JP2022168627A - Oxide superconducting wire - Google Patents

Abstract

To provide an oxide superconducting wire that can reduce electric resistance between a superconductor layer and a protective layer, or a method for producing such an oxide superconducting wire.SOLUTION: An oxide superconducting wire 10 has a substrate 11, a superconductor layer 13 and a protective layer 15. The superconductor layer 13 is formed from an oxide superconductor and is in contact with the protective layer 15. The superconductor layer 13 includes silver and an oxide superconductor. The content of silver in the superconductor layer 13 is from 4.0 vol% to 27.2 vol% relative to the total volume of the superconductor layer 13.SELECTED DRAWING: Figure 1

Description

The present invention relates to an oxide superconducting wire.

Patent Document 1 discloses an oxide superconducting wire comprising a substrate, an intermediate layer, a superconductor layer made of an oxide superconductor, and a protective layer made of silver. A protective layer is formed on the superconductor layer. The protective layer has functions such as bypassing an overcurrent that occurs at the time of an accident and suppressing a chemical reaction that occurs between the superconductor layer and a layer provided on the protective layer.

JP 2017-10833 A

In the structure of Patent Document 1, the oxide superconductor and silver, which are different kinds of materials, are joined at the interface between the superconductor layer and the protective layer. As described above, in a junction (heterojunction) between dissimilar materials, the electrical resistance between the superconductor layer and the protective layer is large, so there is a problem that a bypass current is difficult to flow from the superconductor layer to the protective layer. Also, when connecting an oxide superconducting wire to an input/output electrode such as a superconducting coil, or when connecting oxide superconducting wires to each other, the electrical resistance between the superconducting layer and the protective layer affects the magnitude of the loss. contribute significantly.

It is an object of the present invention to provide an oxide superconducting wire capable of reducing the electrical resistance between the superconducting layer and the protective layer.

In order to solve the above problems, an oxide superconducting wire according to one aspect of the present invention includes a substrate, a superconducting layer laminated above the substrate, and a superconducting layer laminated on the superconducting layer and formed of silver. and a protective layer. The superconductor layer is made of an oxide superconductor and is in contact with the protective layer. The superconductor layer contains silver and an oxide superconductor. The content of silver contained in the superconductor layer is in the range of 4.0 to 27.2 vol % with respect to the entire superconductor layer.

According to the above aspect, the superconductor layer contains silver having a content in the range of 4.0 to 27.2 vol % with respect to the entire superconductor layer. As a result, the silver contained in the superconductor layer and the silver of the protective layer are bonded. In other words, the silver-to-silver homojunction is formed between the superconductor layer and the protective layer. Thereby, the electrical resistance between the superconductor layer and the protective layer can be reduced.

In the superconductor layer of the oxide superconducting wire according to one aspect of the present invention, silver particles in which the silver aggregates may be dispersed.
As a result, the superconductor layer is formed so that silver particles in which silver aggregates are dispersed, so that the electrical resistance between the superconductor layer and the protective layer can be reduced.

In the superconductor layer of the oxide superconducting wire according to one aspect of the present invention, the diameter of the silver particles may be in the range of 0.3 to 1.0 μm.
Thereby, the electrical resistance between the superconductor layer and the protective layer can be reduced.

In the oxide superconducting wire according to one aspect of the present invention, the surface of the superconducting layer in contact with the protective layer may have an arithmetic average roughness Ra in the range of 39.8 to 103.4 nm.
Here, "the surface of the superconducting layer in contact with the protective layer" is the surface that is the interface between the protective layer and the superconducting layer.
This increases the contact area between the superconducting layer and the protective layer, thereby reducing the electrical resistance between the superconducting layer and the protective layer.

In the oxide superconducting wire according to one aspect of the present invention, the superconductor layer may have a critical current density in the range of 0.2 to 1.8 MA/cm ² .
Thus, by setting the critical current density of the superconductor layer in the range of 0.2 to 1.8 MA/cm ² , it is possible to realize an oxide superconducting wire having a high critical current value.

