Superconducting wire

Abstract

To provide a superconducting wire in which the anisotropy of the critical current of a superconducting layer is reduced by an unconventional method.SOLUTION: A superconducting wire 1 is provided with a superconducting layer 12 including a first superconducting layer 121 and a second superconducting layer 122 that are layered in arbitrary order without any other layer, where the first superconducting layer 121 has columnar pinning centers and the second superconducting layer 122 has point pinning centers.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a superconducting wire. [Background technology]

[0002] When a superconducting wire capable of carrying a supercurrent is used in an environment where a magnetic field is present, the magnitude of the critical current changes depending on the angle of the magnetic field penetrating the superconducting wire. In order to widely use superconducting wires in various technical applications, it is necessary to reduce the dependency of the critical current on the magnetic field angle, i.e., the anisotropy of the critical current.

[0003] In recent years, attempts have been made to control the anisotropy of the critical current of REBCO superconducting thin films by incorporating Y2O3, Y2BaCuO5 (Y211), BaHfO3, and BaSnO3 into the same YBCO matrix (see Non-Patent Documents 1 and 2). y (RE is a rare earth element) is a copper oxide superconductor.

[0004] In recent years, attempts have been made to control the anisotropy of the critical current of REBCO superconducting thin films by adjusting conditions such as irradiation energy and incident direction when irradiating heavy ions (see Non-Patent Documents 3 and 4). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] AKJha et al., “Controlling the Critical Current Anisotropy of YBCO Superconducting Films by Incorporating Hybrid Artificial Pinning Centers”, IEEE Trans. Appl. Supercond., 26, 8000404 (2016) [Non-Patent Document 2] AKJha et al., “Isotropic enhancement in the critical current density of YBCO thin films incorporating nanoscale Y2BaCuO5inclusions”, J. Appl. Phys., 122, 093905 (2017) [Non-Patent Document 3] B. Gautam et al., “Microscopic adaptation of BaHfO3and Y2O3 artificial pinning centers for strong and isotropic pinning landscape in YBa2Cu3O7-xthin films”, Supercond. Sci. Technol. 31, 025008 (2018) [Non-Patent Document 4] NM Strickland et al., “Near-isotropic enhancement of the 20 K critical current of REBa2Cu3O7 coated conductors from columnar defects” Supercond. Sci. Technol. 36, 055001 (2023) Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a superconducting wire in which the anisotropy of the critical current of the superconductor layer is reduced by a method different from that of the conventional method. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention provides the following superconducting wire.

[0008] [1] A superconducting wire comprising a superconductor layer including a first superconductor layer and a second superconductor layer stacked in any order without any intervening layers, the first superconductor layer having a columnar pinning center, and the second superconductor layer having a point-like pinning center. [2] The first superconductor layer is made of REBa2Cu3O 6+y (0≦y≦1) (RE is a rare earth element) is used as a base material, BaMO3 (M is Hf, Zr, or Sn) is contained as an impurity, and the second superconductor layer is 6+y The superconducting wire according to the above [1], which has a base material of (0≦y≦1) (RE is a rare earth element) and contains RE2O3 (RE is a rare earth element) as an impurity. [3] The first superconductor layer is EuBa2Cu3O 6+y (0≦y≦1) is used as a base material, BaHfO3 is contained as an impurity, and the second superconductor layer is YBa2Cu3O 6+y (0≦y≦1) as the base material, containing Y2O3 as an impurity, or NdBa2Cu3O 6+y The superconducting wire according to the above [1], which has a base material of (0≦y≦1) and contains Nd2O3 as an impurity. [4] The superconducting wire according to any one of the above [1] to [3], wherein the superconducting layer includes an alternating laminate in which the first superconducting layer and the second superconducting layer are alternately laminated. [5] The superconducting wire according to any one of [1] to [3] above, wherein, when a magnetic field having a magnetic flux density of 8 T or less is applied to the first superconductor layer and the second superconductor layer at a temperature of 65 K, a critical current of the first superconductor layer when the magnetic field is perpendicular to a surface of the first superconductor layer is greater than a critical current of the first superconductor layer when the magnetic field is parallel to the surface of the first superconductor layer, and a critical current of the second superconductor layer when the magnetic field is parallel to the surface of the second superconductor layer is greater than a critical current of the second superconductor layer when the magnetic field is perpendicular to the surface of the second superconductor layer. Effect of the Invention

