Connection structure of superconducting layer, superconducting wire rod, superconducting coil, and superconducting device

Abstract

To provide a connection structure of a superconducting layer, capable of realizing a low-electric resistance and a high-electric strength.SOLUTION: A connection structure of a superconducting layer of an embodiment, comprises: a first superconducting layer; a second superconducting layer; and a connection layer containing a crystal region that is provided to between the first superconducting layer and the second superconducting layer, and contains a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) and a gap. In a cross sectional surface vertical to a front surface of the first superconducting layer, the crystalline region contains a path from the first superconducting layer to the second superconducting layer, and the path contains a plurality of narrow parts, a width of the minimum narrow part having the minimum width of the plurality of narrow parts is 300nm or more, and in the cross sectional surface, an area ratio of the gap is 30% or larger and 70% or less.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] For example, in a nuclear magnetic resonance apparatus (NMR) or a magnetic resonance imaging apparatus (MRI), a superconducting coil is used to generate a strong magnetic field. The superconducting coil is formed by winding a superconducting wire around a winding frame.

[0003] In order to lengthen the superconducting wire, for example, a plurality of 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

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0006] The connection structure of the superconducting layer in the embodiment includes 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 crystal region containing rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids. In a cross-section perpendicular to the surface of the first superconducting layer, the crystal region includes a path from the first superconducting layer to the second superconducting layer, the path includes a plurality of constrictions, the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more, and in the cross-section, the area ratio of the voids is 30% or more and 70% or less.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same or similar members are denoted by the same reference numerals, and the description of the members once described may be omitted as appropriate.

[0009] In this specification, the "particle size" of particles or the like means the major axis of the particles unless otherwise specified. The major axis of a particle is the maximum length among the lengths between any two points on the outer 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 above line segment, and has both ends on the outer periphery of the particle. 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 axis and minor axis of a particle can be obtained, for example, by image analysis of a scanning electron microscope image (SEM image).

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

[0011] (First Embodiment) The connection structure of the superconducting layer of the first embodiment includes 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 crystal region containing rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids. In a cross-section perpendicular to the surface of the first superconducting layer, the crystal region includes a path from the first superconducting layer to the second superconducting layer, the path includes a plurality of constrictions, the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more, and in the cross-section, the area ratio of the voids is 30% or more and 70% or less.

[0012] FIG. 1 is a schematic cross-sectional view of the connection structure of the superconducting layer of the first embodiment. FIG. 2 is a schematic top view of the connection structure of the superconducting layer of the first embodiment. FIG. 1 is a cross-section taken along line AA' of FIG. 2. FIG. 1 is a cross-section perpendicular to the surface of the first superconducting layer 16.

[0013] 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 wire materials and lengthen the superconducting wire material.

[0014] 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.

[0015] The first superconducting member 10 includes a first substrate 12, a first intermediate layer 14, and a first superconducting layer 16. The second superconducting member 20 includes a second substrate 22, a second intermediate layer 24, and a second superconducting layer 26.

[0016] 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-chromium alloy.

[0017] The first superconducting layer 16 is, for example, an oxide superconducting layer. The first superconducting layer 16 contains, for example, rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first superconducting layer 16 contains, 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), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0018] The first superconducting layer 16 is, for example, (RE)Ba 2 Cu 3 O δ (where RE is a rare earth element, 6 ≤ δ ≤ 7). Specifically, the first superconducting layer 16 is, for example, GdBa 2 Cu 3 O δ (6 ≤ δ ≤ 7), YBa 2 Cu 3 O δ (6 ≤ δ ≤ 7), or EuBa 2 Cu 3 O δ (6 ≤ δ ≤ 7).

[0019] The first superconducting layer 16 includes, for example, a single crystal having a perovskite structure.

[0020] The first superconducting layer 16 is formed, for example, on the first intermediate layer 14 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).

[0021] The first intermediate layer 14 is provided between the first substrate 12 and the first superconducting layer 16. The first intermediate layer 14 has a function of improving the crystal orientation of the first superconducting layer 16 formed on the first intermediate layer 14.

[0022] The first intermediate layer 14 contains, for example, a rare earth oxide. The first intermediate layer 14 has, for example, a laminated structure of a plurality of films. The first intermediate layer 14 is, for example, from the first substrate 12 side, yttrium oxide (Y 2 O 3 ), yttria-stabilized zirconia (YSZ), cerium oxide (CeO 2 ) having a laminated structure.

[0023] 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-chromium alloy.

[0024] The second superconducting layer 26 is, for example, a superconducting oxide layer. The second superconducting layer 26 contains, for example, a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The first superconducting layer 16 contains, 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), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0025] The second superconducting layer 26 has, for example, a chemical composition represented by (RE)Ba 2 Cu 3 O δ (where RE is a rare earth element, 6 ≤ δ ≤ 7). The second superconducting layer 26 is, for example, GdBa 2 Cu 3 O δ (6 ≤ δ ≤ 7), YBa 2 Cu 3 O δ (6 ≤ δ ≤ 7), or EuBa 2 Cu 3 O δIt has a chemical composition represented by (6 ≦ δ ≦ 7).

[0026] The second superconducting layer 26 includes, for example, a single crystal having a perovskite structure.

[0027] The second superconducting layer 26 is formed, for example, on the second intermediate layer 24 using the MOD method, the PLD method, or the MOCVD method.

[0028] The second intermediate layer 24 is provided between the second substrate 22 and the second superconducting layer 26. The second intermediate layer 24 has a function of improving the crystal orientation of the second superconducting layer 26 formed on the second intermediate layer 24.

[0029] The second intermediate layer 24 includes, for example, a rare earth oxide. The second intermediate layer 24 has, for example, a laminated structure of a plurality of films. The second intermediate layer 24 is, for example, from the second substrate 22 side, yttrium oxide (Y 2 O 3 ), yttria-stabilized zirconia (YSZ), cerium oxide (CeO 2 ) has a laminated structure.

[0030] The connection layer 30 is provided between the first superconducting layer 16 and the second superconducting layer 26. The connection layer 30 is in contact with the first superconducting layer 16. The connection layer 30 is in contact with the second superconducting layer 26.

[0031] The connection layer 30 is an oxide superconducting layer. The connection layer 30 contains a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30 contains, 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), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0032] FIG. 3 is an enlarged schematic cross-sectional view of a part of the connection layer of the first embodiment. FIG. 3 is a cross-section perpendicular to the surface of the first superconducting layer 16. FIG. 3 is a cross-section including the first superconducting layer 16, the second superconducting layer 26, and the connection layer 30. FIG. 3 is an enlarged schematic cross-sectional view of a part of FIG. 1.

[0033] The connection layer 30 includes a crystal region 31 and voids 32.

[0034] The crystal region 31 is polycrystalline. The crystal region 31 is formed by connecting a plurality of crystal particles. The crystal region 31 has a network structure. The crystal region 31 is porous.

[0035] The crystal region 31 contains a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The crystal region 31 contains 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), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0036] The major phase of the crystal region 31 is a rare earth oxide. The fact that the major phase of the crystal region 31 is a rare earth oxide means that the proportion occupied by the rare earth oxide is the largest among the phases constituting the crystal region 31. The crystal region 31 has, for example, a perovskite structure crystal containing gadolinium (Gd), barium (Ba), copper (Cu), and oxygen (O) as the major phase. In the cross-section of the connection layer 30, for example, the area ratio occupied by the perovskite structure crystal containing gadolinium (Gd), barium (Ba), copper (Cu), and oxygen (O) is 90% or more.

