Oxide superconducting laminate, oxide superconducting wire and connection structure

Abstract

To provide an oxide superconducting laminated body, an oxide superconducting wire material, and a connection structure which can lower connection resistance in a connection part.SOLUTION: An oxide superconducting laminated body 5 includes a substrate 1, a superconducting layer 3 formed of an oxide superconducting body, and a protective layer 4 provided so as to come in contact with the superconducting layer 3 on the superconducting layer 3. A gap is formed inside the protective layer 4. The number of gaps coming in contact with an interface with the superconducting layer 3 out of the gaps formed in the protective layer 4 is less than 12 per 1 μm of the length of the interface, in a cross section in the thickness direction of the protective layer 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an oxide superconducting laminate, an oxide superconducting wire, and a connection structure. [Background technology]

[0002] Patent Document 1 discloses an oxide superconducting wire having a structure in which an intermediate layer, a superconducting layer, and a protective layer are laminated in this order on a substrate. The oxide superconducting wire can be used by connecting it to an object to be connected (another superconducting wire, an electrode, etc.) by soldering or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-89954 Summary of the Invention [Problem to be solved by the invention]

[0004] Oxide superconducting wires may have high connection resistance at the connection points with objects to be connected.

[0005] An object of one aspect of the present invention is to provide an oxide superconducting laminate, an oxide superconducting wire, and a connection structure that can reduce the connection resistance at the connection. [Means for solving the problem]

[0006] One aspect of the present invention provides an oxide superconductor laminate comprising a substrate, a superconducting layer formed on the substrate and made of an oxide superconductor, and a protective layer formed on the superconducting layer in contact with the superconducting layer, wherein voids are formed inside the protective layer, and the number of voids formed in the protective layer that contact the interface with the superconducting layer is less than 12 per 1 μm length of the interface in a cross section along the thickness direction of the protective layer.

[0007] The number of voids in contact with the interface is preferably 0 per 1 μm of the length of the interface.

[0008] The number of voids in contact with the interface is preferably 3 or more per 1 μm of the length of the interface.

[0009] The size of the void in contact with the interface in the length direction of the interface is preferably 11.0 nm to 70.2 nm.

[0010] It is preferable that a mixed region in which a partial region of the protective layer and a partial region of the superconducting layer are mixed is formed between the superconducting layer and the protective layer.

[0011] In a cross-sectional view of the mixed region, the ratio (Li / L) of the interface length (Li) between the superconducting layer and the protective layer to the width or longitudinal length (L) of the oxide superconducting wire is preferably in the range of 0.03 to 1.56.

[0012] It is preferable that at least a part of the interface between the superconducting layer and the protective layer in the mixed region intersects with a direction along the ab plane of the crystal of the oxide superconductor of the superconducting layer.

[0013] One aspect of the present invention provides an oxide superconducting wire in which a stabilizing layer is formed on the outer periphery of the oxide superconducting laminate.

[0014] One aspect of the present invention provides a connection structure having the oxide superconducting wire. [Effects of the Invention]

[0015] According to one aspect of the present invention, it is possible to provide an oxide superconducting laminate, an oxide superconducting wire, and a connection structure that can reduce the connection resistance at the connection portion. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view of an oxide superconducting wire according to an embodiment. [Figure 2] 2 is a schematic diagram showing a part of a cross section of an oxide superconducting layer and a protective layer. FIG. [Figure 3] FIG. 2 is a diagram showing a part of a cross section of an oxide superconducting layer and a protective layer. [Figure 4] 1 is a cross-sectional view showing a connection structure using an oxide superconducting wire according to an embodiment. [Figure 5] (A) is an image of a cross section of an oxide superconducting layer and a protective layer of a comparative example. (B) is an enlarged image of (A). DETAILED DESCRIPTION OF THE INVENTION

[0017] The oxide superconducting laminate and the oxide superconducting wire according to the embodiments of the present invention will be described in detail below with reference to the drawings. The drawings used in the description may show enlarged essential parts for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality.

