Superconductor, superconducting wire rod, superconducting coil, and method for producing superconductor

Abstract

This superconductor includes a compound that is represented by general formula (1) and includes four or more kinds of rare earth metal elements, a portion of the rare earth metal elements being substituted with a Group 2 element. Formula (1): REBa2Cu3O7-δ (in the formula (1), RE comprises four or more different elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu, and satisfies 0 ≤ δ ≤ 1.).

Description

Superconductor, superconducting wire, superconducting coil, and method for manufacturing a superconductor

[0001] This invention relates to a superconductor and a method for manufacturing a superconductor. This application claims priority based on Japanese Patent Application No. 2025-032960, filed in Japan on March 3, 2025, the contents of which are incorporated herein by reference.

[0002] In recent years, superconducting devices such as power transmission cables, superconducting electromagnets, and superconducting current leads, which use superconductors as low-current-loss materials, have been cited as one of the highly efficient and low-current-loss electrical devices that can solve energy, environmental, and resource problems (for example, Patent Document 1). Patent Document 1 describes Nb ３ Sn compound superconductors, Nb ３ The use of Al compound superconductors is disclosed.

[0003] However, for superconducting materials to be put to practical use in these fields, a high superconducting transition temperature T is required. ｃ In addition, a high critical current density Jc at a high magnetic field is also considered an important requirement, and there is a demand for superconductors that exhibit even higher critical current densities.

[0004] Furthermore, superconductors are also used, for example, as magnets to confine plasma in nuclear fusion reactors. One example of how superconductors are used in nuclear fusion reactors is their use as materials for constructing toroidal magnetic field coils in a nuclear fusion reactor that includes a toroidal plasma chamber having a central column (for example, Patent Document 2). A toroidal magnetic field coil is a coil that creates a magnetic field for confining plasma.

[0005] A key challenge in making a nuclear fusion reactor a viable power plant is achieving high economic efficiency. When used in a nuclear fusion reactor, superconductors need to be maintained at a temperature that exhibits superconductivity. Therefore, the cost proportion related to superconductors is high. To maintain the temperature of the superconductor below its transition temperature, cooling means are used. Patent document 2 does not mention specific materials for the toroidal magnetic field coil, but it states that a high-temperature superconductor (HTS) coil with a high transition temperature is used.

[0006] In the International Thermonuclear Experimental Reactor (ITER) project, Nb is used as a material for high-performance and high-quality superconducting strands for the realization of a magnetic confinement nuclear fusion reactor ３ It is described that Sn superconducting strands are used (for example, Non-Patent Document 1).

[0007] International Publication No. 2013 / 154187, Japanese National Publication No. 2016-534327

[0008] Isono Takaaki (1997). "Development of Nb₃Sn Strands for International Thermonuclear Experimental Reactor (ITER) in Japan", pp. 150-157.

[0009] However, conventionally, superconductors exhibiting high critical current density have not been sufficiently known, and a search for new superconductors has been necessary. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a superconductor, a superconducting wire, a superconducting coil, and a method for producing the same having a high critical current density. Also, with an eye toward application as a nuclear fusion reactor, the present invention desirably provides a superconductor, a superconducting wire, and a superconducting coil having high irradiation resistance.

[0010] The present invention provides the following means to solve the above problems.

[0011] [1] A superconductor according to one aspect of the present invention is a compound represented by general formula (1) that has four or more types of rare earth metal elements, wherein a part of the rare earth metal elements is substituted with a Group 2 element. REBa ２ Cu ３ O ７－δ ...(1) (In formula (1), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and 0≤δ≤1 is satisfied)

[0012] [2] The superconductor according to [1] above may be one represented by general formula (2). RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ... (2) (In formula (2), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Z is one or more Group 2 elements selected from the group consisting of Ca, Sr, and Mg, satisfying 0 ≤ δ ≤ 1 and 0 < x < 0.5)

[0013] [3] In the superconductors of [1] and [2] above, the group second element may be Ca.

[0014] [4] In the superconductors described in [1] to [3] above, the composition ratio of the group second elements may be 0.5 at% or more and 35 at% or less. For example, in general formula (2), x may satisfy the condition 0.005 < x < 0.35.

[0015] [5] In the superconductors of [1] to [4] above, the composition ratio of the group second elements may be 1 at% or more and 25 at% or less. For example, in general formula (2), x may be configured to satisfy 0.01 ≤ x < 0.20. Also, in the superconductors of [1] to [4] above, the composition ratio of the group second elements may be 25 at% or less, 20 at% or less, 15 at% or less, 10 at% or less, 3 at% or more, or 5 at% or more. For example, in general formula (2), x may be configured to satisfy x ≤ 0.25, x ≤ 0.20, x ≤ 0.15, x ≤ 0.10, 0.03 ≤ x, or 0.05 ≤ x.

[0016] [6] In the superconductors of [2] and [3] above, the composition ratio of the group second element may be 3 at% or more and 8 at% or less. For example, the general formula (2) may satisfy 0.03 < x ≤ 0.08. In this case, the group second element may be Ca.

[0017] [7] The superconductors described in [1] to [6] above may contain five or more rare earth metal elements.

[0018] [8] In the superconductors described in [1] to [7] above, RE may be represented by general formula (3) in general formula (1). ａ Gd ｂ Dy ｃ Ho ｄ Yb ｅ ... (3) (0.04 ≤ a < 0.85, 0.04 ≤ b < 0.85, 0.04 ≤ c < 0.85, 0.04 ≤ d < 0.85, 0.05 ≤ e < 0.85)

[0019] [9] The superconductors described in [1] to [8] above may have a thin film shape and a film thickness of 50 nm or more and 50 μm or less. When used as superconducting wires for fusion reactors, the film thickness may be 500 nm or more and 5000 nm or less in order to allow sufficient current to flow.

[0020]

[10] A superconducting wire according to one aspect of the present invention comprises a superconducting layer containing the superconductors described in [1] to [9] above.

[0021]

[11] A superconducting coil according to one aspect of the present invention comprises a wound superconducting layer as described in

[10] above.

[0022]

[12] A method for manufacturing a superconductor according to one aspect of the present invention comprises a preparation step of preparing a base layer whose surface is composed of a single crystal, and a deposition step of depositing a superconductor onto the base layer, wherein a target represented by general formula (2) is used in the deposition step. RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ ... (2) (In formula (2), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Z is one or more Group 2 elements selected from the group consisting of Ca, Sr, and Mg, satisfying 0 ≤ δ ≤ 1 and 0 < x < 0.5)

[0023]

[13] The method for manufacturing the superconductor described in

[12] further comprises a target preparation step for preparing the target to be used in the deposition step, wherein in the target preparation step, a powder containing four or more rare earth metal elements, Ba element, Cu element, and a group 2 element may be sintered.

[0024]

[14] In the method for manufacturing the superconductor described in

[12] and

[13] above, the deposition step may be carried out in an environment of 500°C to 1,000°C.

[0025]

[15] The methods for manufacturing superconductors described in

[12] to

[15] above may also be configured such that x satisfies 0.005 ≤ x ≤ 0.35 in general formula (2).