[0009] According to the present invention, it is possible to provide a superconducting wire in which the anisotropy of the critical current of the superconductor layer is reduced by a method different from the conventional method. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a vertical sectional view showing a schematic configuration of a superconducting wire according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a graph showing the dependence of the critical current Ic on the magnetic field angle Θ for the EBHO / YBCO sample and two comparative examples in an environment of a magnetic field of 1.6 T and a temperature of 65 K. [Diagram 3] FIG. 3 is a graph showing the dependence of the critical current Ic on the magnetic field angle Θ of the EBHO / NdBCO sample and two comparative examples in an environment of a magnetic field of 1 T and a temperature of 77.3 K. [Figure 4] FIG. 4 is a graph showing the critical current Ic measured at 65K by changing the strength and angle Θ of the magnetic field applied to the EBHO sample. [Diagram 5] FIG. 5 is a graph showing the dependence of the anisotropy A of the critical current of the EBHO sample on the strength of the magnetic field at a temperature of 65K. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (Structure of superconducting wire) 1 is a vertical cross-sectional view showing a schematic configuration of a superconducting wire 1 according to an embodiment of the present invention. The superconducting wire 1 is a tape-shaped wire through which a superconducting current can flow, and includes a substrate 10, a buffer layer 11 formed on the substrate 10, and a superconductor layer 12 formed on the buffer layer 11.

[0012] The substrate 10 is a tape-shaped substrate made of a metal or an alloy such as Hastelloy.RTM.. For example, the substrate 10 has a thickness of 40 to 60 μm.

[0013] The buffer layer 11 functions as a buffer between the substrate 10 and the superconductor layer 12, and includes at least one layer selected from the group consisting of an Al2O3 layer, a Y2O3 layer, and an MgO layer, and preferably includes two or three layers selected from this group. The buffer layer 11 has a thickness of, for example, 300 to 500 nm. The buffer layer 11 is formed, for example, by a pulsed laser deposition (PLD) method.

[0014] 1, the buffer layer 11 is made of a laminate of an Al2O3 layer 111, a Y2O3 layer 112, an IBAD-MgO layer 113, and a LaMnO3 layer 114. The IBAD-MgO layer 113 is made of an MgO film formed by ion beam assisted deposition (IBAD).

[0015] The superconductor layer 12 includes a first superconductor layer 121 and a second superconductor layer 122 that are laminated in an arbitrary order without any other layers in between. The first superconductor layer 121 is a layer having a columnar pinning center and made of a superconductor as a base material. The second superconductor layer 122 is a layer having a point-like pinning center and made of a superconductor as a base material. Since the superconductor layer 12 includes a laminate of the first superconductor layer 121 and the second superconductor layer 122, the critical current I c The anisotropy of the film can be reduced.

[0016] The superconductor layer 12 may include an alternating laminate in which the first superconductor layer 121 and the second superconductor layer 122 are alternately laminated one by one, with the total number of first superconductor layers 121 and second superconductor layers 122 being three or more. In this case, the critical current I c The anisotropy of the first superconductor layer 121 can be changed (controlled). Either the first superconductor layer 121 or the second superconductor layer 122 may be located at the bottom of the alternating laminate. The number of layers of the first superconductor layer 121 and the number of layers of the second superconductor layer 122 in the alternating laminate may be the same, or one may be one layer more than the other.

