Superconductor and method for producing superconductor

Abstract

To provide a high-temperature superconductor with little decrease in the transition temperature caused by irradiation; and a method for producing the same.SOLUTION: The superconductor is represented by general formula (1): REBa2Cu3O7-δ. (In formula (1), RE consists of Y, Gd, and X, where X comprises one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; and 0≤δ≤1.)SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to superconductors and methods for making superconductors. [Background technology]

[0002] In recent years, one example of highly efficient, low current loss electrical equipment that can solve energy, environmental, and resource problems is superconducting equipment such as power transmission cables, superconducting electromagnets, and superconducting current leads that use superconductors as low current loss materials (for example, Patent Document 1). Patent Document 1 discloses the use of Nb3Sn compound superconductors and Nb3Al compound superconductors.

[0003] Superconductors are also used as magnets for confining plasma in fusion reactors. As an example of a method for utilizing superconductors in a fusion reactor, it is known that they are used as a material for constituting a toroidal magnetic field coil in a fusion reactor including a toroidal plasma chamber having a central pillar (for example, Patent Document 2). The toroidal magnetic field coil is a coil that creates a magnetic field for confining plasma.

[0004] Achieving high economic efficiency is an issue for making a fusion reactor viable as a practical power plant. When used in a fusion reactor, superconductors need to be maintained at a temperature that indicates a superconducting state. Therefore, the cost ratio related to the superconductor is high. In order to maintain the temperature of the superconductor below the transposition temperature, a cooling means is used. Patent Document 2 does not mention a specific material for the toroidal field coil, but does state that a high-temperature superconductor (HTS) coil with a high transposition temperature is used.

[0005] In the International Thermonuclear Reactor (ITER) project, it is described that Nb3Sn superconducting wires will be used as a high-performance, high-quality superconducting wire material in order to realize a magnetic confinement fusion reactor (for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2013 / 154187 [Patent Document 2] Special Publication No. 2016-534327 [Non-patent literature]

[0007] [Non-Patent Document 1] Takaaki Isono (1997). "Development of Nb3Sn strands for the International Thermonuclear Reactor (ITER) in Japan", p.150-157. Summary of the Invention [Problem to be solved by the invention]

[0008] As is well known, a fusion reactor utilizes a fusion reaction that generates He and neutrons by the fusion of deuterium and tritium. Therefore, in a fusion reactor, a toroidal magnetic field coil is required to have high radiation resistance due to the generation of neutron rays. However, the Nb3Sn superconductor disclosed in Patent Document 1 and Non-Patent Document 1 has a lower transition temperature after being irradiated with heavy quantum rays such as neutrons and high-energy particles compared to before irradiation.

[0009] No specific material is disclosed as a superconductor in Patent Document 2. From such conventional techniques, it is desired to discover a high-temperature superconductor whose transition temperature decreases little before and after irradiation.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-temperature superconductor in which the decrease in the transition temperature before and after irradiation with high-energy particles is small, and a method for producing the same. [Means for solving the problem]

[0011] In order to solve the above problems, the present invention provides the following means.

[0012] [1] A superconductor according to one embodiment of the present invention is represented by general formula (1). REBa2Cu3O 7-δ (1) (In formula (1), RE is composed of Y, Gd, and X, X is composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu; 0≦δ≦1)

[0013] [2] In the superconductor of [1] above, in the formula (1), X may be composed of Dy and one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, and Lu.

[0014] [3] The superconductors described in [1] or [2] above contain five or more rare earth elements and have a mixing entropy ΔS of the RE site. mix may be 1.5R or more.

[0015] [4] In any of the superconductors [1] to [3] above, in the above formula (1), RE may be represented by general formula (2). Y a Gd b X c (2) (0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9)

[0016] [5] A method for producing a superconductor according to one embodiment of the present invention includes a preparation step of preparing a base layer having a surface made of a single crystal, and a deposition step of depositing a superconductor on the base layer, wherein a target represented by general formula (1) is used in the deposition step. REBa2Cu3O 7-δ (1) (In formula (1), RE is composed of Y, Gd, and X, X is composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu; 0≦δ≦1)

[0017] [6] In the method for producing a superconductor according to [5] above, in the vapor deposition step, the target may be disposed at a position facing the underlayer, and a pulsed laser may be irradiated onto the target. Effect of the Invention

