Patent Publication Number: US-2019172612-A1

Title: Oxide superconducting wire

Description:
TECHNICAL FIELD 
     The present invention relates to an oxide superconducting wire. 
     Priority is claimed on Japanese Patent Application No. 2016-156430, filed on Aug. 9, 2016, the content of which is incorporated herein by reference. 
     BACKGROUND 
     An RE-Ba—Cu—O based superconductor (here, RE represents a rare earth element) represented by a general formula such as REBa 2 Cu 3 O X  (RE123) shows superconductivity at a temperature (to 90 K) exceeding a liquid nitrogen temperature (77 K). Since this oxide superconductor has a higher critical current density in a magnetic field than other high temperature superconductors, applications to coils, power cables, and the like are expected. A superconducting wire using this oxide superconductor is manufactured by forming an intermediate layer on a substrate, forming an oxide superconducting layer on a surface thereof, and further forming a protective layer of Ag, Cu, or the like on a surface thereof (see, for example, Patent Document 1). 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2015-146318 
     In a case of using an oxide superconducting wire as a coil by impregnating it with a resin, there is a possibility of peeling stress acting to deteriorate the wire, due to a thermal shrinkage difference between the wire and the resin when it is cooled to a temperature exhibiting superconductivity, or hoop stress during conducting. 
     SUMMARY 
     Embodiments of the present invention provide an oxide superconducting wire capable of preventing an oxide superconducting layer and the like from peeling, even if a force such as heat shrinkage acts on a superconducting wire as a structure in which the superconducting wire is processed as a superconducting coil and is solidified with an impregnating resin. 
     According to one or more embodiments of the present invention, an oxide superconducting wire includes a superconducting laminate including a tape-shaped substrate, an intermediate layer provided on one face of the substrate, an oxide superconducting layer provided on the intermediate layer, and a protective layer covering a surface of the oxide superconducting layer, in which two of the superconducting laminates are disposed to be superposed on each other in a thickness direction, and the two superconducting laminates are integrated by a metal layer which is provided at least on both lateral faces of the two superconducting laminates in a width direction, such that the two superconducting laminates form a non-fixed portion therebetween which is not fixed in a longitudinal direction of the superconducting laminate. 
     The superconducting laminate may include a stabilizing layer using plating. 
     The metal layer may be a tape-shaped metal foil, and the metal foil and the superconducting laminate may be bonded with a bonding material therebetween. 
     The metal foil may be a metal foil having higher strength than a copper foil. 
     The non-fixed portion may include a non-adhesive layer that is non-adhesive with respect to the bonding material. 
     The metal layer may be formed using plating. 
     The non-fixed portion may include a non-adhesive layer that is non-adhesive with respect to the plating when forming the metal layer. 
     The non-adhesive layer may be a tape having no adhesion strength at a temperature lower than a temperature at which the non-adhesive layer has adhesion strength. 
     The non-adhesive layer may be formed of an oxide film. 
     The non-adhesive layer may be formed of a silicone resin or a fluororesin. 
     According to one or more embodiments of the present invention, it is possible to prevent an oxide superconducting layer and the like from peeling, even if stress such as heat shrinkage acts on a superconducting wire as a structure in which the superconducting wire is processed as a superconducting coil and is solidified with an impregnating resin. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating an oxide superconducting wire according to one or more embodiments. 
         FIG. 2  is a cross-sectional view illustrating an oxide superconducting wire according to one or more embodiments. 
         FIG. 3  is a cross-sectional view illustrating an oxide superconducting wire according to one or more embodiments. 
         FIG. 4  is a cross-sectional view illustrating an oxide superconducting wire according to one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the present invention will be described based on embodiments with reference to the drawings. 
       FIG. 1  shows a cross-sectional view of an oxide superconducting wire according to one or more embodiments. The cross-sectional view shown in  FIG. 1  schematically shows a structure of a cross section perpendicular to a longitudinal direction of an oxide superconducting wire  10 . The oxide superconducting wire  10  includes two superconducting laminates  16  and  16 , a metal foil  17  provided on the periphery of the superconducting laminates  16  and  16 , and a bonding material  18  bonding the metal foil  17  to the periphery of the superconducting laminates  16  and  16 . 
     The superconducting laminate  16  has a configuration in which a tape-shaped substrate  11 , and an intermediate layer  12 , an oxide superconducting layer  13 , and a protective layer  14  which are laminated in that order on one face (first face) of the substrate  11 . 
     In other words, the superconducting laminate  16  includes the tape-shaped substrate  11 , the intermediate layer  12  provided on one face of the substrate  11 , the oxide superconducting layer  13  provided on the intermediate layer  12 , and the protective layer  14  covering a surface of the oxide superconducting layer  13 . 
