JP2020135988A - Oxide superconducting wire and method for producing the same - Google Patents

Abstract

To provide, in an oxide superconducting wire having a superconducting layer with artificial pins introduced, an oxide superconducting wire that can increase the critical current value, and to provide a method for producing the same.SOLUTION: The oxide superconducting wire is an oxide superconducting wire 10 having a superconducting layer 13 laminated on a substrate 11, and in which the superconducting layer 13 contains an artificial pin composed of an RE-Ba-Cu-O system oxide superconductor (RE is a rare earth element) and ABO(A represents Ba, Sr or Ca, and B represents Hf, Zr or Sn), and, in the cross-sectional TEM image of the superconducting layer, the standard deviation σ of the inclination angle of the artificial pin with respect to the thickness direction of the superconducting layer is in the range of 1.65 to 3.59° and the average of the length of the artificial pins is within the range of 41.03 to 45.54 nm.SELECTED DRAWING: Figure 1

Description

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

REBa as ₂ Cu ₃ O _x (RE is a rare earth element) structure of REBa-Cu-O based oxide superconductor superconducting wires using such, via an intermediate layer on a substrate such as a metal tape, oxide superconductor A structure in which layers are formed is adopted. Particularly in recent years, in order to improve the critical current value in a magnetic field, an artificial pin material has been introduced into the superconducting layer (see Patent Document 1 and Non-Patent Document 1).

Japanese Patent No. 57366522

Tomo Yoshida, et al., “Yttrium-based Coated Conductors With Artifitial Pinning Centers” Fujikura Technical Review, No.47 November, 2017, p.19-25

As a method of increasing the critical current value in the magnetic field of the superconducting wire, there is a method of adding an artificial pin to the superconducting layer. In the case of the method of adding an artificial pin to the superconducting layer, the artificial pin grows in a rod shape to become a pinning center, and the superconducting characteristics in a magnetic field can be enhanced.

The present invention has been made in view of the above circumstances, and provides an oxide superconducting wire having an artificial pin-introduced superconducting layer and an oxide superconducting wire capable of increasing the critical current value and a method for producing the same. That is the issue.

The first aspect of the present invention is an oxide superconducting wire having a superconducting layer laminated on a substrate, wherein the superconducting layer is a RE-Ba-Cu-O-based oxide superconductor (RE is a rare earth element) and ABO. ₃ (A represents Ba, Sr or Ca, B represents Hf, Zr or Sn) includes the artificial pin, and in the cross-sectional TEM image of the superconducting layer, the artificial pin with respect to the thickness direction of the superconducting layer. The standard deviation σ of the inclination angle of is in the range of 1.65 to 3.59 °, and the average length of the artificial pins is in the range of 41.03 to 45.54 nm. It is an oxide superconducting wire.

A second aspect of the present invention is a method for producing an oxide superconducting wire in which a superconducting layer is laminated on a substrate, wherein a RE-Ba-Cu-O-based oxide superconductor (RE is a rare earth element) and ABO ₃ ( A represents Ba, Sr or Ca, and B represents Hf, Zr or Sn). The superconducting layer containing an artificial pin is formed by a pulse laser vapor deposition method (PLD method). This is a method for producing an oxide superconducting wire, characterized in that the vapor deposition rate of the superconducting layer is less than 23 nm / sec.

A third aspect of the present invention is the method for producing an oxide superconducting wire according to a second aspect, wherein the vapor deposition rate of the superconducting layer is 5 to 14 nm / sec.

According to the present invention, since the artificial pin is contained according to a predetermined embodiment, the critical current value can be increased.

It is sectional drawing which shows typically an example of the oxide superconducting wire. It is a graph which shows an example of the relationship between the deposition rate and the critical current density. It is a graph which shows an example of the relationship between the deposition rate and the inclination angle of an artificial pin. It is a graph which shows an example of the relationship between the deposition rate and the length of an artificial pin.

Hereinafter, the present invention will be described with reference to the drawings based on the preferred embodiments.

FIG. 1 shows the oxide superconducting wire of the present embodiment. The oxide superconducting wire material of the present embodiment is the oxide superconducting wire material 10 in which the superconducting layer 13 is laminated on the substrate 11. It is preferable that the surface of the substrate 11 has an intermediate layer 12 between it and the superconducting layer 13. The direction in which the substrate 11, the intermediate layer 12, and the superconducting layer 13 are laminated is the thickness direction. The width direction is a direction perpendicular to the longitudinal direction and the thickness direction.