[0018] [Oxide superconducting laminates and oxide superconducting wires] An oxide superconducting laminate and an oxide superconducting wire according to an embodiment will be described with reference to FIG. Fig. 1 is a cross-sectional view showing an oxide superconducting laminate 5 and an oxide superconducting wire 10 according to an embodiment. Fig. 1 is a view showing a cross section perpendicular to the longitudinal direction of the oxide superconducting laminate 5 and the oxide superconducting wire 10.

[0019] The oxide superconducting wire 10 includes an oxide superconducting laminate 5 and a stabilization layer 6 . The oxide superconductor laminate 5 includes a metal substrate 1, an intermediate layer 2, an oxide superconductor layer 3, and a protective layer 4. The oxide superconductor laminate 5 has a structure in which the oxide superconductor layer 3 and the protective layer 4 are formed on the metal substrate 1 via the intermediate layer 2. That is, the oxide superconductor laminate 5 has a configuration in which the intermediate layer 2, the oxide superconductor layer 3, and the protective layer 4 are laminated in this order on one surface of the metal substrate 1. The oxide superconductor laminate 5 is an example of a "laminate."

[0020] The oxide superconductor laminate 5 is formed in a tape shape. The Y direction is the thickness direction of the oxide superconductor laminate 5, and is the direction in which the metal substrate 1, intermediate layer 2, oxide superconductor layer 3, and protective layer 4 are stacked. The X direction is the width direction of the oxide superconductor laminate 5, and is the direction perpendicular to the length direction and thickness direction of the oxide superconductor laminate 5.

[0021] The metal substrate 1 is made of a metal. Specific examples of metals constituting the metal substrate 1 include nickel alloys such as Hastelloy (registered trademark); stainless steel; and oriented Ni-W alloys in which a texture has been introduced into a nickel alloy. The thickness of the metal substrate 1 may be adjusted appropriately depending on the purpose, and is, for example, in the range of 10 to 500 μm. One surface of the metal substrate 1 (the surface on which the intermediate layer 2 is formed) is referred to as the first main surface 1a, and the surface opposite to the first main surface 1a is referred to as the second main surface 1b. The metal substrate 1 is an example of a "substrate." The first main surface 1a is an example of a "main surface."

[0022] The intermediate layer 2 is provided between the metal substrate 1 and the oxide superconducting layer 3. The intermediate layer 2 is formed on the first main surface 1a of the metal substrate 1. The intermediate layer 2 may have a multi-layer structure, and may have, for example, a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, etc., in this order from the metal substrate 1 side to the oxide superconducting layer 3 side. These layers are not necessarily provided one by one, and some layers may be omitted, or two or more layers of the same type may be repeatedly stacked. Note that the intermediate layer 2 is not an essential component of the oxide superconducting wire 10, and if the metal substrate 1 itself has orientation, the intermediate layer 2 may not be formed.

[0023] The diffusion prevention layer has the function of preventing some of the components of the metal substrate 1 from diffusing and mixing as impurities into the oxide superconducting layer 3. The diffusion prevention layer is made of, for example, Si3N4, Al2O3, GZO (Gd2Zr2O7), etc. The thickness of the diffusion prevention layer is, for example, 10 to 400 nm.

[0024] A bed layer may be formed on the diffusion prevention layer to reduce the reaction at the interface between the metal substrate 1 and the oxide superconducting layer 3 and improve the orientation of the layer formed thereon. Examples of materials for the bed layer include Y2O3, Er2O3, CeO2, Dy2O3, Eu2O3, Ho2O3, and La2O3. The thickness of the bed layer is, for example, 10 to 100 nm.

[0025] The alignment layer is formed from a biaxially oriented material to control the crystal orientation of the cap layer thereon. Examples of materials for the alignment layer include metal oxides such as GdZrO, MgO, ZrO-YO (YSZ), SrTiO, CeO, YO, AlO, GdO, ZrO, HoO, and NdO. The alignment layer is preferably formed by IBAD (Ion-Beam-Assisted Deposition).

