JP2020167007A - Connection structure of superconductive wire and superconductive wire - Google Patents

Abstract

To provide a connection structure of superconductive wires, which can easily adjust an oxygen nonstoichiometric ratio in an oxide superconductive layer after connection and a superconductive wire therewith.SOLUTION: Provided is a connection structure of superconductive wires obtained by connecting terminals of target wires to be connected 10, 20 having oxide superconductive layers 12, 22 via a connection wire 30 having the oxide superconductive layer 32, in which an in-plane degree of orientation angle Δφ vertical to a thickness direction of the oxide superconductive layers 12, 22 of the wires to be connected 10, 20 is 4.0° or larger and smaller than 5.5°, and an in-plane degree of orientation angle Δφ vertical to a thickness direction of the oxide superconductive layer 32 of the wires to be connected 30 is larger by 0.5° or more than an in-plane degree of orientation angle Δφ of the oxide superconductive layers 12, 22 of wires to be connected 10, 20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a connecting structure of a superconducting wire and a superconducting wire.

Since superconducting wires have low current loss, they are used as power supply cables, magnetic coils, and the like. Patent Document 1 describes a superconducting wire having an oxide superconducting layer formed on an intermediate layer provided on a metal substrate and a copper electroplating film formed as a stabilizing layer around the superconducting layer.
Further, in order to obtain a long superconducting wire, it is necessary to connect the ends of a plurality of superconducting wires. For example, in Patent Document 2, the oxide superconducting layers of the superconducting wire are opposed to each other to ensure electrical conduction between the oxide superconducting layers.

Japanese Patent No. 5634166 Japanese Unexamined Patent Publication No. 2013-23569

However, when the superconducting wires are connected so that the oxide superconducting layers face each other, the oxide superconducting layers have a structure sandwiched between the metal substrates of each superconducting wire. At this time, when the oxide superconducting layer is connected, the heat treatment is performed in a state where oxygen is insufficient, so that oxygen may be desorbed from the oxide superconducting layer and the superconducting characteristics may be deteriorated.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a connection structure of a superconducting wire and a superconducting wire in which it is easy to adjust the oxygen non-stoichiometricity of the oxide superconducting layer after connection. To do.

In order to solve the above problems, the present invention is a connecting structure of a superconducting wire in which the ends of the connecting target wire having the oxide superconducting layer are connected via the connecting wire having the oxide superconducting layer. The in-plane orientation Δφ perpendicular to the thickness direction of the oxide superconducting layer of the connecting wire is 4.0 ° or more and less than 5.5 °, and is in the thickness direction of the oxide superconducting layer of the connecting wire. Provided is a connection structure of a superconducting wire, characterized in that the vertical in-plane orientation Δφ is 0.5 ° or more larger than the in-plane orientation Δφ of the oxide superconducting layer of the wire to be connected.

The connection target wire and the connection wire are each composed of a superconducting wire having the oxide superconducting layer on the substrate, and the connection target wire is connected between the connection target wire substrate and the connection wire substrate. The oxide superconducting layer and the oxide superconducting layer of the connecting wire may be arranged so as to face each other.
The oxide superconducting layer of the wire to be connected and the oxide superconducting layer of the connecting wire may be connected so as to be in direct contact with each other.
The connecting wire may be composed of a superconducting wire shorter than the connecting target wire.

Further, the present invention is a superconducting wire in which two or more connecting target wires are connected in the longitudinal direction, and at least one place between the two or more connecting target wires is composed of a connecting structure of the superconducting wire. Provided is a superconducting wire material characterized by being

According to the present invention, since the in-plane orientation Δφ perpendicular to the thickness direction of the oxide superconducting layer of the connecting wire is relatively large, it is easy to adjust the oxygen non-stoichiometricity of the oxide superconducting layer by oxygen diffusion. Become. Since the in-plane orientation Δφ perpendicular to the thickness direction of the oxide superconducting layer of the wire to be connected is relatively small, the superconducting property of the wire to be connected is high, and the average superconducting property of the connected superconducting wire is lowered. It can be suppressed.

