JP2014022228A - Oxide superconductive conductor and production method of oxide superconductive conductor, and superconduction device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of an oxide superconductive conductor in which agglomeration of an Ag atom generated when heating a protective layer can be reduced, and protective performance in an oxide superconduction layer principal plane can be improved; the oxide superconductive conductor; and a superconduction device using the same.SOLUTION: An oxide superconductive conductor 100 includes: a substrate 1; an interlayer 2 and an oxide superconduction layer 3 formed on a principal plane of the substrate 1; a protective layer 4 formed on a principal plane of the oxide superconduction layer 3 and including at least an Ag atom; and a metallic coating layer 5 formed so as to cover a principal plane of the protective layer 4 and including at least an Au atom.

Description

  The present invention relates to an oxide superconducting conductor, a method for producing an oxide superconducting conductor, and a superconducting device using the same.

One of the high-efficiency, low-loss electrical devices that can solve energy, environment, and resource problems in recent years includes superconducting devices such as cables, coils, motors, and magnets that use a superconductor as a low-current-loss material. As superconductors used in these superconducting devices, for example, oxide superconductors such as RE-123 series (REBa ₂ Cu ₃ O _(7-x) : RE is a rare earth element including Y and Gd) are known. ing. This oxide superconductor exhibits superconducting properties near the temperature of liquid nitrogen and can maintain a relatively high critical current density even in a strong magnetic field, so it is considered that it can be applied in a wider range than other superconductors. Therefore, it is expected as a promising material for practical use.

  Here, in order to use an oxide superconductor for an electric device, it is common to process the oxide superconductor into a wire and use it as a power supply conductor or an oxide superconductor such as a magnetic coil. . Specifically, the oxide superconducting conductor is formed by forming an oxide superconducting layer on the main surface of the metal base material via an intermediate layer and covering the main surface of the oxide superconducting layer to form a protective layer. Can be obtained.

  As one method for producing such an oxide superconducting conductor, a method has been proposed in which the oxide superconducting layer is heated and oxygen is appropriately taken into the oxide superconducting layer in order to further improve the superconducting characteristics. For this reason, the protective layer needs to use a material containing at least Ag as a material having a high oxygen permeability. In addition, since contact resistance is generated at the interface between the protective layer and the oxide superconducting layer, heat treatment is generally performed after the formation of the oxide superconducting layer and the protective layer in order to reduce the contact resistance.

  As such an oxide superconducting conductor, for example, as described in Patent Document 1, an oxide superconducting layer is formed on a tape-like substrate via an intermediate layer, and on this oxide superconducting layer, It is generally known to form a highly conductive base stabilizing thin film made of a noble metal such as Ag or Pt or an alloy thereof.

Japanese Patent Application Laid-Open No. 07-073758

  However, the oxide superconductor described in Patent Document 1 has a problem during heat treatment of the oxide superconductor after the formation of the protective layer and the oxide superconductor layer. That is, when the protective layer is heated, the Ag atoms forming the protective layer are locally aggregated on the surface of the oxide superconducting layer as shown in FIG. That is, the protective layer becomes an aggregate of a plurality of Ag particles isolated and dispersed in an island shape. As a result, the oxide superconducting layer is exposed, and the protective layer covering the main surface of the oxide superconducting layer cannot sufficiently cover the main surface of the oxide superconducting layer. As a result, an oxide superconducting conductor with insufficient protection of the main surface of the oxide superconducting layer is formed, and the protection performance of the oxide superconducting layer main surface against external factors such as moisture and mechanical load is reduced. Had. Therefore, the oxide superconducting conductor has room for improvement in protecting the main surface of the oxide superconducting layer.

  The present invention has been made in view of the above circumstances, and can reduce aggregation of Ag atoms generated during heating of the protective layer, and can improve the protection performance on the main surface of the oxide superconducting layer. It is another object of the present invention to provide a method for producing an oxide superconducting conductor and a superconducting device using the same.

  The present inventor has intensively studied to solve the above problems, and has also considered increasing the thickness of Ag in the protective layer so that the protective layer sufficiently protects the main surface of the oxide superconducting layer. That is, as the thickness of Ag in the protective layer increases, the number of Ag atoms increases, so Ag atoms aggregate on the surface of the oxide superconducting layer during heating of the protective layer and move from the original position to another position. Even so, another Ag atom can be deposited at the position of the Ag atom in the original position. For this reason, it was considered that the exposure of the oxide superconducting layer could be reduced. However, even if this method is used, aggregation of Ag atoms cannot be reduced in the end, so that the protective layer cannot sufficiently cover the main surface of the oxide superconducting layer, and the main surface of the oxide superconducting layer cannot be covered. It has been found that the protection remains inadequate and the above problem cannot be solved sufficiently. Accordingly, as a result of further earnest research, the present inventor has found that the above problems can be solved by preliminarily causing aggregation before heating the protective layer, thereby completing the present invention. It came.

