JP2011249162A - Method for manufacturing superconducting wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of differently manufacturing superconducting wire rods of different critical current values.SOLUTION: When differently manufacturing a plurality of superconducting wire rods of different critical current values, in which an intermediate layer by an ion beam assist evaporation method, a cap layer, and an oxide superconducting layer are provided on a substrate, the oxide superconducting layer is formed in the same thickness, the maximum value exists among values of surface roughness Ra at which a critical current value obtained in the oxide superconducting layer of the same thickness in accordance with the value of surface roughness Ra of a substrate surface indicates an upper limit value, a range exists where an oxide superconducting layer indicating a critical current value lower than the upper limit value of the critical current value can be obtained in accordance with the value of surface roughness Ra larger than the maximum value, and within the range, a relation that critical current density falls more as the value of the surface roughness Ra becomes large is used, and a plurality of superconducting rods of different critical current values are differently manufactured according to the surface roughness Ra of the substrate.

Description

  The present invention relates to a manufacturing method capable of separately making superconducting wires having different critical current values.

The RE-123 oxide superconductor (REBa ₂ Cu ₃ O _7-X : RE is a rare earth element) discovered in recent years exhibits superconductivity at a liquid nitrogen temperature or higher, and is therefore an extremely promising material for practical use. There is a strong demand for processing this into a wire and using it as a conductor for power supply. Among them, a superconducting wire using a Y-based oxide superconductor (YBa ₂ Cu ₃ O _7-X ) is strong against an external magnetic field and can maintain a high current density even in a strong magnetic field. In addition to its use as a conductor or as a power supply cable, research and development as a conductor for superconducting fault current limiters is also underway for the purpose of blocking fault currents that may occur when energizing a superconducting wire. .
In these development applications, superconducting wire for power supply and superconducting wire for magnetic coil need superconducting wire for high current as much as possible, but superconducting wire for superconducting fault current limiter has controlled the critical current characteristics to some extent. Superconducting wire is required.
For this reason, conventionally, in order to produce superconducting wires having different critical current values (Ic) or critical current densities (Jc), the superconducting layers are manufactured by changing the film thickness.

Here, as one structural example of this type of RE-123 oxide superconducting wire, an IBAD (Ion-Beam-Assisted Deposition) is formed on a tape-shaped metal substrate 100 with a bed layer 101 as shown in FIG. An oxide superconducting wire C in which an intermediate layer 102 formed by a method, a cap layer 103 formed thereon, and an oxide superconducting layer 104 are stacked is known (see, for example, Patent Document 1). ).
In the above structure, the higher the in-plane orientation of the cap layer 103, the higher the oxide superconducting layer 104 formed thereon, and the higher the in-plane orientation of the oxide superconducting layer 104. The higher the value, the higher the oxide superconducting wire C having excellent superconducting properties such as the critical current value.

Hereinafter, the relationship between the characteristics of the intermediate layer 102 formed by the IBAD method and the superconducting wire C will be described.
As shown in FIG. 8, the intermediate layer forming apparatus used for the IBAD method includes a traveling system for traveling the metal substrate 100 provided with the bed layer 101 in the longitudinal direction, and the surface thereof on the surface of the metal substrate 100. A target 201 facing diagonally, a sputtering beam irradiation device 202 that irradiates the target 201 with ions, and ions (mixed ions of rare gas ions and oxygen ions) obliquely with respect to the surface of the metal substrate 100. ) And an ion source 203 for irradiating these components, and these components are arranged in a vacuum container (not shown).
In order to form the intermediate layer 102 on the bed layer 101 of the metal substrate 100 by this intermediate layer forming apparatus, the inside of the vacuum container is set to a reduced pressure atmosphere, and the sputter beam irradiation apparatus 202 and the ion source 203 are operated. As a result, the target 201 is irradiated with ions from the sputtering beam irradiation apparatus 202, and the constituent particles of the target 201 are knocked out or evaporated to be deposited on the bed layer 101. At the same time, mixed ions of rare gas ions and oxygen ions are radiated from the ion source 203 and irradiated to the surface (bed layer 101) of the metal substrate 100 at a predetermined incident angle (θ).
In this way, by irradiating ions at a predetermined incident angle while depositing the constituent particles of the target 201 on the surface of the bed layer 101, the specific crystal axis of the formed sputtered film is fixed in the ion incident direction. Then, the c-axis of the crystal is oriented in a direction perpendicular to the surface of the metal substrate, and the a-axis and the b-axis are oriented in a certain direction in the plane. For this reason, the intermediate layer 102 formed on the bed layer 101 by the IBAD method has a high degree of in-plane orientation.

On the other hand, the cap layer 103 is epitaxially grown by being formed on the surface of the intermediate layer 102 in which the in-plane crystal axes are oriented as described above, and then grows laterally, so that the crystal grains are self-oriented in the in-plane direction. Composed of a possible material, for example CeO ₂ . Since the cap layer 103 is self-orientated in this manner, a higher in-plane orientation degree than that of the intermediate layer 102 can be obtained. Therefore, when the oxide superconducting layer 104 is formed on the bed layer 101 via the intermediate layer 102 and the cap layer 103, the oxide is aligned with the crystal orientation of the cap layer 103 having a high degree of in-plane orientation. Since the superconducting layer 104 is epitaxially grown, it is possible to obtain the oxide superconducting layer 104 having excellent in-plane orientation and high superconducting characteristics with a large critical current density.