[0026]

[16] The methods for manufacturing superconductors described in

[12] to

[15] above may include five or more rare earth metal elements in general formula (2), and x may satisfy 0.01 ≤ x ≤ 0.25. In this case, the group 2 element may be Ca. Furthermore, in the above methods for manufacturing superconductors, x may be any of the following configurations: x ≤ 0.20, x ≤ 0.15, x ≤ 0.10, 0.03 ≤ x, or 0.05 ≤ x.

[0027] According to the present invention, it is possible to provide a superconductor with a high critical current density and a method for manufacturing the same.

[0028] Figure 2 is a schematic diagram showing a part of the crystal structure of a superconductor according to one embodiment of the present invention. Figure 2 is a partial cross-sectional perspective view of a superconducting wire according to one embodiment of the present invention. Figure 3 is a diagram for explaining the configuration of a superconducting laminate provided on the superconducting wire of Figure 2. Figure 4 is a perspective view showing an example of the configuration of a superconducting coil according to one embodiment of the present invention. Figure 5 is a diagram illustrating a method for manufacturing a superconductor according to one embodiment of the present invention, showing the deposition process performed by the PLD method. Figure 6 is a graph showing the temperature dependence of the critical current density of the superconductors of Examples 1 to 3 and Comparative Example 1 before and after ion irradiation, and the magnetic field dependence of the critical current density of the superconductor of Comparative Example 2. Figure 7(a) is a graph showing the temperature dependence of magnetization before and after ion irradiation for the superconductor of Example 1, and Figure 7(b) shows the transition temperature T of Figure 7(a). ｃ This is a magnified view of the vicinity, showing the temperature dependence of magnetization after irradiation. Figure 8(a) is a graph of the temperature dependence of magnetization before and after ion irradiation for the superconductor of Example 2, and Figure 8(b) shows the transition temperature T of Figure 8(a). ｃThis is a magnified view of the vicinity, showing the temperature dependence of magnetization after irradiation. Figure 9(a) is a graph of the temperature dependence of magnetization before and after ion irradiation for the superconductor of Example 3, and Figure 9(b) shows the transition temperature T of Figure 9(a). ｃ This is a magnified view of the vicinity, showing the temperature dependence of magnetization after irradiation. Figure 10(a) is a graph of the temperature dependence of magnetization before and after ion irradiation for the superconductor of Comparative Example 1, and Figure 10(b) shows the transition temperature T of Figure 10(a). ｃ This is a magnified view of the vicinity, showing the temperature dependence of magnetization after irradiation. Figure 11 shows the analysis results of the superconductor of Example 4 before ion irradiation, where Figure 11(a) shows the X-ray diffraction results, Figure 11(b) shows the temperature dependence of magnetization, and Figure 11(c) shows the magnetic field dependence of critical current density. Figure 12 shows the analysis results of the superconductor of Example 4 after ion irradiation, where Figure 12(a) shows the X-ray diffraction results, Figure 12(b) shows the temperature dependence of magnetization, and Figure 12(c) shows the magnetic field dependence of critical current density. Figure 13 shows the analysis results of the superconductor of Example 5 before ion irradiation, where Figure 13(a) shows the X-ray diffraction results, Figure 13(b) shows the temperature dependence of magnetization, and Figure 13(c) shows the magnetic field dependence of critical current density. Figure 14 shows the analysis results of the superconductor of Example 5 after ion irradiation, where Figure 14(a) shows the X-ray diffraction results, Figure 14(b) shows the temperature dependence of magnetization, and Figure 14(c) shows the magnetic field dependence of critical current density. Figure 15 shows the analysis results of the superconductor of Example 6 before ion irradiation, where Figure 15(a) shows the X-ray diffraction results and Figure 15(b) shows the temperature dependence of magnetization. Figure 16 shows the analysis results of the superconductor of Example 6 after ion irradiation, where Figure 16(a) shows the X-ray diffraction results, Figure 16(b) shows the temperature dependence of magnetization, and Figure 16(c) shows the magnetic field dependence of critical current density.

[0029] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. Note that, for convenience, the drawings used in the following description may show enlarged versions of characteristic parts in order to clearly illustrate the features of the present invention. Therefore, the dimensional ratios of each component may differ from those of the actual components.

[0030] [Superconductor] A superconductor according to one embodiment of the present invention is a compound represented by general formula (1), in which a portion of the rare earth metal element represented by RE is substituted with a group 2 element. In formula (1), RE represents a rare earth metal element. REBa ２ Cu ３ O ７－δ ... (1)

[0031] Figure 1 is a schematic diagram showing a part of the crystal structure of a superconductor according to one embodiment of the present invention. In Figure 1, the atomic sites of the rare earth metal element RE are indicated by the symbols RE1 to RE5. In Figure 1, atoms of the same rare earth metal element may be located at the atomic sites indicated by the symbols RE1 to RE5, or atoms of different rare earth metal elements may be located at each site. As shown in the crystal structure in Figure 1, the superconductor according to one embodiment of the present invention has an RE site layer L in which RE atoms arranged between Ba elements in the c-axis direction are aligned on the c-plane. ＲＥ It has the following. The types and arrangement of rare earth metal elements in Figure 1 are just an example, and the types, number, and arrangement of rare earth metal elements are not limited to this example. Rare earth metal elements are four or more elements selected from the group consisting of Y (yttrium), Gd (gadolinium), 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). These rare earth metal elements exist as trivalent ions in REBCO. The ionic radii of the above rare earth elements are summarized in the table below.

[0032]

[0033] Here, as will be described in detail later, in the superconductor of this embodiment, some of the rare earth metal elements are substituted with group 2 elements, so in formula (1) above, the sum of the amounts of substance of the rare earth metal elements and group 2 elements is adjusted to be 1. In this embodiment, the sum of the amounts of substance of the elements is not limited to a 1 mol configuration, and the amount of substance is arbitrary as long as each element satisfies the elemental composition ratio of formula (1). In the superconductor according to one embodiment of the present invention, four or more types of rare earth metal elements may be uniformly substituted with group 2 elements, or a particular rare earth metal element may be substituted with group 2 elements in a larger amount than other rare earth metal elements. Since group 2 elements become divalent ions, when substituted with rare earth metal elements, the composition according to this embodiment becomes overdoped with hole carriers h. In this embodiment, the introduced group 2 elements may be referred to as artificial pinning centers.

[0034] Generally, the crystal structure of REBCO is referred to as a 123 structure, in which three layers of perovskite structures are stacked in the c-axis direction. In the superconductor according to this embodiment, whether or not some of the rare earth metal elements are substituted with group 2 elements is influenced by the ionic radius. The ionic radii of group 2 elements are as follows: Mg 2+ : Approximately 72pm, Ca 2+ : Approximately 100pm, Sr. 2+ : Approximately 118pm (,Ba 2+ : approx. 135pm)

[0035] Since the ionic radii of these Group II elements are similar to those of the rare earth metal elements mentioned above, they can be substituted without disrupting the crystal structure of REBCO. The Group II elements contained in the superconductor according to this embodiment are, for example, Group II elements other than Ba, and are preferably one or more selected from the group consisting of Mg, Ca, and Sr, with Ca being more preferable.

