JP7847445B2 - Oxide superconducting wires and connecting structures - Google Patents

Description

This invention relates to oxide superconducting wires and connecting structures.

Patent Document 1 discloses an oxide superconducting wire having a structure in which an intermediate layer, a superconducting layer, and a protective layer are sequentially laminated on a substrate.

Japanese Patent Publication No. 2014-110125

However, conventional oxide superconducting wires have a problem: high interfacial resistance between the superconducting layer and the protective layer. High interfacial resistance between the superconducting layer and the protective layer leads to a problem of high connection resistance between the oxide superconducting wire and the object to which it is connected.

This invention has been made in consideration of these circumstances and aims to provide an oxide superconducting wire that reduces interfacial resistance between a superconducting layer and a protective layer, and a connecting structure equipped with this oxide superconducting wire.

The inventors of this invention investigated conventional oxide superconducting wires and obtained the following findings.
In conventional oxide superconducting wires, a protective layer made of a metal such as silver is directly laminated on the surface of the superconducting layer along the thickness direction of the substrate. When an electrode is connected to such an oxide superconducting wire and current is passed through the electrode, the current flows from the superconducting layer to the protective layer in the thickness direction of the substrate.

Incidentally, oxide superconducting wires have a characteristic crystal structure, and it is known that current flows well in the a-axis or b-axis direction, but not well in the c-axis direction. For this reason, conventional oxide superconducting wires having the aforementioned laminated structure have a structure in which current flows in the c-axis direction between the superconducting layer and the protective layer, making it difficult to reduce the interfacial resistance between the superconducting layer and the protective layer.
Based on the above findings, the inventors conducted thorough research and arrived at the present invention.

To solve the above problems, an oxide superconducting wire according to one aspect of the present invention comprises a base material, a superconducting layer provided above the base material and composed of an oxide superconductor, and a protective layer provided on the superconducting layer and in contact with the superconducting layer. The interface between the superconducting layer and the protective layer is aligned with the c-axis of the crystal constituting the oxide superconductor.

In the oxide superconducting wire material according to one aspect of the present invention and the connecting structure according to one aspect of the present invention described later, the phrase "superconducting layer provided above the substrate" means not only that a superconducting layer is provided on the substrate, but also that in a structure where a layer film such as an intermediate layer is arranged between the substrate and the superconducting layer, the superconducting layer substrate is provided above the substrate.

According to one embodiment of the present invention, the interface between the superconducting layer and the protective layer is aligned with the c-axis of the oxide superconductor crystal, which facilitates current flow from the superconducting layer to the protective layer along the a-axis or b-axis of the crystal constituting the oxide superconductor. As a result, the interfacial resistance between the superconducting layer and the protective layer can be reduced.

In an oxide superconducting wire according to one aspect of the present invention, a plurality of recesses having inner wall surfaces are formed in the superconducting layer between the superconducting layer and the protective layer, and the protective layer is formed within the plurality of recesses, and the inner wall surfaces may be parallel to the c-axis.

According to one embodiment of the present invention, an oxide superconducting wire is obtained in which the inner walls of multiple recesses formed in the superconducting layer are parallel to the c-axis. In this structure, current flows more easily from the superconducting layer to the protective layer along the a-axis or b-axis of the crystal constituting the oxide superconductor. As a result, the interfacial resistance between the superconducting layer and the protective layer can be reduced. Furthermore, by forming multiple recesses in the superconducting layer, the surface area of the superconducting layer is increased. Therefore, oxygen heat treatment of the superconducting layer can be carried out efficiently.

In an oxide superconducting wire according to one aspect of the present invention, a plurality of recesses having inner wall surfaces are formed in the superconducting layer between the superconducting layer and the protective layer, the protective layer is formed within the plurality of recesses, and the inner wall surfaces may be inclined with respect to the c-axis.

According to one embodiment of the present invention, an oxide superconducting wire is obtained in which inclined portions are formed on the inner wall surfaces of multiple recesses formed in the superconducting layer. In this structure, current flows more easily from the superconducting layer to the protective layer along the a-axis or b-axis direction of the crystal constituting the oxide superconductor. As a result, the interfacial resistance between the superconducting layer and the protective layer can be reduced. Furthermore, by forming multiple recesses in the superconducting layer, the surface area of the superconducting layer is increased. Therefore, oxygen heat treatment of the superconducting layer can be carried out efficiently.

In one embodiment of the present invention, in the width direction of the oxide superconducting wire, which is perpendicular to the extending direction of the oxide superconducting wire and the thickness direction of the oxide superconducting wire, the superconducting layer has two end regions including the ends of the superconducting layer and a central region between the two end regions. The number of the plurality of recesses formed in the superconducting layer per unit area in the end regions may be greater than the number of the plurality of recesses formed in the superconducting layer per unit area in the central region.

In typical oxide superconducting wires, current flows less easily in the end regions compared to the central region. In contrast, in one embodiment of the present invention, the number of recesses per unit area formed in the end regions is greater than the number of recesses per unit area formed in the central region. Therefore, current flows more easily in the end regions compared to the central region. Consequently, interfacial resistance in the end regions can be reduced. Furthermore, since the surface area of the superconducting layer increases in the end regions, oxygen heat treatment of the superconducting layer in the end regions can be carried out efficiently.