JP 2004-71359 A JP 2007-280710 A JP 2009-16257 A JP 2006-27958 A

  In the oxide superconducting wire C having the above structure, the bed layer 101, the intermediate layer 102, and the cap layer 103 adjust the crystal orientation of the oxide superconducting layer 104 and suppress unnecessary diffusion of elements accompanying heat treatment during film formation. At the same time, it is a layer for obtaining a composite effect such as having an expansion coefficient intermediate between the base material 100 and the oxide superconducting layer 104 to alleviate thermal stress, and by laminating these layers in order. For the first time, it is possible to obtain an oxide superconducting layer 104 having crystal orientation close to a single crystal and excellent in superconducting characteristics.

Further, since it is necessary to grow the cap layer 103 having a crystal orientation close to a single crystal as described above and the oxide superconducting layer 104, the surface of the base material 100 serving as a base for film formation is a smooth surface with few irregularities. There is a need to.
As a technique for reducing the unevenness on the surface of the base material of the oxide superconducting conductor, conventionally, a method of polishing the surface roughness Ra of the base material to 9 nm or less, specifically 3 nm or less by electrolytic polishing (see Patent Document 2). The surface roughness of the intermediate layer in contact with the superconducting layer is reduced to 20 nm or less by an electrolytic polishing method, a chemical polishing method using an acid, a mirror transfer method using a rolling roll (see Patent Document 3), and the substrate surface is subjected to CMP. There is known a method (Patent Document 4) for generating a superconducting layer having an excellent critical current density by setting the surface roughness Ra to 20 nm or less, for example, 2.5 nm by a (Chemical Mechanical Polishing) method.

However, these prior arts disclose that an oxide superconducting layer having a high critical current density can be produced by reducing the unevenness of the substrate surface, that is, processing the unevenness of the substrate surface to a specific fine surface roughness. I'm just doing it.
Therefore, for the oxide superconducting wire C, in order to obtain a superconducting wire in which the critical current characteristics conforming to the standard are controlled to some extent as in the above-described superconducting current limiter application, a plurality of different critical current values (Ic) are used. In order to produce this superconducting wire, it is a common means to change the film thickness of the oxide superconducting layer, which is the main body through which the superconducting current flows.

  However, in consideration of manufacturing an oxide superconducting wire having a low critical current value, the oxide superconducting layer 104 needs to be formed thin. However, reducing the thickness of the oxide superconducting layer 104 involves the possibility that the oxide superconducting layer 104 having uniform superconducting characteristics cannot be generated. That is, even if the superconducting wire is long, uniform superconducting properties are required in the longitudinal direction, so that the thin oxide superconducting layer 104 can exhibit uniform superconducting properties over the entire length of the superconducting wire. Thus, there is a problem that it is not easy to form a uniform film while being thin.

Based on such a background, the present inventors have studied a superconducting conductor having a laminated structure composed of an intermediate layer formed on a substrate based on the IBAD method, a cap layer formed thereon, and an oxide superconducting layer. It was found that there is a clear correlation between the size of the irregularities on the surface of the material and the superconducting properties exhibited by the oxide superconducting layer.
That is, by developing a superconducting conductor having a laminated structure comprising an intermediate layer formed on a substrate based on the IBAD method, a cap layer formed thereon and an oxide superconducting layer, an oxidation having an Ic value of 400 A class that can be put to practical use. However, as the development of these oxide superconductors has progressed, research on superconducting devices suitable for practical applications such as superconducting current limiters has been promoted. Based on the progress of research, there has been a problem of making a superconducting wire showing a gradual Ic value as easily as possible. In view of this problem, the present invention has been reached.

The present invention has been made in view of such conventional circumstances, such as a superconducting wire for power supply, a superconducting wire for a superconducting coil, and a superconducting wire for a high current as much as possible, and a superconducting fault current limiter application. Thus, an object of the present invention is to provide a manufacturing method capable of reliably and easily manufacturing and separating a superconducting wire whose critical current characteristics are controlled to some extent according to the standards.
Another object of the present invention is to provide a superconducting facility in which a superconducting wire corresponding to a high current and a superconducting wire whose critical current characteristics are controlled to some extent are made separately, and they are provided in each superconducting device.

The present invention has the following configuration in order to solve the above problems.
The present invention provides an intermediate layer on which a crystal orientation is adjusted by an ion beam assisted deposition method on a substrate, a cap layer whose crystal orientation is adjusted under the influence of the crystal orientation of the intermediate layer, A superconducting wire comprising at least an oxide superconducting layer whose crystal orientation is adjusted under the influence of the crystal orientation of the cap layer, wherein a plurality of superconducting conductors having different critical current values exhibited by the oxide superconducting layer are provided. When manufacturing and separating the wires, the oxide superconducting layer is formed with the same thickness and the surface roughness Ra of the base material surface, regardless of whether the superconducting wires having different critical current values are manufactured. There is a maximum value among the values of the surface roughness Ra where the critical current value obtained in the oxide superconducting layer of the same thickness has an upper limit value, and the surface roughness Ra is larger than this maximum value. , Surface roughness in this range There exists a range in which an oxide superconducting layer having a critical current value lower than the upper limit value of the previous critical current value can be obtained according to the value of a, and in this range showing the low critical current value, the value of the surface roughness Ra By utilizing the relationship that the critical current value decreases proportionally as the value increases, the surface roughness Ra of the base material is selected and sorted within the range in which the critical current value exhibits the proportional relationship, thereby the critical current exhibited by the oxide superconducting layer. A plurality of superconducting wires having different values are manufactured and separated.

