Superconducting layer connection structure, superconducting wire, superconducting coil, and superconducting device

Abstract

To provide a joint structure of a superconductive layer capable of realizing low electric resistance and high mechanical strength.SOLUTION: A joint structure of a superconductive layer according to an embodiment comprises: a first superconductive layer; a second superconductive layer; a joint layer provided between the first superconductive layer and the second superconductive layer and including a plurality of crystal particles containing rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), wherein the plurality of crystal particles including at least one first particle; the at least one first particle has a first inner region and a first outer region, the first inner region is located inside the first superconducting layer, and the first outer region is located outside the first superconducting layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a connection structure of superconducting layers, a superconducting wire, a superconducting coil, and a superconducting device. [Background technology]

[0002] For example, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems use superconducting coils to generate strong magnetic fields. Superconducting coils are formed by winding superconducting wire around a bobbin.

[0003] To increase the length of superconducting wires, for example, multiple superconducting wires are connected. For example, the ends of two superconducting wires are connected using a connection structure. The connection structure for connecting superconducting wires is required to have low electrical resistance and high mechanical strength. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-41667 Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to provide a connection structure for superconducting layers that can achieve low electrical resistance and high mechanical strength. [Means for solving the problem]

[0006] The superconducting layer connection structure of the embodiment comprises a first superconducting layer, a second superconducting layer, and a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including a plurality of crystalline particles containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), wherein the plurality of crystalline particles include at least one first particle, the at least one first particle having a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a schematic cross-sectional view of a connection structure of superconducting layers according to the first embodiment. [Figure 2] FIG. 3 is an enlarged schematic cross-sectional view of a portion of the connection layer according to the first embodiment. [Figure 3] FIG. 3 is a diagram showing the particle size distribution of crystal particles contained in the connection layer according to the first embodiment. [Figure 4] FIG. 3 is an enlarged schematic cross-sectional view of a first particle of the connection layer according to the first embodiment. [Figure 5] FIG. 10 is an enlarged schematic cross-sectional view of a portion of a connection layer of a comparative example. [Figure 6] FIG. 10 is an enlarged schematic cross-sectional view of a part of a connection layer of a modified example of the first embodiment. [Figure 7] FIG. 4 is a schematic cross-sectional view of a superconducting wire according to a second embodiment. [Figure 8] FIG. 10 is an enlarged schematic cross-sectional view of a portion of the first connection layer of the second embodiment. [Figure 9] FIG. 10 is an enlarged schematic cross-sectional view of a portion of the second connection layer of the second embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view of a first modified example of the superconducting wire of the second embodiment. [Figure 11] FIG. 10 is a schematic cross-sectional view of a second modified example of the superconducting wire of the second embodiment. [Figure 12] FIG. 10 is a schematic cross-sectional view of a third modified example of the superconducting wire of the second embodiment. [Figure 13] FIG. 10 is a schematic cross-sectional view of a fourth modified example of the superconducting wire of the second embodiment. [Figure 14]FIG. 10 is a schematic perspective view of a superconducting coil according to a third embodiment. [Figure 15] FIG. 10 is a schematic cross-sectional view of a superconducting coil according to a third embodiment. [Figure 16] FIG. 10 is a block diagram of a superconducting device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the same or similar components will be designated by the same reference numerals, and the description of components that have already been described may be omitted as appropriate.

[0009] In this specification, the "particle size" of a particle or the like refers to the major axis of the particle unless otherwise specified. The major axis of a particle is the longest length between any two points on the periphery of the particle. The minor axis of a particle is the length of a line segment that passes through the midpoint of the line segment corresponding to the major axis, is perpendicular to the line segment, and has the periphery of the particle as both ends. The aspect ratio of a particle is the ratio of the major axis to the minor axis of the particle (major axis / minor axis). The major and minor axes of a particle can be determined, for example, by image analysis of a scanning electron microscope image (SEM image). The cross-sectional area of ​​a particle can be determined, for example, by image analysis of a scanning electron microscope image.

[0010] The detection of elements contained in particles and the measurement of the atomic concentrations of elements can be performed using, for example, energy dispersive X-ray spectroscopy (EDX) or wavelength dispersive X-ray analysis (WDX). Furthermore, the identification of substances contained in particles can be performed using, for example, powder X-ray diffraction.

[0011] (First embodiment) The connection structure of the superconducting layer of the first embodiment comprises a first superconducting layer, a second superconducting layer, and a connection layer provided between the first superconducting layer and the second superconducting layer and including a plurality of crystalline particles containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), wherein the plurality of crystalline particles include at least one first particle, and the at least one first particle has a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer.

[0012] 1 is a schematic cross-sectional view of a connection structure of superconducting layers according to a first embodiment. The connection structure 100 of the first embodiment is a structure that physically and electrically connects two superconducting layers. The connection structure 100 is used, for example, to connect two superconducting wires and elongate the superconducting wires.

[0013] The connection structure 100 includes a first superconducting member 10, a second superconducting member 20, and a connection layer 30. The connection structure 100 is a structure in which the first superconducting member 10 and the second superconducting member 20 are connected by the connection layer 30. The connection layer 30 is provided between the first superconducting member 10 and the second superconducting member 20.

[0014] The first superconducting member 10 comprises a first substrate 12, a first intermediate layer 14, and a first superconducting layer 16. The second superconducting member 20 comprises a second substrate 22, a second intermediate layer 24, and a second superconducting layer 26.

[0015] The first substrate 12 is, for example, a metal. The first substrate 12 is, for example, a nickel alloy or a copper alloy. The first substrate 12 is, for example, a nickel-tungsten alloy.

[0016] The first superconducting layer 16 is, for example, an oxide superconducting layer. The first superconducting layer 16 includes, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first superconducting layer 16 includes, for example, at least one rare earth element (RE) selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0017] The first superconducting layer 16 is, for example, (RE)Ba2Cu3O δ (RE is a rare earth element, 6≦δ≦7) Specifically, the first superconducting layer 16 has a chemical composition expressed as GdBa2Cu3O δ (6≦δ≦7), YBa2Cu3O δ (6≦δ≦7), or EuBa2Cu3O δ It has a chemical composition expressed as (6≦δ≦7).

[0018] The first superconducting layer 16 includes, for example, a single crystal having a perovskite structure.

[0019] The first superconducting layer 16 is formed on the first intermediate layer 14, for example, by using a metal organic decomposition method (MOD method), a pulsed laser deposition method (PLD method), or a metal organic chemical vapor deposition method (MOCVD method).

[0020] The first intermediate layer 14 is provided between the first substrate 12 and the first superconducting layer 16. The first intermediate layer 14 has the function of improving the crystal orientation of the first superconducting layer 16 formed on the first intermediate layer 14.

[0021] The first intermediate layer 14 includes, for example, a rare earth oxide. The first intermediate layer 14 has, for example, a laminated structure of multiple films. The first intermediate layer 14 has, for example, a structure in which, from the first substrate 12 side, yttrium oxide (YO), yttria-stabilized zirconia (YSZ), and cerium oxide (CeO) are laminated.

[0022] The second substrate 22 is, for example, a metal. The second substrate 22 is, for example, a nickel alloy or a copper alloy. The second substrate 22 is, for example, a nickel-tungsten alloy.

[0023] The second superconducting layer 26 is, for example, an oxide superconducting layer. The second superconducting layer 26 includes, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first superconducting layer 16 includes, for example, at least one rare earth element (RE) selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0024] The second superconducting layer 26 is, for example, (RE)Ba2Cu3O δ (RE is a rare earth element, 6≦δ≦7) The second superconducting layer 26 has a chemical composition expressed as follows. δ (6≦δ≦7), YBa2Cu3O δ (6≦δ≦7), or EuBa2Cu3O δ It has a chemical composition expressed as (6≦δ≦7).

[0025] The second superconducting layer 26 includes, for example, a single crystal having a perovskite structure.

[0026] The second superconducting layer 26 is formed on the second intermediate layer 24 by, for example, the MOD method, the PLD method, or the MOCVD method.

[0027] The second intermediate layer 24 is provided between the second substrate 22 and the second superconducting layer 26. The second intermediate layer 24 has the function of improving the crystal orientation of the second superconducting layer 26 formed on the second intermediate layer 24.

[0028] The second intermediate layer 24 includes, for example, a rare earth oxide. The second intermediate layer 24 has, for example, a laminated structure of multiple films. The second intermediate layer 24 has, for example, a structure in which, from the second substrate 22 side, yttrium oxide (YO), yttria-stabilized zirconia (YSZ), and cerium oxide (CeO) are laminated.

[0029] The connection layer 30 is provided between the first superconducting layer 16 and the second superconducting layer 26. The connection layer 30 contacts the first superconducting layer 16. The connection layer 30 contacts the second superconducting layer 26.