[0037] The crystal region 31 is, for example, (RE)Ba 2 Cu 3 O δ(RE is a rare earth element, 6 ≦ δ ≦ 7) and has a chemical composition represented thereby. Specifically, the crystal region 31 is, for example, GdBa 2 Cu 3 O δ (6 ≦ δ ≦ 7), YBa 2 Cu 3 O δ (6 ≦ δ ≦ 7), or EuBa 2 Cu 3 O δ (6 ≦ δ ≦ 7) and has a chemical composition represented thereby.

[0038] The crystal region 31 is a superconductor.

[0039] The void 32 is filled with, for example, a gas. The void 32 is filled with, for example, air. In a cross section perpendicular to the surface of the first superconducting layer 16, the area ratio of the void 32 is, for example, 30% or more and 70% or less.

[0040] The area ratio of the void 32 in the connection layer 30 can be obtained, for example, by the following method. An SEM image of a cross section perpendicular to the surface of the first superconducting layer 16 is acquired. The acquired SEM image is binarized using image processing software, and the connection layer 30 is divided into a crystal region 31 and a void 32. The area ratio of the void 32 in the connection layer 30 divided into the crystal region 31 and the void 32 is calculated using image processing software. For example, the area ratio of the void 32 in a 20 μm × 20 μm region of the SEM image is calculated.

[0041] In a cross section perpendicular to the surface of the first superconducting layer 16, the median value of the circle-equivalent diameter of the void 32 is, for example, 200 nm or more and 10 μm or less. The median value of the circle-equivalent diameter of the void 32 is calculated, for example, from the SEM image divided into the crystal region 31 and the void 32 by image processing software using image processing software. For example, the median value of the circle-equivalent diameter of the void 32 in a 20 μm × 20 μm region of the SEM image is calculated.

[0042] The crystal region 31 includes at least one path 31x extending from the first superconducting layer 16 to the second superconducting layer 26. In the path 31x, the crystal region 31 is continuous without being segmented. In FIG. 3, the line representing the path 31x is indicated by a double arrow.

[0043] The path 31x is, for example, the shortest path from the position where the crystal region 31 contacts the first superconducting layer 16 to the second superconducting layer 26.

[0044] The length of the path 31x is longer than the thickness (t in FIG. 3) in the first direction from the first superconducting layer 16 to the second superconducting layer 26 of the connection layer 30. The length of the path 31x is, for example, 1.2 times or more and 3 times or less the thickness t of the connection layer 30.

[0045] The thickness t of the connection layer 30 is, for example, 500 nm or more and 30 μm or less.

[0046] The path 31x is formed of, for example, one type of crystal. The path 31x is composed of, for example, only crystals having a perovskite structure containing gadolinium (Gd), barium (Ba), copper (Cu), and oxygen (O). The path 31x may be formed of a plurality of types of crystals.

[0047] The path 31x includes a plurality of narrow portions. The narrow portion is, in other words, a constriction of the crystal region 31 or a necking of the crystal region 31.

[0048] The path 31x shown in FIG. 3 includes three narrow portions: a first narrow portion 3a, a second narrow portion 3b, and a third narrow portion 3c. The number of narrow portions included in the path 31x may be two or four or more. The crystal region 31 is formed by a plurality of crystal particles being connected at the narrow portions.

[0049] Among the first constriction 3a, the second constriction 3b, and the third constriction 3c included in the path 31x shown in FIG. 3, the first constriction 3a has the smallest width. The first constriction 3a, the second constriction 3b, and the third constriction 3c are examples of constrictions. The first constriction 3a is an example of the minimum constriction. Note that the width of the constriction means the minimum width in one constriction.

[0050] FIG. 4 is an enlarged schematic cross-sectional view of a part of the connection layer of the first embodiment. FIG. 4 is an enlarged schematic cross-sectional view of the portion surrounded by the dotted circle in FIG. 3. FIG. 4 is an enlarged schematic cross-sectional view of the crystal region 31 including the first constriction 3a.

[0051] The width (w in FIG. 4) of the first constriction 3a is 300 nm or more. The width (w in FIG. 4) of the first constriction 3a is, for example, 3 μm or less.

[0052] The first constriction 3a is provided between the first wide portion 3w1 and the second wide portion 3w2. The width of the first wide portion 3w1 is wider than the width of the first constriction 3a. The width of the second wide portion 3w2 is wider than the width of the first constriction 3a.

[0053] The first constriction 3a includes a first part 3a1 and a second part 3a2. The first part 3a1 has a crystal structure continuous with the first wide portion 3w1. The second part 3a2 has a crystal structure continuous with the second wide portion 3w2.

[0054] By observing the crystal orientations of the first constriction 3a, the first wide portion 3w1, and the second wide portion 3w2 using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), it is possible to determine whether the first part 3a1 has a crystal structure continuous with the first wide portion 3w1 and whether the second part 3a2 has a crystal structure continuous with the second wide portion 3w2.

[0055] In a region with a width of 40 μm in a second direction perpendicular to a first direction from the first superconducting layer 16 toward the second superconducting layer 26 in a first cross-section perpendicular to the surface of the first superconducting layer 16, the crystal region 31 includes five first paths from the first superconducting layer 16 to the second superconducting layer 26. Each of the first paths includes a plurality of constrictions.

[0056] Also, in a region with a width of 40 μm in the second direction in a second cross-section parallel to the first cross-section, the crystal region 31 includes five second paths from the first superconducting layer 16 to the second superconducting layer 26. Each of the second paths includes a plurality of constrictions.

[0057] Also, in a region with a width of 40 μm in the second direction in a third cross-section parallel to the first cross-section, the crystal region 31 includes five third paths from the first superconducting layer 16 to the second superconducting layer 26. Each of the third paths includes a plurality of constrictions.

[0058] Also, in a region with a width of 40 μm in the second direction in a fourth cross-section parallel to the first cross-section, the crystal region 31 includes five fourth paths from the first superconducting layer 16 to the second superconducting layer 26. Each of the fourth paths includes a plurality of constrictions.

[0059] Also, in a region with a width of 40 μm in the second direction in a fifth cross-section parallel to the first cross-section, the crystal region 31 includes five fifth paths from the first superconducting layer 16 to the second superconducting layer 26. Each of the fifth paths includes a plurality of constrictions.

[0060] For example, the cross-section cut along AA' shown in FIG. 2 is an example of the first cross-section. For example, the cross-section cut along BB' shown in FIG. 2 is an example of the second cross-section. For example, the cross-section cut along CC' shown in FIG. 2 is an example of the third cross-section. For example, the cross-section cut along DD' shown in FIG. 2 is an example of the fourth cross-section. For example, the cross-section cut along EE' shown in FIG. 2 is an example of the fifth cross-section.

[0061] FIG. 5 is an enlarged cross-sectional view of a part of the connection layer of the first embodiment. FIG. 5 is a part of the AA' cross-section shown in FIG. 2. FIG. 5 is an example of the first cross-section. FIG. 5 shows a region with a width of 40 μm in the second direction.

[0062] FIG. 5 includes a SEM image of the connection layer 30 in the AA' cross-section. The connection layer 30 shown in FIG. 5 is binarized using image processing software, and the connection layer 30 is divided into a crystal region 31 and voids 32.