The substrate 11 is a tape-shaped substrate (base material), and has main surfaces (front surface and back surface facing the same) on both sides in the thickness direction. Specific examples of the metal constituting the substrate 11 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 thickness of the substrate 11 may be appropriately adjusted according to the intended purpose, and is, for example, in the range of 10 to 500 μm. A metal thin film such as Ag or Cu may be formed on the back surface, the side surface, or both of the substrate 11 by sputtering or the like in order to improve the bondability.

Superconducting layer 13, for example, the formula REBa ₂ Cu ₃ oxide REBa-Cu-O system represented by O _x superconductor and the like. Examples of the rare earth element RE include one or more of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Be done. The thickness of the superconducting layer 13 is, for example, about 0.5 to 5 μm. Examples of the method for laminating the superconducting layer 13 include a sputtering method, a vacuum vapor deposition method, a laser vapor deposition method, an electron beam vapor deposition method, a pulse laser deposition method (PLD method), a chemical vapor deposition method (CVD method), and an organic metal coating thermal decomposition method. The method (MOD method) and the like can be mentioned. Above all, from the viewpoint of productivity and the like, it is preferable to stack the superconducting layers 13 by the PLD method.

The superconducting layer 13 includes an artificial pin composed of ABO ₃ (A represents Ba, Sr or Ca, and B represents Hf, Zr or Sn). Specific examples of the material constituting the artificial pin (artificial pin material) include at least one kind such as BaHfO ₃ , SrHfO ₃ , CaHfO ₃ , BaZrO ₃ , BaSnO ₃ , a solid solution thereof, or a mixture of two or more kinds. Be done. The artificial pin preferably has a rod shape having a length larger than the thickness. The length of the artificial pin is preferably in the range of 40 to 50 nm on average. Specific examples of the average length of the artificial pins include the range of 41.03 to 45.54 nm. The thickness of the artificial pin is preferably 3 to 5 nm on average, and more preferably 4 to 5 nm on average. When a superconductor containing an artificial pin is deposited in a direction perpendicular to the substrate 11 by the vapor phase method, the superconducting layer tends to have a c-axis perpendicular to the substrate surface. In this case, the artificial pin rod tends to grow in the c-axis direction of the superconductor or in a direction slightly inclined from the c-axis direction.

When the growth direction of the artificial pin rod (longitudinal direction of the rod) is aligned in the c-axis direction, and when a magnetic field is applied in the c-axis direction, a particularly strong pinning force is exhibited. Therefore, the longitudinal direction of the artificial pin is the direction of the superconductor. It is preferable that they are aligned in the c-axis direction. When the longitudinal direction of the artificial pin is inclined from the c-axis direction of the superconductor, the pinning force in the c-axis direction tends to be weakened. In order to obtain a high critical current value in a magnetic field, the standard deviation σ of the inclination angle (inclination) of the artificial pin with respect to the thickness direction of the superconducting layer 13 is preferably in the range of 1 to 5 °. Specific examples of the standard deviation σ of the inclination angle include the range of 1.65 to 3.59 °.

The oxide superconducting wire of the present embodiment preferably has a critical current density Jc of 9 MA / cm ² or more at a temperature of 30 K and a magnetic field of 2 T. Thereby, a high critical current can be obtained.

The method for producing the oxide superconducting wire of the present embodiment preferably includes a step of forming a superconducting layer including the above-mentioned oxide superconductor and artificial pins by a pulse laser vapor deposition method (PLD method). As a method for forming a superconducting layer containing an oxide superconductor and an artificial pin, a method using a mixed target containing the superconducting material and the artificial pin material, a first target containing the superconducting material and a first containing the artificial pin material. A method using two types with two targets can be mentioned. Two or more types of targets containing a superconducting material and an artificial pin material may be used. The first target containing the superconducting material may contain an artificial pin material having a lower concentration than the superconducting material, or may substantially not contain the artificial pin material. The second target containing the artificial pin material may contain a superconducting material having a lower concentration than the artificial pin material, or may substantially not contain the superconducting material. When two or more types of targets having different compositions are used, the targets may be arranged side by side and integrated, or the targets may be arranged at different positions in the space for forming the superconducting layer (deposition space). The concentration of the artificial pin with respect to the superconducting material in the target is, for example, 0.5 to 10 mol%. The concentration of the artificial pin material in the target can be adjusted according to the concentration of the artificial pin (molar concentration, several concentration) with respect to the superconducting layer. The superconducting layer 13 may contain impurities such as RE ₂ O ₃ derived from the target superconducting material.

