JP2007115561A - Tape-shaped rare-earth group oxide superconductor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a tape-shaped rare-earth group oxide superconductor having excellent properties by using a substrate excellent in surface smoothness and orientation. <P>SOLUTION: An Ni-W alloy formed into a predetermined thickness by cold working is subjected to orientation heat treatment at a temperature of 900 to 1,300°C to manufacture a two-axis oriented tape. The tape is electropolished to form a tape-shaped substrate 1 with a surface smoothness of 5 nm or less, on the surface of which a medium layer 2 made of a Ce-Zr-O film and a medium layer 3 made of a Ce-Gd-O film are formed in order. After that, an oxide superconductor layer 4 is formed on it to manufacture a tape-shaped rare-earth group oxide superconductor 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an oxide superconductor, and more particularly to a tape-like rare earth oxide superconductor suitable for use in power equipment such as a superconducting cable and superconducting power storage and a power equipment such as a motor, and a method for manufacturing the same.

  Since the rare earth 123-based oxide superconductor has excellent magnetic field characteristics at liquid nitrogen temperature compared to the Bi-based superconductor, it is possible to maintain a practical high critical current density (Jc). If practical use is successful, in addition to excellent characteristics in the high temperature range, it is possible to produce a method that does not use silver, which is a noble metal, and because liquid nitrogen can be used as a refrigerant, cooling efficiency will be several tens to several hundred times Since it improves, it is very advantageous economically. As a result, it is possible to use the superconducting wire even for devices that have not been applicable from the viewpoint of economic efficiency, and it is predicted that the use and market of the superconducting devices will be greatly expanded.

  The crystal system of rare earth 123-based superconductor (especially Y-123-based superconductor, molar ratio of Y: Ba: Cu = 1: 2: 3) is orthorhombic, and therefore exhibits material properties in terms of current-carrying properties. In order to achieve this, it is required not only to align the CuO plane of the crystal but also to align the in-plane crystal orientation. The reason for this is that a slight misalignment generates twin grain boundaries and deteriorates the current-carrying characteristics.

  The manufacturing method for increasing the in-plane orientation of the crystal of the Y-123 superconductor and forming the wire while aligning the in-plane orientation is the same as the method for producing the thin film. That is, by forming an intermediate layer with improved in-plane orientation and orientation on a tape-shaped metal substrate and using the crystal lattice of this intermediate layer as a template, the crystal of the Y-123 superconducting layer (YBCO layer) This improves the in-plane orientation degree and orientation.

  Since this wire has a biaxial crystal orientation, the critical current value (Ic) is higher than that of a bismuth-based silver sheath wire, and it has excellent magnetic field characteristics at liquid nitrogen temperature. The superconducting equipment used at low temperatures can be used at higher temperatures.

Y-123-based superconducting wires are currently being studied in various manufacturing processes. As a manufacturing technique for a biaxially oriented metal substrate in which an in-plane oriented intermediate layer is formed on a tape-like metal substrate, for example, IBAD ( The Ion Beam Assisted Deposition (RABiTS) method and RABiTS (Rolling Assisted Biaxially Textured Substrate) method are known, and Y-123 superconductivity in which an intermediate layer with improved in-plane orientation and orientation is formed on a non-oriented or oriented metal tape. Many wires have been reported, and a substrate made of Ni or a Ni-based alloy having an oriented texture by heat treatment after a strong rolling process is used as the substrate, and a thin layer of Ni oxide, organic material such as CeO ₂ is formed on this surface A rare earth-based tape-shaped oxide superconductor is known in which an oxide intermediate layer and a Y-based oxide superconducting layer formed by metal salt coating pyrolysis are sequentially formed (for example, Patent Document 1). Ether.).

  Jc of the above Y-123 series superconductor depends on the crystallinity and surface smoothness of the intermediate layer, and its characteristics change greatly depending on the state of the base, that is, the substrate and the intermediate layer. It has been found that it is greatly influenced by the orientation.

