copper oxide superconductors

Abstract

To provide copper oxide superconductors. [Solution] REBa2Cu3O is obtained by doping RE2CuO4 crystals containing at least one rare earth element RE as artificial pins. 7-δ A copper oxide superconductor containing (δ is a real number between 0 and 1).

Description

[Technical Field]

[0001] This disclosure relates to copper oxide superconductors. [Background technology]

[0002] Currently, the development of new technologies for diverse superconductivity applications is rapidly progressing, including next-generation high-resolution medical high-field MRI, superconducting motors (for electric aircraft and ship propulsion), large wind turbines, electromagnets for magnetic levitation trains, and even superconducting coils for nuclear fusion plasma containment. For their implementation, the development of high-performance, low-cost superconducting wires for medium-to-high temperature and high-field applications is urgently needed. REBa2Cu3O is considered the most promising candidate for this purpose. 7-δ Development is underway on coated conductors made by compositing thin films of superconductors (hereinafter also referred to as "RE123-type superconductors") epitaxially grown on single-crystal tape substrates. Furthermore, in order to achieve a high critical current density (Jc) in the magnetic field, it is necessary to introduce magnetic flux pinning points, and the introduction of artificial pinning points of the oxide insulator BaMO3 (M=Zr,Sn,Hf, etc., hereinafter also referred to as "BMO") is being actively researched. The main manufacturing method is the PLD (pulsed laser deposition) method, in which a superconducting thin film is grown on a single-crystal substrate while irradiating a target with an ion beam. Patent document 1 describes a superconducting coil using RE123-type superconductors. Fujikura, a major manufacturer of superconducting wires, has achieved high Jc in superconducting thin films by introducing BMO nanorod-type artificial pins into the superconductivity using this method. However, this method uses expensive vacuum equipment such as lasers and sputtering devices, so the manufacturing cost is very high. Therefore, the MOD (metal-organic deposition) method was developed as a lower-cost method for creating superconducting thin films, and methods for introducing BMO nanoparticles as artificial pins have been studied. However, increasing the amount of introduced artificial pins leads to particle coarsening, resulting in poor pinning efficiency. Furthermore, the crystal lattice distortion associated with coarsening degrades the superconducting properties of the base material, limiting the improvement of current density in a magnetic field. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-20665 [Overview of the project] [Problems that the invention aims to solve]

[0004] To overcome this limitation, we propose a fluorine-free MOD method for RE123-based superconductors in which RE2CuO4 superconductors (hereinafter also referred to as "RE214-based superconductors"), which have a lower Tc (lower temperature critical temperature) than the base material, are introduced as effective artificial pins. This method has two advantages: (1) The 214-based superconductor has the same perovskite structure as the RE123-based superconductor base material, and its lattice constant is very close to that of the base material. Compared to conventional BMO-type artificial pinning points, it is possible to increase the amount of artificial pins introduced without disturbing the crystal structure of the base material. (2) At low temperatures (in the temperature range below the Tc of RE214-based superconductors), the pinning mechanism is a repulsive pinning mechanism due to kinetic energy interaction, unlike the attractive pinning mechanism due to condensation energy interaction of conventional insulators such as BMO. This has a high potential to produce a stronger pinning force than the attractive pinning caused by the condensation energy density of conventional insulators and normal conducting materials, making it possible to achieve even higher critical current densities in magnetic fields. This method originated from prior research by Daisuke Miura and others, one of the inventors, who discovered that when a low-Tc superconductor (such as Nb or NbTa) different from the base material is introduced into an alloy-based superconductor, Nb-Ti, the pinning mechanism of the magnetic flux lines behaves as a repulsive pin due to kinetic energy interaction. I could not find any research papers on RE123-based superconductors that introduce RE214-based superconductors, which have a lower Tc than the base material, as effective artificial pins.

[0005] For the improvement of the high critical current density (Jc) in a magnetic field in conventional RE123-based superconductors, the introduction of insulating BMO-type artificial pinning points has been actively studied. However, when the introduction amount is increased, coarsening of the particle size occurs, the pinning efficiency deteriorates, and furthermore, due to the crystal lattice strain accompanying the coarsening, the superconducting properties of the base material also deteriorate. Therefore, there is a limit to the improvement of the current density in a magnetic field. In order to improve Jc in a magnetic field of a superconductor, it is necessary to introduce effective pinning points inside the superconductor to pin the quantized magnetic flux. However, for RE123-based superconductors, which are high-temperature cuprate superconductors, there has been no research on introducing RE214-based superconductors with low TC as artificial pins within the investigated range.

[0006] This disclosure has been made to solve the above problems and aims to provide a cuprate superconductor.

Means for Solving the Problems

[0007] By introducing this RE214 system as an artificial pin, improvement of Jc in a magnetic field was confirmed with the same volume ratio of introduction as that of BMO. Furthermore, a significant improvement in the introduction amount was achieved compared to BMO. This disclosure has the following aspects. [1] REBa2Cu3O doped with RE2CuO4 crystals containing at least one kind of rare earth element RE as an artificial pin 7-δ (δ is a real number from 0 to 1.) including a cuprate superconductor. [2] The artificial pin has a difference in crystal constants from the REBa2Cu3O 7-δ of 5% or less, and the artificial pin RE is Gd, Y, Nd, or Sm. The cuprate superconductor according to [1]. [3] The artificial pin is further co-added with BMO. The cuprate superconductor according to [2]. [4] The artificial pin constitutes one or more plates, and the REBa2Cu3O 7-δA copper oxide superconductor as described in [1] or [2], wherein the ab plane and the plate are introduced so as to be parallel. [5] The copper oxide superconductor according to [3], wherein the number of crystal lattices arranged continuously in the b-axis direction of the artificial pins constituting the plate is 30 or less, and the number of crystal lattices arranged in the c-axis direction is 1 to 5. [6] The copper oxide superconductor according to [1] or [2], wherein the artificial pin comprises Gd2CuO4. [7] A copper oxide superconductor according to [1] or [2], comprising a plurality of artificial pins having different crystal constants. [8] The Tc of the artificial pin is the REBa2Cu3O 7-δ A copper oxide superconductor described in [1] or [2], with a Tc lower than that of (δ being a real number between 0 and 1). [9] The crystal structure of the artificial pin and the REBa2Cu3O 7-δ A copper oxide superconductor according to [1] or [2], wherein the crystal structure of and are both perovskite structures.

[10] A thin film copper oxide superconductor as described in [1] or [2].

[11] The copper oxide superconductor described in [7], wherein the average film thickness measured by scanning electron microscopy (SEM) observation is 500 nm or less.

[12] A copper oxide superconductor according to [1] or [2], prepared by a fluorine-free organometallic vapor deposition method.

[13] The copper oxide superconductor according to [1] or [2], wherein the total content of the artificial pins is 0.1 volume% or more and 12.0 volume% or less relative to the total volume of the copper oxide superconductor.

[14] The Jc of the aforementioned copper oxide superconductor is 1.0 to 10.0 MA / cm² at 0.5 T under a temperature of 4.2 K. 2 , 0.5~5.0 MA / cm at 3.0T 2 The copper oxide superconductor described above in [1] or [2].

