JP2017010833A - Oxide superconducting wire material and manufacturing method of oxide superconducting wire material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide superconducting wire material having a protective layer low in boundary resistance with an oxide superconducting layer and surely protecting the oxide superconducting layer.SOLUTION: There is provided an oxide superconducting wire material having a laminate by laminating an intermediate layer and an oxide superconducting layer on a tape-like substrate, a first protective layer laminated on a main surface of the oxide superconducting layer of the laminate and a second protective layer laminated on a main surface of the first protective layer, where the first protective layer consists of recrystallized Ag or Ag alloy and the first protective layer contains amorphous Ag or Ag alloy. Thickness of the second protective layer may be 0.1 μm to 2 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an oxide superconducting wire and a method for producing an oxide superconducting wire.

  An oxide superconducting wire formed by laminating an oxide superconducting layer on a tape-like base material is known. Such an oxide superconducting wire includes a stabilization layer (hereinafter referred to as a protective layer) formed by sputtering on the main surface of the oxide superconducting layer (for example, Patent Document 1). The protective layer covers and protects the main surface of the oxide superconducting layer.

JP 2013-97889 A

As such a protective layer, Cu, Ag, or an alloy thereof is used.
Cu has a problem that it diffuses into the oxide superconducting layer and disturbs the composition balance of the oxide superconducting layer to deteriorate the superconducting characteristics. For this reason, although it is suitable to use Ag as a protective layer, since Ag is expensive, it is required to reduce the amount of use by forming a thin protective layer. On the other hand, the protective layer made of Ag has a problem in that pinholes are likely to occur when oxygen annealing treatment is performed to adjust the composition of the oxide superconducting layer after the protective layer is formed.
Therefore, the present inventor has made extensive studies and obtained knowledge for forming a protective layer made of Ag after the oxygen annealing treatment. However, when Ag film formation is performed after oxygen annealing, there is a problem that the interface resistance between the Ag layer and the superconducting layer increases.

  The present invention has been made in view of the above problems, and aims to provide an oxide superconducting wire having a low interface resistance with an oxide superconducting layer and having a protective layer that can reliably protect the oxide superconducting layer. To do.

In order to solve the above problems, a laminate in which an intermediate layer and an oxide superconducting layer are laminated on a tape-shaped substrate, and a first protective layer laminated on the main surface of the oxide superconducting layer of the laminate And a second protective layer laminated on the main surface of the first protective layer, wherein the first protective layer is made of recrystallized Ag or an Ag alloy, and the first protective layer is Including amorphous Ag or Ag alloy.
According to this configuration, the first protective layer made of recrystallized Ag or Ag alloy is laminated on the oxide superconducting layer. Ag or an Ag alloy is recrystallized by performing a heat treatment step (for example, an oxygen annealing treatment step) after film formation. Ag diffuses into the oxide superconducting layer in the heat treatment step to reduce the interface resistance between the oxide superconducting layer and the first protective layer. Further, Ag does not disturb the composition balance of the oxide superconducting layer even if it diffuses into the oxide superconducting layer, so that it does not deteriorate the superconducting characteristics of the oxide superconducting layer. On the other hand, Ag in the first protective layer may aggregate together with recrystallization to form pinholes. According to the above configuration, the second protective layer containing non-recrystallized amorphous Ag or Ag alloy covers the pinhole formed in the first protective layer and prevents the oxide superconducting layer from being exposed. be able to. Thereby, when providing another layer (Cu sputter layer, solder layer, plating layer, etc.) on the second protective layer, the metal component of the other layer does not diffuse into the oxide superconducting layer, Degradation of superconducting characteristics can be prevented.

In the above oxide superconducting wire, the thickness of the second protective layer may be not less than 0.1 μm and not more than 2 μm.
According to this structure, while suppressing the quantity of Ag used in a 2nd protective layer, the pinhole formed in the 1st protective layer can be covered reliably. Further, the second protective layer having such a thickness can be obtained by forming a film by sputtering. When a film having a thickness of 2 μm or more is formed by a single film formation process in the sputtering method, oxygen in the oxide superconducting layer may escape and deterioration of superconducting characteristics may occur. By setting the thickness of the second protective layer to 2 μm or less, the characteristics of the oxide superconducting wire are not deteriorated.

The oxide superconducting wire may further include a stabilizing layer that is made of a plating coating layer and surrounds the outer periphery.
The oxide superconducting wire may further include a stabilization layer made of a metal tape and surrounding the outer periphery with a solder layer interposed therebetween.
According to this configuration, the current characteristic of the oxide superconducting wire can be stabilized by bypassing the current at the time of overcurrent by the stabilization layer made of the metal tape or the plating coating layer. In addition, since the outer periphery is covered with the stabilizing layer, a structure in which moisture does not enter can be realized.