  That is, the present invention relates to a base material, an intermediate layer and an oxide superconducting layer formed on the main surface of the base material, a protective layer formed on the main surface of the oxide superconducting layer and containing at least Ag atoms, An oxide superconducting conductor characterized by having a metal coating layer formed so as to cover the main surface of the layer and containing at least Au atoms.

  According to the oxide superconducting conductor, the metal coating layer containing at least Au atoms is formed so as to cover the main surface of the protective layer. Since the binding energy between Ag atoms in the protective layer and Au atoms in the metal coating layer is larger than the binding energy between Ag atoms in the protective layer, the attractive force between Ag atoms and Au atoms is between Ag atoms. Work more than the power of attraction. As a result, the Ag atoms and the Au atoms are more strongly bonded, so that when the protective layer is heated, the Ag atoms are oxidized to reduce the surface energy of the Ag atoms as much as possible at the interface between the protective layer and the oxide superconducting layer. Aggregation on the surface of the superconducting layer and local solidification can be prevented. Therefore, since the protective layer can sufficiently cover the main surface of the oxide superconducting layer, exposure of the oxide superconducting layer is suppressed as much as possible. As a result, it becomes difficult for moisture to enter the oxide superconducting layer, so that deterioration of critical current characteristics can be reduced. In addition, since the adhesion between the oxide superconducting layer and the protective layer is further improved, it is possible to reduce the impact caused by dropping and the external mechanical load on the main surface of the oxide superconducting layer. Therefore, according to the oxide superconducting conductor of the present invention, it is possible to obtain a highly reliable oxide superconducting conductor with improved protection performance on the main surface of the oxide superconducting layer.

  In the superconducting device according to the present invention, the oxide superconducting conductor is preferably used.

  By using the oxide superconducting conductor in a superconducting device, a highly reliable superconducting device having an oxide superconducting conductor in which the main surface of the oxide superconducting layer is sufficiently covered with a protective layer can be realized. Therefore, since the protection performance of the superconducting device against external factors such as moisture and mechanical load can be improved, it is possible to realize a superconducting device having higher reliability than before.

  The present invention also provides an intermediate layer forming step for forming an intermediate layer on the main surface of the substrate, an oxide superconducting layer forming step for forming an oxide superconducting layer on the main surface of the intermediate layer, and an oxide superconducting layer. A protective layer forming step of forming a thin film containing at least Ag atoms on the main surface of the metal, and forming a protective layer; and forming a thin film containing at least Au atoms so as to cover the main surface of the protective layer; And a heating step of heating at least the oxide superconducting layer.

  According to the above manufacturing method, before heating the protective layer, the metal coating layer containing at least Au atoms is formed so as to cover the main surface of the protective layer. Since the binding energy between Ag atoms in the protective layer and Au atoms in the metal coating layer is higher than the binding energy between Ag atoms in the protective layer, the attractive force between Ag atoms and Au atoms is between Ag atoms. Work more than the power of attraction. As a result, Ag atoms and Au atoms are bonded more firmly. Therefore, even if the protective layer is heated, the Ag atoms are oxidized to minimize the surface energy of Ag atoms at the interface between the protective layer and the oxide superconducting layer. Aggregation on the surface of the superconducting layer and local solidification can be prevented. Therefore, since the protective layer can sufficiently cover the main surface of the oxide superconducting layer, exposure of the oxide superconducting layer can be suppressed as much as possible. As a result, it becomes difficult for moisture to enter the oxide superconducting layer, so that deterioration of critical current characteristics can be reduced. In addition, since the adhesion between the oxide superconducting layer and the protective layer can be further improved, it is possible to reduce the impact caused by dropping and the external mechanical load on the main surface of the oxide superconducting layer. Therefore, according to the method for manufacturing an oxide superconducting conductor of the present invention, it is possible to manufacture a highly reliable oxide superconducting conductor capable of imparting better protection performance to the main surface of the oxide superconducting layer. Can do.

  In the method for producing an oxide superconducting conductor, in the metal coating layer forming step, it is preferable to form a thin film containing at least Au atoms at a temperature of 400 ° C. or lower.

