JP2020087829A - Superconducting wire rod and manufacturing method of superconducting wire rod - Google Patents

Abstract

To provide a superconducting wire rod high in critical current density and a manufacturing method therefor.SOLUTION: A superconducting wire rod has a superconducting layer represented by a composition formula REBaCuO, where RE is a rare earth element, and an artificial pin added to the superconducting wire rod and represented by a composition formula BaMO, where M is at least one selected from a group consisting of Hf, Zr, Sn, Nb, and Ti, in which added concentration of the artificial pin is 5.0 mol% or more, and a crystal orientation of the artificial pin is aligned in a crystal orientation of the superconducting layer.SELECTED DRAWING: Figure 2

Description

The present invention relates to a superconducting wire and a method for manufacturing the superconducting wire.

Superconductors exhibit complete conductivity and can significantly reduce transmission loss due to electrical resistance. Therefore, development of superconducting wire rods using superconductors is under way.

Superconducting wires are required to have improved critical transition temperature and critical current density. The critical transition temperature is a temperature at which superconducting characteristics are exhibited. If the critical transition temperature is high, the cost required for cooling the superconducting wire can be suppressed. The critical current density is the maximum value of current per unit area that can flow in a superconductor with zero resistance. The critical current density of the superconductor decreases in the external magnetic field or the self magnetic field generated by the current itself. This is because the quantized magnetic flux lines penetrate the superconductor and generate induced electromotive force. When the superconducting wire has a high critical current density, power transmission loss can be further reduced.

Non-Patent Document 1 discloses a superconducting wire in which artificial pins are added to the superconducting wire. The artificial pin stops the magnetic flux lines from moving under Lorentz force, and prevents the generation of induced electromotive force due to the change of the magnetic flux lines. Non-Patent Document 1 describes that an artificial pin of 3.5 mol% is added.

T. Yoshida et al., Physica C 504 (2014) p.42-46.

It is expected that the critical current density will be further improved by further increasing the addition concentration of the artificial pin. However, even if the added concentration of artificial pin was simply increased, the critical transition temperature was lowered, and as a result, the critical current density was lowered.

The present invention has been made in view of the above problems, and an object thereof is to provide a superconducting wire having a high critical current density and a method for manufacturing the same.

As a result of earnest studies, the present inventors have found that increasing the film forming temperature of the superconducting layer and decreasing the temperature of oxygen annealing increases the critical current density of the superconducting wire.
That is, the present invention provides the following means in order to solve the above problems.

(1) A superconducting wire according to a first aspect is a superconducting layer represented by a composition formula REBa ₂ Cu ₃ O _y (RE is a rare earth element) and a composition formula BaMO ₃ (M is Hf) added to the superconducting layer. , An artificial pin represented by at least one selected from the group consisting of Zr, Sn, Nb, and Ti), and the addition concentration of the artificial pin is 5.0 mol% or more. The crystal orientation is aligned with the crystal orientation of the superconducting layer.

(2) In the superconducting wire according to the above aspect, the critical current density in the self-magnetic field may be 5.0×10 ⁶ A/cm ² or more at 77K.

(3) In the superconducting wire according to the above aspect, a distance d(005) between adjacent surfaces of the (005) plane in the superconducting layer may be 100% or more and 101% or less of a theoretical value.

(4) In the superconducting wire according to the above aspect, the critical current density may be 0.5×10 ⁶ A/cm ² or more under the conditions of an applied magnetic field of 3 T and a temperature of 77 K.

(5) In the superconducting wire according to the above aspect, the critical transition temperature Tc may be 88K or higher.

(6) A method of manufacturing a superconducting wire according to a second aspect comprises a film forming step of forming a superconducting layer having artificial pins by a pulse laser deposition method, an annealing step of annealing the superconducting layer in an oxygen atmosphere, And the annealing step is performed for 2 hours or more in a temperature range of 450° C. or lower, and the annealing step is performed at a temperature of 200° C. or lower lower than the peritectic temperature of the superconducting layer.

(7) In the annealing step in the method for manufacturing a superconducting wire according to the above aspect, the oxygen partial pressure may be 1 atm or more.