[0036] The composition ratio of Group II elements is, for example, 0.50 at% or more and less than 50.0 at%, preferably 0.80 at% or more and 35.0 at%, more preferably 1.0 at% or more and 25.0 at%, and even more preferably 3.0 at% or more and 20 at%. The composition ratio of Group II elements may be 5.0 at% or more, or 10 at% or less.

[0037] The superconductor according to one embodiment of the present invention, by having four or more such rare earth metal elements, can minimize the decrease in transition temperature before and after irradiation with high-energy particles, even when used in a nuclear fusion reactor or the like where heavy quantum beams such as neutrons or high-energy particles are irradiated. In other words, by including these elements, it is easier to realize a superconductor with excellent irradiation resistance.

[0038] Furthermore, superconductors may be used in superconducting magnets for nuclear fusion reactors, and from this perspective, it is preferable to avoid using superconductors with long half-lives when radioactive. Among the rare earth metal elements mentioned above, Sm and Eu have longer half-lives when radioactive compared to other rare earth metal elements. Therefore, it is preferable that the above element X is four or more elements selected from the group consisting of elements other than Sm and Eu, namely Y, Gd, La, Ce, Pr, Nd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0039] The superconductor according to one embodiment of the present invention preferably contains five or more rare earth metal elements. That is, in the superconductor represented by formula (1), the rare earth metal elements are preferably five or more superconductors represented by, for example, general formula (3). ａ Gd ｂ Dy ｃ Ho ｄ Yb ｅ ... (3) (0.04 ≤ a < 0.85, 0.04 ≤ b < 0.85, 0.04 ≤ c < 0.85, 0.04 ≤ d < 0.85, 0.05 ≤ e < 0.85)

[0040] The superconductor of this embodiment has a mixed entropy ΔS of the atomic sites of the rare earth metal element RE. ｍｉｘHowever, it is a high-entropy superconductor with a gas constant of 1.5R or higher, and may also be 1.4R or higher. Here, R represents the gas constant. In a high-entropy superconductor, four or more types of rare earth elements are present at the atomic sites of the rare earth element RE.

[0041] In equation (1), δ represents the amount of oxygen deficiency. Preferably, δ satisfies 0 ≤ δ ≤ 1 and 0 ≤ δ ≤ 0.6.

[0042] The superconductor according to one embodiment of the present invention preferably contains one or more elements selected from the group consisting of Ca (calcium), Sr (strontium), and Mg (magnesium) among the Group II elements, and more preferably Ca. Among these Group II elements, the ionic radii are smallest in the order of Mg, Ca, and Sr. Compared to the ionic radii of rare earth metal elements, the ionic radius of Mg is small, the ionic radius of Ca is somewhat large, and the ionic radius of Sr is large. By substituting rare earth metal elements with elements that have larger ionic radii than rare earth metal elements, further lattice disorder and strain are generated, leading to improved irradiation resistance through the introduction of dislocations, etc. The elements contained in the superconductor can be identified by general X-ray fluorescence analysis (XRF), electron probe microanalyzer (EPMA), characteristic X-ray spectroscopy (EDS) using a scanning transmission electron microscope (STEM) or scanning electron microscope (SEM), or ICP emission spectroscopy. For the purpose of identifying the contained elements themselves, identification by SEM-EDX is preferred from the viewpoint of simplicity. For the purpose of determining the content ratio of rare earth elements, ICP emission spectroscopy is preferred from the viewpoint of accuracy.

[0043] A superconductor according to one embodiment of the present invention is typically represented by general formula (2). RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ ... (2)

[0044] In general formula (2), the rare earth metal element RE can be a rare earth metal element with the above configuration. Also, in general formula (2), the group second element Z can be a group second element with the above configuration. The group second element Z is preferably one selected from the group consisting of Ca, Sr, and Mg, and more preferably Ca.

[0045] In general formula (2), x represents the amount by which a group 2 element is substituted for a rare earth metal element, and in the formula, x preferably satisfies 0 < x < 0.50, 0.005 < x < 0.35, more preferably 0.008 ≤ x ≤ 0.30, more preferably 0.01 ≤ x ≤ 0.20, and may also be 0.03 ≤ x ≤ 0.20, 0.05 ≤ x ≤ 0.15, or 0.03 ≤ x ≤ 0.08. Furthermore, in a superconductor containing five or more rare earth metal elements, it is preferable for x to satisfy 0.03 ≤ x ≤ 0.08 or 0.16 ≤ x ≤ 0.23 from the viewpoint of increasing the critical current density after irradiation.

[0046] The superconductor according to this embodiment can be in any shape, but it can also be in the form of a thin film. In the form of a thin film superconductor, the film thickness is, for example, 50 nm to 100 μm, and more preferably 100 nm to 50 μm or 5 μm or less. When used as a superconducting wire for a nuclear fusion reactor, the film thickness may be 500 nm to 5000 nm in order to allow sufficient current to flow.

[0047] As described above, the superconductor according to this embodiment has some of the rare earth metal elements replaced by group 2 elements. Consequently, the number of hole carriers increases, and the critical current density Jc can be increased. Furthermore, according to the superconductor according to this embodiment, the irradiation resistance can be improved by interpolating the oxygen vacancy due to the increase in hole carriers and by lattice disorder caused by the inclusion of four or more superconducting polymetallic elements.

[0048] According to the superconductor of one embodiment of the present invention, in a REBCO that has been made highly entropic by multi-element solid solution of rare earth metal elements at the RE site, the hole carriers are overdoped by substituting the Group II elements that become divalent ions with rare earth metal elements that become trivalent ions. This makes it possible to achieve a significant increase in the critical current density Jc before irradiation. Furthermore, by compensating for the decrease in the amount of hole carriers due to oxygen deficiency after irradiation with high-energy particle beams, a high superconducting transition temperature Tc can be maintained even after irradiation. In addition to the introduction of disorder due to high entropy, even greater lattice disorder can be introduced by substituting with Group II elements that have a larger ionic radius than the rare earth metal elements. The introduction of large lattice disorder, strain, and dislocations improves irradiation resistance. Thus, in the superconductor of this embodiment, the critical current density can be increased in a highly entropic REBCO containing four or more types of rare earth metal elements by substituting some of the rare earth metal elements with Group II elements. Furthermore, due to the synergistic effect with the generation of lattice disorder, high critical current densities and superconducting transition temperatures can be achieved even after ion irradiation. Here, as a guideline for practical application, even after ion irradiation testing, a critical current density of 1000 (kA / cm²) can be achieved. ２ The standard is to exhibit a critical current density of approximately ) and the superconductor according to this embodiment can achieve the above standard. The synergistic effect of making REBCO high-entropy and substitution with group 2 elements, which have larger ionic radii and lower valence ions compared to rare earth metal elements, was unexpected even before the experiment, as it was possible to increase the critical current density and improve irradiation resistance, and this can greatly contribute to improving energy efficiency.

[0049] [Superconducting Wire] Figure 2 is a partial cross-sectional perspective view of a superconducting wire according to one embodiment of the present invention. Figure 3 is a diagram illustrating the configuration of a superconducting laminate provided on the superconducting wire of Figure 2. For convenience, the edges of each layer are offset in Figure 3.