The oxide superconducting wire may further include a third protective layer made of Cu or a Cu alloy, which is laminated on the main surface of the second protective layer and is positioned below the stabilization layer.
According to this configuration, the second protective layer is covered with the third protective layer made of Cu or Cu alloy. When a metal tape is used as the stabilization layer, the second protective layer is covered with a third protective layer to suppress alloying between the second protective layer and the solder, and the second protective layer is brittle. Can be prevented. When a plating coating layer is used as the stabilization layer, the third protective layer protects the second protective layer from the plating solution.

The manufacturing method according to an embodiment of the oxide superconducting wire described above provides a laminate in which an intermediate layer and an oxide superconducting layer are laminated on a tape-shaped substrate, and the main surface of the oxide superconducting layer of the laminate In addition, a first protective layer forming step of forming a first protective layer made of Ag or an Ag alloy by sputtering, and a heat treatment for diffusing Ag constituting the first protective layer into the oxide superconducting layer And a second protective layer forming step of forming a second protective layer made of Ag or an Ag alloy on the main surface of the first protective layer by a sputtering method.
According to this configuration, Ag constituting the first protective layer is diffused into the oxide superconducting layer by the heat treatment step, and the interface resistance between the first protective layer and the oxide superconducting layer can be reduced. Moreover, the pinhole of the 1st protective layer which aggregated with recrystallization of the 1st protective layer by a heat treatment process can be covered with a 2nd protective layer. As a result, when other layers (solder layer, plated layer, etc.) are provided on the second protective layer, the components of the other layers are prevented from diffusing into the oxide superconducting layer, and the superconducting characteristics are deteriorated. Can be prevented.
Note that as the heat treatment step, oxygen annealing for supplying oxygen to the oxide superconducting layer may be performed.

  According to the oxide superconducting wire of the present invention, it is possible to provide an oxide superconducting wire having a protective layer that has low interface resistance with the oxide superconducting layer and can reliably protect the oxide superconducting layer.

1 is a cross-sectional perspective view schematically showing an oxide superconducting wire according to a first embodiment. It is a section inclination figure showing the oxide superconducting wire material of a 2nd embodiment typically. It is a section inclination figure showing typically the oxide superconducting wire material of a 3rd embodiment. The SEM image which image | photographed Ag layer of the oxide superconducting wire of the comparative example 1 is shown. The SEM image which image | photographed Ag layer of the oxide superconducting wire of the comparative example 2 is shown. The SEM image which image | photographed Ag layer of the oxide superconducting wire of an Example is shown. The SEM image which image | photographed the cross section of the oxide superconducting wire of an Example is shown.

  Hereinafter, embodiments of an oxide superconducting wire according to the present invention will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. The present invention is not limited to the following embodiment.

<First Embodiment>
FIG. 1 is a schematic cross-sectional view of the oxide superconducting wire 1 according to the first embodiment. The oxide superconducting wire 1 includes a laminated body 16 in which an intermediate layer 11 and an oxide superconducting layer 12 are laminated on a tape-shaped base material 10, and a main surface 12a of the oxide superconducting layer 12 of the laminated body 16. 1 protective layer 13, and a second protective layer 14 stacked on the main surface 13 a of the first protective layer 13.
In FIG. 1, the width direction of the wire is the X direction, the longitudinal direction is the Y direction, and the thickness direction is the Z direction.

  As the base material 10, a nickel alloy represented by Hastelloy (trade name, manufactured by Haynes, USA), an oriented Ni—W alloy in which a texture is introduced into a nickel alloy is applied.