In the present invention, an intermediate layer can be formed on a substrate via a bed layer.
In the present invention, an intermediate layer can be formed on a substrate via a diffusion prevention layer and a bed layer.
In the present invention, the range in which the critical current value obtained in the oxide superconducting layer having the same thickness according to the value of the surface roughness Ra of the substrate surface shows the upper limit value can be set to a range of 2 nm or more and less than 7 nm.

The present invention relates to a Ni alloy base material, an Al ₂ O ₃ diffusion prevention layer, a Y ₂ O ₃ bed layer, an MgO intermediate layer, a RE-123 oxide superconducting layer (REBa ₂ Cu ₃ O _7-X : When manufacturing a superconducting wire as RE (rare earth element), a step of manufacturing a superconducting wire having a critical current value Ic: 400A class with a surface roughness Ra of the substrate surface in the range of 2 nm to 7 nm, A process for producing a superconducting wire having a surface roughness Ra of more than 7 nm and not more than 8 nm and a critical current value Ic: 300A class, and a critical current having a surface roughness Ra of the substrate surface exceeding 8 nm and not more than 8.6 nm. Value Ic: Among the steps of manufacturing a 200A class superconducting wire, and manufacturing the critical current value Ic: 100A class superconducting wire with the surface roughness Ra of the base material surface in the range of more than 8.6 nm and 9 nm or less, Multiple Critical current value indicated oxide superconductor layer to match observed and wherein the separating manufactures different superconducting wires.

According to the method for producing a superconducting wire of the present invention, a range showing a low critical current value according to a value of a surface roughness Ra larger than a region showing a maximum value of the critical current value according to the surface roughness Ra of the substrate. In the range where the low critical current value is present, the surface roughness Ra of the substrate is selected and sorted using the relationship that the critical current value decreases in proportion as the value of the surface roughness Ra increases. Thus, a plurality of superconducting wires having different critical current values exhibited by the oxide superconducting layer can be manufactured and separated. Thereby, an oxide superconducting wire having a small standard value and a critical current value can be formed without reducing the thickness of the oxide superconducting layer.
In the present invention, even if the thickness of the oxide superconducting layer is uniform, only by adjusting the surface roughness Ra of the base material, it is possible to produce oxide superconducting wires having a small standard value in a stepwise manner. The superconducting wire can be made more easily than before.

  Further, as one specific example, a 400A-class oxide superconducting wire can be obtained by setting the surface roughness Ra of the substrate to 2 nm or more and 7 nm or less, and the surface roughness Ra of the substrate is set to more than 7 nm or less than 8 nm. A 300A-class oxide superconducting wire can be obtained, and a 200A-class oxide superconducting wire can be obtained by setting the surface roughness Ra of the substrate to more than 8 nm and not more than 8.6 nm. An oxide superconducting wire of 100A class can be obtained when the thickness is more than 8.6 nm and not less than 9 nm.

The schematic block diagram which shows an example of the superconducting wire which concerns on this invention. The schematic block diagram which shows the other example of the superconducting wire which concerns on this invention. The schematic block diagram which shows an example of the film-forming apparatus for manufacturing the superconducting wire. The schematic block diagram which shows an example of the ion gun used when manufacturing the superconducting wire. Explanatory drawing which shows the correlation of the roughness of a base-material surface, and a critical current value in the oxide superconducting layer obtained by the manufacturing method which concerns on this invention. Explanatory drawing which shows the correlation of the roughness of a base-material surface, and a critical current value in the oxide superconducting layer manufactured by the Example. The schematic block diagram which shows an example of the superconducting wire obtained by the conventional method. The block diagram which shows an example of the arrangement | positioning relationship of the base material in the case of forming into a film by IBAD method, an ion gun, and a target.

Hereinafter, embodiments of a superconducting wire according to the present invention will be described with reference to the drawings.
1 and 2 are schematic perspective views schematically showing an example of a superconducting wire according to the present invention.
The superconducting wire A shown in FIG. 1 has a diffusion prevention layer 11, a bed layer 12, an intermediate layer 15, a cap layer 16, an oxide superconducting layer 17 and a stabilization layer 18 laminated in this order on a tape-like substrate 10A. The superconducting wire B shown in FIG. 2 has a diffusion preventing layer 11, a bed layer 12, an intermediate layer 15, a cap layer 16, an oxide superconducting layer 17 and a stabilizing layer 18 on a tape-like base material 10B. They are stacked in this order. The difference between the superconducting wire A and the superconducting wire B of this embodiment is that the superconducting wire A has a higher critical current value Ic (or critical current density Jc) than the superconducting wire B, and is applied to the superconducting wire A. The surface roughness Ra of the base material 10A is smaller than the surface roughness Ra of the base material 10B applied to the superconducting wire B. Specific examples of the surface roughness Ra of the base material 10A and the base material 10B will be described in detail later.