It is sectional drawing which shows typically the connection structure of the superconducting wire material of embodiment. It is explanatory drawing which conceptually shows the structure of the grain boundary in an oxide superconductor. It is explanatory drawing which conceptually shows the structure of the dislocation group in an oxide superconductor.

Hereinafter, the present invention will be described with reference to the drawings based on the preferred embodiments.
FIG. 1 shows a connection structure of the superconducting wire rod of the present embodiment. This cross-sectional view schematically represents a cross section along the longitudinal direction of the superconducting wire. The vertical direction of the cross-sectional view is the thickness direction of the superconducting wire, and the horizontal direction of the cross-sectional view is the longitudinal direction of the superconducting wire. The direction perpendicular to the paper surface is the width direction of the superconducting wire.

As shown in FIG. 1, the superconducting wires 10, 20, and 30 constituting the connection structure are composed of a long connection target wire 10, 20 and a short connection wire 30. Between the ends of the wire rods 10 and 20, the oxide superconducting layers 12 and 22 of the wire rods 10 and 20 to be connected are connected via the oxide superconducting layer 32 of the wire rod 30 for connection. The oxide superconducting layers 12, 22, and 32 may be laminated on the substrates 11, 21, and 31, respectively. Protective layers 13 and 23 may be provided on the oxide superconducting layers 12 and 22 of the connecting wire rods 10 and 20 that do not face the oxide superconducting layer 32 of the connecting wire 30. FIG. 1 shows only the vicinity of the end portion of the connection target wires 10 and 20 on the side connected to the connection wire 30, and the other parts are not shown. The connection structure of the present embodiment is a portion including one end of the connection target wires 10 and 20 and the connection wire 30. In the longitudinal direction of the wire rods 10 and 20 to be connected, another connection structure may be formed at an end portion on a side (not shown).

When connecting the ends of the connection target wires 10 and 20 to the connection wire 30, the oxide superconducting layers 12 and 22 of the connection target wires 10 and 20 face each other with the oxide superconducting layer 32 of the connection wire 30. The superconducting wires 10, 20 and 30 can be arranged as described above, and the oxide superconducting layers 12, 22 and 32 can be superposed on each other. In the embodiment shown in FIG. 1, a gap is interposed between the end faces of the wire rods 10 and 20 to be connected in the longitudinal direction, but this gap is not essential. For example, the end faces may be butted between the connecting target wires 10 and 20 facing each other in the longitudinal direction.

When the oxide superconducting layers 12, 22 and 32 are directly bonded, the superconductor may be diffusely bonded by heating, for example. A bonding layer (not shown) made of a metal such as silver, a silver alloy, or solder may be provided between the oxide superconducting layers 12, 22, and 32 facing each other. The superconducting wires 10, 20, and 30 may be fixed by providing joints (not shown) such as welding and metal plating between or around the substrates 11, 2, and 31 facing each other.

In order to reduce the electrical resistance of the superconducting connection, the oxide superconducting layers 12 and 22 of the connection target wires 10 and 20 and the connection wire are connected in at least a part of the region where the connection target wires 10 and 20 and the connection wire 30 face each other. It is preferable that the oxide superconducting layer 32 of 30 is connected so as to be in direct contact with it. When the bonding layer is provided between the oxide superconducting layers 12, 22 and 32 facing each other, it is preferable to set the material, film thickness and the like so as to enable oxygen diffusion. After connection, it is preferable to perform oxygen heat treatment (oxygen annealing) in an oxygen atmosphere to recover the deterioration of the oxide superconducting layers 12, 22 and 32. In the oxygen heat treatment, the ratio of the oxide to the metal element of the oxide superconductor can be optimized.