[0030] The connection layer 30 is an oxide superconducting layer. The connection layer 30 includes a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 includes at least one rare earth element (RE) selected from the group consisting of, for example, yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0031] 2 is an enlarged schematic cross-sectional view of a portion of the connection layer of the first embodiment, taken along a line perpendicular to the surface of the first superconducting layer 16. As shown in FIG.

[0032] The connection layer 30 includes a plurality of crystal particles. The connection layer 30 includes first crystal particles 31 and second crystal particles 32. The connection layer 30 may include voids 33. The connection layer 30 is formed by sintering the first crystal particles 31 and the second crystal particles 32.

[0033] The first crystal particles 31 and the second crystal particles 32 are examples of crystal particles.

[0034] The first crystal particle 31 includes at least one first particle 31a and at least one second particle 31b.

[0035] The connection layer 30 is, for example, porous. For example, voids 33 exist between the particles contained in the connection layer 30. The connection layer 30 does not necessarily have to have voids 33.

[0036] The first crystal particles 31 contain a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first crystal particles 31 are rare earth oxides. The first crystal particles 31 are, for example, single crystals or polycrystals having a perovskite structure.

[0037] The first crystal particles 31 are, for example, (RE)Ba2Cu3O δ (RE is a rare earth element, 6≦δ≦7) Specifically, the first crystal particles 31 have a chemical composition expressed as, for example, GdBa2Cu3O δ (6≦δ≦7), YBa2Cu3O δ (6≦δ≦7), or EuBa2Cu3O δ It has a chemical composition expressed as (6≦δ≦7).

[0038] The first crystal grains 31 are superconductors.

[0039] The first crystal particles 31 are, for example, plate-like or flat. A flat shape means that the particle has an aspect ratio of 2 or more. The aspect ratio of a particle is the ratio of the particle's major axis to its minor axis (major axis / minor axis).

[0040] The grain size of the first crystal grains 31 is, for example, 500 nm or more and 5 μm or less. The median grain size of the first crystal grains 31 is, for example, 500 nm or more and 5 μm or less.

[0041] The second crystal particles 32 contain a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The second crystal particles 32 are rare earth oxides. The second crystal particles 32 are, for example, single crystals or polycrystals having a perovskite structure. The second crystal particles 32 are, for example, (RE)Ba2Cu3O δ (RE is rare earth element, 6≦δ≦7)

[0042] The second crystal grains 32 are, for example, superconductors.

[0043] The second crystal particles 32 contain, for example, the same rare earth element as the first crystal particles 31. The chemical composition of the second crystal particles 32 is, for example, the same as the chemical composition of the first crystal particles 31.

[0044] The second crystal particles 32 may contain, for example, a different rare earth element from that contained in the first crystal particles 31. The chemical composition of the second crystal particles 32 may be different from that of the first crystal particles 31, for example.

[0045] The second crystal particles 32 are, for example, spherical or irregular in shape. The aspect ratio of the second crystal particles 32 is, for example, less than 2.

[0046] The grain size of the second crystal grains 32 is smaller than the grain size of the first crystal grains 31. For example, the median value of the grain size of the second crystal grains 32 is smaller than the median value of the grain size of the first crystal grains 31.

[0047] The grain size of the second crystal grains 32 is, for example, 10 nm or more and less than 1 μm. The median grain size of the second crystal grains 32 is, for example, 10 nm or more and less than 1 μm.

[0048] The median grain size of the first crystal grains 31 is, for example, 10 times or more and 1000 times or less than the median grain size of the second crystal grains 32.

[0049] 3 is a diagram showing the particle size distribution of the crystal particles contained in the connection layer of Embodiment 1. FIG. 3 shows the particle size distribution of the first crystal particles 31 and the second crystal particles 32 contained in the connection layer 30.

[0050] 3, the particle size distribution of the crystal particles contained in the connection layer 30 includes a bimodal distribution. The bimodal distribution has a first distribution including a first peak (Pk1 in FIG. 3) and a second distribution including a second peak (Pk2 in FIG. 3).

[0051] The particle size distribution of the crystal particles contained in the connection layer 30 may be a multimodal distribution with three or more peaks.

[0052] The grain size of the crystal grain corresponding to the first peak Pk1 is the first grain size (d1 in FIG. 3), and the grain size of the crystal grain corresponding to the second peak Pk2 is the second grain size (d2 in FIG. 3).

[0053] The first particle size d1 is larger than the second particle size d2, and is, for example, 10 times or more and 1000 times or less than the second particle size d2.

[0054] The first particle size d1 is, for example, 500 nm or more and 5 μm or less, and the second particle size d2 is, for example, 10 nm or more and less than 1 μm.

[0055] The first distribution mainly includes first crystal particles 31. The second distribution mainly includes second crystal particles 32.

[0056] The crystal particles having a particle size corresponding to the first distribution include, for example, plate-like or flat crystal particles. For example, among the crystal particles having a particle size corresponding to the first distribution, the proportion of the number of plate-like or flat crystal particles is greater than the proportion of the number of crystal particles having other shapes.

[0057] The crystal particles having a particle size corresponding to the second distribution include, for example, spherical or irregularly shaped crystal particles. For example, among the crystal particles having a particle size corresponding to the second distribution, the proportion of the number of spherical or irregularly shaped crystal particles is greater than the proportion of the number of crystal particles having other shapes. do.

[0058] The first crystal particles 31 include at least one first particle 31a. That is, at least one of the first crystal particles 31 is a first particle 31a. The first crystal particles 31 also include at least one second particle 31b. That is, at least one of the first crystal particles 31 is a second particle 31b. The first particle 31a and the second particle 31b are included in, for example, a first distribution of particle size distribution of the crystal particles included in the connection layer 30.

[0059] The first particle 31a has a first inner region 31ax and a first outer region 31ay.

[0060] The first internal region 31ax is located inside the first superconducting layer 16. The first internal region 31ax exists closer to the first superconducting layer 16 than the interface between the first superconducting layer 16 and the connecting layer 30. The first internal region 31ax is, for example, buried in the first superconducting layer 16. The first internal region 31ax and the first superconducting layer 16 are, for example, joined together.

[0061] The first external region 31ay is located outside the first superconducting layer 16. The first external region 31ay exists closer to the connecting layer 30 than the interface between the first superconducting layer 16 and the connecting layer 30. The first external region 31ay is located inside the connecting layer 30. Therefore, one first particle 31a exists across both the first superconducting layer 16 and the connecting layer 30.

[0062] Fig. 4 is an enlarged schematic cross-sectional view of a first particle 31a of the connecting layer of the first embodiment. Fig. 4 shows a cross section perpendicular to the surface of the first superconducting layer 16. The surface of the first superconducting layer 16 refers to the interface between the first superconducting layer 16 and the connecting layer 30.

[0063] The fact that the first particle 31a has the first internal region 31ax and the first external region 31ay can be determined from the observed image by observing a cross section perpendicular to the surface of the first superconducting layer 16 and including the connecting layer 30 using, for example, a scanning electron microscope (SEM).

[0064] If it is unclear whether or not the first particle 31a is embedded in the first superconducting layer 16, a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM) can be further used to observe the crystal orientation of the first particle 31a and the crystal orientation of the first superconducting layer 16 located around it, thereby making it possible to determine that the first particle 31a has a first internal region 31ax and a first external region 31ay.

[0065] In a cross section perpendicular to the surface of the first superconducting layer 16, the ratio α (S1 / (S1+S2)) of the area of ​​the first internal region 31ax to the sum (S1+S2) of the area of ​​the first internal region 31ax (S1 in Figure 4) and the area of ​​the first external region 31ay (S2 in Figure 4) is, for example, 10% or more and 90% or less.

[0066] When the area ratio α is 10% or more and 90% or less, the contact resistance at the interface between the first superconducting layer 16 and the connecting layer 30 is reduced, a current path is formed from the first superconducting layer 16 to the first particles 31a, and the amount of current flowing from the first superconducting layer 16 to the connecting layer 30 is increased. Furthermore, when the area ratio α is 10% or more and 90% or less, the first particles 31a are fixed to the first superconducting layer 16, and the anchor effect can prevent the connecting layer 30 from peeling off from the first superconducting layer 16. In other words, a connecting structure with low electrical resistance and high mechanical strength can be formed.

[0067] If the area is less than 10%, the effect of reducing electrical resistance and the effect of increasing mechanical strength may not be obtained.If the area is more than 90%, the first particles 31a may obstruct the current flowing inside the first superconducting layer 16 in a direction parallel to the surface of the first superconducting layer 16.

[0068] In a cross section perpendicular to the surface of the first superconducting layer 16, the area S2 of the first outer region 31ay is larger than, for example, the area S1 of the first inner region 31ax.

[0069] The areas S1 and S2 can be calculated from an image obtained by observing a cross section perpendicular to the surface of the first superconducting layer 16 and including the connecting layer 30 using, for example, a scanning electron microscope (SEM). Specifically, the magnification of the SEM for a certain sample X is set to 2,000 times or more and 10,000 times or less, and all of the first crystal particles 31 that are clearly buried in the first superconducting layer 16 (particles corresponding to 31a in FIG. 2) are selected from one SEM image A. However, particles whose depth from the surface of the first superconducting layer 16 in the first internal region 31ax (dx in FIG. 4) is less than 50 nm are excluded from the selection.