[15] The Jc of the copper oxide superconductor is greater than or equal to 1.2 times that of the REBa2Cu3O not doped with the artificial pinning centers 7-δ The copper oxide superconductor according to [1] or [2], wherein Jc of the copper oxide superconductor is 1.2 times or more that of the copper oxide superconductor

[16] The copper oxide superconductor according to [1] or [2], wherein the value of the c-axis lattice misfit when the artificial pinning centers are stacked in the c-axis direction by 3 units is 4.0 or less

[17] The copper oxide superconductor according to [1] or [2], wherein the peak ratio represented by Gd123(005) / LAO(001) in the XRD peak measured by surface XRD θ-2θ scan is 0.5 or more

[18] A copper oxide superconductor according to any one of [1] or [2], characterized in that it is used in MRI, a superconducting motor for an electric aircraft, a large wind turbine, or a coil for confining a fusion plasma

[19] An artificial pinning center containing at least one rare earth element RE<s

[20] The artificial pinning center according to

[19] , characterized in that BMO is co-added

[21] REBa2Cu3O doped with RE2CuO4 crystals containing at least one rare earth element RE as artificial pinning centers 7-δ (δ is a real number from 0 to 1.) A method for producing a copper oxide superconductor, including producing a thin film by a fluorine-free organic metal vapor deposition method

[22] As the artificial pinning centers, BMO is further co-added to REBa2Cu3O 7-δ (δ is a real number from 0 to 1.) A method for producing a copper oxide superconductor according to

[21] , including producing a thin film by a fluorine-free organic metal vapor deposition method

[23] The fluorine-free organometallic deposition method is a method for producing a copper oxide superconductor according to

[21] or

[22] , comprising preparing a mixture by adding a metal-containing compound to a mixture containing RE, Ba, and Cu in a molar ratio of RE:Ba:Cu=1:2:3 such that the total amount of RE and Cu, or Ba and M added, is 0.1 to 20.0 mol%. [twenty four] A method for producing a copper oxide superconductor according to

[23] , comprising spin-coating the aforementioned mixture onto a LaAlO3(LAO)100 single crystal, drying at 300-500K for 10-60 minutes, and calcining in air at 600-1000K for 10-60 minutes to produce a precursor. [twenty five] The precursor is subjected to a mixture of gases containing nitrogen gas and oxygen gas, with an oxygen partial pressure of 10 -4 ~10 -8 A method for producing a copper oxide superconductor according to

[24] , comprising firing at atm at a flow rate of 0.05 to 1.0 L / min and at 1000 to 1200 K for 10 to 60 minutes under heating conditions of 1 to 10 K / min to form a film.

[26] A method for producing a copper oxide superconductor according to

[25] , comprising annealing the aforementioned film in an oxygen atmosphere at 400 to 800 K for 3 to 10 hours to form a thin film. [Effects of the Invention]

[0008] The copper oxide superconductors of this disclosure can improve the critical current density in a magnetic field. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows molecular model diagrams of the crystal lattices of each material. [Figure 2] This is a schematic diagram illustrating the shape of an artificial pin when a magnetic field is applied such that the magnetic flux lines are oriented vertically. [Figure 3] Figure 3 is a cross-sectional view of a superconducting coil. [Figure 4] Figure 4 is a cross-sectional view showing a copper oxide superconductor according to an embodiment of this disclosure. [Figure 5]Figure 5 is a perspective view of a circular pancake-wound coil. [Figure 6] Figure 6 is a perspective view of a cylindrical layer-wound coil. [Figure 7] Figure 7 is a perspective view of a superconducting wire using the oxide superconducting wire material of this disclosure. [Figure 8] Figure 8 is a perspective view of a laminated tape made by stacking multiple tape-shaped oxide superconducting wires. [Figure 9] Figure 9 is a schematic diagram illustrating a method for producing copper oxide superconductors using a chemical solution method. [Figure 10] Figure 10 is a graph showing the relationship between temperature and time in the drying and calcination processes. [Figure 11] Figure 11 is a graph showing the relationship between temperature and time during the main firing process. [Figure 12] Figure 12 is a graph showing the relationship between temperature and time in the oxygen annealing process. [Figure 13] Figure 13 is a graph showing the lattice constant of the substrate crystal and its temperature dependence. [Figure 14] Figure 14 is a graph showing the relationship between temperature and time in the drying and calcination processes in Example 1. [Figure 15] Figure 15 is a graph showing the relationship between temperature and time during the main firing process in Example 1. [Figure 16] Figure 16 is a graph showing the relationship between temperature and time in the oxygen annealing process in Example 1. [Figure 17] Figure 17 shows the XRD patterns of Gd123 non-doped thin films and Gd214-introduced Gd123 thin films at various volume fractions (0.99 vol% to 5.95 vol%). [Figure 18]Figure 18(a) is a magnified section of the TEM image of a Gd123 thin film into which 1 vol% of Gd214 and 1 vol% of Nd214 have been introduced, Figure 18(b) is the TEM image before magnification, 18(c) is a diagram of the molecular model of the Gd123 thin film into which 1 vol% of Gd214 and 1 vol% of Nd214 have been introduced, and 18(d) is a diagram comparing the magnified TEM image of the introduced portion in Figure 18(a) with the molecular model in Figure 18(c) when the angle of the crystal lattice was changed. [Figure 19] Figure 19 shows TEM images and molecular models of the Gd214 unit cell observed from various angles. [Figure 20] Figure 20(d) is a TEM image of Gd in Figure 18(a) with elemental mapping. Figure 20(e) is a TEM image of Ba in Figure 18(a) with elemental mapping. [Figure 21] Figure 21 is a graph showing the temperature dependence of magnetic susceptibility for Gd123 non-doped thin films and Gd214-introduced Gd123 thin films at various volume fractions (0.99 vol% to 5.95 vol%). [Figure 22] Figure 22 is a graph showing the magnetic field dependence of JC at 4.2 K and 10 K for Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). [Figure 23] Figure 23 is a graph showing the magnetic field dependence of JC at 20 K, 30 K, and 40 K for Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). [Figure 24] Figure 23 is a graph showing the magnetic field dependence of JC at 50 K, 60 K, and 77.3 K for Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). [Figure 25] Figure 25 is a graph showing the magnetic field dependence of Fp (macroscopic pinning force density) at 4.2 K and 10 K for Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). [Figure 26]Figure 26 is a graph showing the magnetic field dependence of Fp at 20 K, 30 K, and 40 K for Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). [Figure 27] Figure 27 is a graph showing the magnetic field dependence of Fp at 50 K, 60 K, and 77.3 K for Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). [Figure 28] Figure 28 is a graph showing the characteristics of the amount of JC introduced into BMO-introduced Gd123 thin films and Gd214-introduced Gd123 thin films at 0 T, 1 T, and 2 T at 4.2 K and 60 K. [Figure 29] Figure 29 is a graph showing the dependence of the peak ratio of Gd123(005) / LAO(001) on the APC volume fraction. [Figure 30] Figure 30(a) is a TEM image of a sample doped with 2 vol% Gd214 artificial pins in a Gd123 matrix. Figure 30(b) is a TEM image of a sample doped with 5 vol% Gd214 artificial pins in a Gd123 matrix. [Figure 31] Figure 31 is a graph comparing the Jc-T characteristics of each sample with 1 vol% artificial pins at 0.5T and 3T. [Figure 32] Figure 32 is a graph comparing the Jc-T characteristics of each sample with 2 vol% artificial pins at 0.5T and 3T. [Figure 33] Figure 33 is a graph showing the volume dependence of Jc on the addition of various artificial pins (4.2~60K, 0.5 T). [Figure 34] Figure 34 is a graph showing the volume dependence of Jc on the addition of various artificial pins (4.2~60K, 3.0 T). [Figure 35] Figures 35(a) and (b) are graphs showing the temperature dependence of JC for each APC-doped film, respectively. [Figure 36] Figure 36 is a graph showing the relationship between the direction of the magnetic field and the Jc value for each material. [Figure 37] Figure 37 shows a schematic diagram of how the plate pins trap magnetic flux lines at 0° and 90°, and corresponding TEM images of the plate pins. [Figure 38] Figure 38 is a schematic diagram showing how plate pins trap magnetic flux lines at 0°, 45°, and 90°. [Figure 39] Figure 39 is a related crystal diagram output using the crystal plotting software VESTA. [Figure 40] Figure 40 shows the crystal diagram of the T' structure and the relationship between Tc and Ce doping amounts. [Figure 41] Figure 41 shows the crystal diagram of the T structure and the relationship between Tc and Sr doping amount. [Figure 42] Figure 42 shows the TEM image when Gd214 is introduced alone. [Figure 43] Figure 43 shows the results when two different RE214s, Gd214 and Sm214, are co-added. [Figure 44] Figure 44 is a schematic diagram showing the Jc accuracy dependence of each APC-doped and undoped film. [Figure 45] Figure 45 shows the Jc accuracy dependence of Gd214 nanoplate APC-doped and undoped films. [Modes for carrying out the invention]

[0010] The following provides further details about this disclosure.