  In this case, compared to a case outside the above range, thermal energy is less likely to be imparted to the Ag atoms, and thus thermal activation is difficult. For this reason, since the diffusion of Ag atoms hardly occurs, Ag atoms aggregate on the surface of the oxide superconducting layer and are not easily solidified locally. Therefore, since the protective layer can more fully cover the main surface of the oxide superconducting layer, exposure of the oxide superconducting layer can be further suppressed. Here, when the film is formed at a temperature lower than 400 ° C., it is difficult to impart thermal energy to Au atoms as in the case of Ag atoms, so that diffusion of Au atoms is difficult to occur. Therefore, since the metal coating layer is deposited unevenly on the main surface of the protective layer, the metal coating layer cannot sufficiently cover the main surface of the protective layer. Therefore, in order to solve this problem, it is necessary to make it difficult for Ag atoms to diffuse and to make Au atoms easily diffuse. Therefore, the film formation temperature range is preferably room temperature to 400 ° C., more preferably 250 ° C. to 400 ° C. Furthermore, in order to more easily commutate the overcurrent generated in the oxide superconducting layer, in the case of forming a stabilizing layer made of a highly conductive metal such as silver or copper on the main surface of the protective layer, Since the protective layer is formed so as to sufficiently cover the main surface of the oxide superconducting layer, the stabilization layer can be formed so as to sufficiently cover the main surface of the protective layer. Accordingly, since the adhesion between the protective layer and the stabilization layer is further improved, it is possible to provide more excellent reliability that overcurrent is easily commutated by the protection layer and the stabilization layer.

  ADVANTAGE OF THE INVENTION According to this invention, aggregation of Ag atom generated at the time of the heating of a protective layer can be reduced, and the protection performance in an oxide superconducting layer main surface can be improved.

1 is a cross-sectional perspective view showing an oxide superconducting conductor according to the present invention. It is a figure which shows the manufacturing method of the oxide superconductor based on this invention in order of a process, Fig.2 (a) is sectional drawing which shows the state which formed the intermediate | middle layer on the main surface of a base material, FIG.2 (b) is FIG. FIG. 2C is a sectional view showing a state in which an oxide superconducting layer is formed on the main surface of the intermediate layer. FIG. 2C is a sectional view showing a state in which a protective layer is formed on the main surface of the oxide superconducting layer. (D) is sectional drawing which shows the state which formed the metal coating layer so that the main surface of a protective layer might be covered. It is a flowchart which shows the manufacturing method of the oxide superconductor based on this invention. It is a photograph figure when the upper surface of the protective layer after heating the oxide superconductor which concerns on this invention at the temperature of 400 degreeC is observed with the electron microscope. It is a photograph figure when the upper surface of the protective layer which Ag atoms aggregated was observed with the electron microscope, after heating the conventional oxide superconductor.

  Hereinafter, an embodiment of an oxide superconducting conductor, a method for producing an oxide superconducting conductor, and a superconducting device using the same will be described in detail with reference to FIGS. Note that the present invention is not limited to such an embodiment. In addition, the drawings used in the following description may show the main part in an enlarged manner for the sake of convenience in order to make the characteristics of the present invention easier to understand. Not necessarily.

  As shown in FIG. 1, an oxide superconducting conductor 100 of this embodiment is configured by laminating an intermediate layer 2, an oxide superconducting layer 3, a protective layer 4 and a metal coating layer 5 in this order on a base material 1. ing.

  The substrate 1 is preferably in the form of a tape, a sheet or a thin plate in order to make a long superconducting conductor having flexibility. The material used for the substrate 1 is preferably a material having a relatively high mechanical strength, heat resistance, and a metal that can be easily processed into a wire, such as stainless steel and hastelloy. Examples thereof include various heat-resistant metal materials such as nickel alloys, or materials obtained by arranging ceramics on these various metal materials. Among them, Hastelloy (trade name, manufactured by Haynes, USA) is preferable as a commercial product. This kind of Hastelloy includes Hastelloy B, C, G, N, W, etc., which have different amounts of components such as molybdenum, chromium, iron, cobalt, etc., and any kind can be used here. Moreover, what is necessary is just to adjust the thickness of the base material 1 suitably according to the objective, and is 10-500 micrometers normally, Preferably it is 20-200 micrometers.

  As the intermediate layer 2, a structure in which a diffusion prevention layer, a bed layer, an alignment layer, and a cap layer are laminated in this order can be applied.

As a result of heat treatment when another layer is formed on the upper surface of this layer, the diffusion preventing layer diffuses part of the constituent elements of the substrate 1 when the substrate 1 or other layers receive a thermal history. And it has a function which suppresses mixing into the oxide superconducting layer 3 side as an impurity. The specific structure of the diffusion preventing layer is not particularly limited as long as it can exhibit the above-described function, but Al ₂ O ₃ , Si ₃ N ₄ , or GZO (which has a relatively high effect of preventing contamination of impurities) A single layer structure or a multilayer structure composed of Gd ₂ Zr ₂ O ₇ ) or the like is desirable.