[0070] Next, a line is drawn around the selected first particle 31a. Next, a straight line is drawn on the surface of the first superconducting layer 16, i.e., on the interface between the first superconducting layer 16 and the connecting layer 30. Finally, the areas S1 and S2 enclosed by the line around the first particle 31a and the line on the surface of the first superconducting layer 16 are calculated, and the area ratio α (S1 / (S1+S2)) is calculated for each first particle 31a. S1 and S2 can also be calculated using commercially available image analysis software.

[0071] Next, all first particles 31a are selected from the first crystal particles 31 in the SEM image A, for which it is unclear whether they are embedded in the first superconducting layer 16. These particles are further observed using a scanning transmission electron microscope (STEM) or a transmission electron microscope (TEM) to observe the crystal orientation of the first particles 31a and the crystal orientation of the first superconducting layer 16 located around them.

[0072] The first superconducting layer 16 is a thin film with a high degree of crystal orientation, with the c-axis aligned in a direction perpendicular to the surface of the first superconducting layer 16, and even if the bulk first particles 31a are embedded in the first superconducting layer 16 in the process of forming the connection structure, the crystal orientations of the two do not completely match, and the two do not completely merge. In other words, the boundary where the crystal orientation directions differ can be defined as the outermost periphery of the first particles 31a.

[0073] After drawing a line around the outermost periphery of the first particle 31a, S1, S2, and α are calculated for each first particle 31a on the STEM image or TEM image in the same manner as in the calculation for the SEM image A. However, first particles 31a whose depth (dx in FIG. 4) from the surface of the first superconducting layer 16 of the first internal region 31ax is less than 50 nm after drawing the outermost periphery are excluded from the calculation.

[0074] From the above, in one SEM image A, S1 can be calculated for each first particle 31a, and their average value is defined as S1a. Similarly, in SEM image A, S2 can be calculated for each first particle 31a, and their average value is defined as S2a. Similarly, in SEM image A, the area ratio (S1 / (S1+S2)) can be calculated for each first particle 31a, and their average value is defined as "average value αa of area ratio α."

[0075] Furthermore, four different SEM images B, C, D, and E of the same sample X are prepared, and S1b, S2b, S1c, S2c, S1d, S2d, S1e, S2e, αb, αc, αd, and αe are calculated using the same procedure. Finally, the average value of S1a to S1e is calculated as S1 for sample X, the average value of S2a to S2e is calculated as S2 for sample X, and the average value of αa to αe is calculated, and these values ​​are defined as "the ratio of the area of ​​the first internal region to the sum of the area of ​​the first internal region and the area of ​​the first external region in sample X."

[0076] The angle (θ in FIG. 4) formed between the c-axis direction (dotted arrow C1 in FIG. 4) of first particle 31a and the c-axis direction (dotted arrow C2 in FIG. 4) of first superconducting layer 16 is, for example, 15 degrees or more and 90 degrees or less. For example, the median value of the angle (θ in FIG. 4) formed between the c-axis direction (dotted arrow C1 in FIG. 4) of first particle 31a and the c-axis direction (dotted arrow C2 in FIG. 4) of first superconducting layer 16 is 15 degrees or more and 90 degrees or less.

[0077] These c-axis directions can be determined by STEM observation or TEM observation.

[0078] The particle size of the first particles 31a is, for example, 500 nm to 5 μm, and the median particle size of the first particles 31a is, for example, 500 nm to 5 μm.

[0079] The depth (dx in FIG. 4) of the first internal region 31ax from the surface of the first superconducting layer 16 is, for example, not less than 100 nm and not more than 1.5 μm.

[0080] The distance between the first particle 31a and the second superconducting layer 26 (dy in FIG. 2) is, for example, equal to or less than half the distance between the first superconducting layer 16 and the second superconducting layer 26 (t in FIG. 2). Note that the distance t between the first superconducting layer 16 and the second superconducting layer 26 is equal to the thickness of the connecting layer 30.

[0081] In a cross section perpendicular to the surface of first superconducting layer 16, the number of first particles 31a present within a range of 1 mm along the surface is, for example, 10 or more and 100 or less.

[0082] The second particle 31b has a second inner region 31bx and a second outer region 31by.

[0083] The second internal region 31bx is located inside the second superconducting layer 26. The second internal region 31bx exists closer to the second superconducting layer 26 than the interface between the second superconducting layer 26 and the connecting layer 30. The second internal region 31bx is, for example, buried in the second superconducting layer 26. The second internal region 31bx and the second superconducting layer 26 are, for example, joined together.

[0084] The second external region 31by is located outside the second superconducting layer 26. The second external region 31by is located closer to the connecting layer 30 than the interface between the second superconducting layer 26 and the connecting layer 30. The second external region 31by is located inside the connecting layer 30.

[0085] In a cross section perpendicular to the surface of second superconducting layer 26, the ratio of the area of ​​second inner region 31bx to the sum of the area of ​​second inner region 31bx and the area of ​​second outer region 31by is, for example, 10% or more and 90% or less.

[0086] When the area ratio α is 10% or more and 90% or less, the contact resistance at the interface between second superconducting layer 26 and connecting layer 30 is reduced, a current path is formed from second superconducting layer 26 to second particles 31b, and the amount of current flowing from second superconducting layer 26 to connecting layer 30 is increased. Furthermore, when the area ratio α is 10% or more and 90% or less, second particles 31b are fixed to second superconducting layer 26, and the anchor effect can prevent connecting layer 30 from peeling off from second superconducting layer 26. In other words, a connecting structure with low electrical resistance and high mechanical strength can be formed.

[0087] If the area is less than 10%, the effect of reducing electrical resistance and the effect of increasing mechanical strength may not be obtained.If the area is more than 90%, second particles 31b may obstruct the current flowing inside second superconducting layer 26 in a direction parallel to the surface of superconducting layer 26.

[0088] The area of ​​the second outer region 31by is, for example, larger than the area of ​​the second inner region 31bx in a cross section perpendicular to the surface of the second superconducting layer 26. The areas of 31by, 31bx, and the area ratio can be calculated by the method described above.

[0089] The angle formed between the c-axis direction of second particle 31b and the c-axis direction of second superconducting layer 26 is, for example, 15 degrees or more and 90 degrees or less. For example, the median value of the angle formed between the c-axis direction of second particle 31b and the c-axis direction of second superconducting layer 26 is, for example, 15 degrees or more and 90 degrees or less. As described above, the c-axis direction can be determined by STEM observation or TEM observation.

[0090] The particle size of the second particles 31b is, for example, 500 nm to 5 μm, and the median particle size of the second particles 31b is, for example, 500 nm to 5 μm.

[0091] The depth of the second internal region 31bx from the surface of the second superconducting layer 26 is, for example, not less than 100 nm and not more than 1.5 μm.

[0092] The distance between second particle 31b and first superconducting layer 16 is, for example, equal to or less than half the distance (t in FIG. 2) between first superconducting layer 16 and second superconducting layer 26. Note that distance t between first superconducting layer 16 and second superconducting layer 26 is equal to the thickness of connecting layer 30.

[0093] In a cross section perpendicular to the surface of second superconducting layer 26, the number of second particles 31b present within a range of 1 mm along the surface is, for example, 10 or more and 100 or less.

[0094] Next, an example of a method for manufacturing the superconducting layer connection structure of the first embodiment will be described.

[0095] First, an oxide superconductor containing rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O) is formed.

[0096] Oxide superconductors are formed by solid-state reaction. 3、 and CuO powders are mixed and compressed to produce a green compact. The green compact is sintered to produce GdBa2Cu3O δ An oxide superconductor with a composition of (6≦δ≦7) is formed. Gd may be replaced with Y, La, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, or Lu.

[0097] The oxide superconductor is crushed to form first crystal particles 31.

[0098] Next, the connection layer 30 is formed using the MOD method.

[0099] An organometallic salt solution is prepared using powders of Gd(OCOCH3)2, Ba(OCOCH3)2, and Cu(OCOCH3)2. The prepared organometallic salt solution is mixed with first crystal particles 31. Gd may be replaced with Y, La, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, or Lu.

[0100] Next, the organometallic salt solution mixed with the first crystal particles 31 is applied onto the first superconducting layer 16. Next, the applied organometallic salt solution is sandwiched between the first superconducting layer 16 and the second superconducting layer 26 and fired to form the connection layer 30. When forming the connection layer 30 by firing, the overlapping first superconducting layer 16 and second superconducting layer 26 are pressed in a direction from the second superconducting layer 26 toward the first superconducting layer 16.

[0101] The organic metal salt solution is baked to form second crystal particles 32. The particle size of the second crystal particles 32 is smaller than the particle size of the first crystal particles 31.