[0011] Copper oxide superconductors REBa2Cu3O contains rare earth elements RE. 7-δ A copper oxide superconductor having (δ is a real number between 0 and 1) as the matrix phase, and containing at least one type of RE2CuO4 crystal as an artificial pinning point. RE214 with a crystal constant difference of 5% or less from the matrix phase is preferred. For the artificial pinning point RE, Gd, Y, Nd, and Sm are more preferred. BMO may also be present.

[0012] Figure 1 shows molecular model diagrams of the crystal lattices of each material, created using the crystal modeling software VESTA.

[0013] Figure 2 is a schematic diagram showing the shape of an artificial pin when a magnetic field is applied so that the magnetic flux lines are in the vertical direction. Figure 2(a) is a one-dimensional pin (bamboo shoot-shaped (rod-shaped) pin) along the c-axis, a two-dimensional pin along the c-axis, Figure 2(c) is a two-dimensional pin perpendicular to the c-axis, and Figure 2(d) is Figure 2(a) shows an artificial pin in which Jc increases when a magnetic field is applied in the c-axis direction. Figure 2(b) shows an artificial pin in which the magnetic field Jc increases when a magnetic field is applied parallel to the ab plane (in other words, perpendicular to the c axis). Because the longer side of the artificial pin is parallel to the magnetic flux, the pinning effect is high and efficient relative to the size of the artificial pin. Figure 2(c) shows an artificial pin in which Jc increases when a magnetic field is applied parallel to the ab plane (in other words, perpendicular to the c axis direction). Figure 2(d) shows an artificial pin in which Jc increases when a magnetic field is applied in any direction. However, because the artificial pin is thick in all directions, it becomes large, but the pinning effect relative to its size is low, making it inefficient. It is difficult to increase Jc because it is difficult to miniaturize the artificial pin when its volume is large. In addition, the crystal structure of the base material is also easily distorted. The copper oxide superconductor of this invention has artificial pins REBa2Cu3O 7-δ Since the artificial pin is introduced in a plate shape so as to be parallel to the ab plane (in other words, perpendicular to the c axis direction), it has the structure shown in Figure 2(b).

[0014] Figure 3 is a partial cross-sectional view of a coil wound with a tape made of the copper oxide superconductor of the present invention shown in Figure 2(b), and includes the artificial pin shown in Figure 2(b). The magnetic field is parallel to the ab plane and perpendicular to the c axis. In Figure 3, the magnetic field is highest in the central portion shown by the thick line, so it is preferable that the pinning effect is strongest in this central portion. Since the artificial pin in this application has a plate shape with a long ab plane, it can also exert a pinning effect in this central portion.

[0015] The copper oxide superconductor of this disclosure preferably includes a plurality of artificial pins with different crystal constants that do not bond to each other. By including multiple types of artificial pins, the artificial pins are introduced independently without bonding to each other, compared to the case where only one type of artificial pin is introduced at the same volume fraction, resulting in miniaturization and increased density. Therefore, it becomes easier to increase the Jc value.

[0016] The crystal structure of the artificial pin and the REBa2Cu3O 7-δ It is preferable that both the crystal structure and the structure are perovskite structures. The difference in lattice constants at room temperature is preferably 0.01 to 0.1 Å, more preferably 0.015 to 0.08 Å, and even more preferably 0.02 to 0.05 Å for all a- to c axis lattices. REBa2Cu3O 7-δ The difference in lattice constants at room temperature between the c-axis of the crystal structure of the artificial pin and the c-axis of the crystal structure of the artificial pin is preferably 3% or less, more preferably 2% or less, even more preferably 1% or less, and particularly preferably 0.5% or less. The critical temperature (Tc) of the artificial pin is the same as that of REBa2Cu3O 7-δ It is preferable that Tc (where δ is a real number between 0 and 1) is lower than the given value.

[0017] The copper oxide superconductor of this disclosure is preferably a thin film.

[0018] When the copper oxide superconductor of this disclosure is a thin film, the average film thickness measured by scanning electron microscopy (SEM) observation is preferably 500 nm or less, more preferably 1 to 500 nm, and even more preferably 10 to 400 nm. When the average film thickness is within the above range, it is easier to increase the current that can be carried.

[0019] The method for producing the copper oxide superconductor described herein is not particularly limited, but may, for example, be a fluorine-free organometallic vapor deposition method.

[0020] The content of the artificial pins is preferably 0.1% by volume or more, and more preferably 0.1 to 12.0% by volume, relative to the total volume of the copper oxide superconductor. With conventional α-Ti pins added to NbTi, the crystal density (JC) improves up to about 25 vol%. Adding RE214 to RE123 thin films also increases the JC to a similar level. The highest JC is obtained with approximately 1.5 vol% BMO and 2 vol% RE214 pins. Adding 1 vol% BMO and 2 vol% RE214 simultaneously can achieve even higher JC levels. Therefore, by simultaneously adding various artificial pins with different crystal constants, the peak JC relative to the amount introduced can be shifted towards higher concentration additions. Keeping the concentration below the above upper limit makes crystallization of the RE123 matrix easier.

[0021] The Jc of the aforementioned copper oxide superconductor is 1.0 to 10.0 MA / cm² at 0.5 T under a temperature of 4.2 K. 2 , 0.5~5.0 MA / cm at 3.0T 2 It is preferable that the above conditions are met.

[0022] The Jc of the copper oxide superconductor is REBa2Cu3O that is not doped with the artificial pins. 7-δ (RE is Gd, Y, Sm, Nd, or Eu) Preferably, the Jc of the copper oxide superconductor is 1.5 times or more.

[0023] When three units of the artificial pins are stacked in the c-axis direction, the c-axis lattice misfit value is preferably ±4.0 or less, more preferably ±2.0, and even more preferably ±0.1.

[0024] In the XRD peaks measured by surface XRDθ-2θ scan, it is preferable that the peak ratio represented by Gd123(005) / LAO(001) is 0.5 or greater.

[0025] Applications of copper oxide superconductors The copper oxide superconductors of this disclosure can be used in MRI, superconducting motors for electric aircraft, large wind turbines, or coils for fusion plasma containment.

[0026] Artificial pins It is preferable that the artificial pin contains at least one type of RE2CuO4 crystal. RE214 with a crystal constant difference of 5% or less from the matrix phase is preferred. For the artificial pinning point RE, Gd, Y, Nd, and Sm are more preferred. BMO may also be present. RE123 copper oxide high-temperature superconductor is a high-temperature superconductor with a Tc of 90 K or higher, which is higher than the boiling point of liquid nitrogen (77.3 K). In recent years, the price of helium has soared, and the cooling cost of low-temperature superconductors has become a concern. However, RE123 can transition to a superconducting state without using liquid helium, so a significant reduction in cooling costs is expected. Furthermore, compared to other high-Tc copper oxide high-temperature superconductors, it has a high HC2 content and is strong against high magnetic fields, so it is expected to have high-magnetic-field applications in 3T MRI and electric aircraft, and research is progressing on it as a next-generation wire material. In addition, the RE123 crystal has a perovskite structure and is composed of a CuO2 plane in the superconducting layer that exhibits superconductivity and a CuO plane in the block layer that supplies carriers. This block layer of the CuO plane acts as intrinsic pinning, as described in 1.3.4 2D PC. Furthermore, due to its high anisotropy and short coherence length, crystal orientation in both the c-axis and ab-axis directions is necessary to produce high-quality RE123 wire.

[0027] The Tc of RE214 copper oxide superconductors is lower than that of RE123, being 18.5 K for Gd214, 32.8 K for Nd214, 30.7 K for Sm214, and 28.9 K for Eu214. Furthermore, as shown in Figure 1, the RE214 crystal adopts the same perovskite structure as RE123 and has relatively similar lattice constants, resulting in less lattice misfit. This is expected to reduce the distortion of the matrix crystallinity when RE214 is introduced into RE123 as an artificial pinning center, thereby reducing the deterioration of superconducting properties. Table 1 shows the Tc and lattice constants of Gd123 and RE214.