The bed layer is used to suppress the reaction of the constituent elements at the interface between the base material 1 and the oxide superconducting layer 3 and improve the orientation of the layer provided on the upper surface than this layer. The specific structure of the bed layer is not particularly limited as long as it can exhibit the above functions, but Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , Dy ₂ O ₃ , Er ₂ O, which have high heat resistance. ₃ , a single layer structure or a multilayer structure composed of rare earth oxides such as Eu ₂ O ₃ and Ho ₂ O ₃ is desirable.

The alignment layer controls the crystal orientation of the cap layer and the oxide superconducting layer 3 formed thereon, suppresses the constituent elements of the substrate 1 from diffusing into the oxide superconducting layer 3, 1 and the oxide superconducting layer 3 have a function of relieving a difference in physical characteristics such as a coefficient of thermal expansion and a lattice constant. The material of the alignment layer is not particularly limited as long as it can express the above function, but when a metal oxide such as Gd ₂ Zr ₂ O ₇ , MgO, ZrO ₂ —Y ₂ O ₃ (YSZ) is used, In an ion beam assisted vapor deposition method (hereinafter also referred to as IBAD method) described later, a layer with high crystal orientation is obtained, and the crystal orientation of the cap layer and the oxide superconducting layer 3 is improved. This is particularly suitable.

The cap layer is used for controlling the crystal orientation of the oxide superconducting layer 3 more strongly than the orientation layer, diffusing elements constituting the oxide superconducting layer 3 into the intermediate layer 2, or laminating the oxide superconducting layer 3. And a function of suppressing the reaction between the gas to be generated and the intermediate layer 2. The material of the cap layer is not particularly limited as long as it can express the above function, but CeO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Gd ₂ O ₃ , Zr ₂ O ₃ , Ho ₂ O ₃ , Metal oxides such as Nd ₂ O ₃ and Zr ₂ O ₃ are preferable from the viewpoint of lattice matching with the oxide superconducting layer 3. Among them, CeO ₂ is particularly preferable because a layer having an even higher degree of orientation than that of the intermediate layer 2 can be obtained. Here, when CeO ₂ is used for the cap layer, the cap layer may include a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion.

The oxide superconducting layer 3 has a function of flowing current when in the superconducting state. The material used for the oxide superconducting layer 3 can be widely applied to an oxide superconductor having a generally known composition, such as a copper oxide such as a Y-based superconductor or a Bi-based superconductor. Examples include superconductors. Examples of the composition of the Y-based superconductor include REBa ₂ Cu ₃ O _(7-x) (RE represents a rare earth element such as Y, La, Nd, Sm, Er, Gd, and x represents oxygen deficiency). Specifically, Y123 (YBa ₂ Cu ₃ O _(7-x) ) and Gd123 (GdBa ₂ Cu ₃ O _(7-x) ) can be mentioned. The composition of the Bi-based superconductor, for _{example, Bi 2 Sr 2 Ca n-} 1 Cu n O 4 + 2n + δ (n is the number of layers of CuO _2, [delta] represents an excess oxygen.) Include. In this copper oxide superconductor, although the base material is an insulator, it becomes a superconductor by taking in oxygen, and has the property of exhibiting superconducting properties. Here, the material of the oxide superconducting layer 3 used in the present invention is a copper oxide superconductor. Unless otherwise specified, the material used for the oxide superconducting layer 3 is a copper oxide superconductor.

  The protective layer 4 bypasses an overcurrent generated at the time of an accident, or suppresses a chemical reaction occurring between the oxide superconducting layer 3 and a layer provided on the upper surface of this layer. It has a function of preventing deterioration of superconducting characteristics caused by entering the other layer and breaking the composition. Moreover, in order to make it easy to take in oxygen to the oxide superconducting layer 3, it has the function to make oxygen permeate | transmit easily at the time of a heating. For this reason, the protective layer 4 is made of a material containing at least Ag. The material may be a mixture or alloy containing a noble metal such as Au or Pt, or a plurality of these may be used. Note that the material of the protective layer 4 used in the present invention is Ag, and hereinafter, the material used for the protective layer 4 is Ag unless otherwise specified.