[0017] Here, the pinning center is a component that prevents the superconducting state from being destroyed by fixing (pinning) the magnetic flux inside the superconductor when a magnetic field is applied to the superconductor, and the presence of the pinning center in the superconductor makes it possible to ensure a sufficient critical current even in a magnetic field. In the first superconductor layer 121, a large pinning effect is exerted in the presence of a magnetic field along the nanorods made of BaMO3 as the columnar pinning centers, that is, in the presence of a magnetic field perpendicular to the surface of the superconducting wire 1, and the critical current can be increased.

[0018] The anisotropy of the critical current is the critical current I, which is a function of the angle Θ of the magnetic field applied to the superconducting wire 1. c The maximum and minimum values ​​of I c max (Θ), I c min (Θ), (I c max (Θ)-I c min (Θ)) / I c min (Θ), and the critical current I c This is closely related to the dependence of the magnetic field on the angle Θ.

[0019] The first superconductor layer 121 is, for example, REBa2Cu3O 6+y (0≦y≦1) (RE is a rare earth element), that is, the base material is REBCO, and BaMO3 (M is Hf, Zr, or Sn) is contained as an impurity that forms a columnar pinning center. In the REBCO superconductor, the impurity BaMO3 forms nanorods that are self-organized columnar defects. The nanorods made of BaMO3 have an orientation almost perpendicular to the first superconductor layer 121, and function as columnar pinning centers.

[0020] The first superconductor layer 121 has a thickness of, for example, 1000 to 1700 nm (when a plurality of first superconductor layers 121 are included in the superconductor layer 12, the total thickness of the layers is the total thickness). The first superconductor layer 121 is formed by, for example, a pulsed laser deposition (PLD) method.

[0021] The second superconductor layer 122 has, for example, REBCO as a base material and contains RE2O3 (RE is a rare earth element) as an impurity that forms a point-like pinning center. In the REBCO superconductor, the impurity RE2O3 forms point-like defects that function as point-like pinning centers. In the second superconductor layer 122, the point-like defects made of RE2O3 as point-like pinning centers can exert a large pinning effect in the presence of a magnetic field parallel to the second superconductor layer 122, i.e., parallel to the surface of the superconducting wire 1, and can increase the critical current.

[0022] The second superconductor layer 122 has a thickness of, for example, 1000 to 1700 nm (when a plurality of second superconductor layers 122 are included in the superconductor layer 12, the total thickness of the layers is the total thickness). The second superconductor layer 122 is formed by, for example, a PLD method.

[0023] The rare earth elements contained in the REBCO constituting the first superconductor layer 121 and the rare earth elements contained in the REBCO constituting the second superconductor layer 122 are each any rare earth element, and may be different rare earth elements or the same rare earth element. For example, the base material of the first superconductor layer 121 and the base material of the second superconductor layer 122 may be different, such as YBCO and EuBCO, or may be the same, such as YBCO and YBCO.

[0024] Furthermore, the thickness of the first superconductor layer 121 and the thickness of the second superconductor layer 122 may be the same or different. Even when the superconductor layer 12 includes an alternate laminate of the first superconductor layer 121 and the second superconductor layer 122, the thickness per layer of the first superconductor layer 121 and the thickness per layer of the second superconductor layer 122 may be the same or different. By adjusting the ratio of the thickness of the first superconductor layer 121 to the thickness of the second superconductor layer 122, the critical current I c It is expected that the anisotropy of

[0025] A protective layer for protecting the superconductor layer 12 from the surrounding atmosphere and for providing good electrical contact may be provided on the superconductor layer 12. This protective layer is made of, for example, a film containing Ag.