The intermediate layer 11 is formed on the base material 10. As an example, the intermediate layer 11 may have a laminated structure of a diffusion prevention layer, an alignment layer, and a cap layer in order from the base material side, but one or both of the diffusion prevention layer and the bed layer may be omitted. .
The diffusion prevention layer is made of Si ₃ N ₄ , Al ₂ O ₃ , GZO (Gd ₂ Zr ₂ O ₇ ) or the like.
The bed layer is a layer for reducing the interfacial reactivity and obtaining the orientation of the film formed thereon. Y ₂ O ₃ , Er ₂ O ₃ , CeO ₂ , Dy ₂ O _3, Er ₂ O ₃ , Eu ₂ O ₃ , Ho ₂ O ₃ , La ₂ O _{3 and the} like.
The orientation layer is formed from a biaxially oriented material in order to control the crystal orientation of the cap layer thereon. As the material of the alignment layer, 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 Examples thereof include metal oxides such as O ₃ , Ho ₂ O ₃ , and Nd ₂ O ₃ . This alignment layer is preferably formed by an IBAD (Ion-Beam-Assisted Deposition) method.
The cap layer is formed on the surface of the above-described alignment layer and is made of a material that allows crystal grains to self-orient in the in-plane direction. Specifically, CeO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Gd _{2 O 3, ZrO 2, YSZ,} Ho 2 O 3, Nd 2 O 3, consist of LaMnO ₃ like. The film thickness of the cap layer can be formed in the range of 50 to 5000 nm.

The oxide superconducting layer 12 may be a known oxide superconductor, and specifically, REBa ₂ Cu ₃ O _7-X (RE is a rare earth element, Sc, Y, La, Ce). , Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu are represented. Examples of the oxide superconducting layer 12 include Y123 (YBa ₂ Cu ₃ O _7-X ) or Gd123 (GdBa ₂ Cu ₃ O _7-X ).

  Oxygen is supplied to the oxide superconducting layer 12 by an oxygen annealing process. The oxygen annealing treatment step is a heat treatment step performed at 300 ° C. to 500 ° C. for 5 to 20 hours in an oxygen atmosphere. Since the oxide superconductor layer 12 has a crystal structure in which oxygen is insufficient after film formation, the crystal structure can be adjusted by supplying oxygen to the oxide superconductor layer 12 by performing an oxygen annealing treatment step. .

  The first protective layer 13 is laminated on the main surface 12 a of the oxide superconducting layer 12. The first protective layer 13 is made of recrystallized Ag or an Ag alloy. The first protective layer 13 may be formed not only on the main surface 12 a of the oxide superconducting layer 12 but also on the side surface 16 b and the back surface 16 c of the stacked body 16.

  The first protective layer 13 serves to protect the oxide superconducting layer 12. Further, the first protective layer 13 bypasses overcurrent. In addition, the chemical reaction occurring between the oxide superconducting layer 12 and a layer provided on the upper surface of this layer is suppressed, and a part of the elements of one layer penetrates into the other layer and the composition is broken. It has functions such as preventing deterioration of superconducting properties.

The first protective layer 13 can be formed by sputtering, for example, at room temperature. The first protective layer 13 formed by sputtering includes amorphous (amorphous structure) Ag, but Ag is recrystallized by a heat treatment step (oxygen annealing treatment step) performed after the film formation. Ag in the first protective layer 13 diffuses into the oxide superconducting layer 12 in the process of recrystallization. The first protective layer 13 decreases the interface resistance with the oxide superconducting layer 12 by diffusing into the oxide superconducting layer 12. That is, the first protective layer 13 reduces the resistance between the oxide superconducting layer 12 and the layers that bypass the overcurrent (the first protective layer 13 and the second protective layer 14). Thereby, when an overcurrent occurs, the current flows smoothly from the oxide superconducting layer 12 side to the protective layer side, and heat generation of the oxide superconducting layer 12 is suppressed. Note that the interface resistance between the first protective layer 13 and the oxide superconducting layer 12 can be made 150 nΩ · cm ² or less by diffusing Ag of the first protective layer 13 into the oxide superconducting layer 12.

  The thickness of the first protective layer 13 during film formation by sputtering is preferably 0.2 μm or more and 1 μm or less. By setting the thickness of the first protective layer 13 to 0.2 μm or more, a sufficient amount of Ag is diffused into the oxide superconducting layer 12 to reduce the interface resistance between the first protective layer 13 and the oxide superconducting layer 12. it can. Moreover, the thickness of the 1st protective layer 13 shall be 1 micrometer or less, the quantity of Ag used for the 1st protective layer 13 can be suppressed, and cost reduction can be aimed at.

  The second protective layer 14 is laminated on the main surface 13 a of the first protective layer 13. The second protective layer 14 includes amorphous (amorphous structure) Ag or an Ag alloy. The second protective layer 14 may be formed not only on the main surface 13 a of the first protective layer 13 but also on the side surface 16 b and the back surface 16 c of the stacked body 16.

  The second protective layer 14 protects the oxide superconducting layer 12 together with the first protective layer 13 and further bypasses overcurrent. In the first protective layer 13, Ag may aggregate together with recrystallization to form pinholes. The second protective layer 14 covers the pinhole formed in the first protective layer 13, prevents the oxide superconducting layer 12 from being exposed, and reliably protects the oxide superconducting layer 12.

