Superconducting wire and method for manufacturing the same

Abstract

This superconducting wire material comprises a superconducting layer containing REBa2Cu3Ox. RE is a rare earth element. The superconducting layer contains a halogen. The halogen concentration in the superconducting layer is less than 2000 mass ppm.

Description

[Technical Field]

[0001] The present disclosure relates to a superconducting wire and a method for manufacturing the same. This application claims priority to Japanese Patent Application No. 2023-040888, filed March 15, 2023. The entire contents of the Japanese patent application are incorporated herein by reference. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2015-106521 (Patent Document 1) describes a superconducting wire. The superconducting wire described in Patent Document 1 has a metal substrate, an intermediate layer disposed on the metal substrate, and an oxide superconducting film disposed on the intermediate layer. The constituent material of the oxide superconducting film is REBa2Cu3O x (RE is a rare earth element). The oxide superconducting film is REBa2Cu3O x The crystals are oriented in the c-axis direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-106521 Summary of the Invention

[0004] The superconducting wire of the present disclosure is REBa2Cu3O x The superconducting layer includes a halogen, and the concentration of the halogen in the superconducting layer is less than 2000 ppm by mass. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a cross-sectional view of a superconducting wire 100 . [Figure 2] FIG. 2 is a process diagram showing a method for manufacturing superconducting wire 100. [Figure 3] FIG. 3 is a cross-sectional view illustrating the preparation step S1. [Figure 4] FIG. 4 is a cross-sectional view illustrating the intermediate layer forming step S2. [Figure 5] FIG. 5 is a cross-sectional view illustrating the solution applying step S3. [Figure 6] FIG. 6 is a cross-sectional view illustrating the first baking step S4. [Figure 7] FIG. 7 is a cross-sectional view illustrating the second baking step S5. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] In the superconducting wire described in Patent Document 1, the oxide superconducting film is formed by the following method. First, a raw material solution is prepared. The raw material solution contains the constituent elements of the oxide superconducting film and chlorine. Second, the raw material solution is applied onto the intermediate layer. Third, a first firing is performed. This causes Ba2Cu3O4Cl4 to be precipitated on the surface of the intermediate layer. Fourth, a second firing is performed. This causes REBa2Cu3O x The crystals of Ba2Cu3O4Cl4 are generated on the intermediate layer and grow in a specific crystal orientation, forming an oxide superconducting film. x This assists in orienting the crystals.

[0007] In the superconducting wire described in Patent Document 1, the raw material solution contains chlorine, so the oxide superconductor conductive membrane Chlorine is contained in the oxide superconductor. conductive membrane The chlorine in REBa2Cu3O x The composition balance of the oxide superconductor is disrupted. conductive membrane This can cause a decrease in the volume of the

[0008] The present disclosure has been made in view of the above-described conventional techniques, and provides a superconducting wire having a reduced halogen concentration in a superconducting layer.

[0009] [Effects of this disclosure] According to the present disclosure, it is possible to provide a superconducting wire having a reduced halogen concentration in the superconducting layer.

[0010] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (1) The superconducting wire according to one embodiment is made of REBa2Cu3O x The superconducting wire according to (1) above has a superconducting layer containing REBa2Cu3O. RE is a rare earth element. The superconducting layer contains a halogen. The concentration of the halogen in the superconducting layer is less than 2000 ppm by mass. x This makes it possible to suppress the imbalance of the composition and the reduction in the volume of the superconducting layer.

[0012] (2) In the superconducting wire of (1) above, the concentration of halogen in the superconducting layer may be 2 ppm by mass or more.

[0013] (3) In the superconducting wire of (1) or (2) above, the halogen may be chlorine. (4) In the superconducting wire according to any one of (1) to (3), the superconducting layer may contain an alkali metal. The concentration of the alkali metal in the superconducting layer may be 1 ppb by mass or more.