The superconducting wire according to the above aspect has a high critical current density and can suppress power transmission loss. Further, the method for producing a superconducting wire according to the above aspect can produce a superconducting wire having a high critical current density.

It is a perspective schematic diagram of the superconducting wire concerning 1st Embodiment. It is a cross-sectional schematic diagram of the superconducting layer of the superconducting wire concerning 1st Embodiment. It is the figure which measured the section of the superconducting layer of the superconducting wire concerning a 1st embodiment with a scanning electron microscope. It is a cross-sectional schematic diagram of the superconducting layer of the superconducting wire concerning another example. 7 is a graph showing the critical current densities of the superconducting wire rods of Example 1, Comparative Example 1 and Comparative Example 2 in a state where an external magnetic field having a measurement temperature of 77K and 3T was applied. 6 is a graph showing the critical current densities of the superconducting wire rods of Example 1 and Comparative Example 2 in a state where an external magnetic field having a measurement temperature of 65K and 5T was applied. It is a figure showing the relation between the maintenance temperature of oxygen annealing and the critical current density in a self-magnetic field. It is a figure showing the relation of film-forming temperature, critical transition temperature, and distance d (005) between adjacent surfaces of a superconducting layer. It is a graph which shows the relationship between the density of an artificial pin, and critical current density.

Hereinafter, the present invention will be described in detail with reference to the drawings.
In the drawings used in the following description, in order to make the features of the present invention easy to understand, there are cases where features are enlarged for the sake of convenience, and the dimensional ratios of each component may differ from the actual ones. is there. Further, the materials, dimensions, and the like illustrated in the following description are examples, and the present invention is not limited to them, and can be appropriately modified and implemented within the scope of the invention.

"First embodiment"
(Superconducting wire)
FIG. 1 is a schematic perspective view of the superconducting wire according to the first embodiment. Superconducting wire 100 includes superconducting layer 10 and base material 20. Hereinafter, the stacking direction of the superconducting layer 10 on the base material 20 is referred to as the z direction, and the major axis direction of the superconducting layer 10 in the plan view from the z direction is referred to as the x direction, and the direction orthogonal to the x direction and the z direction is referred to as the y direction.

The base material 20 is, for example, a laminate of a metal film and an intermediate layer made of an oxide or the like. The metal film is, for example, a Ni-W alloy or Ni-plated Cu. The intermediate layer is, for example, CeO ₂ , LaMnO ₃ , MgO, Y ₂ O ₃ , Gd ₂ Zr ₂ O ₇ or the like. The intermediate layer enhances the orientation of the superconducting layer 10.

The superconducting layer 10 is laminated on one surface of the base material 20. The thickness of the superconducting layer 10 in the z direction is, for example, 1 μm to 3 μm.

FIG. 2 is a schematic cross-sectional view of the superconducting layer 10 of the superconducting wire 100 according to the first embodiment. The superconducting layer 10 has an artificial pin 1 inside. At the boundary between the superconducting layer 10 and the artificial pin 1, there is a strained region 2.

The superconducting layer 10 is a superconductor represented by the composition formula REBa ₂ Cu ₃ O _y . RE is a rare earth element, for example, any one element selected from Er, Ho, Y, Dy, Gd, Eu, Sm, Nd, and La. y is 7-δ, and δ is oxygen deficiency. δ is preferably 0.3, more preferably 0.2, and even more preferably 0.1. The smaller the amount of oxygen deficiency, the more the strain with the artificial pin 1 described later can be suppressed.

The artificial pins 1 are distributed inside the superconducting layer 10. The artificial pin 1 stops the magnetic flux lines generated by the external magnetic field or the self magnetic field from moving under the Lorentz force, and prevents the generation of induced electromotive force due to the change of the magnetic flux lines.