  The second protective layer 14 can be formed by sputtering, for example, at room temperature. The second protective layer 14 formed by the sputtering method includes amorphous (amorphous structure) Ag. After the second protective layer 14 is formed, the second protective layer 14 is maintained in a state containing amorphous Ag in order not to perform a heat treatment process similar to the oxygen annealing process.

The thickness of the second protective layer 14 is preferably 0.1 μm or more and 2 μm or less. By setting the thickness of the second protective layer 14 to 2 μm or less, the amount of Ag used can be suppressed and the cost can be reduced. Further, as will be described later, when the second protective layer 14 exceeding 2 μm is formed by sputtering, oxygen may escape from the oxide superconducting layer 12 and the superconducting characteristics may be deteriorated.
By setting the second protective layer 14 to 0.1 μm or more, when the pin hole is formed in the first protective layer 13, the pin hole can be reliably covered and the oxide superconducting layer 12 can be reliably protected. .

The second protective layer 14 can be formed by a film forming method such as a sputtering method at room temperature. An example of forming the second protective layer 14 by sputtering will be described below.
First, the laminated body 16 in which the target made of Ag or an Ag alloy and the first protective layer 13 are formed is placed in a processing vessel in which the inside is decompressed to introduce Ar gas. At this time, the first protective layer 13 is arranged in the target direction. Next, plasma is generated by ionizing Ar gas by applying a voltage to the target and causing it to discharge. The Ar ions generated in the plasma sputter the target to sputter Ag (or Ag alloy) sputtered particles from the target, and the sputtered particles are deposited on the first protective layer 13 to form the second. A protective layer 14 is formed.

  In the film formation by the sputtering method, when sputtered particles (Ag particles) collide with the film formation target (first protective layer 13), the kinetic energy at the time of collision is converted into thermal energy, and the film formation target temperature rises. When this heat is transmitted to the oxide superconducting layer 12 and the temperature of the oxide superconducting layer 12 rises, oxygen in the oxide superconducting layer 12 may escape and the crystal structure may be damaged, leading to deterioration of superconducting characteristics.

  The temperature rise of the deposition target has a correlation with the film thickness (film formation rate) of the second protective layer 14 formed at a time. In order to suppress deterioration of the superconducting characteristics of the oxide superconducting layer 12, it is preferable that the thickness of the second protective layer 14 formed in one film forming step is 2 μm or less. The second protective layer 14 having a thickness exceeding 2 μm may be formed while suppressing deterioration of characteristics such as superconductivity of the oxide superconducting layer 12 by performing a plurality of film forming steps. However, when the film is formed a plurality of times, the cost increases due to an increase in the amount of Ag used and the complexity of the film formation process. Therefore, it is preferable to form the second protective layer 14 by a single film formation.

  Further, due to the temperature rise of the deposition target in the formation of the second protective layer 14 by sputtering, Ag recrystallization of the second protective layer 14 immediately after the film formation occurs. However, since the heat generation due to the formation of the second protective layer 14 is slight, only a part of the Ag of the second protective layer 14 is recrystallized and an amorphous region remains. Since the second protective layer 14 is only partially recrystallized, Ag aggregation does not progress and pinholes are not generated in the second protective layer. For this reason, the second protective layer 14 can reliably cover the pinhole of the first protective layer 13.

<Manufacturing method>
A method for manufacturing the oxide superconducting wire 1 will be described.
First, a laminate 16 in which an intermediate layer 11 and an oxide superconducting layer 12 are formed on a tape-like base material 10 is prepared.
Next, the first protective layer 13 is formed on the main surface 12a of the oxide superconducting layer 12 of the stacked body 16 by sputtering (first protective layer forming step). At this stage, the first protective layer 13 contains amorphous Ag.

  Next, an oxygen annealing treatment step (heat treatment step) for supplying oxygen to the oxide superconducting layer 12 is performed. Through the oxygen annealing process, all of the amorphous Ag in the first protective layer 13 is recrystallized. In addition, Ag constituting the first protective layer 13 diffuses into the main surface 12 a of the oxide superconducting layer 12 by the oxygen annealing treatment step. Due to the diffusion of Ag, the interface resistance between the first protective layer 13 and the oxide superconducting layer 12 is reduced.

Next, the second protective layer 14 made of Ag or an Ag alloy is formed on the main surface 13a of the first protective layer 13 by sputtering (second protective layer film forming step).
Through the above steps, the oxide superconducting wire 1 can be manufactured.