[0026] The cap layer is formed on the surface of the orientation layer and is made of a material that allows crystal grains to self-align in the in-plane direction. Examples of materials for the cap layer include CeO2, Y2O3, Al2O3, Gd2O3, ZrO2, YSZ, Ho2O3, Nd2O3, and LaMnO3. The thickness of the cap layer is typically in the range of 50 to 5,000 nm.

[0027] The oxide superconducting layer 3 is made of an oxide superconductor. The oxide superconductor is not particularly limited, but for example, the oxide superconductor may be a material represented by the general formula REBa2Cu3O X Examples of the rare earth element RE include RE-Ba-Cu-O-based oxide superconductors (REBCO-based oxide superconductors) represented by (RE123). Examples of the rare earth element RE include one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among these, one of Y, Gd, Eu, and Sm, or a combination of two or more of these elements, is preferred. Generally, X is 7-x (oxygen deficiency amount x: approximately 0 to 1). The oxide superconducting layer 3 has a thickness of, for example, approximately 0.5 to 5 μm. This thickness is preferably uniform in the longitudinal direction. The oxide superconducting layer 3 is formed on the main surface 2 a of the intermediate layer 2 (the surface opposite to the metal substrate 1). The oxide superconducting layer 3 is an example of a “superconducting layer.” The oxide superconducting layer 3 is provided on the first main surface 1a of the metal substrate 1 with the intermediate layer 2 interposed therebetween.

[0028] The protective layer 4 has functions such as bypassing an overcurrent that occurs in the event of an accident and suppressing a chemical reaction that occurs between the oxide superconducting layer 3 and a layer provided on the protective layer 4. Examples of materials for the protective layer 4 include silver (Ag), copper (Cu), gold (Au), an alloy of gold and silver, other silver alloys, copper alloys, and gold alloys. The protective layer 4 covers at least the main surface 3a of the oxide superconducting layer 3 (the surface opposite to the intermediate layer 2 side). The protective layer 4 is in contact with the main surface 3a of the oxide superconducting layer 3. There are no particular limitations on the thickness of the protective layer 4, but it may be, for example, about 1 to 100 μm.

[0029] Reference numeral 5a denotes a first main surface (main surface 4a of protective layer 4) of the oxide superconducting laminate 5. The first main surface 5a is the surface of the oxide superconducting laminate 5 on which the oxide superconducting layer 3 is formed. Reference numeral 5b denotes a side surface of the oxide superconducting laminate 5 (the side surface of the metal substrate 1, the side surface of the intermediate layer 2, the side surface of the oxide superconducting layer 3, and the side surface of the protective layer 4). Reference numeral 5c denotes a second main surface of the oxide superconducting laminate 5 (second main surface 1b of the metal substrate 1), which is the surface opposite to the first main surface 5a. The second main surface 5c is the surface of the oxide superconducting laminate 5 on which the metal substrate 1 is formed.

[0030] The stabilization layer 6 covers the first main surface 5a, the side surfaces 5b, 5b, and the second main surface 5c of the oxide superconducting laminate 5. The stabilization layer 6 is formed to surround the outer periphery of the oxide superconducting laminate 5. The stabilization layer 6 functions as a bypass section that diverts an overcurrent that is generated when the oxide superconducting layer 3 transitions to a normal conducting state.

[0031] Examples of materials that can be used to form the stabilization layer 6 include metals such as copper, copper alloys (e.g., Cu-Zn alloys, Cu-Ni alloys, etc.), aluminum, aluminum alloys, and silver. The thickness of the stabilization layer 6 is, for example, about 10 to 300 μm. The stabilization layer 6 can be formed by plating (e.g., electrolytic plating).

