JP7398663B2 - Superconducting wire and method for manufacturing superconducting wire - Google Patents

Description

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

Superconductors exhibit perfect electrical conductivity and can significantly reduce power transmission losses due to electrical resistance. Therefore, development of superconducting wires using superconductors is progressing.

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

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

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

It is expected that if the concentration of artificial pins added is further increased, the critical current density will further improve. However, even if the concentration of artificial pins was simply increased, the critical transition temperature decreased, resulting in a decrease in the critical current density.

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

As a result of extensive studies, the present inventors have found that the critical current density of the superconducting wire increases when the film formation temperature of the superconducting layer is increased and the oxygen annealing temperature is decreased.
That is, the present invention provides the following means to solve the above problems.

(1) The superconducting wire according to the first aspect includes a superconducting layer represented by the composition formula REBa ₂ Cu ₃ O _y (RE is a rare earth element), and a superconducting layer having a composition formula BaMO ₃ (M is Hf) added to the superconducting layer. , at least one selected from the group consisting of Zr, Sn, Nb, and Ti), and the concentration of the artificial pin added is 5.0 mol% or more, and the artificial pin is 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, the distance d(005) between adjacent planes 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) The method for manufacturing a superconducting wire according to the second aspect includes a film forming step of forming a superconducting layer having artificial pins by a pulsed laser deposition method, an annealing step of annealing the superconducting layer in an oxygen atmosphere, The film forming step is performed at a temperature that is 200 degrees lower than the peritectic temperature of the superconducting layer or more, and the annealing step is performed at a temperature of 450° C. or less for 2 hours or more.

(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 manufacturing a superconducting wire according to the above embodiment can manufacture a superconducting wire having a high critical current density.

FIG. 1 is a schematic perspective view of a superconducting wire according to a first embodiment. FIG. 1 is a schematic cross-sectional view of a superconducting layer of a superconducting wire according to a first embodiment. FIG. 2 is a diagram of a cross section of a superconducting layer of a superconducting wire according to a first embodiment measured using a scanning electron microscope. FIG. 3 is a schematic cross-sectional view of a superconducting layer of a superconducting wire according to another example. 2 is a graph showing the critical current density of the superconducting wires of Example 1, Comparative Example 1, and Comparative Example 2 in a state where the measurement temperature is 77 K and an external magnetic field of 3 T is applied. 2 is a graph showing the critical current density of the superconducting wires of Example 1 and Comparative Example 2 in a state where the measurement temperature is 65K and an external magnetic field of 5T is applied. FIG. 3 is a diagram showing the relationship between the maintenance temperature of oxygen annealing and the critical current density in a self-magnetic field. FIG. 2 is a diagram showing the relationship between film formation temperature, critical transition temperature, and distance d (005) between adjacent surfaces of superconducting layers. It is a graph showing the relationship between the concentration of artificial pins and critical current density.

Hereinafter, the present invention will be described in detail with reference to the drawings as appropriate.
In the drawings used in the following explanation, characteristic parts of the present invention may be shown enlarged for convenience in order to make it easier to understand, and the dimensional ratio of each component may differ from the actual one. be. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be implemented with appropriate changes within the scope of the invention.

"First embodiment"
(Superconducting wire)
FIG. 1 is a schematic perspective view of a superconducting wire according to a first embodiment. The superconducting wire 100 includes a superconducting layer 10 and a base material 20. Hereinafter, the lamination direction of the superconducting layer 10 on the base material 20 will be referred to as the z direction, the long axis direction of the superconducting layer 10 as viewed from the z direction will be referred to as the x direction, and the direction perpendicular to the x direction and the z direction will be 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, 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 improves 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. A strained region 2 exists at the boundary between the superconducting layer 10 and the artificial pin 1.

The superconducting layer 10 is a superconductor represented by the composition formula REBa ₂ Cu ₃ O _y . RE is a rare earth element, and is, 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 vacancy. δ is preferably 0.3, more preferably 0.2, and even more preferably 0.1. The smaller the amount of oxygen vacancies, the more distortion between the artificial pin 1 described later can be suppressed.

The artificial pins 1 are distributed inside the superconducting layer 10. The artificial pin 1 prevents 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 changes in the magnetic flux lines.

For example, the artificial pin 1 extends approximately in the z direction. FIG. 3 is a diagram of a cross section of the superconducting layer 10 of the superconducting wire 100 according to the first embodiment, which was actually measured using a scanning electron microscope (SEM). FIG. 3 is a cross section of a superconducting layer in which 3.5 mol%, 5.0 mol%, 7.5 mol%, and 10.0 mol% of artificial pins were 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 streaks 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 planes that constitute the crystal. For example, in the artificial pin 1 and the superconducting layer 10, crystals are grown 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 streak extending approximately in the z direction (see FIG. 3).

The artificial pin 1 is an oxide represented by the composition formula _BaMO3 . M is at least one selected from the group consisting of Hf, Zr, Sn, Nb, and Ti.