[0050] The superconducting wire 10 shown in Figure 2 comprises a superconducting laminate 5 and a stabilizing layer 6. The stabilizing layer 6 extends along the superconducting laminate 5 and is provided in contact with its main surface and side surfaces. The stabilizing layer 6 is formed to surround the superconducting laminate 5. The stabilizing layer 6 functions as a bypass that commutates current generated when the superconducting layer contained in the superconducting laminate 5, which will be described in detail later, transitions to a normal conducting state.

[0051] Examples of metals that can be used for the stabilization layer 6 include copper, copper alloys, aluminum, aluminum alloys, and silver. Examples of copper alloys that can be used for 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 (e.g., electroplating).

[0052] The superconducting laminate 5 shown in Figure 3 comprises 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; stainless steel; or an oriented Ni-W alloy in which a texture has been introduced into nickel steel. The thickness of the substrate 1 is, for example, 10 to 500 μm. An intermediate layer 2 is provided on the main surface S1 of the substrate 1, for example, but the intermediate layer 2 may be omitted by selecting the substrate 1. In the superconducting laminate 5 shown in Figure 3, in which the substrate 1, intermediate layer 2, and superconducting layer 3 are formed in order, the substrate 1 and intermediate layer 2 together are referred to as the base layer 12.

[0053] The intermediate layer 2 is provided between the substrate 1 and the superconducting layer 3. The intermediate layer 2 is composed of, for example, multiple layers. In Figure 3, an example is shown in which the intermediate layer 2 comprises a first layer 2a, a second layer 2b, and a third layer 2c, in order from the side closest to the substrate 1. The intermediate layer 2 may have, for example, multiple layers, each with a different function, such as a bed layer, an orientation layer, and a cap layer. For example, the surface of the intermediate layer 2 on the superconducting layer 3 side and its vicinity are composed of a single crystal.

[0054] The first layer 2a is, for example, a bed layer. The bed layer plays a role in reducing the reaction at the interface between the substrate 1 and the superconducting layer 3 and improving the orientation of the layer formed thereon. The material of the bed layer is, for example, CeO ２ Er２ O ３ , Y ２ O ３ , Dy ２ O ３ , Eu ２ O ３ , Ho ２ O ３ , La ２ O ３ and the like can be mentioned.

[0055] The second layer 2b is, for example, an orientation layer. When a cap layer is formed on the orientation layer, the orientation layer is provided for controlling the crystal orientation of the cap layer. As the cap layer, for example, Gd ２ Zr ２ O ７ , MgO, ZrO ２ -Y ２ O ３ (YSZ), SrTiO ３ , CeO ２ , Y ２ O ３ , Al ２ O ３ , Gd ２ O ３ , Zr ２ O ３ , Ho ２ O ３ , Nd ２ O ３ and other metal oxides. It is preferable to use an orientation layer formed by an IBAD (Ion Beam Assisted Deposition) method.

[0056] 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 whose crystal grains can be self-oriented in the in-plane direction. As the cap layer, for example, CeO ２ , Y ２ O ３ , Al ２ O ３ , Gd ２ O ３ , ZrO ２ , YSZ, Ho ２ O ３ , Nd ２ O ３ , LaMnO ３ and the like.

[0057] The superconducting layer 3 is formed on the surface S2 of the intermediate layer 2 that is farthest from the substrate 1. The thickness of the superconducting layer 3 is, for example, 0.5 μm to 10 μm.

[0058] It is preferable that the superconducting layer 3 is epitaxially grown on the intermediate layer 2. Superconducting layers, particularly oxide superconductors represented by REBCO, have great anisotropy in superconducting properties depending on crystal orientation.

[0059] Specifically, when the orientation mutual among crystal grains in the superconducting layer is disturbed and the inclination angle at the grain boundary increases, the grain boundary acts as a barrier to superconducting current. This significantly reduces the critical current density Jc.

[0060] Therefore, by epitaxially growing the superconducting layer 3 and highly aligning the crystal orientation, attenuation of transport current can be suppressed and high superconducting properties can be achieved.

[0061] The superconducting layer 3 contains the superconductor according to the above embodiment as a main component. That is, it is preferable that the superconducting layer 3 contains, as a main component, a material in which part of rare earth metal elements is substituted with Group 2 elements in a composition constituted by a superconductor represented by general formula (1), and contains a composition represented by formula (2) as a main component. In the present embodiment, the term "main component" means a composition with a content of 50% by mass or more in the member, preferably 90% by mass or more, and more preferably 99% by mass or more. The superconducting layer 3 may be configured to consist of the superconductor according to the above embodiment. REBa ２ Cu ３ O ７－δ ...(1) (RE is composed of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Lu, and satisfies 0≦δ≦1)

[0062] RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ... (2) (In formula (2), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Z is one or more Group 2 elements selected from the group consisting of Ca, Sr, and Mg, satisfying 0 ≤ δ ≤ 1 and 0 < x < 0.5)

[0063] Figure 3 shows a superconducting laminate 5 in which the base layer 12 comprises a substrate 1 and an intermediate layer 2 consisting of three layers. However, in this embodiment, the superconducting laminate 5 may have an intermediate layer made of a single material, as long as the surface and its vicinity are made of a single crystal. Alternatively, the intermediate layer 2 may be omitted, and a single crystal SrTiO ３ A substrate, or a substrate made of a single-crystal MgO substrate, may be used.

[0064] [Superconducting Coil] Figure 4 is a perspective view showing an example of the configuration of a superconducting coil according to one embodiment of the present invention. The coil 20 shown in Figure 4 comprises a superconducting wire 10 according to the above embodiment. The coil 20 is formed by winding the superconducting wire 10. The coil 20 according to one embodiment of the present invention is, for example, a toroidal magnetic field coil that creates a magnetic field for plasma confinement in a nuclear fusion reactor. The coil according to this embodiment is, for example, a multilayer wound coil in which a superconducting wire is wound multiple times around a winding core. The coil according to this embodiment is manufactured by winding a superconducting wire around a winding core. The superconducting coil according to this embodiment only needs to have one or more coils 20, and may have a configuration in which multiple coils 20 are arranged in the axial direction.

[0065] [Method for Manufacturing Superconductors] The method for manufacturing superconductors according to the above embodiment will be described below. A method for manufacturing superconductors according to one embodiment of the present invention comprises a preparation step of preparing a base layer 12 whose surface is composed of single crystals and a deposition step of depositing a superconductor on the base layer 12. In the method for manufacturing superconductors according to this embodiment, a target represented by general formula (2) is used in the deposition step. When manufacturing superconducting wires as superconductors, it is preferable to continuously form each layer using, for example, a reel-to-reel manufacturing apparatus, and when manufacturing superconducting laminates, it is preferable to continuously form each layer using a roll-to-roll manufacturing apparatus. RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ ... (2) (In formula (2), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Z is one or more Group 2 elements selected from the group consisting of Ca, Sr, and Mg, satisfying 0 ≤ δ ≤ 1 and 0 < x < 0.5)

[0066] (Preparation process) First, a base layer 12 whose surface is composed of single crystals is prepared. The base layer 12 is composed of, for example, a substrate 1 and an intermediate layer 2. The intermediate layer 2 can be formed on the substrate 1 by, for example, a physical vapor deposition method such as the PLD method, or a vapor deposition method such as the chemical vapor deposition method, followed by firing. The preparation process is carried out, for example, so that at least one surface of the base layer 12 and its vicinity are composed of single crystals. The preparation process is carried out in a predetermined number of steps, for example, depending on the number of layers that make up the intermediate layer 2 to be formed.