[0028] [Table 1]

[0029] The spacing between magnetic flux lines is determined by the magnitude of the applied magnetic field; therefore, the higher the magnetic field, the narrower the spacing between the flux lines, and the transition from superconductivity to normal conductivity occurs when the spacing is zero. Miniaturization of artificial pins means increased density. A higher density distribution allows for pinning effect on a greater number of magnetic flux lines. Furthermore, the pinning efficiency of each individual pin also improves. In the present invention, it is preferable that the artificial pins are made of randomly introduced, refined plates. Preferably, the number of crystal lattices arranged continuously in the b-axis direction of the artificial pins on a single plate is 15 or less, more preferably 1 to 15, more preferably 3 to 13, and even more preferably 5 to 10. The number of crystal lattices arranged in the c-axis direction is preferably 1 to 3.

[0030] ≪Applications≫ The copper oxide superconductors of this disclosure can be used in a variety of fields, including medical MRI, superconducting power cables, superconducting linear motors, electric aircraft, superconducting generators, and superconducting electromagnets in nuclear fusion reactors.

[0031] Figure 4 is a cross-sectional view showing an oxide superconducting wire containing a copper oxide superconductor according to an embodiment of the present disclosure. The oxide superconducting wire 10 includes a laminate 9 on a metal substrate 7, in which a diffusion prevention layer 6, a bed layer 5, an orientation layer 4, a cap layer 3, a superconducting layer 1 composed of the copper oxide superconductor of the present disclosure, and a protective layer 2 are laminated in that order, and the outer periphery of the laminate 9 is covered with a stabilizing layer 8. The oxide superconducting wire 10 is in the form of a tape.

[0032] (Metal substrate 7) A specific example of the metal constituting the metal substrate 7 is a nickel alloy, such as Hastelloy (registered trademark). The thickness of the metal substrate 7 can be adjusted as appropriate depending on the purpose, for example, within the range of 10 to 1000 μm.

[0033] (Diffusion prevention layer 6) The diffusion prevention layer 6 has the function of suppressing the diffusion of some of the components of the metal substrate 7 and their incorporation into the oxide superconducting layer 1 as impurities. The diffusion prevention layer 6 is composed of, for example, Si3N4, Al2O3, GZO (Gd2Zr2O7), etc. The thickness of the diffusion prevention layer 6 is, for example, 10 to 400 nm.

[0034] (Bed level 5) A bed layer 5 may be formed on the diffusion prevention layer 6 to reduce the reaction at the interface between the metal substrate 7 and the oxide superconducting layer 1 and to improve the orientation of the layer formed thereon. Examples of materials for the bed layer include Y2O3, Er2O3, CeO2, Dy2O3, Eu2O3, Ho2O3, and La2O3. The thickness of the bed layer 5 is, for example, 10 to 100 nm.

[0035] (Orientation layer 4) The orientation layer 4 is formed from a biaxially oriented material to control the crystal orientation of the cap layer above it. Examples of materials for the orientation layer 4 include metal oxides such as Gd2Zr2O7, MgO, ZrO2-Y2O3(YSZ), SrTiO3, CeO2, Y2O3, Al2O3, Gd2O3, Zr2O3, Ho2O3, and Nd2O3.

[0036] (Cap layer 3) The cap layer 3 is formed on the upper surface of the orientation layer described above and is made of a material that allows the crystal grains to self-orient in the in-plane direction. Examples of materials for the cap layer 3 include CeO2, Y2O3, Al2O3, Gd2O3, ZrO2, YSZ, Ho2O3, Nd2O3, and LaMnO3. The thickness of the cap layer 3 can be in the range of 50 to 5000 nm.

[0037] (Superconducting layer 1) The superconducting layer 1 is composed of the copper oxide superconductor of this disclosure. The plane formed by the length direction and the width direction is the ab plane, and the thickness direction is the c axis. The thickness of the superconducting layer 1 is, for example, about 0.5 to 5 μm. This thickness is preferably uniform in the longitudinal direction.

[0038] (Protective layer 2) The protective layer 2 is laminated on one side of the superconducting layer 1 (the side opposite to the side facing the cap layer 3). The protective layer 2 has functions such as bypassing overcurrents generated during an accident and suppressing chemical reactions that occur between the superconducting layer 1 and the layer provided on top of the protective layer 2. Examples of materials for the protective layer 2 include silver (Ag), copper (Cu), gold (Au), alloys of gold and silver, other silver alloys, copper alloys, gold alloys, etc. The thickness of the protective layer 2 is, for example, in the range of 1 to 30 μm. The protective layer 2 may be composed of two or more metals or two or more metal layers. The protective layer 2 can be formed by vapor deposition, sputtering, etc.

[0039] (Stabilization layer 8) The stabilization layer 8 covers the entire outer surface of the superconducting laminate 9. The stabilization layer 8 has functions such as bypassing overcurrents generated during a fault and mechanically reinforcing the oxide superconducting layer 1 and the protective layer 2. The stabilization layer 8 is made of, for example, a copper (Cu) plating layer. The thickness of the stabilization layer 8 is not particularly limited, but is, for example, in the range of 1 to 300 μm.

[0040] <Pancake-wound coil> Figure 5 is a perspective view of an annular pancake-wound coil. The pancake-wound coil 100 in Figure 5 is constructed by winding a tape-shaped oxide superconducting wire 10 many times in the thickness direction and stacking them.

[0041] <Layered wound coil> Figure 6 is a perspective view of a cylindrical layered coil. The layered coil 101 in Figure 6 is constructed by winding a tape-shaped oxide superconducting wire 10 helically many times in the thickness direction and stacking them. The thickness of the wound tape and the radius of the central gap are similar to those of a pancake-wound coil.

[0042] <Superconducting wire> Figure 7 is a perspective view of a superconducting wire 103 using the oxide superconducting wire 10 of this disclosure. In the superconducting wire 103 of Figure 7, a central copper wire C is wound multiple times in a helical manner in the thickness direction with tape-shaped oxide superconducting wire 10, and an insulating layer is formed by winding polyimide tape or the like around it to create an insulating layer.

[0043] <Laminated Tape> Figure 8 is a perspective view of a laminated tape formed by stacking multiple tape-shaped oxide superconducting wires 10. In Figure 8, the laminated tape 104 is insulated by winding a polyimide tape or the like around the laminate, which is made up of multiple tape-shaped oxide superconducting wires 10, to form an insulating layer I.

[0044] ≪Method for manufacturing copper oxide superconductors≫ REBa2Cu3O contains rare earth elements RE. 7-δ A copper oxide superconductor having (δ is a real number between 0 and 1) as the matrix phase, and containing at least one type of RE2CuO4 crystal as an artificial pinning point. For RE214, the difference in crystal constant from the matrix phase is preferably within 5%. For the artificial pinning point RE, Gd, Y, Nd, and Sm are more preferred. BMO may also be present. The conditions used in the fluorine-free organometallic vapor deposition method can be those that are already known.

[0045] To form a perovskite-type oxide on a substrate, an amorphous thin film that produces this composition is formed on the substrate. Methods for forming the amorphous thin film include MBE, vacuum deposition, CVD, and coating pyrolysis, but coating pyrolysis is preferable because it has fewer restrictions on the deposition atmosphere and allows for easy large-area deposition. The coating pyrolysis method employs a precursor solution coating technique based on chemical solution methods, including spin coating, dip coating, spray coating, and inkjet coating. A solution of a metal-organic compound producing the above composition is coated onto a substrate using a coating method such as spin coating, spray coating, or inkjet coating. After drying, the organic components in the metal-organic compound are decomposed to form an amorphous thin film. Preferably, the metal-organic compound is an organometallic salt or alkoxide salt. Examples of such organic compounds include β-diketonate, long-chain alkoxides with 6 or more carbon atoms, and organic acid salts that may contain halogens. Examples of such organic acids include 2-ethylhexanoic acid, naphthenic acid, caprylic acid, and stearic acid. Among these, the metal salt of 2-ethylhexanoic acid represented by the following chemical formula (1) is preferred. The decomposition of the organic components in the metal-organic compound can be carried out, for example, by calcination by heating and holding at a temperature of 300-600°C, or by irradiation with ultraviolet light using an ultraviolet lamp. The solution should be one in which the metal-organic compound dissolves, and examples include aromatic hydrocarbons such as toluene, and fatty acids such as octic acid and neodecanoic acid.