[0032] FIG. 2 is a schematic diagram showing a portion of a cross section of the oxide superconducting layer 3 and protective layer 4 of the oxide superconducting laminate 5. FIG. 2 shows a cross section along the thickness direction of the protective layer 4 (a cross section perpendicular to the longitudinal direction of the oxide superconducting wire 10). As shown in FIG. 2, "7" denotes the interface between the oxide superconducting layer 3 and the protective layer 4. As shown in the schematic diagram of FIG. 2, the interface 7 between the oxide superconducting layer 3 and the protective layer 4 can be observed using a transmission electron microscope (TEM). When observing the cross section of the oxide superconducting wire 10 with a TEM, the observation can be performed at any magnification. For example, the cross section of the oxide superconducting layer 3 and the protective layer 4 shown in FIG. 2 has a width of 1 μm in the depicted area, and the total length of the linear interface 7 is also 1 μm.

[0033] One or more voids are formed inside the protective layer 4. The voids may or may not be in contact with the interface 7. Gas such as air, oxygen, or an organic compound gas may be present in the voids.

[0034] If there are voids in contact with the interface 7 inside the protective layer 4, the number of such voids is less than 12 per 1 μm of the length of the interface 7. This prevents a decrease in the contact area between the oxide superconducting layer 3 and the protective layer 4. This reduces the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4. If there are voids in contact with the interface 7, the oxide superconducting layer 3 and the protective layer 4 are not in electrical contact at the voids. Therefore, the fewer the number of voids in contact with the interface 7, the lower the interfacial resistance. The number of voids in contact with the interface 7 is preferably zero, or 3 to less than 12, per 1 μm of the length of the interface 7. If the number of voids in contact with the interface 7 is zero, or 3 to less than 12, per 1 μm of the length of the interface 7, the lower the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4. If there are no voids in contact with the interface 7, the entire length of the interface 7 contacts the oxide superconducting layer 3 in FIG. 2 .

[0035] 2, the protective layer 4 has either the following form (i) or (ii): (i) There are zero voids in contact with the interface 7 (i.e., the entire length of the interface 7 is in contact with the oxide superconducting layer 3); or (ii) There are more than zero and fewer than 12 voids in contact with the interface 7 per 1 μm of the length of the interface 7.

[0036] The number of voids in contact with interface 7 may be the average number of voids in multiple observation images (e.g., TEM images with a field of view of several μm square) of a cross section that includes the interface between oxide superconducting layer 3 and protective layer 4. The number of voids in contact with interface 7 may be the average number of voids in three or more observation images. The number of voids in contact with interface 7 may be the average number per μm of length of interface 7, for example, for an interface 7 with a length of 3 μm or more.

[0037] 2, voids V1 to V8 formed inside protective layer 4 are in contact with interface 7. Therefore, the number of voids in contact with interface 7 is 8 per 1 μm of length of interface 7. Note that voids V9 to V16 are not in contact with interface 7, and therefore are not included in the "number of voids in contact with interface 7."

[0038] The size of the voids in contact with interface 7 (the dimension in the longitudinal direction of interface 7) is not particularly limited. The size of the voids that can affect the interface resistance between oxide superconducting layer 3 and protective layer 4 is, for example, 0.1 nm or more. The size of the voids is, for example, 100 nm or less. The size of the voids can be exemplified as 11.0 nm to 70.2 nm. The longitudinal direction of interface 7 is the direction perpendicular to the thickness direction of protective layer 4 (the left-right direction in FIG. 2 ).

[0039] 2, the shapes of the voids V1 to V8 are semicircular, but the shape of the voids in contact with the interface 7 is not particularly limited. The shape of the voids in the cross section of the protective layer 4 may be arched, circular, elliptical, etc. The three-dimensional shape of the voids is, for example, hemispherical.

[0040] Fig. 3 is a diagram showing a part of a cross section of the oxide superconducting layer 3 and the protective layer 4 of the oxide superconducting laminate 5. In Fig. 3, the dashed line shown in the diagram indicates the interface 7 between the oxide superconducting layer 3 and the protective layer 4. In Fig. 3, the length of the dashed line shown in the diagram is the length of the interface 7. 3, a mixed region 8 may be formed between the oxide superconducting layer 3 and the protective layer 4. The mixed region 8 is a region where a partial region 3A of the oxide superconducting layer 3 and a partial region 4A of the protective layer 4 are mixed.