The artificial pin 1 extends, for example, in the substantially z direction. FIG. 3 is a diagram in which the cross section of the superconducting layer 10 of the superconducting wire 100 according to the first embodiment is actually measured with a scanning electron microscope (SEM). FIG. 3 is a cross section of a superconducting layer in which artificial pins of 3.5 mol%, 5.0 mol%, 7.5 mol% and 10.0 mol% are added to EuBa ₂ Cu ₃ O _y , respectively. In FIG. 3, the artificial pin 1 can be confirmed as a large number of black stripes extending in the z direction.

The artificial pin 1 has the same crystal orientation as the superconducting layer 10. The crystal orientation is a direction perpendicular to the crystal plane that constitutes the crystal. For example, in the artificial pin 1 and the superconducting layer 10, crystals grow in the c-axis direction. The c-axis direction of the artificial pin 1 and the superconducting layer 10 is, for example, the z direction. Therefore, the artificial pin 1 is confirmed as a thin black line extending substantially in the z direction (see FIG. 3 ).

The artificial pin 1 is an oxide represented by the composition formula BaMO ₃ . M is at least one selected from the group consisting of Hf, Zr, Sn, Nb, and Ti.

The addition amount of the artificial pin 1 is 5.0 mol% or more. The addition amount of the artificial pin 1 may be 7.0 mol% or more, or 10.0 mol% or more. As shown in FIG. 3, no clear structural defect is confirmed in the crystal structure even when the added amount of artificial pin 1 is 5.0 mol% or more.

The strained region 2 is formed at the boundary between the artificial pin 1 and the superconducting layer 10. The artificial pin 1 and the superconducting layer 10 have the same crystal orientation as described above. On the other hand, BaMO ₃ forming the artificial pin 1 and REBa ₂ Cu ₃ O _y forming the superconducting layer 10 have different lattice constants. The strained region 2 is a region in which the crystal structure is strained in order to reduce the difference in lattice constant between the artificial pin 1 and the superconducting layer 10.

The strained region 2 spreads in the xy plane in order to reduce the difference in c-axis length between the artificial pin 1 and the superconducting layer 10. There is a portion where the strain is eliminated between the adjacent strain regions 2, and the adjacent strain regions 2 do not interfere with each other.

FIG. 4 is a schematic sectional view of a superconducting layer 10' according to another example. The superconducting layer 10' shown in FIG. 4 has an artificial pin 1 inside and a strained region 2'at the boundary between the artificial pin 1 and the superconducting layer 10'. The strained regions 2'expand in the xy directions, and the strained regions 2'adjacent to each other interfere with each other.

In the superconducting layer 10, electrons are conducted along the CuO plane. When the CuO surface is disturbed, the critical transition temperature at which superconductivity is exhibited is lowered. If the CuO surface is disturbed, superconductivity itself does not appear in some cases. In the strained region 2 ′, the CuO plane is tilted from the xy plane in order to reduce the difference in c-axis length (lattice constant in the z direction) between the artificial pin 1 and the superconducting layer 10. When the strained regions 2'expand until the strained regions 2'adjacent to each other interfere with each other, the CuO surface becomes non-flat and the critical transition temperature decreases. Further, as the critical transition temperature decreases, the critical current density also decreases.

The spread of the strained region 2 can be suppressed by the manufacturing method. As will be described later in detail, when the film forming temperature is increased, the Young's modulus of the superconducting layer 10 becomes small and the range in which the strain spreads becomes narrow. Further, when the annealing temperature is lowered, the amount of oxygen introduced into the superconducting layer 10 is increased and the lattice constant of the superconducting layer 10 is reduced. When the lattice constant of the superconducting layer 10 becomes small, the difference in lattice constant with the artificial pin 1 becomes small, and the strain is suppressed.

The smaller the difference between the lattice constant of the superconducting layer 10 and the lattice constant of the artificial pin 1, the more the strain is suppressed. The inter-adjacent surface distance d(005) of the (005) plane in the superconducting layer 10 is preferably 100% or more and 101% or less of the theoretical value, and more preferably 100% or more and 100.6% or less of the theoretical value. Yes, and more preferably 100% or more and 100.5% or less of the theoretical value. The distance d(005) between the adjacent surfaces of the superconducting layer 10 becomes smaller as the amount of oxygen introduced into the superconducting layer 10 increases.