In the manufacturing method of the present embodiment, it is preferable to slow down the vapor deposition rate of the superconducting layer 13 containing the artificial pin. The vapor deposition rate of the superconducting layer 13 is preferably less than 23 nm / sec, more preferably 5 to 14 nm / sec, for example. The critical current value can be increased by slowing the deposition rate.

From the viewpoint of orientation control of the superconducting layer 13, it is preferable to provide the intermediate layer 12 on the surface of the substrate 11 made of metal and to form the superconducting layer 13 on the intermediate layer 12. The intermediate layer 12 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 substrate 11 side to the superconducting layer 13 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 diffusion prevention layer has a function of suppressing a part of the components of the substrate 11 from diffusing and being mixed into the superconducting layer 13 side as impurities. Examples of the material of the diffusion prevention layer include Si ₃ N ₄ , Al ₂ O ₃ , GZO (Gd ₂ Zr ₂ O ₇ ) and the like. The thickness of the diffusion prevention layer is, for example, 10 to 400 nm.

The bed layer is used to reduce the reaction at the interface between the substrate 11 and the superconducting layer 13 and to improve the orientation of the layer formed on the bed layer. Examples of the material of the bed layer include Y ₂ O ₃ , Er ₂ O ₃ , CeO ₂ , Dy ₂ O ₃ , Eu ₂ O ₃ , Ho ₂ O ₃ , La ₂ O _{3 and the} like. The thickness of the bed layer is, for example, 10 to 100 nm.

The alignment layer is formed from a biaxially oriented material to control the crystal orientation of the cap layer above it. The material of the alignment layer is, for example, Gd ₂ Zr ₂ O ₇ , MgO, ZrO _2- Y ₂ O ₃ (YSZ), SrTIO ₃ , CeO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , Gd ₂ O ₃ , Metal oxides such as Zr ₂ O ₃ , Ho ₂ O ₃ , and Nd ₂ O ₃ can be exemplified. This alignment layer is preferably formed by an IBAD (Ion-Beam-Assisted Deposition) method.

The cap layer is made of a material that is formed on the surface of the above-mentioned alignment layer and allows crystal grains to self-orient in the in-plane direction. The material of the cap layer, for _{example, 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, LaMnO 3 , and the like. The thickness of the cap layer is in the range of 50 to 5000 nm.

It is preferable to provide a protective layer on the surface of the superconducting layer 13. The protective layer has functions such as bypassing an overcurrent generated at the time of an accident and suppressing a chemical reaction occurring between the superconducting layer 13 and a layer provided on the protective layer. Examples of the material of the protective layer include silver (Ag), copper (Cu), gold (Au), an alloy of gold and silver, other silver alloys, copper alloys, and gold alloys. The protective layer covers at least the surface of the superconducting layer 13 (the surface opposite to the substrate 11 side in the thickness direction). Further, the protective layer may cover a part or all of a region selected from the side surface of the superconducting layer 13, the side surface of the intermediate layer 12, the side surface of the substrate 11, and the back surface of the substrate 11.

The superconducting wire 10 may have a stabilizing layer around the laminate including the substrate 11 and the superconducting layer 13. Examples of the region forming the stabilizing layer include the back surface of the substrate 11, the front surface of the superconducting layer 13, and the side surface of the substrate 11 or the superconducting layer 13. When the superconducting wire 10 has a protective layer, a stabilizing layer may be provided on the protective layer. The material used for the stabilizing layer may differ depending on the use of the superconducting wire material 10. For example, when used in a superconducting cable or a superconducting motor, a metal with good conductivity is preferably used because it needs to function as the main part of the bypass that commutates the overcurrent generated at the time of transition to the normal conducting state. Be done. Examples of the metal having good conductivity include metals such as copper, copper alloy, aluminum, and aluminum alloy. Further, when used in a superconducting current limiter, a high resistance metal is preferably used because it is necessary to instantly suppress the overcurrent generated at the time of transition to the normal conduction state. Examples of the high resistance metal include Ni-based alloys such as Ni—Cr.

Although the present invention has been described above based on a preferred embodiment, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

The superconducting wire 10 can be used in various forms such as a tape shape, a cable shape, and a coil shape. In order to manufacture a superconducting coil using the superconducting wire 10, the superconducting wire 10 is wound along the outer peripheral surface of the winding frame in the required number of layers to form a coil shape (multilayer winding coil), and then the wound superconducting wire 10 is covered. As described above, the superconducting wire 10 can be fixed by impregnating a resin such as an epoxy resin. Further, the superconducting wire member 10 can have an external terminal. The portion having the external terminal may have a cross-sectional structure different from that of the other portion.