[0063] In FIG. 5, the black region is the crystal region 31. Also, in FIG. 5, the white region is the void 32. Also, in FIG. 5, the white dotted line is the path.

[0064] As shown in FIG. 5, in the region with a width of 40 μm in the second direction of the AA' cross-section, the crystal region 31 includes five first paths 31x1 from the first superconducting layer 16 to the second superconducting layer 26. The five first paths 31x1 do not intersect each other.

[0065] In FIG. 5, the line representing the first path 31x1 is indicated by a dotted line. Each of the first paths 31x1 includes a plurality of constrictions. Note that the crystal region 31 may include six or more first paths 31x1. When the crystal region 31 includes six or more first paths 31x1, for example, any five first paths 31x1 are selected.

[0066] Similar to FIG. 5, in the region with a width of 40 μm in the second direction of the BB' cross-section, the crystal region 31 includes five second paths from the first superconducting layer 16 to the second superconducting layer 26. Also, similar to FIG. 5, in the region with a width of 40 μm in the second direction of the CC' cross-section, the crystal region 31 includes five third paths from the first superconducting layer 16 to the second superconducting layer 26. Also, similar to FIG. 5, in the region with a width of 40 μm in the second direction of the DD' cross-section, the crystal region 31 includes five fourth paths from the first superconducting layer 16 to the second superconducting layer 26. Also, similar to FIG. 5, in the region with a width of 40 μm in the second direction of the EE' cross-section, the crystal region 31 includes five fifth paths from the first superconducting layer 16 to the second superconducting layer 26.

[0067] Among the five first paths, five second paths, five third paths, five fourth paths, and five fifth paths, the proportion of the paths with the width of the minimum constriction being 300 nm or more is, for example, 80% or more.

[0068] Next, an example of a manufacturing method of the connection structure of the superconducting layer of the first embodiment will be described.

[0069] First, an oxide superconductor containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) is formed.

[0070] The oxide superconductor is formed, for example, by a solid-phase reaction method. In the formation of the oxide superconductor, Gd 2 O 3 , BaCO 3、 and CuO powders are mixed and compression-molded to produce a green compact. By sintering the green compact, GdBa 2 Cu 3 O δ (6 ≦ δ ≦ 7) composition of the oxide superconductor is formed. Gd may be replaced with Y, La, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu.

[0071] By pulverizing the oxide superconductor, a plurality of crystal grains are produced. The plurality of crystal grains are heat-treated in an oxygen atmosphere. The plurality of crystal grains are classified to prepare a crystal grain group having a median major axis length of 1 μm or more and 10 μm or less and a unimodal distribution. The median aspect ratio of the crystal grains of the above crystal grain group is, for example, 5 or less.

[0072] Next, the connection layer 30 is formed using the MOD method.

[0073] Gd(OCOCH 3 ) 2 , Ba(OCOCH 3 ) 2 , and Cu(OCOCH 3 ) 2Prepare an organometallic salt solution using the powder. Mix the prepared crystal particle group into the prepared organometallic salt solution. Gd may be replaced with Y, La, Nd, Sm, Eu, Dy, Ho, Er, Tm, Yb, or Lu.

[0074] Next, apply the organometallic salt solution mixed with crystal particles onto the first superconducting layer 16. The organometallic salt solution mixed with crystal particles is a slurry. After drying the first superconducting member 10 with the slurry applied thereon to an appropriate thickness, bake it in oxygen at 700 °C or higher and 850 °C or lower to form the connection layer 30.

[0075] Next, perform the first heat treatment. In the first heat treatment, bake the connection layer 30 formed on the first superconducting layer 16 while sandwiching it between the first superconducting layer 16 and the second superconducting layer 26. In the first heat treatment, apply pressure to the stacked first superconducting layer 16 and the second superconducting layer 26 in the direction from the second superconducting layer 26 toward the first superconducting layer 16.

[0076] In the first heat treatment, by baking the organometallic salt solution at a low oxygen partial pressure of 1000 ppm or less, a constricted portion that connects adjacent crystal particles is formed.

[0077] The firing temperature of the first heat treatment is 720 °C or higher and 850 °C or lower. If the firing temperature is less than 720 °C, the formation of the constricted portion becomes insufficient. Also, if the firing temperature is less than 720 °C, the area ratio of the voids in the connection layer 30 increases. Therefore, the electrical resistance of the connection structure 100 of the superconducting layer increases, and the mechanical strength also decreases.

[0078] Moreover, if the firing temperature of the first heat treatment exceeds 850 °C, the superconducting properties of the first superconducting layer 16, the second superconducting layer 26, and the connection layer 30 disappear.

[0079] The firing is performed while sandwiching the entire connection structure with a metal plate such as stainless steel and applying pressure. The pressure during pressing is 10 MPa or more and 100 MPa or less. If the pressure during pressing is less than 10 MPa, the formation of the constricted portion becomes insufficient, resulting in a high electrical resistance of the connection structure 100 of the superconducting layer and a low mechanical strength. On the other hand, if the pressure during pressing exceeds 100 MPa, the area ratio of the voids in the connection layer 30 becomes less than 30%.

[0080] After the first heat treatment, a second heat treatment is performed. The second heat treatment is an oxygen annealing in an oxygen atmosphere. The second heat treatment is performed, for example, at 500°C.

[0081] During the second heat treatment, oxygen is supplied into the connection layer 30 through the voids 32, and superconducting characteristics are exhibited in the crystal region 31.

[0082] By the above manufacturing method, the first superconducting layer 16 and the second superconducting layer 26 are connected. By the above manufacturing method, the connection structure 100 of the superconducting layer of the first embodiment is formed.

[0083] Next, the operation and the like of the connection structure of the superconducting layer of the first embodiment will be described.

[0084] For example, in a nuclear magnetic resonance apparatus (NMR) or a magnetic resonance imaging apparatus (MRI), a superconducting coil is used to generate a strong magnetic field. The superconducting coil is formed by winding a superconducting wire around a winding frame.

[0085] In order to lengthen the superconducting wire, for example, a plurality of superconducting wires are connected. For example, the ends of two superconducting wires are connected using a connection structure. The connection structure for connecting the superconducting wires is required to have a low electrical resistance and a high mechanical strength. A low electrical resistance means, that is, a high critical current.

[0086] FIG. 6 is an enlarged schematic cross-sectional view of a part of the connection layer of the comparative example. FIG. 6 corresponds to FIG. 3. The connection layer 90 of the comparative example is different from the connection layer 30 of the first embodiment in that the path 31y of the crystal region 31 from the first superconducting layer 16 to the second superconducting layer 26 does not include a constriction.

[0087] As shown in FIG. 6, the connection layer 90 of the comparative example includes a continuous path 31y in which the crystal region 31 extends from the first superconducting layer 16 to the second superconducting layer 26. However, the path 31y is continuous by point contact between two adjacent crystal particles, and no constriction connecting the two adjacent crystal particles is formed.

[0088] The connection layer 90 of the comparative example is manufactured, for example, by not using an organometallic salt solution in the method for manufacturing the connection structure of the superconducting layer of the first embodiment. By not using an organometallic salt solution, no constriction connecting adjacent crystal particles is formed during firing at 850° C. or lower.