     In addition, the superconducting laminate  16  may further have a stabilizing layer  15  using plating. 
     In the present specification, a direction in which the layers such as the substrate  11 , the intermediate layer  12 , the oxide superconducting layer  13 , and the protective layer  14  are laminated is a thickness direction (a thickness direction of the oxide superconducting wire and a thickness direction of the superconducting laminate). In addition, a width direction (a width direction of the oxide superconducting wire and a width direction of the superconducting laminate) is a direction perpendicular to a longitudinal direction and the thickness direction (of the oxide superconducting wire and the superconducting laminate). A lateral face of the superconducting laminate is each lateral face (one lateral face or both lateral faces) on both sides in the width direction. 
     The substrate  11  is a tape-shaped metal substrate and has main faces (one face and a back face opposite the one face) on both sides in the thickness direction. Specific examples of the metal forming the substrate  11  include a nickel alloy represented by Hastelloy (registered trademark), stainless steel, and an oriented Ni—W alloy obtained by introducing a texture to a nickel alloy. A thickness of the substrate  11  may be appropriately adjusted according to a purpose, for example, in a range of 10 to 500 μm. In order to improve the bonding property with respect to the bonding material  18 , a metal thin film of Ag, Cu, or the like may be further formed on the back face, the lateral face, or both the back face and the lateral face of the substrate  11 . In addition, this metal thin film (second protective layer) may be integrated with the protective layer  14  formed on the surface of the oxide superconducting layer  13 . 
     The intermediate layer  12  is provided between the substrate  11  and the oxide superconducting layer  13 . The intermediate layer  12  may have a multilayer structure. For example, as the intermediate layer  12 , a diffusion prevention layer, a bed layer, a textured layer, a cap layer, and the like may be laminated on the substrate  11  in order from the substrate  11  to the oxide superconducting layer  13 . Each of the layers forming the intermediate layer  12  is not necessarily provided one by one, and there may be a case where some layers are omitted, or a case where two or more layers having the same type are repeatedly laminated. 
     The diffusion prevention layer has a function of preventing a part of a component of the substrate  11  from diffusing and mixing into the oxide superconducting layer  13  as impurities. The diffusion prevention layer is formed of, for example, Si 3 N 4 , Al 2 O 3 , and GZO (Gd 2 Zr 2 O 7 ). A thickness of the diffusion prevention layer is, for example, 10 to 400 nm. 
     On the diffusion prevention layer, the bed layer may be formed in order to reduce a reaction at an interface between the substrate  11  and the oxide superconducting layer  13  and improve the orientation of the layers formed thereon. Examples of a material of the bed layer include Y 2 O 3 , Er 2 O 3 , CeO 2 , Dy 2 O 3 , Eu 2 O 3 , Ho 2 O 3 , and La 2 O 3 . A thickness of the bed layer is, for example, 10 to 100 nm. 
     The textured layer is formed of a biaxially textured material in order to control a crystal orientation of the cap layer on the textured layer. Examples of the material of the textured layer can include metal oxides such as Gd 2 Zr 2 O 7 , MgO, ZrO 2 —Y 2 O 3  (YSZ), SrTiO 3 , CeO 2 , Y 2 O 3 , Al 2 O 3 , Gd 2 O 3 , Zr 2 O 3 , Ho 2 O 3 , and Nd 2 O 3 . In one or more embodiments, the textured layer is formed by an ion-beam-assisted deposition (IBAD) method. 
     The cap layer is formed on a surface of the textured layer described above and is formed of a material which enables grains to show self-epitaxy in an in-plane direction. Examples of the material of the cap layer include CeO 2 , Y 2 O 3 , Al 2 O 3 , Gd 2 O 3 , ZrO 2 , YSZ, Ho 2 O 3 , Nd 2 O 3 , and LaMnO 3 . A thickness of the cap layer is, for example, in a range of 50 to 5000 nm. 
     The oxide superconducting layer  13  is formed of an oxide superconductor. The oxide superconductor is not particularly limited, but examples thereof include an RE-Ba—Cu—O based oxide superconductor represented by a general formula of REBa 2 Cu 3 O X  (RE123). Examples of the rare earth element RE include one or two or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among these, one of Y, Gd, Eu, and Sm or a combination of two or more of these elements is included in one or more embodiments. In general, X is 7-x (oxygen deficiency amount x: approximately 0 to 1). A thickness of the superconducting layer is, for example, approximately 0.5 to 5 μm. In one or more embodiments, the thickness of the superconducting layer is uniform in the longitudinal direction. 
     The protective layer  14  has a function of bypassing an overcurrent or suppressing a chemical reaction occurring between the oxide superconducting layer  13  and a layer provided on the protective layer  14 . 