In an oxide superconducting wire according to one aspect of the present invention, the superconducting layer has two end regions including the ends of the superconducting layer and a central region between the two end regions, in the width direction of the oxide superconducting wire which is perpendicular to the extending direction of the oxide superconducting wire and the thickness direction of the oxide superconducting wire. The number of the plurality of recesses formed in the superconducting layer per unit area in the central region may be greater than the number of the plurality of recesses formed in the superconducting layer per unit area in the end regions.

In typical oxide superconducting wires, current flows more easily in the central region than in the end regions. In contrast, in one embodiment of the present invention, the number of recesses per unit area formed in the central region is greater than the number of recesses per unit area formed in the end regions. Therefore, more current flows in the central region. Consequently, the interfacial resistance in the central region can be further reduced. Furthermore, since the surface area of the superconducting layer increases in the central region, oxygen heat treatment of the superconducting layer in the central region can be carried out efficiently.

In one embodiment of the present invention, the depth of the recess may be less than the average thickness of the superconducting layer.

According to one embodiment of the present invention, a recess is formed in the superconducting layer without penetrating it. This allows for the reduction of interfacial resistance between the superconducting layer and the protective layer while maintaining the conductivity of the superconducting layer.

In one embodiment of the present invention, the ratio of the total opening area of the multiple recesses to the area of the superconducting layer in a plan view may be 0.30% or more and 0.60% or less.

According to one embodiment of the present invention, the interfacial resistance between the superconducting layer and the protective layer can be reduced.

To solve the above problems, a connection structure according to one aspect of the present invention connects an oxide superconducting wire according to the above-described aspect to an object to be connected.

According to the above-described aspect of the present invention, the objective is to provide an oxide superconducting wire that can reduce the interfacial resistance between the superconducting layer and the protective layer, and a connection structure equipped with this oxide superconducting wire.

This is a schematic enlarged cross-sectional view showing an oxide superconducting wire according to the first embodiment of the present invention. This is a schematic enlarged cross-sectional view showing a superconducting layer constituting an oxide superconducting wire according to a first embodiment of the present invention, illustrating a method for forming a recess in the superconducting layer. This is a schematic enlarged cross-sectional view showing a superconducting layer constituting an oxide superconducting wire according to a first embodiment of the present invention, illustrating a method for forming a recess in the superconducting layer. This is a schematic enlarged cross-sectional view showing a superconducting layer constituting an oxide superconducting wire according to a first embodiment of the present invention, illustrating a method for forming a recess in the superconducting layer. This is a schematic enlarged cross-sectional view showing a recess formed in the superconducting layer constituting the oxide superconducting wire according to the first embodiment of the present invention. This is a schematic enlarged cross-sectional view showing a recess formed in the superconducting layer constituting the oxide superconducting wire according to the first embodiment of the present invention. This is a schematic enlarged plan view showing a superconducting layer constituting an oxide superconducting wire according to the first embodiment of the present invention, illustrating a region in which a plurality of recesses are formed in the superconducting layer. This is an enlarged cross-sectional view schematically showing a part of a connection structure according to a second embodiment of the present invention. This is an enlarged cross-sectional view schematically showing a part of the connection structure according to the third embodiment of the present invention. This graph shows experimental results illustrating embodiments of the present invention.

The oxide superconducting wire and connecting structure according to embodiments of the present invention will be described in detail below with reference to the drawings. For convenience, the drawings used in this description may show enlarged versions of key parts to clearly illustrate the features of the present invention; therefore, the dimensional ratios of each component may not be the same as those of the actual components.

In the diagrams referenced in the following description, the X, Y, and Z directions, corresponding to a three-dimensional Cartesian coordinate system, are shown (symbols X, Y, and Z). The X direction corresponds to the width direction of the oxide superconducting wire. The Y direction corresponds to the extension direction of the oxide superconducting wire. The Z direction corresponds to the thickness direction of the oxide superconducting wire. In the following description, "plan view" refers to a diagram of the oxide superconducting wire viewed from the Z direction.

(First Embodiment)
(Oxide superconducting wires)
An oxide superconducting wire according to the first embodiment will be described with reference to Figure 1.
The oxide superconducting wire 1 according to this embodiment comprises a base material 10, an intermediate layer 11 provided on the base material 10, a superconducting layer 12 provided on the intermediate layer 11, a protective layer 13 provided on the superconducting layer 12, and a stabilizing layer 14 provided on the protective layer 13. The oxide superconducting wire 1 may also include an insulating coating layer covering the base material 10, the intermediate layer 11, the superconducting layer 12, the protective layer 13, and the stabilizing layer 14.

The height of the oxide superconducting wire 1, that is, the length from the bottom surface of the substrate 10 to the top surface of the protective layer 13 (length in the Z direction in Figure 1), is, for example, 80 μm.
The width of the oxide superconducting wire 1, that is, the length from the left end to the right end of the oxide superconducting wire 1 (the length in the X direction in Figure 1), is, for example, 12 mm.