In the case of the connection structure of the present embodiment, the in-plane orientation in the direction (a-axis direction or b-axis direction) perpendicular to the thickness direction (c-axis direction) of the oxide superconducting layers 12 and 22 of the wire rods 10 and 20 to be connected. The degree Δφ is preferably less than 5.5 °. As a result, the superconducting characteristics of the oxide superconducting layers 12 and 22 of the wire rods 10 and 20 to be connected can be kept good.
Further, the in-plane orientation Δφ in the direction (a-axis direction or b-axis direction) perpendicular to the thickness direction (c-axis direction) of the oxide superconducting layers 12 and 22 of the wire rods 10 and 20 to be connected is 4.0 ° or more. Is preferable. As a result, the critical current Ic of the superconducting wire can be increased after the heat treatment as compared with the case before the heat treatment.
Further, the in-plane orientation Δφ in the direction (a-axis direction or b-axis direction) perpendicular to the thickness direction (c-axis direction) of the oxide superconducting layer 32 of the connecting wire 30 is the oxide of the connecting wires 10 and 20. It is preferable that the superconducting layers 12 and 22 are 0.5 ° or more larger than the in-plane orientation Δφ. As a result, the superconducting characteristics of the oxide superconducting layer 32 of the connecting wire 30 can be kept good.
The in-plane orientation Δφ is the value of the full width at half maximum (FWHM) of the crystal axis dispersion measured by performing X-ray analysis measurement of the oxide superconducting layer. The smaller the value of the in-plane orientation Δφ, the better the crystal orientation.
The in-plane orientation Δφ in the direction perpendicular to the thickness direction of the oxide superconducting layer is hereinafter simply referred to as the in-plane orientation Δφ.

Even if the oxide superconducting layer 32 of the connecting wire 30 faces the oxide superconducting layers 12 and 22 at the ends of the connecting wire rods 10 and 20, and the oxide superconducting layers 12, 22 and 32 overlap each other, oxidation occurs. Since the in-plane orientation Δφ of the physical superconducting layer 32 is relatively large, the oxygen diffusion rate of the oxide superconducting layer 32 becomes high. This facilitates the adjustment of the oxygen non-stoichiometric properties of the oxide superconducting layers 12, 22, and 32 by oxygen diffusion. Further, since the in-plane orientation Δφ of the oxide superconducting layers 12 and 22 of the connecting target wires 10 and 20 is relatively small and the superconducting characteristics of the long connecting target wires 10 and 20 are high, the connected superconducting wires 10 , 20, 30 can suppress the deterioration of the average superconducting characteristics.

The reason why the oxygen diffusion rate of the oxide superconducting layer 32 having a large in-plane orientation Δφ is considered to be high is as follows. As shown in FIG. 2, when the difference in crystal orientations 41, 42, 43 between adjacent local regions in the crystal is large, grain boundaries 47 are formed, and each region is a crystal grain 44 surrounded by grain boundaries 47. It becomes 45,46. Further, as shown in FIG. 3, if the difference between the crystal orientations 41 and 42 between the adjacent local regions in the crystal is small, the grain boundary is not formed and the dislocation group 48 is formed. That is, when the in-plane orientation Δφ of the crystal is large, the regions having different crystal orientations increase in the crystal, and the defect structures such as the grain boundaries 47 and the dislocation group 48 where oxygen can diffuse increase, so that oxygen diffusion occurs. It is considered to be advantageous. In FIG. 2, the crystal grains 44, 45, and 46 are simply shown as hexagons, but this is not intended for the shape of the particles.

The oxygen heat treatment is preferably performed at least once before or after connecting the connecting wires 10 and 20 to the connecting wires 30. When the oxide superconducting layers 12 and 22 are exposed after the connection, it is preferable to laminate the protective layers 13 and 23 such as silver on at least the exposed oxide superconducting layers 12 and 22. It is also possible to stack two or more protective layers 13 and 23 in the thickness direction. For example, silver or a silver alloy that can permeate oxygen under high temperature conditions may be laminated before the oxygen heat treatment, and copper or the like may be laminated on the silver or the silver alloy after the oxygen heat treatment. The connection target wires 10 and 20 in which the protective layers 13 and 23 are formed over the entire length of the connection target wires 10 and 20 are prepared, and the protective layer is formed from the end of the connection target wires 10 and 20 before being connected to the connection wire 30. A part of 13 and 23 may be removed by etching or the like.