<Effect>
According to the oxide superconducting wire 1 of the present embodiment, Ag is diffused into the oxide superconducting layer 12 because the oxide superconducting layer 12 is formed with the first protective layer 13 recrystallized through heat treatment. . Thereby, the interface resistance between the oxide superconducting layer 12 and the first protective layer 13 can be reduced to 150 nΩ · cm ² or less. The first protective layer 13 is covered with a second protective layer 14. Therefore, even if pinholes are formed in the first protective layer 13 due to Ag aggregation due to recrystallization of the first protective layer 13, the second protective layer 14 covers the pinholes and is oxidized. The physical superconducting layer 12 can be prevented from being exposed.
In addition, since the 2nd protective layer 14 consists of Ag or an Ag alloy, even if Ag diffuses in the oxide superconducting layer 12, a composition of an oxide superconductor is not destroyed. On the other hand, for example, when Cu is used as the second protective layer, Cu contacts the oxide superconducting layer in the pinhole of the first protective layer 13. When Cu comes into contact with the oxide superconducting layer, it diffuses and affects the composition of the superconductor constituting the oxide superconducting layer, possibly leading to a decrease in superconducting characteristics. By using Ag or an Ag alloy as the second protective layer 14, it is possible to provide the oxide superconducting wire 1 in which the superconducting characteristics do not deteriorate.

Second Embodiment
The schematic diagram of the cross section of the oxide superconducting wire 20 of 2nd Embodiment is shown in FIG. Hereinafter, the oxide superconducting wire 20 will be described with reference to FIG. In addition, about the component of the same aspect as the above-mentioned embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

The oxide superconducting wire 20 includes a laminate 16 having a base material 10, an intermediate layer 11, and an oxide superconducting layer 12, a first protective layer 13, a second protective layer 14, and a third protective layer 23. And a solder layer 21 and a stabilization layer 22. The oxide superconducting wire 20 of the second embodiment is described as having a configuration in which a third protective layer 23, a solder layer 21, and a stabilizing layer 22 are further provided around the oxide superconducting wire 1 of the first embodiment. it can.
Hereinafter, in the description of the second and third embodiments, the wire in the same mode as the oxide superconducting wire 1 (see FIG. 1) of the first embodiment is referred to as a preliminary oxide superconducting wire 1A.

  The third protective layer 23 is formed by surrounding the outer periphery of the preliminary oxide superconducting wire 1A. That is, the third protective layer 23 is formed on the main surface 14 a of the second protective layer 14 and the side surface 16 b and the back surface 16 c of the stacked body 16. Note that the third protective layer 23 may be formed only on the main surface 14 a of the second protective layer 14. The third protective layer 23 is made of Cu or a Cu alloy. The third protective layer 23 protects the oxide superconducting layer 12 together with the first protective layer 13 and the second protective layer 14, and further bypasses overcurrent.

  Further, the third protective layer 23 prevents the metal (for example, Sn) constituting the solder layer 21 from diffusing into the second protective layer 14 and being alloyed. When the second protective layer 14 containing Ag and the solder layer 21 come into contact with each other, the metal constituting the solder (Sn as an example) diffuses into the second protective layer 14 to form an alloy, so that the second protective layer 14 Becomes brittle. The third protective layer 23 is provided between the second protective layer 14 and the solder layer 21, thereby preventing the diffusion of solder to the second protective layer 14 and increasing the strength of the second protective layer 14. Can be maintained.

The thickness of the third protective layer 23 is not less than 0.3 μm and not more than 2.1 μm. By setting the thickness of the third protective layer 23 to 2.1 μm or less, the amount of Cu used can be suppressed and the cost can be reduced. In addition, by setting the thickness of the third protective layer 23 to 2.1 μm or less, even when the third protective layer 23 is formed by sputtering, oxygen escape due to heat of the film formation process is performed. The superconducting characteristics are not deteriorated by suppressing.
By making the 3rd protective layer 23 0.3 micrometer or more, peeling of the stabilization layer 22 by alloying of Cu can be prevented. Although Cu is not as remarkable as Ag, it is alloyed with the metal (for example, Sn) which comprises the solder layer 21, and becomes brittle. When this embrittlement reaches the entire thickness of the third protective layer 23, the stabilization layer 22 is easily peeled off starting from the boundary between the second protective layer 14 and the third protective layer 23. Since the diffusion of the metal constituting the solder into Cu or Cu alloy is less than 0.3 μm, the stabilization layer 22 is peeled off by Cu alloying by setting the third protective layer 23 to 0.3 μm or more. Can be prevented.