According to the above aspect of the present invention, it is possible to provide an oxide superconducting wire capable of reducing the electrical resistance between the superconducting layer and the protective layer, or a method for producing such an oxide superconducting wire. .

1 is a cross-sectional view of an oxide superconducting wire according to an embodiment; FIG. 1 is a schematic diagram of a PLD device; FIG. FIG. 2 is a diagram showing a manufacturing process of the oxide superconducting wire of FIG. 1; It is a figure which shows the process following FIG. 3A. It is a figure which shows the process following FIG. 3B. It is a figure which shows the process following FIG. 3C.

The oxide superconducting wire of this embodiment will be described below with reference to the drawings.
As shown in FIG. 1, oxide superconducting wire 10 has laminate 16 in which substrate 11, intermediate layer 12, superconductor layer 13, and protective layer 15 are laminated in this order.

In this embodiment, an oxide superconducting wire 10 having an intermediate layer 12 will be described. Note that the intermediate layer 12 is not an essential component in the oxide superconducting wire 10 . If the substrate 11 itself has orientation, the superconducting layer 13 may be laminated on the substrate 11 without forming the intermediate layer 12 on the substrate 11 .

The substrate 11 is a tape-shaped metal substrate. Specific examples of metals constituting the metal substrate include nickel alloys represented by Hastelloy (registered trademark), stainless steel, and oriented Ni—W alloys in which a texture is introduced into a nickel alloy. The dimensions of the substrate 11 are, for example, 10 mm wide, 0.1 mm thick, and 1000 mm long.

The intermediate layer 12 may have a multilayer structure, and may have, for example, a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, etc. in order from the substrate 11 side to the superconductor layer 13 side. These layers are not necessarily provided one by one, and some layers may be omitted, or two or more layers of the same kind may be repeatedly laminated. Intermediate layer 12 may be a metal oxide. By forming the superconductor layer 13 on the intermediate layer 12 excellent in orientation, it becomes easy to obtain the superconductor layer 13 excellent in orientation.

A superconductor layer 13 is laminated above the substrate 11 . In this embodiment, the superconductor layer 13 is laminated on the intermediate layer 12 . The superconductor layer 13 is in contact with the intermediate layer 12 and the protective layer 15 .
Superconductor layer 13 contains silver and an oxide superconductor.
Examples of oxide superconductors include RE-Ba-Cu-O-based oxide superconductors represented by the general formula REBa ₂ Cu ₃ O _y (RE123). The rare earth element RE includes one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In the general formula of RE123, y is 7-x (the amount of oxygen deficiency). The thickness of the superconductor layer 13 is, for example, approximately 2 μm. The superconducting layer 13 is preferably formed with the crystal orientation adjusted so as to develop current anisotropy. Specifically, when the c-axis of the crystal is oriented perpendicular to the surface (film formation surface) of the substrate 11, and the a-axis or b-axis through which current easily flows is oriented in the longitudinal direction of the substrate 11, the film is formed. good. This makes it possible to obtain good critical current characteristics.

In general, the oxide superconducting wire 10 has the property that the critical current characteristics are lowered in a magnetic field. In order to suppress the deterioration of critical current characteristics in a magnetic field, artificial pins may be introduced into the superconductor layer 13 to suppress the movement of magnetic flux lines. For example, artificial pinned nanorods of BaZrO ₃ (BZO), BaSnO ₃ (BSO), BaHfO ₃ (BHO) may be introduced into the superconductor layer 13 .

In FIG. 1, oxide superconducting wire 10 has interface 14 located between superconducting layer 13 and protective layer 15 . At the interface 14, the silver of the protective layer 15 and the silver contained in the superconductor layer 13 are bonded.

