Layered product and method for producing layered product

Abstract

This layered product comprises: at least one first layer that contains a copper oxide superconductor as a primary component; and at least one second layer that contains a high entropy super conductor represented by general formula (2) as a primary component. Formula (2): RE2Ba2Cu3O7-δ. (In formula (2), RE2 is constituted from three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and 0≤δ≤1.)

Description

Laminate and method for manufacturing laminate

[0001] The present invention relates to a laminate and a method for manufacturing the laminate. This application claims priority to Japanese Patent Application No. 2024-093048, filed on June 7, 2024, the contents of which are incorporated herein by reference.

[0002] Superconducting magnets using superconductors play an essential role in magnetic confinement nuclear fusion reactors. Furthermore, rare-earth copper oxide high-temperature superconductors, REBa2Cu3O, which have superconducting properties far superior to conventional low-temperature superconductors, are essential for the commercialization and miniaturization of nuclear fusion reactors. 7-d (REBCO) is expected to be a promising candidate material for magnet applications.

[0003] Evaluation of flux pinning properties in two-dimensional artificially pinned RE123 films, Department of Materials Science, Kyushu University, Masashi Mukaida, Hideki Kai, Makoto Takamura, Yosuke Tanaka, Department of Materials Science, Tohoku University, Masashi Namba, Satoshi Awaji, Kazuo Watanabe

[0004] In previous research, PrBa2Cu3O, a simple substance containing Pr, was used as a method for introducing artificial pinning centers. 7-d is YBa2Cu3O 7-d are alternately laminated.

[0005] However, when a superconducting magnet is used in a nuclear fusion reactor, if the superconductor is continuously irradiated with neutrons generated during the nuclear fusion reaction, the superconducting transition temperature T ｃ and critical current density J ｃ The problem is that the neutron flux increases due to the increased plasma density, and the protective barrier becomes thinner, making neutron shielding more difficult, and the problem of radiation damage becomes even more serious.

[0006] The inventors have been developing HE-REBCO (hereinafter referred to as HE-REBCO) by incorporating the concept of high-entropy alloys into REBCO. As a result of He ion irradiation experiments on the HE-REBCO thin film fabricated, the superconducting transition temperature Tｃ The results showed that the decrease in β-reducing ability was significantly suppressed (Fig. 15). 7-z In the REBCO superconductor represented by the formula (YBa2Cu3O), there is one rare earth element present at the RE site. 7-z ) compared to three types (Y 0.33 Gd 0.33 Dy 0.33 Ba2Cu3O 7-z ), four kinds (Y 0.25 Gd 0.25 Dy 0.25 Ho 0.25 Ba2Cu3O 7-z ) or five kinds (Y 0.20 Gd 0.20 Dy 0.20 Ho 0.20 Yb 0.20 Ba2Cu3O 7-z ) is the superconducting transition temperature T ｃ As shown in FIG. 15, in the superconductor having one rare earth element at the RE site, the superconducting transition temperature before ion irradiation was 86.0 K, and the superconducting transition temperature T ｃ is 73.0 K, and the superconducting transition temperature T ｃ In contrast, the decrease in the superconducting transition temperature T before and after irradiation of REBCO superconductors with three, four, and five rare earth elements present at the RE site was 13.0 K. ｃ The decreases in temperature were 0.5 K, 1.0 K, and 1.0 K, respectively. In addition, the superconducting transition temperatures after the irradiation tests were all 81.5 K or higher.

[0007] There are two main reasons why improved radiation resistance is required: 1. The need for smaller and thinner protective walls due to the miniaturization of reactors. 2. The increase in the amount of neutron irradiation per unit area.

[0008] The HE-REBCO invented by the inventors in their previous research has a superconducting transition temperature T ｃ Although it has high radiation resistance with respect to the critical current density J cRegarding YBCO, as can be seen in Figure 15, the superconducting transition temperature T ｃ Therefore, an object of the present invention is to provide a laminate capable of suppressing a decrease in the superconducting transition temperature after irradiation, and a method for manufacturing such a laminate.

[0009] The present invention provides the following means to solve the above problems.

[0010] [1] A laminate according to one aspect of the present invention comprises at least one first layer containing a copper oxide-based superconductor as a main component, and at least one second layer containing a high-entropy superconductor represented by general formula (2) as a main component. ２ Cu ３ O ７－δ ... (2) (In formula (2), RE2 is composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and 0≦δ≦1)

[0011] [2] In the laminate of [1] above, the first layer may be configured to contain, as a main component, a rare-earth copper oxide superconductor represented by general formula (1), where RE1 is composed of one element selected from a first group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or two elements selected from a second group consisting of an element from the first group and Sr, Ba, and Ca, and satisfies 0≦x≦1.

[0012] [3] In the laminate of the above [1] or [2], the first layer may contain a bismuth-based copper oxide superconductor or a lanthanum-based copper oxide superconductor as a main component.

[0013] [4] In the laminate of any one of [1] to [3] above, the first layer and the second layer may be provided in direct contact with each other or in contact with each other via a thin film.

[0014] [5] The laminate of any one of [1] to [4] above may include a plurality of the second layers, and may have at least a portion of the first layer sandwiched between the second layers in the stacking direction.

[0015] [6] The laminate of any one of [1] to [5] above may comprise a plurality of the first layers, a plurality of the second layers, and a superconducting layer consisting of an alternating laminate portion in which the first layers and the second layers are alternately laminated either directly or via a thin film.

[0016] [7] The laminate of the above [1] to [6] may be composed of the first layer and the second layer.

[0017] [8] The laminate of the above [1] to [7] may be such that in the above formula (2), RE2 is composed of Y, Gd, and X, and X is composed of one or more elements selected from the group consisting of Sr, Ba, Ca, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0018] [9] The laminates of the above [1] to [8], wherein in the above formula (2), X may be composed of Dy and one or more elements selected from the group consisting of Sr, Ba, Ca, La, Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, and Lu.

[0019]

[10] In the laminates of the above [1] to [9], RE2 in the above formula (2) may be composed of four or more kinds of rare earth elements.

[0020]

[11] The laminate of the above [1] to

[10] , wherein in the above formula (2), RE2 is composed of five or more kinds of rare earth elements, and the mixing entropy ΔS of the RE2 site of the second layer is ｍｉｘ may be 1.39R or more.

[0021]

[12] The laminates of the above [1] to

[11] may have a structure in which, in the above formula (2), RE2 is represented by general formula (3): Y ａ Gd ｂ X ｃ ... (3) (0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9).

[0022]

[13] The laminate of any one of the above [1] to

[12] may comprise an underlayer having a surface made of a single crystal, and a superconducting layer including a sandwich structure formed on the underlayer, and the second layer may be located on the outermost surface of the superconducting layer, the outermost surface being the furthest from the underlayer.

[0023]

[14] In the laminate of any one of the above [1] to

[13] , the underlayer has an outermost surface made of SrTiO ３ It may be made of a single crystal.

[0024]

[15] A method for producing a laminate according to one aspect of the present invention includes a lamination process including a first step of forming a first layer mainly composed of a copper oxide-based superconductor, and a second step of forming a second layer mainly composed of a high-entropy superconductor represented by general formula (2) on the first layer directly or via a thin film. ２ Cu ３ O ７－δ ... (2) In formula (2), RE2 is composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and 0≦δ≦1)

[0025]

[16] In the method for producing a laminate according to

[15] above, in the first step, a first layer containing as a main component a rare earth copper oxide superconductor represented by general formula (1) may be formed. ２ Cu ３ O ７－ｘ ... (1) (In formula (1), RE1 is composed of one element selected from a first group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or two elements selected from the first group and a second group consisting of Sr, Ba, and Ca, and satisfies 0≦x≦1.)