[0014] (5) In the superconducting wire of (4) above, the alkali metal may be sodium. (6) The superconducting wire according to any one of (1) to (5) above may further include a substrate and an intermediate layer disposed on the substrate. The superconducting layer may have a first main surface and a second main surface opposite the first main surface. The superconducting layer may be disposed on the intermediate layer such that the first main surface faces the intermediate layer. The amount of Ba2Cu3O4X2 precipitated on the second main surface may be greater than the amount of Ba2Cu3O4X2 precipitated in the superconducting layer. X is a halogen.

[0015] (7) In one embodiment, a method for manufacturing a superconducting wire is provided for forming a superconducting wire by forming a superconducting wire on an intermediate layer disposed on a substrate. xThe method includes a step of forming a superconducting layer composed of: RE is a rare earth element; the step of forming the superconducting layer includes a step of applying a solution containing the constituent elements of the superconducting layer onto the intermediate layer; a step of heating the applied solution to form a precursor of the superconducting layer; and a step of heating the precursor to form the precursor into the superconducting layer. The solution contains a halogen. At least one of the solution, the precursor, and the atmosphere used for heating the precursor contains an alkali metal. According to the method for manufacturing a superconducting wire described above in (7), it is possible to reduce the concentration of halogen in the superconducting layer.

[0016] (8) In the method for producing a superconducting wire according to (7) above, the concentration of the alkali metal in the solution may be 1 ppb by mass or more.

[0017] (9) In the method for producing a superconducting wire according to (7) above, the partial pressure of the alkali metal in the atmosphere may be 1000 Pa or less.

[0018] (10) In any of the above methods for producing a superconducting wire (7) to (9), the halogen may be chlorine.

[0019] (11) In any of the above methods for producing a superconducting wire (7) to (10), the alkali metal may be sodium.

[0020] [Details of the embodiments of the present disclosure] Next, details of an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and redundant description will not be repeated. A superconducting wire according to the embodiment is referred to as a superconducting wire 100.

[0021] (Configuration of superconducting wire 100) The configuration of superconducting wire 100 will be described below with reference to FIG.

[0022] As shown in FIG. 1, the superconducting wire 100 has a substrate 10, an intermediate layer 20, and a superconducting layer 30. The superconducting wire 100 may further have a protective layer and a stabilizing layer. In this case, the protective layer is made of, for example, silver or a silver alloy, and the stabilizing layer is made of, for example, copper or a copper alloy. The protective layer is disposed on the superconducting layer 30. The stabilizing layer is disposed on the protective layer.

[0023] The substrate 10 has a main surface 10a and a main surface 10b. The main surface 10a and the main surface 10b are end surfaces in the thickness direction of the substrate 10. The main surface 10b is the surface opposite to the main surface 10a.

[0024] The substrate 10 is, for example, a clad material having a stainless steel tape member, a copper (Cu) layer disposed on the tape member, and a nickel (Ni) layer disposed on the copper layer. The crystal axis of the copper layer is oriented. The crystal axis of the nickel layer is also oriented along the crystal axis of the copper layer. The nickel layer forms the main surface 10a. The substrate 10 is not limited to the above-mentioned clad material and may be made of a material other than a clad material. The substrate 10 may be, for example, Hastelloy (registered trademark). The substrate 10 may be a tape member made of a biaxially oriented metal material or a tape member made of a non-oriented metal material.

[0025] The intermediate layer 20 has a main surface 20a and a main surface 20b. The main surface 20a and the main surface 20b are end surfaces in the thickness direction of the intermediate layer 20. The intermediate layer 20 is disposed on the substrate 10 so that the main surface 20a faces the main surface 10a (so that the main surface 20a faces the main surface 10a).