The oxide superconducting layers 12, 22, and 32 are composed of, for example, an oxide superconductor containing a rare earth element. Examples of the oxide superconductor include a RE-Ba-Cu-O-based oxide superconductor represented by the general formula REBa ₂ Cu ₃ O _7-x (RE123) and the like. Examples of the rare earth element RE include one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The thickness of the oxide superconducting layers 12, 22, and 32 is, for example, about 0.5 to 5 μm.

Artificial pins made of different materials may be introduced into the oxide superconducting layers 12, 22, and 32 as artificial crystal defects. Examples of dissimilar materials used for introducing artificial pins into the oxide superconducting layers 12, 22, and 32 include BaSnO ₃ (BSO), BaZrO ₃ (BZO), BaHfO ₃ (BHO), and BaTIO ₃ (BTO). At least one or more of SnO ₂ , TiO ₂ , ZrO ₂ , LaMnO ₃ , ZnO and the like can be mentioned.

The in-plane orientation Δφ of the oxide superconducting layers 12 and 22 of the wire rods 10 and 20 to be connected is not particularly limited, but is, for example, 4.0 °, 4.2 °, 4.5 °, 4.8 °, 5 Values of 0.0 °, 5.3 °, 5.4 ° or intermediate or near these can be mentioned. Here, the in-plane orientation Δφ of the oxide superconducting layer 12 and the in-plane orientation Δφ of the oxide superconducting layer 22 may be about the same or different.
The in-plane orientation Δφ of the oxide superconducting layer 32 of the connecting wire 30 is not particularly limited, but is, for example, 4.5 °, 4.8 °, 5.0 °, 5.3 °, 5.4 °, and the like. Values of 5.5 °, 6.0 °, 6.2 °, 7.0 °, 7.5 °, 8.0 °, or intermediate or near these, and even higher can be mentioned.
The difference between the in-plane orientation Δφ of the oxide superconducting layer 32 and the in-plane orientation Δφ of the oxide superconducting layers 12 and 22 is not particularly limited, but is, for example, 0.5 °, 0.6 °, 0.8. °, 1.0 °, 1.2 °, 1.5 °, 1.8 °, 2.0 °, 3.0 °, 5.0 °, or intermediate or near these, or even higher Can be mentioned. Here, the difference between the in-plane orientation Δφ of the oxide superconducting layer 32 and the in-plane orientation Δφ of the oxide superconducting layer 12, and the in-plane orientation Δφ of the oxide superconducting layer 32 and the surface of the oxide superconducting layer 22. It is preferable that at least one of the differences from the internal orientation degree Δφ has the above-mentioned difference (for example, a difference of 0.5 ° or more).

The protective layers 13 and 23 bypass the overcurrent generated at the time of an accident, suppress the chemical reaction occurring between the oxide superconducting layers 12 and 22 and the layers provided on the protective layers 13 and 23, and the like. Has the function of. Examples of the protective layers 13 and 23 include a silver (Ag) layer or a layer containing Ag (for example, an Ag alloy layer). The Ag alloy preferably contains 50% or more of silver in terms of molar ratio or weight ratio. The thickness of the protective layers 13 and 23 is preferably about 1 to 30 μm, and when the protective layers 13 and 23 are thinned, the thickness may be 10 μm or less, 5 μm or less, 2 μm or less, or the like. Further, a stabilizing layer (not shown) such as a copper plating layer may be provided around the superconducting wires 10, 20, and 30.

The widths of the superconducting wires 10, 20, and 30 are not particularly limited, and examples thereof include 1 to 20 mm. The lengths of the wire rods 10 and 20 to be connected are not particularly limited, and examples thereof include 1 m or more, 10 m or more, 100 m or more, 200 m or more, 500 m or more, and 1 km or more. It is also possible to connect a plurality of superconducting wires to form a longer wire. The length of the connecting wire 30 may be as short as 1 m or less, for example. The ratio of the lengths of the connecting wire rods 10 and 20 to the connecting wire rod 30 may be, for example, 10 times or more, 100 times or more, or 1000 times or more. The length at which the oxide superconducting layers 12, 22 and 32 overlap between the connection target wires 10 and 20 and the connection wire 30 is not particularly limited, and examples thereof include 5 mm or more, 10 mm or more, and 20 mm or more.

