Manufacturing method of superconducting wire

Abstract

To provide a method of manufacturing a superconducting wire rod including an oxide superconductive film having a high degree of orientation, and capable of reducing a manufacturing time of the superconducting wire rod.SOLUTION: A process of forming an oxide superconductive film incudes performing a process of laminating a superconducting layer of an oxide superconducting material. The process of laminating the superconducting layer includes a calcined film forming process, a polycrystallization process, and a sintering heat treatment process. The calcined film forming process includes performing a coated film forming process and a calcination heat treatment process. In the coated film forming process, a solution of a metal organic compound is coated to form a coated film. In the calcination heat treatment process, an organic constituent of the metal organic compound is thermally decomposed by heat-treating the coated film to form a calcined film. In the polycrystallization process, the calcined film is thermally treated to form a polycrystal layer including polycrystal of the oxide superconducting material. In the sintering heat treatment process, polycrystal is oriented by heat-treating the polycrystal layer to form the superconducting layer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a method for producing a superconducting wire. [Background technology]

[0002] Patent Document 1 (JP Patent Publication 2007-165153 A) discloses a method for manufacturing a superconducting wire, including a step of forming an oxide superconducting film by using a coating pyrolysis method (MOD (Metal Organic Decomposition) method). The method for forming an oxide superconducting film by the MOD method includes the following steps: A solution in which a metal organic compound including an organic compound of a rare earth element (RE), an organic compound of barium (Ba), and an organic compound of copper (Cu) is dissolved is applied to a substrate to form a coating film on the substrate; The coating film is heat-treated (calcined) at a temperature of about 500°C to pyrolyze the organic components of the metal organic compound contained in the coating film, thereby obtaining a calcined film; The calcined film is further heat-treated (calcined) at a high temperature (for example, a temperature of about 800°C) to form an oxide superconducting film. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-165153 A Summary of the Invention

[0004] A method for manufacturing a superconducting wire according to an embodiment of the present disclosure includes a step of forming an oxide superconducting film on a support substrate. The step of forming the oxide superconducting film includes a step of stacking superconducting layers of an oxide superconducting material at least once. The step of stacking the superconducting layers includes a calcined film forming step, a polycrystallization step, and a firing heat treatment step. The calcined film forming step includes a step of forming a coating film and a calcination heat treatment step at least once. In the coating film forming step, a solution of a metal organic compound is applied to form a coating film. The metal organic compound is a compound of a metal element and an organic component that constitute an oxide superconducting material. In the calcination heat treatment step, the coating film is heat-treated to pyrolyze the organic component, thereby forming a calcined film. In the polycrystallization step, the calcined film is heat-treated to form a polycrystalline layer containing polycrystals of the oxide superconducting material. In the firing heat treatment step, the polycrystalline layer is heat-treated to orient the polycrystals, thereby forming a superconducting layer. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic cross-sectional view of the superconducting wire of the first and second embodiments. [Diagram 2] FIG. 2 is a flowchart showing the method for producing a superconducting wire according to the first and second embodiments. [Diagram 3] FIG. 3 is a flowchart showing the steps of forming the oxide superconducting film of the first and second embodiments. [Figure 4] FIG. 4 is a flowchart showing the steps of laminating the superconducting layers of the oxide superconducting materials of the first and second embodiments. [Diagram 5] FIG. 5 is a flowchart showing the calcined film forming step of the first embodiment. [Figure 6] FIG. 6 is a schematic partially enlarged cross-sectional view showing a process for forming an oxide superconducting film. [Figure 7] FIG. 7 is a schematic partially enlarged cross-sectional view showing a process for forming an oxide superconducting film. [Figure 8] FIG. 8 is a flowchart showing the calcined film forming step of the second embodiment. [Figure 9]FIG. 9 is a diagram showing a two-dimensional X-ray diffraction image of the oxide superconducting film of the example. [Figure 10] FIG. 10 is a diagram showing an X-ray diffraction chart of the oxide superconducting film of the example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] [Problem that this disclosure aims to solve] The oxide superconducting film of a superconducting wire needs to have a high degree of orientation. The method for producing a superconducting wire disclosed in Patent Document 1 can increase the degree of orientation of the oxide superconducting film, but has the problem of a long heat treatment time. Therefore, it is desirable to increase the degree of orientation of the oxide superconducting film and shorten the time required to produce a superconducting wire. The present disclosure has been made in view of the above problems, and has an object to provide a method for producing a superconducting wire that includes an oxide superconducting film with a high degree of orientation and can shorten the time required to produce a superconducting wire.

[0007] [Effects of this disclosure] According to the method for producing a superconducting wire of the present disclosure, it is possible to increase the degree of orientation of the oxide superconducting film and to shorten the time required for producing the superconducting wire.

[0008] [Overview of the embodiment] The embodiments of the present disclosure will be listed and described.