[0026]

[17] In the method for manufacturing a laminate according to the above

[15] or

[16] , the first step may form a first layer containing a bismuth-based copper oxide superconductor or a lanthanum-based copper oxide superconductor as a main component.

[0027]

[18] In the method for producing a laminate according to any one of

[15] to

[17] above, in the second step, the second layer may be formed directly on the first layer.

[0028]

[19] The manufacturing method of the laminate according to any one of

[15] to

[18] above may include an alternating lamination step in which the first step and the second step are alternately performed in the lamination step to form a superconducting layer consisting of alternating lamination portions.

[0029]

[20] In the method for manufacturing a laminate described in

[15] to

[19] above, in the formula (2), RE2 is composed of Y, Gd, and X, and X may be 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.

[0030]

[21] In the method for manufacturing a laminate described above in

[15] to

[20] , in the first step, the first layer may be formed on an underlayer whose surface is made of a single crystal.

[0031]

[22] In the manufacturing method of the laminate according to any one of

[15] to

[21] above, the lamination step may be carried out by any one of a pulsed laser deposition method, a molecular beam epitaxy method, and an organometallic compound decomposition method.

[0032]

[23] In the manufacturing method of the laminate according to any one of

[15] to

[22] above, in the laminating step, the first layer and the second layer may be formed by a pulsed laser deposition method using a plurality of targets including a first target for forming the first layer and a second target for forming the second layer.

[0033]

[24] In the method for manufacturing a laminate according to any one of

[15] to

[23] above, the first target may be placed on a rotatable first holder, the second target may be placed on a rotatable second holder, the first holder and the second holder may be provided on a rotatable mounting table, the first step may be performed with the first target rotated, the second step may be performed with the second target rotated, and switching between the first step and the second step may be performed by rotating the mounting table.

[0034] According to the present invention, it is possible to provide a laminate and a method for manufacturing the laminate that can suppress the decrease in the superconducting transition temperature after irradiation for copper oxide superconductors other than HE-REBCO. Also, it is possible to provide a method for manufacturing the laminate that can suppress the decrease in the superconducting transition temperature after irradiation for HE-REBCO. ｃ It was confirmed that the above-mentioned characteristics could be improved by combining with copper oxide superconductors with high critical current density before and after irradiation, such as rare earth copper oxide superconductors.

[0035] [Correction pursuant to Rule 91, 17.06.2025] A partial cross-sectional perspective view of a superconducting wire according to one embodiment of the present invention. A diagram for explaining the configuration of a superconducting laminate provided in the superconducting wire of FIG. 1. A cross-sectional view schematically showing the structure of a laminate, which is the superconducting layer provided in FIG. 2. FIGS. 4(a) and 4(b) are cross-sectional views showing modifications of the superconducting layer of FIG. 3. A cross-sectional view showing another modification of the superconducting layer of FIG. 3. A schematic diagram showing an example of the configuration of a laminate according to one embodiment of the present invention, in which a superconducting layer having alternating laminates of first and second layers is laminated on an underlayer, and an example of the crystalline structure of the superconducting layer. A diagram for explaining a manufacturing method of a laminate according to one embodiment of the present invention, showing the process of manufacturing the laminate by the PLD method. FIG. 8(a) is an electron microscope image of the cross-section of the superconducting laminate of Example 1, and FIG. 8(b) is an electron microscope image of the cross-section of the laminate of Comparative Example 1. FIG. 9(a) is an X-ray diffraction image of the superconducting laminate of Example 1, and FIG. 9(b) is an X-ray diffraction image of the laminate of Comparative Example 1. 11(a) is a graph showing the temperature dependence of the critical current density on the magnetic field before and after ion irradiation for the superconductor laminate of Example 1. FIG. 11(a) is a graph showing the temperature dependence of the critical current density on the magnetic field before and after ion irradiation for the superconductor laminate of Comparative Example 1, and FIG. 11(b) is a graph showing the temperature dependence of the critical current density on the magnetic field before and after ion irradiation for the superconductor laminate of Comparative Example 2. FIG. 12(a) is a graph showing the temperature dependence of the magnetization before and after ion irradiation for the superconductor laminate of Example 1, and FIG. 12(b) is an enlarged view of FIG. 12(a). FIG. 13(a) is a graph showing the temperature dependence of the magnetization before and after ion irradiation for the superconductor laminate of Comparative Example 1, and FIG. 13(b) is an enlarged view of FIG. 13(a). FIG. 14(a) is a graph showing the temperature dependence of the magnetization before and after ion irradiation for the superconductor laminate of Comparative Example 2, and FIG. 14(b) is an enlarged view of FIG. 14(a). 1 is a graph showing the results of irradiation experiments on REBCO and HE-REBCO, showing the critical current density before and after irradiation with 1 MeV He ions (energy equivalent to that of a neutron beam).

[0036] An example of an embodiment of the present invention will be described in detail below with reference to the drawings. The drawings used in the following description may conveniently show enlarged characteristic portions to make the features of the present invention easier to understand, or may show an example of an embodiment. Therefore, the dimensional ratios of each component may differ from the actual ones, or only specific means may be described. The present invention is not limited to these examples, and can be implemented by appropriately modifying and combining the design within the scope of its gist.

[0037] [Superconducting wire] Fig. 1 is a partial cross-sectional perspective view of a superconducting wire according to one embodiment of the present invention. Fig. 2 is a diagram for explaining the configuration of a superconducting laminate provided in the superconducting wire of Fig. 1. For convenience, Fig. 2 shows the ends of each layer shifted. Fig. 3 is a cross-sectional view schematically showing the structure of a laminate, which is a superconducting layer provided in Fig. 2.

[0038] The superconducting wire 10 shown in Fig. 1 includes a laminate 5 and a stabilization layer 6. The stabilization layer 6 extends along the laminate 5 and is provided so as to contact the main surface and side surfaces of the laminate 5. The stabilization layer 6 is formed so as to surround the laminate 5. The stabilization layer 6 functions as a bypass section that diverts an overcurrent that is generated when a superconducting layer included in the laminate 5, the details of which will be described later, transitions to a normal conducting state.

[0039] Examples of the material for the stabilization layer 6 include metals such as copper, copper alloy, aluminum, aluminum alloy, 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 (for example, electrolytic plating). The stabilization layer 6 may be a single layer or multiple layers.

[0040] <Laminate> The laminate 5 shown in FIG. 2 includes a substrate 1, an intermediate layer 2, and a superconducting layer 3. While FIG. 2 illustrates an example in which the intermediate layer 2 and the superconducting layer 3 are formed on one main surface of the substrate 1, this embodiment is not limited to this example, and the intermediate layer 2 and the superconducting layer 3 may be formed on both main surfaces of the substrate 1. A laminate according to one embodiment of the present invention includes at least one first layer 3a containing a copper oxide-based superconductor as a main component and at least one second layer 3b containing a high-entropy superconductor (hereinafter referred to as an HE-superconductor) represented by general formula (2) as a main component. Examples of the copper oxide-based superconductor contained as a main component in the first layer 3a include a REBCO-based superconductor represented by general formula (1), as well as a bismuth-based copper oxide superconductor and a lanthanum-based copper oxide superconductor, which will be described in detail below. First, a configuration in which the copper oxide-based superconductor contained as a main component in the first layer 3a is a REBCO-based superconductor will be described. Furthermore, the first layer 3a and the second layer 3b may be composed of the above-mentioned materials. RE1Ba ２ Cu ３ O ７－ｘ ... (1) RE2Ba ２ Cu ３ O ７－δ... (2) (in formula (1), RE1 is composed of one element selected from a first group consisting of Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium), or two elements selected from a second group consisting of the first group and Sr (strontium), Ba (barium), and Ca (calcium), and 0≦x≦1 is satisfied; In formula (2), RE2 is composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, where 0≦δ≦1. The elements contained in each layer of the superconducting layer 3 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 a scanning electron microscope (SEM), or ICP optical 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 identifying the content ratio of rare earth elements, identification by ICP optical emission spectroscopy is preferred from the viewpoint of accuracy.