[0089] Further, the connection layer 90 of the comparative example is manufactured, for example, by making the median value of the major axis of the crystal particles larger than 10 μm, making the firing temperature lower than 700° C., or making the pressure during pressing less than 10 MPa in the method for manufacturing the connection structure of the superconducting layer of the first embodiment. By making the median value of the major axis of the crystal particles larger than 10 μm, making the firing temperature lower than 700° C., or making the pressure during pressing less than 10 MPa, the formation of constrictions from the organometallic salt solution is suppressed.

[0090] In the connection structure 100 of the superconducting layer of the first embodiment, the crystal region 31 of the connection layer 30 includes a path 31x extending from the first superconducting layer 16 to the second superconducting layer 26. The path 31x includes a plurality of constrictions, and the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more. Also, the area ratio of the voids 32 is 30% or more and 70% or less.

[0091] In the connection layer 30 of the first embodiment, since the path 31x includes a constriction portion where the width of the minimum constriction portion is 300 nm or more, the minimum path width is wider than that of the connection layer 90 of the comparative example in which adjacent crystal particles are in point contact and the path 31y does not include a constriction portion. The wider minimum path width results in a lower electrical resistance of the path. Also, the wider minimum path width results in higher mechanical strength.

[0092] Therefore, the connection layer 30 of the first embodiment can achieve lower electrical resistance and higher mechanical strength compared to the connection layer 90 of the comparative example. Thus, according to the first embodiment, a connection structure 100 of a superconducting layer having low electrical resistance and high mechanical strength can be realized.

[0093] From the viewpoint of realizing a connection structure 100 of a superconducting layer having low electrical resistance and high mechanical strength, the width of the minimum constriction portion is preferably 500 nm or more, and more preferably 700 nm or more.

[0094] From the viewpoint of realizing a connection structure 100 of a superconducting layer having low electrical resistance and high mechanical strength, among the five first paths, five second paths, five third paths, five fourth paths, and five fifth paths included in the connection layer 30, the ratio of the paths in which the width of the minimum constriction portion is 300 nm or more is preferably 80% or more, and more preferably 90% or more.

[0095] From the viewpoint of reducing the area ratio of the crystal region 31 of the connection layer 30 and setting the area ratio of the voids 32 of the connection layer 30 to 30% or more, the width of the minimum constriction portion is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less.

[0096] By setting the area ratio of the voids 32 of the connection layer 30 to 30% or more, during oxygen annealing, oxygen is sufficiently supplied into the connection layer 30. When oxygen is sufficiently supplied, sufficient superconducting characteristics are exhibited in the crystal region 31. Therefore, a connection structure 100 of a superconducting layer having low electrical resistance can be realized.

[0097] From the perspective of realizing the connection structure 100 of the superconducting layer with low electrical resistance, the area ratio of the voids 32 in the connection layer 30 is preferably 35% or more, and more preferably 40% or more.

[0098] Also, by setting the area ratio of the voids 32 in the connection layer 30 to 70% or less, the mechanical strength of the connection layer 30 is maintained. Therefore, the connection structure 100 of the superconducting layer with high mechanical strength can be realized.

[0099] From the perspective of realizing the connection structure 100 of the superconducting layer with high mechanical strength, the area ratio of the voids 32 in the connection layer 30 is preferably 65% or less, and more preferably 60% or less.

[0100] The median value of the equivalent circle diameter of the voids 32 is preferably 200 nm or more and 10 μm or less, and more preferably 500 nm or more and 5 μm or less. By satisfying the lower limit value of the median value of the equivalent circle diameter of the voids 32, the supply of oxygen into the connection layer 30 is promoted during oxygen annealing. Therefore, the connection structure 100 of the superconducting layer with low electrical resistance can be realized. Also, by satisfying the upper limit value of the median value of the equivalent circle diameter of the voids 32, the mechanical strength of the connection structure 100 of the superconducting layer is further improved.

[0101] As described above, according to the connection structure of the superconducting layer of the first embodiment, low electrical resistance and high mechanical strength can be realized.

[0102] (Second Embodiment) The superconducting wire of the second embodiment includes a first superconducting wire including a first superconducting layer, a second superconducting wire including a second superconducting layer, a third superconducting layer, a first connection layer provided between the first superconducting layer and the third superconducting layer and including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) and voids, and a second connection layer provided between the second superconducting layer and the third superconducting layer and including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) and voids. In a cross section perpendicular to the surface of the first superconducting layer, the crystal region of the first connection layer includes a path from the first superconducting layer to the third superconducting layer, the path includes a plurality of constrictions, the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more, and in the cross section, the area ratio of the voids in the first connection layer is 30% or more and 70% or less. The superconducting wire of the second embodiment uses the connection structure of the superconducting layer of the first embodiment as a structure for connecting the first superconducting wire and the second superconducting wire. Hereinafter, for the content overlapping with the first embodiment, some descriptions will be omitted.

[0103] FIG. 7 is a schematic cross-sectional view of the superconducting wire of the second embodiment. The superconducting wire 400 of the second embodiment includes a first superconducting wire 401, a second superconducting wire 402, and a connecting member 403. In the superconducting wire 400 of the second embodiment, the first superconducting wire 401 and the second superconducting wire 402 are connected using the connecting member 403, thereby being lengthened.

[0104] The first superconducting wire 401 includes a first substrate 12, a first intermediate layer 14, a first superconducting layer 16, and a first protective layer 18. The second superconducting wire 402 includes a second substrate 22, a second intermediate layer 24, a second superconducting layer 26, and a second protective layer 28. The connecting member 403 includes a third substrate 42, a third intermediate layer 44, and a third superconducting layer 46.

[0105] The first superconducting wire 401, the second superconducting wire 402, and the connecting member 403 have the same structure as the first superconducting member 10 and the second superconducting member 20 of the first embodiment.

[0106] The connection layer 30 includes a first connection layer 30a and a second connection layer 30b.

[0107] The first connection layer 30a is provided between the first superconducting layer 16 and the third superconducting layer 46. The first connection layer 30a is in contact with the first superconducting layer 16. The first connection layer 30a is in contact with the third superconducting layer 46.

[0108] The second connection layer 30b is provided between the second superconducting layer 26 and the third superconducting layer 46. The second connection layer 30b is in contact with the second superconducting layer 26. The second connection layer 30b is in contact with the third superconducting layer 46.

[0109] The first connection layer 30a between the first superconducting layer 16 and the third superconducting layer 46 and the second connection layer 30b between the second superconducting layer 26 and the third superconducting layer 46 are continuous.

[0110] The connection layer 30, for example, does not exist between the first superconducting layer 16 and the second superconducting layer 26. Between the first superconducting layer 16 and the second superconducting layer 26 is, for example, an air gap. Also, the first superconducting layer 16 and the second superconducting layer 26 may be in contact.

[0111] 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, for example, includes a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O). The connection layer 30, for example, includes 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), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0112] The connection layer 30 of the second embodiment has the same configuration as the connection layer 30 of the first embodiment shown in FIG. 3.

[0113] FIG. 8 is an enlarged schematic cross-sectional view of a part of the first connection layer of the second embodiment. FIG. 8 corresponds to FIG. 3 of the first embodiment.

[0114] The first connection layer 30a of the second embodiment differs from the connection layer 30 of the first embodiment only in that the second superconducting layer 26 in FIG. 3 is replaced by the third superconducting layer 46.

[0115] FIG. 9 is an enlarged schematic cross-sectional view of a part of the second connection layer of the second embodiment. FIG. 9 corresponds to FIG. 3 of the first embodiment.