[0009] (1) The method for manufacturing a superconducting wire 1 according to the present disclosure includes a step of forming an oxide superconducting film 20 on a support substrate 10. The step of forming the oxide superconducting film 20 includes a step (S11) of stacking a superconducting layer 25 of an oxide superconducting material at least once. The step (S11) of stacking the superconducting layer 25 includes a calcined film forming step (S12), a polycrystallization step (S16), and a firing heat treatment step (S17). The calcined film forming step (S12) includes a coating film forming step (S13) and a calcination heat treatment step (S14) performed at least once. In the coating film forming step (S13), a solution of a metal organic compound is applied to form a coating film. The metal organic compound is a compound of a metal element and an organic component that constitute an oxide superconducting material. In the calcined heat treatment step (S14), the coating film is heat-treated to pyrolyze the organic component, thereby forming a calcined film. In the polycrystallization step (S16), the calcined film is heat-treated to form a polycrystalline layer containing polycrystals of the oxide superconducting material. In the firing heat treatment step (S17), the polycrystalline layer is heat-treated to orient the polycrystals, thereby forming a superconducting layer 25.

[0010] In the polycrystallization step (S16), carbon dioxide (CO2), which inhibits the orientation of the superconducting film during the firing heat treatment step (S17), is discharged from the calcined film. This allows the heat treatment time of the firing heat treatment step (S17) to be reduced, thereby shortening the production time of the oxide superconducting film 20. This allows the production time of the superconducting wire 1 to be shortened.

[0011] (2) In the method for producing superconducting wire 1 according to (1) above, the step of forming oxide superconducting film 20 includes repeating the step (S11) of stacking superconducting layer 25 multiple times.

[0012] This makes it possible to increase the thickness of oxide superconducting film 20. The critical current of superconducting wire 1 can be increased.

[0013] (3) In the method for producing superconducting wire 1 according to (1) or (2) above, the calcined film forming step (S12) includes repeating the coating film forming step (S13) and the calcination heat treatment step (S14) multiple times.

[0014] Since the polycrystallization step (S16) and the firing heat treatment step (S17) only need to be performed once after the coating film formation step (S13) and the calcination heat treatment step (S14) are repeated multiple times, the number of times the polycrystallization step (S16) and the firing heat treatment step (S17) are performed can be reduced. The time required to produce the oxide superconducting film 20 can be reduced, and the time required to manufacture the superconducting wire 1 can be reduced.

[0015] (4) In the method for producing superconducting wire 1 according to any one of (1) to (3) above, the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of 1% or more.

[0016] When the carbonate contained in the calcined film is thermally decomposed in the firing heat treatment step (S17), CO2 is generated from the calcined film, which causes a problem of inhibiting the orientation of the superconducting film. Therefore, it is desirable to thermally decompose the carbonate contained in the calcined film in the polycrystallization step (S16) performed between the calcined film formation step (S12) and the firing heat treatment step (S17). On the other hand, if the oxygen concentration in the polycrystallization step (S16) is less than 1%, the carbonate contained in the calcined film is thermally decomposed, but the crystallization of the superconducting material proceeds excessively, and the size of each crystal grain constituting the polycrystal increases, resulting in a problem that only an oxide superconducting film having a low degree of orientation is obtained. By performing the polycrystallization step (S16) in an atmosphere having an oxygen concentration of 1% or more, the size of each crystal grain constituting the polycrystal of the oxide superconducting material is prevented from becoming excessively large in the polycrystallization step (S16), and an oxide superconducting film 20 having a higher degree of orientation can be formed. The degree of crystal orientation of the oxide superconducting film 20 can be improved.

[0017] (5) In the method for producing superconducting wire 1 according to any one of (1) to (4) above, the polycrystallization step (S16) is performed at a heat treatment temperature of 700° C. or higher.

[0018] Therefore, the degree of crystal orientation of the oxide superconducting film 20 can be improved. (6) In the method for producing superconducting wire 1 according to any one of (1) to (5) above, the time for heat treating the calcined film in the polycrystallization step (S16) is 1 minute or longer.

[0019] Therefore, the carbonate contained in the calcined film is sufficiently thermally decomposed, and CO2 is sufficiently released from the calcined film, so that the degree of crystal orientation of the oxide superconducting film 20 can be improved.

[0020] (7) In the method for producing superconducting wire 1 according to (6) above, the time for heat treating the calcined film in the polycrystallization step (S16) is 70 minutes or less.

[0021] Since the size of each crystal grain constituting the polycrystal does not become excessively large, the degree of crystal orientation of the oxide superconducting film 20 can be improved.

[0022] (8) In the manufacturing method of superconducting wire 1 according to any one of (1) to (3) above, the polycrystallization step (S16) is carried out in an atmosphere having an oxygen concentration of 0.01% or more and less than 1%, and at a heat treatment temperature of 650°C or more and less than 800°C.