When the protective layer 4 is heated, the metal coating layer 5 includes a plurality of Ag atoms in which Ag atoms contained in the protective layer 4 aggregate on the surface of the oxide superconducting layer 3 and locally solidify and disperse in an island shape. In order to suppress the aggregation of particles and prevent the oxide superconducting layer 3 from being exposed, it is formed so as to cover the main surface of the protective layer 4. In order to prevent such agglomeration of Ag atoms, the attracting force between the Ag atoms and the atoms of the metal coating layer 5 only needs to be greater than the attracting force between the Ag atoms. The bond energy between the 4 Ag atoms and the atom of the metal coating layer 5 may be larger than the bond energy between the Ag atoms in the protective layer 4. Therefore, a material containing at least Au is used for the metal coating layer 5. Further, this material may be a mixture or alloy containing materials such as Pt and Al, and a plurality of these may be used.
The film thickness of the metal coating layer 5 can usually be selected in the range of 10 nm or more and 2000 nm or less, but the effect of suppressing the aggregation of Ag atoms can be obtained, and if the film thickness is made too large, the production cost is high because Au is expensive. Therefore, it is preferable to select a film thickness of 10 nm or more and 100 nm or less, and it is more preferable to select a range of 10 nm or more and 30 nm or less.
Further, the interface resistance value between the oxide superconducting layer 3, the protective layer 4, and the metal coating layer 5 is 10 in order to more appropriately bypass the overcurrent generated at the time of an accident so that the oxide superconducting conductor 100 is not burned. It is preferably ⁻⁸ cm ² or less. In addition, the material of the metal coating layer 5 used in the present invention is Au. Hereinafter, unless otherwise specified, the material used for the metal coating layer 5 is Au.

  If necessary, the oxide superconducting conductor 100 may have a structure in which a stabilization layer (not shown) is formed on the main surface of the metal coating layer 5. The use of the stabilization layer varies depending on the use of the oxide superconductor 100. For example, when used for a superconducting cable, a superconducting motor, etc., it is used as a main part of a bypass that commutates an overcurrent generated when a quench occurs and a transition to a normal conducting state occurs. At this time, the material used for the stabilization layer should be made of a relatively inexpensive material such as copper, a Cu-Zn alloy (brass), a Cu alloy such as a Cu-Ni alloy, aluminum, an aluminum alloy, or stainless steel. Of these, copper is more preferable because it has high conductivity and is inexpensive. In addition, when used in a superconducting fault current limiter, the stabilization layer is used to instantaneously suppress an overcurrent that occurs when quenching occurs and transitions to a normal conducting state. At this time, examples of the material used for the stabilization layer include high resistance metals such as Ni-based alloys such as Ni-Cr. The structure of the stabilization layer is the same as that of the other layers. The stabilization layer is bent along the outer shape of the oxide superconducting conductor 100 from the protective layer 4 side of the oxide superconducting conductor 100. A C-type structure covering the back surface of the material 1 is used. Here, with the C-type structure, the side surface of the oxide superconducting layer 3 can be covered relatively stably, so that the water resistance of the oxide superconducting conductor 100 can be improved.

  If necessary, the structure of the oxide superconducting conductor 100 is such that the base material 1, the intermediate layer 2, the oxide superconducting layer 3, the protective layer 4, the metal coating layer 5 and the stabilization layer are all laminated. A structure in which a tape-like, sheet-like, or thin plate-like insulating coating layer (not shown) is formed so as to cover the periphery may be adopted. The insulating coating layer has a function of reinforcing the oxide superconducting conductor 100 by providing insulation from the outside. The material used for the insulating coating layer is not particularly limited as long as it is an insulating material, and examples thereof include polyimide.

  Next, with reference to FIGS. 1-3, the manufacturing method of the oxide superconductor 100 which concerns on this invention is demonstrated. Here, FIG. 2 is a diagram showing the manufacturing method of the oxide superconducting conductor 100 according to the present invention in the order of steps, and FIG. 3 is a flowchart showing the manufacturing method of the oxide superconducting conductor 100 according to the present invention.

  First, as shown in FIG. 2A, an intermediate layer 2 is formed by laminating a diffusion prevention layer, a bed layer, an orientation layer, and a cap layer in this order on one surface of a tape-like substrate 1. (Step 1 (Here, S1 in FIG. 3 is replaced with Step 1. Hereinafter, it may be replaced in the same manner.)).

  Since the diffusion preventing layer is not particularly limited in crystallinity, it can be formed by a film forming method such as a normal sputtering method. Moreover, the film thickness of a layer should just be 10-400 nm normally. Here, if the film thickness of the diffusion preventing layer is less than 10 nm, there is a possibility that the diffusion of the constituent elements of the substrate 1 cannot be sufficiently prevented only by the diffusion preventing layer. On the other hand, when the film thickness of the diffusion preventing layer exceeds 400 nm, the internal stress of the diffusion preventing layer increases, which may cause the whole including the other layers to easily peel from the substrate 1.