[0041] The partial region 3A may be a convex portion protruding from the oxide superconducting layer 3 into the protective layer 4, or may be an independent island. The partial region 4A may be a convex portion protruding from the protective layer 4 into the oxide superconducting layer 3, or may be an independent island.

[0042] As shown in FIG. 3, when the mixed region 8 is formed, the interface 7 between the oxide superconducting layer 3 and the protective layer 4 is not flat. The interface 7 is formed by layers 3 and 4 intertwining vertically. The length of the interface 7 (the length of the dashed line) shown in FIG. 3 is approximately 5.6 μm, calculated from the scale bar in the figure. The length of the interface 7 is longer than the width of the image in FIG. 3 (approximately 3.6 μm). Therefore, when the mixed region 8 is formed, the contact area between the oxide superconducting layer 3 and the protective layer 4 is larger than in the case of a flat interface without the mixed region 8. Therefore, the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4 is lower. It can be said that the contact area between the oxide superconducting layer 3 and the protective layer 4 is correlated with the length of the interface 7 obtained by cross-sectional observation of the oxide superconducting layer 3 and the protective layer 4. For example, when observing the cross section of the oxide superconducting layer 3 and the protective layer 4, the contact area is larger in the case where the interface 7 is linear than in the case where the interface 7 is observed to be curved in the thickness direction of the layers 3 and 4.

[0043] Furthermore, since the crystals that make up the oxide superconductor have electrical anisotropy, the following can be assumed as the reason why the interface resistance is lowered when the mixed region 8 is formed. The oxide superconductor contained in the oxide superconducting layer 3 is crystalline. The a-axis and b-axis of the crystal are aligned along the plane of the oxide superconducting layer 3. The c-axis of the crystal is aligned perpendicular to the plane of the oxide superconducting layer 3. The plane formed by the a-axis and b-axis (ab-plane) coincides with the plane of the oxide superconducting layer 3 (the left-right direction in Figure 3). Oxide superconductors have the property that electricity flows easily along the ab-plane and does not flow easily along the c-axis. Therefore, if the interface 7 between the oxide superconducting layer 3 and the protective layer 4 is perpendicular to the ab-plane, the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4 is thought to be low. If the interface 7 between the oxide superconducting layer 3 and the protective layer 4 is parallel to the ab-plane, the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4 is thought to be high. In the mixed region 8, the oxide superconducting layer 3 and the protective layer 4 are intertwined with each other, so that at least a part of the interface 7 between the oxide superconducting layer 3 and the protective layer 4 in the mixed region 8 intersects with the direction along the ab plane of the crystal of the oxide superconductor in the oxide superconducting layer 3. Therefore, the interfacial resistance can be reduced at this interface. At least a part of the interface 7 between the oxide superconducting layer 3 and the protective layer 4 in the mixed region 8 may be perpendicular to the direction along the ab plane of the crystal of the oxide superconductor.

[0044] The interface between the oxide superconducting layer 3 and the protective layer 4 in the mixed region 8 is, for example, at least one of the interface between the partial region 3A and the protective layer 4, the interface between the partial region 4A and the oxide superconducting layer 3, and the interface between the partial region 3A and the partial region 4A.

[0045] [Method for producing oxide superconducting laminate and oxide superconducting wire] Next, a description will be given of an example of a method for manufacturing the oxide superconducting laminate and the oxide superconducting wire 10. Note that the manufacturing method described below is just an example, and other manufacturing methods may also be adopted.

[0046] As shown in Fig. 1, an intermediate layer 2 is formed on a metal substrate 1. The intermediate layer 2 can be formed by using, for example, the known IBAD method.