[0023] Since the oxygen concentration in the polycrystallization step (S16) is 0.01% or more and less than 1%, the carbonate contained in the calcined film is thermally decomposed. When the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of less than 1%, the heat treatment temperature is set to less than 800°C, which prevents the size of each crystal grain constituting the polycrystal of the oxide superconducting material from becoming excessively large in the polycrystallization step (S16), and makes it possible to form an oxide superconducting film 20 having a higher degree of orientation. The degree of crystal orientation of the oxide superconducting film 20 can be improved.

[0024] (9) In the method for producing superconducting wire 1 according to any one of (1) to (8) above, in the firing heat treatment step (S17), a part or the whole of the polycrystal grows via a liquid phase.

[0025] Since the manufacturing method of the superconducting wire 1 includes the polycrystallization step (S16), even if the oxide superconducting film 20 is thick, the oxide superconducting film 20 having a high degree of orientation can be formed in a shorter time. Furthermore, the polycrystals generated in the polycrystallization step (S16) tend to generate a liquid phase of the oxide superconducting material. Then, an oxide superconducting film 20 having a higher degree of orientation can be formed by a part of the polycrystal growing through the liquid phase. Therefore, the oxide superconducting film 20 with an improved degree of orientation can be formed in a shorter time. The superconducting wire 1 including the oxide superconducting film 20 with an improved degree of orientation can be manufactured in a shorter time.

[0026] (10) In the method for producing superconducting wire 1 according to any one of (1) to (9) above, oxide superconducting film 20 has a thickness of 1 μm or more.

[0027] Therefore, the critical current of superconducting wire 1 can be increased. [Details of the embodiment] The details of the embodiments will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated. At least some of the configurations of the embodiments described below may be arbitrarily combined.

[0028] (Embodiment 1) A superconducting wire 1 of the present embodiment will be described with reference to Fig. 1. The superconducting wire 1 includes a support substrate 10 and an oxide superconducting film 20. The superconducting wire 1 may further include a protective layer 30 and a stabilizing layer 40.

[0029] The support substrate 10 supports the oxide superconducting film 20. The support substrate 10 includes a substrate 11 and an intermediate layer 12. The intermediate layer 12 is disposed on the substrate 11. The substrate 11 is, for example, a clad material in which a copper (Cu) layer and a nickel (Ni) layer are laminated on a tape formed of stainless steel. The intermediate layer 12 is disposed between the substrate 11 and the oxide superconducting film 20. The intermediate layer 12 is, for example, formed of at least one layer selected from the group consisting of a cerium oxide (CeO2) layer, an yttria stabilized zirconia (YSZ) layer, an yttria (Y2O3) layer, and a lanthanum manganate (LaMnO3) layer. The intermediate layer 12 is, for example, formed by magnetron sputtering.

[0030] The configuration of the support substrate 10 is not limited to the above. For example, the substrate 11 may be a tape made of Hastelloy (registered trademark) or the like, and the intermediate layer 12 may be formed of an intermediate layer including an IBAD (Ion Beam Assisted Deposition) layer.

[0031] The intermediate layer 12 may have a multi-layer structure and may include, for example, an underlayer, an alignment layer, and a cap layer. The underlayer is laminated on the substrate 11. The alignment layer is laminated on the underlayer. The cap layer is laminated on the alignment layer.

[0032] The underlayer has a multi-layer structure of a diffusion prevention layer and a bed layer, a single-layer structure of a diffusion prevention layer, or a single-layer structure of a bed layer. The diffusion prevention layer desirably has a single-layer structure or a multi-layer structure made of silicon nitride (Si3N4), aluminum oxide (Al2O3, also called "alumina"), GZO (Gd2Zr2O7), or the like. The bed layer has a single-layer structure or a multi-layer structure made of rare earth oxides such as Y2O3, Er2O3, CeO2, Dy2O3, Er2O3, Eu2O3, Ho2O3, or La2O3.

[0033] Examples of materials constituting the alignment layer include metal oxides such as Gd2Zr2O7, MgO, ZrO2-Y2O3 (YSZ), SrTiO3, CeO2, Y2O3, Al2O3, Gd2O3, Zr2O3, Ho2O3, and Nd2O3. The alignment layer may have a single layer structure or a multi-layer structure.

[0034] Examples of materials constituting the cap layer include CeO2, LaMnO3, Y2O3, Al2O3, Gd2O3, Zr2O3, etc. The cap layer may have a single layer structure or a multi-layer structure.

[0035] Support substrate 10 may further include an underlayer (not shown) disposed on intermediate layer 12. The underlayer improves the orientation of the crystal axes of oxide superconducting film 20, for example, the orientation in the c-axis direction. Support substrate 10 has a main surface 10a. Main surface 10a extends in the longitudinal direction (x direction) of superconducting wire 1 and in the width direction (y direction) of superconducting wire 1. Main surface 10a of support substrate 10 may be formed by intermediate layer 12 or may be formed by the underlayer (not shown).