[0041] In this embodiment, the main component means a composition whose content in the member is 50% by mass or more, preferably 90% by mass or more, and more preferably 99% by mass or more.

[0042] (Substrate) The substrate 1 is made of, for example, a metal. The substrate 1 is made of, for example, a nickel alloy, stainless steel, an oriented Ni-W alloy in which a texture is introduced into nickel steel, Hastelloy (registered trademark), etc. The thickness of the substrate 1 is, for example, 10 to 500 μm.

[0043] An intermediate layer 2 is preferably provided on the main surface S1 of the substrate 1, but the intermediate layer 2 can be omitted. In the 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. 2, the substrate 1 and the intermediate layer 2 are collectively referred to as the base layer 12.

[0044] (Intermediate Layer) 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. FIG. 3 shows an example in which the intermediate layer 2 includes, in order from the side closest to the substrate 1, a first intermediate layer 2a, a second intermediate layer 2b, and a third intermediate layer 2c. The intermediate layer 2 has, for example, multiple layers, such as a bed layer, an orientation layer, and a cap layer, each with different functions. For example, the surface of the intermediate layer 2 facing the superconducting layer 3 and its vicinity are composed of a single crystal. The intermediate layer 2 may have a configuration other than three layers, such as a single layer. When the intermediate layer 2 is a single layer, any of the materials exemplified below as the first intermediate layer 2a, the second intermediate layer 2b, and the third intermediate layer 2c may be used, and it is preferable that the surface is single crystal.

[0045] The first intermediate layer 2a is, for example, a bed layer. The bed layer serves to reduce the reaction at the interface between the substrate 1 and the superconducting layer 3 and to improve the orientation of the layer formed thereon. Examples of the material for the bed layer include CeO ２ , Er ２ O ３ , Y ２ O ３ , Dy ２ O ３ , Eu ２ O ３ , Ho ２ O ３ , La ２ O ３ etc.

[0046] The second intermediate layer 2b is, for example, an orientation layer. When a cap layer is formed thereon, the orientation layer is provided to control the crystal orientation of the cap layer. The orientation layer may be, 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 , Ho２ O ３ , Nd ２ O ３ The alignment layer is preferably formed by an IBAD (Ion Beam Assisted Deposition) method.

[0047] The third intermediate 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 self-orient in the in-plane direction. For example, the cap layer may be made of CeO ２ , Y ２ O ３ , Al ２ O ３ , Gd ２ O ３ , ZrO ２ , Y.S.Z., Ho ２ O ３ , Nd ２ O ３ , LaMnO ３ It is formed by the following:

[0048] (Superconducting Layer) The superconducting layer 3 is formed on the underlayer 12. The superconducting layer 3 includes at least one first layer 3a and at least one second layer 3b.

[0049] In the superconducting layer 3, the first layer 3a and the second layer 3b are provided, for example, in direct contact with each other or in contact with each other via a thin film, and are preferably provided in direct contact with each other. Fig. 3 shows a configuration in which the first layer 3a and the second layer 3b are provided in direct contact with each other, and the configuration in which the first layer 3a and the second layer 3b are provided in contact with each other via a thin film will be described in detail later.

[0050] The superconducting layer 3 shown in Fig. 3 comprises a first layer 3a and a plurality of second layers 3b sandwiching the first layer 3a from both sides in the stacking direction, and is composed of the first layer 3a and the second layer 3b. In this embodiment, such a structure in which the first layer 3a is sandwiched between the second layers 3b from both sides in the stacking direction is referred to as a sandwich structure. The superconducting layer 3 shown in Fig. 3 is composed of an alternating laminated portion in which the first layers 3a and the second layers 3b are alternately stacked. Furthermore, the superconducting layer 3 shown in Fig. 3 has the second layers 3b formed as the outermost layers on both sides in the stacking direction.

[0051] As will be described in detail later, in the superconducting layer 3 of the laminate according to one embodiment of the present invention, the REBCO-based superconductor represented by formula (1) contained as a main component in the first layer 3a has a critical current density J ｃ While the superconducting transition temperature T ｃ The HE-superconductor contained as a main component in the second layer 3b and expressed by formula (2) has a low superconducting transition temperature T ｃ While the resistance to ion irradiation is high, the critical current density J ｃ is not higher than that of the REBCO-based superconductor contained as the main component in the first layer 3a.

[0052] In the superconducting layer 3 provided in the laminate according to this embodiment, oxygen atoms that are blown off from the first layer 3a when irradiated with ions are trapped in the second layer 3b and returned to the first layer 3a. Therefore, the ion irradiation resistance of the copper oxide superconductor of the first layer 3a is improved, and the superconducting transition temperature T ｃ This effect is believed to be particularly significant in a configuration in which an extremely thin film is provided between the first layer 3a and the second layer 3b, as described below, or in a configuration in which the first layer 3a contains another copper oxide-based superconductor. Furthermore, in a configuration in which the first layer 3a is in contact with the second layer 3b, as shown in FIG. 3, particularly in a configuration having a sandwich structure sandwiched between the second layers 3b on both sides in the stacking direction, or in a configuration in which the superconducting layer 3 has one or more sandwich structures, the REBCO crystal structure is maintained in the stacking direction, and atoms in the first layer 3a are trapped in the second layer 3b regardless of the direction in which ions are irradiated in the stacking direction. Thus, it is believed that the superconducting layer 3 has at least one sandwich structure, and more preferably has multiple sandwich structures. In this embodiment, the critical current density J after irradiation is significantly higher than that of an HE-superconductor. ｃ The first layer 3a is made of a REBCO-based superconductor having excellent properties, and has a high J ｃ and T ｃ It is possible to achieve both.

[0053] First Layer 3a As described above, the first layer 3a contains, for example, a REBCO-based superconductor represented by general formula (1) as a main component. In formula (1), RE1 is one selected from the following options, which is important for determining the critical current density J ｃ In formula (1), x represents the amount of oxygen deficiency. x is in the range of 0≦x≦1, and preferably in the range of 0≦x≦0.6. ２ Cu ３ O ７－ｘ ... (1) (In formula (1), RE1 is composed of one element selected from a first group consisting of Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or two elements selected from a second group selected from the first group and a second group including Sr, Ba, and Ca, and satisfies 0≦x≦1.) Furthermore, in formula (1), RE1 is preferably one or two elements selected from the group consisting of Y, La, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. This is because, compared with Sr, Ba, and Ca, other rare earth elements from the above group are more likely to exhibit superconductivity when located at the RE site of REBCO, and the laminate according to this embodiment may be used in a superconducting magnet for a nuclear fusion reactor. However, since superconductivity can be exhibited even when Sr, Ba, and Ca are solid-solved with other rare earth elements, when two rare earth elements are contained at the RE1 site, a configuration containing an element selected from the first group and an element selected from the second group is also possible. In this case, it is preferable that the ratio of the element selected from the second group to the sum of the elements in the first group is 80 at. % or less and 50 at. % or less, i.e., the content is lower than that of the element selected from the first group.