[0116] The second connection layer 30b of the second embodiment differs from the connection layer 30 of the first embodiment only in that the first superconducting layer 16 in FIG. 3 is replaced by the second superconducting layer 26 and the second superconducting layer 26 in FIG. 3 is replaced by the third superconducting layer 46.

[0117] In the superconducting wire 400 of the second embodiment, for example, current flows from the first superconducting wire 401 through the first connection layer 30a, the connection member 403, and the second connection layer 30b to the second superconducting wire 402.

[0118] By connecting the first superconducting wire 401 and the connection member 403 using the first connection layer 30a, the connection structure connecting the first superconducting wire 401 and the connection member 403 has low electrical resistance and high mechanical strength. Also, by connecting the second superconducting wire 402 and the connection member 403 using the second connection layer 30b, the connection structure connecting the second superconducting wire 402 and the connection member 403 has low electrical resistance and high mechanical strength.

[0119] Therefore, the connection structure connecting the first superconducting wire 401 and the second superconducting wire 402 has low electrical resistance and high mechanical strength. Thus, the superconducting wire 400 has low electrical resistance and high mechanical strength.

[0120] It is also possible to connect three or more superconducting wires to form a longer superconducting wire.

[0121] (First modification example) FIG. 10 is a schematic cross-sectional view of a first modification example of the superconducting wire of the second embodiment. The superconducting wire 410 of the first modification example of the second embodiment is different from the superconducting wire 400 of the second embodiment in that it includes a reinforcing member 60.

[0122] The reinforcing member 60 is provided between the first superconducting wire 401 and the second superconducting wire 402. The reinforcing member 60 is provided, for example, between the first superconducting layer 16 and the second superconducting layer 26.

[0123] The reinforcing member 60 is in contact with, for example, the first superconducting wire 401 and the second superconducting wire 402. The reinforcing member 60 is in contact with, for example, the connection layer 30.

[0124] By providing the reinforcing member 60, the mechanical strength of the superconducting wire 410 is improved.

[0125] The reinforcing member 60 is, for example, a metal or a resin. The reinforcing member 60 is, for example, solder. The reinforcing member 60 is, for example, solder containing silver (Ag) and indium (In).

[0126] (Second modification example) FIG. 11 is a schematic cross-sectional view of a second modification example of the superconducting wire of the second embodiment. The superconducting wire 420 of the second modification example of the second embodiment is different from the superconducting wire 400 of the second embodiment in that the first connection layer 30a and the second connection layer 30b are separated from each other.

[0127] The first connection layer 30a and the second connection layer 30b are separated.

[0128] (Third modification example) FIG. 12 is a schematic cross-sectional view of a third modification of the superconducting wire of the second embodiment. The superconducting wire 430 of the third modification of the second embodiment is different from the superconducting wire 420 of the second modification of the second embodiment in that a part of the surface of the first superconducting layer 16 facing the third superconducting layer 46 is exposed, and a part of the surface of the second superconducting layer 26 facing the third superconducting layer 46 is exposed.

[0129] There is a region where the connection layer 30 does not exist near the end of the upper surface of the first superconducting layer 16 on the side of the second superconducting layer 26. Also, there is a region where the connection layer 30 does not exist near the end of the upper surface of the second superconducting layer 26 on the side of the first superconducting layer 16.

[0130] (Fourth Modification) FIG. 13 is a schematic cross-sectional view of a fourth modification of the superconducting wire of the second embodiment. The superconducting wire 440 of the fourth modification of the second embodiment is different from the superconducting wire 430 of the third modification of the second embodiment in that it includes a reinforcing member 60.

[0131] The reinforcing member 60 is provided between the first superconducting wire 401 and the second superconducting wire 402. The reinforcing member 60 is provided, for example, between the first superconducting layer 16 and the second superconducting layer 26. The reinforcing member 60 is provided, for example, between the first superconducting layer 16 and the third superconducting layer 46. The reinforcing member 60 is provided, for example, between the second superconducting layer 26 and the third superconducting layer 46. The reinforcing member 60 is provided, for example, between the first connection layer 30a and the second connection layer 30b.

[0132] By providing the reinforcing member 60, the mechanical strength of the superconducting wire 440 is improved.

[0133] The reinforcing member 60 is, for example, a metal or a resin. The reinforcing member 60 is, for example, solder. The reinforcing member 60 is, for example, solder containing silver (Ag) and indium (In).

[0134] As described above, according to the second embodiment and the modifications, a superconducting wire having a low electrical resistance and a high mechanical strength, which is lengthened by connecting two superconducting wires, can be realized.

[0135] (Third Embodiment) The superconducting coil of the third embodiment includes the superconducting wire of the second embodiment. Hereinafter, some descriptions may be omitted for the content overlapping with the second embodiment.

[0136] FIG. 14 is a schematic perspective view of the superconducting coil of the third embodiment. FIG. 15 is a schematic cross-sectional view of the superconducting coil of the third embodiment.

[0137] The superconducting coil 700 of the third embodiment is used, for example, as a coil for generating a magnetic field in a superconducting device such as an NMR, an MRI, a heavy particle beam therapy device, or a superconducting magnetic levitation railway vehicle.

[0138] The superconducting coil 700 includes a bobbin 110, a first insulating plate 111a, a second insulating plate 111b, and a winding portion 112. The winding portion 112 has a superconducting wire 120 and an inter-wire layer 130.

[0139] FIG. 14 shows a state excluding the first insulating plate 111a and the second insulating plate 111b.

[0140] The bobbin 110 is formed of, for example, a fiber-reinforced plastic. The superconducting wire 120 is, for example, in a tape shape. As shown in FIG. 14, the superconducting wire 120 is wound around the bobbin 110 in a concentric so-called pancake shape centered on the winding central axis C.

[0141] In FIG. 14, the first direction is the coil diameter direction. The second direction is the coil circumferential direction. The first direction is the direction in which the winding central axis C extends.

[0142] The inter-wire layer 130 has a function of fixing the superconducting wire 120. The inter-wire layer 130 has a function of suppressing the superconducting wire 120 from being destroyed by vibrations during the use of the superconducting device or by mutual friction.

[0143] 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 a 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.

[0144] For the superconducting wire 120, the superconducting wire of the second embodiment is used.

[0145] As described above, according to the third embodiment, by providing a superconducting wire having low electrical resistance and high mechanical strength, a superconducting coil with improved characteristics can be realized.

[0146] (Fourth Embodiment) The superconducting device of the fourth embodiment is a superconducting device including the superconducting coil of the third embodiment. Hereinafter, descriptions of parts overlapping with the third embodiment will be partially omitted.

[0147] FIG. 16 is a block diagram of the superconducting device of the fourth embodiment. The superconducting device of the fourth embodiment is a heavy particle beam therapy device 800. The heavy particle beam therapy device 800 is an example of a superconducting device.

[0148] The heavy particle beam therapy device 800 includes an incident system 50, a synchrotron accelerator 52, a beam transport system 54, an irradiation system 56, and a control system 58.

[0149] The incident system 50 has a function of, for example, generating carbon ions used for treatment and performing preliminary acceleration for incidence on the synchrotron accelerator 52. The incident system 50 includes, for example, an ion source and a linear accelerator.