[0067] (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. That is, a material with a composition similar to that represented by formula (2) of the superconductor according to the above embodiment can be used, and both δ and x can be the same as in the configuration of the above embodiment. For example, the target is produced by, for example, mixing predetermined elements or oxides of metal elements in a ratio similar to the ratio of each metal element in formula (2), and then firing. That is, the target is produced by sintering a mixture containing powders of four or more rare earth metal elements, Ba element, Cu element, and Group II elements, each in their elemental form or oxide. In the mixture, the ratio of the amount of substance of the Group II elements to the sum of the amounts of substance of the rare earth metal elements and Group II elements can be the same as the numerical range of x in the above embodiment. In other words, the above ratio can be, for example, 0.005 or more and less than 0.50, and preferably 0.008 or more and 0.35 or less. The above ratio may also be 0.01 or more, 0.03 or more, or 0.05 or more, and may be 0.25 or less, 0.20 or less, 0.15 or less, or x ≤ 0.10 or less.

[0068] In this embodiment, it is preferable to mix four or more rare earth metal elements, and it is preferable to mix five or more rare earth metal elements. Furthermore, it is preferable to use any of the elements selected from the group consisting of Mg, Ca, and Sr as the group 2 element, it is more preferable to use one or both of Ca and Sr, and it is even more preferable to use Ca. The firing for producing the target may be performed in one step or in multiple steps.

[0069] (Vapor Deposition Process) Next, a superconductor is deposited onto the base layer 12. The vapor deposition process is carried out by physical vapor deposition (PVD) methods such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), or sputtering. In the vapor deposition process, it is preferable to place the target T opposite the base layer 12 and irradiate the target T with a laser.

[0070] Figure 5 is a diagram illustrating a method for manufacturing a superconductor according to one embodiment of the present invention, showing the deposition process performed by the PLD method. The PLD method will be explained with reference to Figure 5. The PLD method is performed using a PLD apparatus. The target T and the underlayer 12 are placed facing each other in the chamber of the PLD apparatus. The atmosphere inside the chamber can be, for example, an atmospheric atmosphere. The deposition process is performed, for example, while adjusting the chamber to have a low oxygen partial pressure and heating the underlayer 12.

[0071] The partial pressure of oxygen inside the chamber is, for example, 1 × 10⁻⁶. －５ The pressure can be between Pa and 50 Pa, and preferably between 1 Pa and 20 Pa. The temperature of the substrate (set temperature) can be adjusted, for example, between 200°C and 1000°C.

[0072] The PLD device irradiates a target T with laser light L and focuses the laser light L onto the surface of the target T using a focusing lens or the like. A pulsed laser is used as the laser light L irradiated onto the target T. The laser density is, for example, 0.1 J / cm². ２ 5J / cm or more ２ Do the following:

[0073] By focusing a laser beam onto the surface of target T, the constituent particles of target T are knocked out or evaporated, generating a plume P. The constituent particles of target T contained in the plume P are deposited on the surface of the underlying layer 12, forming a thin film composed of the constituent particles of target T on the surface of the underlying layer 12. Therefore, by changing the composition of the constituent particles of target T, the composition of the thin film formed on the underlying layer 12 can be changed. In other words, to form a superconductor of a desired composition on the underlying layer 12, a target T with the same composition as the desired superconductor should be used.

[0074] In the vapor deposition process, the temperature of the atmosphere to which the underlayer 12 is exposed is, for example, 0°C to 1,000°C, and preferably 30°C to 300°C. This temperature can be confirmed by measuring the temperature inside the chamber in which the vapor deposition process is carried out.

[0075] Therefore, the target T is the target fabricated in the target preparation step described above. That is, a target satisfying the composition of formula (2) above can be used. The composition of target T is the same as the composition of the desired superconductor, and the numerical range of x for the superconductor is adopted. In the deposition step, the film thickness is, for example, 50 nm to 100 μm, and more preferably 100 nm to 50 μm or 5 μm or less. When used as a superconducting wire for a nuclear fusion reactor, the film thickness may be set to 500 nm to 5000 nm in order to allow sufficient current to flow.

[0076] According to the method for manufacturing a superconductor according to this embodiment, a superconducting wire can be formed in which the superconductor according to the above embodiment is formed as a thin film.

[0077] (Annealing process) The laminate obtained by the vapor deposition process may also be annealed. Annealing can be performed, for example, by heating in an oxygen atmosphere consisting of oxygen or oxygen and an inert gas at a temperature of 100°C to 700°C, preferably at a temperature of 200°C to 500°C. Annealing can increase the critical current density Jc. The effect of annealing is particularly pronounced when five or more rare earth metal elements are included, and the critical current density before irradiation can be increased. The annealing process can be performed, for example, when the oxygen partial pressure is 2.5 × 10⁻⁶ ４ This can be done at Pa or higher, 3.0 x 10 ４ It is preferable to perform the procedure at Pa or higher, 5.0 × 10 ４ It is more preferable to perform the procedure at Pa or higher.

[0078] Furthermore, the present invention is not limited to the configuration according to the above embodiment, and can be implemented with various modifications as appropriate within the scope of the gist described in the claims. For example, although the above example described a method for forming a superconducting wire, the method for manufacturing a thin film composed of a superconductor may involve preparing a single-crystal substrate consisting of only one layer as the underlayer 12 and depositing the film, or it may not be necessary to use an underlayer 12 having multiple layers.

[0079] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range. The elements contained in the superconducting layer 3 are analyzed by the same method as the analysis method for the elements contained in the superconductor.

[0080] Throughout this disclosure, singular expressions should be understood to include the concept of their plural form unless otherwise specified. Therefore, singular articles (for example, "a," "an," and "the" in English) should be understood to include the concept of their plural form unless otherwise specified.

[0081] The following describes embodiments of the present invention. The present invention is not limited to the following embodiments. For example, the elements located at the sites of the rare earth metal element RE in the superconductor and their combinations are not limited to the configurations of the following embodiments, and can be implemented by combining various rare earth metal elements according to the above embodiments. As mentioned above, the ionic radii of the rare earth metal elements are close in value. Therefore, it is considered that substitution with group 2 elements is possible without disrupting the crystal structure even when using rare earth metal elements.

[0082] [Example 1] (Y 0.19 Gd 0.19 Dy 0.19 Ho 0.19 Yb 0.19 )Ca 0.05 Ba2Cu3O 7-δ First, the base layer was prepared. Strontium titanate (SrTiO) was used as the substrate. ３ A single crystal substrate was prepared.