[0036] The oxide superconducting film 20 is disposed on the main surface 10a of the support substrate 10. The oxide superconducting film 20 is laminated on the support substrate 10 in the normal direction (z direction) of the main surface 10a. The oxide superconducting film 20 is in contact with the main surface 10a. When the oxide superconducting film 20 is in a superconducting state, a current flows mainly in the longitudinal direction (x direction) of the superconducting wire 1. The thickness direction of the oxide superconducting film 20 is the normal direction (z direction) of the main surface 10a.

[0037] The oxide superconducting film 20 is made of an oxide superconducting material such as REBCO. x(x is 6 to 8, more preferably 6.8 to 7). Here, RE is a rare earth element. RE is, for example, at least one element selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, lutetium, and ytterbium.

[0038] The crystal grains constituting the lower layer of the oxide superconducting film 20 are oriented, so that the crystal grains constituting the oxide superconducting film 20 are oriented. For example, the c-axis of the oxide superconducting material is mainly oriented along the normal direction (z direction) of the main surface 10a of the support substrate 10. When the substrate 11 includes, for example, the above-mentioned copper layer, the crystal grains of the copper layer are oriented by heat treatment. When the support substrate 10 has the intermediate layer 12, it is only necessary that the crystal grains of the oxide constituting the intermediate layer 12 have orientation. For example, when the intermediate layer 12 oriented by IBAD is formed on the substrate 11 such as Hastelloy (registered trademark), the crystal grains constituting the oxide superconducting film 20 formed on the intermediate layer 12 are oriented.

[0039] The oxide superconducting film 20 has a thickness T. The thickness T is, for example, not less than 1.0 μm and not more than 5.0 μm. The thickness T of the oxide superconducting film 20 may be not less than 1.5 μm and not more than 5.0 μm. When the thickness T of the oxide superconducting film 20 is 1.0 μm or more, the critical current of the superconducting wire 1 can be increased. When the thickness T of the oxide superconducting film 20 is 5.0 μm or less, a decrease in the critical current density of the superconducting wire 1 is suppressed, and a good degree of orientation of the oxide superconducting film 20 is easily maintained.

[0040] The protective layer 30 is disposed on the oxide superconducting film 20. The protective layer 30 is laminated on the oxide superconducting film 20 in the normal direction (z direction) of the main surface 10a of the support substrate 10. The protective layer 30 is made of, for example, silver (Ag). The protective layer 30 may be made of copper. The stabilization layer 40 is disposed on the protective layer 30. The stabilization layer 40 is laminated on the protective layer 30 in the normal direction (z direction) of the main surface 10a of the support substrate 10. The stabilization layer 40 has, for example, a thickness larger than that of the protective layer 30. The stabilization layer 40 is made of, for example, copper. When a quench (a phenomenon in which a superconducting state transitions to a normal conducting state) occurs in the oxide superconducting film 20, the protective layer 30 and the stabilization layer 40 bypass the current flowing through the oxide superconducting film 20 to prevent the superconducting wire 1 from burning.

[0041] A method for manufacturing superconducting wire 1 of the present embodiment will be described with reference to FIGS. 2, the method for manufacturing superconducting wire 1 of the present embodiment includes a step (S10) of forming oxide superconducting film 20 on support substrate 10, a step (S20) of forming protective layer 30 on oxide superconducting film 20, and a step (S30) of forming stabilization layer 40 on protective layer 30. In step S20, protective layer 30 is formed by, for example, sputtering. In step S30, stabilization layer 40 is formed by, for example, plating. Step S10 will be described in detail below.

[0042] Referring to FIG. 3, the step (S10) of forming an oxide superconducting film 20 includes a step (S11) of stacking a superconducting layer 25 of an oxide superconducting material, and a step (S18) of determining whether the total thickness of superconducting layer 25 has reached a target thickness (e.g., thickness T).

[0043] Step S11 is performed at least once. When it is determined in step S18 that the total thickness of superconducting layer 25 reaches the target thickness by performing step S11 once, step S10 ends. In this case, oxide superconducting film 20 is formed of one superconducting layer 25. As shown in FIG. 6, when it is determined in step S18 that the total thickness of superconducting layer 25 does not reach the target thickness (e.g., thickness T) by performing step S11 once, step S11 is repeated multiple times until the total thickness of superconducting layer 25 reaches the target thickness (e.g., thickness T). In this case, oxide superconducting film 20 is formed of multiple superconducting layers 25 as shown in FIG. 7.

[0044] 4, the step (S11) of laminating the superconducting layer 25 includes a calcined film forming step (S12), a polycrystallization step (S16), and a firing heat treatment step (S17). With reference to FIG. 5, the calcined film forming step (S12) includes a coating film forming step (S13) and a calcination heat treatment step (S14).