[0026] The first superconductor layer 121 and the second superconductor layer 122 are formed by crystal growth in the c-axis direction. That is, the thickness direction of the first superconductor layer 121 and the second superconductor layer 122 is parallel to the c-axis, and the in-plane direction is parallel to the a-axis and the b-axis. The critical current when a magnetic field perpendicular to the surface of the first superconductor layer 121 and the second superconductor layer 122, i.e., a magnetic field parallel to the c-axis, is applied is defined as I c (B / / c), the critical current when a magnetic field parallel to the surfaces of the first superconductor layer 121 and the second superconductor layer 122, i.e., a magnetic field parallel to the a-axis and b-axis, is applied is I c If (B / / ab), when a magnetic field of a predetermined magnitude is applied to the first superconductor layer 121 and the second superconductor layer 122 under a predetermined temperature condition (for example, when a magnetic field with a magnetic flux density of 8 T or less is applied to the first superconductor layer 121 and the second superconductor layer 122 at a temperature of 65 K), the I c (B / / c) is I c (B / / ab) and the I c (B / / ab) is I c It is preferable that the anisotropy of the critical current of superconducting wire 1 having first superconductor layer 121 and second superconductor layer 122 is greater than (B / / c). In this case, the anisotropy of the critical current of superconducting wire 1 having first superconductor layer 121 and second superconductor layer 122 can be reduced more effectively.

[0027] (Evaluation of superconducting wire) An evaluation was carried out on the anisotropy of the critical current in the superconducting wire 1. The method and results are described below.

[0028] First, EuBa2Cu3O 6+y The first superconductor layer 121 is made of a base material of YBa2Cu3O (0≦y≦1) and contains BaHfO3 as an impurity to form a columnar pinning center. 6+yA superconducting wire 1 (referred to as an EBHO / YBCO sample) was manufactured using a base material (0≦y≦1) and having a two-layer superconductor layer 12 on which a second superconductor layer 122 containing Y2O3 as an impurity that forms a point-like pinning center was laminated.

[0029] Also, EuBa2Cu3O 6+y The first superconductor layer 121 is made of NdBa2Cu3O (0≦y≦1) and contains BaHfO3 as an impurity, which forms a columnar pinning center. 6+y A superconducting wire 1 (referred to as an EBHO / NdBCO sample) was manufactured using a base material (0≦y≦1) and having an eight-layer structure in which second superconductor layers 122 containing Nd2O3 as an impurity forming point-like pinning centers were alternately stacked one by one. The thickness of each of the first superconductor layer 121 and the second superconductor layer 122 in the EBHO / NdBCO sample was 0.37 μm.

[0030] The superconductor layer 12 of the EBHO / YBCO sample and the EBHO / NdBCO sample was formed by the PLD method using a tape-shaped substrate 10 made of Hastelloy C276 with a thickness of 40 to 50 μm and a width of 12 mm, and a buffer layer 11 consisting of a laminate of an Al2O3 layer 111, a Y2O3 layer 112, an IBAD-MgO layer 113, and a LaMnO3 layer 114.

[0031] Then, a bridge with a width of 30 μm was formed in the superconductor layer 12 of each of the EBHO / YBCO sample and the EBHO / NdBCO sample, and the critical current was measured. The bridge was formed by microfabricating the superconductor layer 12 with a 10 nanosecond pulse laser with a wavelength of 539 nm and power of 200 kHz (300 mW).

[0032] Figure 2 shows the critical current I of the EBHO / YBCO sample and two comparative samples (referred to as the EBHO sample and the YBCO sample) under a magnetic field of 1.6 T and a temperature of 65 K. c EBHO sample is EuBa2Cu3O 6+yThe superconducting wire has a base material of BaHfO3 (0≦y≦1) and only a first superconducting layer 121 containing BaHfO3 as an impurity, which forms a columnar pinning center, as a superconducting layer. The superconducting layer 12 of the EBHO / YBCO sample is replaced with one first superconducting layer 121. The YBCO sample is YBa2Cu3O 6+y The superconducting wire has a base material of 0≦y≦1 and only a second superconductor layer 122 containing Y2O3 as an impurity forming a point-like pinning center as a superconductor layer. This corresponds to a case where the superconductor layer 12 of the EBHO / YBCO sample is replaced with one second superconductor layer 122. The critical current I c The value of is the critical current I of a typical superconducting wire with a width of 4 mm. c This is the value per 4 mm width, converted to the value of

[0033] The magnetic field angle Θ indicates the angle of the magnetic field based on the direction perpendicular to the superconductor layer 12 through which a current flows. That is, when the direction perpendicular to the superconductor layer 12 (c-axis direction) is parallel to the magnetic field direction (B / / c), the magnetic field angle is 0°, and when the direction of the magnetic field is parallel to the in-plane direction of the superconductor layer 12 (direction parallel to the a-axis and b-axis) (B / / ab), the magnetic field angle is 90°.