  The bed layer can be formed by a film forming method such as a normal sputtering method because crystallinity is not particularly limited as in the case of the diffusion preventing layer. Moreover, the film thickness of a layer should just be 10-100 nm normally. In addition, it is not always necessary to use both the diffusion preventing layer and the bed layer, and it is sufficient that a structure using at least one of these layers is used. In some cases, both layers may be omitted. When omitting both the diffusion preventing layer and the bed layer, an alignment layer described below is formed directly on the substrate 1.

  There are many methods for forming the alignment layer, such as a vacuum deposition method, a laser deposition method, and an IBAD method, but it is preferable to use the IBAD method because the crystal orientation of the superconducting layer 3 and the cap layer can be controlled to be higher. Here, the IBAD method is a method of orienting crystal axes by irradiating an ion beam such as Ar at a predetermined angle with respect to a crystal deposition surface during deposition. In addition, the alignment layer may have a single layer structure using one of the materials described above, or a plurality of layers may have a multilayer structure.

For the formation of the cap layer, when CeO ₂ is used, the film can be formed by a pulse laser deposition method (hereinafter sometimes referred to as a PLD method), a sputtering method, or the like, but a high film formation rate can be obtained. It is preferable to use the PLD method. Moreover, the film thickness of a cap layer should just be 50 nm or more, However 100 nm or more is preferable in order to acquire sufficient orientation. However, since crystal orientation will worsen when too thick, Preferably it is the range of 50-5000 nm, More preferably, it is the range of 100-5000 nm.

Next, as shown in FIG. 2B, the oxide superconducting layer 3 is formed on the main surface of the intermediate layer 2 (step 2). The oxide superconducting layer 3 can be formed by sputtering, vacuum vapor deposition, laser vapor deposition, physical vapor deposition such as PLD or electron beam vapor deposition, chemical vapor deposition (CVD), or coating pyrolysis. A chemical vapor deposition method such as the MOD method (MOD method) can be used, and the laser vapor deposition method is particularly preferable. Generally, the copper oxide superconductor used for the oxide superconducting layer 3 has a two-dimensional CuO ₂ plane composed of copper and oxygen in the crystal structure. Here, in order for the superconducting current to flow in this CuO ₂ plane, it is necessary to form a c-axis oriented film so that the CuO ₂ plane is connected. Therefore, in order to form such a film, it is necessary to set the surface temperature of the substrate 1 at the time of film formation in a range of around 800 ° C. If the temperature is lower than this range, an a-axis oriented film is formed and the path of the superconducting current is interrupted. If the temperature is higher than this range, the film itself cannot be formed. The oxide superconducting layer 3 has a film thickness of about 500 to 5000 nm and preferably a uniform thickness.

  Subsequently, as shown in FIG. 2C, a thin film containing at least Ag atoms is formed on the main surface of the oxide superconducting layer 3 to form the protective layer 4 (step 3). The protective layer 4 can be formed by a known method, but it is preferable to form the protective layer 4 by a sputtering method using a film forming apparatus such as a DC sputtering apparatus or an RF sputtering apparatus. Moreover, the film thickness of the protective layer 4 should just be normally 1-30 micrometers.

  Next, as shown in FIG. 2D, a thin film containing at least Au atoms is formed so as to cover the main surface of the protective layer 4 to form the metal coating layer 5 (step 4). Here, although the metal coating layer 5 can be formed by a known method, it is preferably formed by a sputtering method using a film forming apparatus such as a DC sputtering apparatus or an RF sputtering apparatus. Moreover, the film thickness of the metal coating layer 5 should just be 10-2000 nm normally. When the film forming temperature exceeds 400 ° C., Ag atoms in the protective layer 4 are likely to aggregate, and therefore, the Ag atoms may be locally solidified to easily expose the oxide superconducting layer 3. On the other hand, if the film formation temperature is lower than room temperature, Au atoms are not sufficiently diffused and the protective layer 4 may not be sufficiently covered. Therefore, it is preferable to form a film at room temperature or higher and 400 ° C. or lower.

  Next, the oxide superconducting layer 3 is heated in a heating furnace (not shown) (step 5). Here, since the base material of the oxide superconducting layer 3 is an insulator, the oxide superconducting layer 3 does not exhibit superconducting characteristics as it is. For this reason, by supplying oxygen to the oxide superconducting layer 3 and injecting carriers, the insulator changes to a metal and becomes a superconductor, and exhibits superconducting characteristics. Therefore, as a heating condition, the atmosphere in the heating furnace is preferably an atmosphere containing oxygen gas. In addition, when the protective layer 4 is formed after the oxide superconducting layer 3 is formed and heated, a relatively large contact electric resistance is generated at the interface between the oxide superconducting layer 3 and the protective layer 4. Furthermore, if the oxide superconducting layer 3 is heated without forming the metal coating layer 5 after forming the protective layer 4, Ag atoms in the protective layer 4 aggregate. Therefore, in order to solve these problems, it is necessary to heat the oxide superconducting layer 3 after the formation of the protective layer 4 and the metal coating layer 5. The heating temperature is preferably 250 to 450 ° C. in order to prevent aggregation more appropriately. Here, when the amount of oxygen taken into the oxide superconducting layer 3 is adjusted more appropriately, the superconducting characteristics such as critical current characteristics are further improved. Therefore, in order to make the amount of oxygen taken in more appropriate, the heating time is preferably 5 to 10 hours. Thereby, oxygen in the heating furnace atmosphere can be appropriately supplied to the oxide superconducting layer 3 through the protective layer 4 and the metal coating layer 5.