[0150] The synchrotron accelerator 52 has a function of accelerating the carbon ion beam incident from the incident system 50 to an energy suitable for treatment. The superconducting coil 700 of the third embodiment is used for the synchrotron accelerator 52.

[0151] The beam transport system 54 has a function of transporting the carbon ion beam incident from the synchrotron accelerator 52 to the irradiation system 56. The beam transport system 54 has, for example, a deflection electromagnet.

[0152] The irradiation system 56 has a function of irradiating a patient, who is an irradiation target, with the carbon ion beam incident 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 an arbitrary direction. The superconducting coil 700 of the third embodiment is used for the rotating gantry.

[0153] The control system 58 controls the incident 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.

[0154] In the heavy particle beam therapy apparatus 800 of the fourth embodiment, the superconducting coil 700 of the third embodiment is used for the synchrotron accelerator 52 and the rotating gantry. Therefore, the heavy particle beam therapy apparatus 800 with excellent characteristics is realized.

[0155] In the fourth embodiment, the case of the heavy particle beam therapy apparatus 800 is described as an example of the superconducting device. However, the superconducting device may be a nuclear magnetic resonance apparatus (NMR), a magnetic resonance imaging apparatus (MRI), or a superconducting magnetic levitation railway vehicle.

Example

[0156] (Example 1) Two long oxide superconducting wires with a length of 10 cm and one short oxide superconducting wire with a length of 10 mm were prepared. In each oxide superconducting wire, an intermediate layer and a GdBa 2 Cu 3 O δ layer (oxide superconducting layer) were formed, and the oxide superconducting layer was covered with a protective layer of silver and copper. The protective layer of a 1.5-cm portion from the ends of the two long superconducting wires and the protective layer of the entire surface of the short superconducting wire were wet-etched using a mixed solution of nitric acid, ammonia, and hydrogen peroxide to expose the oxide superconducting layer.

[0157] Gd 2 O 3 and BaCO 3 Powders of and CuO were prepared, weighed appropriately, and then thoroughly mixed to produce a mixed powder. The mixed powder was heat-treated at 900 °C to obtain a calcined body. The calcined body was pulverized, and the obtained powder was compression-molded to produce a compact.

[0158] By sintering the obtained compact at 960 °C, a GdBa 2 Cu 3 O δ (6 ≤ δ ≤ 7) composition oxide superconductor was produced. The obtained oxide superconductor was wet-pulverized to produce a plurality of crystal particles. The plurality of crystal particles were heat-treated in an oxygen atmosphere at 470 °C. After the heat treatment, the crystal particles were sorted by a sieve or the like to produce a group of crystal particles (superconductor powder) of the superconductor having a median major axis of 2.1 μm.

[0159] The obtained superconductor powder was mixed with a solution (organometallic salt solution) mainly composed of an organic compound containing the same kind of metal element as the superconductor powder to produce a slurry. The superconductor powder and the solution were mixed at a weight ratio of 2:1.

[0160] The obtained slurry was applied to the exposed oxide superconductor layer of the above short superconducting wire, and after drying, it was fired at 800 °C. Then, the exposed portions of the superconducting layers of the two long superconducting wires were placed adjacent to each other with the superconducting layers facing upward, and the slurry surfaces of the superconducting wires coated with the slurry were overlapped.

[0161] The overlapped superconducting wires were sandwiched between metal plates from above and below and fixed at a pressure value of 70 MPa.

[0162] Next, the first heat treatment was performed. In the first heat treatment, while the superconducting wire was sandwiched between metal plates, it was heated to 820 °C at a low oxygen partial pressure.

[0163] Next, a second heat treatment was performed. In the second heat treatment, oxygen gas was introduced into the furnace, and the superconducting wire was heated to 450 °C in an oxygen atmosphere. By the second heat treatment, a connection structure of the superconducting wire was formed.

[0164] The characteristics of the obtained connection structure of the superconducting wire were evaluated. As indices of electrical resistance and mechanical strength, the critical current value Ic at 77 K and the critical current value at 77 K when bent at R = 15 cm were evaluated. Terminals were attached to both ends of the superconducting wire after connection, and the critical current value was measured.

[0165] Taking the critical current value at 77 K of this connection structure as the reference value 1.0, the relative critical current values in the following examples and comparative examples are shown.

[0166] Furthermore, taking the critical current value at 77 K when this connection structure was bent at R = 15 cm as the reference value 1.0, the relative critical current values when the connection structures in the following examples and comparative examples were bent in the same manner are shown.

[0167] This connection structure was cut with a cross-section perpendicular to the surface of the superconducting wire, and SEM observation and STEM observation were performed.

[0168] From the SEM image including the entire thickness of the connection layer and the region where the width of the connection layer was 40 μm, using image processing software, the crystal region and voids of the connection layer were distinguished by binarization. After calculating their respective areas, the void ratio (area ratio of voids) was calculated.

[0169] Also, regarding the voids, the equivalent circular diameter of the closed voids was calculated, and the median value of the equivalent circular diameters of all the voids was calculated.

[0170] In the above SEM image, a path including a plurality of constrictions passing through the crystal region was traced from the upper and lower superconducting layers sandwiching the connection layer, and the width of the minimum constriction having the minimum width among the constrictions and the length of the path were measured. From the measured length of the path, the ratio of the length of the path to the thickness of the connection layer was calculated.

[0171] In the SEM images, five shortest non-intersecting paths were traced for each. Four SEM images of similar connection layers were prepared, and five shortest paths passing through the crystal regions were traced for each. The minimum width of each constriction of the obtained 25 paths was examined, and the ratio of the paths with a minimum constriction width of 300 nm or more was calculated.

[0172] When the minimum constriction was observed by STEM, it was confirmed that the first widened portion and the second widened portion, which exist sandwiching the constriction, each had a crystal structure continuous with the constriction.

[0173] These characteristics and the results of the image processing are shown in Table 1.

[0174] (Example 2) A connection structure was formed and evaluated in the same manner as in Example 1, except that the first heat treatment temperature was set to 840°C.

[0175] (Example 3) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconducting powder with a median major axis of 8.0 μm was produced and the pressure value was set to 50 MPa.

[0176] (Example 4) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconducting powder with a median major axis of 5.0 μm was produced and the pressure value was set to 50 MPa.

[0177] (Example 5) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconducting powder with a median major axis of 3.5 μm was produced.

[0178] (Example 6) A connection structure was formed and evaluated in the same manner as in Example 1, except that the pressure value was set to 100 MPa.

[0179] (Example 7) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconducting powder with a median major axis of 10 μm was produced and the pressure value was set to 50 MPa.

[0180] (Example 8) A connection structure was formed and evaluated in the same manner as in Example 1, except that the pressure value was set to 60 MPa.

[0181] (Example 9) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconducting powder with a median major axis of 8.0 μm was produced.

[0182] (Example 10) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconducting powder with a median major axis of 3.5 μm was produced and the pressure value was set to 50 MPa.

[0183] (Example 11) An oxide superconducting wire having an intermediate layer and a YBa 2 Cu 3 O δ layer formed thereon was used, and Y 2 O 3 was used instead of Gd 2 O 3 to produce an oxide superconductor with a composition of YBa 2 Cu 3 O δ (6 ≦ δ ≦ 7). A connection structure was formed and evaluated in the same manner as in Example 1, except that a solution mainly composed of an organic compound containing the same metal elements as the obtained superconducting powder was used.