  The solder layer 21 is disposed between the third protective layer 23 and the stabilization layer 22 made of a metal tape, and joins them. Conventionally known solder can be used for the solder layer 21, but it is preferable to use solder having a melting point of 300 ° C. or lower. Thereby, since it becomes possible to solder a metal tape and the 3rd protective layer 23 at the temperature of 300 degrees C or less, it can suppress that the characteristic of the oxide superconducting layer 12 deteriorates with the heat of soldering.

  The stabilization layer 22 is made of a metal tape solder-bonded to the third protective layer 23. The stabilization layer 22 covers the preliminary oxide superconducting wire 1 </ b> A in a substantially C shape in cross section via the third protective layer 23 and the solder layer 21. The portion not covered with the metal tape (that is, between the side end portions of the metal tape) is buried with the melted solder layer 21 to form an embedded portion 21b.

  The stabilization layer 22 wraps the metal tape from the main surface side (the oxide superconducting layer 12 side) of the preliminary oxide superconducting wire 1A so as to form a substantially C shape in cross-section while melting the solder layer 21 by a roll. It can be formed by bending. In addition, it is preferable to use what gave solder plating beforehand to one side used as a metal tape on both surfaces or an inner side. In this case, solder plating becomes the solder layer 21. By processing in this way, the melted solder (solder plating previously applied to the metal tape) is concentrated in the gap between the side end portions of the metal tape to form the embedded portion 21b.

  The material of the metal tape constituting the stabilization layer 22 is not particularly limited as long as it has good conductivity. For example, it is preferable to use a copper alloy such as copper, brass (Cu—Zn alloy), a Cu—Ni alloy, or a relatively inexpensive material such as stainless steel. To copper. The stabilization layer 22 serves as a bypass that commutates overcurrent. Further, when the oxide superconducting wire 20 is used for a superconducting fault current limiter, the stabilization layer 22 is used for instantaneously suppressing an overcurrent generated when a quench occurs and the state is changed to a normal conducting state. In this case, the material used for the stabilization layer 22 is preferably a high-resistance metal such as a Ni-based alloy such as Ni—Cr.

In the oxide superconducting wire 20 of the second embodiment, since the stabilization layer 22 is formed in the transverse cross section of the preliminary oxide superconducting wire 1A, a structure that does not allow moisture to enter inside can be realized. In addition, a stabilization layer can be formed by spirally winding a metal tape around the outer periphery of the preliminary oxide superconducting wire 1A via the third protective layer 23 and the solder layer 21.
In the oxide superconducting wire 20 of the present embodiment, the third protective layer 23 can be omitted. That is, the preliminary oxide superconducting wire 1 </ b> A may be directly surrounded by the stabilization layer 22 via the solder layer 21. When the third protective layer 23 is omitted, the second protective layer 14 may be formed not only on the main surface 13 a of the first protective layer 13 but also on the side surface 16 b and the back surface 16 c of the stacked body 16. Even in such a case, a structure that does not allow moisture to enter the inside can be realized.

<Third Embodiment>
FIG. 3 is a schematic cross-sectional view of the oxide superconducting wire 30 according to the third embodiment. Hereinafter, the oxide superconducting wire 30 will be described with reference to FIG. In addition, about the component of the same aspect as the above-mentioned embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The oxide superconducting wire 30 includes a laminate 16 having a base material 10, an intermediate layer 11 and an oxide superconducting layer 12, a first protective layer 13, a second protective layer 14, and a third protective layer 23. And a plating coating layer (stabilization layer) 32. In the oxide superconducting wire 30 of the third embodiment, a third protective layer 23 similar to that of the second embodiment is further formed around the oxide superconducting wire 1 (preliminary oxide superconducting wire 1A) of the first embodiment. Further, it can be described that the surface of the third protective layer 23 is provided with a plating coating layer 32 (stabilization layer) by a plating method.

  The plating coating layer 32 functions as a stabilization layer. The plating coating layer 32 is made of a highly conductive metal material. The plating coating layer 32 serves as a bypass for commutating overcurrent. Since the plating coating layer 32 completely blocks the preliminary oxide superconducting wire 1A from the outside, it is possible to reliably prevent moisture from entering the oxide superconducting layer 12.

  Examples of the metal used for the plating coating layer 32 include copper, nickel, gold, silver, chromium, and tin. Among these metals, one or a combination of two or more can be used. Moreover, when using the oxide superconducting wire 30 for a superconducting fault current limiter, the material used for the plating coating layer 32 includes, for example, a high resistance metal such as a Ni-based alloy such as Ni—Cr.