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

An intermediate layer was formed on a tape-shaped substrate made of Hastelloy (registered trademark) by using an ion beam sputtering method or the like. Using the EuBa ₂ Cu ₃ O _x target in which the addition of BaHfO ₃ as an artificial pin material, to form a superconducting layer by a PLD method to produce the superconducting wire. Each superconducting wire was prototyped by changing the vapor deposition rate.

For the prototype superconducting wire, the critical current value in the magnetic field was measured by the four-terminal method. The measurement conditions for the critical current value were a temperature of 30 K and a magnetic field of 2 T. From the critical current value of the superconducting wire and the cross-sectional area of the superconducting layer, the critical current density Jc at a temperature of the superconducting layer of 30K and a magnetic field of 2T was calculated. FIG. 2 shows an example of the relationship between the vapor deposition rate of the superconducting layer and the critical current density Jc. In the region where the deposition rate was less than 23 nm / sec, the critical current density tended to increase monotonically as the deposition rate decreased. It was found that the value of the critical current density was as high as 9 MA / cm ² or more, which is a guideline for a suitable critical current density, when the vapor deposition rate was in the range of 5 to 14 nm / sec. In the region where the vapor deposition rate is less than 23 nm / sec, the artificial pin rod introduced into the superconducting layer grows along the c-axis direction, and the shape tends to be uniform, and it is considered that the critical current density increases due to the pinning effect.

In order to measure the inclination angle and length of the artificial pin, a cross-sectional observation using a TEM (transmission electron microscope) was performed on a sample of the superconducting layer formed at each vapor deposition rate. These cross-sectional TEM images are images of cross-sections parallel to the thickness direction of the superconducting layer. The artificial pin rod confirmed by cross-sectional structure observation showed a tendency to grow linearly along the crystal c-axis direction of the superconductor when the deposition rate was low. On the other hand, when the vapor deposition rate was high, the growth direction of the artificial pin rod was inclined from the crystal c-axis direction, showing a tendency to grow in a random direction.

Sample No. The cross sections parallel to the thickness direction of the superconducting layers 1 to 6 were observed with a TEM (transmission electron microscope), and the inclination angle and length of the artificial pin appearing in the superconducting layer in the region of 140 nm × 170 nm were measured. .. The inclination angle is the inclination angle of the artificial pin with respect to the thickness direction of the superconducting layer. The length is the length of the artificial pin along the cross section. When the length direction of the artificial pin does not follow the cross section, such as when the length is less than the thickness, it was excluded from the measurement targets of the inclination angle and the length. FIG. 3 shows an example of the relationship between the vapor deposition rate and the inclination angle of the artificial pin (inclination from the c-axis direction). FIG. 4 shows an example of the relationship between the vapor deposition rate and the length of the artificial pin (rod length). In these graphs, the results of Samples 3-6 with the same deposition rate of 32 nm / sec are shown together. Table 1 shows the minimum value, maximum value, average value, and standard deviation of the inclination angle of the artificial pin measured for each sample. Table 2 shows the minimum value, maximum value, average value, and standard deviation of the length of the artificial pin.

10 ... Oxide superconducting wire, 11 ... Substrate, 12 ... Intermediate layer, 13 ... Superconducting layer.

Claims (3)

An oxide superconducting wire with a superconducting layer laminated on a substrate.
The superconducting layer is derived from RE-Ba-Cu-O oxide superconductor (RE is a rare earth element) and ABO ₃ (A represents Ba, Sr or Ca, and B represents Hf, Zr or Sn). Including artificial pins
In the cross-sectional TEM image of the superconducting layer, the standard deviation σ of the inclination angle of the artificial pin with respect to the thickness direction of the superconducting layer is within the range of 1.65 to 3.59 °, and the length of the artificial pin is An oxide superconducting wire having an average in the range of 41.03 to 45.54 nm. A method for manufacturing an oxide superconducting wire in which a superconducting layer is laminated on a substrate.
Includes an artificial pin consisting of a RE-Ba-Cu-O oxide superconductor (RE is a rare earth element) and ABO ₃ (A represents Ba, Sr or Ca, and B represents Hf, Zr or Sn). The superconducting layer has a step of forming a film by a pulsed laser vapor deposition method (PLD method).
A method for producing an oxide superconducting wire, wherein the vapor deposition rate of the superconducting layer is less than 23 nm / sec. The method for producing an oxide superconducting wire according to claim 2, wherein the vapor deposition rate of the superconducting layer is 5 to 14 nm / sec.

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