[0047] Next, the oxide superconducting layer 3 is formed on the intermediate layer 2. The oxide superconducting layer 3 can be formed by a vapor deposition method such as a PLD method or an MOCVD method. For example, the oxide superconducting layer 3 can be formed by a first step and a second step. In the first step, for example, film formation is performed by PLD using a target made of a REBCO-based material. In the second step, for example, film formation is performed by PLD using a target made of a REBCO-based material and Ag. The second step is a step of performing deposition using a target containing an oxide superconductor and the material of the protective layer 4. The target used in the second step has an Ag content of 10 to 50 vol%.

[0048] The deposition rate of the material in the PLD method can be appropriately set by adjusting, for example, the pulse frequency of the laser in the PLD device, the atmospheric pressure during film formation, and the like. By changing the deposition rate in the PLD method in the second step, it is possible to adjust the number of voids contained in protective layer 4 or in the interface between superconducting layer 3 and protective layer 4. For example, if the deposition rate is increased, the number of voids contained in protective layer 4 or in the interface between superconducting layer 3 and protective layer 4 tends to decrease. Conversely, if the deposition rate is decreased, the number of voids contained in protective layer 4 or in the interface between superconducting layer 3 and protective layer 4 tends to increase. The size of the voids is roughly the same regardless of the deposition rate.

[0049] Next, a protective layer 4 is formed on the oxide superconducting layer 3. The protective layer 4 can be formed by a sputtering method or the like. This results in an oxide superconducting laminate 5. By forming this protective layer 4, the mixed region 8 described above is formed.

[0050] Next, oxygen annealing is performed. Specifically, the oxide superconducting laminate 5 is heated in an oxygen atmosphere (in the presence of an oxygen-containing gas) to, for example, 300 to 1000°C. The oxygen-containing gas is, for example, oxygen gas or air. This oxygen annealing may be performed after the protective layer 4 is formed, or may be performed before the protective layer 4 is formed (after the oxide superconducting layer 3 is formed). By the above steps, the oxide superconducting laminate 5 shown in FIG. 1 is obtained.

[0051] Next, after obtaining the oxide superconductor laminate 5, a stabilization layer 6 is formed on the outer periphery of the oxide superconductor laminate 5. The stabilization layer 6 can be formed by plating or the like. Through the above steps, oxide superconducting wire 10 shown in FIG. 1 is obtained.

[0052] [Connection structure] FIG. 4 is a cross-sectional view showing a connection structure 20 using oxide superconducting wire 10. As shown in FIG. 4, connection structure 20 is configured by connecting two oxide superconducting wires 10. Stabilization layer 6 of one oxide superconducting wire 10 and stabilization layer 6 of the other oxide superconducting wire 10 are electrically connected via solder layer 9. The connection structure 20 makes it possible to manufacture a long oxide superconducting wire with reduced connection resistance.

[0053] 4 has a structure in which the stabilization layer 6 of one oxide superconducting wire 10 and the stabilization layer 6 of the other oxide superconducting wire 10 are connected via a solder layer 9, but the protective layer 4 of one oxide superconducting wire 10 and the protective layer 4 of the other oxide superconducting wire 10 may also be connected via a solder layer 9. Alternatively, the protective layer 4 of one oxide superconducting wire 10 and the stabilization layer 6 of the other oxide superconducting wire 10 may also be connected via a solder layer 9. It is also possible to partially remove the stabilization layer 6 of one oxide superconducting wire 10 to expose the protective layer 4, and then connect the protective layer 4 or the stabilization layer 6 of the other oxide superconducting wire 10 to the exposed protective layer 4 via a solder layer 9.

[0054] 4, two oxide superconducting wires 10 are connected to each other, but the connection structure may also have a structure including two oxide superconducting wires and an oxide superconducting wire that serves as an intermediate connector that connects them. Even when the configuration of this embodiment is adopted only for the intermediate connector, the connection resistance can be reduced.

[0055] The oxide superconducting wire 10 can be electrically connected to an object to be connected, such as an electrode, in addition to other superconducting wires. Even in this case, the connection resistance can be reduced at the connection portion between the oxide superconducting wire 10 and the object to be connected.