     Examples of a material of the protective layer  14  include silver (Ag), copper (Cu), gold (Au), an alloy of gold and silver, other silver alloys, a copper alloy, and a gold alloy. The protective layer  14  covers at least the surface of the oxide superconducting layer  13  (a face on a side opposite a substrate  11  side in the thickness direction). Further, the protective layer  14  may cover a part or the entirety of a region selected from the lateral face of the oxide superconducting layer  13 , the lateral face of the intermediate layer  12 , and the lateral face and the rear surface of the substrate  11 . The protective layer  14  may be formed of two or more types of metal layers. The protective layer  14  may be formed of two or more metal layers. The thickness of the protective layer  14  is, for example, approximately 1 to 30 μm, and in a case where the protective layer  14  is thinned, the thickness thereof may also be 10 μm or less. 
     The stabilizing layer  15  using plating (plating stabilizing layer) can be formed as metal plating (not shown) of Cu, Ag, Al, or the like, for example, on the lateral face of the superconducting laminate  16  or on the outer peripheral surface such as on the protective layer  14 . Instead of the plating stabilizing layer, or in combination with the plating stabilizing layer, metal foil, metal tape, or the like may be laminated on the periphery of the superconducting laminate  16  as the stabilizing layer  15  (the stabilizing layer  15  may be configured to cover the outer periphery of the superconducting laminate  16 ). In this case, it is possible to perform bonding to the substrate  11 , the oxide superconducting layer  13 , the protective layer  14 , and the like by providing a bonding material (not shown) such as solder on an inner face of the stabilizing layer  15 . 
     The stabilizing layer  15  is formed such that a single layer of the stabilizing layer  15  corresponds to only the one superconducting laminate  16 , without spanning the two superconducting laminates  16  and  16  (without forming a single layer of the stabilizing layer  15  to tie the superconducting laminates  16  and  16 ). According to one or more embodiments, stabilizing layer  15  is formed of a material having low electric resistance that functions as a shunt circuit. According to one or more embodiments, stabilizing layer  15  is formed of a material having high thermal conductivity that ensures heat exchange with the refrigerant. A thickness of the stabilizing layer  15  is, for example, approximately 15 to 300 μm. 
     In one or more embodiments, two superconducting laminates  16  and  16  are superposed in the thickness direction, and a gap portion  19  is provided between the superconducting laminates  16  and  16 . The gap portion  19  forms a non-fixed portion which is not fixed in the longitudinal direction of the superconducting laminates  16  and  16 . The non-fixed portion is not limited to a non-contact portion, and surfaces of the two superconducting laminates  16  and  16  may be partially or entirely in contact with each other via the gap portion  19 . 
     In addition, the metal foil  17  is provided to cover at least both sides in the width direction of the two superconducting laminates  16  and  16  (both lateral faces of the two superconducting laminates  16  and  16 ). The metal foil  17  and the superconducting laminates  16  and  16  are bonded with the bonding material  18  therebetween. The metal foil  17  is bonded to two superconducting laminates  16  and  16  so as to span both sides of the gap portion  19 . In other words, the metal foil  17  is bonded to the two superconducting laminates  16  and  16  such that the gap portion  19  is provided between the two superconducting laminates  16  and  16  (such that the two superconducting laminates  16  and  16  are disposed apart from each other). Accordingly, the two superconducting laminates  16  and  16  are integrated as one oxide superconducting wire  10 . 
     That is, in one or more embodiments, the two superconducting laminates  16  and  16  are disposed to be superposed on each other in the thickness direction of the oxide superconducting wire  10 , and the two superconducting laminates are integrated by a metal layer which is provided at least on both lateral faces of the two superconducting laminates in the width direction, such that the two superconducting laminates  16  and  16  form a non-fixed portion therebetween which is not fixed in a longitudinal direction of the superconducting laminates  16  and  16 . 
     Examples of a method of forming the superconducting laminates  16  and  16  to be non-fixed therebetween include a method in which, when performing the bonding with the bonding material  18 , facing faces are not wetted with the bonding material  18  by providing a face (non-coated face) which is not coated with a flux on one or both of the faces (two facing faces) on which the superconducting laminates  16  and  16  face each other. Examples of the flux include a resin based flux, an inorganic based flux, an organic based flux, a water soluble flux, and a solvent based flux, and generally include an activator such as acids and salts. For example, in a case of a liquid flux in which the metal surface is activated at the time of coating and a function of the activator is deactivated due to drying or the like, even when a flux coated face is in contact with a non-coated face, the non-coated face is not easily activated by the flux. Also in a case of coating the metal foil  17  with the flux, the entire inner face of metal foil  17  may be coated with the flux. 