(Base material 10)
The base material 10 is a tape-shaped metal substrate. Specific examples of metals that make up the metal substrate include nickel alloys such as Hastelloy (registered trademark), stainless steel, and oriented Ni-W alloys in which a texture is introduced into a nickel alloy.

(Middle class 11)
The intermediate layer 11 may have a multilayer structure, and for example, it may have a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, etc., in the order from the substrate 10 toward the superconducting layer 12. In a structure in which these multiple layers are provided in the intermediate layer 11, the number of each layer is not limited to one. Some of these multiple layers constituting the intermediate layer 11 may be omitted. Furthermore, a structure in which two or more layers of the same type are repeatedly laminated may be adopted. The intermediate layer 11 may be a metal oxide. By forming a superconducting layer 12 on an intermediate layer 11 with excellent orientation, it becomes easy to obtain a superconducting layer 12 with excellent orientation.

(Protective layer 13)
The protective layer 13 is provided on the superconducting layer 12 and is in contact with the superconducting layer 12.
The protective layer 13 functions as a current path that acts as a bypass path for overcurrents generated due to some kind of fault when current is supplied to the oxide superconducting wire 1. The protective layer 13 is made of a metallic material. For this reason, the protective layer 13 can also be called a metallic protective layer. The protective layer 13 is preferably made of silver (Ag) or a material containing at least silver (Ag). The protective layer 13 may be, for example, a silver alloy or a mixture containing silver. The material forming the protective layer 13 may also be a mixture or alloy containing precious metals such as gold (Au) or platinum (Pt) and silver (Ag), and multiple of these materials may be used.

(Stabilization layer 14)
The material for the stabilizing layer 14 can be selected from copper, copper alloys such as Cu-Zn alloy (brass) and Cu-Ni alloy, aluminum, aluminum alloy, stainless steel, and other materials.
The stabilizing layer 14 may be composed of multiple layers. Alternatively, the stabilizing layer 14 may be formed by metal plating. The stabilizing layer 14 may have a structure in which the entire laminate, including the substrate 10, the protective layer 13, and the layer between the substrate 10 and the protective layer 13, is covered with a plating layer.

(Superconducting layer 12)
As will be described later, the superconducting layer 12 has a surface 12F and a plurality of recesses 12G formed on the surface 12F. In other words, between the superconducting layer 12 and the protective layer 13, the superconducting layer 12 has a plurality of recesses 12G having an inner wall surface 12I and a bottom surface 12B.
The superconducting layer 12 has the function of conducting electric current when in a superconducting state.
The superconducting layer 12 is composed of rare-earth high-temperature superconductors.
Specifically, the material used for the superconducting layer 12 can be a wide range of oxide superconductors with commonly known compositions, such as copper oxide superconductors like Y-type superconductors and Bi-type superconductors.

Examples of Y-type superconductor compositions include REBa ₂ Cu ₃ O _7-x (where RE represents rare earth elements such as Y, La, Nd, Sm, Er, and Gd, and x represents an oxygen vacancy).
Specific compositions of Y-type superconductors include Y123 (YBa ₂ Cu ₃ O _7-x ) and Gd123 (GdBa ₂ Cu ₃ O _7-x ).
Examples of Bi _{-based superconductor compositions include Bi₂Sr₂Ca₂n⁻¹Cu₂n₂O₄⁺²⁻¹ ( where} n represents the number of _{CuO₂ layers} and δ represents excess oxygen). The parent material of this oxide superconductor is an insulator, but through oxygen annealing, the oxide superconductor incorporates oxygen _, becoming an oxide superconductor with a well-ordered crystalline structure and exhibiting superconducting properties.

(Structure of the recess 12G in the superconducting layer 12)
Each of the multiple recesses 12G has an inner wall surface 12I and a bottom surface 12B. The superconducting layer 12 is in contact with the protective layer 13 at its surface 12F, inner wall surface 12I, and bottom surface 12B. In other words, the protective layer 13 is formed inside the multiple recesses 12G.
In the example shown in Figure 5, the shape of the recess 12G is shown such that the angle between the inner wall surface 12I and the bottom surface 12B is a right angle. The shape of the recess 12G is not limited to the shape shown in Figure 5. The corner between the inner wall surface 12I and the bottom surface 12B may have an R shape (a rounded shape).
Furthermore, in the example shown in Figure 5, the bottom surface 12B is flat. The bottom surface 12B is not limited to being flat. At least a part of the bottom surface 12B may be curved. The entire bottom surface 12B may be curved. In other words, the recess 12G having the inner wall surface 12I and the bottom surface 12B may be formed in a substantially U-shape. The recess 12G may also be called a groove.

The depth d of the recess 12G is smaller than the average thickness t of the superconducting layer 12 before the recess 12G was formed. That is, the relationship d < t is satisfied between the depth d of the recess 12G and the average thickness t of the superconducting layer 12. In this embodiment, the average thickness t of the superconducting layer 12 is, for example, about 2.1 μm. The depth d of the recess 12G is, for example, about 0.5 μm. The diameter of the recess 12G is, for example, about 50 μm.