[0018] According to the present invention, it is possible to provide a high-temperature superconductor in which the decrease in the transition temperature before and after irradiation with high-energy particles is small, and a method for producing the same. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram of a crystal structure of a superconductor according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a partial cross-sectional perspective view of a superconducting wire according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a diagram for explaining the configuration of a superconducting laminate provided in the superconducting wire of FIG. [Figure 4] FIG. 1 is a diagram for explaining a method for producing a superconductor according to an embodiment of the present invention, showing a state in which a deposition process is performed by a PLD method. [Diagram 5] FIG. 5(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation of the superconductor of Example 1, and FIG. 5(b) is an enlarged view of the vicinity of the transition temperature Tc of FIG. 5(a). [Figure 6] FIG. 6(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation of the superconductor of Example 2, and FIG. 6(b) is an enlarged view of the vicinity of the transition temperature Tc of FIG. 6(a). [Figure 7] FIG. 7(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation of the superconductor of Example 3, and FIG. 7(b) is an enlarged view of the vicinity of the transition temperature Tc in FIG. 7(a). [Figure 8] 1 is a graph showing the temperature dependence of magnetization before and after He ion irradiation for the superconductor of Comparative Example 1. [Figure 9]FIG. 9(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation for the superconductor of Comparative Example 2, and FIG. 9(b) is an enlarged view of the vicinity of the transition temperature Tc in FIG. 9(a). [Figure 10] FIG. 10(a) is a graph showing the critical current density of the sample of Example 1 before He ion irradiation, and FIG. 10(b) is a graph showing the critical current density of the sample of Example 1 after He ion irradiation. [Figure 11] FIG. 11(a) is a graph showing the critical current density of the sample of Example 2 before He ion irradiation, and FIG. 11(b) is a graph showing the critical current density of the sample of Example 2 after He ion irradiation. [Figure 12] FIG. 12(a) is a graph showing the critical current density of the sample of Example 3 before He ion irradiation, and FIG. 12(b) is a graph showing the critical current density of the sample of Example 3 after He ion irradiation. [Figure 13] FIG. 13(a) is a graph showing the critical current density of the sample of Comparative Example 1 before He ion irradiation, and FIG. 13(b) is a graph showing the critical current density of the sample of Comparative Example 1 after He ion irradiation. [Figure 14] FIG. 14(a) is a graph showing the critical current density of the sample of Comparative Example 2 before He ion irradiation, and FIG. 14(b) is a graph showing the critical current density of the sample of Comparative Example 2 after He ion irradiation. [Figure 15] FIG. 15(a) is a graph showing the critical current density of the sample of Comparative Example 3 before He ion irradiation, and FIG. 15(b) is a graph showing the critical current density of the sample of Comparative Example 3 after He ion irradiation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics of the present invention easier to understand. For this reason, the dimensional ratios of each component may differ from the actual ones.

[0021] [Superconductors] FIG. 1 is a schematic diagram of a crystal structure of a superconductor according to one embodiment of the present invention. A superconductor according to one embodiment of the present invention is a superconductor represented by general formula (1). REBa2Cu3O 7-δ (1)

[0022] In formula (1), RE represents a rare earth metal element. The atomic site of the rare earth element RE is indicated by the symbol RE in FIG. 1. In a superconductor according to an embodiment of the present invention, three or more rare earth elements Y (yttrium), Gd (gadolinium), and X are present at the atomic site of the rare earth element RE. X is one or more rare earth elements selected from the group consisting of La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium). In formula (1), δ represents the amount of oxygen vacancy. δ is in the range of 0≦δ≦1, and preferably in the range of 0≦δ≦0.6.

[0023] In the above formula (1), RE may be represented by general formula (2): Y a Gd b X c (2) (0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9).

[0024] In formula (1), the rare earth element RE preferably includes at least one of Dy and Yb in addition to Y and Gd. That is, the rare earth element RE preferably includes Y, Gd and Dy, Y, Gd and Yb, or Y, Gd, Dy and Yb. When the rare earth element RE includes Y, Gd and Dy, X is composed of Dy and one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb and Lu. When the rare earth element RE includes Y, Gd and Yb, X is composed of Yb and one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm and Lu. When the rare earth element RE includes Y, Gd, Dy, and Yb, X may or may not include an element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, and Lu, in addition to Dy and Yb.

[0025] The superconductor of this embodiment has a mixing entropy ΔS of the atomic site of the rare earth element RE. mix is 1.1R or more, preferably 1.39R or more, and more preferably 1.5R or more. Here, R represents a gas constant. In the high-entropy superconductor, for example, five or more kinds of rare earth elements are present at the atomic site of the rare earth element RE. Examples of such a superconductor include those containing Y, Gd, Dy, Ho, and Yb as the rare earth element RE. A superconductor represented by the general formula (1) containing Y, Gd, Dy, Ho, and Yb as the rare earth element RE contains five or more kinds of rare earth elements, and may contain one or more selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Er, Tm, and Lu in addition to the rare earth elements. Such a high-entropy superconductor containing Y, Gd, and Dy has a high transition temperature T c and high critical current density J c The critical current density J c is the critical current value per unit area of ​​the superconductor.