  The base materials 10A and 10B that can be applied to the superconducting wires A and B can be used as a base material for ordinary superconducting wires, and need only have high strength, and may be in the form of a tape to make a long cable. Preferably, those made of a heat resistant metal are preferred. For example, various metal materials such as silver, platinum, stainless steel, copper, nickel alloys such as Hastelloy, or ceramics arranged on these various metal materials can be used. Among various heat resistant metals, nickel alloys are preferable. Especially, if it is a commercial item, Hastelloy (trade name made by US Haynes Co., Ltd.) is suitable. Any type can be used. What is necessary is just to adjust the thickness of the base material 11 suitably according to the objective, and it can usually be set as the range of 10-500 micrometers.

The difference between the base material 10A and the base material 10B is the value of the surface roughness Ra. The value of the surface roughness Ra of the substrate 10A is formed in any value in the range of 2 nm or more and 7 nm or less, and the value of the surface roughness Ra of the substrate 10B is any value in the range of more than 7 nm or less than 9 nm. Is formed.
The selection of the value of the surface roughness Ra of the base material 10A and the base material 10B will be described in detail later.

The diffusion prevention layer 11 is formed for the purpose of preventing the diffusion of the constituent elements of the base material 11, and silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ , also referred to as “alumina”), or consists _{GZO (Gd 2 Zr 2 O 7} ) or the like, a thickness of 10~400nm example.
When the thickness of the diffusion preventing layer 12 is less than 10 nm, there is a possibility that the diffusion of the constituent elements of the substrate 10 cannot be sufficiently prevented. On the other hand, when the thickness of the diffusion preventing layer 11 exceeds 400 nm, the internal stress of the diffusion preventing layer 11 increases, and there is a possibility that the whole including the other layers is easily peeled off from the base material 10. Further, since the crystallinity of the diffusion preventing layer 11 is not particularly limited, it may be formed by a film forming method such as a normal sputtering method.

The bed layer 12 has high heat resistance and is intended to reduce interfacial reactivity, and is used to obtain the orientation of a film disposed thereon. Such a bed layer 12 is, for example, a rare earth oxide such as yttria (Y ₂ O ₃ ), and is represented by a composition formula (α ₁ O ₂ ) _2x (β ₂ O ₃ ) _(1-x). It can be illustrated. More _{specifically, Er 2 O 3, CeO 2} , Dy 2 O 3, Er 2 O 3, Eu 2 O 3, Ho 2 O 3, can be exemplified _La 2 _{O 3} and the like. The bed layer 12 is formed by a film forming method such as a sputtering method, and has a thickness of 10 to 100 nm, for example.

The intermediate layer 15 may have either a single layer structure or a multilayer structure, and is selected from materials biaxially oriented in order to control the crystal orientation of the cap layer 16 laminated thereon. Specifically, preferred materials for the intermediate layer 15 are Gd ₂ Zr ₂ O ₇ , MgO, ZrO ₂ —Y ₂ O ₃ (YSZ), SrTiO ₃ , CeO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Gd _2. Examples thereof include metal oxides such as O ₃ , Zr ₂ O ₃ , Ho ₂ O ₃ , and Nd ₂ O ₃ .
If the intermediate layer 15 is formed with a good crystal orientation (for example, a crystal orientation of 15 ° or less) by the IBAD method, the crystal orientation of the cap layer 16 formed thereon has a good value (for example, the crystal orientation). Thus, the oxide superconducting layer 17 capable of exhibiting excellent superconducting characteristics can be obtained with the crystal orientation of the oxide superconducting layer 17 formed on the cap layer 16 being good. Can be.

The thickness of the intermediate layer 15 may be appropriately adjusted according to the purpose, but can usually be in the range of 5 to 300 nm.
The intermediate layer 15 is laminated by an ion beam assisted deposition method (hereinafter abbreviated as IBAD method). The metal oxide layer formed by this IBAD method is preferable in that it has a high crystal orientation and a high effect of controlling the crystal orientation of the oxide superconducting layer 17 and the cap layer 16. The IBAD method is a method of orienting crystal axes by irradiating an ion beam at a predetermined angle with respect to the underlying vapor deposition surface during vapor deposition as described above. Usually, an argon (Ar) ion beam is used as the ion beam. For example, the intermediate layer 15 made of Gd ₂ Zr ₂ O ₇ , MgO, or ZrO ₂ —Y ₂ O ₃ (YSZ) reduces the value of ΔΦ (FWHM: full width at half maximum), which is an index representing the degree of crystal orientation in the IBAD method. This is particularly preferable because it can be performed.

As shown in FIG. 3, the ion beam assisted sputtering apparatus 20 in the case of manufacturing the intermediate layer 15 has a target 22 disposed so as to face a film formation region 21 where a tape-like substrate or the like is disposed. The sputter ion source source 23 is disposed so as to face the diagonal direction with respect to the assist ion source source so as to face the normal line of the film forming region 21 at a predetermined angle (for example, 45 °) from the diagonal direction. 25 is arranged and configured.
The ion beam assisted sputtering apparatus 20 of this example is a film forming apparatus provided in a form accommodated in a vacuum chamber, and includes a first roll 28 and a second roll 29 on which a tape-like base material 27 is disposed oppositely. A structure in which the film is reciprocally wound a plurality of times and reciprocated in the film formation region 21 can be exemplified.
The ion source sources 23 and 25 applied in this embodiment are configured to include an extraction electrode 31, a filament 32, and an introduction tube 33 for Ar gas or the like inside the container 30, and emit ions from the tip of the container 30. This device can irradiate in parallel.