A method for forming the superconducting layer 12 will be explained with reference to Figures 2 to 4.
First, as shown in Figure 2, an intermediate layer 11 is laminated on a substrate 10 by a known method, and then a superconducting layer 12 is laminated on the intermediate layer 11.

Next, as shown in Figure 3, laser light is irradiated onto the surface 12F of the superconducting layer 12. This partially etches the surface 12F of the superconducting layer 12 to the location where the laser light is irradiated, forming recesses 12G. By switching between the laser light emission state (ON) and the non-emission state (OFF) and changing the relative position of the laser light source and the superconducting layer 12, multiple recesses 12G can be continuously formed on the superconducting layer 12. In a plan view, the planar pattern of the recesses with multiple recesses 12G is, for example, a dot pattern.

The conditions for irradiating with laser light are not particularly limited. By adjusting the irradiation time and intensity of the laser light onto the surface 12F of the superconducting layer 12, the depth of each of the multiple recesses 12G can be adjusted.

In a plan view, the shape of the recess 12G is, for example, circular. As a variation, the shape of the recess 12G may be elliptical, or it may be a known shape such as a roughly triangular shape, a roughly rectangular shape, a roughly polygonal shape, or a roughly star shape with straight sides. In such known shapes, the corners located where two sides intersect may have a chamfered shape.

The shape of the recess 12G in plan view depends on the irradiation shape of the laser light used to form the recess 12G by irradiating the surface 12F of the superconducting layer 12, that is, the shape of the laser light projected onto the surface 12F of the superconducting layer 12. The shape of the recess 12G in plan view can be freely set according to the degree of freedom of this laser light irradiation shape.

Next, after multiple recesses 12G are formed on the surface 12F of the superconducting layer 12, a protective layer 13 is formed on the surface 12F of the superconducting layer 12, as shown in Figure 4. The protective layer 13 is formed on the surface 12F of the superconducting layer 12 and also in each of the multiple recesses 12G so as to penetrate into their interiors. Within the multiple recesses 12G, the protective layer 13 is in contact with the inner wall surface 12I and the bottom surface 12B.

(Crystal structure on the inner wall surface 12I of the recess 12G)
Next, with reference to Figures 5 and 6, the crystal structure of the inner wall surface 12I of the recess 12G of the superconducting layer 12 will be described.
In Figures 5 and 6, the symbol c indicates the c-axis direction of the crystal structure of the oxide superconductor constituting the superconducting layer 12. The symbols a and b indicate the a-axis direction and b-axis direction of the crystal structure of the oxide superconductor constituting the superconducting layer 12.

As shown in Figure 5, the interface BF between the superconducting layer 12 and the protective layer 13 is aligned with the c-axis of the crystalline structure of the oxide superconductor. In other words, the interface BF between the superconducting layer 12 and the protective layer 13, and the inner wall surface 12I of the recess 12G, are parallel to the c-axis. More specifically, on the inner wall surface 12I, multiple crystals CR constituting the oxide superconductor are arranged parallel to the c-axis. These multiple crystals CR arranged in this way are part of the interface BF.
Each of the multiple crystals CR has a crystal plane CF aligned with the c-axis. In other words, the crystal plane CF is parallel to the c-axis. Therefore, high conductivity is obtained at the interface BF due to the a-axis or b-axis.

Figure 6 is a cross-sectional view that is a further enlarged view of the inner wall surface 12I of the recess 12G shown in Figure 5, and shows the case in which an inclined portion 12K is formed on the inner wall surface 12I.
As shown in Figures 1 and 3 to 5, the inner wall surface 12I of the recess 12G extends in the thickness direction of the oxide superconducting wire, that is, it is parallel to the Z direction.

However, microscopic observation of the inner wall surface 12I reveals that it is not necessarily parallel to the Z direction. As shown in Figure 6, an inclined portion 12K may be formed on the inner wall surface 12I. The inclined portion 12K follows an inclination direction D relative to the Z direction.

The inclined portion 12K forms part of the interface BF between the superconducting layer 12 and the protective layer 13.
In the inclined section 12K, the multiple crystals CR constituting the oxide superconductor are arranged in a step-like manner. The multiple crystals CR arranged in a step-like manner are part of the interface BF.
Each of the multiple crystals CR has a crystal plane CF that is aligned with the c-axis. In other words, the crystal plane CF is parallel to the c-axis.

With the inner wall surface 12I extending along the inclination direction D, the crystal plane CF is in contact with the protective layer 13 in the region indicated by symbol R. In other words, regardless of whether the entire inner wall surface 12I is inclined along the inclination direction D or extends along the Z direction, at the interface BF between the superconducting layer 12 and the protective layer 13, the crystal plane CF extends along the c-axis. Therefore, high conductivity is obtained at the interface BF due to the a-axis or b-axis.

(Area where multiple recesses 12G are formed)
Figure 7 is a schematic enlarged plan view showing the superconducting layer 12.
Referring to Figure 7, the region in the superconducting layer 12 where multiple recesses are formed will be explained.
In the X direction, the superconducting layer 12 has two end regions 12ER including the end 12E of the superconducting layer 12, and a central region 12C located between the two end regions 12ER.
In this embodiment, the number of recesses 12G formed in the superconducting layer 12 in the edge region 12ER per unit area is greater than the number of recesses 12G formed in the superconducting layer 12 in the central region 12C per unit area.