[0045] In the coating film forming step (S13), a solution of a metal organic compound is applied, and then the solution is dried to form a coating film. A raw material solution in the MOD method is used as the solution of the metal organic compound. The solution of the metal organic compound is, for example, a solution in which a metal organic compound is dissolved in an organic solvent. The metal organic compound is a compound of a metal element and an organic component that constitute an oxide superconducting material. When forming a REBCO-based superconducting layer 25, the metal organic compound is, for example, an RE carboxylate, a Ba carboxylate, and a Cu carboxylate. The carboxylate may be a monocarboxylate or a dicarboxylate. The monocarboxylate has high solubility and dissolution stability in a solvent. The monocarboxylate having a carbon number of 1 to 4 is, for example, a formate, an acetate, a propionate, or a butyrate. The dicarboxylate having a carbon number of 1 to 4 is, for example, an oxalate, a malonate, or a succinate. Metal organic compounds having other known compositions can also be used.

[0046] The method of applying the solution of the metal organic compound is not particularly limited, and may be, for example, a die coating method or an inkjet method. In the step of laminating the first superconducting layer 25, the solution of the metal organic compound is applied to the main surface 10a of the support substrate 10. In the step of laminating the second and subsequent superconducting layers 25, the solution of the metal organic compound is applied to the outermost surface of the already formed superconducting layer 25.

[0047] In the calcination heat treatment step (S14), the coating film is heat-treated to thermally decompose the organic components of the metal organic compound, thereby forming a calcined film. For example, the coating film is heat-treated at a heat treatment temperature equal to or higher than the thermal decomposition temperature of the metal organic compound and lower than the production temperature of the oxide superconducting material. The metal organic compound contained in the coating film is thermally decomposed to form a calcined film. The calcined film is mainly formed of a precursor of the oxide superconducting material. The precursor of the oxide superconducting material is composed of an oxide of a metal element constituting the oxide superconducting material and a carbonate of a metal element constituting the oxide superconducting material. When forming a REBCO-based superconducting layer 25, the precursor of the oxide superconducting material is composed of a rare earth element oxide (e.g., Gd2O3), a carbonate of Ba (e.g., BaCO3), and an oxide of copper (e.g., CuO).

[0048] The heat treatment temperature in the calcination heat treatment step (S14) is, for example, about 500°C. The temperature rise rate from room temperature to the heat treatment temperature is, for example, about 0.5 to 20°C / min. The atmosphere in which the calcination heat treatment step (S14) is performed has, for example, an oxygen concentration of 20% or more. The atmosphere in which the calcination heat treatment step (S14) is performed may have an oxygen concentration of 50% or more, or may have an oxygen concentration of 100%. In this specification, the unit of oxygen concentration, "%", means volume percentage. The heat treatment time in the calcination heat treatment step (S14) is, for example, about 30 minutes. The heat treatment time in the calcination heat treatment step (S14) may be 10 minutes or less, or may be 2 minutes or less.

[0049] As described above, the precursor of the oxide superconducting material that forms the calcined film contains carbonates of metal elements that constitute the oxide superconducting material (e.g., BaCO3, etc.). In order to generate the oxide superconducting material from this precursor, it is necessary to decompose the carbonates contained in the calcined film. Therefore, the polycrystallization step (S16) is performed.

[0050] In the polycrystallization step (S16), the calcined film is heat-treated at a heat treatment temperature higher than the heat treatment temperature in the calcination heat treatment step (S14). The precursor of the oxide superconducting material undergoes a chemical reaction to form a polycrystalline layer containing polycrystals of the oxide superconducting material. The average grain size of the grains of the multiple crystal grains constituting the polycrystal is, for example, 300 nm or less. The average grain size may be 200 nm or less, or 100 nm or less.

[0051] The polycrystallization step (S16) is performed in an atmosphere containing oxygen. For example, the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of 1% or more. This reduces the partial pressure of CO2 generated by thermally decomposing carbonates contained in the calcined film, and CO2 is sufficiently discharged from the calcined film. The chemical reaction of the precursor of the oxide superconducting material proceeds without being hindered by CO2, and the oxide superconducting material is sufficiently generated. In addition, the size of each crystal grain constituting the polycrystal of the oxide superconducting material is prevented from becoming excessively large, and the polycrystal of the oxide superconducting material can be sufficiently formed. The polycrystallization step (S16) may be performed in an atmosphere having an oxygen concentration of more than 10%, an atmosphere having an oxygen concentration of 11% or more, an atmosphere having an oxygen concentration of 23% or more, an atmosphere having an oxygen concentration of 50% or more, or an atmosphere having an oxygen concentration of 100% (oxygen partial pressure of 1 atm).

[0052] The polycrystallization step (S16) is performed at a heat treatment temperature of, for example, 700°C or higher. The heat treatment temperature in the polycrystallization step (S16) may be 750°C or higher, 780°C or higher, 800°C or higher, 810°C or higher, or 820°C or higher. The heat treatment temperature in the polycrystallization step (S16) may be 900°C or lower, or 860°C or lower. The time for which the calcined film is heat treated in the polycrystallization step (S16) is 1 minute or longer. The time for which the calcined film is heat treated in the polycrystallization step (S16) may be 10 minutes or longer. The time for which the calcined film is heat treated in the polycrystallization step (S16) may be 120 minutes or shorter, 70 minutes or shorter, or 60 minutes or shorter.