[0026] In addition, it is preferable to avoid using superconductors that have a long half-life when radioactive, assuming that they may be used in superconducting magnets for nuclear fusion reactors. Among the above X elements, Sm and Eu have a long half-life when radioactive, compared to other X elements. Therefore, it is preferable that the above X element is one or more elements other than Sm and Eu, that is, selected from the group consisting of Dy, La, Ce, Pr, Nd, Tb, Ho, Er, Tm, Yb, and Lu.

[0027] According to the superconductor of this embodiment, three or more kinds of rare earth elements RE are contained, and a high mixing entropy ΔS is obtained at the atomic site of the rare earth element RE. mix In addition, the high mixing entropy ΔS mix Due to this, a solid solution is easily formed. Therefore, it shows high structural stability, heat resistance, and acid resistance. Furthermore, as described above, the superconductor according to this embodiment has the Y element, the Gd element, and the X element which is another rare earth element, so that even when it is used in a nuclear fusion reactor or the like where heavy quantum beams such as neutrons or high-energy particles are irradiated, the decrease in the transition temperature before and after irradiation with high-energy particles can be reduced. That is, according to this embodiment, a superconductor showing excellent radiation resistance with respect to the transition temperature can be realized. Therefore, according to the superconductor of this embodiment, the cooling means for maintaining the temperature at which the superconductor functions can be simplified, or the energy required for cooling can be reduced.

[0028] [Superconducting wire] Fig. 2 is a partial cross-sectional perspective view of a superconducting wire according to an embodiment of the present invention. Fig. 3 is a diagram for explaining the configuration of a superconducting laminate provided in the superconducting wire of Fig. 2. For convenience, Fig. 3 shows the ends of each layer shifted.

[0029] The superconducting wire 10 shown in Fig. 2 includes a superconducting laminate 5 and a stabilization layer 6. The stabilization layer 6 extends along the superconducting laminate 5 and is provided so as to be in contact with the main surface and the side surface of the superconducting laminate. The stabilization layer 6 is formed so as to surround the superconducting laminate 5. The stabilization layer 6 functions as a bypass section that is generated when a superconducting layer included in the superconducting laminate 5, the details of which will be described later, transitions to a normal conducting state, or that diverts current.

[0030] Examples of the material of the stabilization layer 6 include metals such as copper, copper alloy, aluminum, aluminum alloy, and silver. Examples of copper alloys that can be used as the stabilization layer 6 include Cu-Zn alloys and Cu-Ni alloys. The thickness of the stabilization layer 6 is, for example, several μm to 300 μm. The stabilization layer 6 can be formed by plating (for example, electrolytic plating).

[0031] The superconducting laminate 5 shown in FIG. 3 includes a substrate 1, an intermediate layer 2, and a superconducting layer 3. The substrate 1 is made of, for example, a metal. The substrate 1 is, for example, a nickel alloy, a stainless steel, or an oriented Ni-W alloy in which a texture is introduced into nickel steel. The thickness of the substrate 1 is, for example, 10 to 500 μm. It is preferable that an intermediate layer 2 is provided on the main surface S1 of the substrate 1, but the intermediate layer 2 can be omitted. In the superconducting laminate 5 in which the substrate 1, the intermediate layer 2, and the superconducting layer 3 are formed in this order as shown in FIG. 3, the substrate 1 and the intermediate layer 2 are collectively referred to as the underlayer 12, and in a superconductor in which the intermediate layer 2 is omitted and the substrate 1 and the superconducting layer 3 are formed in contact with the substrate 1, the substrate 1 is referred to as the underlayer.

[0032] The intermediate layer 2 is provided between the substrate 1 and the superconducting layer 3. The intermediate layer 2 is composed of, for example, a plurality of layers. FIG. 3 shows an example in which the intermediate layer 2 includes, in order from the side closer to the substrate 1, a first layer 2a, a second layer 2b, and a third layer 2c. The intermediate layer 2 has, for example, a plurality of layers, such as a bed layer, an orientation layer, and a cap layer, each of which has a different function. For example, the surface of the intermediate layer 2 on the superconducting layer 3 side and its vicinity are composed of a single crystal.

[0033] The first layer 2a is, for example, a bed layer. The bed layer serves to reduce reactions at the interface between the substrate 1 and the superconducting layer 3 and to improve the orientation of the layer formed thereon. Examples of materials for the bed layer include CeO2, Er2O3, Y2O3, Dy2O3, Eu2O3, Ho2O3, and La2O3.