  Next, you may form a stabilization layer on the main surface of the metal coating layer 5 as needed. Here, the stabilization layer is not particularly limited as long as it is a known method, but is preferably formed by a method of directly bonding using a solder, a sputtering method, a vapor deposition method, or the like. The thickness of the stabilizing layer is not particularly limited and can be adjusted as appropriate, but is preferably 10 to 300 μm.

  If necessary, the entire circumference of the laminate in which the base material 1, the intermediate layer 2, the oxide superconducting layer 3, the protective layer 4, the metal coating layer 5, and the stabilizing layer are laminated is formed in a tape shape or a sheet shape. Alternatively, it may be covered with a thin insulating coating layer. Here, the coating method of the insulating coating layer is not particularly limited as long as it is a known method, but it is preferable to wind the laminated body so as to cover the laminated body with a rotating machine. Thus, by providing the insulating coating layer, insulation from the outside can be achieved and the oxide superconducting conductor 100 can be reinforced.

  Through the above steps, an oxide superconducting conductor 100 including a base material 1, an intermediate layer 2, an oxide superconducting layer 3, a protective layer 4 and a metal coating layer 5 can be produced as shown in FIG.

  When the oxide superconducting conductor 100 is manufactured as described above, the metal coating layer 5 containing at least Au atoms is formed so as to cover the main surface of the protective layer 4. Aggregation on the surface of the oxide superconducting layer 3 and local solidification can be prevented. Therefore, the protective layer does not become an aggregate layer in which Ag particles are isolated and dispersed, and the protective layer 4 can sufficiently cover the main surface of the oxide superconducting layer 3, so that the oxide superconducting layer 3 is exposed as much as possible. It is suppressed. As a result, it becomes difficult for moisture to enter the oxide superconducting layer 3, so that it is possible to reduce deterioration of the critical current characteristics. In addition, since the adhesion between the oxide superconducting layer 3 and the protective layer 4 is further improved, it is possible to reduce the impact caused by dropping and the external mechanical load on the main surface of the oxide superconducting layer 3. Therefore, according to the oxide superconducting conductor 100 of the present invention, it is possible to obtain the oxide superconducting conductor 100 having higher reliability with improved protection performance on the main surface of the oxide superconducting layer 3.

  Further, by using the oxide superconducting conductor 100 obtained as described above for a superconducting device, the reliability including the oxide superconducting conductor 100 in which the main surface of the oxide superconducting layer 3 is sufficiently covered with the protective layer 4 is provided. High superconducting equipment can be realized. Therefore, since the protection performance of the superconducting device against external factors such as moisture and mechanical load can be improved, it is possible to realize a superconducting device having higher reliability than before. Here, the superconducting device is not particularly limited as long as it has the oxide superconducting conductor 100, and examples thereof include a superconducting cable, a superconducting coil, a superconducting transformer, a superconducting current limiter, and a superconducting power storage device.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

Example 1
A tape-shaped substrate body having a width of 10 mm, a thickness of 0.1 mm, and a length of 2000 mm made of Hastelloy (trade name Hastelloy C-276, manufactured by Haynes, USA) is prepared, and the surface roughness is obtained with Al ₂ O ₃ abrasive grains. After polishing to Ra of 4 to 5 nm, the substrate was washed with alcohol and an organic solvent.

  Next, an intermediate layer was formed by laminating a diffusion prevention layer, a bed layer, an alignment layer, and a cap layer in this order on a tape-like substrate under the following formation conditions. Details are described below.

Next, a diffusion preventing layer of Al ₂ O ₃ was laminated on the tape-shaped substrate by ion beam sputtering. Here, the thickness of the layer was 80 nm.

Next, a bed layer of Y ₂ O ₃ was laminated on the diffusion prevention layer by ion beam sputtering. Here, the film thickness of the layer was 30 nm.

  Next, an MgO alignment layer was laminated on the bed layer by the IBAD method. Here, the film thickness of the layer was 10 nm.