[0083] Next, the target was prepared. For the target preparation, first, Y2O3 (99.9% purity), Gd2O3 (99.9% purity), Dy2O3 (99.9% purity), Ho2O3 (99.9% purity), Yb2O3 (99.9% purity), CaO (98% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed out so that the molar ratio of the metal elements in the composition was 19 / 100:19 / 100:19 / 100:19 / 100:19 / 100:1 / 20:2:3, and the mixture was prepared by mixing them in a mortar and pestle.

[0084] Next, the mixed powder was transferred to a crucible and subjected to primary calcination (pre-firing) at 930°C for 20 hours, followed by furnace cooling to room temperature.

[0085] Next, the calcined mixed powder was mixed in an agate mortar and molded into pellets under pressure. Then, for secondary firing, the pelletized mixed powder was heated at 930°C for 8 hours, followed by 300°C for 18 hours, and then cooled to room temperature.

[0086] Next, the substrate and target were placed in the chamber so that they faced each other. Then, a rotary pump was used to evacuate the chamber until the oxygen partial pressure reached 10 Pa. The substrate was heated using a heater to reach the set temperature of 920°C. After the substrate reached the set temperature, it was left to stabilize for 10 minutes.

[0087] To remove impurities from the target surface, pre-ablation was performed by closing the shutter and allowing the target to rotate and revolve. Then, the shutter was opened, and the laser energy density was set to 1.3 J / cm². ２ The film deposition was carried out with the settings as follows. During film deposition, oxygen was introduced into the chamber while the exhaust volume was adjusted by valve to maintain the oxygen partial pressure inside the chamber at 2 × 10⁻¹⁰. １ The temperature was maintained at Pa. In addition, the temperature inside the chamber (substrate temperature) during the deposition process was adjusted to be maintained at 720°C.

[0088] After the film deposition was complete, the heater was turned off and the temperature of the substrate was lowered while maintaining the oxygen partial pressure. After the temperature of the substrate reached 450°C, the oxygen partial pressure was reduced to 9 × 10⁻⁶ until it reached room temperature. ４ It was furnace-cooled at Pa for 90 minutes. In this way, the composition formula (Y 0.19 Gd 0.19 Dy 0.19 Ho 0.19 Yb 0.19 ) Ca 0.05 Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the specified formula] was formed on a substrate and an intermediate layer.

[0089] [Example 2] (Y 0.18 Gd 0.18 Dy 0.18 Ho 0.18 Yb 0.18 ) Ca 0.10 Ba2Cu3O 7-δ Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.18 Gd 0.18 Dy 0.18 Ho 0.18 Yb 0.18 )Ca 0.10Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the specified formula] was formed on a base layer.

[0090] In Example 2, the target was prepared using the following procedure. First, as the target material, Y2O3 (99.9% purity), Gd2O3 (99.9% purity), Dy2O3 (99.9% purity), Ho2O3 (99.9% purity), Yb2O3 (99.9% purity), CaO (98% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed out so that the molar ratio of the metal elements in each composition was 9 / 50:9 / 50:9 / 50:9 / 50:9 / 50:1 / 10:2:3, and the mixture was mixed in a mortar to prepare a mixed powder. The firing conditions for producing the target using the mixed powder were the same as in Example 1.

[0091] [Example 3] (Y 0.16 Gd 0.16 Dy 0.16 Ho 0.16 Yb 0.16 )Ca 0.20 Ba2Cu3O 7-δ Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.16 Gd 0.16 Dy 0.16 Ho 0.16 Yb 0.16 )Ca 0.20 Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the specified formula] was formed on a base layer.

[0092] In Example 3, the target was prepared using the following procedure. First, as the target material, Y2O3 (99.9% purity), Gd2O3 (99.9% purity), Dy2O3 (99.9% purity), Ho2O3 (99.9% purity), Yb2O3 (99.9% purity), CaO (98% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed in a molar ratio of 4 / 25:4 / 25:4 / 25:4 / 25:4 / 25:1 / 5:2:3 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 in Example 1.

[0093] [Comparative Example 1] (YBa2Cu3O 7-δ ) Except for changing the target, the composition formula YBa was obtained in the same manner as in Example 1. ２ Cu ３ O ７－δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the specified formula] was formed on a base layer.

[0094] In Comparative Example 1, the target was prepared using the following procedure. First, Y2O3 (99.9% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed in a molar 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 in Example 1.

[0095] [Comparative Example 2] (Y 0.2 Gd 0.2 Dy 0.2 Ho 0.2 Yb 0.2 ) Ba2Cu3O 7-δ ) Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.2 Gd 0.2 Dy 0.2 Ho 0.2 Yb 0.2 )Ba2Cu3O 7-δA superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the given formula] was formed on a base layer. In other words, in Comparative Example 2, unlike Examples 1 to 3, alkali metals were not included.

[0096] In Comparative Example 2, the target was prepared using the following procedure. First, as the target material, Y2O3 (99.9% purity), Gd2O3 (99.9% purity), Dy2O3 (99.9% purity), Ho2O3 (99.9% purity), Yb2O3 (99.9% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed in a molar ratio of 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 the target using the mixed powder were the same as in Example 1.

[0097] [Example 4] (Y 0.198 Gd 0.198 Dy 0.198 Ho 0.198 Yb 0.198 )Ca 0.010 Ba2Cu3O 7-δ ) Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.198 Gd 0.198 Dy 0.198 Ho 0.198 Yb 0.198 )Ca 0.010 Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the specified formula] was formed on a base layer.

[0098] In Example 4, the target was prepared using the following procedure. First, as the target material, Y2O3 (99.9% purity), Gd2O3 (99.9% purity), Dy2O3 (99.9% purity), Ho2O3 (99.9% purity), Yb2O3 (99.9% purity), CaO (99.9% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed in a molar ratio of 99 / 500:99 / 500:99 / 500:99 / 500:99 / 500:1 / 100:2:3 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 in Example 1.

[0099] [Example 5] (Y 0.16 Yb 0.16 Ho 0.16 Lu 0.16 Tm 0.16 W 0.16 )Ca 0.05 Ba2Cu3O 7-δ Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.16 Yb 0.16 Ho 0.16 Lu 0.16 Tm 0.16 W 0.16 )Ca 0.05 Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by was formed on a base layer. In the composition, the elemental composition ratio was Y:Yb:Ho:Lu:Tm:Er = 1:1:1:1:1:1, and the elemental composition ratio of the total number of rare earth elements to the Ca element was 95 / 100:5 / 100.

[0100] In Example 5, the target was prepared using the following procedure. First, as the target material, Y2O3 (99.9% purity), Yb2O3 (99.9% purity), Ho2O3 (99.9% purity), Lu2O3 (99.9% purity), Tm2O3 (99.9% purity), Er2O3 (99.9% purity), CaO (98% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed so that the molar ratio of the metal elements in each composition was 19 / 120:19 / 120:19 / 120:19 / 120:19 / 120:19 / 120:1 / 20:2:3, and the mixture was mixed in a mortar to prepare a mixed powder. The firing conditions for producing the target using the mixed powder were the same as in Example 1.

[0101] [Example 6] (Y 0.16 Gd 0.16 Dy 0.16 Ho 0.16 Yb 0.16 )Sr 0.20 Ba2Cu3O 7-δ Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.16 Gd 0.16 Dy 0.16 Ho 0.16 Yb 0.16 )Sr 0.20 Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of a superconductor represented by [the specified formula] was formed on a base layer.