Among them, the method using the IBAD substrate has the highest characteristics. In this method, particles generated from a target are deposited by laser vapor deposition on a non-magnetic, high-strength tape-like Ni substrate (Hastelloy, etc.) while irradiating the Ni substrate with ions from an oblique direction. An intermediate layer (CeO ₂ , Y ₂ O ₃ , YSZ, etc.) or an intermediate layer that suppresses reaction with an element that has a high orientation and that forms a superconductor is formed (YSZ or Rx ₂ Zr ₂ O). ₇ / CeO ₂ or _Y 2 _{O 3} or the like:. Rx is the Y, Nd, Sm, Gd, Ei, Yb, Ho, Tm, Dy, Ce, indicating the La or Er) in provided, the CeO ₂ thereon A superconducting wire in which a YBCO layer is formed by PLD after being formed by PLD (see, for example, Patent Documents 2 to 4).

  However, this process has the advantage that a dense and smooth intermediate layer film can be obtained because all the intermediate layers are made by a vacuum process by a vapor phase method, but the manufacturing speed is slow and the equipment cost is high. In addition to the IBAD method, several film formation processes using the gas phase have been studied, but effective means to solve the cost and manufacturing speed problems are Not reported.

  The most effective process for realizing low cost is a MOD process in which an organic acid salt or an organometallic compound is used as a raw material, and an oxide layer is formed by performing a heat treatment after coating. Although this process is simple, a film having a sufficient function as an intermediate layer can be obtained due to cracks generated by volume reduction during pyrolysis, diffusion of substrate elements due to imperfect grain growth, and poor crystallinity. Was difficult.

In general, CeO ₂ is used as an intermediate layer of a Y-based superconductor as described above. This is because the CeO ₂ intermediate layer has good compatibility with the YBCO layer and has low reactivity with the YBCO layer. Because of what is known as one of the best intermediate layers. If this CeO ₂ intermediate layer is produced by the MOD method, cracks will occur due to the difference in thermal expansion coefficient from the substrate, etc., and it will not function as an intermediate layer. When a solid solution in which Gd is added to CeO ₂ is formed on the Ni substrate by the MOD method, the generation of cracks can be suppressed, but the element diffusion from the Ni or Ni alloy substrate cannot be suppressed.

Zr-based intermediate layers have also been studied and reported to be effective in preventing element diffusion from the substrate. Some research institutions have reported that Jc exceeding 1 MA / cm ² can be obtained for the wire using this Zr-based intermediate layer.

JP 2004-171841 A JP-A-4-329867 Japanese Patent Laid-Open No. 4-331895 JP 2002-202439 A

  As described above, in the MOD process, the smoothness of the substrate surface is one of the factors that determine the superconducting properties including all the orientations of the intermediate layer and the superconducting layer. Since the orientation of the intermediate layer starts from the vicinity of the substrate, improving the smoothness of the substrate surface not only improves the properties of the film formed thereon, but also reduces the thickness of the intermediate layer. Until now, surface polishing of a tape-shaped surface has often been performed using a mechanical polishing method, which has caused a problem that the temperature of the substrate surface increases and the orientation of the substrate is impaired.

  The present invention has been made in order to solve the above problems, and improves the smoothness of the substrate surface, and is a rare earth-based tape-like material excellent in the orientation and superconducting properties of the intermediate layer and the superconducting layer formed thereon. An object of the present invention is to provide an oxide superconductor and a manufacturing method thereof.

  The rare earth-based tape-shaped oxide superconductor of the present invention and the manufacturing method thereof have been made to solve the above problems, and the rare-earth-based tape-shaped oxide superconductor of the present invention is made of an inorganic material on a substrate. In an oxide superconductor in which one or more intermediate layers are formed and an oxide superconducting layer is provided thereon, a biaxially oriented substrate having a surface smoothness of 5 nm or less by electropolishing is used as the substrate. It is a thing.