[0026] The intermediate layer 20 has, for example, an yttria (Y2O3) layer, an yttria-stabilized zirconia (YSZ) layer disposed on the yttria layer, and a cerium oxide (CeO2) layer disposed on the yttria-stabilized zirconia layer. The layer structure of the intermediate layer 20 is not limited to this. As described above, since the crystal axes of the nickel layer of the substrate 10 are oriented, the crystal axes of each layer of the intermediate layer 20 are also oriented. The intermediate layer 20 may have a two-layer structure or a single-layer structure.

[0027] The superconducting layer 30 is disposed on the intermediate layer 20 (main surface 20b). As described above, the crystal axis of the intermediate layer 20 is oriented, and therefore the c-axis, which is the crystal axis of the superconducting layer 30, is also oriented along the crystal axis of the intermediate layer 20. Typically, the superconducting layer 30 is made of a material (REBa2Cu3O described later) that is a material having a crystal orientation similar to that of the intermediate layer 20. x ) is oriented so that the c-axis of the crystal is along the normal direction of the main surface 20b. Here, "the c-axis is oriented so that the c-axis is along the normal direction of the main surface 20b" means that the inclination angle of the c-axis with respect to the normal direction of the main surface 20b is within 15°. The superconducting layer 30 has a main surface 30a and a main surface 30b. The main surface 30a and the main surface 30b are end surfaces of the superconducting layer 30 in the thickness direction. The main surface 30a faces the intermediate layer 20 (main surface 20b). The main surface 30b is the surface opposite to the main surface 30a.

[0028] The constituent material of the superconducting layer 30 is REBa2Cu3O x Here, RE is a rare earth element. Examples of rare earth elements include gadolinium (Gd), yttrium (Y), and europium (Eu). However, rare earth elements are not limited to these. The superconducting layer 30 contains a halogen. Examples of halogens include chlorine (Cl). However, halogens are not limited to this. The superconducting layer 30 may contain an alkali metal. Examples of alkali metals include sodium (Na). However, alkali metals are not limited to this. The alkali metal does not have to be contained in the superconducting layer 30.

[0029] The concentration of halogen in the superconducting layer 30 is less than 2000 ppm by mass. The concentration of halogen in the superconducting layer 30 may be 1800 ppm by mass or less, or may be 1500 ppm by mass or less. The concentration of halogen in the superconducting layer 30 is, for example, 2 ppm by mass or more. The concentration of alkali metal in the superconducting layer 30 is, for example, 2000 ppm by mass or less. The concentration of alkali metal in the superconducting layer 30 is, for example, 1 ppb by mass or more. The concentrations of halogen and alkali metal in the superconducting layer 30 are measured by ICP (Inductively Coupled Plasma) analysis, that is, a method in which the superconducting layer 30 is dissolved in a solution and the ion concentration in the solution is analyzed. The concentration of halogen (alkali metal) in the superconducting layer 30 is the mass ratio of halogen (alkali metal) to the total mass of all elements contained in the superconducting layer 30. That is, the total mass of all elements constituting the superconducting layer 30 is 100 percent.

[0030] Ba2Cu3O4X2 may be precipitated at the interface between the superconducting layer 30 and the main surface 20b, in the superconducting layer 30, and on the main surface 30b. X is a halogen. The amount of Ba2Cu3O4X2 precipitated on the main surface 30b may be greater than the amount of Ba2Cu3O4X2 precipitated in the superconducting layer 30.

[0031] (Method for manufacturing superconducting wire 100) A method for manufacturing superconducting wire 100 will be described below with reference to FIGS.

[0032] As shown in Fig. 2, the method for manufacturing the superconducting wire 100 includes a preparation step S1, an intermediate layer forming step S2, a solution applying step S3, a first firing step S4, and a second firing step S5. The intermediate layer forming step S2 is performed after the preparation step S1. The solution applying step S3 is performed after the intermediate layer forming step S2. The first firing step S4 is performed after the solution applying step S3. The second firing step S5 is performed after the first firing step S4.

[0033] 3, in the preparation step S1, a substrate 10 is prepared. No intermediate layer 20 is disposed on the substrate 10 prepared in the preparation step S1.

