Patent Application
20120028808
The present invention relates to a superconductor comprised of a type II superconductor inside of which ordinary conducting particles are dispersed, more particularly relates to a superconductor with a high critical current density and with a small magnetic field angle dependency.
Various studies have been made on a superconductor film comprised of a type II superconductor, that is, an oxide superconductor film, in which a plurality of columnar or rod-shaped crystals extending in a film thickness direction and comprised of an ordinary conducting substance, called “nanorods”, are dispersed and in which these nanorods are used as pinning centers.
It is known that such a superconductor film has a high critical current density due to nanorods which are formed internally acting as effective pinning centers.
PLT 1 discloses, as a superconductor film with a high critical current density and a small magnetic field angle dependency, a structure comprised of a superconductor layer of a superconducting substance expressed by REBa2Cu3Ox in which columnar crystals comprised of an ordinary conducting substance containing Ba and arranged intermittently in the film thickness direction are formed.
However, progress is being made in development of superconductive magnetic energy storage (SMES), cables, transformers, etc., using superconducting tape. Further improvements in properties are being required from such applications. The conventional magnetic field angle dependency has been insufficient.
PLT 1: Japanese Patent Publication (A) No. 2008-130291
The present invention was made in view of the above situation and has as its object the provision of a superconductor with superior dependency of the critical current density on the magnetic field angle compared with the past.
The inventors worked to solve the above problem by intensively studying of nanorod arrangement in a superconductor. As a result, they discovered that by making the nanorods slant in the superconductor and by further making adjacent nanorods be in a skew position, the dependency on the magnetic field angle is improved.
The present invention was made based on the above discovery and has as its gist the following.
(1) An oxide superconducting tape comprised of a substrate on which a GdBa2Cu3O7-δ (δ=0 to 1) superconductor layer is formed, characterized in that, inside of said superconductor layer, columnar or rod-shaped BaZrO3 crystals are dispersed such that they are inclined from c-axis of the superconducting crystals and that BaZrO3 crystals adjacent in longitudinal directions are in a skew position.
According to the present invention, it is possible to obtain a previously nonexistent superconductor with little dependency of the critical current density on the magnetic field.
Below, the present invention will be explained in detail.
BaZrO3 crystals are inclined from a c-axis (growth direction of GdBa2Cu3O7-δ) and are formed such that they generally grow along the c-axis direction. This slant is not particularly defined, but the presence, in a single superconducting crystal, of BaZrO3 crystals having various slants in a range of 0 to 60° or so is preferable for reducing the magnetic field angle dependency of the critical current density.
Furthermore, BaZrO3 crystals are dispersed such that BaZrO3 crystals adjacent in longitudinal directions are in skew position. The torsional angle between BaZrO3 crystals and adjacent BaZrO3 crystals are not restricted. It is preferrable that there are various torsional angles between BaZrO3 crystals and adjacent BaZrO3 crystals in order to reduce the magnetic field angle dependency of the critical current density.
For the substrate 20, an Ni-based alloy substrate comprised of Ni, Ni—Cr, Ni—W, etc., a Cu-based alloy substrate comprised of Cu, Cu—Ni, etc., an Fe-based alloy substrate comprised of Fe—Si, stainless steel, etc. can be used. Further, a substrate comprised of a metal substrate on which a plurality of biaxially oriented layers comprised of inorganic materials are formed can be used.
The ratio of the superconducting substance of GdBa2Cu3O7-δ and the BaZrO3 forming the nanorods is not particularly limited. Usually, by weight ratio, it is 99.5:0.5 to 95:5 or so.
If the ratio of BaZrO3 is too small, the effect of improvement of the critical current density in a magnetic field cannot be obtained. Further, in general, as the ratio of the BaZrO3 becomes larger, the critical temperature, critical current density in the self magnetic field, and other superconducting properties fall. The ratio of the BaZrO3 is set to the optimal ratio by the film forming conditions at the time of production of the superconductor film or the usage environment of the superconducting tape (temperature, magnetic field, etc.)
The length of the nanorods is not particularly limited. It is usually 1 to 200 nm or so. For the object of the present invention, that is, the improvement of the magnetic field angle dependency of the critical current density, making the rods a short length is effective.