[0102] In Example 6, the target was prepared using the following procedure. First, Y2O3 (99.9% purity), Gd2O3 (99.9% purity), Dy2O3 (99.9% purity), Ho2O3 (99.9% purity), Yb2O3 (99.9% purity), SrO (99.9% purity), BaCO3 (98% purity), and CuO (99.9% purity) were weighed out so that the molar ratio of the metal elements in each composition was 4 / 25:4 / 25:4 / 25:4 / 25:4 / 25:1 / 5:2:3, and the mixture was mixed in a mortar to prepare a mixed powder. The firing conditions for producing the target using the mixed powder were the same as in Example 1.

[0103] (Critical Current Density Test) The critical current density J was determined by measuring the magnetic field dependence of magnetization for the superconductors of Examples 1 to 6, Comparative Example 1, and Comparative Example 2. ｃ The critical current density J was measured. ｃ The measurements were performed for each sample under conditions of 0–7T at a temperature of 4.2K. The measurement results are shown in the figure.

[0104] Furthermore, the superconductors of Examples 1 to 3 and Comparative Example 1 were irradiated with 300 keV Ar ions. Subsequently, the critical current density of the irradiated superconductors was measured again. In addition, the superconductors of Examples 4 to 6 were irradiated with 100 keV H + Ions were irradiated. Then, the critical current density was measured again on the irradiated superconductor. In other words, the irradiation resistance test conditions for Examples 4 to 6 were more likely to cause a decrease in superconducting properties due to irradiation than the irradiation resistance test conditions for Examples 1 to 3 and Comparative Example 1. Therefore, the characteristics after irradiation for Examples 4 to 6 tend to decrease compared to the characteristics before irradiation. In addition, for Examples 4 to 6, the dependence of the external magnetic field on the critical current density at other temperatures was evaluated, in addition to the critical current density at 4.2 K.

[0105] Figure 6 is a graph showing the magnetic field dependence of the critical current density of the superconductors in Examples 1 to 3 and Comparative Example 1 before and after ion irradiation, as well as the magnetic field dependence of the critical current density of the superconductor in Comparative Example 2. As shown in Figure 6, all superconductors showed high critical current densities. Furthermore, it was confirmed that the superconductor in Example 1 showed the highest critical current density before ion irradiation among Examples 1 to 3. It is expected that particularly high critical current densities will be shown, similar to Example 1, if the range is 0.03 < x < 0.08.

[0106] In the superconductor after ion irradiation testing, Comparative Example 1 showed approximately 1.0 × 10⁻¹⁰ in a zero-magnetic-field environment. ２ (kA / cm ２ The critical current density was found to be at its maximum at 1.0 × 10¹⁶, and it was confirmed that the critical current density decreased rapidly when even a small magnetic field strength was applied. In contrast, the superconductor according to this embodiment has a critical current density of approximately 1.0 × 10¹⁶ in a no-magnetic-field environment. ３ (kA / cm２ ) and even after applying a magnetic field, the critical current density did not decrease sharply, confirming excellent irradiation resistance. Although not shown in Figure 6, in a sample (Comparative Example 2) which was the same as in Example 1 except that it was not substituted with a group 2 element, the critical current density was approximately 1.0 × 10⁻¹⁰ at a magnetic field of 0 T when ion irradiation was performed in the same manner as in Example 1. ２ kA / cm ２ The behavior decreases with increasing magnetic field, and it is believed that one of the reasons for the effectiveness of the present invention is that by substituting a trivalent rare earth metal element with a divalent group second element, the hole carriers are overdoped, and the decrease in the amount of hole carriers due to oxygen deficiency during high-energy particle beam irradiation is suppressed.

[0107] (Superconducting Transition Temperature Test) The temperature dependence of the magnetization of the superconductors was measured for the superconducting laminates of Examples 1 to 6 and Comparative Example 1 using a magnetic property measurement system (MPMS-3). Next, the superconductors of Examples 1 to 6 and Comparative Example 1 were irradiated with 300 KeV Ar ions, and the temperature dependence of the magnetization of the superconductors after irradiation was measured.

[0108] Table 1 shows the transition temperature T of each sample before and after irradiation. ｃ To summarize, as shown in Table 1, in Comparative Example 1, the transition temperature T was reduced by ion irradiation. ｃ While the transition temperature decreased by 25K in the first example, in Examples 1 to 6, the decrease in transition temperature due to ion irradiation was 13K or less, confirming that Examples 1 to 6 exhibited excellent irradiation resistance. This is thought to be due to the effect of having four or more rare earth metal elements and group 2 elements, which cause large lattice disorder in the superconductor, and the suppression of the decrease in carrier amount due to irradiation by overdoping through the substitution of rare earth metal elements with group 2 elements.

[0109] Figures 11 and 12 show the analysis results of the superconductor of Example 4 before and after ion irradiation, respectively. Figures 11(a) and 12(a) show the X-ray diffraction results. Figures 11(b) and 12(b) show the temperature dependence of magnetization. Figures 11(c) and 12(c) show the magnetic field dependence of critical current density. As shown in Figures 11 and 12, in Example 4, the superconducting transition temperature T before and after irradiation is particularly important. ｃ The small change in the critical current density (J) was confirmed, indicating excellent resistance to irradiation. Furthermore, the critical current density (J) was measured at all temperatures. ｃ This is a high value, and in particular, at 4.2K, it was 1.0 × 10⁻¹⁰ at all measurement points up to an external magnetic field strength of 7T. ３ (kA / cm ２ It was confirmed that it showed values ​​higher than ).

[0110] Figures 13 and 14 show the analysis results of the superconductor of Example 5 before and after ion irradiation, respectively. Figures 13(a) and 14(a) show the X-ray diffraction results. Figures 13(b) and 14(b) show the temperature dependence of magnetization. Figures 13(c) and 14(c) show the magnetic field dependence of critical current density. As shown in Figures 13 and 14, it was confirmed that Example 5 exhibited a high critical current density. Furthermore, despite the high energy ion irradiation conditions, the transition temperature T before and after the irradiation test was not high. c The change in the critical current density after irradiation remained at 33.0 K, and the critical current density J remained constant. ｃ Within the range of an external magnetic field of ~7T, it is 1.0 × 10⁻¹⁰ ２ It is considered to have excellent irradiation resistance, exceeding kA / cm.

[0111] Figures 15 and 16 show the analysis results of the superconductor of Example 6 before and after ion irradiation, respectively. Figures 15(a) and 16(a) show the X-ray diffraction results. Figures 15(b) and 16(b) show the temperature dependence of magnetization. Figure 16(c) shows the magnetic field dependence of critical current density. In Example 6, despite the high energy ion irradiation conditions, the transition temperature T before and after the irradiation test was observed. c The change in the critical current density after irradiation remained at 28.0 K, and the critical current density J remained constant. ｃ Within the range of an external magnetic field of ~7T, it is 1.0 × 10⁻¹⁰ ２It is considered to have excellent irradiation resistance, exceeding kA / cm. Furthermore, the critical current density after irradiation is J. c Based on the results of Examples 1 to 3 and the ion irradiation conditions, it is considered that the superconductor before irradiation exhibits a critical current density equivalent to or greater than that of Examples 1 to 3. Furthermore, for the sample of Example 6, observation of the atomic arrangement by TEM and EDS analysis have confirmed that Sr elements are substituted at the RE sites in the crystal structure of REBCO.