[0034] The second layer 2b is, for example, an orientation layer. The orientation layer is provided to control the crystal orientation of a cap layer when the cap layer is formed thereon. The cap layer is formed of, for example, a metal oxide such as Gd2Zr2O7, MgO, ZrO2-Y2O3 (YSZ), SrTiO3, CeO2, Y2O3, Al2O3, Gd2O3, Zr2O3, Ho2O3, or Nd2O3. It is preferable to use an orientation layer formed by an IBAD (Ion Beam Assisted Deposition) method.

[0035] The third layer 2c is, for example, a cap layer. The cap layer is formed on the surface of the orientation layer and is made of a material that allows crystal grains to self-orient in the in-plane direction. The cap layer is made of, for example, CeO2, Y2O3, Al2O3, Gd2O3, ZrO2, YSZ, Ho2O3, Nd2O3, LaMnO3, etc.

[0036] The superconducting layer 3 is formed on a surface S2 of the intermediate layer 2 that is the farthest from the substrate 1. The superconducting layer 3 has a thickness of, for example, 0.5 μm to 10 μm.

[0037] The superconducting layer 3 is made of the superconductor according to the above embodiment. That is, the superconducting layer 3 is made of a superconductor represented by the general formula (1). REBa2Cu3O 7-δ (1) In formula (1), RE is composed of Y, Gd, and X; X is composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and satisfies 0≦δ≦1.

[0038] 3 shows a superconducting laminate 5 in which the underlayer 12 includes a substrate 1 and an intermediate layer 2, the superconducting laminate 5 according to this embodiment may be a layer made of a single material as long as the surface and its vicinity are made of a single crystal. That is, the underlayer 12 may be made of a single layer. For example, the underlayer may be made of a single crystal SrTiO3 substrate or a single crystal MgO substrate.

[0039] The superconducting wire 10 is wound to form a coil. The coil according to one embodiment of the present invention is, for example, a toroidal magnetic field coil that creates a magnetic field for confining plasma in a nuclear fusion reactor. The coil according to this embodiment is, for example, a multi-layered coil in which the superconducting wire is wound multiple times around a winding core. The coil according to this embodiment is produced by winding the superconducting wire around a winding core.

[0040] [Manufacturing methods for superconductors] The method for producing the superconductor according to the above embodiment will be described below. The method for producing the superconductor according to one embodiment of the present invention includes a preparation step of preparing an underlayer 12 whose surface is made of a single crystal, and a deposition step of depositing a superconductor on the underlayer 12. The method for producing the superconductor according to this embodiment uses a target represented by the following general formula (1) in the deposition step. REBa2Cu3O 7-δ (1) (In formula (1), RE is composed of Y, Gd, and X, X is composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu; 0≦δ≦1 is satisfied.)

[0041] A method for producing a superconductor will be described below by taking a method for producing a superconducting laminate as an example.

[0042] (preparation process) First, the underlayer 12 whose surface is made of a single crystal is prepared. The underlayer 12 is made of, for example, only the substrate 1 or the substrate 1 and the intermediate layer 2. FIG. 3 shows an example in which the underlayer 12 is made of the substrate 1 and the intermediate layer 2 formed on the substrate 1, but the present invention is not limited to this example, and the intermediate layer 2 can be omitted. The intermediate layer 2 can be formed on the substrate 1 by, for example, a physical vapor deposition method such as a PLD method or a deposition method such as a chemical vapor deposition method, or by baking. In the preparation step, for example, a process is performed so that at least one surface of the underlayer 12 and its vicinity are made of a single crystal. The preparation step is performed, for example, in a predetermined number of times depending on the number of intermediate layers 2 to be formed.

[0043] (Target preparation process) Next, a target to be used in the deposition process is prepared. The target is a composition corresponding to the composition of the desired superconductor. The composition of the composition constituting the target is, for example, the same as the composition of the superconductor to be produced. The target is, for example, a polycrystalline body having the same composition as the superconductor to be produced. The target is produced, for example, by mixing simple substances or oxides of predetermined metal elements in a predetermined ratio and firing. In this embodiment, in order to produce a superconductor that essentially contains at least Y and Gd as the rare earth element RE and further has one or more other rare earth elements as the X element, three or more types of simple substances or oxides of rare earth elements are mixed, preferably four or more types are mixed, and more preferably five or more types are mixed. The firing for producing the target may be performed once or may be performed in multiple steps.