[0054] Second layer 3b As described above, the second layer 3b contains, as a main component, a HE-REBCO superconductor represented by general formula (2). In formula (2), 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. RE2Ba ２ Cu ３ O ７－δ... (2) (In formula (2), RE2 is composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and 0≦δ≦1).

[0055] In formula (2), RE2 is composed of Y, Gd, and X, and X may be composed of one or more elements selected from the group consisting of Sr, Ba, Ca, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Furthermore, since the laminate according to this embodiment may be used in a superconducting magnet for a nuclear fusion reactor, RE2 in formula (2) is preferably composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Compared to other elements in the above group, Sr, Ba, Ca, Ce, and Pr are considered to be materials that are less likely to exhibit superconductivity by themselves, and the total content of these elements in the HE-REBCO superconductor is preferably 80 at. % or less, and more preferably 50 at. % or less. % or less is more preferable.

[0056] For example, in the HE-REBCO superconductor contained as a main component in the second layer 3b, RE2 may have a structure represented by general formula (3). ａ Gd ｂ X ｃ ... (3) (In formula (3), X is the rare earth element, and 0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9)

[0057] The HE-REBCO superconductor contained as the main component in the second layer 3b has a mixing entropy ΔS of the atomic site of RE2, which is a rare earth element. ｍｉｘ is 1.1R or more, preferably 1.39R or more, and more preferably 1.5R or more for an HE-superconductor. Here, R represents the gas constant. Mixing entropy ΔS ｍｉｘ REBCO superconductors with RE2 of 1.1R or more are composed of three or more rare earth elements. ｍｉｘA HE-REBCO superconductor having an RE2 of 1.39R or more is, for example, composed of four or more rare earth elements.

[0058] In the case of an HE-superconductor, for example, RE2 is composed of five or more kinds of rare earth elements. That is, five or more kinds of rare earth elements are present at the atomic site of the rare earth element RE2. Examples of such superconductors 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 kinds selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb, Er, Tm, and Lu in addition to the above rare earth elements. In the results of FIG. 15, such an HE-superconductor showed no difference from those containing three or more kinds of rare earth elements and those containing four or more kinds of rare earth elements, but had high ion irradiation resistance and a transition temperature T ｃ and critical current density J ｃ The inventors' research has revealed that the critical current density J tends to be maintained. ｃ is the critical current value per unit area of ​​the superconductor.

[0059] Here, the superconducting layer 3 provided in the laminate 5 is not limited to the configuration shown in Fig. 3 and may have other configurations. For example, it may have the configurations shown in Fig. 4 and Fig. 5. Fig. 4(a) and Fig. 4(b) are cross-sectional views showing modified examples of the superconducting layer of Fig. 3, and Fig. 5 is a cross-sectional view showing another modified example of the superconducting layer of Fig. 3.

[0060] The superconducting layer 3A shown in FIG. 4( a) differs from the superconducting layer 3 in that it includes a plurality of first layers 3 a and second layers 3 b. The superconducting layer 3A has a two-sandwich structure. Thus, the number of layers constituting the superconducting layer is not limited to the number shown in FIG. 3. The number of first layers 3 a and second layers 3 b constituting the superconducting layer is preferably two or more, and more preferably three or more. Furthermore, the compositions of the plurality of first layers 3 a included in the superconducting layer 3A may be the same or different, and for example, the types of rare earth elements contained therein may be different. Similarly, the compositions of the plurality of second layers 3 b included in the superconducting layer 3A may be the same or different.

[0061] The superconducting layer 3B shown in FIG. 4(b) differs from the superconducting layer 3 in that the number of first layers 3a is equal to or greater than the number of second layers 3b and that the first layers 3a are located at the outermost layers in the stacking direction. FIG. 4(b) shows an example in which the number of first layers 3a and second layers 3b is the same. As shown in FIG. 4(b), the number of first layers 3a may be equal to or greater than the number of second layers 3b, and the outermost layers in the stacking direction may be the first layers 3a. In the example shown in FIG. 4(b), one of the two outermost layers is the first layer 3a, but both may be second layers 3b. Even with this configuration, the movement of atoms in the first layer 3a due to ions irradiated from the outside in the stacking direction is trapped in the second layer 3b, maintaining the structure of the first layer 3a and maintaining a high critical current density J even after ion irradiation. ｃ In such a configuration, it is preferable to include first layers 3a sandwiched between second layers 3b on both sides in the stacking direction, in addition to the first layer 3a provided as the outermost layer.

[0062] The superconducting layer 3C shown in FIG. 5 has a thin film 3c disposed between a first layer 3a and a second layer 3b. The thin film 3c has a thickness of 200 nm or less, preferably 10 nm or less. The thickness of the thin film 3c is equal to or less than the thickness of the smaller of the adjacent first layer 3a and second layer 3b, preferably 0.5 times or less. The positions and number of thin films 3c formed in the superconducting layer 3C are not limited to the example shown in FIG. 5 and can be selected arbitrarily. The second layer 3b is preferably located at the outermost surface farthest from the underlayer 12. It is also preferable that the second layer 3b is the layer closest to the underlayer 12.

[0063] The thin film 3c is a layer containing, as a main component, a metal, an alloy containing one or more metal elements, or a superconducting material. Examples of metals include Ag, Cu, and Au. Examples of alloys include oxides such as CeO2 and fluorides such as BaF2. Examples of superconducting materials include a REBCO-based superconductor represented by general formula (1) and an HE-REBCO superconductor represented by general formula (2). As described above, the thin film is a layer containing, as a main component, a metal, an alloy, or a superconducting material. When the main component of the thin film 3c is a REBCO-based superconductor, the rare earth element RE contained therein can be any of the rare earth elements that can be contained in the first layer 3a and the second layer 3b, and the number of elements can be any. In this way, a configuration in which a layer containing one or two types of REBCO as a main component, or a layer containing three or more types of REBCO as a main component, is provided successively may be used.

[0064] The thickness and thickness ratio of the first layer 3a and the second layer 3b can be set arbitrarily depending on the desired characteristics. The average thickness of each layer of the first layer 3a can be calculated by observing the cross section using an electron microscope, measuring the thickness at any three or more points, and averaging the measured values. The average thickness of the first layer 3a in the entire superconducting layer 3 can be determined as the arithmetic mean of the above average values. The average thickness of each layer of the second layer 3b and the average thickness of the second layer 3b in the entire superconducting layer 3 can be measured and calculated using the same methods as those for the first layer 3a.

[0065] The thickness of the first layer 3a can be, for example, 10 nm to 10 μm, and preferably 100 nm to 500 nm. The thickness of the second layer 3b can be, for example, 10 nm to 10 μm, and preferably 100 nm to 500 nm. The thinner the first layer 3a and the second layer 3b, the higher the proportion of the interface between the first layer 3a and the second layer 3b in the entire superconducting layer 3, and it is thought that this can exert the effect of trapping atoms when ions are irradiated, so it is preferable that the upper limit is as described above.