[0046] [ka]

[0047] In equation (1), M is a metal ion. As for metal ions, Ba 2+ ,Cu 2+ ,Zr 2+ Ce 2+ ,Sn 2+ ,Hf 2+ ,Gd 2+ , and Y 2+ This includes having the same number of 2-ethylhexanoate ions as the valence of the metal ions.

[0048] The method for producing the copper oxide superconductor of this disclosure involves, in the fluorine-free organometallic deposition method, adding a mixture containing RE, Ba, and Cu in a molar ratio of RE:Ba:Cu=1:2:3 to a mixture in which RE214 is added in a ratio of RE:Cu=2:1, or to a mixture in which BMO is added in a ratio of Ba:M=1:1. The volume of the artificial pin is V APC The volume of the base material is V RE123 As x mol% = (V APC )x / {(V Gd123 )100-x+(V APC The volume fraction is calculated from the molar ratio according to the formula )x} vol%. The mixture to be added is prepared so that its volume fraction is between 1 and 12 vol%. The process may also include preparing a mixture by adding a metal-containing compound such that the total amount of RE and Cu, or Ba and M added, is 0.1 to 20.0 mol%. This mass ratio allows for the production of copper oxide superconductors with an artificial pin content of 0.1 to 20 vol%.

[0049] Figure 9 is a schematic diagram illustrating a method for manufacturing copper oxide superconductors using a chemical solution method. The method for manufacturing copper oxide superconductors shown in Figure 9 includes: (1) a coating step of applying a solution containing a metal compound onto a substrate; (2) a drying step of drying the coated solution; (3) a calcination step of calcining the dried solution to obtain an amorphous precursor; (4) a final calcination step of performing a final calcination on the obtained precursor; and (5) an oxygen annealing step of performing an oxygen annealing on the final calcined material.

[0050] (1) Coating process As the metal compound, metal salts of 2-ethylhexanoic acid are preferred, and Zr, Ce, Sn, Hf, Gd, and Y salts of 2-ethylhexanoic acid are more preferred. The amount of metal-containing compound added is preferably 0.5 to 10.0 mol%, more preferably 1.0 to 8.0 mol%, and even more preferably 1.0 to 6.0 mol%. In the coating process, the mixture is spin-coated onto the ab-plane of a LaAlO3(LAO)100 single crystal. Because crystals tend to grow in the horizontal plane, it is difficult to grow the artificial pin crystal in the c-axis direction, and it is easier to grow it in a plate-like shape along the ab-plane.

[0051] (2) Drying process In the drying process, it is preferable to dry the spin-coated solution at 300-500K for 10-60 minutes. The drying time is preferably 10 to 60 minutes, more preferably 15 to 55 minutes, and even more preferably 20 to 50 minutes.

[0052] (3) Pre-firing process The process may also include pre-calcining (firing) the dried coating film in air at 600-1000K for 10-60 minutes to produce an amorphous precursor. The drying temperature is preferably 300-500K, more preferably 330-480K, and even more preferably 350-450K. The firing temperature is preferably 600-1000K, and more preferably 800-1000K. The baking time is preferably 10 to 60 minutes, more preferably 15 to 55 minutes, and even more preferably 20 to 50 minutes.

[0053] It is preferable to repeat the coating process and calcination process three times to build up multiple amorphous layers as a precursor. The thickness of the precursor formed in the three cycles is preferably 300 to 1000 nm.

[0054] Figure 10 is a graph showing the relationship between temperature and time in the drying process and the calcination process. In the calcination process, it is preferable to perform temperature control in four stages: a stage of maintaining a constant temperature for a certain period of time (1-1), a stage of raising the temperature to a predetermined temperature in a certain period of time (1-2), a stage of maintaining the predetermined temperature for a certain period of time (1-3), and a stage of cooling from the predetermined temperature within a certain period of time (1-4).

[0055] (4) Firing process The method for producing a copper oxide superconductor according to this disclosure further comprises raising the precursor in a mixed gas containing nitrogen gas and oxygen gas, with an oxygen partial pressure of 10 -4 ~10 -8The process may also include firing (main firing) at an atm at a flow rate of 0.05 to 1.0 L / min, at 1000 to 1200 K for 10 to 60 minutes, under heating conditions of 1 to 10 K / min, to form a film. The partial pressure of oxygen is 10 -4 ~10 -8 ATM is preferred, 10 -3 ~10 -7 ATM is more preferred, 10 -4 ~10 -6 ATMs are even more preferable. The flow rate of oxygen gas is preferably 0.05 to 1.0 L / min, more preferably 0.1 to 0.8 L / min, and even more preferably 0.15 to 0.5 L / min. The firing temperature is preferably 1000-1200K, more preferably 1050-1180K, and even more preferably 1100-1170K. The heating time during baking is preferably 10 to 60 minutes, more preferably 15 to 55 minutes, and even more preferably 20 to 50 minutes. The heating rate during firing is preferably 1 to 10 K / min, more preferably 2 to 8 K / min, and even more preferably 3 to 7 K / min.

[0056] Figure 11 is a graph showing the relationship between temperature and time in the main firing process. In the main firing process, it is preferable to perform temperature control in four stages: a stage in which the temperature is raised to a predetermined temperature in a certain amount of time (2-1), a stage in which the temperature is raised to a predetermined temperature in a certain amount of time (2-2), a stage in which the predetermined temperature is maintained for a certain amount of time (2-3), and a stage in which the temperature is cooled from the predetermined temperature within a certain amount of time (2-4).

[0057] (5) Oxygen annealing process The method for producing a copper oxide superconductor according to this disclosure may further include annealing the film in an oxygen atmosphere at 400 to 800 K for 3 to 10 hours to form a thin film. The annealing temperature is preferably 400-800K, more preferably 350-750K, and even more preferably 300-700K. The annealing time is preferably 3 to 10 hours, more preferably 3.5 to 9.5 hours, and even more preferably 4 to 9 hours.

[0058] Figure 12 is a graph showing the relationship between temperature and time in the oxygen annealing process. In this firing process, it is preferable to perform temperature control in four stages: a stage of raising the temperature to a predetermined temperature in a certain amount of time (3-1), a stage of maintaining the predetermined temperature for a certain amount of time (3-2), a stage of cooling to a predetermined temperature within a certain amount of time (3-3), and a stage of cooling from the predetermined temperature within a certain amount of time (3-4). [Examples]

[0059] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0060] <Preparation of coating solution> The metal salts in the coating solution were selected based on the following conditions. (1) Do not use fluorine, which can cause cracks on the substrate surface. (2) To ensure that the prepared sample does not contain impurities, organometallic salts that become gaseous during calcination are used. (3) It dissolves in the solvent toluene. The above three conditions were taken into consideration when making the selection. As a result, gadolinium octoate, barium octoate, and copper octoate were used as metal salts. In particular, among the metal salts that meet the conditions, octoate metal salts have the advantage of being easy to synthesize and having a stable molecular weight of 144.2, making the process simple and highly reproducible. Under the same conditions, gadolinium octoate and copper octoate were used as additive metal salts to introduce the pinning center. In this study, Nikka Octix Gadolinium, Nikka Octix Barium, and Nikka Octix Copper, manufactured by Nippon Chemical Industries, Ltd., which contain octoate metal salts dissolved in toluene, were used. Table 2 shows the reagents used for thin film preparation.

[0061] [Table 2]

[0062] <Selection of circuit board> Figure 13 is a graph showing the lattice constant of the substrate crystal and its temperature dependence. Compared with the temperature dependence of the lattice constant of Y123, NdGaO3, SrTiO3, and LaAlO3 are examples of heterojunction substrates with good lattice matching. Table 2.2 shows a list of currently popular substrates. LaAlO3 was selected as having the physical properties closest to those of Gd123 under the above conditions.