[0053] The polycrystallization step (S16) is performed, for example, in an atmosphere having an oxygen concentration of 0.01% or more and less than 1%, and at a heat treatment temperature of 650°C or more and less than 800°C. When the oxygen concentration and the heat treatment temperature are in the above ranges, the partial pressure of CO2 generated by thermally decomposing the carbonate contained in the calcined film is low, and CO2 is sufficiently discharged from the calcined film. The chemical reaction of the precursor of the oxide superconducting material proceeds without being hindered by CO2, and the oxide superconducting material is sufficiently generated. In addition, when the oxygen concentration and the heat treatment temperature are in the above ranges, the size of each crystal grain constituting the polycrystal of the oxide superconducting material is prevented from becoming excessively large, and the polycrystal of the oxide superconducting material can be sufficiently formed. In this case, the time for heat treating the calcined film may be 1 minute or more, or may be 10 minutes or more. In addition, the time for heat treating the calcined film in this case may be 120 minutes or less, 70 minutes or less, or 60 minutes or less.

[0054] In the firing heat treatment step (S17), the polycrystalline layer is heat-treated at a temperature equal to or higher than the formation temperature of the oxide superconducting material to orient the polycrystals. In this way, a superconducting layer 25 with improved crystal orientation is obtained. The heat treatment temperature in the firing heat treatment step (S17) is, for example, 780°C or higher and 870°C or lower. The atmosphere in the firing heat treatment step (S17) is, for example, an argon atmosphere containing oxygen. The oxygen concentration in the atmosphere is, for example, more than 0 ppm and 3000 ppm or lower. The oxygen concentration may be 1000 ppm or lower. The heating rate and the cooling rate up to the heat treatment temperature in the firing heat treatment step (S17) are, for example, 10°C / min or higher and 1000°C / min or lower. The heating rate and the cooling rate may be the same or different. In the atmosphere, the temperature is raised from room temperature to the heat treatment temperature, and then cooled.

[0055] In the firing heat treatment step (S17), a part of the polycrystal may grow through a liquid phase. For example, the temperature and atmosphere in the firing heat treatment step (S17) are adjusted so that a liquid phase can be generated within the above-mentioned temperature range and oxygen concentration range of the atmosphere. This adjustment allows a part of the polycrystal to grow through a liquid phase. The conditions for melting a part of the polycrystal are appropriately set depending on the type, composition, etc. of the oxide superconducting material.

[0056] (Embodiment 2) A method for producing superconducting wire 1 of the present embodiment will be described with reference to Figures 1 to 4 and 6 to 8. The method for producing superconducting wire 1 of the present embodiment includes similar steps to the method for producing superconducting wire 1 of embodiment 1, but differs from the method for producing superconducting wire 1 of embodiment 1 in the following points.

[0057] 8, in the method for producing the superconducting wire 1 of the present embodiment, the calcined film forming step (S12) includes repeating a plurality of times the coating film forming step (S13) and the calcination heat treatment step (S14). In the calcined film forming step (S12), a plurality of layers of calcined films are formed.

[0058] Specifically, the calcined film forming step (S12) includes step S15 in addition to the coating film forming step (S13) and the calcination heat treatment step (S14). In step S15, it is determined whether the number of repetitions of steps S13 and S14 has reached the target number. If it is determined in step S15 that the number of repetitions of steps S13 and S14 has not reached the target number, steps S13 and S14 are performed again. In this way, the coating film forming step (S13) and the calcination heat treatment step (S14) are repeated multiple times until the number of repetitions of steps S13 and S14 reaches the target number. The solution applied in step S13 after it is determined in step S15 that the number of repetitions of steps S13 and S14 has not reached the target number is applied onto the calcined film that has already been formed.

[0059] 4, the calcined films are collectively heat-treated to perform the polycrystallization step (S16) and the firing heat treatment step (S17). Therefore, the number of times the polycrystallization step (S16) and the firing heat treatment step (S17) are performed can be reduced compared to the number of times the coating film formation step (S13) and the calcination heat treatment step (S14) are performed.

[0060] <Example> The present disclosure will be described in detail below with reference to examples. However, the present disclosure is not limited to the examples.

[0061] Referring to Table 1, in samples No. 1 to No. 37, the support substrate 10 is formed of a substrate 11 which is a clad material in which a copper (Cu) layer and a nickel (Ni) layer are laminated on a tape formed of stainless steel, and an intermediate layer 12 which is a laminate of a cerium oxide (CeO2) layer, an yttria stabilized zirconia (YSZ) layer, and an yttria (Y2O3) layer. The composition of the metal elements contained in the solution of the metal organic compound is Gd:Ba:Cu=1:2:3, and the oxide superconducting film 20 is GdBa2Cu3O x The oxide superconducting film 20 is made of (GdBCO). The thickness T of the oxide superconducting film 20 is 2 μm.