The substrates 11, 21, 31 are, for example, tape-shaped substrates having main surfaces on both sides in the thickness direction. The substrates 11, 21, 31 may be composed of, for example, a metal substrate and an intermediate layer. Specific examples of the metal constituting the metal substrate include nickel alloys typified by Hastelloy (registered trademark), stainless steel, and oriented NiW alloys in which a texture is introduced into the nickel alloy. The intermediate layer is formed on the main surface on the side where the oxide superconducting layer is formed on the metal substrate. When an oriented substrate in which the arrangement of metal crystals is aligned and oriented is used as the substrates 11,21,31, the oxide superconducting layers 12, 22, directly on the substrates 11,21,31 without forming an intermediate layer, 32 can be formed. The thickness of the metal substrate may be appropriately adjusted according to the intended purpose, and is, for example, in the range of 10 to 1000 μm.

The intermediate layer may have a multi-layer structure, and may have a diffusion prevention layer, a bed layer, an alignment layer, a cap layer, and the like in the order from the metal substrate side to the oxide superconducting layer side, for example. These layers are not always provided one by one, and some layers may be omitted, or two or more layers of the same type may be repeatedly laminated. The intermediate layer may be a metal oxide. By forming the oxide superconducting layer on the intermediate layer having excellent orientation, it becomes easy to obtain the oxide superconducting layer having excellent orientation.

The in-plane orientation Δφ of the oxide superconducting layer or the intermediate layer can be controlled by changing the film forming conditions such as the deposition in the ion beam assisted film formation (IBAD) method: changing the etching ratio, changing the temperature, frequency, etc. It can be carried out. For example, in the IBAD method, the crystal axis is oriented by irradiating the vapor-deposited surface with an ion beam such as argon (Ar) at a predetermined angle. At this time, the in-plane orientation degree Δφ can be controlled by, for example, changing the balance between the vapor-deposited particles and the assist ion beam. Further, by controlling the in-plane orientation Δφ of a layer such as an intermediate layer provided under the oxide superconducting layer, the in-plane orientation Δφ of the oxide superconducting layer can be controlled.

The method for forming the intermediate layer and the oxide superconducting layer is not particularly limited as long as an appropriate film formation can be performed according to the composition of the metal oxide. Examples of the film forming method include a dry film forming method such as a sputtering method, a vapor deposition method, an ion beam assisted film forming method (IBAD method), and a wet film forming method such as a sol-gel method. Examples of the vapor deposition method include an electron beam vapor deposition method, a pulse laser vapor deposition method (PLD method), and a chemical vapor deposition method (CVD method).

In the superconducting wire material connected by the present embodiment, at least one of the superconducting connecting portions is composed of the connecting structure according to the above-described embodiment. When obtaining a superconducting wire in which two or more connecting target wires are connected in series in the longitudinal direction via a superconducting connecting portion, the superconducting connecting portions existing apart from each other in the longitudinal direction may have the same configuration, and the superconducting connections having different configurations may be obtained. The parts may be used together.

In order to secure electrical insulation from the periphery of the superconducting wire, an insulating tape such as polyimide may be wrapped around the outer circumference of the superconducting wire, or a resin layer may be formed. An insulating coating layer such as an insulating tape or a resin layer is not indispensable, and an insulating coating layer may be appropriately provided depending on the use of the superconducting wire, or a configuration without an insulating coating layer may be provided.
To manufacture a superconducting coil using a superconducting wire, for example, the superconducting wire is wound along the outer peripheral surface of the winding frame in the required number of layers to form a coil-shaped multi-layered coil, and then the wound superconducting wire is covered. Can be impregnated with a resin such as an epoxy resin to fix the superconducting wire.

Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. Modifications include addition, replacement, omission, and other changes of components in each embodiment. It is also possible to appropriately combine the components used in the two or more embodiments.

Hereinafter, the present invention will be specifically described with reference to Examples.

By forming an intermediate layer containing CeO ₂ on a metal substrate and then forming an oxide superconducting layer on the intermediate layer, superconducting wires having different in-plane orientation Δφ of the oxide superconducting layer are produced. Each superconducting wire was heat-treated at a temperature of 300 ° C. for 30 minutes in an oxygen (O ₂ ) atmosphere. Before the heat treatment and after the heat treatment, each superconducting wire was cooled to a liquid nitrogen temperature and the critical current Ic was measured. The ratio of the increase in Ic after the heat treatment as compared with the Ic before the heat treatment was determined as the Ic increase rate. That is, when Ic before the heat treatment is Ic0 and Ic after the heat treatment is Ic1, the rate of increase in Ic is the ratio of Ic1 / Ic0.

As shown in Table 1, it was confirmed that the Ic increase rate was low when the in-plane orientation Δφ was small, but the Ic increase rate was high and the oxygen diffusion rate was high as the in-plane orientation Δφ was large. Therefore, by using a superconducting wire having an oxide superconducting layer having a large in-plane orientation Δφ as the connecting wire for connecting the ends of the connecting target wire which is the main wire of the connected superconducting wire, before connection or Oxygen heat treatment after connection can be advantageously performed. As a specific example, the in-plane orientation Δφ of the oxide superconducting layer of the connecting target wire, which is the main wire of the superconducting wire, is 4.2 °, and the in-plane orientation Δφ of the oxide superconducting layer of the connecting wire is 5. 3 ° can be mentioned. Further, when the in-plane orientation Δφ of the oxide superconducting layer is set to 4.0 ° or more, Ic can be increased after the heat treatment as compared with before the heat treatment. The conditions of the oxygen heat treatment are not limited to the examples of this example, and may be performed at a higher temperature or for a longer period of time, for example.

10, 20 ... Connection target wire (superconducting wire) 11,21 ... Connection target wire substrate, 12, 22 ... Connection target wire oxide superconducting layer, 13, 23 ... Connection target wire protection layer, 30 ... Connection Wire rod (superconducting wire), 31 ... Connection wire substrate, 32 ... Oxide superconducting layer of connecting wire, 41, 42, 43 ... Crystal orientation, 44, 45, 46 ... Crystal grain, 47 ... Grain boundary, 48 ... Dislocation group.

Claims (5)

A connection structure of a superconducting wire whose connection target wire having an oxide superconducting layer is connected via a connecting wire having an oxide superconducting layer.
The in-plane orientation Δφ perpendicular to the thickness direction of the oxide superconducting layer of the wire to be connected is 4.0 ° or more and less than 5.5 °.
The in-plane orientation Δφ perpendicular to the thickness direction of the oxide superconducting layer of the connecting wire is 0.5 ° or more larger than the in-plane orientation Δφ of the oxide superconducting layer of the connecting wire. Connection structure of superconducting wire. The connection target wire and the connection wire are each composed of a superconducting wire having the oxide superconducting layer on the substrate.
It is characterized in that the oxide superconducting layer of the connecting wire and the oxide superconducting layer of the connecting wire are arranged so as to face each other between the substrate of the connecting wire and the substrate of the connecting wire. The connection structure of the superconducting wire according to claim 1. The connection structure for a superconducting wire according to claim 1 or 2, wherein the oxide superconducting layer of the wire to be connected and the oxide superconducting layer of the connecting wire are connected so as to be in direct contact with each other. The connection structure for a conductive wire according to any one of claims 1 to 3, wherein the connecting wire is composed of a superconducting wire shorter than the connection target wire. A superconducting wire in which two or more wire to be connected are connected in the longitudinal direction.
A superconducting wire rod, characterized in that at least one place between the two or more connecting wire rods is composed of a connecting structure of the superconducting wire rod according to any one of claims 1 to 4.

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