZ layers could be formed independent on substrate crystalinity. These films should be effective buffer layers for large-scale application of thin films of oxide superconductors for tape- shaped cables, magnetic shields, microwave apparatuses, and other applications, using polycrystalline substrates.