[0066] The ratio of the thickness of the first layer 3a to the total thickness of the superconducting layer 3, i.e., the ratio of the thickness of the first layer 3a to the sum of the thicknesses of the first layer 3a and the second layer 3b, can be, for example, 10% to 90% or may be 25% to 40%. In an example, a superconducting layer with a thickness ratio of 33% was confirmed to achieve both a high critical current density and high radiation resistance. Therefore, a configuration in which the thickness ratio of the first layer 3a to the second layer 3b is approximately 1:2 is expected to be desirable for achieving both of these effects. From the viewpoint of increasing the critical current density, the ratio is preferably 30% to 90% and from the viewpoint of increasing the radiation resistance, and is preferably 10% to 40%.

[0067] Thus, one embodiment of the present invention provides a method for determining the superconducting transition temperature T c High critical current density J c By alternately stacking conventional REBCO with T c and J c The present invention relates to improving the radiation resistance against both of the above.

[0068] As will be described later, one embodiment of the present invention proposes a multilayer film (laminate) in which multiple targets of conventional REBCO and HE-REBCO are alternately stacked using a film formation technique such as PLD (Fig. 6). As a film formation method, in addition to PLD, film formation methods used for REBCO film formation, such as molecular beam epitaxy (MBE), sputtering, evaporation, chemical vapor deposition (CVD), and metal organic deposition (MOD), can also be applied.

[0069] The second layer 3b, which can be said to be a protective film layer of the first layer 3a, is preferably made of REBCO containing RE elements (three or more selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu). More preferably, after irradiation, T c HE-REBCO, which exhibits minimal degradation, is used as the second layer 3b. An example of the superconducting wire stack structure is shown in Figure 3: HE-REBCO layer (second layer 3b) / REBCO layer (first layer 3a) / HE-REBCO layer (second layer 3b) / buffer layer (undersubstrate) (intermediate layer 2) / metal tape (substrate 1). The following undersubstrates, which are commonly used for REBCO superconductors, are used. Typical undersubstrates include SrTiO3, MgO, KTaO, DyScO3, LaGaO3, PrGaO3, NdGaO3, LaAlO3, YAlO3, Sr2AlTaO6, LSAT, LaSrGaO4, LaSrAlO4, NdCaAlO4, MgAl2O4, Si, YSZ, CeO2, and Al2O3. Hastelloy (registered trademark) and Ni-W alloys can also be used for the metal tape.

[0070] FIG. 6 shows a schematic diagram of a superconducting layer including a first layer 3a containing REBCO (conventional REBCO) as a main component and a second layer 3b containing HE-REBCO as a main component. c The second layer 3b, which is mainly composed of HE-REBCO, which has little deterioration, functions as a protective film against irradiation. c The conventional REBCO layer with high T c and J c Furthermore, the large disorder, distortion, and stacking faults in the HE-REBCO layer are expected to not only improve the radiation resistance but also act as flux pinning centers, which can pin magnetic fluxes. c2 and J c It is expected to lead to improvements.

[0071] (Modifications) In the above embodiment, the first layer 3 a includes a REBCO-based superconductor as a main component, but the present invention is not limited to the above configuration, and other copper oxide superconductors can be used. For example, the first layer 3 a may include a bismuth-based copper oxide superconductor or a lanthanum-based copper oxide superconductor as a main component, or may be composed of these copper oxide superconductors.

[0072] Bismuth-based copper oxide superconductors include Bi ２ Sr ２ CuO ７－ｄ (Bi2201), Bi ２ Sr ２ CaCu ２ O ９－ｄ (Bi2212) and Bi ２ Sr ２ Ca ２ Cu ３ O １１－ｄ (Bi2223). In these formulas, d represents the amount of oxygen vacancy, and for example, 0≦d≦1. Note that the bismuth-based copper oxide superconductor includes derivative substances. That is, the bismuth-based copper oxide superconductor may have a structure in which part of the Bi in the composition represented by the above chemical formula is replaced with Pb. Here, the content of Pb is, for example, equal to or less than the content of Bi.

[0073] Lanthanum-based copper oxide superconductors include La ２ CuO ４ and its derivatives. ２ CuO ４ The derivative material of La is, for example, a structure in which La is replaced by a rare earth element, and La ２ CuO ４ The composition constituting such a copper oxide-based superconductor can be identified by elemental analysis similar to that in the above embodiment, and the crystal structure can be identified by XRD.

[0074] In one embodiment of the present invention, a multilayer copper oxide high-temperature superconductor film is fabricated by pulsed laser deposition (PLD) using multiple deposition targets (Figure 7). cThe HE-REBCO superconductor, which has high resistance to high-energy ion irradiation, is used as a protective film, and an alternating laminated film is fabricated with copper oxide superconductors other than HE-REBCO superconductors, such as ordinary REBCO superconductors (Fig. 6). This allows for the high critical current density J of ordinary REBCO to be achieved. c This is expected to realize a high magnetic field pinning effect due to HE-REBCO and improve the radiation tolerance of the superconducting properties against ion irradiation.

[0075] FIG. 7 shows an example of the configuration of a superconducting wire manufacturing method described later, illustrating the PLD method using a rotatable multi-target system having multiple rotatable holders. The multiple holders include a first holder H1 for accommodating a first target T1 and a second holder H2 for accommodating a second target T2, which are alternately arranged on a mounting table 20. The first target T1 is a target for forming a first layer 3a containing, as a main component, a copper oxide-based superconductor other than an HE-superconductor. The first target T1 is composed of, for example, a REBCO-based superconductor represented by general formula (1), a bismuth-based copper oxide superconductor, or a lanthanum-based copper oxide superconductor. The second target T2 is a target for forming a second layer 3b containing, as a main component, an HE-REBCO-based superconductor. Each target corresponds to a raw material for forming each layer and has the same composition as the corresponding layer to be formed. An alternating layered film can be formed on an underlayer by irradiating each target with a pulsed laser. Switching between the first process using the first target T1 and the second process using the second target T2 can be performed by rotating the mounting table 20.

[0076] [Method for Manufacturing Superconducting Wire] A method for manufacturing the superconducting wire according to the above embodiment will be described below. The method for manufacturing the superconducting wire according to one embodiment of the present invention includes a step of manufacturing the laminate 5 and a step of forming a stabilization layer 6 on the outer periphery of the laminate.

[0077] <Step of manufacturing laminate> In the method of manufacturing a superconducting wire according to this embodiment, the step of manufacturing the laminate 5 includes, for example, a first step of forming a first layer 3a represented by general formula (1) and a second step of forming a second layer 3b represented by general formula (2) on the first layer 3a directly or via a thin film 3c. In this embodiment, the first step and the second step may be collectively referred to as a vapor deposition step. ２ Cu ３ O ７－ｘ ... (1) RE2Ba ２ Cu ３ O ７－δ ... (2) (In formulas (1) and (2), RE1, RE2, x, and δ are the same as in the above embodiment.)

[0078] The vapor deposition process can be performed by, for example, pulsed laser deposition (PLD), molecular beam epitaxy (MBE), metal organic decomposition (MOD), sputtering, evaporation, or chemical vapor deposition (CVD), and is preferably performed by any one of PLD, MBE, and MOD. Hereinafter, with reference to FIG. 7 , an example of a method for manufacturing a laminate according to this embodiment will be described, taking as an example a configuration in which a superconducting layer including a first layer 3 a and a second layer 3 b is formed by PLD. FIG. 7 is a diagram for explaining a method for manufacturing a laminate according to one embodiment of the present invention, and is a schematic diagram showing how a laminate is manufactured by PLD.