[0063] <Fabrication of thin films> (1) Coating process 30 μl of the coating solution was dropped onto a single-crystal substrate, and the substrate was uniformly coated using a spin coater SC-200 manufactured by Oshikane Co., Ltd., by rotating it at 350 rpm for 10 seconds and then at 3500 rpm for 30 seconds. (2) Drying process The substrate surface was dried at 120°C for 30 minutes using a constant temperature chamber SDN27P from Sansho Co., Ltd., to volatilize the toluene contained in the coating solution. (3) Pre-firing process Using a tabletop uniform heating and warming device, the material was calcined at 600°C in an atmospheric environment for 30 minutes to remove organic matter contained in the metal salts of the coating solution, and then cooled. The above steps (1) to (3) were carried out according to the sequence shown in Figure 14. The precursor was obtained by performing steps (1) to (3) above three times and then applying a multi-coating. (4) Firing process The precursor was crystallized on the substrate by performing the main firing according to the sequence shown in Figure 15 using a tabletop uniform heating apparatus. The main firing sequence involved raising the temperature to 400°C in 15 minutes, then raising the temperature to 880°C at a rate of 5°C / min, firing at that temperature for 30 minutes, and then cooling. (5) Oxygen annealing process The crystals were annealed in an oxygen atmosphere using a tabletop uniform heating apparatus according to the sequence shown in Figure 16 to remove residual stress and stabilize the crystals, followed by oxygen doping. The oxygen annealing sequence involved raising the temperature to 350°C in 15 minutes, firing at 350°C for 6 hours, and then lowering the temperature to 200°C in 50 minutes for cooling. A RE123 thermal conductive thin film was fabricated through the above process.

[0064] <X-ray Diffraction Measurement> To examine the crystal structure and atomic arrangement, the samples were evaluated using Rigaku's X-Ray Diffraction (XRD). Figure 17 shows the XRD patterns of the Gd123 non-doped thin film and the Gd214-introduced Gd123 thin films with each volume ratio (0.99 vol% to 5.95 vol%). In all the thin films, XRD peaks at the (00n) plane are observed, indicating that crystal growth occurs with c-axis orientation. In the BMO-introduced Gd123 thin film, the matrix stops crystal growth at about 3 vol%, while in the Gd214-introduced Gd123 thin film, it was confirmed that the matrix still undergoes crystal growth even when introduced at about 6 vol%, achieving a significant increase in the introduction amount. Also, the peak of Gd214 overlaps with the peak of Gd123 where the lattice constants are close and the angles at which the peaks appear are close, making it difficult to see on the graph. Table 3 summarizes the comparison of the full width at half maximum (FWHM) of the XRD peaks between the BMO-introduced Gd123 thin film and the Gd214-introduced Gd123 thin film with the same volume ratio. The non-doped sample without artificial pinning has the smallest FWHM, followed by the Gd214-introduced thin film, and the BaCeO3-introduced thin film has the largest FWHM. From this, it can be seen that Gd214 is less likely to distort the crystallinity of the matrix when introduced as an artificial pin compared to BMO.

[0065]

Table 3

[0066] <TEM Observation> A scanning transmission electron microscope (STEM: Scanning Transmission Electron Microscopy) is a microscope that can obtain a projection magnified image of a sample at a magnification ranging from several hundred times to several million times by measuring the spatial distribution of the electron transmittance of the sample from the intensity of the electron beam transmitted through the sample after irradiating the sample with an electron beam. The internal crystal structure of the sample was observed using STEM.

[0067] TEM samples were prepared by scraping the surface of a thin film with a razor and placing the scraped material on a microgrid. This method is extremely simple and low-cost compared to ion milling or FIB, yet it successfully allowed for detailed observation of the crystal structure and constituent elements. One possible reason for this success is that the RE123 superconductor grows in layers, allowing the crystal to be peeled off thin enough to be observed by TEM simply by scraping the surface of the thin film with a razor.

[0068] Figure 18(a) is a magnified section of the TEM image of a Gd123 thin film into which 1 vol% of Gd214 and 1 vol% of Nd214 have been introduced, Figure 18(b) is the TEM image before magnification, Figure 18(c) is a diagram of the molecular model of the Gd123 thin film into which 1 vol% of Gd214 and 1 vol% of Nd214 have been introduced, and Figure 18(d) is a diagram comparing the magnified TEM image of the introduced portion in Figure 18(a) with the molecular model in Figure 18(c) when the angle of the crystal lattice was changed. The white grains in Figure 18(a) are Gd and Ba. The lighter, smaller Cu and O atoms are not visible; only the heavier, larger Gd and Ba atoms are. From Figures 18(a) and (b), it can be inferred that the Gd214 crystal, enclosed in the red frame, is introduced into the atomic arrangement of the Gd123 crystal with its c axis aligned. To explain this, first, let's look at the three white grains enclosed in yellow in Figure 18(a). From the crystal structure of Gd123, it is presumed that the white grain in the center is a Gd atom, and the two white grains on either end are Ba atoms. Therefore, the three white grains enclosed in yellow are thought to be the unit cell of the Gd123 crystal.

[0069] Next, we will explain the six white grains enclosed in yellow within the red frame in Figure 18(a). From the crystal structure of Gd214, there are four Gd atoms per unit cell. However, when observing the unit cell from various angles using VESTA, there is an angle where six Gd atoms can be seen per unit cell, as shown in Figure 19(c). It is presumed that six Gd atoms are visible because the crystal was observed oriented at such an angle. From this, it can be concluded that the six white grains enclosed in yellow within the red frame are the unit cells of the Gd214 crystal. Figure 20(d) is an elemental mapping of Gd in Figure 18(a). Figure 20(e) is an elemental mapping of Ba in Figure 18(a). From this, it can be seen that Figure 18(a) is an atomic arrangement of Gd123 and Gd214. Furthermore, in multiple locations in Figures 18(a) and (b), Gd214 cells with approximately 20 unit cells can be observed, and it is thought that a similar number of crystals are arranged in the depth direction. Therefore, it is inferred that Gd214 is a plate-like two-dimensional pin. In other words, it is thought that Gd214 is introduced as a planar pin parallel to the ab plane.

[0070] Figure 21 shows the temperature dependence of magnetic susceptibility for Gd123 non-doped thin films and Gd214-introduced Gd123 thin films of various volume fractions (0.99 vol% to 5.95 vol%). It can be seen that all thin films undergo a superconducting transition around 90 K. Table 4 summarizes the measured values ​​for each doping amount. Samples with 1-3 vol% doping obtained Tc values ​​exceeding 90 K. Focusing on the sharpness of the superconducting transition, the superconducting transition occurs rapidly up to about 3 vol%, but becomes smoother as the doping amount increases further. From these findings, it is thought that at doping amounts exceeding 3 vol%, the pins distort the crystallinity of the base material, degrading the superconducting properties. Note that in Table 4, B * This represents the characteristic magnetic field, Jc(B * ) represents the characteristic pin force, n eff represents the effective pin density, and f p represents the elemental pin force, and Tc represents the critical temperature.

[0071] [Table 4]

[0072] <Magnetic field dependence> Figures 22-24 show the magnetic field dependence of JC for Gd214-introduced Gd123 thin films at 4.2 K-77.3 K for various volume fractions (0.99 vol%-5.95 vol%). Tables 5-7 summarize the JC values ​​for each introduction amount at each magnetic field. At all temperatures and magnetic fields, JC improved as the introduction amount of Gd214 increased from non-doped to 0.99 vol% and 1.98 vol%, and at higher introduction amounts, JC gradually decreased as the introduction amount increased, with the 4.96 vol% and 5.95 vol% introduced samples showing a JC lower than that of the non-doped thin film. Furthermore, at 0 T and 77.3 K, the 1.98 vol% Gd214-introduced Gd123 thin film achieved approximately 3.28 times the JC of the non-doped thin film.

[0073] [Table 5]

[0074] [Table 6]

[0075] [Table 7]

[0076] Figures 25-27 show the magnetic field dependence of FP (Fiscal Generation) for Gd214-introduced Gd123 thin films at 4.2 K-77.3 K for various volume fractions (0.99 vol%-5.95 vol%). Tables 8-10 summarize the FP values ​​for each introduction amount at each magnetic field. At all temperatures and magnetic fields, as the introduction amount of Gd214 increased from non-doped to 0.99 vol% and 1.98 vol%, the FP improved. Beyond that introduction amount, the FP gradually decreased as the introduction amount increased, and the FP of the 4.96 vol% and 5.95 vol% introduced samples fell below that of the non-doped thin film. Furthermore, at 1 T and 77.3 K, the 1.98 vol% Gd214-introduced Gd123 thin film achieved approximately 4.73 times the FP of the non-doped thin film.