[0056] [Effects of the oxide superconducting laminate and oxide superconducting wire according to the embodiment] The oxide superconducting laminate 5 and the oxide superconducting wire 10 have a small number of voids in contact with the interface 7 in the protective layer 4, which allows for a large contact area between the oxide superconducting layer 3 and the protective layer 4. This reduces the interface resistance between the oxide superconducting layer 3 and the protective layer 4. Therefore, when the oxide superconducting laminate or the oxide superconducting wire 10 is connected to an object to be connected (another superconducting wire, an electrode, etc.), the electrical resistance at the connection can be reduced. In the oxide superconducting laminate and the oxide superconducting wire 10, the electrical resistance at the joints is low, which reduces Joule heat generated at the joints. The low interfacial resistance between the oxide superconducting layer 3 and the protective layer 4 makes it easier for a bypass current to flow from the oxide superconducting layer 3 to the protective layer 4 during a quench.

[0057] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments and various modifications are possible within the scope of the present invention. For example, the structure of the oxide superconducting laminate is not limited to the structure shown in Fig. 1. The oxide superconducting laminate may include layers other than the metal substrate, intermediate layer, oxide superconducting layer, and protective layer. [Example]

[0058] The present invention will be specifically described below with reference to examples. Example 1 A sample of oxide superconducting wire 10 shown in FIG. 1 was produced as follows. An intermediate layer 2 was formed on one surface (first main surface 1a) of a tape-shaped metal substrate 1 made of Hastelloy (registered trademark) by the IBAD method or the like.

[0059] An oxide superconducting layer 3 was formed on the intermediate layer 2 through a first step and a second step. In the first step, a REBCO-based material (EuBa2Cu3O y In the second step, a target made of REBCO-based material (EuBa2Cu3O y The film was formed by PLD using a target made of Ag and Si. In the second step, the film was formed at a deposition rate of 0.1 Å / sec.

[0060] A protective layer 4 made of Ag was formed by sputtering on the oxide superconducting layer 3. In this way, an oxide superconducting laminate 5 was obtained. The oxide superconducting laminate 5 was subjected to oxygen annealing treatment by heating it to 500° C. in an oxygen atmosphere. A stabilization layer 6 was formed by copper plating on the outer periphery of the oxide superconducting laminate 5. In this way, an oxide superconducting wire 10 was obtained.

[0061] A cross section of the protective layer 4 along the thickness direction was observed by TEM, and the presence or absence of voids in contact with the interface 7 was confirmed from the TEM image of the cross section. If voids were present, the number of voids per 1 μm length of the interface 7 and the size of the voids (the size in the longitudinal direction of the interface 7) were investigated. In Example 1, the number of voids per 1 μm length of the interface 7 was 7. The size of the voids was in the range of 11.0 nm to 70.2 nm. In order to quantitatively evaluate the size (size) of the contact area between the oxide superconducting layer 3 and the protective layer 4, the ratio of the interface length (L) between the oxide superconducting layer 3 and the protective layer 4 to the length (L) in the width direction or longitudinal direction of the oxide superconducting wire 10 was measured. i ) ratio (L i The larger the value of the ratio Li / L, the larger the contact area between the oxide superconducting layer 3 and the protective layer 4. i The measurement method was to import a TEM image of the cross section of the oxide superconducting wire 10 into the image processing software "ImageJ", and measure the length of the interface 7 shown in the TEM image using the drawing tool and length measurement tool of this image processing software. iThe value of Li / L can be a substitute index for knowing the size (dimension) of the contact area between the oxide superconducting layer 3 and the protective layer 4. In Example 1, the value of the ratio Li / L was 1.03.

[0062] Next, to evaluate the connection resistivity, two oxide superconductor laminates 5 were prepared, and the protective layers 4 of both were electrically connected via a solder layer 9. The connection resistivity was then determined at 77 K and 4 K. The results are shown in Table 1. The connection resistivity was determined by dividing the connection resistance obtained by measurement by the connection area. The connection resistance can be measured using a four-terminal resistance measurement method. Another method (attenuation method) involves constructing a closed circuit with a known inductance L and the desired circuit resistance R, and measuring the time change in the decaying current to determine the connection resistance. For the example and comparative example samples shown in Table 1, the connection resistivity at 77 K was measured using the four-terminal resistance measurement method. The connection resistivity at 4 K was measured using the attenuation method.