The content of silver contained in superconductor layer 13 is in the range of 4.0 to 27.2 vol % with respect to the entire superconductor layer 13 . In this way, the superconductor layer 13 contains silver, which is the same material as the constituent material of the protective layer 15 to be described later, so that the electrical resistance between the superconductor layer 13 and the protective layer 15 can be reduced. The content of silver contained in superconducting layer 13 can be specified by, for example, ICP emission spectroscopic analysis.
Hereinafter, the electrical resistance between the superconducting layer 13 and the protective layer 15 is simply referred to as "interlayer resistance R".

The protective layer 15 has functions such as bypassing an overcurrent generated at the time of an accident, suppressing a chemical reaction occurring between the superconducting layer 13 and a layer provided on the protective layer 15, and the like. The protective layer 15 is made of silver (Ag). The protective layer 15 can be formed by a sputtering method or the like. The thickness of the protective layer 15 is, for example, in the range of 1-30 μm.

The silver contained in the superconductor layer 13 is dispersed in the superconductor layer 13 in the form of aggregated silver particles. The diameter of silver particles, which are aggregates of silver atoms, is, for example, in the range of 0.3 to 1.0 μm. A plurality of silver particles are aggregated in the superconductor layer 13 . Thus, a plurality of silver particles are present between superconductor layer 13 and protective layer 15 .
Some of the plurality of silver particles dispersed in superconductor layer 13 are integrated with protective layer 15 . Moreover, the plurality of silver particles contained in superconducting layer 13 do not exist near the interface between intermediate layer 12 and superconducting layer 13 . The silver particles are located at a distance of 0.2 to 1.0 μm from the surface of the intermediate layer 12 toward the protective layer 15 .

In the superconducting layer 13, the surface roughness (arithmetic mean roughness Ra) of the surface of the superconducting layer 13 in contact with the protective layer 15 is, for example, in the range of 39.8 to 103.4 nm.
The critical current density of the superconducting layer 13 obtained from the critical current Ic flowing in the longitudinal direction of the oxide superconducting wire 10 is, for example, in the range of 0.2 to 1.8 MA/cm ² .

As described above, the oxide superconducting wire 10 of the present embodiment includes the substrate 11, the intermediate layer 12 laminated on the substrate 11, the superconducting layer 13 laminated on the intermediate layer 12, and the superconducting layer a protective layer 15 laminated on 13 and containing silver. Superconductor layer 13 contains silver and an oxide superconductor. Furthermore, the content of silver contained in superconductor layer 13 is in the range of 4.0 to 27.2 vol % with respect to the entire superconductor layer 13 . According to this configuration, the silver of superconductor layer 13 and the silver of protective layer 15 are bonded. In other words, the superconducting layer 13 and the protective layer 15 are homojunctions of silver. Thereby, the electrical resistance (interlayer resistance R) between the superconductor layer 13 and the protective layer 15 can be reduced.

Since the superconductor layer 13 contains silver, the surface roughness (arithmetic surface roughness Ra) of the surface of the superconductor layer 13 in contact with the protective layer 15 is increased. The surface roughness (arithmetic surface roughness Ra) of the superconductor layer 13 is in the range of 39.8 to 103.4 nm. Thereby, the contact area between the superconductor layer 13 and the protective layer 15 is increased, and the electrical resistance between the superconductor layer 13 and the protective layer 15 is reduced.

Also, the critical current density of the superconductor layer 13 is in the range of 0.2 to 1.8 MA/cm ² . As a result, not only can the interlayer resistance R be greatly reduced, but also an oxide superconducting wire having a high critical current value can be realized.

Next, an example of a method for manufacturing the oxide superconducting wire 10 configured as described above will be described. The manufacturing method described below is merely an example, and other manufacturing methods may be employed.