     In this manner, the non-fixed portion is included between the superconducting laminates  16  and  16  and at least both lateral face portions in the width direction of the superconducting laminates  16  and  16  are covered with the metal foil  17 . Accordingly, even when an external force acts on the metal foil  17 , an inner portion of the superconducting laminate  16  (in particular, the oxide superconducting layer  13  and an interface between the oxide superconducting layer  13  and a layer on the periphery of the oxide superconducting layer  13 ) does not receive the external force. Therefore, the oxide superconducting layer  13  does not easily peel off and becomes the oxide superconducting wire  10  having high strength. According to one or more embodiments, when the metal foil  17  is bonded to three faces that are both lateral faces of the superconducting laminate  16  and the back face of the superconducting laminate  16  on which the substrate  11  is provided, it is possible to improve sealability against moisture. 
     Next, as an example of another form of the non-fixed portion,  FIG. 2  shows a cross-sectional view of an oxide superconducting wire according to one or more embodiments. An oxide superconducting wire  20  is formed in the same manner as that of the embodiments described above, except that the non-fixed portion is formed of a non-adhesive layer  21 . 
     The non-adhesive layer  21  can be formed by interposing a material (non-adhesive material) having a non-adhesive property with respect to the bonding material  18 , between the superconducting laminates  16  and  16 . The non-adhesive layer  21  may be laminated on one or both of the facing faces (two facing faces) at which the superconducting laminates  16  and  16  face each other. In addition, the flux non-coated face according to the embodiments described above can be used in combination with the non-adhesive layer  21 . 
     For example, it is possible to provide the non-adhesive layer  21  on a surface (first facing face) of one (first) superconducting laminate  16  and provide the flux non-coated face on a surface (second facing face) of the other (second) superconducting laminate  16 . 
     Examples of the non-adhesive material forming the non-adhesive layer  21  include an oxide film, a silicone resin, and a fluororesin such as Teflon (registered trademark). In a case where the oxide film is selected as the non-adhesive material, it is also possible to form the oxide film by oxidizing the metal at a surface portion of the superconducting laminate  16 , and it is possible to form a film of a metal oxide such as alumina from the outside. In a case where the resin such as a silicone resin or a fluororesin is used as the non-adhesive material, the resin can be selected from various states such as a liquid state, a gel state, a sol state, and a solid state to be used. In addition, as the non-adhesive material, it is also possible to use a tape having adhesion strength at a temperature at which the bonding material  18  becomes a liquid and having no adhesion strength at a temperature (adhesion temperature) at which the bonding material  18  becomes a solid, for example, a temperature sensitive sticking agent and an adhesive. 
     Next, in common with the embodiments described above, steps of bonding the metal foil  17  to the periphery of the superconducting laminates  16  and  16  will be described. 
     The metal foil  17  is tape-shaped (metal tape) and extends in the longitudinal direction of the oxide superconducting wires  10  and  20 . The metal foil  17  has a cross-sectional shape bent in the width direction from one face of one superconducting laminate  16  at the periphery of the superconducting laminates  16  and  16  (The metal foil  17  has a cross-sectional shape bent from the back face of the substrate  11  provided on one superconducting laminate  16  so as to cover the lateral face of the superconducting laminate  16 ). Accordingly, since the lateral face of the oxide superconducting layer  13  can be stably covered, the water resistance of the oxide superconducting wires  10  and  20  can be improved. 
     In one or more embodiments, the metal foil  17  completely covers the one face of the first superconducting laminate  16 , and includes a connecting portion  17   a  that connects lateral face portions  17   b  and  17   b  on both sides, the lateral face portions  17   b  and  17   b  that respectively cover both lateral faces of the superconducting laminates  16  and  16 , and bent end portions  17   c  and  17   c  folded back along the one face of the second superconducting laminate  16 . One or both of the bent end portions  17   c  and  17   c  may be omitted and the end portion in the width direction of the metal foil  17  may be provided on the lateral face portion  17   b.    
     In an unfolded state of the metal foil  17 , the lateral face portion  17   b  and the bent end portion  17   c  can be provided on both sides in the width direction of the connecting portion  17   a , in that order. In one or more embodiments, the bent end portions  17   c  and  17   c  are formed of both end portions of the metal foil  17  so as to cover both end portions in the width direction of the second superconducting laminate  16 . In one or more embodiments, the connecting portion  17   a  and the bent end portion  17   c  are substantially flat. For example, the connecting portion  17   a  and the bent end portion  17   c  may be parallel to each other. A thickness of the metal foil  17  is, for example, approximately 15 to 300 μm. 
     A material used for the metal foil  17  may vary depending on the application of the oxide superconducting wires  10  and  20 . For example, in a case in which it is used for a superconducting cable, a superconducting motor, or the like, it is necessary that it function as a main part of a bypass that commutates an overcurrent generated at the transition to a normal conducting state. Therefore, a metal with good conductivity is suitably used. Examples of the metal with good conductivity include metals such as copper, a copper alloy, aluminum, and an aluminum alloy. In this case, the metal foil  17  also functions as a stabilizing layer. 