The amount of artificial pin 1 added is 5.0 mol% or more. Further, the amount of the artificial pin 1 added may be 7.0 mol% or more, or 10.0 mol% or more. As shown in FIG. 3, even if the amount of artificial pin 1 added is 5.0 mol% or more, no obvious structural defects are observed in the crystal structure.

The strain 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 distorted in order to alleviate the difference in lattice constant between the artificial pin 1 and the superconducting layer 10.

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

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

In the superconducting layer 10, electrons are conducted along the CuO plane. When the CuO surface is disordered, the critical transition temperature at which superconductivity occurs decreases. Furthermore, if the CuO surface is disturbed, superconductivity itself may not occur depending on the case. In the strained region 2', the CuO plane is inclined from the xy plane in order to alleviate 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' spread to the extent that they interfere with adjacent strained regions 2', the CuO surface becomes no longer flat and the critical transition temperature decreases. Furthermore, as the critical transition temperature decreases, the critical current density also decreases.

The expansion of the strained region 2 can be suppressed by the manufacturing method. Although details will be described later, when the film formation temperature is increased, the Young's modulus of the superconducting layer 10 becomes smaller, and the range in which strain spreads becomes narrower. Further, when the annealing temperature is lowered, the amount of oxygen introduced into the superconducting layer 10 increases, and the lattice constant of the superconducting layer 10 becomes smaller. When the lattice constant of superconducting layer 10 becomes smaller, the difference in lattice constant from artificial pin 1 becomes smaller, and 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 distortion is suppressed. The distance d(005) between adjacent planes of the (005) plane in the superconducting layer 10 is preferably 100% or more and 101% or less of the theoretical value, more preferably 100% or more and 100.6% or less of the theoretical value. It is more preferably 100% or more and 100.5% or less of the theoretical value. The distance d (005) between 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 distance between adjacent planes d(005)) is, for example, 11. 650 Å, 11.659 Å for Er, 11.659 Å for Er, 11.670 Å for Ho, 11.657 Å for Y, 11.668 Å for Dy, 11.703 Å for Gd, For Eu, it is 11.704 Å, for Sm, it is 11.721 Å, for Nd, it is 11.736 Å, and for La, it is 11.783 Å. For example, when the rare earth element constituting the superconducting layer 10 is Y, the actual value of the c-axis length (obtained from the diffraction peak position of the (005) plane in X-ray diffraction (XRD)) in the superconducting layer 10 is 11.7665 Å. It is preferably at most 11.7199 Å, more preferably at most 11.7190 Å, even more preferably at most 11.7190 Å. Further, when the rare earth element constituting the superconducting layer 10 is Gd, the measured value is preferably 11.8200 Å or less, more preferably 11.7732 Å or less, and even more preferably 11.7200 Å or less. . Further, when the rare earth element constituting the superconducting layer 10 is Eu, the measured value is preferably 11.8210 Å or less, more preferably 11.7742 Å or less, and even more 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.

The 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. Being in a self-magnetic field means that no external magnetic field is applied. A specific method for measuring critical current density is shown below. The critical current density is measured using, for example, a four-terminal method, an MPMS (Magnetic Property Measurement System) device manufactured by Quantum Design, Inc., USA, or the like. Although the measurement of the critical current density may vary somewhat depending on the measurement method, it is preferable that the critical current density be satisfied by any of the methods. Among the measurement methods, an example using an MPMS device will be specifically explained. 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 detection element (SQUID element) and the superconducting magnet with liquid helium. The measurement sample is processed into a size of 3.1 mm x 3.1 mm. After cooling the measurement sample to the measurement temperature (for example, 77 K), an external magnetic field is applied to the measurement sample. The external magnetic field to be applied is changed in the order of, for example, 0T, 7T, -7T, 7T, and 0T. As a result, a change in magnetic susceptibility of the measurement sample is measured. Specifically, the change in magnetic susceptibility measures the hysteresis in the first and fourth quadrants. Then, the obtained change in magnetic susceptibility is changed into a critical current density Jc using an extended Bean model. Through such a procedure, Jc(B) at an arbitrary temperature is determined.

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 conditions of an applied magnetic field of 5 T and a temperature of 65 K. The direction of application of the applied magnetic field is such that the z direction is 0 degrees and the inclination angle in the y direction is θ. It is preferable that the superconducting wire 100 satisfy the above-mentioned critical current density regardless of the angle θ of 0 degrees to 90 degrees.

Further, the superconducting wire 100 preferably has a critical transition temperature Tc of 88K or higher, more preferably a critical transition temperature Tc of 90K or higher. By suppressing the spread width of the strained region 2 in the x and y directions, the critical transition temperature Tc becomes higher.