First, the PLD (Pulsed Laser Deposition) method will be described. The PLD method uses a PLD device 20 as shown in FIG. The PLD device 20 has a light source 21 and a condenser lens 22 . The light source 21 emits laser light L. As shown in FIG. The condensing lens 22 converges the laser light L onto the surface 23 a of the target 23 . As a result, constituent particles of the target 23 are ejected or evaporated to generate a plume 24 . The constituent particles of the target 23 contained in the plume 24 are deposited on the layered object 25 to form a thin film of the constituent particles on the surface of the layered object 25 . Therefore, by changing the composition of the constituent particles of the target 23, the composition of the thin film formed on the layered object 25 can be appropriately changed. Although FIG. 2 shows a state in which thin films are simultaneously formed on a plurality of stacking objects 25, the number of stacking objects 25 may be one.

When manufacturing the oxide superconducting wire 10, a substrate 11 is prepared as shown in FIG. 3A.
Next, as shown in FIG. 3B, the intermediate layer 12 is laminated on the substrate 11 . The intermediate layer 12 may be formed by the PLD method or other known methods.

Next, as shown in FIG. 3C, superconductor layer 13 is laminated on intermediate layer 12 . The superconductor layer 13 is formed with c-axis orientation (orientation in the thickness direction) by the PLD method. At this time, the substrate 11 (FIG. 3B) with the intermediate layer 12 formed on the surface becomes the stacking object 25 in FIG. A block of an oxide superconductor containing silver that constitutes the superconductor layer 13 is the target 23 in FIG.

Next, as shown in FIG. 3D, a protective layer 15 is laminated on the superconductor layer 13 . The protective layer 15 is formed by a sputtering method or the like. Thereby, the laminated body 16 is obtained.

Next, oxygen annealing treatment is performed. More specifically, the laminate 16 is heated to 300-500° C. in an oxygen atmosphere. The oxygen annealing treatment may be performed after forming the superconductor layer 13 (before forming the protective layer 15). By performing the oxygen annealing, the superconducting layer 13 is doped with oxygen, so that the superconducting layer 13 can exhibit superconductivity.

As described above, the method for manufacturing the oxide superconducting wire 10 of the present embodiment includes the step of laminating the intermediate layer 12 on the substrate 11, and forming the superconducting layer 13 containing silver and an oxide superconductor by the PLD method. lamination on superconductor layer 13; lamination of silver protective layer 15 on superconductor layer 13 to obtain laminate 16; doping superconductor layer 13 with oxygen; and a step of performing an oxygen annealing treatment. By forming the superconductor layer 13 by the PLD method in this manner, the oxide superconductor and silver can be deposited as the superconductor layer 13 more densely. Therefore, the electrical resistance between superconducting layer 13 and protective layer 15 can be more reliably reduced.

Hereinafter, the above embodiments will be described with reference to comparative examples and examples.
As shown in Table 1, oxide superconducting wires of Comparative Example 1 and Examples 1 to 9 were produced.
Table 1 shows the following items for each of the oxide superconducting wires of Comparative Example 1 and Examples 1-9.
・Constituent material of superconducting layer ・Thickness (μm) of superconducting layer
- Content of Ag (silver) when the content of Eu (europium) in the superconductor layer is 1 mol - Content of Ag (silver) contained in the superconductor layer (wt%)
・ Content (vol%) of Ag (silver) contained in the superconductor layer
・Surface roughness Ra (nm)
・Critical current density Jc [MA/cm ² ]
・Critical current Ic [A]
・Connection resistance ratio ・Evaluation result

" _EuBCO +BHO" described in "Materials Constituting Superconductor Layer" in Table 1 means a mixture of an oxide superconducting material of _EuBa2Cu3Oy and an artificial pin material of _BaHfO3 .

"Ag content (wt%)" means the silver content (wt%) with respect to the entire superconductor layer (100 wt%). "Ag content (vol%)" means the silver content (vol%) with respect to the entire superconductor layer (100vol%).
That is, the superconductor layer of Comparative Example 1 does not contain silver. The superconductor layers of Examples 1-9 contain silver. In Examples 1-9, the range of silver content in the superconductor layer was 4.0-27.2 vol %.
In Comparative Example 1 and Examples 1 to 9, the content of silver contained in the superconductor layer was measured by ICP emission spectrometry using the solution obtained by dissolving the superconductor layer.