[0077] [Table 8]

[0078] [Table 9]

[0079] [Table 10]

[0080] Figure 28 shows graphs of the JC introduction amount characteristics at 4.2 K and 60 K at 0 T, 1 T, and 2 T for BMO-introduced Gd123 thin films and Gd214-introduced Gd123 thin films. Compared to BMO, Gd214 shows a higher introduction amount. Furthermore, compared to BMO, the decrease in JC after reaching the JC peak is more gradual for Gd214, suggesting that the strain stress on the matrix material due to increasing introduction amount is gentler. Regarding the peak in JC in the 1.98 vol% Gd214-introduced Gd123 thin film, it is thought that this is due to the coarsening of the pin size as the introduction amount of Gd214 increases. In previous studies, there was a problem that the superconducting properties decreased with increasing introduction amount even with BMO introduction. At that time, it was hypothesized that the pin size was coarsening as the introduction amount increased. Therefore, when multiple types of BMO were introduced simultaneously to miniaturize the pin size, an improvement in superconducting properties was confirmed. Therefore, in this study as well, it is thought that the coarser pin size causes the base material to be subjected to strain stress from Gd214, distorting its crystallinity, and that the pinning is not performed efficiently.

[0081] Figure 29 shows the volume fraction dependence of the Gd123(005) peak normalized by LAO(001). In Gd214-doped films up to 6 vol%, the crystallinity of the matrix material is not impaired at all. This is thought to be because Gd214, which has a lattice constant very close to that of the matrix material and a c-axis orientation close to that of the matrix material, was introduced. On the other hand, degradation begins at 1.5 vol% in Zr-doped films, but no degradation of the matrix crystal is observed up to 2 vol% in Zr-Ce co-doped films. This indicates that BMOs with different lattice constants grow independently and are finely dispersed in the matrix material, demonstrating that more BMOs can be introduced without impairing the crystallinity of the matrix material.

[0082] Figure 30(a) is a TEM image of a Gd123 film doped with 6 vol% Gd214. It was confirmed that crystals containing Gd (presumably Gd214) are oriented in the Gd123 matrix. The white grains are Gd or Ba, and the light elements Cu and O are not visible. The triple crystals that occupy many faces are Ba-Gd-Ba Gd123 crystals. The crystals within the yellow frame are Gd214 and show a different atomic column from the matrix. This is a cross-sectional image, and the yellow frame has a similar size in depth, forming a plate-like structure. Figure 30(b) is a TEM image of a Gd123 film doped with 2 vol% BMO (M=Zr, Ce, Sn, Hf). Since this crystal does not contain Cu and contains large amounts of Ba and O, it is considered to be a BMO crystal. The diameter of this crystal is approximately 5 nm, which is finer than the single type of BMO reported in previous studies. Compared to Figure 30(a), it can be seen that the thickness has increased in the c-axis direction.

[0083] Figure 31 is a graph comparing the Jc-T characteristics of each sample with 1 vol% artificial pin at 0.5T and 3T. It can be seen that Jc increases sharply below 20K.

[0084] Figure 32 is a graph comparing the Jc-T characteristics of each sample with 2 vol% artificial pins at 0.5T and 3T. Similarly, in the case of 2 vol%, it can be seen that Jc increases sharply below 20K. This is because the artificial pins also become superconductors and their electrical resistance becomes zero. From 20K to 80K, the decrease in Jc is gradual, suggesting that the superconducting state can be maintained even with cooling by liquid nitrogen due to the action of the artificial pins.

[0085] Figures 33 and 34 show the APC volume fraction dependence of Jc(0.5 T) and Jc(3.0 T) for various APC-doped films at different temperatures. All APC-doped films showed higher Jc than undoped films. In BMO-doped films, Jc improved significantly as the type of M doped increased compared to a 2 vol% BMO-doped film. On the other hand, Gd214-doped films maintained higher Jc than undoped films up to 5 vol% doping at all temperatures and magnetic fields. This indicates that the introduction of Gd214 is an effective method for improving Jc in high-concentration doping.

[0086] Figures 35(a) and (b) show the temperature dependence of Jc for APC-doped and undoped films at 0.5 T and 3.0 T, respectively. All APC-doped films showed superior Jc-BT characteristics compared to undoped films. The highest Jc at 4.2 K in both magnetic fields was obtained with the 2vol%Gd214 doped film, with a value of 8.13 [MA / cm²] at 0.5 T. 2 ], 3.0T with 3.05[MA / cm 2 ] was. These values ​​were 1.99 times and 2.21 times higher than those of the undoped film, respectively. At all magnetic fields and temperatures, the Jc-BT characteristics of the BMO co-doped film were superior to those of the film with BMO alone. For example, at 20K and 3.0T, the 0.94 vol% BMO co-doped film showed a Jc-BT of 1.51 [MA / cm²]. 2 This shows that the ratio is 1.24 times that of a 2.61 vol% BCoO-doped film. This supports the idea that co-doping with BMO is an effective way to improve Jc in a magnetic field. Furthermore, in films with Gd214 introduced, the improvement in Jc-BT properties below 20K is remarkable. This suggests that the Gd214 crystals in the matrix transition to a superconducting phase, and that the pinning mechanism switches from an attractive pinning mechanism due to condensation energy interaction to a repulsive pinning mechanism due to kinetic energy interaction.

[0087] The graph in Figure 36 has the horizontal axis representing the θ when a magnetic field is applied in the c-axis direction for each material, with θ being 0 degrees and the direction perpendicular to the magnetic field being 90 degrees. The vertical axis represents the Jc value. In Figure 36, GdBCO represents the undoped material, Gd214+BMO represents the material doped with artificial pins in the shape shown in Figure 2(b), BMO NPs represents the material doped with artificial pins in the shape shown in Figure 2(d), and BMO NRs represents the material doped with artificial pins in the shape shown in Figure 2(a). From the results in Figure 36, the artificial pins of the present invention show the largest Jc value when a magnetic field is applied perpendicular to the c-axis. It is thought that the Jc value of the undoped material is high due to intrinsic pinning of the block layer and defect pins such as dislocations. REBa2Cu3O 7-δ In this case, the current flows along the ab plane and in a direction perpendicular to the internal magnetic field. As shown in Figure 2(b), the length direction of the magnetic flux lines is parallel to the ab plane of the artificial pin, so Jc is greatly improved. Also, in this invention, the artificial pin is REBa2Cu3O 7-δ It is introduced in a plate-like manner between them, but REBa2Cu3O 7-δ Because the difference in the c-axis lattice constant between it and the artificial pin is small, REBa2Cu3O 7-δ It is easy to maintain its crystallinity. The magnetic flux lines are efficiently pinned by a plate of artificial pins that are long in the ab-axis direction, and their motion is hindered, so REBa2Cu3O 7-δ This allows the superconducting properties to be fully utilized, resulting in no current loss and enabling the flow of large currents.

[0088] Figure 37 shows a schematic diagram of how the plate pins trap magnetic flux lines at 0° and 90°, and corresponding TEM images of the plate pins. Figure 38 is a schematic diagram showing how plate pins trap magnetic flux lines at 0°, 45°, and 90°. As shown in Figures 37 and 38, introducing 5 Vol% of magnetic flux increases the plate thickness (and slightly increases the plate surface area). At 0°, increased thickness increases the interaction volume between the magnetic flux and the pin, thus increasing the pinning force, but at 90°, there is little change. Therefore, introducing thin, fine plates as artificial pins is less wasteful in terms of volume and improves pinning efficiency at both 0° and 90°. The 45° shown in the figure below is somewhere in between.

[0089] Figure 39 is a related crystal diagram output using the crystal plotting software VESTA. Currently, the new artificial pin is called RE214 (Figure 39), but we would like to use a broader Nd 2-x Ce x We will apply for this as a CuO4 structure (T' structure or NCCO structure). This time, we focused our research on the case where x=0, but our laboratory also has experience in fabricating structures where x≠0 (experience with Ce doping). As shown in Figure 40, the physical properties including Tc of materials with a T' structure change with Ce concentration. Therefore, since it is possible to control Tc with Ce concentration in RE214-based materials that constitute nanoplates in a Gd123 matrix, we believe it is necessary to apply for this as a T' structure in a broad sense. The table shows a list of RE214 crystals that are candidates for the T' structure with similar lattice constants.