Next, the operation and effects of the oxide superconducting wire 1 configured as described above will be explained.
In the oxide superconducting wire 1, the interface BF between the superconducting layer 12 and the protective layer 13 is aligned with the c-axis of the crystal CR that constitutes the oxide superconductor of the superconducting layer 12. This makes it easier for current to flow from the superconducting layer 12 to the protective layer 13 along the a-axis or b-axis of the crystal CR that constitutes the oxide superconductor. As a result, the interfacial resistance between the superconducting layer 12 and the protective layer 13 can be reduced.

Furthermore, between the superconducting layer 12 and the protective layer 13, the superconducting layer 12 has a plurality of recesses 12G having inner wall surfaces 12I. The protective layer 13 is formed within these plurality of recesses 12G. The inner wall surfaces 12I are parallel to the c-axis. This results in a structure where the inner wall surfaces 12I of the plurality of recesses 12G formed in the superconducting layer 12 are parallel to the c-axis. In this structure, current flows more easily from the superconducting layer 12 to the protective layer 13 along the a-axis or b-axis direction of the crystal CR constituting the oxide superconductor. As a result, the interfacial resistance between the superconducting layer 12 and the protective layer 13 can be reduced. By forming a plurality of recesses 12G in the superconducting layer 12, the surface area of the superconducting layer 12 is increased. Therefore, oxygen heat treatment of the superconducting layer 12 can be carried out efficiently.

Furthermore, a sloping portion 12K may be formed on the inner wall surface 12I. In this structure, current flows more easily from the superconducting layer 12 to the protective layer 13 along the a-axis or b-axis direction of the crystal CR constituting the oxide superconductor. As a result, the interfacial resistance between the superconducting layer 12 and the protective layer 13 can be reduced.

Furthermore, in a plan view of the superconducting layer 12, the number of recesses 12G per unit area formed in the superconducting layer 12 in the edge region 12ER is greater than the number of recesses 12G per unit area formed in the superconducting layer 12 in the central region 12C. Therefore, current flows more easily in the edge region 12ER compared to the central region 12C. Consequently, the interfacial resistance in the edge region 12ER can be reduced. Since the surface area of the superconducting layer 12 increases in the edge region 12ER, oxygen heat treatment of the superconducting layer 12 in the edge region 12ER can be carried out efficiently.

Furthermore, since the depth d of the recess 12G is smaller than the average thickness t of the superconducting layer 12, the recess 12G is formed in the superconducting layer 12 without penetrating it. This allows for the reduction of interfacial resistance between the superconducting layer 12 and the protective layer 13 while maintaining the conductivity of the superconducting layer 12.

Furthermore, in a plan view, the ratio of the total opening area of the multiple recesses 12G to the area of the superconducting layer 12 is between 0.30% and 0.60%. This reduces the interfacial resistance between the superconducting layer 12 and the protective layer 13.

(Modified version of the first embodiment)
In the first embodiment described above, with reference to Figure 7, a case was explained in which the number of recesses 12G per unit area formed in the superconducting layer 12 in the edge region 12ER is greater than the number of recesses 12G per unit area formed in the superconducting layer 12 in the central region 12C. The present invention is not limited to such a configuration.

As a variation of the variation of the first embodiment, the number of multiple recesses 12G formed in the superconducting layer 12 in the central region 12C per unit area may be greater than the number of multiple recesses 12G formed in the superconducting layer 12 in the edge region 12ER per unit area.
In this case, more current flows through the central region 12C compared to the edge region 12ER. Therefore, the interfacial resistance in the central region 12C can be further reduced. Since the surface area of the superconducting layer 12 increases in the central region 12C, oxygen heat treatment of the superconducting layer 12 in the central region 12C can be carried out efficiently.

(Second Embodiment)
(Connection structure)
A connection structure according to the second embodiment will be described with reference to Figure 8.
In Figure 8, the same reference numerals are used for components identical to those in the first embodiment, and their descriptions are omitted or simplified. Furthermore, the stabilizing layer 14 is not shown in Figure 8.
In the connection structure 20 according to this embodiment, the oxide superconducting wire 1 (first oxide superconducting wire) according to the first embodiment described above and the object to be connected are connected via solder 15.

In this embodiment, the object to be connected is an oxide superconducting wire 2 (second oxide superconducting wire) having the same configuration as oxide superconducting wire 1. That is, in this embodiment, the object to be connected has a structure in which two oxide superconducting wires are connected so that they overlap each other in the Z direction. Oxide superconducting wire 1 may be referred to as "one oxide superconducting wire," and oxide superconducting wire 2 may be referred to as "the other oxide superconducting wire." "One oxide superconducting wire" may also be referred to as the first oxide superconducting wire.

The oxide superconducting wire 2 comprises a base material 10, an intermediate layer 11 provided on the base material 10, a superconducting layer 12 provided on the intermediate layer 11, and a protective layer 13 provided on the superconducting layer 12, similar to the structure shown in Figure 1. Multiple recesses 12G are formed on the surface 12F of the superconducting layer 12 of the oxide superconducting wire 2.