     In addition, in a case of using the oxide superconducting wires  10  and  20  for a superconducting fault current limiter, it is necessary to instantaneously suppress the overcurrent generated at the transition to the normal conducting state. Therefore, a high resistance metal is suitably used for the metal foil  17 . Examples of a high resistance metal include a Ni based alloy such as Ni—Cr. In addition, in order to further improve peeling strength of the superconducting laminate  16 , it is possible to use a metal tape such as SUS having higher strength than a Cu foil or the like, as the metal foil  17 . 
     Examples of a bonding material forming the bonding material  18  include Sn—Pb based, Pb—Sn—Sb based, Sn—Pb—Bi based, Bi—Sn based, Sn—Cu based, Sn—Pb—Cu based, or Sn—Ag based solder, or the like, Sn, an Sn alloy, In, an In alloy, Zn, a Zn alloy, Ga, and a Ga alloy. A melting point of the bonding material is, for example, 500° C. or lower and further 300° C. or lower. A thickness of the bonding material  18  is, for example, 1 to 10 μm. 
     Examples of a method of providing the metal foil  17  and the bonding material  18  on the periphery of the superconducting laminates  16  and  16  include a method including a step of disposing the metal foil  17  on the periphery of the first superconducting laminate  16 , a step of bending the metal foil  17  along an external form of the superconducting laminates  16  and  16  (forming), a step of heating and pressing the superconducting laminates  16  and  16  and the metal foil  17  to melt a part or all of the bonding material  18  (re-melting or re-flowing), and a step of solidifying the bonding material by cooling it in its entirety while continuing the pressing. 
     Specific examples of the forming include a step in which the superconducting laminates  16  and  16  are disposed on the flat metal foil  17 , both end portions in the width direction of the metal foil  17  are then bent toward the lateral faces of the superconducting laminates  16  and  16 , and both end portions in the width direction of the metal foil  17  are further bent along the second superconducting laminate  16 . According to the forming, it is possible to efficiently produce a product having the same cross sectional shape continuous in the longitudinal direction of the superconducting wire. 
     The distribution of the bonding material  18  to the inner surface of the metal foil  17  is not particularly limited, but it is preferable to consider a bonding property to the superconducting laminate  16 , prevention of moisture penetration, electrical conductivity through the bonding material  18 , and the like. For example, the bonding material  18  may have a bonding material  18   a  bonding the connecting portion  17   a  of the metal foil  17  and the superconducting laminate  16 . In addition, the bonding material  18  may have a bonding material  18   b  bonding the lateral face portion  17   b  of the metal foil  17  and the superconducting laminate  16 . In addition, the bonding material  18  may also have a bonding material  18   c  bonding the bent end portion  17   c  of the metal foil  17  and the superconducting laminate  16 . A space of the metal foil  17  and the superconducting laminate  16  may be completely filled with the bonding material  18  and may have an area in which the bonding material  18  is not formed on a portion thereof. 
     A thickness of the bonding material  18   b  used for the lateral face portion  17   b  can be made larger than the thickness of the bonding materials  18   a  and  18   c  used for the connecting portion  17   a  or the bent end portion  17   c . In one or more embodiments, the thickness of the bonding material  18   b  of the lateral face portion is, for example, 5% or more, 10% or more, 20% or more of the width of the superconducting laminate  16 , or 50% or more, 100% or more, twice or more of the thickness of the superconducting laminate  16 , or 100 μm or more, 200 μm or more, or 500 μm or more. 
     In one or more embodiments of manufacturing the oxide superconducting wires  10  and  20  having a large thickness of the bonding material  18   b  on the lateral face portion, the step of bending the metal foil  17  (forming) is performed by bringing a jig into contact with the outer face side of the metal foil  17  or the like such that a distance between the lateral face of the superconducting laminate  16  and the metal foil  17  increases. 
     When the thickness of the bonding material  18   b  covering the lateral face of the superconducting laminate  16  is increased, when the lateral face of the superconducting laminate  16  has unevenness, the bonding material  18   b  can easily adhere thereto. In addition, since the bonding material  18   b  is a layer formed of a single material over the entire thickness of the superconducting laminate  16  and does not have a weak interface on the inner portion, it is possible to enhance the strength of the end portion in the width direction of the oxide superconducting wires  10  and  20 . In addition, a starting point of delamination of the superconducting laminate  16  is not easily generated, and it is possible to improve the peeling strength. For example, when a strong external force acts on the superconducting wire due to an electromagnetic force during conducting, thermal shrinkage of an insulating material (a resin) or the like on the periphery of the wire, residual stress, or the like, even in a case where stress concentrates at the end portion of the width direction than in the center portion, peeling between the layers forming the superconducting wire can be suppressed. 