[0090] [Table 11]

[0091] Additionally, the T structure (K2NiF4 structure) is also considered a candidate with a similar lattice constant. Here too, Tc can be adjusted by changing the concentration of the added elements.

[0092] [Table 12]

[0093] Figure 40 shows the crystal diagram of the T' structure and the relationship between Tc and Ce doping amounts. Figure 41 shows the crystal diagram of the T structure and the relationship between Tc and Sr doping amount. Figure 42 shows the TEM image when Gd214 is introduced alone. Figure 43 is a schematic diagram showing the co-addition of two different RE214 compounds, Gd214 and Sm214. In Figure 42, (a) corresponds to the 1 vol% introduction condition, and (b) corresponds to the 5 vol% introduction condition. When 5 vol% is introduced, it can be seen that the Gd214 in the thin film is coarsened in the ab plane and the c axis direction. To suppress this coarsening of artificial pins, this study aims to refine the artificial pins and improve the critical current density (Jc) by co-doping different RE214s, Gd214 and Sm214, as shown in Figure 43. The principle of refinement is the same as in the case of BMO co-doping, because RE214s with different lattice constants grow crystals independently.

[0094] Figure 44 is a schematic diagram of the Jc accuracy dependence of each APC-doped and undoped film. The red line in Figure 44 shows the Jc accuracy dependence of the film co-doped with BMO and RE214. At a magnetic field application angle of 90° (B / / ab), the RE214 nanoplate acts most effectively, resulting in the maximum JC. (It is expected that the addition of BMO nanoparticles (APCs) will result in a higher JC than when RE214 is doped alone.) Furthermore, in regions other than the 90° (B / / ab) magnetic field application angle, the RE214 side face acts as a pinning point in addition to BMO, so it is expected that the JC will be higher than that of the BMO NPs-doped film. The BMO nanoparticles (BMO NPs) shown by the blue line are spherical APCs, so they act idiosyncratically with respect to the angle of the applied magnetic field. Therefore, the Jc is slightly improved at all angles compared to the undoped film (black line). BMO nanorods (BMO NRs, pink) are bamboo shoot-shaped APCs that grow along the c-axis. They are fabricated using the PLD method. Due to the shape of the one-dimensional pins along the C-axis, they exhibit maximum pinning force when B / / c, but are almost non-functional when B / / ab.

[0095] Figure 45 shows the Jc accuracy dependence of Gd214 nanoplate APC-doped and undoped films. Figure 45 shows the actual measurement data for RE214-doped films. As expected, a significant improvement in Jc was observed at 90° due to the nanoplates. Furthermore, compared with the undoped film, it was confirmed that the edges of the RE214 effectively act as pinning points. In the future, by co-adding RE214 and BMO, we expect to see an improvement in Jc across all aspects. By adding multiple types of RE214 and BMO, further refinement and an increase in the amount added can be expected.

Claims

1. RE containing at least one rare earth element RE ２ CuO ４ REBa doped with crystals as artificial pins ２ Cu ３ O ７－δ A copper oxide superconductor containing (δ is a real number between 0 and 1).

2. The artificial pin is the REBa ２ Cu ３ O ７－δ The copper oxide superconductor according to claim 1, characterized in that the difference in crystal constants with respect to is 5% or less, and the artificial pin RE is Gd, Y, Nd, or Sm.

3. The copper oxide superconductor according to claim 2, characterized in that the artificial pin is further co-doped with BMO.

4. The artificial pin forms one or more plates, and the REBa ２ Cu ３ O ７－δ The copper oxide superconductor according to claim 1 or 2, which is introduced so that the a-b plane of is parallel to the plate.

5. The copper oxide superconductor according to claim 3, wherein the number of crystal lattices arranged continuously in the b-axis direction of the artificial pins constituting the plate is 30 or less, and the number of crystal lattices arranged in the c-axis direction is 1 to 5.

6. The aforementioned artificial pin is Gd ２ CuO ４ A copper oxide superconductor according to claim 1 or 2, comprising:

7. A copper oxide superconductor according to claim 1 or 2, comprising a plurality of artificial pins having different crystal constants.

8. The Tc of the artificial pin is the REBa ２ Cu ３ O ７－δ A copper oxide superconductor according to claim 1 or 2, wherein the Tc is lower than that of (δ is a real number between 0 and 1).

9. The crystal structure of the artificial pin and the REBa ２ Cu ３ O ７－δ The copper oxide superconductor according to claim 1 or 2, wherein both the crystal structure and the crystal structure are perovskite structures.

10. A copper oxide superconductor according to claim 1 or 2, which is a thin film.

11. The copper oxide superconductor according to claim 7, wherein the average film thickness measured by scanning electron microscopy (SEM) observation is 500 nm or less.

12. A copper oxide superconductor according to claim 1 or 2, manufactured by a fluorine-free organometallic vapor deposition method.

13. The copper oxide superconductor according to claim 1 or 2, wherein the total content of the artificial pins is 0.1 volume% or more and 12.0 volume% or less relative to the total volume of the copper oxide superconductor.

14. The Jc of the copper oxide superconductor is 1.0 to 10.0 MA / cm at 0.5 T under a temperature of 4.2 K. ２ , 0.5-5.0 MA / cm at 3.0T ２ The copper oxide superconductor according to claim 1 or 2.

15. The Jc of the copper oxide superconductor is REBa that is not doped with the artificial pin. ２ Cu ３ O ７－δ A copper oxide superconductor according to claim 1 or 2, wherein the Jc is 1.2 times or more that of a copper oxide superconductor.

16. The copper oxide superconductor according to claim 1 or 2, wherein the value of the c-axis lattice misfit when three units of the artificial pins are stacked in the c-axis direction is 4.0 or less.

17. The copper oxide superconductor according to claim 1 or 2, wherein the peak ratio represented by Gd123(005) / LAO(001) in the XRD peak measured by surface XRDθ-2θ scan is 0.5 or more.

18. A copper oxide superconductor according to either claim 1 or 2, A copper oxide superconductor characterized by its use in MRI, superconducting motors for electric aircraft, large wind turbines, or coils for encapsulating nuclear fusion plasma.

19. An artificial pin characterized by containing at least one rare earth element RE.

20. The artificial pin according to claim 19, characterized in that the artificial pin is co-added with BMO.

21. RE containing at least one rare earth element RE ２ CuO ４ REBa doped with crystals as artificial pins ２ Cu ３ O ７－δ (δ is a real number between 0 and 1.) A method for producing a copper oxide superconductor, comprising fabricating a thin film by a fluorine-free organometallic vapor deposition method.

22. As the aforementioned artificial pin, REBa with BMO co-added ２ Cu ３ O ７－δ (δ is a real number between 0 and 1.) A method for producing a copper oxide superconductor according to claim 21, comprising preparing a thin film by a fluorine-free organometallic vapor deposition method.

23. The fluorine-free organometallic vapor deposition method is a method for producing a copper oxide superconductor according to claim 21 or 22, comprising preparing a mixture by adding a metal-containing compound to a mixture containing RE, Ba, and Cu in a molar ratio of RE:Ba:Cu = 1:2:3 such that the total amount of RE and Cu, or Ba and M added, is 0.1 to 20.0 mol%.

24. The aforementioned mixture is LaAlO ３ A method for producing a copper oxide superconductor according to claim 23, comprising spin-coating a (LAO)100 single crystal, drying it at 300 to 500 K for 10 to 60 minutes, and firing it in air at 600 to 1000 K for 10 to 60 minutes to produce a precursor.

25. The precursor is placed in a mixed gas containing nitrogen gas and oxygen gas, with an oxygen partial pressure of 10 －４ ~10 －８ A method for producing a copper oxide superconductor according to claim 24, comprising firing at a flow rate of 0.05 to 1.0 L / min at atm, at 1000 to 1200 K for 10 to 60 minutes under heating conditions of 1 to 10 K / min to form a film.

26. A method for producing a copper oxide superconductor according to claim 25, comprising annealing the aforementioned film in an oxygen atmosphere at 400 to 800 K for 3 to 10 hours to form a thin film.

Images