[0044] (vapor deposition process) Next, a superconductor is deposited on the underlayer 12. The deposition process is performed by, for example, a pulsed laser deposition (PLD) method, a molecular beam epitaxy (MBE) method, a physical vapor deposition (PVD) method such as a sputtering method, etc. In the deposition process, it is preferable to place a target T at a position facing the underlayer 12 and irradiate the target T with a laser.

[0045] Fig. 4 is a diagram for explaining a method for producing a superconductor according to one embodiment of the present invention, showing a state in which a deposition step is performed by the PLD method. The PLD method will be explained with reference to Fig. 4. The PLD method is performed using a PLD apparatus. The target T and the underlayer 12 are placed in a chamber of the PLD apparatus so as to face each other. The atmosphere in the chamber can be, for example, an air atmosphere. The deposition step is performed, for example, by adjusting the chamber to have a low oxygen partial pressure and heating the underlayer 12.

[0046] The oxygen partial pressure in the chamber is, for example, 1×10 -5 The pressure can be from 1 Pa to 50 Pa, and preferably from 1 Pa to 20 Pa. The temperature (set temperature) of the underlayer can be adjusted to, for example, from 200° C. to 1000° C.

[0047] The PLD device irradiates a target T with a laser beam L and focuses the laser beam L on the surface of the target T using a focusing lens or the like. A pulsed laser is used as the laser beam L irradiated onto the target T. The laser density is, for example, 0.1 J / cm. 2 More than 5J / cm 2 To the following:

[0048] By focusing a laser on the surface of the target T, constituent particles of the target T are knocked out or evaporated to generate a plume P. The constituent particles of the target T contained in the plume P are deposited on the surface of the underlayer 12, so that a thin film composed of the constituent particles of the target T is formed on the surface of the underlayer 12. Therefore, by changing the composition of the constituent particles of the target T, it is possible to change the composition of the thin film formed on the underlayer 12. In other words, when a superconductor of a desired composition is to be formed on the underlayer 12, it is sufficient to use a target T having the same composition as the desired superconductor.

[0049] Therefore, the target T can be one represented by the above formula (1). In formula (1), the element X in the rare earth element RE preferably contains Dy and one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, and Lu, and more preferably is composed of these elements. In formula (1), δ represents the amount of oxygen vacancy, and δ is in the range of 0≦δ≦1.

[0050] In the above formula (1), RE may be represented by general formula (2). Y a Gd b X c (2) (0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9)

[0051] In formula (1), the rare earth element RE preferably contains at least one of Dy and Yb in addition to Y and Gd. That is, the rare earth element RE preferably contains Y, Gd and Dy, Y, Gd and Yb, or Y, Gd, Dy and Yb.

[0052] In order to prepare a superconductor containing five or more rare earth elements, it is preferable that the target T contains five or more rare earth elements. For example, in order to prepare a superconductor containing Y, Gd, Dy, Ho, and Yb as rare earth elements RE, it is preferable that the target T contains Y, Gd, Dy, Ho, and Yb. A superconductor formed by using such a target has a high mixed entropy and a high critical current density even after irradiation with high-energy particles.

[0053] In addition, from the viewpoint of preventing the formed superconductor from having a long half-life upon radioactivity, it is preferable that the X element of the composition represented by formula (1) contained in the target T is an element other than Sm and Eu, that is, one or more elements selected from the group consisting of Dy, La, Ce, Pr, Nd, Tb, Ho, Er, Tm, Yb, and Lu.

[0054] After forming a superconducting layer made of a superconductor on the underlayer 12, the superconducting laminate is cooled in a furnace and then taken out. When cooling in the furnace, the oxygen partial pressure can be set to a value higher than the oxygen partial pressure during the formation of the superconducting thin film. For example, the oxygen partial pressure during cooling in the furnace can be set to the same as the oxygen partial pressure in the atmosphere.

[0055] According to the method for manufacturing a superconductor according to the present embodiment, it is possible to form a superconducting wire in which the superconductor according to the above embodiment is formed as a thin film. In the above example, a method for forming a superconducting wire has been described, but in a method for manufacturing a thin film made of a superconductor, it is sufficient to prepare a single crystal substrate consisting of only one layer as the underlayer 12 and perform deposition, and it is not necessary to use a layer having multiple layers as the underlayer 12. EXAMPLES

[0056] [Example 1] EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0057] First, the underlayer was prepared. A strontium titanate (SrTiO3) single crystal substrate was prepared.

[0058] Next, the target was prepared. In the preparation of the target, first, Y2O3 (purity 99.9%), Gd2O3 (purity 99.9%), Dy2O3 (purity 99.9%), BaCO3 (purity 98%) and CuO (purity 99.9%) were weighed out as the target materials in a mass ratio of 1 / 3:1 / 3:1 / 3:2:3, and mixed in a mortar to prepare a mixed powder.