     A supplying method of the bonding material  18  is not particularly limited. The bonding material  18  may be attached to one or both of the superconducting laminates  16  and  16  and the metal foil  17  in advance. Alternatively, a liquid or solid bonding material may be supplied between the superconducting laminates  16  and  16  and the metal foil  17 . It is possible to use two or more types of supplying methods in combination. Examples of the method of attaching the bonding material  18  to the superconducting laminates  16  and  16  or the metal foil  17  include a method of sputtering the bonding material, a method of plating the bonding material (such as electroplating), a method of using a molten bonding material (such as hot-dipping), and a combination of two or more of these. 
     In one or more embodiments, the width of the metal foil  17  in a deployed state is shorter than the circumference surrounding all of the two superconducting laminates  16  and  16 . Accordingly, when the metal foil  17  is formed so as to surround the outer periphery of the superconducting laminate  16 , end portions in the width direction of the metal foil  17  do not overlap each other. Therefore, the end portion of the metal foil  17  does not easily float from the superconducting laminate  16 . In one or more embodiments, a gap formed between the end portions in the width direction of the metal foil  17  is sealed by providing a closing portion  18   d  using solder, welding, or the like. 
     The closing portion  18   d  may be formed of the bonding material with which a gap portion is formed between both end portions in the width direction of the metal foil  17 . The bonding material with which the closing portion  18   d  is filled can be formed after bonding the superconducting laminates  16  and  16  and the metal foil  17 . In addition to this, the closing portion  18   d  can be formed by a welding portion. The welding portion may include some of the materials diffused from members of the periphery during welding, for example, some of the materials of the substrate  11 , the protective layer  14 , the stabilizing layer  15 , the metal foil  17 , the bonding material  18 , and the like. When forming the welding portion, a material such as a metal may be further supplied from the outside. The outer face of the closing portion  18   d  may protrude or recess from the outer face of the metal foil  17  or may be flush with the outer face of the metal foil  17 . 
     In one or more embodiments, the two superconducting laminates  16  and  16  are disposed such that the oxide superconducting layers  13  and  13  are provided between the substrates  11  and  11 . The current flowing through the oxide superconducting wires  10  and  20  may flow over the plurality of oxide superconducting layers  13  and  13 . Accordingly, it is possible to increase a current-carrying amount of the oxide superconducting wire. 
     In one or more embodiments, one or both of the oxide superconducting layers  13  and  13  may be disposed on an outside of the respective substrates  11  and  11 . 
       FIG. 3  shows a cross-sectional view of an oxide superconducting wire according to one or more embodiments. In an oxide superconducting wire  30  according to one or more embodiments, both of the oxide superconducting layers  13  and  13  are disposed on the outside of the substrates  11  and  11 . The current flowing through the oxide superconducting wire  30  may flow over the plurality of oxide superconducting layers  13  and  13  via the metal foil  17  or the like. Accordingly, it is possible to increase the current-carrying amount of the oxide superconducting wire. In this case, since the substrate  11  is not interposed between the oxide superconducting layer  13  and the metal foil  17  and an area where the metal foil  17  is bonded to the oxide superconducting layer  13  via the protective layer  14  or the bonding material  18  is wide, it is possible to make the metal foil  17  function better as the stabilizing layer. 
     In accordance with one or more embodiments,  FIG. 3  shows a case of a superconducting laminate  36  that includes the substrate  11 , the intermediate layer  12 , the oxide superconducting layer  13 , and the protective layer  14 , but does not include a stabilizing layer  15  (see  FIGS. 1 and 2 ). A method of manufacturing the oxide superconducting wire  30  is the same as that of the embodiments described above. 
     In one or more embodiments, the superconducting laminates  16  and  36  optionally have the stabilizing layer  15 . 
     The metal layer integrating the plurality of superconducting laminates is not limited to the metal foil, and for example, may be a metal layer such as a plated layer. The metal layer integrating the plurality of superconducting laminates is a metal layer disposed to span the plurality of superconducting laminates, and hereinafter will be referred to as an “integrating metal layer”. 
     Examples of a general method of manufacturing an oxide superconducting wire include a manufacturing method including a step of manufacturing a superconducting laminate which may or may not have a stabilizing layer, a step of superposing the superconducting laminate in a thickness direction, and a step of integrating the superconducting laminates so as not to be fixed therebetween, by forming an integrated metal layer at least on both sides (both lateral faces) in a width direction of the superconducting laminate. 