[0112] Based on the comparison of Examples 1 to 6 and Comparative Examples 1 and 2, it is considered particularly preferable that the amount of Group II elements substituted for rare earth metal elements in REBCO be between 1.0 at% and 20.0 at%. Regardless of the combination of rare earth elements, and even when the Group II element species is Sr, it was confirmed that improvements in critical current density and irradiation resistance with respect to the transition temperature Tc can be obtained compared to REBCO in which the rare earth element sites are not substituted with Group II elements, similar to substitution with Ca. Since all Group II elements become divalent ions, it is thought that substitution with rare earth metal elements results in an overdoped state of hole carriers h in the composition according to this embodiment without disrupting the crystal structure, thus producing the above effects. Since this effect is considered to be similar regardless of the rare earth element species, the present invention is not limited to the compositions described in the examples.

[0113]

[0114] (Appendix) [Manufacture example 1] ((Y 0.16 Gd 0.16 Dy 0.16 Ho 0.16 Yb 0.16 )Mg 0.20 Ba2Cu3O 7-δ Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.16 Gd 0.16 Dy 0.16 Ho 0.16 Yb 0.16 )Mg 0.20 Ba2Cu3O 7-δA superconducting laminate was fabricated in which a superconducting layer composed of superconductors represented by was formed on a base layer. In Manufacturing Example 1, the target was prepared by the following procedure. In preparing the target, first, Y2O3 (purity 99.9%), Gd2O3 (purity 99.9%), Dy2O3 (purity 99.9%), Ho2O3 (purity 99.9%), Yb2O3 (purity 99.9%), MgO (purity 98%), BaCO3 (purity 98%), and CuO (purity 99.9%) were weighed out so that the molar ratio of the metal elements in each composition was 4 / 25:4 / 25:4 / 25:4 / 25:4 / 25:1 / 5:2:3, and mixed in a mortar to prepare a mixed powder. The firing conditions for fabricating the target using the mixed powder were the same as in Example 1.

[0115] [Manufacturing Example 2] (Y 0.19 EU 0.19 Sm 0.19 Nd 0.19 Dy 0.19 )Ca 0.05 Ba2Cu3O 7-δ Except for changing the target by adjusting the conditions of the target preparation process, the composition formula (Y 0.19 EU 0.19 Sm 0.19 Nd 0.19 Dy 0.19 )Ca 0.05 Ba2Cu3O 7-δ A superconducting laminate was fabricated in which a superconducting layer composed of superconductors represented by was formed on a base layer. In Manufacturing Example 2, the target was prepared by the following procedure. In preparing the target, first, Y2O3 (purity 99.9%), Eu2O3 (purity 99.9%), Sm2O3 (purity 99.9%), Nd2O3 (purity 99.9%), Dy2O3 (purity 99.9%), CaO (purity 99.9%), BaCO3 (purity 98%), and CuO (purity 99.9%) were weighed out so that the molar ratio of the metal elements in each composition was 19 / 100:19 / 100:19 / 100:19 / 100:19 / 100:1 / 20:2:3, and mixed in a mortar to prepare a mixed powder. The firing conditions for fabricating the target using the mixed powder were the same as in Example 1.

[0116] The samples from Production Examples 1 and 2 were also confirmed to possess a critical current density. Similar to the sample from Example 6, observation of the atomic arrangement by TEM and EDS analysis of the sample from Production Example 1 confirmed that Sr elements were substituted at the RE sites in the REBCO crystal structure.

[0117] 1 Substrate 2 Intermediate layer 2a First layer 2b Second layer 2c Third layer 3 Superconducting layer 5 Superconducting laminate 6 Stabilizing layer 10 Superconducting wire 12 Underlayer RE, RE1-RE5 Rare earth metal elements h Hole carrier

Claims

1. A superconductor represented by general formula (1), having four or more rare earth metal elements, wherein some of the rare earth metal elements are substituted with group 2 elements. REBa ２ Cu ３ O ７－δ ... (1) (In equation (1), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, satisfying 0 ≤ δ ≤ 1) 2. The superconductor according to claim 1, represented by general formula (2). RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ ... (2) (In formula (2), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Z is one or more Group 2 elements selected from the group consisting of Ca, Sr, and Mg, satisfying 0 ≤ δ ≤ 1 and 0 < x < 0.5) 3. The superconductor according to claim 1 or 2, wherein the group second element is Ca.

4. The superconductor according to any one of claims 1 to 3, wherein the composition ratio of the group 2 elements is 0.5 at% or more and 35 at% or less.

5. The superconductor according to any one of claims 1 to 4, wherein the composition ratio of the group 2 elements is 1 at% or more and 25 at% or less.

6. The superconductor according to any one of claims 1 to 5, wherein the composition ratio of the group 2 elements is 3 at% or more and 8 at% or less.

7. A superconductor according to any one of claims 1 to 6, comprising five or more rare earth metal elements.

8. The superconductor according to any one of claims 1 to 7, wherein in general formula (1), RE is represented by general formula (3): Y ａ Gd ｂ Dy ｃ Ho ｄ Yb ｅ ... (3), wherein 0.04≤a<0.85, 0.04≤b<0.85, 0.04≤c<0.85, 0.04≤d<0.85, 0.05≤e<0.85 9. A superconductor according to any one of claims 1 to 8, having a thin film shape and having a film thickness of 50 nm or more and 50 μm or less.

10. A superconducting wire comprising a superconducting layer containing the superconductor described in any one of claims 1 to 9 as a main component.

11. A superconducting coil comprising the superconducting wire described in claim 10, wherein the superconducting wire is wound around it.

12. A method for manufacturing a superconductor, comprising: a preparation step of preparing a substrate layer whose surface is composed of single crystals; and a deposition step of depositing a superconductor onto the substrate layer, wherein the deposition step uses a target represented by general formula (2). RE １－ｘ Z ｘ Ba ２ Cu ３ O ７－δ ... (2) (In formula (2), RE consists of four or more elements selected from the group consisting of Y, Gd, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and Z is one or more Group 2 elements selected from the group consisting of Ca, Sr, and Mg, satisfying 0 ≤ δ ≤ 1 and 0 < x < 0.5) 13. The method for manufacturing a superconductor according to claim 12, further comprising a target preparation step for preparing the target to be used in the deposition step, wherein in the target preparation step, a powder containing four or more rare earth metal elements, Ba element, Cu element, and a group 2 element is sintered.

14. The method for manufacturing a superconductor according to claim 12 or 13, wherein the deposition process is carried out in an environment of 500°C to 1,000°C.

15. A method for manufacturing a superconductor according to any one of claims 12 to 14, wherein in general formula (2), x is 0.005 ≤ x ≤ 0.35 or less.

16. A method for manufacturing a superconductor according to any one of claims 12 to 15, wherein the general formula (2) contains five or more rare earth metal elements, and x is 0.01 ≤ x ≤ 0.25.

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