[0059] Next, the mixed powder was transferred to a crucible and heated at 930° C. for 20 hours as a primary firing (calcination), and then cooled to room temperature.

[0060] The calcined mixed powder was then mixed in an agate mortar and pressure-molded into pellets. The pellet-shaped mixed powder was then heated at 930°C for 8 hours, then at 300°C for 18 hours, and then cooled to room temperature.

[0061] Next, the underlayer and the target were placed in the chamber so as to face each other. Next, the chamber was evacuated using a rotary pump until the oxygen partial pressure in the chamber reached 10 Pa. The underlayer was heated using a heater until the set temperature reached 920° C. After the underlayer reached the set temperature, it was left for 10 minutes to stabilize.

[0062] To remove impurities on the target surface, the shutter was closed and the target was rotated and revolved to perform pre-ablation. Then, the shutter was opened and the laser energy density was 1.3 J / cm 2 During film formation, oxygen was introduced into the chamber while adjusting the exhaust volume with a valve to maintain the oxygen partial pressure in the chamber at 1×10 1 The temperature was maintained at 10 Pa.

[0063] After the deposition was completed, the heater was turned off and the temperature of the underlayer was lowered while maintaining the oxygen partial pressure. After the temperature of the underlayer reached 450°C, the oxygen partial pressure was reduced to 2×10 4 The mixture was cooled in the furnace for 90 minutes at 1000 Pa. 1 / 3 Gd 1 / 3 Dy 1 / 3 Ba2Cu3O 7-δ A superconducting laminate was produced in which a superconducting layer made of a superconductor represented by the formula (I) was formed on an underlayer made of a substrate and an intermediate layer.

[0064] [Example 2] The same method as in Example 1 was used except that the target was changed. 0.25 Gd 0.25 Dy 0.25 Ho 0.25 Ba2Cu3O 7-δ A superconducting laminate was produced in which a superconducting layer made of a superconductor represented by the following formula was formed on an underlayer.

[0065] In Example 2, the target was prepared by the following procedure. In the preparation of the target, first, Y2O3 (purity 99.9%), Gd2O3 (purity 99.9%), Dy2O3 (purity 99.9%), Ho2O3 (purity 99.9%), BaCO3 (purity 98%) and CuO (purity 99.9%) were weighed as the target materials in a substance ratio of 1 / 4:1 / 4:1 / 4:2:3, and mixed in a mortar to prepare a mixed powder. The firing conditions for producing the target using the mixed powder were the same as those in Example 1.

[0066] [Example 3] The same method as in Example 1 was used except that the target was changed. 0.2 Gd 0.2 Dy 0.2 Ho 0.2 Yb 0.2 Ba2Cu3O 7-δ A superconducting laminate was produced in which a superconducting layer made of a superconductor represented by the following formula was formed on an underlayer.

[0067] In Example 3, the target was prepared by the following procedure. In the preparation of the target, first, Y2O3 (purity 99.9%), Gd2O3 (purity 99.9%), Dy2O3 (purity 99.9%), Ho2O3 (purity 99.9%), Yb2O3 (purity 99.9%), BaCO3 (purity 98%) and CuO (purity 99.9%) were weighed as target materials in a substance ratio of 1 / 5:1 / 5:1 / 5:1 / 5:1 / 5:1 / 5:2:3, and mixed in a mortar to prepare a mixed powder. The firing conditions for producing a target using the mixed powder were the same as those in Example 1.

[0068] [Comparative Example 1] The composition formula was YBa2Cu3O in the same manner as in Example 1, except that the target was changed. 7-δ A superconducting laminate was produced in which a superconducting layer made of a superconductor represented by the following formula was formed on an underlayer.

[0069] In Comparative Example 1, the target was prepared by the following procedure. In the preparation of the target, first, Y2O3 (purity 99.9%), BaCO3 (purity 98%), and CuO (purity 99.9%) were weighed as the target materials in a substance ratio of 1:2:3 (mol), and mixed in a mortar to prepare a mixed powder. The firing conditions for producing the target using the mixed powder were the same as those in Example 1.

[0070] [Comparative Example 2] The same method as in Example 1 was used except that the target was changed. 0.25 Sm 0.25 EU 0.25 Dy 0.25 Ba2Cu3O 7-δ A superconducting laminate was produced in which a superconducting layer made of a superconductor represented by the following formula was formed on an underlayer.