As shown in Figure 8, the surface of the protective layer 13 of oxide superconducting wire 1 (the oxide superconducting wire located at the bottom in Figure 8) and the surface of the protective layer 13 of oxide superconducting wire 2 (the oxide superconducting wire located at the top in Figure 8) are facing each other.
In this state, the protective layer 13 located at the end of the oxide superconducting wire 1 and the protective layer 13 located at the end of the oxide superconducting wire 2 are electrically connected via solder 15. Furthermore, the formation regions 12H of the multiple recesses 12G formed in the superconducting layers 12 of each of the oxide superconducting wires 1 and 2 face the solder 15.

Although not shown in Figure 8, each end of the two oxide superconducting wires is connected to another oxide superconducting wire via solder. This connection structure also employs the same electrical connection structure using solder 15 shown in Figure 8. In other words, a long oxide superconducting wire (connection structure) is obtained in which multiple oxide superconducting wires are soldered together along the direction of extension of the oxide superconducting wire.

With a connection structure 20 having this configuration, the interfacial resistance between the superconducting layer 12 and the protective layer 13 can be reduced by using oxide superconducting wires 1 and 2. Therefore, the connection resistance with the oxide superconducting wires 1 and 2 can be reduced. Consequently, long oxide superconducting wires with reduced connection resistance can be manufactured.

As described above, the multiple recesses 12G contribute to reducing the interfacial resistance between the superconducting layer 12 and the protective layer 13. Therefore, since the formation regions 12H of the multiple recesses 12G face the solder 15, the connection resistance of the connection structure 20 can be further reduced.

Note that in the structure shown in Figure 8, the stabilization layers 14 of the oxide superconducting wires 1 and 2 are omitted. However, the connection structure 20 according to the embodiment of the present invention is not limited to the structure shown in Figure 8. As shown in Figure 1, each of the oxide superconducting wires 1 and 2 may be provided with a stabilization layer 14. In this case, the stabilization layer 14 of oxide superconducting wire 1 and the stabilization layer 14 of oxide superconducting wire 2 are connected via solder 15. Even with this structure, it is possible to manufacture long oxide superconducting wires with reduced connection resistance.

Furthermore, in the structure shown in Figure 8, multiple recesses 12G are formed in the superconducting layer 12 of the oxide superconducting wire 2, but the recesses 12G do not necessarily have to be formed in the superconducting layer 12 of the oxide superconducting wire 2. In this structure, an oxide superconducting wire 1 having a superconducting layer 12 with multiple recesses 12G is connected to an oxide superconducting wire 2 having a superconducting layer 12 without multiple recesses 12G. Even in this case, the effect of reducing the connection resistance of the connection structure 20 can be obtained.

(Third Embodiment)
(Connection structure)
A connection structure according to the third embodiment will be described with reference to Figure 9.
In Figure 9, the same reference numerals are used for components identical to those in the first embodiment, and their descriptions are omitted or simplified. Furthermore, the stabilizing layer 14 is not shown in Figure 9.
In the connection structure 30 according to this embodiment, the oxide superconducting wire 1 (first oxide superconducting wire) according to the first embodiment described above and the object to be connected are connected via solder 15.

In this embodiment, the object to be connected is the electrode 25. In the example shown in Figure 9, only the electrode 25 is shown as the object to be connected, but the electrode 25 may be provided on a substrate.
In other words, in this embodiment, the object to be connected has a structure in which the oxide superconducting wire 1 and the electrode 25 are connected so that they overlap each other in the Z direction.

As shown in Figure 9, the surface of the protective layer 13 of the oxide superconducting wire 1 (located at the bottom in Figure 9) and the surface of the electrode 25 (located at the top in Figure 9) are facing each other.
In this state, the protective layer 13 located at the end of the oxide superconducting wire 1 and the electrode 25 are electrically connected via the solder 15. Furthermore, the formation regions 12H of the multiple recesses 12G formed in the superconducting layer 12 of the oxide superconducting wire 1 face the solder 15.

With this configuration, the connection structure 30 uses an oxide superconducting wire 1 that can reduce the interfacial resistance between the superconducting layer 12 and the protective layer 13. Therefore, the connection resistance between the oxide superconducting wire 1 and the electrode 25 can be reduced. Consequently, a connection structure with reduced connection resistance can be manufactured.

As described above, the multiple recesses 12G contribute to reducing the interfacial resistance between the superconducting layer 12 and the protective layer 13. Therefore, since the formation regions 12H of the multiple recesses 12G face the solder 15, the connection resistance of the connection structure 20 can be further reduced.

Although the stabilization layer 14 of the oxide superconducting wire 1 is omitted in the structure shown in Figure 9, the connection structure 30 according to the embodiment of the present invention is not limited to the structure shown in Figure 9. As shown in Figure 1, the oxide superconducting wire 1 may also be provided with a stabilization layer 14. In this case, the stabilization layer 14 of the oxide superconducting wire 1 and the stabilization layer 14 of the electrode 25 are connected via solder 15.
Even with this structure, it is possible to manufacture a connection structure with reduced connection resistance.