The vacuum chamber used in the embodiment is a container that partitions the outside and the film formation space, has airtightness, and has pressure resistance because the inside is in a high vacuum state. The vacuum chamber is connected to a gas supply means for introducing a carrier gas and a reactive gas into the vacuum chamber, and an exhaust means for exhausting the gas in the vacuum chamber. In FIG. For brevity, only the arrangement relationship of each device is shown.
The target 12 used here can be a target having a composition suitable for forming the intermediate layer 15 of the above-described material.
By using the ion beam assisted sputtering apparatus 20 having the structure shown in FIG. 3, the IBAD method can be realized, and the target intermediate layer 15 can be formed.

The cap layer 16 is formed through a process of epitaxial growth on the surface of the intermediate layer 15, and then grain growth (overgrowth) in the lateral direction (plane direction), and crystal grains are selectively grown in the in-plane direction. The ones made are preferred. Such a cap layer has a higher in-plane orientation degree than the intermediate layer 15 made of the metal oxide layer.
The material of the cap layer is not particularly limited as long as it can exhibit the above functions, but specifically, preferred examples include CeO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Gd ₂ O ₃ , and Zr ₂ O. ₃ , Ho ₂ O ₃ , Nd ₂ O _{3 and the} like. When the material of the cap layer is CeO ₂ , the cap layer may contain a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.

The CeO ₂ layer can be formed by a PLD method (pulse laser deposition method), a sputtering method, or the like, but it is desirable to use the PLD method from the viewpoint of obtaining a high film formation rate. The film formation conditions for the CeO ₂ layer by the PLD method can be performed in an oxygen gas atmosphere at a substrate temperature of about 500 to 1000 ° C. and about 0.6 to 100 Pa.
The film thickness of the CeO ₂ layer may be 50 nm or more, but is preferably 100 nm or more in order to obtain sufficient orientation. However, if it is too thick, the crystal orientation deteriorates, so that it can be in the range of 50 to 5000 nm, more preferably in the range of 100 to 5000 nm.

The oxide superconducting layer 17 may be a known one, and specifically, a material made of REBa ₂ Cu ₃ O _y (RE represents a rare earth element such as Y, La, Nd, Sm, Er, Gd) is exemplified. it can. Examples of the oxide superconducting layer 17 include Y123 (YBa ₂ Cu ₃ O _7-X ) or Gd123 (GdBa ₂ Cu ₃ O _7-X ).
The oxide superconducting layer 17 is laminated by a physical vapor deposition method such as sputtering, vacuum vapor deposition, laser vapor deposition, electron beam vapor deposition, chemical vapor deposition (CVD), or thermal coating decomposition (MOD). In particular, from the viewpoint of productivity, the PLD (pulse laser deposition) method, the TFA-MOD method (organic metal deposition method using trifluoroacetate, coating pyrolysis method) or the CVD method may be used. preferable.

Here, as described above, when the oxide superconducting layer 17 is formed on the cap layer 16 having a good orientation, the oxide superconducting layer 17 laminated on the cap layer 16 also matches the orientation of the cap layer 16. Crystallize as follows. Therefore, the oxide superconducting layer 17 formed on the cap layer 16 has almost no disorder in the crystal orientation, and in each of the crystal grains constituting the oxide superconducting layer 17, The c-axis that hardly allows electricity to flow in the thickness direction is oriented, and the a-axis or the b-axis is oriented in the length direction of the metal substrate 11. Therefore, the obtained oxide superconducting layer 17 is excellent in quantum connectivity at the crystal grain boundary, and hardly deteriorates in the superconducting characteristics at the crystal grain boundary, so that it is easy to flow electricity in the length direction of the metal base 2. A sufficiently high critical current density is obtained.
The stabilization layer 18 laminated on the oxide superconducting layer 17 is formed as a layer made of a metal material having good conductivity, such as Ag, and a low contact resistance with the oxide superconducting layer 17. Furthermore, it is good also as a laminated structure which combined the layer of highly conductive metal materials, such as Cu. The reason why the stabilization layer 18 is made of Ag is that it has the property of making it difficult for the doped oxygen to escape from the oxide superconductor in the annealing step of doping the oxide superconductor with oxygen.

<About the surface roughness Ra of the substrate>
Next, a case where the oxide superconducting wire A and the oxide superconducting wire B are separately formed by adjusting the surface roughness Ra of the base materials 10A and 10B will be described.
The oxide superconducting wire A is applied to a superconducting coil cable, a superconducting power transmission cable, and the like, and needs to have a higher critical current value than the oxide superconducting wire B. The oxide superconducting wire B is used for applications such as a superconducting current limiting device, and may have a critical current value lower than the critical current value of the oxide superconducting wire A. Also, depending on the standards and requirements of the superconducting fault current limiter to be applied, even if the critical current value is lower than the critical current value of the oxide superconducting wire A, any of several stages of critical current values according to the standard can be obtained. It is preferable to be set to such a value. For example, as an example, the critical current value of the oxide superconducting wire A needs to be 400 A class, while the critical current value of the superconducting wire B is required to be 300 A class, 200 A class, or 100 A class.
Here, the display of the class indicates a value that can at least compensate the value of the corresponding standard current value. For example, the 400A class is a superconducting wire that can obtain a critical current value Ic in a range of ± 15% (340A to 460A) with 400A as a reference, and the 300A class is a range of ± 15% with 300A as a reference. (255A to 345A) is a superconducting wire that can obtain a critical current value Ic, and the 200A class is a superconducting wire that can obtain a critical current value Ic in a range of ± 15% (170A to 230A) with reference to 200A. , 100A class means a superconducting wire that can obtain a critical current value Ic in a range of ± 15% (85A to 115A) with 100A as a reference.