[0071] In Comparative Example 3, the target was prepared by the following procedure. In the preparation of the target, first, Y2O3 (purity 99.9%), Sm2O3 (purity 99.9%), Eu2O3 (purity 99.9%), Dy2O3 (purity 99.9%), BaCO3 (purity 98%) and CuO (purity 99.9%) were weighed as the target materials in a substance ratio of 1 / 4:1 / 4:1 / 4:1 / 4:2:3 (mol), and mixed in a mortar to prepare a mixed powder. The firing conditions for producing the target using the mixed powder were the same as those in Example 1.

[0072] (Evaluation of radiation resistance with respect to superconducting transition temperature) For the superconducting laminates of Examples 1 to 3 and Comparative Examples 1 and 2, the temperature dependence of magnetization of the superconductor was measured using a magnetic property measurement system (MPMS-3). Next, the superconductors of Examples 1 to 3 and Comparative Example 1 were irradiated with He ions with the same energy (1 MeV) as that of neutron beams. Next, the temperature dependence of magnetization of the irradiated superconductors was measured again. The superconducting transition temperatures T c The superconducting transition temperature T cwas evaluated as the temperature at which the magnetization begins to drop during zero field cooling (ZFC).

[0073] FIG. 5(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation of the superconductor of Example 1, and FIG. 5(b) is a graph showing the transition temperature T c As shown in Fig. 5(a) and Fig. 5(b), the superconductor of Example 1 had a superconducting transition temperature T c The transition temperature T was 86.5 K, whereas the transition temperature T was 86 K after He ion irradiation. In the graphs below showing the temperature dependence of time before He ion irradiation, some graphs overlap and some graphs are not visible in part or in whole. c An enlarged view of the vicinity is also shown.

[0074] FIG. 6(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation of the superconductor of Example 2, and FIG. 6(b) is a graph showing the transition temperature T c As shown in Fig. 6(a) and Fig. 6(b), the superconductor of Example 2 had a superconducting transition temperature T c The superconducting transition temperature was 84.5 K before and after He ion irradiation, and 83.5 K after.

[0075] FIG. 7(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation of the superconductor of Example 3, and FIG. 7(b) is a graph showing the transition temperature T c As shown in Fig. 7(a) and Fig. 7(b), the superconductor of Example 3 had a superconducting transition temperature T c The superconducting transition temperature was 82.8 K before and after He ion irradiation, and 81.8 K after.

[0076] 8 is a graph showing the temperature dependence of magnetization before and after He ion irradiation for the superconductor of Comparative Example 1. As shown in FIG. 8, the superconductor of Comparative Example 1 has a superconducting transition temperature T c The superconducting transition temperature was 73.0 K after He ion irradiation, whereas it was 86 K before irradiation.

[0077] 9(a) is a graph showing the temperature dependence of magnetization before and after He ion irradiation for the superconductor of Comparative Example 2, and FIG. 9(b) is an enlarged view of the vicinity of the transition temperature Tc in FIG. 9(a). As shown in FIG. 9(a) and FIG. 9(b), the superconductor of Comparative Example 2 has a superconducting transition temperature T c The superconducting transition temperature was 40.0 K after He ion irradiation, whereas it was 85.5 K before irradiation.

[0078] As shown in Fig. 8, Fig. 9(a) and Fig. 9(b), the superconducting transition temperature of the superconductor of Comparative Example 1 was decreased by 13K by high-energy He ion irradiation, and the superconducting transition temperature of the superconductor of Comparative Example 2 was decreased by 45.5K by high-energy He ion irradiation. On the other hand, as shown in Fig. 5(a) to Fig. 7(b), the superconductors of Examples 1 to 3 were confirmed to be high-temperature superconductors with excellent irradiation resistance, since the transition temperature of the superconductor of Comparative Example 1 was greatly decreased after high-energy He ion irradiation, it can be seen that the function as a high-temperature superconductor was greatly deteriorated. Specifically, the superconducting transition temperatures of the samples of Comparative Example 1 and Comparative Example 2 were 73.0K and 40.0K, respectively, after high-energy He ion irradiation, which are lower than the temperature (77.0K) of liquid nitrogen. Therefore, the composition of Comparative Example 1 cannot be utilized as a superconductor at liquid nitrogen temperature before or after irradiation with high-energy particles.

[0079] (Evaluation of radiation resistance with respect to critical current density) For the superconductors of Examples 1 to 3 and Comparative Example 1 to Comparative Example 3 below, the critical current density J was measured by measuring the magnetic field dependence of magnetization. cThe critical current density J c The measurements were performed on each sample at temperatures of 2K, 4.2K, 10K, 20K, 50K, and 77.3K, and in magnetic field environments of 0 to 7T.