     In one or more embodiments, the integrating metal layer is formed continuously in the longitudinal direction of the superconducting laminate so as to cover at least the non-fixed portion between the superconducting laminates. In addition, in order to protect the oxide superconducting layer from moisture, air, or the like, in one or more embodiments, both end portions (both lateral faces) in the width direction of the oxide superconducting layer are covered with the integrating metal layer. In order for the integrating metal layer to function also as the stabilizing layer, in one or more embodiments, the integrating metal layer is formed using Cu, Ag, Al, or the like having excellent electrical conductivity and excellent thermal conductivity. 
     Next, as an example of another form of the integrating metal layer,  FIG. 4  shows a cross-sectional view of an oxide superconducting wire according to one or more embodiments. An oxide superconducting wire  40  according to one or more embodiments is formed in the same manner as embodiments described above, except that a plated layer  47  is formed as an integrating metal layer on the periphery of the two superconducting laminates  16  and  16 . A non-fixed layer in one or more embodiments is not limited to the same one as the non-adhesive layer  21  according to embodiments described above, and can be configured similarly to the gap portion  19  according to embodiment described above. 
     In a case where a plated layer  47  is used as the integrating metal layer, in a plating step, it is possible to narrow the gap between the superconducting laminates  16  and  16  such that the plating is not formed between the superconducting laminates  16  and  16  superimposed in the thickness direction or laminate the non-adhesive layer  21  using the non-adhesive material to the plating. The non-adhesive layer  21  may be laminated on one or both of the facing faces (two facing faces) at which the superconducting laminates  16  and  16  face each other, and may be sandwiched without being fixed to both of the superconducting laminates  16  and  16 . 
     In addition, in the plating step, it is possible to maintain an integrated state without a gap between the superconducting laminates  16  and  16  or between the superconducting laminates  16  and  16  and the non-adhesive layer  21 , by pressing faces (non-facing faces) opposite the faces at which the two superconducting laminates  16  and  16  face each other with a roller or the like. 
     The stabilizing layer  15  of the superconducting laminate  16  can be omitted. However, in one or more embodiments, an underlayer of metal or the like is formed on the outer face of the superconducting laminate  16  such that the plated layer  47  easily adheres to the back face or lateral face of the substrate  11 . In one or more embodiments where the stabilizing layer  15  of Cu or the like is provided on the periphery of the superconducting laminate  16 , the adhesion with the plated layer  47  of Cu or the like is excellent. A thickness of the plated layer  47  is, for example, approximately 15 to 300 μm. 
     Examples of the non-adhesive material to the plating include an oxide film, a silicone resin, and a fluororesin such as Teflon (registered trademark). In a case where the oxide film is used as the non-adhesive material, it is also possible to form the oxide film by oxidizing the metal at a surface portion of the superconducting laminate, and it is possible to form a film of a metal oxide such as alumina from the outside. In a case where the resin such as a silicone resin or a fluororesin is used as the non-adhesive material, the resin can be selected from various states such as a liquid state, a gel state, a sol state, and a solid state to be used. 
     In addition, as the non-adhesive material, it is also possible to use a tape having adhesion strength at a temperature (for example, a normal temperature or a high temperature) at the time of a plating step and having no adhesion at a temperature (for example, a low temperature or a normal temperature) after the plating step, for example, a temperature sensitive sticking agent and an adhesive. Accordingly, when forming the plated layer  47 , the plating does not adhere to the surface of the superconducting laminate  16 , and it is possible to prevent the superconducting laminates  16  and  16  from being fixed to each other. The plating step may be carried out at room temperature or at a high temperature. 
     In a case where the tape having no adhesion at a temperature lower than the temperature at which adhesion is exhibited is used as the non-adhesive material, a tape having no adhesion at the low temperature (for example, liquid nitrogen temperature) at which the oxide superconducting wire is used may be used. In this case, the tape may have adhesion at the normal temperature (for example, around 20 to 30° C.). Here, the adhesion strength of the tape means an adhesion strength (adhesive force) capable of fixing the superconducting laminates  16  and  16  therebetween. 
     In addition, the non-adhesive layer  21  may be interleaving paper having no adhesion or having weak adhesion. The interleaving paper may be a sheet or a film of a resin or the like having heat resistance. 
     When compared to a case where the metal foil  17  is the integrating metal layer (for example, see  FIG. 2 ), in a case where the plated layer  47  is the integrating metal layer, the bonding material  18  can be omitted. In addition, it is also possible to form a circumferentially continuous plated layer  47  in, for example, the entire circumference of the two superconducting laminates  16  and  16  without forming the closing portion  18   d  in the gap at the end portion in the width direction of the metal foil  17 . In the case of  FIG. 4 , the plated layer  47  includes connecting portions  47   a  and  47   a  connecting the lateral face portions  47   b  and  47   b  on both sides and lateral face portions  47   b  and  47   b  respectively covering both lateral faces of the superconducting laminates  16  and  16 . The connecting portion  47   a  may be laminated on the surface (non-facing face) of one or both of the superconducting laminates  16 . 