The theoretical value of the c-axis length of the (005) plane in the superconducting layer 10 (corresponding to about 5 times the inter-adjacent surface distance d(005)) is, for example, when the rare earth element forming the superconducting layer 10 is Yb. 650Å, 11.659Å for Er, 11.65Å for Er, 11.670Å for Ho, 11.657Å for Y, 11.668Å for Dy, 11.703Å for Gd, In the case of Eu, 11.704Å, in Sm, 11.721Å, in Nd, 11.736Å, and in La, 11.783Å. The measured value of the c-axis length (obtained from the diffraction peak position of the (005) plane of X-ray diffraction (XRD)) in the superconducting layer 10 is, for example, 11.7665Å when the rare earth element forming the superconducting layer 10 is Y. It is preferably below, more preferably below 11.7199 Å, even more preferably below 11.7190 Å. When the rare earth element forming the superconducting layer 10 is Gd, the measured value is preferably 11.8200Å or less, more preferably 11.7322Å or less, and further preferably 11.7200Å or less. .. When the rare earth element forming the superconducting layer 10 is Eu, the measured value is preferably 11.82110 Å or less, more preferably 11.7742 Å or less, and further preferably 11.7300 Å or less. ..

As described above, in the superconducting wire 100 according to the first embodiment, the spread of strain in the superconducting layer 10 is suppressed. Therefore, the superconducting wire 100 can realize a high critical current density.

Superconducting wire 100 preferably has a critical current density in a self-magnetic field of 5.0×10 ⁶ A/cm ² or more at 77K. “In the self-magnetic field” means that no external magnetic field is applied. The specific method for measuring the critical current density is shown below. The critical current density is measured using, for example, a 4-terminal method, an MPMS (Magnetic Property Measurement System) device manufactured by Quantum Design, Inc., USA. The measurement of the critical current density may be slightly different depending on the measuring method, but it is preferable that the critical current density is satisfied by any method. Among the measurement methods, an example using an MPMS device will be specifically described. The MPMS device can measure magnetism by arbitrarily changing the temperature and magnetic field of the material. The measurement is performed by cooling the magnetization detecting element (SQUID element) and the superconducting magnet with liquid helium. The measurement sample is processed into a size of 3.1 mm×3.1 mm. After cooling the measurement sample to the measurement temperature (for example, 77K), an external magnetic field is applied to the measurement sample. The external magnetic field to be applied is sequentially changed to 0T, 7T, -7T, 7T, 0T, for example. As a result, the change in magnetic susceptibility of the measurement sample is measured. For the change in magnetic susceptibility, specifically, the hysteresis in the first quadrant and the fourth quadrant is measured. Then, the change of the obtained magnetic susceptibility is changed to the critical current density Jc by using the extended bean model. By such a procedure, Jc(B) at an arbitrary temperature is obtained.

Further, the superconducting wire 100 preferably has a critical current density of 0.5×10 ⁶ A/cm ² or more under the conditions of an applied magnetic field of 3 T and a temperature of 77 K. Further, the superconducting wire 100 preferably has a critical current density of 1.5×10 ⁶ A/cm ² or more under the conditions of an applied magnetic field of 5 T and a temperature of 65 K. The applied direction of the applied magnetic field is 0 degree in the z direction and θ is the inclination angle in the y direction. It is preferable that the superconducting wire 100 satisfy the above critical current density regardless of the angle θ of 0° to 90°.

Further, the superconducting wire 100 preferably has a critical transition temperature Tc of 88K or higher, and more preferably a critical transition temperature Tc of 90K or higher. The critical transition temperature Tc is increased by suppressing the spread width of the strained region 2 in the xy directions.

The specific method for measuring the critical transition temperature is shown below. The measurement of the critical transition temperature is performed by using, for example, an MPMS (Magnetic Property Measurement System) device manufactured by Quantum Design, Inc. in the same manner as the measurement of the critical current density. First, the measurement sample is processed into a size of 3.1 mm×3.1 mm. Then, the measurement sample is cooled to 5 K, the temperature is raised under the condition of 0.5 K/min, and the temperature change of the magnetic susceptibility is measured. Then, the change in magnetic susceptibility corresponding to the superconducting-normal conducting transition is measured to determine the critical transition temperature.