[0034] 4, in the intermediate layer forming step S2, the intermediate layer 20 is formed on the substrate 10. The intermediate layer 20 is formed by sequentially depositing each layer constituting the intermediate layer 20 by, for example, magnetron sputtering.

[0035] The superconducting layer 30 is formed by performing a solution application step S3, a first firing step S4, and a second firing step S5, i.e., by a metal organic decomposition (MOD) method. Fig. 5 is a cross-sectional view illustrating the solution application step S3. As shown in Fig. 5, in the solution application step S3, a coating film 31 is formed on the intermediate layer 20. The coating film 31 is formed by applying a solution onto the intermediate layer 20 and drying the applied solution.

[0036] The solution contains a solvent and constituent elements of the superconducting layer 30 mixed in the solvent. The solution contains a halogen and an alkali metal. More specifically, the solution contains alcohol as a solvent, hydrochloric acid as a halogen source, sodium as an alkali metal, and rare earth elements, barium, and copper as constituent elements of the superconducting layer 30. The concentration of the alkali metal in the solution may be 1 ppb by mass or more. An example of the halogen and alkali metal being contained in the solution is when the halogen and alkali metal are added to the solution.

[0037] As shown in Fig. 6, in the first firing step S4, the coating film 31 is heated to form a calcined film 32. The calcined film 32 is made of a precursor of the superconducting layer 30. The precursor of the superconducting layer 30 is subjected to a drying process to remove the organic solvent and then to a calcined film of REBa2Cu3O x The raw material may be subjected to a heat treatment for forming nanocrystals or a heat treatment for promoting decomposition of the raw material. The heating in the first firing step S4 is carried out in an atmosphere containing oxygen.

[0038] 7, in the second firing step S5, the calcined film 32 is heated to form the superconducting layer 30. The heating in the second firing step S5 is performed in an oxygen-containing atmosphere at a temperature higher than that in the first firing step S4.

[0039] During the heating in the second firing step S5, REBa2Cu3O x The crystals of REBa2Cu3O are epitaxially grown and oriented so that their c-axes are aligned along the normal direction of the main surface 20b. x There are some areas where epitaxial growth of Ba2Cu3O4X2 is difficult to occur, but in these areas, Ba2Cu3O4X2 precipitates. Around the precipitated Ba2Cu3O4X2, REBa2Cu3O x Since the epitaxial growth of REBa2Cu3O is easily caused by the halogen content of the solution, x This promotes the orientation of the crystals.

[0040] By sequentially repeating the solution application step S3, the first firing step S4, and the second firing step S5, the film thickness of the superconducting layer 30 increases, resulting in the superconducting wire 100 having the structure shown in Fig. 1. Note that, as the solution application step S3, the first firing step S4, and the second firing step S5 are sequentially repeated, halogens are unevenly distributed on and near the main surface 30b of the superconducting layer 30. Therefore, when the superconducting layer 30 is formed by the MOD method using a solution containing halogen, the amount of Ba2Cu3O4X2 precipitated on the main surface 30b becomes larger than the amount of Ba2Cu3O4X2 precipitated in the superconducting layer 30.

[0041] <Modification> In the above example, a solution containing an alkali metal was used, but the alkali metal may be contained in the atmosphere during the second firing step S5 rather than in the solution. In this case, the partial pressure of the alkali metal in the atmosphere may be 1000 Pa or higher. The gas constituting the atmosphere during the second firing step S5 may contain, for example, oxygen, an inert gas, and an alkali metal. The inert gas is, for example, argon or nitrogen. The pressure of this atmosphere is, for example, atmospheric pressure (101.3 kPa). The alkali metal may also be contained in the calcined film 32. Note that, as an example of the atmosphere or calcined film 32 containing an alkali metal, an alkali metal may be added to the atmosphere or calcined film 32.