[0079] (Preparation Step) First, an underlayer 12 having a surface made of a single crystal is prepared. The underlayer 12 is made of, for example, only the substrate 1, or the substrate 1 and an intermediate layer 2. The intermediate layer 2 can be formed on the substrate 1 by, for example, physical vapor deposition such as PLD, or vapor deposition such as chemical vapor deposition, 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. For example, the preparation step is performed a predetermined number of times depending on the number of intermediate layers 2 to be formed.

[0080] (Target Preparation Step) Next, a target to be used in the vapor deposition step is prepared. Since vapor deposition is performed layer by layer, when preparing a laminate including a superconducting layer 3 having a first layer 3a and a second layer 3b, a target for the first layer 3a (first target T1) and a target for the second layer 3b (second target T2) are prepared. The target has a composition corresponding to the composition of the desired superconductor. The composition of the target is, for example, the same as the composition of the superconductor to be prepared. The target is, for example, a polycrystalline body having the same composition as the superconductor to be prepared. That is, a target having a composition similar to that represented by formulas (1) and (2) of the superconductor according to the above embodiment can be used, and both δ and x can be the same as those in the above embodiment. In this embodiment, the step of preparing a target for the first layer 3a may be referred to as the first target preparation step, and the step of preparing a target for the second layer 3b may be referred to as the second target preparation step.

[0081] When the first layers 3a included in the superconducting layers are different for each layer, a first target T1 for the first layers 3a corresponding to the composition of each layer is prepared in the first target preparation step. Similarly, when the second layers 3b included in the superconducting layers are different for each layer, a second target T2 for the second layers 3b corresponding to the composition of each layer is prepared in the second target preparation step.

[0082] For example, the target is prepared by mixing and firing predetermined metal elemental substances or oxides in a ratio similar to the ratio of the metal elements in formulas (1) and (2). That is, the target is prepared by sintering powder of elements or oxides containing a predetermined rare earth element, Ba, Cu, and a Group 2 element. The firing to prepare the target may be performed once or in multiple stages.

[0083] (Vapor Deposition Process) Next, a superconducting layer including a first layer 3a and a second layer 3b is formed on the underlayer 12. As described above, the vapor deposition process can be performed by a PLD method using, for example, the PLD apparatus shown in FIG. 7. The PLD apparatus includes, for example, a mounting table 20 provided with a first holder H1 for mounting a first target T1 and a second holder H2 for mounting a second target T2. The mounting table 20 is configured to be rotatable. In the mounting table 20, the first holder H1 and the second holder H2 are each rotatable on the mounting table 20, for example. The mounting table 20 may rotate only in the direction shown in the figure, but is preferably configured to rotate in the opposite direction as well. In other words, the PLD apparatus can be considered a so-called revolution-type apparatus. While FIG. 7 shows multiple first targets T1 and multiple second targets T2, the number of targets may be any number greater than or equal to one. The mounting table 20 may also be configured to include a holder on which a target having the same composition as the thin film 3c is mounted. When forming the thin film 3c, the target may be irradiated with a laser to form the thin film 3c at a predetermined position on the underlayer 12.

[0084] The atmosphere in the chamber may be, for example, an air atmosphere. The deposition process is performed, for example, by adjusting the chamber to have a low oxygen partial pressure and heating the underlayer 12.

[0085] 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.

[0086] The PLD device irradiates a target with laser light L and focuses the laser light L on the surface of the target using a focusing lens or the like. A pulsed laser is used as the laser light L irradiated onto the target. The laser density is, for example, 0.1 J / cm. ２ 5J / cm or more ２ Do the following:

[0087] By focusing a laser on the surface of the target, constituent particles of the target are knocked out or evaporated, generating a plume P. The constituent particles of the target contained in the plume P are deposited on the surface of the base layer 12, thereby forming a thin film composed of the constituent particles of the target on the surface of the base layer 12. Therefore, the composition of the thin film formed on the base layer 12 can be changed by changing the composition of the target.

[0088] First Step In the first step, a first layer 3a is formed on an underlayer having a surface made of a single crystal. In the first step, for example, a laser is irradiated onto a first target T1 provided opposite the underlayer 12, to form the first layer 3a on the underlayer 12. Here, "on the underlayer 12" is not limited to a configuration in contact with the underlayer 12, but means being located in the stacking direction relative to the underlayer 12.

[0089] In the second step, a second layer 3 b is formed on the underlayer 12 having a single-crystal surface. In the second step, for example, a laser is irradiated onto a first target T1 provided opposite the underlayer 12, thereby forming a first layer 3 a on the underlayer 12.

[0090] The order of the first and second steps in the vapor deposition process is performed in accordance with the stacking order of the first layer 3 a and the second layer 3 b in the superconducting layer formed on the underlayer 12. Switching between the first and second steps is performed, for example, by rotating the mounting table 20. The vapor deposition process preferably includes a step of successively performing the first and second steps to form a stack including a portion where the first layer 3 a and the second layer 3 b contact each other, and more preferably includes a step of successively performing the second step, the first step, and the second step to form a stack having a sandwiched structure in which the first layer 3 a is sandwiched between the second layers 3 b in the stacking direction. For example, in this embodiment, it is preferable to include an alternating stacking step of alternately performing the first and second steps to form a superconducting layer consisting of alternating stacked portions.

[0091] The first and second steps may be performed with or without the first and second targets T1 and T2 being rotated by the rotation of the first and second holders H1 and H2, but are preferably performed with the targets rotated. Rotation of the targets slightly shifts the laser irradiation position on the targets, which is thought to lead to an increase in the entropy of the rare earth elements and a more uniform film thickness.

[0092] In this embodiment, the second layer 3b, which is a protective film for improving radiation resistance, is made of a high-entropy REBCO superconductor containing three or more kinds of RE, such as REBaCuO 7-x It differs from the prior art in that it is alternately laminated with superconductors, and this configuration provides high resistance to ion irradiation.

[0093] In this embodiment, by alternately laminating an HE-REBCO superconductor having high radiation resistance with a normal REBCO superconductor, not only can the upper critical magnetic field c2 be improved by the magnetic field pinning effect, but also the radiation resistance of the superconducting properties against high-energy ion irradiation such as neutron beams can be expected to be improved. Note that, in the above example, a configuration in which a REBCO-based superconductor represented by general formula (1) is formed as the first layer 3a in the first step is exemplified, but a configuration in which a copper oxide-based superconductor such as a bismuth-based copper oxide superconductor, a lanthanum-based copper oxide superconductor, or a derivative thereof is formed may also be used. These copper oxide superconductors can also be formed by changing the material and using the same method.

[0094] Thus, according to this embodiment, HE-REBa2Cu3O 7-δ By alternately laminating the protective film and the copper oxide superconductor, the superconducting transition temperature T after irradiation with ions, neutrons, etc. is lower than when using a copper oxide superconductor. ｃ In particular, by using a REBCO-based superconductor represented by the general formula (1) as the copper oxide-based superconductor, a high critical current density is exhibited before and after ion irradiation, compared with the case where only HE-REBCO is used, and thus the superconducting transition temperature T c Ion irradiation resistance and high critical current density J c It is also possible to achieve both of these.

[0095] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various omissions, substitutions, modifications, and alterations are possible within the scope of the gist of the present invention as set forth in the claims. These embodiments and their modifications are included in the scope of the invention as set forth in the claims and their equivalents, as well as in the scope and gist of the invention.

[0096] 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. Furthermore, the features described in different embodiments may be combined in practice.

[0097] Throughout this disclosure, singular terms should be understood to include the plural concept unless otherwise specified. Thus, singular articles (e.g., "a," "an," "the," etc. in English) should be understood to include the plural concept unless otherwise specified.