The method for producing a rare earth-based tape-shaped oxide superconductor of the present invention is as follows: (i) Ni or Ni-based alloy or Cu or Cu-based alloy tape is heat-treated in a temperature range of 900 to 1300 ° C. and biaxially oriented. A process of manufacturing a tape; and (b) a process of continuously subjecting the tape to electrolytic polishing to manufacture a tape-like substrate having a surface smoothness of 5 nm or less; and (c) a Ce, Gd on the substrate. Alternatively, an intermediate layer (A) containing one kind of element selected from Sm and Zr and / or a CeO ₂ film or an intermediate layer (B) made of a Ce—Gd—O film with a predetermined amount of Gd added thereto is formed. And (c) a step of forming an oxide superconducting layer on the intermediate layer (B).

  According to the present invention, by using a biaxially oriented substrate having excellent surface smoothness by electropolishing, the orientation of the intermediate layer and the superconducting layer formed thereon is improved. It is possible to obtain a rare earth-based tape-shaped oxide superconductor having excellent resistance.

  The rare earth-based tape-shaped oxide superconductor of the present invention uses a biaxially oriented substrate having a surface smoothness of 5 nm or less as a substrate by electropolishing, and an intermediate layer made of one or more inorganic materials on the substrate. And an oxide superconducting layer are sequentially provided. On this oxide superconducting layer, a metallic stabilization layer is usually laminated.

  As the above biaxially oriented substrate, Ni or a Ni-based alloy obtained by adding one or more elements to this or Cu or a Cu-based alloy obtained by adding one or more elements to this is cold-rolled. In this case, the heat treatment is performed in a temperature range of 900 to 1300 ° C. in an inert gas atmosphere containing hydrogen in order to prevent surface oxidation of the substrate. Applied. By this heat treatment, Ni or Ni-based alloy or Cu or Cu-based alloy can be highly oriented. This heat treatment can employ either a continuous method or a batch method.

  The Ni-based alloy or Cu-based alloy is an alloy obtained by adding any one or more elements selected from W, Sn, Zn, Mo, Cr, V, Ta or Ti to Ni or Cu. In this case, the amount of the additive element is preferably in the range of 0.1 to 15 at%. If the amount of the additive element is less than 0.1 at%, the substrate strength is weak and may be deteriorated by the subsequent process. If it exceeds 15 at%, it is difficult to obtain biaxial orientation by cold rolling and heat treatment. In addition, the additive element diffuses into the intermediate layer by the subsequent process, thereby degrading the superconducting properties.

  The process of electropolishing Ni or Ni-base alloy or Cu or Cu-base alloy subjected to the above heat treatment includes a cleaning process using pure water on the substrate surface, a drying process, an electropolishing process, a cleaning process comprising a plurality of steps, and It consists of a final rinse step with pure water, and these steps are performed continuously. Each process other than the drying process is equipped with a water tank with an appropriate volume and a wire holding mechanism for continuously passing the wire through the water tank, and the temperature at which the temperature in the water tank is kept constant as necessary. A control mechanism and a control mechanism that keeps the hydrogen ion concentration (pH) constant are provided.

  In addition to the above, the electrolytic polishing step includes a power feeding mechanism for applying a predetermined current and voltage to the tape-shaped substrate. The electrolytic solution used for electrolytic polishing and the applied current and voltage are appropriately selected depending on the material to be polished, the surface state, the arrangement of the electrodes, and the like. The moving speed of the wire also depends on the polishing conditions (current, voltage, electrolyte temperature, The number is selected as appropriate.

  The number of steps in the cleaning process after electropolishing is determined as necessary, and it is desirable to perform cleaning so that the hydrogen ion concentration of the final stage solution is 6.5 to 7.5 in pH. This cleaning step is followed by a final rinse step using pure water. The tape-like substrate that has finished these steps is wound up by a winder installed at the final end of the electropolishing line. At this time, in order to protect the polishing surface, paper or a plastic spacer can be inserted as necessary.