[0102] By controlling the mixing ratio of the first crystal particles 31 and the organic metal salt solution and adjusting the pressure when pressurizing the superposed first and second superconducting layers 16 and 26 and the firing temperature, it is possible to form the first particles 31a and the second particles 31b in the connecting layer 30. It is known that the higher the pressure when pressurizing the superposed first and second superconducting layers 16 and 26 and the higher the firing temperature, the more the bonding reaction between the connecting layer 30 and the first and second superconducting layers 16 and 26 progresses, resulting in a stronger connection structure. However, if the pressure during firing is increased too much, for example by two times, cracks may occur in the first or second superconducting layer 16 or 26, resulting in a deterioration in connection characteristics.

[0103] Therefore, for example, the pressure is increased once before firing to create a starting point where the superconductor powder contained in the slurry will be embedded in the oxide superconducting layer, that is, a starting point where bonding will begin. By creating a starting point where bonding will begin, the superconductor powder can be embedded in the oxide superconducting layer without increasing the pressure during firing.

[0104] Furthermore, by adjusting the pressure during pressurization and the firing temperature, the area ratio between the first inner region 31ax and the first outer region 31ay of the first particle 31a can be adjusted to a desired value. Furthermore, by adjusting the pressure during pressurization and the firing temperature, the area ratio between the second inner region 31bx and the second outer region 31by of the second particle 31b can be adjusted to a desired value.

[0105] The mixing ratio of the first crystal particles to the organometallic salt solution is preferably, for example, first crystal particles:organometallic salt solution mixture=4:1 to 1:4. The pressure to be applied is preferably a relative pressure value before firing of 0.8 to 2.2 and a relative pressure value during firing of 0.8 to 1.5. The firing temperature is preferably 700°C to 850°C. The desired connection layer can be manufactured by appropriately selecting from these ranges.

[0106] According to the above method, it is considered that the first particles 31a and the second particles 31b are formed by the first crystal particles 31 being embedded in the first superconducting layer 16 or the second superconducting layer 26 due to the application of pressure during firing. It is also considered that the above method causes a chemical reaction between the first crystal particles 31 and the first superconducting layer 16 or between the first crystal particles 31 and the second superconducting layer 26 to proceed due to the application of pressure during firing, thereby forming the first particles 31a and the second particles 31b.

[0107] By the above method, the first superconducting layer 16 and the second superconducting layer 26 are connected together. By the above method, the superconducting layer connection structure 100 of the first embodiment is formed.

[0108] Next, the operation of the superconducting layer connection structure of the first embodiment will be described.

[0109] For example, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) systems use superconducting coils to generate strong magnetic fields. Superconducting coils are formed by winding superconducting wire around a bobbin.

[0110] To increase the length of superconducting wires, for example, multiple superconducting wires are connected. For example, the ends of two superconducting wires are connected using a connection structure. The connection structure for connecting superconducting wires is required to have low electrical resistance and high mechanical strength.

[0111] In the superconducting layer connection structure 100 of the first embodiment, the connection layer 30 that connects the first superconducting layer 16 and the second superconducting layer 26 includes first particles 31a and second particles 31b. By including the first particles 31a and the second particles 31b in the connection layer 30, the superconducting layer connection structure 100 can be realized with low electrical resistance and high mechanical strength. This will be described in detail below.

[0112] Fig. 5 is an enlarged schematic cross-sectional view of a portion of a connection layer of a comparative example. Fig. 5 is a view corresponding to Fig. 2. Connection layer 90 of the comparative example differs from connection layer 30 of the first embodiment in that it does not include first particles 31a and second particles 31b.

[0113] In the connection structure 100 of the first embodiment, the first crystal grains 31 include first grains 31a having first internal regions 31ax. The first grains 31a have first internal regions 31ax, which increases the contact area with the first superconducting layer 16, thereby reducing the contact resistance between the first grains 31a and the first superconducting layer 16. Therefore, the electrical resistance of the connection structure 100 can be made even lower than that of the connection structure of the comparative example.

[0114] Furthermore, in the connection structure 100 of the first embodiment, the first crystal grains 31 include second grains 31b having second internal regions 31bx. The second grains 31b have second internal regions 31bx, which increases the contact area with the second superconducting layer 26 and reduces the contact resistance between the second grains 31b and the second superconducting layer 26. Therefore, the electrical resistance of the connection structure 100 can be made even lower than that of the connection structure of the comparative example.

[0115] From the viewpoint of reducing the electrical resistance of the connection structure 100, the angle (θ in Figure 4) formed between the c-axis direction of the first particle 31a (dotted arrow C1 in Figure 4) and the c-axis direction of the first superconducting layer 16 (dotted arrow C2 in Figure 4) is preferably 15 degrees or more, more preferably 30 degrees or more, and even more preferably 45 degrees or more.

[0116] Current in the first grains 31a and the first superconducting layer 16 mainly flows in a plane perpendicular to the c-axis direction. The c-axis of the first superconducting layer 16 is oriented in a direction perpendicular to the surface of the first superconducting layer 16, as shown in FIG. 4 . Therefore, current in the first superconducting layer 16 mainly flows in a direction parallel to the surface of the first superconducting layer 16.

[0117] 4, by tilting the c-axis direction of the first particle 31a toward the c-axis direction of the first superconducting layer 16, the component of the current flowing through the first particle 31a that flows toward the second superconducting layer 26 increases. Therefore, the electrical resistance of the connection structure 100 can be reduced.

[0118] For the same reason, the angle formed between the c-axis direction of the second particle 31b and the c-axis direction of the second superconducting layer 26 is preferably 15 degrees or more, more preferably 30 degrees or more, and even more preferably 45 degrees or more.

[0119] From the viewpoint of reducing the electrical resistance of the connection structure 100, the distance between the first particle 31a and the second superconducting layer 26 (dy in FIG. 2) is preferably equal to or less than half, more preferably equal to or less than one-third, and even more preferably equal to or less than one-fourth of the distance between the first superconducting layer 16 and the second superconducting layer 26 (t in FIG. 2). By reducing the distance dy between the first particle 31a and the second superconducting layer 26, the electrical resistance between the first particle 31a and the second superconducting layer 26 is reduced. Therefore, the electrical resistance of the connection structure 100 can be reduced.

[0120] For the same reason, the distance between the second particle 31b and the first superconducting layer 16 is preferably not more than half the distance (t in Figure 2) between the first superconducting layer 16 and the second superconducting layer 26, more preferably not more than one-third, and even more preferably not more than one-fourth.

[0121] From the viewpoint of reducing the electrical resistance of the connection structure 100, the area S2 of the first outer region 31ay is preferably larger than the area S1 of the first inner region 31ax. When the area S2 of the first outer region 31ay is larger than the area S1 of the first inner region 31ax, the contribution of the first particles 31a to the current path in the connection layer 30 increases. Therefore, the electrical resistance of the connection structure 100 can be reduced.

[0122] For the same reason, the area of ​​the second outer region 31by is preferably larger than the area of ​​the second inner region 31bx.

[0123] For example, when a superconducting coil is manufactured by winding a superconducting wire having the connection structure of the comparative example shown in Fig. 5 around a bobbin, stress is applied between the first superconducting layer 16 and the connection layer 90. If the mechanical strength of the interface between the first superconducting layer 16 and the connection layer 90 is insufficient, the first superconducting layer 16 and the connection layer 90 may peel off at the interface when stress is applied between the first superconducting layer 16 and the connection layer 90. Similarly, if the mechanical strength of the interface between the second superconducting layer 26 and the connection layer 90 is insufficient, the second superconducting layer 26 and the connection layer 90 may peel off at the interface.

[0124] In the connection structure 100 of the first embodiment, the first crystal grains 31 include first grains 31a having a first inner region 31ax and a first outer region 31ay. The first grains 31a are present across the first superconducting layer 16 and the connection layer 30, so that the first grains 31a exhibit an anchor effect, increasing the mechanical strength of the interface between the first superconducting layer 16 and the connection layer 30. Therefore, even when stress is applied between the first superconducting layer 16 and the connection layer 30, peeling between the first superconducting layer 16 and the connection layer 30 at the interface is suppressed. Therefore, the connection structure 100 can have even higher mechanical strength than the connection structure of the comparative example.

[0125] Furthermore, in the connection structure 100 of the first embodiment, the first crystal grains 31 include second grains 31b having second inner regions 31bx and second outer regions 31by. Therefore, for the same reason as in the case of the first grains 31a, even when stress is applied between the second superconducting layer 26 and the connection layer 30, peeling at the interface between the second superconducting layer 26 and the connection layer 30 is suppressed. Therefore, the connection structure 100 can have even higher mechanical strength than the connection structure of the comparative example.

[0126] From the viewpoint of increasing the mechanical strength of the connection structure 100, the ratio (S1 / (S1+S2)) of the area of ​​the first inner region 31ax to the sum (S1+S2) of the area of ​​the first inner region 31ax (S1 in FIG. 4) and the area of ​​the first outer region 31ay (S2 in FIG. 4) is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. By increasing the ratio of the area of ​​the second inner region 31bx, the anchoring effect exerted by the first particles 31a is enhanced. Therefore, the mechanical strength of the connection structure 100 is increased.