In Table 1, the surface roughness Ra means the arithmetic mean roughness Ra of the surface of the superconductor layer in contact with the protective layer. The surface roughness Ra is a value measured after forming the superconducting layer and before forming a protective layer on the superconducting layer. A stylus surface measuring device (KLA-Tencor, D-100) was used to measure the surface roughness Ra.

Critical current density Jc [MA/cm ² ] and critical current Ic [A] are results measured at a temperature of 77K. The critical current density Jc is the critical current value per unit cross-sectional area of the superconductor layer.

The connection resistance ratio is defined as R _C0 [nΩ·cm ² ] as the connection resistance of the connection structure produced using the oxide superconducting wire of the comparative example in which the superconducting layer does not contain silver, and the superconducting layer contains silver. _{The ratio of R C1 to} R _C0 ⁽ R _C1 /R _C0 ).

Specifically, first, two oxide superconducting wires of Comparative Example 1 (the superconducting layer does not contain silver) were prepared, and a connection structure in which the protective layers 15 faced each other and were solder-connected with a connection length of 2 cm was formed. made.
Next, the electrical resistance between one superconducting layer of the two oxide superconducting wires and the other superconducting layer of the two oxide superconducting wires is measured, and the electrical resistance is defined as _RC0 . did. The electrical resistance was measured by the four-terminal resistance measurement method after making the object to be measured into a superconducting state. Similarly, a connection structure was produced from each of the oxide superconducting wires of Examples 1 to 9 (the superconducting layer contains silver), and the connection resistance of each connection structure was _measured . [nΩ·cm ² ]. Then, the value of the connection resistance ratio (R _C1 /R _C0 ) was obtained for each of the connection structures of Examples 1-9. The connection resistance ratio of Comparative Example 1 was set to 1.0.

The electrical resistances (R _C0 and R _C1 ) of the connection structure described above are the electrical resistance (interlayer resistance R) between the superconductor layer 13 and the protective layer 15 and the electrical resistance between the protective layer 15 and the connection solder. It can be considered as a sum with resistance. Of these, the electrical resistance between the protective layer 15 and the connecting solder is considered to be the same regardless of Comparative Example 1 and Examples 1-9. Therefore, it is considered that the difference in the connection resistance of the connection structure is caused by the difference in the interlayer resistance R between Comparative Example 1 and Examples 1-9. Therefore, by comparing the connection resistances of the connection structures produced in each of Comparative Example 1 and Examples 1 to 9, it is possible to know the magnitude relationship between interlayer resistances R in each of Comparative Example 1 and Examples 1 to 9. can.

The connection resistance ratio (R _C1 /R _C0 ) is based on the interlayer resistance R of Comparative Example 1 (the superconductor layer does not contain silver) in Examples 1 to 9 (the superconductor layer contains silver ) can be used as an index to know how much the interlayer resistance R has decreased. For example, in Table 1, the connection resistance ratio of Example 1 is 0.4, and the connection resistance ratio of Example 2 is 0.5. From this, it can be seen that Example 1 achieves a better reduction effect than Example 2 with respect to the effect of reducing interlayer resistance R due to the superconductor layer containing silver.

In the "evaluation results" in Table 1, a connection resistance ratio of 1 or more indicates "improper", and a connection resistance ratio of less than 1 indicates "good".

From the results shown in Table 1, the following points were clarified.

(Regarding connection resistance ratio)
Compared to Comparative Example 1, in which the connection resistance ratio is 1, the range of connection resistance ratios in Examples 1 to 9 was 0.3 to 0.6. In Examples 1 to 9, an evaluation result of "good" was obtained. In other words, it was found that the interlayer resistance R was greatly reduced by containing silver in the superconductor layer as shown in Examples 1-9.