  The substrate after the electrolytic polishing is subjected to post heat treatment as necessary. The post-heat treatment temperature is performed to remove residues that cannot be removed by washing with water after polishing to obtain a clean surface, and in an inert gas atmosphere containing hydrogen at 700 to 1000 ° C. to prevent surface oxidation of the substrate. Applied. This post-heat treatment can employ either a continuous system or a batch system.

The intermediate layer is formed in a single-layer or multi-layer structure. In the case of the single-layer structure, an intermediate layer (B) made of a CeO ₂ film or a Ce—Gd—O film in which a predetermined amount of Gd is added thereto is In the case of a two-layer structure, an intermediate layer (A) containing one kind of element selected from Ce, Gd, or Sm and Zr is formed between the intermediate layer (B) and the composite substrate.

  The intermediate layer has a single-layer structure when the superconducting layer is formed by a vapor phase method and the substrate temperature can be maintained at a low temperature, and the superconducting layer is formed at a high temperature such as a MOD method or a CVD method. In some cases, a two-layer structure is required.

  The intermediate layer (A) can be formed by any of the MOD method, the pulse laser deposition method, the sputtering method, and the CVD method. However, when the intermediate layer (A) is formed by the MOD method, the intermediate layer (A) includes an element constituting the intermediate layer. It is formed by applying a mixed solution such as octylate, naphthenate, neodecanoate, or triacetate, followed by heat treatment, and it is uniformly dissolved in one or more organic solvents, and is formed on the substrate. If it can apply | coat, it will not be restrict | limited by this example. The amount of the metal element in the mixed solution is preferably 0.08 to 0.5 mol / l, and particularly preferably 0.1 to 0.3 mol / l. When the amount of the metal element is less than 0.08 mol / l, the oxide film formed by one coating and heat treatment becomes thin and a uniform intermediate layer cannot be formed, and 0.5 mol / l If it exceeds 1, the oxide film formed at one time becomes thick, and not only the surface smoothness is impaired, but also the crystallinity is lowered.

  Although the film thickness of the intermediate layer (A) is controlled by the number of times of repeating the coating and heat treatment steps, it is effective to obtain a desired thickness by 3 to 5 coatings in consideration of the surface smoothness. The film thickness is preferably 30 nm to 300 nm. Examples of the coating method include a spin coating method, a dip coating method, and an ink jet method. However, the coating method is not limited by this example as long as a film can be uniformly formed on the substrate.

When the intermediate layer is formed in a two-layer structure, the CeO ₂ or Ce—Gd—O film of the intermediate layer (B) is formed by the MOD method, the pulse laser vapor deposition method, the sputtering method or the like as the intermediate layer (A) described above. Alternatively, the film may be formed by any of CVD methods, and the amount of Gd added in the Ce—Gd—O film is preferably 50 at% or less in terms of the amount of metal element. When the amount of Gd added exceeds 50 at%, the crystal system changes, and when a YBCO superconducting film is formed thereon, good orientation cannot be obtained. This film thickness is preferably 50 nm to 3 μm. The reason for this is that if the film thickness is less than 50 nm, the effect of preventing the element diffusion of the substrate is small, and if it exceeds 3 μm, there is a possibility that the film may crack.

By forming a YBCO superconducting film on the intermediate layer (B), a YBa ₂ CuO _7-X superconductor having a Jc of 1 MA / cm ₂ or more can be obtained. For this film forming process, any of a MOD method, a pulse laser deposition method, a sputtering method, and a CVD method can be used.

  As a raw material for forming a YBCO superconducting film by the MOD method, an organic acid salt or an organic metal compound containing Y, Ba, and Cu in a predetermined molar ratio is used. The number of moles is a ratio of Y: Ba: Cu = 1: (2 + a) :( 3 + b), and 0.01 <a <0.3 and 0.01 <b <0.5. If the number of moles is outside this range, problems such as the inability to form a superconducting layer or the generation of many impurities occur. Examples of the MOD raw material include octylate, naphthenate, neodecanoate, and triacetate of each element. The MOD raw material can be uniformly dissolved in one or more organic solvents, and can be dissolved on the substrate. The present invention is not limited by this example as long as it can be applied.