[0127] For the same reason, the ratio of the area of ​​the second inner region 31bx to the sum of the area of ​​the second inner region 31bx and the area of ​​the second outer region 31by is preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more. The area ratios of S1 and S2 can be calculated using the method described above.

[0128] From the viewpoint of increasing the mechanical strength of the connection structure 100, the depth (dx in FIG. 4) of the first internal region 31ax from the surface of the first superconducting layer 16 is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more. When the first internal region 31ax penetrates deep into the first superconducting layer 16, the anchor effect exerted by the first particles 31a becomes greater. Therefore, the mechanical strength of the connection structure 100 is increased.

[0129] For the same reason, the depth of the second internal region 31bx from the surface of the second superconducting layer 26 is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1 μm or more.

[0130] In a cross section perpendicular to the surface of the first superconducting layer 16, the number of first particles 31a present within a range of 1 mm along the surface is preferably 10 or more, more preferably 20 or more, and even more preferably 50 or more. As the density of the first particles 31a increases, the interface resistance between the first superconducting layer 16 and the connection layer 30 decreases. Therefore, the electrical resistance of the connection structure 100 decreases. Furthermore, as the density of the first particles 31a increases, the anchor effect exerted by the first particles 31a increases. Therefore, the mechanical strength of the connection structure 100 increases.

[0131] For the same reason, in a cross section perpendicular to the surface of the second superconducting layer 26, the number of second particles 31b present within a range of 1 mm along the surface is preferably 10 or more, more preferably 20 or more, and even more preferably 50 or more.

[0132] As shown in Fig. 3, in the connection structure 100 of superconducting layers of the first embodiment, the grain size distribution of the crystal grains contained in the connection layer 30 includes a bimodal distribution. The connection structure 100 includes first crystal grains 31 with large grain sizes, thereby reducing the crystal grain interfaces in the connection layer 30. This prevents the interface resistance of the crystal grain interfaces from increasing the electrical resistance of the connection layer 30. This reduces the electrical resistance of the connection structure 100.

[0133] Furthermore, in the connection structure 100 of the superconducting layer of the first embodiment, the second crystal grains 32 having a small grain size fill the spaces between the first crystal grains 31 having a large grain size. The presence of the second crystal grains 32 between the first crystal grains 31 increases the bonding strength between the first crystal grains 31. This increases the mechanical strength of the connection layer 30, and therefore the mechanical strength of the connection structure 100.

[0134] (Variation) The connection structure of the modified example of the first embodiment differs from the connection structure of the first embodiment in that the first particles are in contact with the second superconducting layer, or part of the particles is buried on the second superconducting layer side.

[0135] 6 is an enlarged schematic cross-sectional view of a part of a connection layer of a modified example of the first embodiment, and corresponds to FIG.

[0136] The connection layer 30 of the connection structure of the modified example includes a first particle 31a in contact with the second superconducting layer 26. The connection layer 30 of the connection structure of the modified example also includes a second particle 31b in contact with the first superconducting layer 16. The connection layer 30 of the connection structure of the modified example may also include a third particle 31c that has both a first inner region 31cx1 and a second inner region 31cx2, in addition to an outer region 31cy.

[0137] The particle size of first particle 31a in contact with second superconducting layer 26 is, for example, larger than the distance (t in FIG. 6) between first superconducting layer 16 and second superconducting layer 26. The particle size of second particle 31b in contact with first superconducting layer 16 is, for example, larger than the distance (t in FIG. 6) between first superconducting layer 16 and second superconducting layer 26. The particle size of third particle 31c spanning both first superconducting layer 16 and second superconducting layer 26 is, for example, larger than the distance (t in FIG. 6) between first superconducting layer 16 and second superconducting layer 26.

[0138] The connection layer 30 of the connection structure of the modified example has a further lower electrical resistance by including first particles 31a in contact with the second superconducting layer 26. Furthermore, the connection layer 30 of the connection structure of the modified example has a further lower electrical resistance by including second particles 31b in contact with the first superconducting layer 16. Furthermore, the connection layer 30 of the connection structure of the modified example has a further lower electrical resistance by including third particles 31c that extend across both the first superconducting layer 16 and the second superconducting layer 26.

[0139] As described above, the connection structure of the superconducting layers of the first embodiment can achieve low electrical resistance and high mechanical strength.

[0140] (Second embodiment) The superconducting wire of the second embodiment comprises a first superconducting wire including a first superconducting layer, a second superconducting wire including a second superconducting layer, a third superconducting layer, a first connecting layer provided between the first superconducting layer and the third superconducting layer and including a plurality of crystal particles including rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), and a second connecting layer provided between the second superconducting layer and the third superconducting layer and including a plurality of crystal particles including rare earth elements (RE), barium (Ba), copper (Cu), and oxygen (O), wherein the plurality of crystal particles included in the first connecting layer include at least one first particle, and the at least one first particle has a first internal region and a first external region, wherein the first internal region is located inside the first superconducting layer and the first external region is located outside the first superconducting layer. The superconducting wire of the second embodiment uses the superconducting layer connection structure of the first embodiment as a structure for connecting the first superconducting wire and the second superconducting wire. Hereinafter, some of the description overlapping with the first embodiment will be omitted.

[0141] 7 is a schematic cross-sectional view of a superconducting wire according to the second embodiment. Superconducting wire 400 according to the second embodiment includes first superconducting wire 401, second superconducting wire 402, and connecting member 403. Superconducting wire 400 according to the second embodiment is elongated by connecting first superconducting wire 401 and second superconducting wire 402 using connecting member 403.

[0142] First superconducting wire 401 includes first substrate 12, first intermediate layer 14, first superconducting layer 16, and first protective layer 18. Second superconducting wire 402 includes second substrate 22, second intermediate layer 24, second superconducting layer 26, and second protective layer 28. Connection member 403 includes third substrate 42, third intermediate layer 44, and third superconducting layer 46.

[0143] First superconducting wire 401, second superconducting wire 402, and connecting member 403 have the same structures as first superconducting member 10 and second superconducting member 20 of the first embodiment.

[0144] The connection layer 30 includes a first connection layer 30a and a second connection layer 30b.

[0145] The first connecting layer 30a is provided between the first superconducting layer 16 and the third superconducting layer 46. The first connecting layer 30a contacts the first superconducting layer 16. The first connecting layer 30a contacts the third superconducting layer 46.

[0146] The second connecting layer 30b is provided between the second superconducting layer 26 and the third superconducting layer 46. The second connecting layer 30b contacts the second superconducting layer 26. The second connecting layer 30b contacts the third superconducting layer 46.

[0147] The first connecting layer 30a between the first superconducting layer 16 and the third superconducting layer 46 and the second connecting layer 30b between the second superconducting layer 26 and the third superconducting layer 46 are continuous.

[0148] For example, the connection layer 30 does not exist between the first superconducting layer 16 and the second superconducting layer 26. For example, there is an air gap between the first superconducting layer 16 and the second superconducting layer 26. Furthermore, the first superconducting layer 16 and the second superconducting layer 26 may be in contact with each other.

[0149] The connection layer 30 is an oxide superconducting layer. The connection layer 30 includes a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 includes, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 includes, for example, at least one rare earth element (RE) selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0150] The connection layer 30 of the second embodiment has the same configuration as the connection layer 30 of the first embodiment shown in FIG.

[0151] Fig. 8 is an enlarged schematic cross-sectional view of a part of the first connection layer of the second embodiment, which corresponds to Fig. 2 of the first embodiment.

[0152] The first connecting layer 30a of the second embodiment differs from the connecting layer 30 of the first embodiment only in that the second superconducting layer 26 in FIG.

[0153] Fig. 9 is an enlarged schematic cross-sectional view of a part of the second connection layer of the second embodiment, and corresponds to Fig. 2 of the first embodiment.

[0154] The second connecting layer 30b of the second embodiment differs from the connecting layer 30 of the first embodiment only in that the first superconducting layer 16 in FIG. 2 is replaced with a second superconducting layer 26, and the second superconducting layer 26 in FIG. 2 is replaced with a third superconducting layer 46.

[0155] In superconducting wire 400 of the second embodiment, for example, current flows from first superconducting wire 401 to second superconducting wire 402 through first connection layer 30a, connection member 403, and second connection layer 30b.

[0156] First superconducting wire 401 and connecting member 403 are connected using first connecting layer 30a, so that the connection structure connecting first superconducting wire 401 and connecting member 403 has low electrical resistance and high mechanical strength. Also, second superconducting wire 402 and connecting member 403 are connected using second connecting layer 30b, so that the connection structure connecting second superconducting wire 402 and connecting member 403 has low electrical resistance and high mechanical strength.