[0063] Example 2 Oxide superconducting wire 10 was produced in the same manner as in Example 1, except that in the second step of forming oxide superconducting layer 3, the deposition rate was set to 0.2 Å / sec. The number of voids per 1 μm of length at interface 7 was 3. The void size was 20.1 nm to 65.4 nm. The value of the ratio Li / L was 1.12. The results are shown in Table 1.

[0064] Example 3 Oxide superconducting wire 10 was produced in the same manner as in Example 1, except that in the second step of forming oxide superconducting layer 3, the deposition rate was set to 0.4 Å / sec. The number of voids in contact with interface 7 was zero. The value of the ratio Li / L was 1.56. The results are shown in Table 1.

[0065] (Comparative Example) Oxide superconducting wire 10 was produced in the same manner as in Example 1, except that oxide superconducting layer 3 was formed only in the first step. Cross-sectional TEM images are shown in Figures 6(A) and 6(B). Figure 6(B) is an enlarged image of Figure 6(A). As shown in Figure 6(B), numerous voids V were observed within the protective layer 4. The number of voids in contact with the interface 7 was 12 per 1 μm of the length of the interface 7. The ratio Li / L was 1.03. The results are shown in Table 1.

[0066] [Table 1]

[0067] As shown in Table 1, in Examples 1 to 3, no voids were observed in contact with the interface 7. In Examples 1 to 3, the connection resistivity at 77K and 4K was kept low. In contrast to this, in the comparative example, voids were observed in contact with the interface 7. In the comparative example, the connection resistivity at 77K and 4K was high. [Explanation of symbols]

[0068] 1...metal substrate (substrate), 3...oxide superconducting layer (superconducting layer), 3A...partial region, 4...protective layer, 4A...partial region, 5...oxide superconducting laminate, 7...interface, 8...mixed region, 10...oxide superconducting wire, 20...connection structure, V,V1~V16...void.

Claims

1. A substrate; a superconducting layer formed on the substrate and made of an oxide superconductor; a protective layer provided on the superconducting layer in contact with the superconducting layer, A void is formed inside the protective layer, the number of the voids formed in the protective layer that are in contact with the interface with the superconducting layer is less than 12 per 1 μm of length of the interface in a cross section along the thickness direction of the protective layer; Oxide superconducting laminate.

2. The number of the voids in contact with the interface is 0 per 1 μm of the length of the interface. The oxide superconducting laminate according to claim 1.

3. the number of the voids in contact with the interface is 3 or more per 1 μm of the length of the interface; The oxide superconducting laminate according to claim 1.

4. The size of the void in contact with the interface in the length direction of the interface is 11.0 nm to 70.2 nm. The oxide superconducting laminate according to claim 3 .

5. a mixed region in which a partial region of the protective layer and a partial region of the superconducting layer are mixed is formed between the superconducting layer and the protective layer; The oxide superconducting laminate according to any one of claims 1 to 4.

6. In a cross-sectional view of the mixed region, a ratio (Li / L) of the interface length (Li) between the superconducting layer and the protective layer to the length (L) of the oxide superconducting wire in the width direction or longitudinal direction is in the range of 1.03 to 1.

56. The oxide superconducting laminate according to claim 5 .

7. at least a part of the interface between the superconducting layer and the protective layer in the mixed region intersects with a direction along the a-b plane of the crystal of the oxide superconductor of the superconducting layer; 7. The oxide superconducting laminate according to claim 5 or 6.

8. A stabilization layer is formed on the outer periphery of the oxide superconducting laminate according to any one of claims 1 to 7. Oxide superconducting wire.

9. The oxide superconducting wire according to claim 8, Connection structure.

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