[0062] The manufacturing conditions of samples No. 1 to No. 37 are basically the same. Specifically, the calcination film formation step (S12) is performed in an atmosphere having an oxygen concentration of 100%, at a heat treatment temperature of 500° C., and for a heat treatment time of 30 minutes. In the main calcination heat treatment step (S17), heat treatment is performed in an argon atmosphere containing oxygen under conditions that can generate a liquid phase.

[0063] However, the manufacturing conditions of Samples No. 1 to No. 37 are different in the polycrystallization step (S16). Samples No. 1 to No. 7, Samples No. 12 to No. 17, Samples No. 19 to No. 23, and Samples No. 26 to No. 29 are samples obtained through the polycrystallization step (S16) that satisfies the following three conditions. The first condition is that the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of 1% or more. The second condition is that the polycrystallization step (S16) is performed at a heat treatment temperature of 700°C or more. The third condition is that the time for heat treating the calcined film in the polycrystallization step (S16) is 1 minute or more. In contrast, Samples No. 8, No. 9, No. 11, and No. 18 are samples obtained through the polycrystallization step (S16) that does not satisfy at least one of the above three conditions. Sample No. 10 is a sample obtained without carrying out the polycrystallization step (S16).

[0064] Samples No. 30 to No. 37 are samples obtained through a polycrystallization step (S16) that satisfies the following three conditions a, b, and c. Condition a is that the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of 0.01% or more and less than 1%. Condition b is that the polycrystallization step (S16) is performed at a heat treatment temperature of 650°C or more and less than 800°C. Condition c is that the time for heat treating the calcined film in the polycrystallization step (S16) is one minute or more.

[0065] In order to evaluate the degree of crystal orientation of the oxide superconducting film 20 of sample No. 1 to sample No. 37, the c-axis orientation rate was determined for the oxide superconducting film 20 of sample No. 1 to sample No. 37. The c-axis orientation rate was determined by the following method.

[0066] A two-dimensional detector is used to obtain X-ray diffraction images (see FIG. 9 for an example) of the oxide superconducting film 20 of each of samples No. 1 to No. 37. In X-ray diffraction using a two-dimensional detector, a highly oriented crystal plane of the measurement object is observed as a short arc-shaped diffraction image along the circumferential direction (χ direction), and a less oriented crystal plane of the measurement object is observed as a ring-shaped diffraction image along the χ direction. In X-ray diffraction using a two-dimensional detector, the diffraction intensity of each crystal plane of the measurement object is obtained by integrating the diffraction intensity of each crystal plane of the measurement object along the χ direction. A D8 DISCOVER (manufactured by Bruker) is used as the two-dimensional detector, and CuKα (wavelength: 1.54060 angstroms) is used as the radiation source.

[0067] 10, when the GdBCO constituting the oxide superconducting film 20 is c-axis oriented, the peaks corresponding to the (005) plane and the peaks corresponding to the (006) plane appear strongly in the X-ray diffraction chart obtained by the two-dimensional detector. In contrast, when the GdBCO constituting the oxide superconducting film 20 is not c-axis oriented, the peaks corresponding to the (103) plane or the (013) plane appear strongly in the X-ray diffraction chart obtained by the two-dimensional detector. Therefore, the c-axis orientation rate is defined as the value obtained by dividing the intensity of the peak corresponding to the (005) plane by the sum of the intensity of the peak corresponding to the (005) plane and the intensity of the peak corresponding to the (103) plane.

[0068] Table 1 shows the c-axis orientation rates of the oxide superconducting films 20 of Samples No. 1 to No. 37.

[0069] [Table 1]

[0070] In this embodiment, a sample having a c-axis orientation rate of 95% or more is evaluated as a good product, that is, a sample with a high degree of crystal orientation. A sample having a c-axis orientation rate of less than 95% is evaluated as a defective product, that is, a sample with a low degree of crystal orientation. From the c-axis orientation rates of Samples No. 1 to No. 7, Sample No. 10, Sample No. 12 to No. 17, Sample No. 19 to No. 23, and Sample No. 26 to No. 29, it can be seen that a superconducting wire having a high degree of crystal orientation of the oxide superconducting film 20 can be manufactured in a relatively short time by performing the polycrystallization step (S16) that satisfies the above three conditions. In addition, from Samples No. 24 and No. 25, even in an atmosphere having an oxygen concentration of less than 1%, a superconducting wire having a high degree of crystal orientation of the oxide superconducting film 20 can be obtained by extending the heating time to a certain extent (for example, 70 minutes) at a heat treatment temperature of 700°C or more. However, when the polycrystallization step (S16) that satisfies the above three conditions is performed, a superconducting wire having an oxide superconducting film 20 with a high degree of crystal orientation can be manufactured more efficiently and in a relatively short time.