[0157] Therefore, the connection structure connecting first superconducting wire 401 and second superconducting wire 402 has low electrical resistance and high mechanical strength. Therefore, superconducting wire 400 has low electrical resistance and high mechanical strength.

[0158] It is also possible to connect three or more superconducting wires to form a longer superconducting wire.

[0159] (First Modification) 10 is a schematic cross-sectional view of a first modified example of the superconducting wire of the second embodiment. Superconducting wire 410 of the first modified example of the second embodiment differs from superconducting wire 400 of the second embodiment in that it includes a reinforcing member 60.

[0160] Reinforcing material 60 is provided between first superconducting wire 401 and second superconducting wire 402. Reinforcing material 60 is provided between first superconducting layer 16 and second superconducting layer 26, for example.

[0161] Reinforcing material 60 is in contact with, for example, first superconducting wire 401 and second superconducting wire 402. Reinforcing material 60 is in contact with connecting layer 30, for example.

[0162] By providing reinforcing material 60, the mechanical strength of superconducting wire 410 is improved.

[0163] The reinforcing material 60 is, for example, a metal or a resin. The reinforcing material 60 is, for example, a solder. The reinforcing material 60 is, for example, a solder containing silver (Ag) and indium (In).

[0164] (Second Modification) 11 is a schematic cross-sectional view of a second modified example of the superconducting wire of the second embodiment. Superconducting wire 420 of the second modified example of the second embodiment differs from superconducting wire 400 of the second embodiment in that first connection layer 30a and second connection layer 30b are spaced apart from each other.

[0165] The first connecting layer 30a and the second connecting layer 30b are spaced apart.

[0166] (Third Modification) 12 is a schematic cross-sectional view of a third modified example of the superconducting wire of the second embodiment. Superconducting wire 430 of the third modified example of the second embodiment differs from superconducting wire 420 of the second modified example of the second embodiment in that a part of the surface of first superconducting layer 16 facing third superconducting layer 46 is exposed, and a part of the surface of second superconducting layer 26 facing third superconducting layer 46 is exposed.

[0167] There is a region where the connecting layer 30 is not present on the upper surface of the first superconducting layer 16 near the end on the second superconducting layer 26 side. There is also a region where the connecting layer 30 is not present on the upper surface of the second superconducting layer 26 near the end on the first superconducting layer 16 side.

[0168] (Fourth Modification) 13 is a schematic cross-sectional view of a fourth modified example of the superconducting wire of the second embodiment. Superconducting wire 440 of the fourth modified example of the second embodiment differs from superconducting wire 430 of the third modified example of the second embodiment in that it includes a reinforcing member 60.

[0169] The reinforcing material 60 is provided between the first superconducting wire 401 and the second superconducting wire 402. The reinforcing material 60 is provided, for example, between the first superconducting layer 16 and the second superconducting layer 26. The reinforcing material 60 is provided, for example, between the first superconducting layer 16 and the third superconducting layer 46. The reinforcing material 60 is provided, for example, between the second superconducting layer 26 and the third superconducting layer 46. The reinforcing material 60 is provided, for example, between the first connecting layer 30a and the second connecting layer 30b.

[0170] By providing reinforcing material 60, the mechanical strength of superconducting wire 440 is improved.

[0171] The reinforcing material 60 is, for example, a metal or a resin. The reinforcing material 60 is, for example, a solder. The reinforcing material 60 is, for example, a solder containing silver (Ag) and indium (In).

[0172] As described above, according to the second embodiment and the modified example, a superconducting wire that is long and has low electrical resistance and high mechanical strength can be realized by connecting two superconducting wires.

[0173] (Third embodiment) The superconducting coil of the third embodiment includes the superconducting wire of the second embodiment. Hereinafter, some of the description that overlaps with the second embodiment may be omitted.

[0174] Fig. 14 is a schematic perspective view of a superconducting coil according to the third embodiment, and Fig. 15 is a schematic cross-sectional view of the superconducting coil according to the third embodiment.

[0175] The superconducting coil 700 of the third embodiment is used as a coil for generating a magnetic field in superconducting equipment such as NMR, MRI, heavy particle beam therapy equipment, or superconducting magnetic levitation trains.

[0176] Superconducting coil 700 includes a bobbin 110, a first insulating plate 111a, a second insulating plate 111b, and a winding portion 112. Winding portion 112 includes superconducting wire 120 and inter-wire layers .

[0177] FIG. 14 shows a state in which the first insulating plate 111a and the second insulating plate 111b are removed.

[0178] The reel 110 is made of, for example, fiber-reinforced plastic. The superconducting wire 120 is, for example, tape-shaped. As shown in FIG. 14 , the superconducting wire 120 is wound around the reel 110 in a concentric, so-called pancake shape around a winding central axis C.

[0179] 14, the first direction is the coil radial direction, the second direction is the coil circumferential direction, and the first direction is the direction in which the winding central axis C extends.

[0180] Inter-wire layer 130 has a function of fixing superconducting wire 120. Inter-wire layer 130 has a function of preventing superconducting wire 120 from being damaged by vibration during use of the superconducting device or by friction between wires.

[0181] The first insulating plate 111a and the second insulating plate 111b are formed of, for example, fiber-reinforced plastic. The first insulating plate 111a and the second insulating plate 111b have the function of insulating the winding portion 112 from the outside. The winding portion 112 is located between the first insulating plate 111a and the second insulating plate 111b.

[0182] The superconducting wire 120 is the superconducting wire of the second embodiment.

[0183] As described above, according to the third embodiment, by using a superconducting wire having low electrical resistance and high mechanical strength, a superconducting coil with improved characteristics can be realized.

[0184] (Fourth embodiment) The superconducting device of the fourth embodiment is a superconducting device equipped with the superconducting coil of the third embodiment. Hereinafter, some of the description overlapping with the third embodiment will be omitted.

[0185] 16 is a block diagram of a superconducting device according to a fourth embodiment. The superconducting device according to the fourth embodiment is a heavy ion beam therapy device 800. The heavy ion beam therapy device 800 is an example of a superconducting device.

[0186] The heavy ion beam therapy device 800 includes an injection system 50 , a synchrotron accelerator 52 , a beam transport system 54 , an irradiation system 56 , and a control system 58 .

[0187] The injection system 50 has a function of generating, for example, carbon ions to be used in therapy and pre-accelerating the ions to be injected into the synchrotron accelerator 52. The injection system 50 has, for example, an ion generation source and a linear accelerator.

[0188] The synchrotron accelerator 52 has a function of accelerating the carbon ion beam injected from the injection system 50 to an energy level suitable for treatment. The synchrotron accelerator 52 uses the superconducting coil 700 of the third embodiment.

[0189] The beam transport system 54 has a function of transporting the carbon ion beam injected from the synchrotron accelerator 52 to the irradiation system 56. The beam transport system 54 has, for example, a bending electromagnet.

[0190] The irradiation system 56 has a function of irradiating a patient, who is an irradiation target, with the carbon ion beam injected from the beam transport system 54. The irradiation system 56 has, for example, a rotating gantry that enables the carbon ion beam to be irradiated from any direction. The rotating gantry uses the superconducting coil 700 of the third embodiment.

[0191] The control system 58 controls the injection system 50, the synchrotron accelerator 52, the beam transport system 54, and the irradiation system 56. The control system 58 is, for example, a computer.

[0192] In the heavy ion beam therapy device 800 of the fourth embodiment, the superconducting coil 700 of the third embodiment is used in the synchrotron accelerator 52 and the rotating gantry, thereby realizing the heavy ion beam therapy device 800 with excellent characteristics.

[0193] In the fourth embodiment, a heavy ion beam therapy device 800 has been described as an example of a superconducting device, but the superconducting device may also be a nuclear magnetic resonance device (NMR), a magnetic resonance imaging device (MRI), or a superconducting magnetic levitation railway vehicle. [Example]

[0194] Example 1 Hastelloy substrate with an intermediate layer and GdBa2Cu3O 7-δ Two 10 cm long oxide superconducting wires were prepared, each having a layer (oxide superconducting layer) formed on the wire and covered with a protective layer of silver and copper. One end was wet-etched 1.0 cm from the end using a mixed solution of nitric acid, ammonia, and hydrogen peroxide to expose the oxide superconducting layer.

[0195] Powders of Gd2O3, BaCO3, and CuO were prepared, weighed appropriately, and then thoroughly mixed. The mixed powder was compressed to produce a green compact. The resulting green compact was sintered at 930°C to produce GdBa2Cu3O 7-δ The resulting oxide superconductor was pulverized in a mortar and pestle, and particles of the appropriate diameter were selected using a sieve to produce superconductor powder with a major axis of 10 μm or less and a minor axis of 2 μm or less.

[0196] The obtained superconductor powder was mixed with an organometallic salt solution in which Gd(OCOCH3)2, Ba(OCOCH3)2, and Cu(OCOCH3)2 were dissolved in a weight ratio of 1:2 to prepare a slurry.