As described above, the superconducting wire 100 according to the first embodiment has a high critical current density. The superconducting wire 100 having a high critical current density can be used in various environments. The superconducting wire 100 according to the first embodiment can be used for a cable, a transformer, a current limiting device, a silicon pulling magnet, a linear motor car, a superconducting power storage device (SMES), and the like.

"Second embodiment"
(Method for manufacturing superconducting wire)
The method for manufacturing a superconducting wire includes a film forming step of forming a superconducting layer having artificial pins by a pulse laser vapor deposition method, and an annealing step of annealing the superconducting layer in an oxygen atmosphere.

In the film forming step, the superconducting layer 10 is formed on the base material 20. The film formation is performed using a pulse laser deposition (PLD) method.

First, a sintered body of the precursor material of the superconducting layer 10 and the artificial pin 1 is produced. The sintered body is produced by the solid phase reaction method. As the precursor material, for example, an oxide of a rare earth element, barium carbonate, or copper oxide is used. The above-mentioned materials are used for the artificial pin 1. The artificial pin 1 is added at a predetermined molar ratio with respect to the charged amount of the precursor material.

Next, the sintered body and the base material 20 are arranged to face each other in the chamber. The inside of the chamber is made into an oxygen atmosphere and the sintered body is irradiated with a laser. A plume is generated in the portion irradiated with the laser, and a few atomic layers are scattered from the surface of the sintered body and deposited on the base material 20.

The film-forming temperature in the film-forming step is 200° C. lower than the peritectic temperature of the superconducting layer. The peritectic temperature refers to a temperature at which the main substance (superconductor except the artificial pin) forming the superconducting layer 10 separates from one solid phase state into another solid phase and a liquid phase. The film forming temperature in the film forming step is preferably 150° C. or more lower than the peritectic temperature of the superconducting layer, more preferably 100° C. or more lower than the peritectic temperature of the superconducting layer, and further preferably, the superconducting layer. It is above the peritectic temperature.

The peritectic temperature is, for example, 900° C. when the rare earth element forming the superconducting layer 10 is Yb, 970° C. when Er, 990° C. when Ho, 1005° C. when Y, 1005° C. when Dy, The temperature is 1045° C. for Gd, 1050° C. for Eu, 1060° C. for Sm, 1086° C. for Nd, and 1073° C. for La. The film formation temperature is preferably 760° C. or higher when the molar ratio of the artificial pin 1 is 5.0 mol% and the rare earth element is Yb, 830° C. or higher when Er is used, and 860° C. or higher when Ho is used. Preferably, Y is 865°C or higher, Dy is 865°C or higher, Gd is 905°C or higher, Eu is 910°C or higher, and Sm is 920°C or higher. In the case of Nd, it is preferably 946° C. or higher.

The film forming temperature is specifically the temperature obtained under the following conditions. First, a substrate which is a non-film forming body is connected to each turn in the film forming chamber at intervals of about several cm. All of these substrates are installed so as to enter the film formation region. Then, a thermocouple is placed on the outermost surface layer of the substrate (for example, the CeO ₂ layer as the intermediate layer) with Ag paste. Then, the inside of the chamber is set in the same manner as the actual film forming conditions, and the temperature of the outermost surface of the substrate is measured. At this time, the substrate is sent at an arbitrary linear velocity with respect to the set temperature, and the temperature change is recorded in real time. The relationship between the set temperature of the film forming chamber and the actually measured temperature obtained by such a procedure is obtained. The actual film forming temperature is converted using this result.

When the film forming temperature of the superconducting layer 10 is high, the Young's modulus of the artificial pin 1 and the superconducting layer 10 during crystal growth becomes small. Young's modulus is a proportional coefficient of strain and stress in the expansion/contraction direction and the coaxial direction. The larger the Young's modulus, the higher the rigidity and the more difficult it is to stretch. That is, the higher the film forming temperature, the more easily the crystal lattice of the superconducting layer 10 is distorted, and the difference in lattice constant between the artificial pin 1 and the superconducting layer 10 can be relaxed with a short width.