(About critical current density)
Furthermore, among Examples 1 to 9, the critical current density Jc of Example 7 was 0.2 MA/cm ² and the critical current density Jc of Example 1 was 1.8 MA/cm ² . Examples 2-6,
The critical current densities Jc of 8 and 9 ranged from 0.2 to 1.8 MA/cm ² . As a result, if the critical current density Jc of the superconducting layer is within the range of 0.2 to 1.8 MA/cm ² , not only can the interlayer resistance R be significantly reduced, but also an oxidation catalyst having a high critical current value can be obtained. It has become clear that a material superconducting wire can be realized.
Furthermore, the critical current densities Jc of Examples 1, 2 and 9 ranged from 1.3 to 1.8 MA/cm ² , which is higher than the critical current densities Jc of the other Examples. If the critical current density Jc is within the range of 1.3 to 1.8 MA/cm2, an oxide superconducting wire having a higher critical current density Jc can be realized.

(Surface Roughness of Superconductor Layer)
The silver content in Example 1 is 4.0 vol %. The silver content in Example 9 is 27.2 vol %. In the order from Example 1 to Example 9, the silver content in Examples 1 to 9 increases in order. Regarding the surface roughness Ra, it was found that there is a tendency that the surface roughness Ra generally increases in the order from Example 1 to Example 9. In other words, in Examples 1 to 9, it was found that the surface roughness Ra tends to increase as the silver content increases. As the surface roughness Ra increases, the contact area between the superconductor layer and the protective layer increases. Therefore, it is considered that the effect of reducing the interlayer resistance R is enhanced.

(Regarding the particle size of silver contained in the superconductor layer)
For each of Examples 1 to 9, the cross section of superconductor layer 13 was observed using an electron microscope, and the observed silver particle diameter (silver particle diameter) was measured. As observation conditions, the magnification of the electron microscope was set to 10000 times. The maximum width of the silver particles measured in the direction parallel to the substrate 11 was defined as the silver particle diameter. As a result, the particle size of silver was in the range of 0.3 to 1.0 μm.

The technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

For example, a stabilization layer (not shown) may be provided around the laminate 16 . When the stabilizing layer is provided, it is possible to bypass an overcurrent generated in an accident and to mechanically reinforce the superconducting layer 13 and the protective layer 15 . Copper, for example, can be used as the material of the stabilization layer.

In addition, it is possible to appropriately replace the components in the above-described embodiments with well-known components without departing from the scope of the present invention, and the above-described embodiments and modifications may be combined as appropriate.

DESCRIPTION OF SYMBOLS 10... Oxide superconducting wire 11... Substrate 12... Intermediate layer 13... Superconductor layer 14... Interface 15... Protective layer 23... Target

Claims (5)

a substrate;
a superconductor layer laminated above the substrate;
a protective layer laminated on the superconductor layer and formed of silver;
The superconductor layer is formed of an oxide superconductor and is in contact with the protective layer,
the superconductor layer comprises silver and an oxide superconductor;
The oxide superconducting wire, wherein the content of silver contained in the superconductor layer is in the range of 4.0 to 27.2 vol% with respect to the entire superconductor layer. In the superconductor layer, silver particles in which the silver is aggregated are dispersed,
The oxide superconducting wire according to claim 1. The diameter of the silver particles is in the range of 0.3 to 1.0 μm,
The oxide superconducting wire according to claim 2. The arithmetic mean roughness Ra of the surface of the superconductor layer in contact with the protective layer is in the range of 39.8 to 103.4 nm.
The oxide superconducting wire according to any one of claims 1 to 3. the critical current density of the superconductor layer is in the range of 0.2 to 1.8 MA/ ^cm2 ;
The oxide superconducting wire according to any one of claims 1 to 4.

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