[0098] [Example 1] Strontium titanate (SrTiO ３ A laminate was produced by forming a layer composed of REBCO(RE5) having five rare earth elements at the RE2 site in general formula (2) as a second layer on a single crystal of REBCO(RE5), a layer composed of REBCO(RE1) having one rare earth element at the RE1 site in general formula (1) as a first layer, and a layer composed of RE5.

[0099] First, the underlayer was prepared. ３ A single crystal substrate was prepared, followed by preparation of a first target and a second target.

[0100] For the first target, Y2O3 (purity 99.9%), BaCO3 (purity 98%), and CuO (purity 99.9%) were weighed out in a ratio of 1:2:3 and mixed in a mortar to prepare a mixed powder. For the second target, Y2O3 (purity 99.9%), Nd2O3 (purity 99.9%), Sm2O3 (purity 99.9%), Eu2O3 (purity 99.9%), Gd2O3 (purity 99.9%), BaCO3 (purity 98%), and CuO (purity 99.9%) were weighed out in a ratio of 28 / 100:16 / 100:18 / 100:18 / 100:20 / 100:2:3 and mixed in a mortar to prepare a mixed powder.

[0101] Next, the mixed powder for the first target and the mixed powder for the second target were transferred to separate crucibles and heated at 930°C for 20 hours as a primary firing (calcination), followed by furnace cooling to room temperature. Next, the pre-fired mixed powder was mixed in an agate mortar and pressure-molded into a pellet. Next, as a secondary firing, the pellet-shaped mixed powder was heated at 930°C for 8 hours, then at 300°C for 18 hours, followed by furnace cooling to room temperature, to produce the first target and the second target.

[0102] Next, the first target and the second target were placed in a first holder H1 and a second holder H2 in a chamber, respectively, in a PLD apparatus such as that shown in Figure 7, with the underlayer and the target facing each other. Next, a rotary pump was used to evacuate the chamber until the oxygen partial pressure 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 15 minutes to stabilize.

[0103] To remove impurities from the target surface, the shutter was closed and the target was rotated and revolved to perform pre-ablation. Then, in the second step, the shutter was opened and a laser energy density of 1.3 J / cm was applied. ２ The second target T2 was irradiated with a laser, and film formation was performed so that a second layer was formed in contact with the underlayer 12. During film formation, oxygen was introduced into the chamber while adjusting the exhaust rate with a valve, and the oxygen partial pressure in the chamber was kept at 2×10 １The temperature in the chamber (substrate temperature) during the deposition process was adjusted to be maintained at 720°C. 0.28 Nd 0.16 Sm 0.18 EU 0.18 Gd 0.20 ) Ba2Cu3O 7-δ A second layer made of a superconductor represented by the formula:

[0104] Next, the mounting table was rotated, and after pre-ablation was performed in the same manner as above, the first target T1 was irradiated with a laser to form a first layer in contact with the second layer. 7-x The conditions for depositing the first layer were the same as those for depositing the second layer, except that target T2 was changed to target T1.

[0105] Next, the mounting table was rotated, and pre-ablation was performed in the same manner as above. Then, the second target T2 was irradiated with a laser to form a second layer in contact with the first layer. After that, 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 9x10 ４ The chamber was heated, and the target was switched by rotating the mounting table to form the second layer, the first layer, and the second layer in this order, followed by furnace cooling to produce a laminate in which the second layer (RE5) / first layer (RE1) / second layer (RE5) were formed in this order on the base layer.

[0106] Comparative Example 1 Using the same underlayer as in Example 1 and a first target prepared by the same method as in Example 1, a film of composition formula YBa2Cu3O was deposited on the underlayer by PLD. 7-x In Comparative Example 1, the film formation time was changed from the first step of Example 1 in order to make the thickness of the superconducting layer closer to the thickness of the superconducting layer having the sandwiched structure of Example 1.

[0107] Comparative Example 2 Using the same underlayer as in Example 1 and a second target prepared in the same manner as in Example 1, a compound having the composition formula (Y 0.28 Nd 0.16 Sm 0.18 EU 0.18 Gd 0.20 ) Ba2Cu3O 7-δ In Comparative Example 2, the film formation time was changed from the second step in Example 1 in order to make the thickness of the superconducting layer closer to the thickness of the superconducting layer having the sandwiched structure in Example 1.

[0108] (Cross-section observation) The cross sections of the laminates of Example 1 and Comparative Example 1 were observed using a scanning electron microscope. FIG. 8(a) is an SEM image of the cross section of the superconducting laminate of Example 1, and FIG. 8(b) is an SEM image of the cross section of the laminate of Comparative Example 1. In addition, the boundaries of each layer were identified from the brightness of the scanning electron microscope, and the thickness of each layer was measured. As a result, in Example 1, the second layer, first layer, and second layer formed in this order from the underlayer side were all 90 nm thick, while the thickness of the superconducting layer in Comparative Example 1 was 150 nm, and the thickness of the superconducting layer in Comparative Example 2 was 240 nm.

[0109] (Irradiation Resistance Test) The superconducting laminates of Example 1, Comparative Example 1, and Comparative Example 2 were irradiated with He ions having the same energy (1 MeV) as that of neutron rays. Below, each measurement shows the results of both before and after ion irradiation for the same sample.

[0110] (X-ray Diffraction) X-ray diffraction was performed on the superconducting laminates of Example 1 and Comparative Example 1. Fig. 9(a) is an X-ray diffraction image of the superconducting laminate of Example 1, and Fig. 9(b) is an X-ray diffraction image of the laminate of Comparative Example 1. By comparing the results before and after the ion irradiation test in Fig. 9(a) and Fig. 9(b), it was confirmed that there was no change in the crystal structure due to the ion irradiation.

[0111] (Critical Current Density Test) The critical current density J was measured for each of the superconducting laminates of Example 1, Comparative Example 1, and Comparative Example 2 before and after ion irradiation using a magnetic property measurement system (MPMS-3). ｃ The critical current density J ｃThe measurements were carried out for each sample under the conditions of 0 to 7T in temperature environments of 4.2K, 20K, 50K, and 77.3K.

[0112] 10, 11(a), and 11(b) are graphs showing the magnetic field dependence of the critical current density at each temperature before and after ion irradiation of the superconductor laminates of Example 1, Comparative Example 1, and Comparative Example 2. First, as shown in Fig. 11(b), Comparative Example 2, which has a superconducting layer made of HE-REBCO, has a low critical current density, and in an environment of 20 K before ion irradiation, the critical current density drops significantly in an external magnetic field of 5.0 T or more, and in an environment of 50 K before ion irradiation, the critical current density drops significantly with a slight external magnetic field, superconductivity is not confirmed at temperatures higher than 50 K, and superconductivity cannot be maintained after the ion irradiation test.

[0113] 11(a), it was confirmed that Comparative Example 1, in which YBCO was formed on the underlayer, exhibited a higher critical current density than Comparative Example 2, in which HE-REBCO was formed, before ion irradiation in all temperature ranges. Furthermore, it was confirmed that the critical current density significantly decreased after the ion irradiation test, as in Comparative Example 1.