In the annealing step, the superconducting layer is annealed in an oxygen atmosphere. Annealing is performed in a temperature range of 450° C. or lower for 2 hours or more. Annealing is preferably performed in a temperature range of 350° C. or lower for 1 hour or more, and more preferably in a temperature range of 300° C. or lower for 1 hour or more.

Further, it is preferable that the annealing step maintain the temperature at a predetermined temperature. The predetermined maintenance temperature is preferably 350°C or lower, and more preferably 300°C or lower. The time of maintaining at the predetermined maintaining temperature is preferably 1 hour or more, more preferably 2 hours or more. The temperature during annealing is measured by the same method as the temperature during film formation.

The annealing conditions may be changed depending on the rare earth element forming the superconducting layer 10. For example, 450° C. or lower for Er, 400° C. or lower for Ho, 450° C. or lower for Y, 350° C. or lower for Dy, 400° C. or lower for Gd, 350° C. or lower for Eu, It is preferable to anneal at 350° C. or lower for Sm, 300° C. or lower for Nd, and 300° C. or lower for La. Further, for example, for Er, 2 hours or more, for Ho, 2 hours or more, for Y, 2 hours or more, for Dy, 2 hours or more, for Gd, 2 hours or more, and for Eu, 2 It is preferable to anneal for at least 2 hours, for Sm 2 hours or more, for Nd 2 hours or more, and for La 2 hours or more.

The oxygen partial pressure in the annealing step is preferably 1 atm or more, more preferably 1.1 atm or more.

In the annealing step, the annealing temperature, the annealing time, and the oxygen partial pressure are particularly preferably within the following ranges. For example, when the annealing temperature is 350° C., the annealing time is preferably 2 hours or more, and the oxygen partial pressure is preferably 1 atm or more. Further, for example, when the annealing temperature is 250° C., the annealing time is preferably 2 hours or more, and the oxygen partial pressure is preferably 1 atm or more. For example, when the annealing temperature is 400° C., the annealing time is preferably 2 hours or more, and the oxygen partial pressure is preferably 1 atm or more.

When the superconducting layer 10 is annealed under the above conditions, sufficient oxygen is introduced into the superconducting layer 10. When oxygen is sufficiently introduced into superconducting layer 10, the lattice constant of superconducting layer 10 becomes short. As a result, the strain between the artificial pin 1 and the superconducting layer 10 is reduced.

As described above, according to the method for manufacturing the superconducting wire according to the second embodiment, the width of the strained region 2 can be narrowed. As a result, a superconducting wire having a high critical transition temperature and a high critical current density can be obtained.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications are possible within the scope of the gist of the present invention described in the claims. Can be modified and changed.

<Study 1>
In Study 1, the effect of the difference in the additive amount of the artificial pin on the critical current density was confirmed.

(Example 1)
First, a base material was prepared. The base material was made by stacking CeO ₂ /LaMnO ₃ /MgO/Y ₂ O ₃ /Gd ₂ Zr ₂ O ₇ on Hastelloy C276. The base material had a width of 10 mm, a length of 100 mm and a thickness of 0.1 mm.

Then, a sintered body of the precursor material for the superconducting layer and the artificial pin was prepared by the solid-phase reaction method. Precursor material of the superconducting _layer, using a _{Eu 2 O 3, BaCO 3,} CuO. The artificial pin was BaHfO ₃ . The artificial pin was added at a ratio of 5.0 mol% with respect to the precursor material. The sintered body was fired at 900° C. after sufficiently mixing these materials.

Next, the sintered body and the base material were arranged in the chamber so as to face each other. The inside of the chamber was made into an oxygen atmosphere and the sintered body was irradiated with a laser to form a superconducting layer. The laser is a XeCl excimer laser (wavelength: 308 nm), oxygen pressure: 600 mTorr (80 Pa), substrate-target distance: 97-98 mm, laser oscillation energy: 500-600 mJ, laser energy density: 2-3 J/cm ^2. Irradiation was carried out under the condition that the substrate feed rate was 30 m/h. The temperature during film formation of the superconducting layer was 910° C. or higher.