In the oxide superconducting wires A and B, when the laminated structure shown in FIGS. 1 and 2 is adopted, the critical currents indicated by the oxide superconducting wires A and B correspond to the surface roughness Ra of the base materials 10A and 10B. The value fluctuates at a constant rate. In the present embodiment, the oxide superconducting wire is made by dividing into 400A class, 300A class, 200A class, and 100A class using the phenomenon that the fluctuation ratio is constant.
For that purpose, we made prototype oxide superconducting wires made by changing only the surface roughness Ra of the substrate between 2 nm and 10 nm, and measured the critical current value obtained from these prototype oxide superconducting wires. Then, from the measurement result, the correlation with the value of the surface roughness Ra is grasped, and 400A class, 300A class, 200A class, and 100A class superconducting wires are made according to the relationship. For example, a plurality of types of base materials whose surface roughness is set to a specific value within a range of 2 nm to 9 nm are prepared. An oxide superconducting wire is prototyped using these substrates as follows.

As a method for controlling the surface roughness Ra of the substrate, when the substrate surface is polished by polishing, polishing is performed using abrasive particles having an average particle diameter of 3 μm as the particle diameter of alumina (Al ₂ O ₃ ) particles. The surface roughness Ra of the substrate can be set to 9 nm, and the surface of the substrate is polished by using abrasive particles having an average particle size of 2.5 μm as the particle size of alumina (Al ₂ O ₃ ) particles. The roughness Ra can be 8.6 nm, and the surface roughness Ra of the base material is reduced by polishing with abrasive particles having an average particle diameter of 2.0 μm as the particle diameter of alumina (Al ₂ O ₃ ) particles. The surface roughness Ra of the substrate can be 7.4 nm by polishing with abrasive particles having an average particle diameter of 1.5 μm as the particle diameter of alumina (Al ₂ O ₃ ) particles. it is possible to, alumina _(Al 2 O ) By polishing with abrasive particles having an average particle diameter of 1μm as size of the particles, the surface roughness Ra of the base material can be 7 nm.
In addition, when the surface of the substrate is polished by polishing, the surface roughness Ra of the substrate is set to 6.5 nm by polishing using abrasive particles having an average particle diameter of 2 μm as the particle diameter of the diamond abrasive grains. The surface roughness Ra of the substrate can be set to 4.9 nm by polishing with abrasive particles having an average particle size of 1.5 μm as the particle size of the diamond abrasive particles. By polishing with abrasive particles having an average particle diameter of 1 μm, the surface roughness Ra of the substrate can be 3.4 nm, and by setting the average particle diameter of the diamond abrasive grains to 0.5 μm, The surface roughness can be 2 nm.

In addition, conditions other than the surface roughness Ra of the base material are prototyped and tested for all the superconducting wires. That is, the diffusion preventing layer 11, the bed layer 12, the intermediate layer 15, the cap layer 16, and the oxide are formed except that the surface roughness Ra of the substrate is changed using a Ni alloy (trade name Hastelloy) substrate. The superconducting wire 17 for making the superconducting layer 17 and the stabilizing layer 18 is made as a trial under the same conditions.
For example, when a prototype superconducting wire is manufactured, an Al ₂ O ₃ layer having a thickness of 150 nm is formed by ion beam sputtering as the diffusion prevention layer 11 formed on the plurality of substrates having the above-described surface roughness Ra. Then, a Y ₂ O ₃ layer having a thickness of 30 nm is formed as the bed layer 12 by an ion beam sputtering method, a MgO layer having a thickness of 10 nm is formed as the intermediate layer 15 by an IBAD method, and a 500 nm thickness is formed by a pulse laser deposition method. A CeO ₂ layer is formed, a Gd ₂ Ba ₂ Cu ₃ O _7-x layer having a thickness of 1 μm is formed by a pulse laser deposition method, an Ag layer having a thickness of 10 μm is formed as a stabilization layer, and oxygen annealing is performed at 500 ° C. For 10 hours, after furnace cooling, the oxide superconducting wire is taken out.