[0042] As described above, the solution used in the solution application step S3 contains an alkali metal, and therefore the calcined film 32 also contains an alkali metal. During heating in the second firing step S5, the alkali metal in the calcined film 32 vaporizes. The vaporized alkali metal reacts with chlorine in the superconducting layer 30 and is discharged to the outside. Therefore, in the superconducting wire 100, the halogen concentration in the superconducting layer 30 is reduced to less than 2000 ppm by mass, compared to when the solution does not contain an alkali metal. The halogen concentration in the superconducting layer 30 can be reduced to, for example, 1800 ppm by mass or less, and can also be reduced to 1500 ppm by mass or less.

[0043] In addition, in the superconducting wire 100, the concentration of halogen in the superconducting layer 30 is reduced, so that REBa2Cu3O x This can prevent the composition balance from being disrupted and the volume of the superconducting layer 30 from decreasing.

[0044] In the superconducting wire 100, since the solution used in the solution application step S3 contains an alkali metal, the alkali metal may remain in the superconducting layer 30. However, even if the alkali metal remains in the superconducting layer 30, the alkali metal is unlikely to adversely affect the superconducting properties of the superconducting layer 30. The halogen concentration in the superconducting layer 30 is similarly reduced not only when the solution used in the solution application step S3 contains an alkali metal, but also when the alkali metal is contained in the calcined film 32 or the atmosphere in the second firing step S5.

[0045] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0046] 10 substrate, 10a, 10b main surfaces, 20 intermediate layer, 20a, 20b main surfaces, 30 superconducting layer, 30a, 30b main surfaces, 31 coating film, 32 calcined film, 100 superconducting wire, S1 preparation step, S2 intermediate layer formation step, S3 solution coating step, S4 first firing step, S5 second firing step.

Claims

1. REBa ２ Cu ３ O ｘ a superconducting layer including RE is a rare earth element, The superconducting layer contains a halogen and an alkali metal.

2. A superconducting wire as described in claim 1, wherein the concentration of the halogen in the superconducting layer is less than 2000 ppm by mass.

3. 2. The superconducting wire according to claim 1, wherein the concentration of the halogen in the superconducting layer is 2 ppm by mass or more.

4. 2. The superconducting wire according to claim 1, wherein the halogen is chlorine.

5. 2. The superconducting wire according to claim 1, wherein the concentration of the alkali metal in the superconducting layer is 1 ppb by mass or more.

6. 2. The superconducting wire according to claim 1, wherein the alkali metal is sodium.

7. A substrate; an intermediate layer disposed on the substrate; the superconducting layer has a first main surface and a second main surface opposite to the first main surface, the superconducting layer is disposed on the intermediate layer such that the first main surface faces the intermediate layer, Ba on the second principal surface ２ Cu ３ O ４ X ２ The amount of precipitation of Ba in the superconducting layer is ２ Cu ３ O ４ X ２ The amount of precipitation is greater than that of 6. The superconducting wire according to claim 1, wherein X is a halogen.

8. REBa is placed on the intermediate layer disposed on the substrate. ２ Cu ３ O ｘ forming a superconducting layer comprising: RE is a rare earth element, the step of forming the superconducting layer includes a step of applying a solution containing constituent elements of the superconducting layer onto the intermediate layer, a step of heating the applied solution to form a precursor of the superconducting layer, and a step of heating the precursor to form the superconducting layer, the solution comprises a halogen; At least one of the solution, the precursor, and the atmosphere in which the precursor is heated contains an alkali metal.

9. 9. The method for producing a superconducting wire according to claim 8, wherein the concentration of the alkali metal in the solution is 1 ppb by mass or more.

10. 9. The method for producing a superconducting wire according to claim 8, wherein a partial pressure of the alkali metal in the atmosphere is 1000 Pa or less.

11. 9. The method for producing a superconducting wire according to claim 8, wherein the halogen is chlorine.

12. 12. The method for manufacturing a superconducting wire according to claim 8, wherein the alkali metal is sodium.

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