[0071] For example, from the c-axis orientation ratios of Samples No. 1 to No. 9, it is understood that a superconducting wire having a high degree of crystal orientation of the oxide superconducting film 20 can be manufactured by performing the polycrystallization step (S16) in an atmosphere having an oxygen concentration of 1% or more. From the c-axis orientation ratios of Samples No. 1 and Samples No. 11 to No. 17, it is understood that a superconducting wire having a high degree of crystal orientation of the oxide superconducting film 20 can be manufactured by performing the polycrystallization step (S16) at a heat treatment temperature of 700° C. or more. From the c-axis orientation ratios of Samples No. 1 and Samples No. 18 to No. 23, it is understood that a superconducting wire having a high degree of crystal orientation of the oxide superconducting film 20 can be manufactured by performing the polycrystallization step (S16) for a heat treatment time of 1 minute or more. A comparison of Samples No. 20 to No. 23 with Samples No. 26 to No. 29 shows that even at a heating temperature of 900° C., a superconducting wire having a high degree of crystal orientation in the oxide superconducting film 20 can be obtained. In Samples No. 1 and No. 11 to No. 23, the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of 100% and with the heat treatment temperature and heat treatment time changed, but if the polycrystallization step (S16) is performed in an atmosphere having an oxygen concentration of 1% or more, a similar tendency in the c-axis orientation rate can be obtained when the heat treatment temperature and heat treatment time are changed in the same way.

[0072] From the c-axis orientation rates of samples No. 30 to No. 37, it can be seen that even in an atmosphere having an oxygen concentration of 0.01% or more and less than 1%, by setting the heat treatment temperature to 650°C or more and less than 800°C, a superconducting wire having a high degree of crystal orientation of the oxide superconducting film 20 can be obtained.

[0073] The disclosed embodiments 1 and 2 are illustrative in all respects and should not be considered as limiting. The scope of the present disclosure is defined by the claims rather than the above-described embodiments, and is intended to include all modifications within the scope of the claims and meanings equivalent thereto. [Explanation of symbols]

[0074] 1. Superconducting wire 10 Support substrate 10a Main surface 11 Substrate 12 Middle Class 20 Oxide superconducting film 25 Superconducting layer 30 protective layer 40 Stabilizing Layer

Claims

1. The method includes forming an oxide superconducting film on a support substrate, The step of forming the oxide superconducting film includes performing a step of laminating a superconducting layer of an oxide superconducting material at least once, The step of laminating the superconducting layer includes a calcination film formation step, a polycrystallization step, and a firing heat treatment step, The calcined film forming step includes performing a coating film forming step and a calcination heat treatment step at least once, In the coating film forming step, a coating film is formed by coating a solution of a metal organic compound, the metal organic compound being a compound of a metal element constituting the oxide superconducting material and an organic component, In the calcination heat treatment step, the coating film is heat-treated to pyrolyze the organic components, thereby forming a calcined film; In the polycrystallization step, the calcined film is heat-treated to form a polycrystalline layer containing polycrystals of the oxide superconducting material, and the time for heat-treating the calcined film in the polycrystallization step is 70 minutes or less. In the firing heat treatment step, the polycrystalline layer is heat-treated to orient the polycrystals, thereby forming the superconducting layer.

2. 2. The method for producing a superconducting wire according to claim 1, wherein the step of forming the oxide superconducting film includes repeating the step of stacking the superconducting layers a plurality of times.

3. 3. The method for producing a superconducting wire according to claim 1, wherein the calcined film forming step includes repeating the coating film forming step and the calcination heat treatment step a plurality of times.

4. 3. The method for producing a superconducting wire according to claim 1, wherein the polycrystallization step is performed in an atmosphere having an oxygen concentration of 1% or more.

5. 3. The method for producing a superconducting wire according to claim 1, wherein the polycrystallization step is performed at a heat treatment temperature of 700° C. or higher.

6. 3. The method for producing a superconducting wire according to claim 1, wherein the time for which the calcined film is heat-treated in the polycrystallization step is 1 minute or more.

7. 3. The method for producing a superconducting wire according to claim 1, wherein the polycrystallization step is performed in an atmosphere having an oxygen concentration of 0.01% or more and less than 1%, and at a heat treatment temperature of 650°C or more and less than 800°C.

8. 3. The method for producing a superconducting wire according to claim 1, wherein in the firing heat treatment step, a part or the whole of the polycrystal grows via a liquid phase.

9. 3. The method for producing a superconducting wire according to claim 1, wherein the oxide superconducting film has a thickness of 1 μm or more.

10. A method for manufacturing a superconducting wire as described in claim 1 or claim 2, wherein the time for heat treating the coating film in the pre-sintering heat treatment process is 30 minutes or less.

11. A method for manufacturing a superconducting wire as described in claim 1 or claim 2, wherein the polycrystallization process is carried out in an atmosphere having an oxygen partial pressure of 1 atm.

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