The plating coating layer 32 is formed by, for example, an electroplating method. That is, the plating coating layer 32 is formed by applying electricity to the surface of the preliminary oxide superconducting wire 1A, which is the object to be plated, with the object to be plated immersed in a plating solution. The third protective layer 23 covers the second protective layer 14 to protect the second protective layer from the plating solution. Further, as shown in the present embodiment, when the third protective layer 23 is formed so as to surround the outer periphery of the preliminary oxide superconducting wire 1A, the current flows uniformly on the surface, and the uniform thickness The plating coating layer 32 can be formed.
In the oxide superconducting wire 30, the third protective layer 23 can be omitted. In other words, the preliminary oxide superconducting wire 1 </ b> A may be directly surrounded by the plating coating layer 32. When the third protective layer 23 is omitted, the second protective layer 14 may be formed not only on the main surface 13 a of the first protective layer 13 but also on the side surface 16 b and the back surface 16 c of the stacked body 16. Even in such a case, it is possible to realize a structure that suppresses moisture intrusion into the interior.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further in detail, this invention is not limited to these Examples.
<Preparation of sample>
First, the surface of a tape-like base material having a width of 10 mm, a thickness of 0.075 mm, and a length of 10 m made of Hastelloy C-276 (trade name of Haynes, USA) was polished using alumina having an average particle diameter of 3 μm. Next, the surface of the substrate was degreased and washed with acetone.
Next, Al ₂ O ₃ (diffusion prevention layer; film thickness 100 nm) is formed on the main surface of the substrate by sputtering, and Y ₂ O ₃ (bed layer; film thickness 30 nm) is formed thereon by ion beam sputtering. ) Was formed. Next, MgO (alignment layer; film thickness: 5 to 10 nm) is formed on the bed layer by an ion beam assisted deposition method (IBAD method), and then CeO ₂ (cap layer; by a pulse laser deposition method (PLD method). A film thickness of 500 nm) was formed. Next, GdBa ₂ Cu ₃ O _7-x (oxide superconducting layer; film thickness: 2.0 μm) was formed on the CeO ₂ layer by the PLD method.
The sample A produced in this way is commonly used in the following sample production.

(Comparative Example 1)
1 μm of Ag was formed on the oxide superconducting layer by sputtering for the sample A described above. Next, this sample was subjected to oxygen annealing in an oxygen atmosphere at 500 ° C. for 10 hours, and taken out after 26 hours of furnace cooling.
The oxide superconducting wire of Comparative Example 1 was obtained through the above procedure.

  In FIG. 4, the SEM image which image | photographed Ag layer of the oxide superconducting wire of the comparative example 1 is shown. As shown in the SEM image of FIG. 4, Ag is recrystallized by the heat treatment process accompanying oxygen annealing. Moreover, Ag is aggregated by recrystallization and the oxide superconducting layer is exposed. For this reason, in the oxide superconducting wire of Comparative Example 1, the Ag layer cannot sufficiently protect the oxide superconducting layer.

(Comparative Example 2)
The sample A described above was subjected to oxygen annealing in an oxygen atmosphere at 500 ° C. for 10 hours, and then taken out after cooling in the furnace for 26 hours. Next, 1 μm of Ag was formed on the oxide superconducting layer by sputtering.
The oxide superconducting wire of Comparative Example 2 was obtained through the above procedure.

  In FIG. 5, the SEM image which image | photographed Ag layer of the oxide superconducting wire of the comparative example 2 is shown. As shown in the SEM image of FIG. 5, the Ag layer covers the oxide superconducting layer without being agglomerated while maintaining an amorphous state.

(Example)
A 0.5 μm Ag film was formed on the oxide superconducting layer by sputtering (corresponding to the first protective layer) for the sample A described above. Next, this sample was subjected to oxygen annealing in an oxygen atmosphere at 500 ° C. for 10 hours, and taken out after 26 hours of furnace cooling. A 0.5 μm thick Ag film was formed on the oxide superconducting layer by sputtering (corresponding to the second protective layer).
Through the above procedure, the oxide superconducting wire of the example was obtained.