[0114] In contrast, Example 1, which has a sandwich structure in which HE-REBCO is formed on both main surfaces of YBCO, was confirmed to exhibit a critical current density that was significantly higher than that of Comparative Example 2 in all temperature ranges before ion irradiation and was equal to or higher than that of Comparative Example 1. Comparing Comparative Example 1 and Comparative Example 2, it was predicted that Example 1 would have a lower critical current density than Comparative Example 1 due to the inclusion of multiple rare earth elements at the RE site, but such an increase in critical current density was unexpected. Furthermore, after ion irradiation, although the critical current density was lower than that before ion irradiation, it exhibited a higher critical current density than Comparative Example 1 in all temperature ranges, and maintained superconductivity even when a magnetic field of 7.0 T was applied in all temperature ranges below 50 K. In other words, it can be said that the superconducting laminate of this example achieves both ion irradiation resistance and high critical current density.

[0115] (Evaluation of Radiation Resistance in Relation to Superconducting Transition Temperature) The temperature dependence of the magnetization of the superconductor was measured for the superconducting laminates of Example 1, Comparative Example 1, and Comparative Example 2 before and after ion irradiation using a magnetic property measurement system (MPMS-3). ｃ is the temperature at which the magnetization begins to drop during zero field cooling (ZFC).

[0116] [Correction based on Rule 91 17.06.2025] Figure 12(a) is a graph of the temperature dependence of magnetization before and after ion irradiation of the superconducting laminate of Example 1, and Figure 12(b) is an enlarged view of Figure 12(a). Figure 13(a) is a graph of the temperature dependence of magnetization before and after ion irradiation of the superconducting laminate of Comparative Example 1, and Figure 13(b) is an enlarged view of Figure 13(a). Figure 14(a) is a graph of the temperature dependence of magnetization before and after ion irradiation of the superconducting laminate of Comparative Example 2, and Figure 14(b) is an enlarged view of Figure 14(a). From the measurement results of each sample, the superconducting transition temperature T ｃ are summarized in Table 1.

[0117]

[0118] As shown in Table 1, in Comparative Example 1 in which a YBCO superconducting layer was formed and in Comparative Example 2 in which an HE-REBCO superconducting layer was formed, the superconducting transition temperature changed significantly before and after irradiation. On the other hand, in Example 1 having a sandwich structure in which the first layer is sandwiched between the second layers, the superconducting transition temperature was high both before and after ion irradiation, and it can be said that the irradiation resistance was improved.

[0119] In Example 1, as shown in Figure 12(b), two stages of transition were observed: one with a slight change in transition temperature compared to before irradiation, and the other with a large change in transition temperature. This is thought to be due to the presence of two layers with different compositions, the first layer 3a and the second layer 3b. The table shows the transitions with a slight change in transition temperature, but the transition temperatures with a large change in transition temperature are the same as those of Comparative Example 1, and it can be said that the irradiation resistance is higher than that of REBCO.

[0120] The present invention improves the radiation resistance of superconducting materials, contributing to the extension of the life of fusion reactors.

[0121] REFERENCE SIGNS LIST 1 substrate 2 intermediate layer 2a first intermediate layer 2b second intermediate layer 2c third intermediate layer 3, 3A, 3B, 3C superconducting layer 3a first layer 3b second layer 3c thin film 5 laminate 6 stabilization layer 10 superconducting wire 12 base layer 20 mounting table H1 first holder H2 second holder S1 main surface S2 surface T1 first target T2 second target

Claims

1. A laminate RE2Ba comprising at least one first layer containing a copper oxide superconductor as a main component and at least one second layer containing a high-entropy superconductor represented by general formula (2) as a main component. ２ Cu ３ O ７－δ ... (2) (In formula (2), RE2 is composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and 0≦δ≦1).

2. The laminate according to claim 1, wherein the first layer contains a rare earth copper oxide superconductor represented by general formula (1) as a main component. ２ Cu ３ O ７－ｘ ... (1) (In formula (1), RE1 is composed of one element selected from a first group consisting of Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or two elements selected from a second group consisting of an element of the first group and Sr, Ba, and Ca, and satisfies 0≦x≦1.) 3. The laminate according to claim 1, wherein the first layer contains a bismuth-based copper oxide superconductor or a lanthanum-based copper oxide superconductor as a main component.

4. The laminate according to claim 1, wherein the first layer and the second layer are provided in direct contact with each other or in contact with each other via a thin film.

5. The laminate according to claim 1, comprising a plurality of said second layers, at least part of which has a sandwiched structure in which said first layer is sandwiched between said second layers on both sides in the stacking direction.

6. The laminate according to claim 1, comprising a plurality of said first layers, a plurality of said second layers, and a superconducting layer consisting of an alternating laminate portion in which said first layers and said second layers are alternately laminated either directly or via a thin film.

7. The laminate of claim 1, consisting of said first layer and said second layer.

8. The laminate according to claim 1, wherein in the above formula (2), RE2 is composed of Y, Gd, and X, and X is composed of one or more elements selected from the group consisting of Sr, Ba, Ca, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

9. In the above formula (2), RE2 is composed of five or more kinds of rare earth elements, and the mixing entropy ΔS of the RE2 site of the second layer ｍｉｘ The laminate according to claim 1, wherein R is 1.39R or more.

10. The laminate according to claim 1, wherein in the formula (2), RE2 is represented by the general formula (3). ａ Gd ｂ X ｃ ... (3) (0.05≦a≦0.9, 0.05≦b≦0.9, 0.05≦c≦0.9) 11. The laminate according to claim 5, comprising: an underlayer having a surface made of a single crystal; and a superconducting layer including the sandwich structure formed on the underlayer, wherein the second layer is located on the outermost surface of the superconducting layer, the outermost surface being the furthest from the underlayer.

12. The outermost surface of the underlayer is SrTiO ３ The laminate according to claim 11, which is composed of a single crystal.

13. A method for manufacturing a laminate, RE2Ba, comprising a lamination process including a first step of forming a first layer mainly composed of a copper oxide superconductor, and a second step of forming a second layer mainly composed of a high-entropy superconductor represented by general formula (2) directly or via a thin film on the first layer. ２ Cu ３ O ７－δ ... (2) In formula (2), RE2 is composed of three or more elements selected from the group consisting of Sr, Ba, Ca, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and 0≦δ≦1).

14. The method for producing a laminate according to claim 13, wherein in the first step, a first layer containing as a main component a rare earth copper oxide superconductor represented by general formula (1) is formed. ２ Cu ３ O ７－ｘ ... (1) (In formula (1), RE1 is composed of one element selected from a first group consisting of Y, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or two elements selected from a second group consisting of an element of the first group and Sr, Ba, and Ca, and satisfies 0≦x≦1.) 15. The method for producing a laminate according to claim 13, wherein in the first step, a first layer containing a bismuth-based copper oxide superconductor or a lanthanum-based copper oxide superconductor as a main component is formed.

16. The method for producing a laminate according to claim 13, wherein in the second step, the second layer is formed directly on the first layer.

17. The method for producing a laminate according to claim 13, wherein the lamination step includes an alternate lamination step in which the first step and the second step are alternately performed to form a superconducting layer consisting of alternately laminated portions.

18. The method for producing a laminate according to claim 13, wherein in the above formula (2), RE2 is composed of Y, Gd, and X, and 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.

19. The method for producing a laminate according to claim 13, wherein in the first step, the first layer is formed on an underlayer whose surface is made of a single crystal.

20. A method for manufacturing a laminate described in claim 19, wherein a first target for forming the first layer is placed on a rotatable first holder, a second target for forming the second layer is placed on a rotatable second holder, the first holder and the second holder are provided on a rotatable mounting table, the first step is performed with the first target rotated, the second step is performed with the second target rotated, and switching between the first step and the second step is performed by rotating the mounting table.

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