  Examples of the present invention will be described below.

Example 1
FIG. 1 shows a cross section perpendicular to the axial direction of the tape of the rare earth-based tape-shaped oxide superconductor of the present invention. The rare-earth-based tape-shaped oxide superconductor 10 is made of Ni—W alloy by cold working. After forming into a predetermined thickness, a tape with biaxial orientation is produced by performing an orientation heat treatment at a temperature of 900-1300 ° C., and this tape is electropolished to a surface smoothness of 5 nm or less. An intermediate layer 2 made of a Ce—Zr—O film and an intermediate layer 3 made of a Ce—Gd—O film are sequentially formed on the surface of the substrate 1, and an oxide superconducting layer 4 is formed thereon.

  The above-mentioned electropolishing process of the biaxially oriented tape is shown in FIG.

As a substrate shown in FIG. 1, a Ni-3 at% W alloy is cold-worked to produce a tape having a length of 70 μm × 10 mm and a length of 100 m, and subjected to an orientation heat treatment at a temperature of 1100 ° C. to be biaxially oriented. A tape-shaped substrate having the following was manufactured. This tape-shaped substrate is subjected to electrolytic polishing using a continuous polishing apparatus comprising a cleaning tank, a drying furnace, an electrolytic tank using dilute sulfuric acid as an electrolytic solution, a four-stage cleaning tank, and a final rinsing tank as shown in FIG. did. Thereafter, a post-heat treatment was performed at 700 ° C. in an Ar / H ₂ stream. The surface roughness of this substrate was measured using an atomic force microscope. The results are shown in Table 1.

  Moreover, as a comparative example, using a Ni-3 at% W alloy, a tape of 70 μm thickness × 10 mm width 100 m in length in a state of rough rolling (without mirror finish on the roll surface) and finish rolling (with mirror finish on the roll surface) ) In the state of 70 μm thickness × 10 mm width and 250 m in length, and the surface roughness of these substrates was measured using an atomic force microscope. The results are shown in Table 1.

  As is clear from the above results, the electropolished substrate exhibits a surface roughness of 1.2 nm or less over the entire length and has excellent surface smoothness, whereas the rolled substrate is finish-rolled. Even a substrate subjected to a surface roughness of 9 nm or more is inferior in surface smoothness.

Example 2
Using the tape-like substrate made of the Ni-3 at% W alloy subjected to electropolishing in Example 1, a predetermined amount of an octylic acid solution of Ce and Zr with a metal content was applied on the substrate by a dip coating method. After calcination, the surface roughness was measured by the same method as in Example 1. On this film, CeO ₂ was formed by pulse deposition so that the film thickness was 200 nm. Next, a superconducting film was formed on the CeO ₂ film by the MOD method. The heat treatment for superconducting generation was performed at 750 ° C. for 2 hours, and the thickness of the superconducting film was 0.5 μm.

  Table 2 shows Jc in liquid nitrogen of the rare earth-based tape-shaped oxide superconductor produced as described above, together with the surface roughness of the Ce—Zr—O layer, the metal content, the number of coatings, and the film thickness.

  Further, as comparative examples, the metal content of the roughly rolled tape in Example 1 (Comparative Example d), the finish-rolled tape (Comparative Example e), and the electropolished tape of Example 2 above. In the case where the number of coatings and the film thickness were changed (Comparative Example f), Jc of the rare earth-based tape-shaped oxide superconductor manufactured by the same method as in Example 2 was used, and the surface roughness of the Ce—Zr—O layer was Table 2 shows the metal content, the number of coatings, and the film thickness.

As is apparent from the above results, the mixed solution containing the elements constituting the intermediate layer was applied and calcined at a metal element amount of 0.5 mol / l or less, 1.0 to 1.8 MA / cm A high Jc value of ² is indicated. On the other hand, a roughly rolled tape (Comparative Example d), a finish-rolled tape (Comparative Example e), and a mixed solution in which the amount of metal elements constituting the intermediate layer exceeds 0.5 mol / l. Both the coated and calcined products showed low Jc values.