[0197] The obtained slurry was applied to the exposed oxide superconducting layer of one of the superconducting wires, and then fired at 780° C. Thereafter, the part of the superconducting wire to which the slurry was applied and the part of the other superconducting wire where the superconducting layer was exposed were placed face to face and superimposed.

[0198] The overlapping wires were sandwiched between jigs from above and below and pressed. The pressure applied during firing was set at a reference value of 1.0, and a pressure of 1.2 was applied when the wires were first sandwiched, then the pressure was reduced to 1.0 before firing began.

[0199] While still sandwiched between the jigs, the wire was heated to 780°C in an air atmosphere to perform a first heat treatment, then cooled to near room temperature, oxygen gas was introduced into the furnace, and the wire was heated to 500°C in an oxygen atmosphere to perform a second heat treatment, thereby forming a connection structure for the superconducting wire.

[0200] Terminals were attached to both ends of the superconducting wire after connection, and the temperature dependence of electrical resistance was measured, confirming a clear superconducting transition at around 93 K with a transition width of approximately 1 K. The critical current value at 77 K for this connection structure is set as the reference value of 1.0, and relative critical current values ​​are shown in the following examples and comparative examples.

[0201] Furthermore, the critical current value at 77K when this connection structure is bent at R=15 cm is set as the reference value of 1.0, and the relative critical value currents when the connection structures of the following examples and comparative examples are bent in the same manner are shown.

[0202] This connection structure was cut in a cross section perpendicular to the surface of the superconducting layer of the superconducting wire and observed using SEM and STEM. Part of the superconductor powder contained in the connection layer was embedded in the superconducting wire and had a first inner region and a first outer region (first particle). From the observed SEM and STEM images, the area of ​​the first internal region (S1), the area of ​​the first external region (S2), and the ratio α (S1 / (S1+S2)) of the area of ​​the first internal region to the sum of the areas of the first internal region and the first external region were calculated, and it was found that S2 > S1 and α = 10%.

[0203] From the observed STEM image, the angle θ formed between the c-axis direction of one first particle and the c-axis direction of the first superconducting layer in which the particle is embedded was 15 degrees.

[0204] From the observed SEM image, it was found that the distance between one first particle and the second superconducting layer was half the distance between the first superconducting layer and the second superconducting layer (the thickness of the connecting layer) (referred to as the distance ratio β). The particle size of one first particle was 5 μm. The depth of the first internal region from the surface of the first superconducting layer was 1.0 μm (referred to as the buried depth). The number of first particles present within a range of 1 mm along the surface of the first superconducting layer was 10.

[0205] The particle size distribution was measured, and the first peak was at 5 μm and the second peak was at 100 nm.

[0206] These properties are shown in Table 1. [Table 1]

[0207] (Comparative Example 1) Hastelloy substrate with an intermediate layer and GdBa2Cu3O7-δ Two 10 cm long oxide superconducting wires were prepared, each having a layer (oxide superconducting layer) formed on the wire and covered with a protective layer of silver and copper. One end was wet-etched 1.0 cm from the end using a mixed solution of nitric acid, ammonia, and hydrogen peroxide to expose the oxide superconducting layer.

[0208] An organometallic salt solution containing Gd(OCOCH3)2, Ba(OCOCH3)2, and Cu(OCOCH3)2 was applied to the exposed oxide superconducting layer of one of the superconducting wires, and then fired at 780°C. The part of the superconducting wire to which the slurry was applied and the part of the other superconducting wire where the superconducting layer was exposed were placed face to face and superimposed.

[0209] The overlapped wires were sandwiched between jigs from above and below, and a relative pressure of 1.2 was applied once, and then the relative pressure was reduced to 1.0.

[0210] While still sandwiched between the jigs, the wire was heated to 780°C in an air atmosphere to perform a first heat treatment, then cooled to near room temperature, oxygen gas was introduced into the furnace, and the wire was heated to 500°C in an oxygen atmosphere to perform a second heat treatment, thereby forming a connection structure for the superconducting wire.

[0211] As in Example 1, electrical resistance measurement, SEM observation, STEM observation, and particle size distribution measurement were performed, and the results are shown in Table 1. In this connection structure, the particle size distribution had one peak, and the peak particle size was 100 nm, indicating that the connection layer was formed only by small particles. Furthermore, none of these particles were embedded in the superconducting layer. The characteristics are shown in Table 1.

[0212] (Comparative Example 2) A connection structure was formed and evaluated in the same manner as in Example 1, except that the weight ratio of the superconductor powder to the organometallic salt solution was set to 1:4 and the pressure value before firing was set to 1.0. In this connection structure, none of the particles forming the connection layer were embedded in the superconducting layer.

[0213] Example 2 GdBa2Cu3O 7-δAn oxide superconductor of the composition was prepared and crushed, and then particles with a long diameter of 1 μm or less were selected using a sieve or the like, the pressure value before firing was set to 1.5, and the first heat treatment temperature was set to 800°C. Except for this, a connection structure was formed and evaluated in the same manner as in Example 1.

[0214] Example 3 A connection structure was formed and evaluated in the same manner as in Example 1, except that the relative pressure value before firing was set to 1.1.

[0215] Example 4 A connection structure was formed and evaluated in the same manner as in Example 1, except that the relative pressure value before firing was set to 2.0 and the first heat treatment temperature was set to 820°C.

[0216] Example 5 After producing superconductor powder with a major axis of 10 μm or less and a minor axis of 2 μm or less, a connection structure was formed and evaluated in the same manner as in Example 1, except that plate-shaped superconductor powder with a thickness of 1 μm or less was selected.

[0217] Example 6 GdBa2Cu3O 7-δ An oxide superconductor having the composition was prepared and pulverized, and then a connection structure was formed and evaluated in the same manner as in Example 1, except that particles having a major axis of 1 μm or less were selected using a sieve or the like.

[0218] Example 7 A connection structure was formed and evaluated in the same manner as in Example 1, except that the relative pressure value before firing was 1.0 and the first heat treatment temperature was 770°C.

[0219] Example 8 A connection structure was formed and evaluated in the same manner as in Example 1, except that the relative pressure value before firing was 1.4 and the first heat treatment temperature was 790°C.

[0220] Example 9 GdBa2Cu3O 7-δAn oxide superconductor having the composition was prepared and pulverized, and then particles having a major axis of 0.5 μm or less were selected using a sieve or the like, and a connection structure was formed and evaluated in the same manner as in Example 1.

[0221] Example 10 GdBa2Cu3O 7-δ An oxide superconductor having the composition was prepared and pulverized, and then particles having a major axis of 15 μm or less were selected using a sieve or the like, and a connection structure was formed and evaluated in the same manner as in Example 1.

[0222] Examples 11 to 14 A connection structure was formed and evaluated in the same manner as in Example 1, except that the weight ratio of the superconductor powder to the organic metal salt solution was changed as shown in Table 1.

[0223] (Examples 15 and 16) Connection structures were formed and evaluated in the same manner as in Example 1, except that the relative pressure value during firing was changed as shown in Table 1.

[0224] From the above, it was found that Examples 1 to 16, which have a superconducting layer connection structure in which at least one particle has a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer, have lower electrical resistance and higher mechanical strength than Comparative Examples 1 and 2, which do not have particles with portions that are present in both the superconducting layer and the connection layer.

[0225] Furthermore, Examples 1, 2, 6, 11, 12, 13, and 14 listed in Table 1, in which the area ratio α was 10% or more and 90% or less, S2 > S1, the angle θ was 15 degrees or more, the structure was bimodal, the distance ratio β was 1 / 2 or less, the particle size of the first particles was 500 nm or more and 5 μm or less, the embedding depth was 100 nm or more and 1.5 μm or less, and the number of first particles was 10 or more, had a higher relative critical current value at 77 K or a higher relative critical current value at 77 K when curved than Examples 3 to 5, 7 to 10, 15, and 16, which were outside any of the above ranges. Therefore, it was found that Examples 1, 2, 6, 11, 12, 13, and 14 had lower electrical resistance or higher mechanical strength than Examples 3 to 5, 7 to 10, 15, and 16.

[0226] Moreover, it was found that Examples 2, 12, and 13 had particularly low electrical resistance and particularly high mechanical strength.

[0227] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. For example, components of one embodiment may be replaced or changed with components of another embodiment. These embodiments and modifications thereof are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0228] (Technical proposal 1) a first superconducting layer; a second superconducting layer; and a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including a plurality of crystal particles including a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O); A connection structure of a superconducting layer, wherein the plurality of crystal particles include at least one first particle, the at least one first particle having a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer.

[0229] (Technical proposal 2) A superconducting layer connection structure according to Technical Proposal 1, wherein in a cross section perpendicular to the surface of the first superconducting layer, the ratio of the area of ​​the first internal region to the sum of the area of ​​the first internal region and the area of ​​the first external region is 10% or more and 90% or less.

[0230] (Technical proposal 3) A connection structure of superconducting layers according to Technical Solution 1 or Technical Solution 2, wherein in a cross section perpendicular to the surface of the first superconducting layer, the area of ​​the first outer region is larger than the area of ​​the first inner region.