As explained above, by forming nanorods in the superconductor film, it is possible to obtain a superconductor film with a high critical current density and a small magnetic field angle dependency. The mechanism by which the magnetic field angle dependency of the critical current density becomes smaller in a superconductor film in which nanorods are formed is believed to be as follows: By arranging nanorods in various directions, the arranged nanorods function as pinning points of magnetic flux at various angles. As a result, the anisotropy of the magnetic field angle dependency of the critical current density due to the structure is improved.
Next, the method of production of the superconductor film of the present invention will be explained.
The superconductor film of the present invention can be produced, for example, by using the pulsed laser deposition method (PLD method), sputter method, vacuum deposition method, or other known methods.
Specifically, the superconducting substance and the substance forming the nanorods are mixed by a predetermined ratio and sintered to prepare a target. The target is then mounted in a pulsed laser deposition apparatus.
Next, the substrate mounted in the pulsed laser deposition apparatus is heated in a reduced pressure oxygen atmosphere while forming a superconductor layer including nanorods extending in the film direction on the substrate.
The substrate which is used is not particularly limited. A biaxially oriented substrate (PLD—CeO2/IBAD—Gd2Zr2O7/Ni superalloy), (PLD-CeO2/LaMnO3/IBAD—MgO/Gd2Zr2O7/Ni superalloy) substrate, etc. are preferable.
Since a superconductor film is formed as explained above, by increasing the film forming temperature and pulse layer energy density, it is possible to improve the mobility of the adsorbed atoms which reach the substrate and by using a multi-plume method to pseudo lower the pulse laser oscillation frequency (lowering the supersaturation degree at the time of film formation), it is possible to adjust the length and angle of the nanorods.
A target comprised of GdBa2Cu3O7+ZrO2 (5 mol %) and GdBa2Cu3O7+BaZrO3 (5 mol %) mixed together was fabricated and attached to a PLD apparatus.
After this, under conditions of a pulse energy of 500 to 600 mJ (corresponding to 2 to 3 J/cm2), frequency of 177 Hz (4-plume), substrate temperature of 850 to 900° C., and process pressure of 600 mTorr (=80 Pa), the pulsed laser deposition method (PLD method) was used to form a film and prepare a superconductor film.
For the substrate, a biaxially oriented substrate including a Gd2Zr2O7 layer formed by the ion-beam assisted deposition method (IBAD method) (PLD—CeO2/IBAD—Gd2Zr2O7/Ni superalloy) was used.
The prepared superconductor film was sliced by an FIB apparatus to prepare plate-shaped and pillar-shaped STEM samples. The STEM-CT method was used to analyze the dispersed state of the BZO nanorods.
A pure GdBa2Cu3O7 target was fabricated and attached to a PLD apparatus.
After this, under conditions of a pulse energy of 500 to 600 mJ (corresponding to 2 to 3 J/cm2), frequency of 177 Hz (4-plume), substrate temperature of 850 to 900° C., and process pressure of 600 mTorr (=80 Pa), the pulsed laser deposition method (PLD method) was used to form a film and prepare a superconductor film.
For the substrate, a biaxially oriented substrate including a Gd2Zr2O7 layer formed by the ion-beam assisted deposition method (IBAD method) (PLD—CeO2/IBAD—Gd2Zr2O7/Ni superalloy) was used.
The prepared superconductor film was sliced by an FIB apparatus to prepare plate-shaped and pillar-shaped STEM samples. The STEM-CT method was used to analyze the dispersed state of the BZO nanorods.
From these results, it was confirmed that the superconductor film of the present invention is comprised of a superconductor layer inside of which columnar or rod-shaped BaZrO3 crystals are dispersed such that they are inclined from the c-axis of the superconducting crystals and that BaZrO3 crystals adjacent in longitudinal directions are in a skew position.
According to the present invention, it is possible to obtain a previously nonexistent superconductor with a small magnetic field angle dependency of the critical current density and possible to apply this to SMES, cables, transformers, etc., so the industrial applicability is large.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-172400 | Jul 2010 | JP | national |