[0034] According to FIG. 2, when the magnetic field angle Θ is 90°, the critical current I c becomes larger, and the critical current I c As a result, in the EBHO / YBCO sample having the superconductor layer 12 in which the first superconductor layer 121 and the second superconductor layer 122 are laminated, the critical current I c In the dependence of the magnetic field angle Θ, a complementary effect is created between the first superconductor layer 121 and the second superconductor layer 122, so that the strengths of one layer compensate for the weaknesses of the other layer and vice versa.

[0035] For the EBHO / YBCO sample, (Ic max (Θ)-I c min (Θ)) / I c min (Θ)(I c max (Θ), I c min (Θ) are functions of Θ, c The critical current I c The anisotropy A of the EBHO sample is 0.35, and the critical current I c As a result, if the superconductor layer 12 has two layers, the first superconductor layer 121 and the second superconductor layer 122, the critical current I c It has been demonstrated that the anisotropy A of the

[0036] Also, according to Figure 2, in the EBHO sample, I c (B / / c) is I c (B / / ab), and the I c (B / / ab) is I c (B / / c). As a result, in the EBHO / YBCO sample in which the first superconductor layer 121 constituting the EBHO sample and the second superconductor layer 122 constituting the YBCO sample are laminated, the first superconductor layer 121 and the second superconductor layer 122 have a high I c (B / / c) and I c It is believed that the anisotropy A is effectively reduced by (B / / ab) complementing each other.

[0037] Figure 3 shows the critical current I of the EBHO / NdBCO sample and two comparative samples (referred to as the EBHO sample and the NdBCO sample) in an environment of a magnetic field of 1 T and a temperature of 77.3 K. c 1 is a graph showing the dependence of the EBHO sample on the magnetic field angle Θ. 6+yThe superconducting wire has a base material of BaHfO3 (0≦y≦1) and only a first superconducting layer 121 containing BaHfO3 as an impurity forming a columnar pinning center as a superconducting layer. The superconducting layer 12 of the EBHO / NdBCO sample is replaced with one first superconducting layer 121. The NdBCO sample is NdBa2Cu3O 6+y The superconducting wire has only the second superconductor layer 122 containing Nd2O3 as an impurity, which forms a point-like pinning center, as a superconductor layer. This corresponds to the superconductor layer 12 of the EBHO / NdBCO sample being replaced with one second superconductor layer 122. The critical current I c The values ​​are per 4 mm width.

[0038] For the EBHO / NdBCO sample, the critical current I c The anisotropy A of the EBHO sample is 0.39, and the critical current I c This is a significant decrease compared to the anisotropy A of 0.93 and 1.12 in the previous study.

[0039] Also, according to Figure 3, in the EBHO sample, I c (B / / c) is I c (B / / ab), and I c (B / / ab) is I c (B / / c). As a result, in the EBHO / NdBCO sample in which the first superconductor layer 121 constituting the EBHO sample and the second superconductor layer 122 constituting the NdBCO sample are laminated, the first superconductor layer 121 and the second superconductor layer 122 have a high I c (B / / c) and I c It is believed that the anisotropy A is effectively reduced by (B / / ab) complementing each other.

[0040] Figure 4 shows the critical current I measured at 65 K by changing the strength and angle Θ of the magnetic field applied to the EBHO sample. c , which shows the value of the critical current I for each magnetic field strength in the EBHO sample. c The dependence of the critical current I on the magnetic field angle Θ is shown in Fig. 4.c The value is a value per 4 mm width. Also, "2 T" to "15 T" shown in Fig. 4 indicate the magnitude of the magnetic flux density of the magnetic field applied to the EBHO sample.