[0184] (Example 12) An oxide superconducting wire having an intermediate layer and an EuBa 2 Cu 3 O δ layer formed thereon was used, and Eu 2 O 3 was used instead of Gd 2 O 3 to produce EuBa 2 Cu 3 Oδ A connection structure was formed and evaluated in the same manner as in Example 1, except that an oxide superconductor having a composition of (6 ≦ δ ≦ 7) was produced and a solution mainly composed of an organic compound containing the same metal elements as the obtained superconductor powder was used.

[0185] (Comparative Example 1) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconductor powder having a median major axis of 500 nm was produced. In this connection structure, the width of the minimum constriction portion was narrow.

[0186] (Comparative Example 2) A connection structure was formed and evaluated in the same manner as in Example 1, except that ethanol was used instead of the solution mainly composed of the organic compound containing the metal element and the first heat treatment temperature was set to 950°C. In this connection structure, although there were very few voids and it was a dense connection layer, the superconducting characteristics of the superconducting layer of the superconducting wire disappeared because the heat treatment temperature was high.

[0187] (Comparative Example 3) A connection structure was formed and evaluated in the same manner as in Example 1, except that the pressure value was set to 120 MPa. In this connection structure, the void ratio of the connection layer was low.

[0188] (Comparative Example 4) A connection structure was formed and evaluated in the same manner as in Example 1, except that superconductor powder having a median major axis of 5.0 μm was produced and the first heat treatment temperature was set to 700°C. In this connection structure, the void ratio of the connection layer was high.

[0189] From the above, in Examples 1 to 12 where the width of the minimum constriction portion, which has the smallest width among the plurality of constriction portions in a path passing through the crystal region from the upper and lower superconducting layers sandwiching the connection layer and including a plurality of constriction portions, is 300 nm or more, and the area ratio of the voids contained in the connection layer is 30% or more and 70% or less, it was found that they have lower electrical resistance and higher mechanical strength than Comparative Example 1 where the width of the minimum constriction portion is narrower than 300 nm, Comparative Example 2 and Comparative Example 3 where the void ratio is lower than 30%, and Comparative Example 4 where the void ratio is higher than 70%.

[0190] In addition, in Examples 1 to 5, 11, and 12 described in Table 1, the median value of the voids in terms of a circle is 200 nm or more and 10 μm or less, the length of the path with respect to the thickness of the connection layer is 1.2 or more and 3.0 or less, and the ratio of the paths with a minimum constriction width of 300 nm or more is 80% or more. These examples have a higher relative critical current value at 77K or a higher relative critical current value at 77K during bending than Examples 6 to 10 that deviate from any of the above ranges. Therefore, it was found that Examples 1 to 5, 11, and 12 have a lower electrical resistance or a higher mechanical strength as compared with Examples 6 to 10.

[0191]

Table 1

[0192] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. For example, the components of one embodiment may be replaced or changed with those of another embodiment. These embodiments and their modifications are included in the scope and gist of the invention and are included in the invention described in the claims and its equivalent scope.

[0193] Hereinafter, the technical solutions of the present invention will be described. The following technical solutions are included in the scope of the present invention.

[0194] (Technical Solution 1) a first superconducting layer, a second superconducting layer, a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids, in a cross section perpendicular to the surface of the first superconducting layer, the crystal region includes a path from the first superconducting layer to the second superconducting layer, The path includes a plurality of constrictions, and the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more. In the cross section, the area ratio of the voids is 30% or more and 70% or less, and it is a connection structure of a superconducting layer. (Technical solution 2) The width of the minimum constriction is 3 μm or less, and it is a connection structure of a superconducting layer according to Technical solution 1. (Technical solution 3) In the cross section, the median value of the circle-equivalent diameter of the voids is 200 nm or more and 10 μm or less, and it is a connection structure of a superconducting layer according to Technical solution 1 or Technical solution 2. (Technical solution 4) The length of the path is longer than the thickness of the connection layer in the first direction from the first superconducting layer to the second superconducting layer, and it is a connection structure of a superconducting layer according to any one of Technical solutions 1 to 3. (Technical solution 5) The minimum constriction is provided between a first wide portion and a second wide portion. The minimum constriction includes a first portion having a crystal structure continuous with the first wide portion and a second portion having a crystal structure continuous with the second wide portion, and it is a connection structure of a superconducting layer according to any one of Technical solutions 1 to 4. (Technical solution 6) In a region with a width of 40 μm in a second direction perpendicular to a first direction from the first superconducting layer to the second superconducting layer in a first cross section perpendicular to the surface of the first superconducting layer, the crystal region includes five first paths from the first superconducting layer to the second superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the second direction in a second cross section parallel to the first cross section, the crystal region includes five second paths from the first superconducting layer to the second superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the second direction in a third cross section parallel to the first cross section, the crystal region includes five third paths from the first superconducting layer to the second superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the fourth cross-section parallel to the first cross-section, in the second direction, the crystal region includes five fourth paths extending from the first superconducting layer to the second superconducting layer and including a plurality of constrictions. In a region with a width of 40 μm in the fifth cross-section parallel to the first cross-section, in the second direction, the crystal region includes five fifth paths extending from the first superconducting layer to the second superconducting layer and including a plurality of constrictions. Among the five first paths, the five second paths, the five third paths, the five fourth paths, and the five fifth paths, the ratio of the paths in which the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more is 80% or more. The superconducting layer connection structure according to any one of Technical Solutions 1 to 5. (Technical Solution 7) A first superconducting wire including a first superconducting layer, A second superconducting wire including a second superconducting layer, A third superconducting layer, A first connection layer provided between the first superconducting layer and the third superconducting layer, including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids, A second connection layer provided between the second superconducting layer and the third superconducting layer, including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids, In a cross-section perpendicular to the surface of the first superconducting layer, the crystal region of the first connection layer includes a path extending from the first superconducting layer to the third superconducting layer, The path includes a plurality of constrictions, and the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more, In the cross-section, the area ratio of the voids in the first connection layer is 30% or more and 70% or less. The superconducting wire. (Technical Solution 8) The width of the minimum constriction is 3 μm or less. The superconducting wire according to Technical Solution 7. (Technical Solution 9) In the cross-section, the median value of the circular conversion diameter of the voids in the first connection layer is 200 nm or more and 10 μm or less, the superconducting wire according to Technical Proposal 7 or Technical Proposal 8. (Technical Proposal 10) The length of the path is longer than the thickness of the first connection layer in the first direction from the first superconducting layer to the third superconducting layer, the superconducting wire according to any one of Technical Proposals 7 to 9. (Technical Proposal 11) The minimum constriction portion is provided between the first wide portion and the second wide portion. The minimum constriction portion includes a first portion having a crystal structure continuous with the first wide portion and a second portion having a crystal structure continuous with the second wide portion, the superconducting wire according to any one of Technical Proposals 7 to 10. (Technical Proposal 12) In a region with a width of 40 μm in a second direction perpendicular to the first direction from the first superconducting layer to the second superconducting layer in a first cross-section perpendicular to the surface of the first superconducting layer, the crystal region includes five first paths extending from the first superconducting layer to the third superconducting layer and including a plurality of constriction portions. In a region with a width of 40 μm in the second direction in a second cross-section parallel to the first cross-section, the crystal region includes five second paths extending from the first superconducting layer to the third superconducting layer and including a plurality of constriction portions. In a region with a width of 40 μm in the second direction in a third cross-section parallel to the first cross-section, the crystal region includes five third paths extending from the first superconducting layer to the third superconducting layer and including a plurality of constriction portions. In a region with a width of 40 μm in the second direction in a fourth cross-section parallel to the first cross-section, the crystal region includes five fourth paths extending from the first superconducting layer to the third superconducting layer and including a plurality of constriction portions. In a region with a width of 40 μm in the second direction in a fifth cross-section parallel to the first cross-section, the crystal region includes five fifth paths extending from the first superconducting layer to the third superconducting layer and including a plurality of constriction portions. Among the five first paths, the five second paths, the five third paths, the five fourth paths, and the five fifth paths, the ratio of the paths in which the width of the minimum constriction among the plurality of constrictions is 300 nm or more is 80% or more. The superconducting wire according to any one of Technical Solutions 7 to 11. (Technical Solution 13) In a cross-section perpendicular to the surface of the second superconducting layer, the crystal region includes a path from the second superconducting layer to the third superconducting layer. The path includes a plurality of constrictions, and the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more. In the cross-section, the area ratio of the voids in the second connection layer is 30% or more and 70% or less. The superconducting wire according to any one of Technical Solutions 7 to 12. (Technical Solution 14) A superconducting coil including the superconducting wire according to any one of Technical Solutions 7 to 13. (Technical Solution 15) A superconducting device including the superconducting coil according to Technical Solution 14.