Next, the superconducting characteristics are measured by immersing the plurality of prototype superconducting wires in liquid nitrogen.
Then, a correlation diagram shown in FIG. 5 is obtained in which the horizontal axis represents the value of the surface roughness Ra and the vertical axis represents the measurement result of the Jc value. When the correlation is read from FIG. 5 and the value of the surface roughness Ra of the substrate is selected by obtaining the relationship of this correlation diagram, any oxide superconducting wire of 400A class, 300A class, 200A class, or 100A class is obtained. Since it can be determined that it can be obtained, by adjusting only the surface roughness Ra of the substrate according to the required characteristics, the subsequent generation of each layer is performed under the conditions of the same material and the same thickness, and the oxide having the target critical current value Superconducting wire can be obtained.
As shown in FIG. 5, when the substrate surface roughness Ra is in the range of 2 nm or more and less than 7 nm, the critical current value can be secured to 400 A class, and thereafter the surface roughness Ra value increases in the range of 7 nm to 9 nm. The critical current value gradually decreases proportionally to obtain 300A-class, 200A-class, and 100A-class oxide superconducting wire. This is because the oxide superconducting wire of this embodiment is formed using the IBAD method. Since the thin intermediate layer 15 is provided as an axial alignment layer, and the intermediate layer 15 is affected by the surface roughness Ra of the substrate surface, the critical current of the oxide superconducting wire finally obtained according to this influence This is because it affects the value. From this situation, this is an operational effect that cannot be obtained with an oxide superconducting wire having another laminated structure that does not have the biaxially oriented thin intermediate layer 15 based on the IBAD method.
As shown in FIG. 5, the superconducting wire A having the intermediate layer 15 formed by the IBAD method and controlling the surface roughness of the substrate has a critical current value Ic (in the range of surface roughness Ra of 2 to 7 nm in B. Alternatively, there is an upper limit value of the critical current density Jc), and there is a maximum value (near 7 nm) in the range of the surface roughness Ra 2 to 7 nm indicating the upper limit value, and the critical current value increases as the surface roughness Ra increases from here. There is a region where Ic (or critical current density Jc) decreases proportionally (range of surface roughness Ra of 7 to 9 nm).

For example, in the case of a superconducting wire having another structure to which the intermediate layer of the IBAD method is not applied, it is unclear whether the critical current value of the superconducting wire simply has a proportional relationship with the surface roughness Ra of the base material. It is unclear whether there is an inflection point at which the critical current value Ic (or critical current density Jc) decreases proportionally.
If it is the intermediate layer 15 by the IBAD method, it reacts sensitively to the surface roughness Ra of the substrate, and only the surface roughness Ra of the substrate is changed, and all the other layers are manufactured under the same conditions. An oxide superconducting wire of any of 400A class, 300A class, 200A class, and 100A class can be reliably obtained in conjunction with the value of roughness Ra.
For example, if the oxide superconducting wire A is manufactured with the surface roughness Ra of the substrate 10A in the range of 4 nm, and the oxide superconducting wire B is manufactured with the surface roughness Ra of the substrate 10B of 8.5 nm, the 400A class The oxide superconducting wire A and the 200A-class oxide superconducting wire B can be reliably produced. Further, if the oxide superconducting wire B is manufactured by setting the surface roughness Ra of the base material 10B to 7.5 nm, the 300A-class oxide superconducting wire B can be manufactured, and the surface roughness Ra of the base material 10B can be reduced. If the oxide superconducting wire B is manufactured at 8.5 nm, a 200A-class oxide superconducting wire B can be manufactured. If the surface roughness Ra of the base material 10B is 9 nm, the oxide superconducting wire B is manufactured. For example, a 100A-class oxide superconducting wire B can be manufactured.

The oxide superconducting wire A obtained in the present embodiment is used, for example, as a superconducting coil conductor or a power transmitting superconducting conductor that requires a high critical current value, and the oxide superconducting wire B is a superconducting conductor for a superconducting current limiter. It is applied to applications that can be applied at a critical current value lower than that of the oxide superconducting wire A.
Conventionally, when manufacturing an oxide superconducting wire with a low critical current value, a method of reducing the thickness of the oxide superconducting layer has been adopted, but in this case, a thin superconducting layer becomes a long superconducting wire. Although there was a possibility that uniform superconducting characteristics could not be obtained in the length direction, the critical current was maintained even if the oxide superconducting layer having the same thickness was provided by adjusting the surface roughness Ra of the substrate as in this embodiment. Since oxide superconducting wires having different values can be made separately, there is an effect that an oxide superconducting wire whose critical current value is suppressed according to the standard and requirements can be reliably and easily manufactured.

  As mentioned above, although embodiment of the superconducting wire which concerns on this invention was described, in the embodiment, each part which comprises a superconducting wire is an example, Comprising: It can change suitably in the range which does not deviate from the range of this invention.

Specific examples of the present invention will be described below, but the present invention is not limited to these examples.
A plurality of tape-shaped Hastelloy 276 (trade name of US Haynes Co., Ltd.) having a width of 10 mm and a length of 30 m are prepared, and the surface roughness Ra of these substrates is 9 nm, 8.6 nm, 7.9 nm, 7.4 nm, 7 nm. , 6.5 nm, 4.9 nm, 3.4 nm, and 2 nm. To polish the surface roughness Ra to 9 nm, use abrasive grains having an average particle diameter of 3 μm alumina. To polish to 8.6 nm, use abrasive grains having an average grain diameter of alumina of 2.5 μm to polish to 7.9 nm. To grind to 7.4 nm, use abrasive grains with an average particle diameter of alumina of 1.5 μm to polish to 7.4 nm, and to grind to 7 nm, average grain diameter of alumina Using 1 μm abrasive grains, diamond abrasive grains having an average particle diameter of 2 μm are used for polishing to 6.5 nm, and diamond abrasive grains having an average particle diameter of 1.5 μm are used for polishing to 4.9 nm. The diamond abrasive grains having an average particle diameter of 1 μm were used for polishing, and the diamond abrasive grains having an average particle diameter of 0.5 μm were used for polishing to 2 nm.