Furthermore, each of the connection structures 20 shown in Figure 8 and 30 shown in Figure 9 has a structure in which the oxide superconducting wire and the object to be connected are connected via solder 15.

The above describes preferred embodiments of the present invention, and it should be understood that these are illustrative examples of the invention and should not be considered limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the invention. Therefore, the invention should not be considered limited by the foregoing description, but rather limited by the claims.

In the embodiments described above, a structure in which an intermediate layer 11 is arranged between the substrate 10 and the superconducting layer 12 (first embodiment) was described.
In the present invention, it is sufficient for the superconducting layer to be provided above the substrate, the superconducting layer may be provided on the substrate, or the superconducting layer may be in direct contact with the substrate.

Next, the present invention will be specifically described with reference to examples.

(1) Measurement results of interfacial resistance between the superconducting layer 12 and the protective layer 13 Table 1 shows the results of measuring the interfacial resistance between the superconducting layer 12 and the protective layer 13 when the depth of the recess 12G and the area ratio of the recess 12G are changed.

The measurement method for the interfacial resistance (interfacial resistance of the superconducting layer/Ag protective layer) shown in Table 1 will be explained below.
First, as shown in Figure 8, a connecting structure is prepared in which two oxide superconducting wires 1 and 2 are joined together. Each of the two oxide superconducting wires 1 and 2 has the same layer configuration (same specifications). Each of the two oxide superconducting wires 1 and 2 has a layer configuration in which an intermediate layer 11, a superconducting layer 12 with recesses 12G formed thereon, and a protective layer 13 are sequentially laminated on a base material 10. The protective layers 13 of the two oxide superconducting wires 1 and 2 are connected via solder 15.

Next, with the connection structure in a superconducting state, the resistance between the protective layer 13 of oxide superconducting wire 1 and the protective layer 13 of oxide superconducting wire 2 is measured. The resistance at this time is the sum of the interfacial resistance R1 at the interface between the superconducting layer 12 and the protective layer 13 in oxide superconducting wire 1, and the interfacial resistance R2 at the interface between the superconducting layer 12 and the protective layer 13 in oxide superconducting wire 2. Note that interfacial resistances R1 and R2 are the same value.

Therefore, the interfacial resistance between the superconducting layer 12 and the protective layer 13 in a single oxide superconducting wire is half the resistance value measured as described above. Although resistance also exists between the protective layer 13 and the solder 15, this resistance is very small compared to the interfacial resistances R1 and R2 described above. Therefore, the resistance between the protective layer 13 and the solder 15 can be ignored.

In Table 1, the comparative example shows an oxide superconducting wire in which no recesses 12G are formed in the superconducting layer 12. Examples 1 and 2 show oxide superconducting wires in which multiple recesses 12G are formed in the superconducting layer 12.
In each of Examples 1 and 2, a laser beam was irradiated onto the surface 12F of the superconducting layer 12 to partially etch the surface 12F and form a plurality of recesses 12G (see Figure 3). The size of each of the plurality of recesses 12G was set to a depth of 0.5 μm and a diameter of 50 μm. The average thickness of the superconducting layer 12 was 2.1 μm.

In contrast, Example 3, shown in Table 1, differs from Example 1 in that the depth of the recess 12G is 1.0 μm. In Example 3, the distance between two adjacent recesses 12G is 0.16 mm, so the area ratio of the recesses 12G in Example 3 is the same as in Example 1.

As is clear from the results of the interfacial resistance (interfacial resistance between the superconducting layer 12 and the protective layer 13) shown in Table 1, the interfacial resistance value for the comparative example was 30 (× ^10⁻⁹ Ω/ ^cm² ), the interfacial resistance value for Example 1 was 27 (× ^10⁻⁹ Ω/ ^cm² ), the interfacial resistance value for Example 2 was 25 (× ^10⁻⁹ Ω/ ^cm² ), and the interfacial resistance value for Example 3 was 24 (× ^10⁻⁹ Ω/ ^cm² ).

The results shown in Table 1 clearly show that the interfacial resistance of Examples 1 to 3, in which multiple recesses 12G are formed in the superconducting layer 12, is lower than that of the Comparative Example, in which multiple recesses 12G are not formed in the superconducting layer 12.
Comparing Examples 1 and 2, it became clear that increasing the area ratio of the recess 12G lowers the interfacial resistance.
Comparing Examples 1 and 3, it became clear that increasing the depth of the recess 12G lowers the interfacial resistance.

(2) Measurement results of oxygen heat treatment time Figure 10 shows the results of investigating the relationship between heat treatment time and critical current value for the oxide superconducting wires of the comparative example, Example 1, and Example 2 described above.
The results in Figure 10 were obtained under the following conditions.

(Heat treatment condition 1)
The atmosphere inside the heat treatment furnace was set to an oxygen atmosphere. Oxide superconducting wires were placed inside the heat treatment furnace. The temperature inside the heat treatment furnace was set to 200°C or higher and maintained for 4 to 12 hours. After the heat treatment was completed and the temperature inside the heat treatment furnace had fallen below 50°C, the oxide superconducting wires were removed from the heat treatment furnace.