Next, a CeO ₂ cap layer was laminated on the alignment layer by the PLD method to form an intermediate layer. Here, the film thickness of the layer was 300 nm.

  By the above method, the intermediate layer was formed on the tape-shaped substrate.

Next, an oxide superconducting layer of GdBa ₂ Cu ₃ O _7-x was formed on the intermediate layer by the PLD method. Here, the film thickness of the layer was 1 μm.

  Next, an Ag protective layer was formed on the oxide superconducting layer by DC sputtering. Here, the film thickness of the layer was 300 nm.

  Thereafter, a metal coating layer of Au was formed on the protective layer at 400 ° C. by DC sputtering. Here, the thickness of the layer was 100 nm. At this time, as shown in FIG. 4, even when the protective layer was heated at 400 ° C. during the formation of the metal coating layer, Ag atoms were hardly aggregated.

  And the laminated body in which each layer was formed was oxygen-annealed in a heating furnace at 500 ° C. for 10 hours, and oxygen in the heating furnace atmosphere was supplied to the oxide superconducting layer through the protective layer and the metal coating layer. Then, after cooling in the furnace for 26 hours, it was taken out from the furnace to obtain an oxide superconducting conductor.

(Example 2)
An oxide superconducting conductor was produced in the same manner as in Example 1 except that the thickness of the metal coating layer formed in Example 1 was 30 nm in Example 2.

(Comparative Example 1)
An oxide superconducting conductor was produced in the same manner as in Example 1 except that the metal coating layer was not formed on the Ag stabilizing layer.

(Comparative Example 2)
An oxide superconducting conductor was produced in the same manner as in Comparative Example 1 except that the thickness of the Ag stabilizing layer formed in Comparative Example 1 was 2000 nm in Comparative Example 2.

  Thereafter, as a durability evaluation for the samples of Examples 1 and 2 and Comparative Examples 1 and 2, the maintenance ratio of the critical current value after 24 hours in the oxide superconducting conductor was evaluated as follows.

The oxide superconducting conductors produced according to Examples 1 and 2 and Comparative Examples 1 and 2 were held for 24 hours in an environment of a temperature of 121 ° C., a humidity of 100%, and 2 atmospheres. Next, the oxide superconducting conductor after 24 hours was immersed in liquid nitrogen and cooled, and the critical current value was measured by a four-terminal method. At this time, the measurement temperature was 77 K, and the magnetic field was 0 Tesla. Here, the maintenance rate of the critical current value after 24 hours,
The following formula: critical current value retention rate (%) = critical current value after 24 hours / critical current value immediately after production × 100
Calculated according to The results of the maintenance ratio of the critical current value calculated by the above method are summarized in Table 1 below.

  From the results shown in Table 1, it was found that the oxide superconducting conductors of Examples 1 and 2 exhibited a superior critical current value retention rate as compared with the oxide superconducting conductors of Comparative Examples 1 and 2. Further, it was found that even when the film thickness of the metal coating layer was reduced from 100 nm to 30 nm as in the sample of Example 2, a high critical current value retention rate could be maintained. This provides a low-cost oxide superconducting conductor that can maintain the critical current value relatively high without using a generally expensive Au metal coating layer that is relatively thick. I understood that I could do it.

  From the above, it was confirmed that according to the oxide superconducting conductor of the present invention, a working electrode capable of reducing deterioration of critical current characteristics can be produced.

  DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Intermediate | middle layer, 3 ... Oxide superconductor layer, 4 ... Protective layer, 5 ... Metal coating layer, 100 ... Oxide superconductor.

Claims (4)

A substrate;
An intermediate layer and an oxide superconducting layer formed on the main surface of the substrate;
A protective layer formed on the main surface of the oxide superconducting layer and containing at least Ag atoms;
A metal coating layer formed so as to cover the main surface of the protective layer and containing at least Au atoms;
An oxide superconducting conductor characterized by comprising:   A superconducting device comprising the oxide superconducting conductor according to claim 1. An intermediate layer forming step of forming an intermediate layer on the main surface of the substrate;
An oxide superconducting layer forming step of forming an oxide superconducting layer on the main surface of the intermediate layer;
A protective layer forming step of forming a protective layer by forming a thin film containing at least Ag atoms on the main surface of the oxide superconducting layer;
A metal coating layer forming step of forming a metal coating layer by forming a thin film containing at least Au atoms so as to cover the main surface of the protective layer;
A heating step of heating at least the oxide superconducting layer;
A method for producing an oxide superconducting conductor, comprising:   4. The method for producing an oxide superconductor according to claim 3, wherein in the metal coating layer forming step, a thin film containing at least Au atoms is formed at a temperature of room temperature to 400 ° C.