The following layers were laminated on these substrates using the substrates having the surface roughness Ra, and oxygen annealing was performed to obtain oxide superconducting wires.
A 150 nm thick Al ₂ O ₃ diffusion prevention layer is formed on the substrate by ion beam sputtering, a 30 nm thick Y ₂ O ₃ bed layer is formed by ion beam sputtering, and the thickness is measured by IBAD. An intermediate layer of 10 nm MgO is formed, a cap layer of CeO _{2 having} a thickness of 500 nm is formed by pulse laser deposition, and a composition of Gd ₂ Ba ₂ Cu ₃ O _{7-x having a} thickness of 1 μm is formed by pulse laser deposition. An oxide superconducting layer was formed, an Ag stabilizing layer having a thickness of 10 μm was formed, oxygen annealing was performed at 500 ° C. for 10 hours, and furnace cooling was performed to obtain an oxide superconducting wire.

Each oxide superconducting wire was cooled with liquid nitrogen and subjected to Ic measurement. The current value when the voltage at both ends became 1 μV / cm ² was defined as Ic. The result is shown in FIG.
From the results shown in FIG. 6, a correlation equivalent to the correlation shown in FIG. 5 can be obtained. From the results shown in FIG. 6, in order to obtain an oxide superconducting wire having a critical current value of 400 A, the surface of the substrate It can be realized when the roughness Ra is in the range of 2 nm or more and 7 nm or less, and in order to obtain an oxide superconducting wire having a critical current value of 300 A, the surface roughness Ra of the substrate is in the range of more than 7 nm and 8 nm or less. In order to obtain an oxide superconducting wire having a critical current value of 200 A class, it is feasible if the surface roughness Ra of the base material is in the range of more than 8 nm and 8.6 nm or less. It can be seen that the oxide superconducting wire can be obtained by setting the surface roughness Ra of the substrate to a range of more than 8.6 nm and not more than 9 nm.

  INDUSTRIAL APPLICABILITY The present invention is used as a technique capable of separately making a superconducting wire applied to a superconducting conductor for power supply, a superconducting coil, and the like, and an oxide superconducting wire that suppresses a critical current value applied to a superconducting fault current limiter. be able to.

  A, B ... superconducting wire, 10A, 10B ... base material, 11 ... diffusion preventing layer, 12 ... bed layer, 15 ... intermediate layer, 16 ... cap layer, 17 ... oxide superconducting layer, 18 ... stabilization layer.

Claims (5)

On the base material, an intermediate layer in which the crystal orientation is adjusted by an ion beam assisted deposition method, a cap layer in which the crystal orientation is adjusted under the influence of the crystal orientation of the intermediate layer, and the cap layer A superconducting wire comprising at least an oxide superconducting layer whose crystal orientation is arranged under the influence of crystal orientation, and producing a plurality of superconducting wires having different critical current values exhibited by the oxide superconducting layer. When dividing,
Even when producing any superconducting wire with different critical current values, the oxide superconducting layer is formed to the same thickness,
There is a maximum value among the values of the surface roughness Ra where the critical current value obtained in the oxide superconducting layer having the same thickness according to the value of the surface roughness Ra of the substrate surface has an upper limit value. And a range in which an oxide superconducting layer having a critical current value lower than the upper limit value of the previous critical current value according to the value of the surface roughness Ra in this range is obtained. In the range where the low critical current value is present and the surface roughness Ra is increased, the critical current value is proportionally decreased. In the range where the critical current value is proportional, the base material is used. A method for producing an oxide superconducting wire, wherein a plurality of superconducting wires having different critical current values indicated by the oxide superconducting layer are produced by selecting and sorting the surface roughness Ra.   The method for producing an oxide superconducting wire according to claim 1, wherein an intermediate layer is formed on the base material via a bed layer.   The method for producing an oxide superconducting wire according to claim 1, wherein an intermediate layer is formed on the base material via a diffusion preventing layer and a bed layer.   The range in which the critical current value obtained in the oxide superconducting layer having the same thickness according to the value of the surface roughness Ra of the substrate surface shows an upper limit value is 2 nm or more and less than 7 nm. The manufacturing method of the oxide superconducting wire described in 1. Ni alloy base material, Al ₂ O ₃ diffusion prevention layer, Y ₂ O ₃ bed layer, MgO intermediate layer, RE-123 oxide superconducting layer (REBa ₂ Cu ₃ O _7-X : RE is a rare earth element) ), A process for producing a superconducting wire having a critical current value Ic: 400A class with a surface roughness Ra of the surface of the base material in the range of 2 nm to 7 nm, and a surface roughness Ra of the base material surface. Of a superconducting wire having a critical current value Ic: 300A class with a surface roughness Ra of more than 8 nm and 8.6 nm or less, and a critical current value Ic: 200A. A plurality of steps of manufacturing a superconducting wire of a grade A and a superconducting wire of a critical current value Ic: 100A class with a surface roughness Ra of the substrate surface in the range of more than 8.6 nm and 9.0 nm or less. Combination Method of manufacturing an oxide superconducting wire according to claim 1, the critical current value is equal to or separating manufactures different superconducting wires shown by the oxide superconducting layer Te.

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