Next, the produced superconducting layer was annealed with the following profile. The annealing profile was maintained at 500° C. for 1 hour, then lowered to 250° C., maintained at 250° C. for 3 hours, and then gradually cooled to room temperature. The time required for film formation was 7 hours or longer, and the film was exposed to an oxygen atmosphere in a temperature range of 250° C. or lower for 6 hours or longer. The oxygen partial pressure at this time was 1.1 atm. The superconducting wire according to Example 1 was manufactured by the above procedure.

(Comparative Example 1)
Comparative Example 1 is different from Example 1 in that the amount of artificial pin added was 3.5 mol %. Other conditions were the same as in Example 1.

(Comparative example 2)
Comparative Example 2 differs from Example 1 in that the rare earth elements are Y and Gd and no artificial pin is added. Other conditions were the same as in Example 1.

FIG. 5 is a graph showing the critical current densities of the superconducting wires of Example 1, Comparative Example 1 and Comparative Example 2 in the state where an external magnetic field having a measurement temperature of 77K and 3T was applied. The horizontal axis is the direction of applying the external magnetic field, where the z direction is 0 degree and the tilt angle in the y direction is θ. θ=90° coincides with the y direction. The vertical axis represents the critical current density of the superconducting wire.

The critical current density was improved in both Example 1 and Example 2 as compared with Comparative Example 2 in which the artificial pin was not added. In addition, comparing Example 1 and Comparative Example 1, it can be seen that Example 1 has improved critical current density at any angle with respect to Comparative Example 1. The superconducting wire of Example 1 has a critical current density of 0.6×10 ⁶ A/cm ² or more at any angle.

FIG. 6 is a graph showing the critical current densities of the superconducting wire rods of Example 1 and Comparative Example 2 in the state where an external magnetic field having a measurement temperature of 65K and 5T was applied. The horizontal axis is the direction of applying the external magnetic field, where the z direction is 0 degree and the tilt angle in the y direction is θ. θ=90° coincides with the y direction. The vertical axis represents the critical current density of the superconducting wire.

The critical current density was improved in both Example 1 and Example 2 as compared with Comparative Example 2 in which the artificial pin was not added. Further, the superconducting wire of Example 1 has a critical current density of 1.5×10 ⁶ A/cm ² or more at any angle.

<Study 2>
In Study 2, the behavior of the critical current density when the temperature of oxygen annealing was changed was investigated. Study 2 was performed when the artificial pin concentration was 5.0 mol% (series of Example 1) and 3.5 mol% (series of Comparative Example 1). In each case, the maintaining temperature during oxygen annealing was set to 250°C, 300°C, 350°C, 400°C and 450°C. The critical current density was measured in a self magnetic field without applying an external magnetic field. Other conditions were prepared and evaluated in the same procedure as in Example 1.

FIG. 7 is a diagram showing the relationship between the maintaining temperature of oxygen annealing and the critical current density in a self-magnetic field. The horizontal axis represents the temperature for maintaining oxygen annealing, and the vertical axis represents the critical current density in the self-magnetic field. As shown in FIG. 7, when the artificial pin concentration was 5.0 mol% and the oxygen annealing maintenance temperature was 350° C. or lower, the critical current density in the self-magnetic field was 5.0×10 ⁶ A/cm ^2. That's it. When the oxygen annealing temperature exceeded 400° C., the critical current density did not reach 5.0×10 ⁶ A/cm ² even when the oxygen annealing time was sufficiently long.

<Study 3>
In Study 3, changes in the critical transition temperature and changes in the distance d(005) between adjacent surfaces of the superconducting layer were examined when the film forming temperature during film formation was changed.

In Study 3, the artificial pin concentration was set to 10 mol %. The film forming temperatures were 1040° C., 1060° C., 1080° C., 1100° C., 1120° C., 1140° C. and 1160° C., respectively.