[0231] (Technical proposal 4) A connection structure of a superconducting layer described in any one of Technical Solutions 1 to 3, wherein the angle formed between the c-axis direction of at least one first particle and the c-axis direction of the first superconducting layer is 15 degrees or more.

[0232] (Technical proposal 5) A connection structure of a superconducting layer according to any one of Technical Schemes 1 to 4, wherein the particle size distribution of the plurality of crystal particles includes a bimodal distribution.

[0233] (Technical proposal 6) the bimodal distribution has a first distribution including a first peak and a second distribution including a second peak; a first particle size corresponding to the first peak is larger than a second particle size corresponding to the second peak; The connection structure of the superconducting layer according to Technical Solution 5, wherein the at least one first particle is included in the first distribution.

[0234] (Technical proposal 7) A connection structure of a superconducting layer described in any one of Technical Solutions 1 to 6, wherein the distance between the at least one first particle and the second superconducting layer is less than half the distance between the first superconducting layer and the second superconducting layer.

[0235] (Technical proposal 8) A connection structure of superconducting layers described in any one of Technical Solutions 1 to 7, wherein the at least one first particle is in contact with the second superconducting layer.

[0236] (Technical proposal 9) A connection structure of a superconducting layer described in any one of Technical Solutions 1 to 8, wherein the plurality of crystal particles includes at least one second particle, and the at least one second particle has a second internal region and a second external region, the second internal region being located inside the second superconducting layer, and the second external region being located outside the second superconducting layer.

[0237] (Technical proposal 10) A connection structure of a superconducting layer according to any one of Technical Schemes 1 to 9, wherein the particle diameter of the at least one first particle is 500 nm or more and 5 μm or less.

[0238] (Technical proposal 11) A connection structure of a superconducting layer described in any one of Technical Proposals 1 to 10, wherein in a cross section perpendicular to the surface of the first superconducting layer, the depth of the first internal region from the surface of the first superconducting layer is 100 nm or more and 1.5 μm or less.

[0239] (Technical proposal 12) A connection structure of a superconducting layer described in any one of Technical Solutions 1 to 11, wherein in a cross section perpendicular to the surface of the first superconducting layer, the number of the first particles present within a range of 1 mm along the surface is 10 or more.

[0240] (Technical proposal 13) a first superconducting wire including a first superconducting layer; a second superconducting wire including a second superconducting layer; a third superconducting layer; and a first connection layer provided between the first superconducting layer and the third superconducting layer, the first connection layer including a plurality of crystal particles including a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O); a second connection layer provided between the second superconducting layer and the third superconducting layer, the second connection layer including a plurality of crystal particles including a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O); A superconducting wire, wherein the plurality of crystal particles included in the first connection layer include at least one first particle, the at least one first particle having a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer.

[0241] (Technical proposal 14) A superconducting wire according to Technical Proposal 13, wherein in a cross section perpendicular to the surface of the first superconducting layer, the ratio of the area of ​​the first internal region to the sum of the area of ​​the first internal region and the area of ​​the first external region is 10% or more.

[0242] (Technical proposal 15) A superconducting wire according to Technical Scheme 13 or 14, wherein in a cross section perpendicular to the surface of the first superconducting layer, the area of ​​the first outer region is larger than the area of ​​the first inner region.

[0243] (Technical proposal 16) A superconducting wire according to Technical Scheme 13 to Technical Scheme 15, wherein the angle formed between the c-axis direction of the at least one first particle and the c-axis direction of the first superconducting layer is 15 degrees or more.

[0244] (Technical proposal 17) A superconducting wire according to any one of Technical Schemes 13 to 16, wherein the particle size distribution of the plurality of crystal particles contained in the first connection layer includes a bimodal distribution.

[0245] (Technical proposal 18) the bimodal distribution has a first distribution including a first peak and a second distribution including a second peak; a first particle size corresponding to the first peak is larger than a second particle size corresponding to the second peak; The superconducting wire according to Technical Solution 17, wherein the at least one first particle is included in the first distribution.

[0246] (Technical proposal 19) A superconducting coil comprising the superconducting wire described in any one of Technical Schemes 13 to 18.

[0247] (Technical proposal 20) A superconducting device equipped with a superconducting coil as described in Technical Proposal 19. [Explanation of symbols]

[0248] 16 First superconducting layer 26 Second superconducting layer 30 Connection Layer 30a First connection layer 30b Second connection layer 31 First crystal particle 31a First particle 31ax First Internal Region 31ay First external region 31b Second particle 31bx Second internal area 31by Second External Region 46 Third Superconducting Layer 100 Connection structure 400 Superconducting wire 401 First superconducting wire 402 Second Superconducting Wire 700 Superconducting Coil 800 Heavy particle beam therapy equipment (superconducting equipment)

Claims

1. a first superconducting layer; a second superconducting layer; and a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including a plurality of crystal particles containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O); A connection structure of a superconducting layer, wherein the plurality of crystal grains include at least one first grain, the at least one first grain having a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer.

2. 2. The superconducting layer connection structure according to claim 1, wherein in a cross section perpendicular to the surface of the first superconducting layer, the ratio of the area of ​​the first internal region to the sum of the area of ​​the first internal region and the area of ​​the first external region is 10% or more and 90% or less.

3. 2. The superconducting layer connection structure according to claim 1, wherein an area of ​​said first outer region is larger than an area of ​​said first inner region in a cross section perpendicular to the surface of said first superconducting layer.

4. 2. The superconducting layer connection structure according to claim 1, wherein the angle formed between the c-axis direction of said at least one first particle and the c-axis direction of said first superconducting layer is 15 degrees or more.

5. The superconducting layer connection structure according to claim 1 , wherein the particle size distribution of the plurality of crystal grains includes a bimodal distribution.

6. the bimodal distribution has a first distribution including a first peak and a second distribution including a second peak; a first particle size corresponding to the first peak is larger than a second particle size corresponding to the second peak; The superconducting layer connection structure according to claim 5 , wherein the at least one first particle is included in the first distribution.

7. 2. The superconducting layer connection structure according to claim 1, wherein the distance between the at least one first particle and the second superconducting layer is equal to or less than half the distance between the first superconducting layer and the second superconducting layer.

8. 2. The superconducting layer connection structure according to claim 1, wherein said at least one first particle is in contact with said second superconducting layer.

9. 2. The superconducting layer connection structure according to claim 1, wherein the plurality of crystal grains include at least one second grain, the at least one second grain having a second inner region and a second outer region, the second inner region being located inside the second superconducting layer, and the second outer region being located outside the second superconducting layer.

10. 2. The superconducting layer connection structure according to claim 1, wherein the particle diameter of said at least one first particle is 500 nm or more and 5 [mu]m or less.

11. 2. The superconducting layer connection structure according to claim 1, wherein the depth of the first internal region from the surface of the first superconducting layer in a cross section perpendicular to the surface of the first superconducting layer is 100 nm or more and 1.5 μm or less.

12. 2. The superconducting layer connection structure according to claim 1, wherein the number of said first particles present within a range of 1 mm along the surface in a cross section perpendicular to the surface of said first superconducting layer is 10 or more.

13. a first superconducting wire including a first superconducting layer; a second superconducting wire including a second superconducting layer; a third superconducting layer; and a first connection layer provided between the first superconducting layer and the third superconducting layer, the first connection layer including a plurality of crystal particles containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O); a second connection layer provided between the second superconducting layer and the third superconducting layer, the second connection layer including a plurality of crystal particles containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O); A superconducting wire, wherein the plurality of crystal particles included in the first connection layer include at least one first particle, the at least one first particle having a first internal region and a first external region, the first internal region being located inside the first superconducting layer, and the first external region being located outside the first superconducting layer.

14. 14. The superconducting wire according to claim 13, wherein in a cross section perpendicular to the surface of the first superconducting layer, the ratio of the area of ​​the first internal region to the sum of the area of ​​the first internal region and the area of ​​the first external region is 10% or more.

15. 14. The superconducting wire according to claim 13, wherein in a cross section perpendicular to a surface of the first superconducting layer, an area of ​​the first outer region is larger than an area of ​​the first inner region.

16. 14. The superconducting wire according to claim 13, wherein the angle formed between the c-axis direction of the at least one first particle and the c-axis direction of the first superconducting layer is 15 degrees or more.

17. The superconducting wire according to claim 13 , wherein the grain size distribution of the plurality of crystal grains included in the first connection layer includes a bimodal distribution.

18. the bimodal distribution has a first distribution including a first peak and a second distribution including a second peak; a first particle size corresponding to the first peak is larger than a second particle size corresponding to the second peak; 18. The superconducting wire of claim 17, wherein the at least one first particle is included in the first distribution.

19. A superconducting coil comprising the superconducting wire according to any one of claims 13 to 18.

20. A superconducting device comprising the superconducting coil according to claim 19.

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