[0080] [Comparative Example 3] The same method as in Example 1 was used except that the target was changed. 0.2 Sm 0.2 EU 0.2 Dy 0.2 Ho 0.2 Ba2Cu3O 7-δ A superconducting laminate was produced in which a superconducting layer made of a superconductor represented by the following formula was formed on an underlayer.

[0081] In Comparative Example 3, the target was prepared by the following procedure. In the preparation of the target, first, Y2O3 (purity 99.9%), Sm2O3 (purity 99.9%), Eu2O3 (purity 99.9%), Dy2O3 (purity 99.9%), Ho2O3 (purity 99.9%), BaCO3 (purity 98%) and CuO (purity 99.9%) were weighed as target materials in a substance ratio of 1 / 5:1 / 5:1 / 5:1 / 5:1 / 5:2:3 (mol), and mixed in a mortar to prepare a mixed powder. The firing conditions for producing a target using the mixed powder were the same as those in Example 1.

[0082] FIG. 10(a) is a graph showing the critical current density of the sample of Example 1 before He ion irradiation, and FIG. 10(b) is a graph showing the critical current density of the sample of Example 1 after He ion irradiation. FIG. 11(a) is a graph showing the critical current density of the sample of Example 2 before He ion irradiation, and FIG. 11(b) is a graph showing the critical current density of the sample of Example 2 after He ion irradiation. FIG. 12(a) is a graph showing the critical current density of the sample of Example 3 before He ion irradiation, and FIG. 12(b) is a graph showing the critical current density of the sample of Example 3 after He ion irradiation. FIG. 13(a) is a graph showing the critical current density of the sample of Comparative Example 1 before He ion irradiation, and FIG. 13(b) is a graph showing the critical current density of the sample of Comparative Example 1 after He ion irradiation. FIG. 14(a) is a graph showing the critical current density of the sample of Comparative Example 2 before He ion irradiation, and FIG. 14(b) is a graph showing the critical current density of the sample of Comparative Example 2 after He ion irradiation. FIG. 15(a) is a graph showing the critical current density of the sample of Comparative Example 3 before He ion irradiation, and FIG. 15(b) is a graph showing the critical current density of the sample of Comparative Example 3 after He ion irradiation. In all of the above graphs, a correlation was confirmed in which the critical current density was lower at lower temperatures and higher at higher temperatures, and also lower in a stronger magnetic field environment and higher in a weaker magnetic field environment.

[0083] It was confirmed that the superconductor having five kinds of rare earth elements including Y and Gd as the rare earth elements RE as in Example 3 exhibits a high critical current density compared to other superconductors containing multiple rare earth elements. Therefore, it can be said that the superconductor of Example 3 exhibits a high superconducting transition temperature and a high critical current density even after irradiation with high-energy particles.

[0084] In contrast, the superconducting transition temperature is low in the superconductor containing only Y as a rare earth element as in Comparative Example 1 and the superconductor as in Comparative Example 2. Moreover, the superconductor containing five kinds of rare earth elements but not Gd as in Comparative Example 3 has a critical current density significantly lower than that of the superconductor of Example 3. [Explanation of symbols]

[0085] 1: substrate, 2: intermediate layer, 3: superconducting layer, 5: superconducting laminate, 6: stabilization layer, 10: superconducting wire, 12: underlayer, T: target, L: laser light, P: plume, RE: rare earth element

Claims

1. A superconductor represented by general formula (1). REBa ２ Cổ ３ O ７－δ ・・・(1) (In formula (1), RE is composed of Y, Gd and X, X is composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; 0≦δ≦1)

2. 2. The superconductor according to claim 1, wherein in the above formula (1), X is composed of Dy and one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, and Lu.

3. Contains five or more rare earth elements, Mixing entropy ΔS of RE site ｍｉｘ The superconductor according to claim 1 or 2, wherein R is 1.5R or more.

4. 3. The superconductor according to claim 1, wherein in the above formula (1), RE is represented by general formula (2). Y ａ Gd ｂ X ｃ ・・・(2) (0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9)

5. A preparation step of preparing a base layer having a surface made of a single crystal; a deposition step of depositing a superconductor on the underlayer, A method for producing a superconductor, wherein a target represented by general formula (1) is used in the vapor deposition step. REBa ２ Cổ ３ O ７－δ ・・・(1) (In formula (1), RE is composed of Y, Gd and X, X is composed of one or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu; 0≦δ≦1)

6. 6. The method for producing a superconductor according to claim 5, wherein in the vapor deposition step, the target is placed at a position facing the underlayer, and a pulse laser is irradiated onto the target.

Images