FIG. 8 is a diagram showing the relationship among the film forming temperature, the critical transition temperature, and the c-axis length of the superconducting layer. The horizontal axis is the film forming temperature, the left column on the vertical axis is the critical transition temperature, and the right column is the c-axis length of the superconducting layer. The c-axis length was determined from the diffraction peak position of the (005) plane of X-ray diffraction (XRD). The results shown in FIG. 8 are the results before oxygen annealing.

The critical transition temperature increased as the film forming temperature increased. It is conceivable that the Young's modulus of the superconducting layer decreased and the width of the strained region narrowed as the film forming temperature increased. The critical transition temperature is improved by forming a conduction path of electrons when a region where strain is released is formed between adjacent strain regions.

Further, the c-axis length of the superconducting layer became narrower as the film forming temperature increased. It is considered that this is because the width of the strained region was narrowed and the c-axis length obtained as the average value of the superconducting layer was narrowed. When the c-axis length becomes narrow, the difference in lattice constant between the artificial pin and the superconducting layer becomes small, and the strain is suppressed.

In Study 3, the critical transition temperature was improved because it was before oxygen annealing, but the critical current density was not sufficient. That is, the critical current density could not be improved unless sufficient oxygen was introduced by oxygen annealing.

<Study 4>
In Study 4, the relationship between the concentration of artificial pins and the critical current density was investigated when sufficient oxygen annealing was not performed on the superconducting layer.

The sample preparation conditions of Study 4 differ from Example 1 in that the concentration of the artificial pin was changed and the oxygen annealing profile was set as follows. The concentrations of the artificial pin were 0% (pure), 3.5%, 5%, and 10%, respectively. The profile of oxygen annealing was maintained at 500° C. for 1 hour and then gradually cooled to room temperature. The film formation time was 7 hours or longer, and the passage time in the temperature range of 250° C. or lower was 3 hours.

FIG. 9 is a graph showing the relationship between the concentration of artificial pins and the critical current density. The horizontal axis represents the measured temperature, and the vertical axis represents the critical current density in the external magnetic field 3T. As the artificial pin concentration increased, the critical current density at each measurement temperature decreased. This result was opposite to the results of Example 1 and Comparative Example 1 in Study 1. Examination 4 is considered to be because the oxygen annealing conditions were not sufficient and sufficient oxygen was not introduced into the superconducting layer.

1 Artificial Pin 2, 2'Strained Area 10, 10' Superconducting Layer 20 Base Material 100 Superconducting Wire

Claims (7)

A superconducting layer represented by the composition formula REBa ₂ Cu ₃ O _y (RE is a rare earth element);
An artificial pin added to the superconducting layer and represented by a composition formula BaMO ₃ (M is at least one selected from the group consisting of Hf, Zr, Sn, Nb, and Ti),
The addition concentration of the artificial pin is 5.0 mol% or more,
A superconducting wire rod in which the crystal orientation of the artificial pin is aligned with the crystal orientation of the superconducting layer. The superconducting wire according to claim 1, which has a critical current density in a self-magnetic field of not less than 5.0×10 ⁶ A/cm ² at 77K. The superconducting wire according to claim 1 or 2, wherein a distance d(005) between adjacent surfaces of the (005) plane in the superconducting layer is 100% or more and 101% or less of a theoretical value. The superconducting wire according to claim 1, which has a critical current density of 0.5×10 ⁶ A/cm ² or more under the conditions of an applied magnetic field of 3 T and a temperature of 77 K. 5. The superconducting wire according to any one of claims 1 to 4, which has a critical transition temperature Tc of 88K or higher. A film forming step of forming a superconducting layer having an artificial pin by a pulse laser deposition method,
An annealing step of annealing the superconducting layer in an oxygen atmosphere,
The film forming step is performed under a temperature condition of 200° C. or less lower than the peritectic temperature of the superconducting layer,
The method of manufacturing a superconducting wire, wherein the annealing step is performed in a temperature range of 450° C. or lower for 2 hours or more. The method for manufacturing a superconducting wire according to claim 6, wherein the partial pressure of oxygen is 1 atm or more in the annealing step.