  The rare earth-based tape-shaped oxide superconductor according to the present invention can be used for cables, power equipment and power equipment.

It is sectional drawing perpendicular | vertical to the axial direction of the tape which shows one Example of the rare earth type tape-shaped oxide superconductor by this invention. It is a flowchart which shows the electropolishing process used for the surface treatment of a board | substrate in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tape-like board | substrate 2 Intermediate layer which consists of Ce-Zr-O film | membrane 3 Intermediate layer which consists of Ce-Gd-O film | membrane 4 Oxide superconducting layer 10 Rare earth type tape-shaped oxide superconductor

Claims (13)

  An oxide superconductor in which one or more intermediate layers of an inorganic material are formed on a substrate and an oxide superconducting layer is provided thereon has a surface smoothness of 5 nm or less by electropolishing as the substrate. A rare earth-based tape-shaped oxide superconductor using an axially oriented substrate.   2. The rare earth-based tape-shaped oxide superconductor according to claim 1, wherein the substrate is Ni or a Ni-based alloy or Cu or a Cu-based alloy. The Ni-base alloy or Cu-base alloy is made of an alloy obtained by adding any one or more elements selected from W, Sn, Zn, Mo, Cr, V, Ta, and Ti to Ni or Cu. The rare earth-based tape-shaped oxide superconductor according to claim 2.   The rare earth-based tape-shaped oxide superconductor according to claim 3, wherein the amount of additive element is 0.1 to 15 at%.   The rare earth-based tape-shaped oxide superconductor according to any one of claims 1 to 4, wherein the biaxially oriented substrate is heat-treated in a temperature range of 900 to 1300 ° C. The rare earth-based tape-shaped oxide superconductor according to claim 1, wherein the intermediate layer is made of a CeO ₂ film or a Ce-Gd-O film.   The rare earth-based tape-shaped oxide superconductor according to claim 6, wherein the intermediate layer is a layer formed by any one of a MOD method, a pulse laser deposition method, a sputtering method, and a CVD method. The intermediate layer includes an intermediate layer (A) containing one kind of element selected from Ce, Gd, or Sm and Zr, and a CeO ₂ film or a Ce—Gd—O film formed on the intermediate layer (A). The rare earth-based tape-shaped oxide superconductor according to claim 1, comprising an intermediate layer (B).   9. The rare earth system according to claim 8, wherein each of the intermediate layers (A) and (B) comprises a layer formed by any one of a MOD method, a pulse laser deposition method, a sputtering method, and a CVD method. Tape-shaped oxide superconductor.   The intermediate layers (A) and (B) are formed by applying a heat treatment after applying a mixed solution of octylate, naphthenate, neodecanoate or triacetate containing the elements constituting the intermediate layer. The rare earth-based tape-shaped oxide superconductor according to claim 9.   11. The rare earth-based tape-shaped oxide superconductor according to claim 10, wherein the amount of metal element in the mixed solution containing the elements constituting the intermediate layer is 0.08 to 0.5 mol / l.   12. The rare earth-based tape-shaped oxide superconductor according to claim 11, wherein the amount of metal element is 0.1 to 0.3 mol / l. (A) a step of producing a biaxially oriented tape by heat-treating a Ni or Ni-based alloy or Cu or Cu-based alloy tape in a temperature range of 900 to 1300 ° C;
(B) Continuously electropolishing the tape to produce a tape-like substrate having a surface smoothness of 5 nm or less;
(C) On the substrate, an intermediate layer (A) comprising one kind of element selected from Ce, Gd or Sm and Zr and / or an intermediate layer (B) comprising a CeO ₂ film or a Ce—Gd—O film Forming a step;
(D) forming an oxide superconducting layer on the intermediate layer (B);
A method for producing a rare earth-based tape-shaped oxide superconductor.

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