[0041] Figure 5 shows the critical current I of the EBHO sample at 65K. c 5 is a graph showing the dependence of anisotropy A on the strength of the magnetic field. The anisotropy A in FIG. 5 was measured based on the data in FIG.

[0042] Critical current in EBHO sample I c The range where the anisotropy A of the magnetic field becomes low is determined by the competition between columnar pinning and point pinning. At low magnetic field strength, the magnetic flux tends to align parallel to the columnar defects (nanorods), so that the columnar defects are the first to suppress the critical current I c and its dependence on the magnetic field angle Θ. However, as the magnetic flux density increases, the interactions between the magnetic fluxes become larger compared to their interactions with the columnar defects.

[0043] At a certain magnetic field strength (B * At this magnetic field strength B * At the critical current I c The dependence of on the magnetic field angle Θ qualitatively changes from the characteristic behavior of columnar pinning to that of isotropic random pinning with a point center. That is, as the magnetic field strength B * When the magnetic field strength is smaller than B, columnar pinning becomes dominant. * When θ is larger than θ, columnar pinning becomes dominant.

[0044] In Fig. 5, the transition from columnar pinning to point pinning occurs at B * The position of B is shown by the dashed line. * is about 8T, and B * At the critical current I c The anisotropy A of is minimized.

[0045] (Effects of the embodiment) According to the above-described embodiment of the present invention, since the superconductor layer 12 includes a laminate of a first superconductor layer 121 having a columnar pinning center and a second superconductor layer 122 having a point-like pinning center, it is possible to provide a superconducting wire 1 in which the anisotropy of the critical current is reduced.

[0046] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. Furthermore, the components of the above embodiment can be combined in any manner without departing from the spirit of the invention.

[0047] In addition, the above-described embodiments do not limit the scope of the invention according to the claims. Also, it should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. [Explanation of symbols]

[0048] 1. Superconducting wire 10 Substrate 11 Buffer layer 12 Superconductor layer 121 First superconductor layer 122 Second superconductor layer

Claims

1. The superconductor layer includes a first superconductor layer and a second superconductor layer that are laminated in any order without any other layers therebetween; the first superconductor layer has a columnar pinning center; The second superconductor layer has a point-like pinning center. Superconducting wire.

2. The first superconductor layer is ２ Cu ３ O ６＋ｙ (0≦y≦1) (RE is a rare earth element) as the base material, BaMO ３ (M is Hf, Zr, or Sn) as an impurity, The second superconductor layer is ２ Cu ３ O ６＋ｙ (0≦y≦1) (RE is a rare earth element) is used as the base material, and RE ２ O ３ (RE is a rare earth element) as an impurity, The superconducting wire according to claim 1 .

3. The first superconductor layer is EuBa ２ Cu ３ O ６＋ｙ (0≦y≦1) is used as the base material, and BaHfO ３ as an impurity, The second superconductor layer is YBa ２ Cu ３ O ６＋ｙ (0≦y≦1) is the base material, and Y ２ O ３ or NdBa as an impurity ２ Cu ３ O ６＋ｙ (0≦y≦1) is used as the base material, and Nd ２ O ３ as an impurity, The superconducting wire according to claim 1 .

4. The superconductor layer includes an alternating laminate in which the first superconductor layer and the second superconductor layer are alternately laminated. The superconducting wire according to any one of claims 1 to 3.

5. when a magnetic field having a magnetic flux density of 8 T or less is applied to the first superconductor layer and the second superconductor layer at a temperature of 65 K, the critical current of the first superconductor layer when the magnetic field is perpendicular to a surface of the first superconductor layer is larger than the critical current of the first superconductor layer when the magnetic field is parallel to the surface of the first superconductor layer, and the critical current of the second superconductor layer when the magnetic field is parallel to the surface of the second superconductor layer is larger than the critical current of the second superconductor layer when the magnetic field is perpendicular to the surface of the second superconductor layer. The superconducting wire according to any one of claims 1 to 3.

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