Explanation of Reference Numerals

[0195] 3a First constriction (constriction, minimum constriction) 3a1 First part 3a2 Second part 3b Second constriction (constriction) 3c Third constriction (constriction) 3w1 First wide part 3w2 Second wide part 16 First superconducting layer 26 Second superconducting layer 30 Connection layer 30a First connection layer 30b Second connection layer 31 Crystal region 31x Path 31x1 First path 32 Void 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 device (superconducting device) t Thickness

Claims

1. a first superconducting layer, a second superconducting layer, a connection layer provided between the first superconducting layer and the second superconducting layer, the connection layer including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids, in a cross-section perpendicular to the surface of the first superconducting layer, the crystal region includes a path from the first superconducting layer to the second superconducting layer, the path includes a plurality of constrictions, and the width of the minimum constriction having the smallest width among the plurality of constrictions is 300 nm or more, in the cross-section, the area ratio of the voids is 30% or more and 70% or less, a connection structure of a superconducting layer.

2. The connection structure of the superconducting layer according to claim 1, wherein the width of the minimum constriction is 3 μm or less.

3. The connection structure of the superconducting layer according to claim 1, wherein in the cross-section, the median value of the circle-equivalent diameter of the voids is 200 nm or more and 10 μm or less.

4. The connection structure of the superconducting layer according to claim 1, wherein the length of the path is longer than the thickness of the connection layer in a first direction from the first superconducting layer to the second superconducting layer.

5. The minimum constriction is provided between a first wide portion and a second wide portion, the minimum constriction includes a first portion having a crystal structure continuous with the first wide portion and a second portion having a crystal structure continuous with the second wide portion, the connection structure of the superconducting layer according to claim 1.

6. In a region having a width of 40 μm in a second direction perpendicular to a first direction from the first superconducting layer to the second superconducting layer in a first cross-section perpendicular to the surface of the first superconducting layer, the crystal region includes five first paths from the first superconducting layer to the second superconducting layer and including a plurality of constrictions, In a region having a width of 40 μm in the second direction in a second cross-section parallel to the first cross-section, the crystal region includes five second paths from the first superconducting layer to the second superconducting layer and including a plurality of constrictions, In a region having a width of 40 μm in the second direction in a third cross-section parallel to the first cross-section, the crystal region includes five third paths from the first superconducting layer to the second superconducting layer and including a plurality of constrictions, In a region having a width of 40 μm in the second direction in a fourth cross-section parallel to the first cross-section, the crystal region includes five fourth paths from the first superconducting layer to the second superconducting layer and including a plurality of constrictions, In a region with a width of 40 μm in the fifth cross-section parallel to the first cross-section and in the second direction, the crystal region includes five fifth paths extending from the first superconducting layer to the second superconducting layer and including a plurality of constrictions. Among the five first paths, the five second paths, the five third paths, the five fourth paths, and the five fifth paths, the ratio of the paths in which the width of the narrowest constriction among the plurality of constrictions is 300 nm or more is 80% or more. The superconducting layer connection structure according to claim 1.

7. A first superconducting wire including a first superconducting layer, A second superconducting wire including a second superconducting layer, A third superconducting layer, A first connection layer provided between the first superconducting layer and the third superconducting layer and including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids, A second connection layer provided between the second superconducting layer and the third superconducting layer and including a crystal region containing a rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and voids. In a cross-section perpendicular to the surface of the first superconducting layer, the crystal region of the first connection layer includes a path extending from the first superconducting layer to the third superconducting layer. The path includes a plurality of constrictions, and the width of the narrowest constriction having the smallest width among the plurality of constrictions is 300 nm or more. In the cross-section, the area ratio of the voids in the first connection layer is 30% or more and 70% or less. The superconducting wire.

8. The superconducting wire according to claim 7, wherein the width of the narrowest constriction is 3 μm or less.

9. In the cross-section, the median value of the circular equivalent diameter of the voids in the first connection layer is 200 nm or more and 10 μm or less. The superconducting wire according to claim 7.

10. The length of the path is longer than the thickness of the first connection layer in the first direction from the first superconducting layer to the third superconducting layer. The superconducting wire according to claim 7.

11. The narrowest constriction is provided between a first wide portion and a second wide portion. The narrowest constriction includes a first portion having a crystal structure continuous with the first wide portion and a second portion having a crystal structure continuous with the second wide portion. The superconducting wire according to claim 7.

12. In a region with a width of 40 μm in a second direction perpendicular to a first direction from the first superconducting layer toward the second superconducting layer in a first cross section perpendicular to the surface of the first superconducting layer, the crystal region includes five first paths from the first superconducting layer to the third superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the second direction in a second cross section parallel to the first cross section, the crystal region includes five second paths from the first superconducting layer to the third superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the second direction in a third cross section parallel to the first cross section, the crystal region includes five third paths from the first superconducting layer to the third superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the second direction in a fourth cross section parallel to the first cross section, the crystal region includes five fourth paths from the first superconducting layer to the third superconducting layer and includes a plurality of constrictions. In a region with a width of 40 μm in the second direction in a fifth cross section parallel to the first cross section, the crystal region includes five fifth paths from the first superconducting layer to the third superconducting layer and includes a plurality of constrictions. Among the five first paths, the five second paths, the five third paths, the five fourth paths, and the five fifth paths, the ratio of the paths in which the width of the minimum constriction having the minimum width among the plurality of constrictions is 300 nm or more is 80% or more. The superconducting wire according to claim 7.

13. In a cross section perpendicular to the surface of the second superconducting layer, the crystal region includes a path from the second superconducting layer to the third superconducting layer. The path includes a plurality of constrictions, and the width of the minimum constriction having the minimum width among the plurality of constrictions is 300 nm or more. In the cross section, the area ratio of the voids in the second connection layer is 30% or more and 70% or less. The superconducting wire according to claim 7.

14. A superconducting coil comprising the superconducting wire according to claim 7.

15. A superconducting device comprising the superconducting coil according to claim 14.

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