FIG. 6 shows an SEM image obtained by photographing the Ag layer of the oxide superconducting wire of Example, and FIG. 7 shows an SEM image obtained by photographing a cross section. As shown in the SEM image of FIG. 6, the Ag layer completely covers the oxide superconducting layer to prevent exposure. Further, the surface of the second protective layer has an uneven shape following the surface shape of the aggregated first protective layer. Furthermore, as shown in the SEM image of FIG. 7, the Ag layer as the second protective layer contains amorphous, but part of Ag is recrystallized. This is considered to be because a part of Ag was recrystallized by heat during film formation.
In FIG. 7, the thin film portion formed on the second protective layer is carbon deposited when the cross section is processed by FIB (focused ion beam).

<Evaluation>
(Critical current characteristics)
The critical current characteristics of Comparative Example 1, Comparative Example 2, and Example were measured.
Three oxide superconducting wires of Comparative Example 1, Comparative Example 2, and Example were prepared, and their critical current values (Ic) were measured using a four-terminal method. Table 1 shows the average values of Ic of the three oxide superconducting wires.

(Interface resistance)
The interface resistance between the oxide superconducting wire and the Ag layer was measured.
In Comparative Example 1, Comparative Example 2, and Examples, the Ag layers of the oxide superconducting wires were opposed to each other and soldered to measure the electrical resistance. Table 1 shows the results of calculating the resistance value obtained by subtracting the electrical resistance value of the solder from each electrical resistance value as the interface resistance between the oxide superconducting wire and the Ag layer.

  Regarding the critical current value (Ic), as shown in Table 1, there is no significant difference in the critical resistance values of Comparative Example 1, Comparative Example 2, and Example. That is, it was confirmed that even when Ag film formation was performed after oxygen annealing as in Example and Comparative Example 2, it was possible to perform Ag film formation without causing oxygen to escape from the oxide superconducting layer. It was done.

  Regarding the interfacial resistance, as shown in Table 1, it can be seen that the oxide superconducting wires of Comparative Example 1 and Examples have a lower interfacial resistance value between the oxide superconducting layer and the Ag layer than Comparative Example 2. This indicates that Ag was diffused into the oxide superconducting layer by the heat treatment step (oxygen annealing) step after the Ag film formation, thereby suppressing the interface resistance.

  From the imaging photographs of the surface (FIGS. 4 to 7) and the measurement results of the critical current value and the interface resistance value shown in Table 1, the superiority of the oxide superconducting wire of the example was confirmed.

  Although the embodiments of the present invention have been described above, the configurations and combinations thereof in the embodiments are examples, and the addition, omission, replacement, and other configurations of the configurations are within the scope not departing from the spirit of the present invention. It can be changed. Further, the present invention is not limited by the embodiment.

DESCRIPTION OF SYMBOLS 1, 20, 30 ... Oxide superconducting wire, 1A ... Preliminary oxide superconducting wire, 10 ... Base material, 11 ... Intermediate layer, 12 ... Oxide superconducting layer, 13 ... First protective layer (Ag layer), 14 ... Second protective layer (Ag layer), 16 ... laminate, 21 ... solder layer, 22 ... stabilization layer (metal tape), 23 ... third protective layer (Cu layer), 32 ... stabilization layer (plating coating) layer)

Claims (6)

A laminate in which an intermediate layer and an oxide superconducting layer are laminated on a tape-shaped substrate;
A first protective layer laminated on the main surface of the oxide superconducting layer of the laminate;
A second protective layer laminated on the main surface of the first protective layer,
The first protective layer is made of recrystallized Ag or an Ag alloy,
The first protective layer is an oxide superconducting wire containing amorphous Ag or an Ag alloy.   2. The oxide superconducting wire according to claim 1, wherein the thickness of the second protective layer is 0.1 μm or more and 2 μm or less.   The oxide superconducting wire according to claim 1, further comprising a stabilizing layer made of a plating coating layer and surrounding the outer periphery.   The oxide superconducting wire according to claim 1 or 2, further comprising a stabilization layer made of a metal tape and surrounding the outer periphery with a solder layer interposed therebetween.   5. The oxide superconducting wire according to claim 3, further comprising a third protective layer made of Cu or a Cu alloy, which is laminated on a main surface of the second protective layer and is located below the stabilization layer. Prepare a laminate in which an intermediate layer and an oxide superconducting layer are laminated on a tape-shaped substrate,
A first protective layer forming step of forming a first protective layer made of Ag or an Ag alloy by sputtering on the main surface of the oxide superconducting layer of the laminate;
A heat treatment step of diffusing Ag constituting the first protective layer into the oxide superconducting layer;
A method for producing an oxide superconducting wire, comprising: a second protective layer forming step of forming a second protective layer made of Ag or an Ag alloy on the main surface of the first protective layer by a sputtering method.