     As the integrating metal layer, it is possible to use two or more types of metal layers in combination. For example, an integrating metal layer covering one side (first lateral face) in the width direction of the superconducting laminate and an integrating metal layer covering the other side (second lateral face) may be separated as separate metal layers. Materials of the separate metal layers may be the same as or different from each other. 
     The integrating metal layer may cover a part or the entire face (non-facing face) opposite the faces at which the two superconducting laminates face each other. One or both of the non-facing faces may not be covered by the integrating metal layer. 
     In order to prepare a superconducting coil using a tape-shaped oxide superconducting wire, a superconducting wire is wound around a required number of layers along the outer peripheral surface of a bobbin to form a coil shape (multilayer wound coil), and then the wound superconducting wire is impregnated with a resin such as an epoxy resin so as to cover the superconducting wire, and the superconducting wire can be fixed. 
     Hereinbefore, the present invention has been described based on the embodiments described above. However, the present invention is not limited to the embodiments described above, and approximate modifications can be made in a range not departing from the present invention. 
     For example, it is possible to omit, combine, or modify one or two or more of the configurations included in the embodiments described above. 
     The oxide superconducting wire can include an external terminal. In a portion having the external terminal, a sectional structure different from other portions may be provided. 
     The non-fixed portion may not be fixed at least at a low temperature (for example, liquid nitrogen temperature) at which an oxide superconducting wire is used by superconductivity, and may not be fixed or may be fixed at a normal temperature (for example, around 20 to 30° C.). 
     EXAMPLES 
     Hereinafter, embodiments of the present invention will be described using examples. The present invention is not limited to only the examples. 
     Example 1 
     (1) A surface of a substrate (12 mm in width x 1000 mm in length x 0.75 mm in thickness) of Hastelloy (registered trademark) C-276 (trade name of Haynes International, Inc.) was polished. 
     (2) The surface of the substrate was degreased and cleaned with acetone. 
     (3) A 100 nm diffusion prevention layer of Al 2 O 3  was formed on the substrate by ion beam sputtering. 
     (4) A 30 nm bed layer of Y 2 O 3  was formed on the diffusion prevention layer by ion beam sputtering. 
     (5) A 5 to 10 nm textured layer of MgO was formed on the bed layer by an ion beam assisted deposition method. 
     (6) A 500 nm cap layer of CeO 2  was formed on the textured layer by a pulsed laser deposition method. 
     (7) A 2 μm oxide superconducting layer of GdBa 2 Cu 3 O 7-x  was formed on the cap layer by the pulsed laser deposition method. 
     (8) A 2 μm protective layer of Ag was formed on the oxide superconducting layer by sputtering from the direction of the surface of the oxide superconducting layer. 
     (9) The superconducting laminate was subjected to oxygen annealing. 
     (10) The superconducting laminate was slit processed to 4 mm in width. 
     (11) A 1 μm film of Cu was formed on a front face and a back face of the superconducting laminate by sputtering. 
     (12) A 20 μm stabilizing layer (optional) of Cu was formed on the entire circumference of the superconducting laminate by plating. 
     (13) Soldering was performed on the periphery of the two superconducting laminates superposed in a thickness direction by using an oxygen-free copper foil having a thickness of 20 μm to obtain an oxide superconducting wire. At the time of bonding, flux was not applied to faces at which the two superconducting laminates faced each other (for example, the facing face on an oxide superconducting layer side), such that solder did not adhere. The solder used for the bonding is not limited to an alloy, and may be Sn. In addition, a material to which the solder does not adhere may be laminated on the facing face. 
     Example 2 
     (1) In the same manner as in (1) to (12) of Example 1, a superconducting laminate having a stabilizing layer of Cu on the outer periphery was prepared. 
     (2) Interleaving paper was placed between the two superconducting laminates, and a plating process was carried out on the periphery of the superconducting laminates superposed in the thickness direction (lateral face and non-facing face) to obtain an oxide superconducting wire. In one or more embodiments, the interleaving paper has no adhesion or has weak adhesion. 
     According to these examples, in the oxide superconducting wire, the two superconducting laminates are not fixed therebetween. Therefore, it is possible to suppress the delamination of the superconducting laminate. 
     DESCRIPTION OF REFERENCE NUMERAL 
     
         
         
           
               10 ,  20 ,  30 ,  40  Oxide superconducting wire 
               11  Substrate 
               12  Intermediate layer 
               13  Oxide superconducting layer 
               14  Protective layer 
               15  Stabilizing layer 
               16 ,  36  Superconducting laminate 
               17  Metal layer (metal foil) 
               18  Bonding material 
               19  Non-fixed portion (gap portion) 
               21  Non-fixed portion (non-adhesive layer) 
               47  Metal layer (plated layer) 
           
         
       
    
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.