(Heat treatment conditions 2)
The atmosphere inside the heat treatment furnace was set to an oxygen atmosphere. The oxide superconducting wire was placed inside the heat treatment furnace. The temperature inside the heat treatment furnace was set to 500°C or higher and maintained for 12 hours. After the heat treatment was completed and the temperature inside the heat treatment furnace had fallen below 50°C, the oxide superconducting wire was removed from the heat treatment furnace. Heat treatment condition 2 is a heat treatment condition for ensuring sufficient oxygen heat treatment.

(Measurement of critical current (I _c ))
The oxide superconducting wires of Comparative Example, Example 1, and Example 2 were heat-treated according to heat treatment condition 1, and then the critical current ( _Ic ) of each of the oxide superconducting wires of Comparative Example, Example 1, and Example 2 was measured.

(Measurement of reference critical current (I _c0 ))
The oxide superconducting wires of the Comparative Example, Example 1, and Example 2 were heat-treated under heat treatment condition 2, and then the reference critical current (I _c0 ) of each of the oxide superconducting wires of the Comparative Example, Example 1, and Example 2 was measured.

(Normalization of critical current)
The critical current ( _Ic ) of each oxide superconducting wire in Comparative Example, Example 1, and Example 2 was normalized by _I0 . That is, the value of _Ic / _Ic0 was determined. The point at which the value of _Ic / _Ic0 was 0.97 or higher was defined as the minimum oxygen heat treatment time.

As is clear from Figure 10, the minimum oxygen heat treatment time in the comparative example was 10 hours. The minimum oxygen heat treatment time in Example 1 was 9 hours. The minimum oxygen heat treatment time in Example 2 was 8 hours.
In other words, it was found that in the oxide superconducting wires of Examples 1 and 2, in which recesses 12G are formed in the superconducting layer 12, the minimum oxygen heat treatment time can be shortened compared to the oxide superconducting wire of the comparative example, in which recesses 12G are not formed in the superconducting layer 12.
Furthermore, in Example 2, where the ratio of the opening areas of the multiple recesses 12G is 0.6%, it was found that the minimum oxygen heat treatment time could be shortened compared to Example 1, where the ratio of the opening areas of the multiple recesses 12G is 0.3%.

1…Oxide superconducting wire (first oxide superconducting wire), 2…Oxide superconducting wire (second oxide superconducting wire), 10…Substrate, 11…Intermediate layer, 12…Superconducting layer, 12B…Bottom surface, 12C…Central region, 12E…End, 12ER…End region, 12F…Surface, 12G…Recess, 12H…Formation region, 12I…Inner wall surface, 12K…Inclined portion, 13…Protective layer, 14…Stabilizing layer, 15…Solder, 20…Connecting structure, 25…Electrode, 30…Connecting structure, BF…Interface, CF…Crystal plane, CR…Crystal

Claims (7)

Substrate and
A superconducting layer, made of an oxide superconductor, is provided above the aforementioned substrate,
A protective layer provided on the superconducting layer and in contact with the superconducting layer,
Equipped with,
Between the superconducting layer and the protective layer, the superconducting layer has a plurality of recesses having inner wall surfaces.
The protective layer is formed in the plurality of recesses,
The inner wall surface is parallel to the c-axis direction.
Oxide superconducting wire. Substrate and
A superconducting layer, made of an oxide superconductor, is provided above the aforementioned substrate,
A protective layer provided on the superconducting layer and in contact with the superconducting layer,
Equipped with,
Between the superconducting layer and the protective layer, the superconducting layer has a plurality of recesses having inner wall surfaces.
The protective layer is formed in the plurality of recesses,
The inner wall surface is inclined with respect to the c-axis direction .
Oxide superconducting wire. In the width direction of the oxide superconducting wire, which is perpendicular to the extending direction in which the oxide superconducting wire extends and the thickness direction of the oxide superconducting wire, the superconducting layer has two end regions including the ends of the superconducting layer and a central region between the two end regions.
The number of the plurality of recesses formed in the superconducting layer per unit area in the end region is greater than the number of the plurality of recesses formed in the superconducting layer per unit area in the central region.
The oxide superconducting wire according to claim 1 or claim 2 . In the width direction of the oxide superconducting wire, which is perpendicular to the extending direction of the oxide superconducting wire and the thickness direction of the oxide superconducting wire, the superconducting layer has two end regions including the ends of the superconducting layer and a central region between the two end regions.
The number of the plurality of recesses formed in the superconducting layer per unit area in the central region is greater than the number of the plurality of recesses formed in the superconducting layer per unit area in the edge region.
The oxide superconducting wire according to claim 1 or claim 2 . The depth of the recess is smaller than the average thickness of the superconducting layer.
The oxide superconducting wire according to claim 1 or claim 2 . In a plan view, the ratio of the total opening area of the multiple recesses to the area of the superconducting layer is 0.30% or more and 0.60% or less.
The oxide superconducting wire according to claim 1 or claim 2 . The oxide superconducting wire material according to claim 1 or claim 2 ,
The object to which the oxide superconducting wire is connected ,
A connection structure having the following properties.