A specific method for measuring the critical transition temperature is shown below. The measurement of the critical transition temperature, like the measurement of the critical current density, is performed using, for example, an MPMS (Magnetic Property Measurement System) device manufactured by Quantum Design, Inc. in the United States. First, a measurement sample is processed into a size of 3.1 mm x 3.1 mm. Then, the measurement sample is cooled to 5K, the temperature is increased at 0.5K/min, and the temperature change in magnetic susceptibility is measured. The change in magnetic susceptibility corresponding to the superconducting-normal conducting transition is then 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 with a high critical current density can be used in various environments. The superconducting wire 100 according to the first embodiment can be used for cables, transformers, current limiters, silicon pulling magnets, linear motor cars, superconducting power storage devices (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 pulsed laser 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 . Film formation is performed using a pulsed 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 a solid phase reaction method. As the precursor material, for example, oxides of rare earth elements, barium carbonate, and copper oxide are used. For the artificial pin 1, the above-mentioned material is used. The artificial pin 1 is added at a predetermined molar ratio to the amount of precursor material charged.

Next, the sintered body and the base material 20 are placed facing 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 area irradiated with the laser, and several 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 process is set to a temperature that is 200 degrees lower than the peritectic temperature of the superconducting layer or higher. The peritectic temperature refers to the temperature at which the main substance (superconductor excluding artificial pins) constituting 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 at least 150 degrees lower than the peritectic temperature of the superconducting layer, more preferably at least 100 degrees lower than the peritectic temperature of the superconducting layer, and even more preferably at least 100 degrees lower than the peritectic temperature of the superconducting layer. It is above the peritectic temperature.

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

Specifically, the film-forming temperature is a temperature determined under the following conditions. First, a substrate, which is not a film-forming body, is connected to each turn in a film-forming chamber at intervals of about several centimeters. All of these substrates are placed within the film forming region. Next, a thermocouple is installed on the outermost layer of the substrate (for example, _two intermediate layers of CeO) using Ag paste. Then, the inside of the chamber is set to the same conditions as the actual film forming conditions, and the temperature of the outermost surface of the substrate is measured. At this time, the substrate is fed at an arbitrary linear speed relative to the set temperature, and temperature changes are recorded in real time. The relationship between the set temperature of the film forming chamber determined by such a procedure and the actually measured temperature is determined. Using this result, the actual film forming temperature is calculated.

If the film formation 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 direction coaxial with the stretching direction. The larger the Young's modulus, the higher the rigidity and the harder it is to stretch. That is, the higher the film-forming temperature is, 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 alleviated 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 at a temperature of 350° C. or lower for one hour or more, and more preferably for one hour or more at a temperature of 300° C. or lower.

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

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

Further, 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, annealing time, and 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. 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 superconducting layer 10 is annealed under the above conditions, sufficient oxygen is introduced into superconducting layer 10. When enough oxygen is introduced into the superconducting layer 10, the lattice constant of the 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 a superconducting wire according to the second embodiment, the width of the strained region 2 can be narrowed. As a result, a superconducting wire with a high critical transition temperature and 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 may be made within the scope of the gist of the present invention described within the scope of the claims. It is possible to transform and change.

<Consideration 1>
In Study 1, we confirmed the effect of different amounts of artificial pins on the critical current density.

(Example 1)
First, a base material was prepared. The base material was made by laminating 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.

Next, a sintered body of the precursor material of the superconducting layer and the artificial pin was produced by a solid phase reaction method. Eu ₂ O ₃ , BaCO ₃ , and CuO were used as precursor materials for the superconducting layer. The artificial pin was made of _BaHfO3 . Artificial pins were added at a ratio of 5.0 mol% to the precursor material. After thoroughly mixing these materials, the sintered body was fired at 900°C.

Next, the sintered body and the base material were placed facing each other in the chamber. A superconducting layer was formed by irradiating the sintered body with a laser while creating an oxygen atmosphere in the chamber. The laser used was a XeCl excimer laser (wavelength: 308 nm), oxygen pressure: 600 mTorr (80 Pa), substrate-target distance: 97 to 98 mm, laser oscillation energy: 500 to 600 mJ, laser energy density: 2 to 3 J/cm ² The irradiation was carried out under the conditions that the substrate feeding speed 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 according to the following profile. The annealing profile was held at 500°C for 1 hour, then lowered to 250°C, kept at 250°C for 3 hours, and then slowly cooled to room temperature. The time required for film formation was 7 hours or more, and the film was exposed to an oxygen atmosphere for 6 hours or more at a temperature of 250° C. or lower. The oxygen partial pressure at this time was 1.1 atm. A superconducting wire according to Example 1 was produced using the above procedure.

(Comparative example 1)
Comparative Example 1 differs 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 were Y and Gd and no artificial pins were 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 when the measurement temperature was 77 K and an external magnetic field of 3 T was applied. The horizontal axis is the direction in which the external magnetic field is applied, with the z direction being 0 degrees and the inclination angle in the y direction being θ. θ=90° coincides with the y direction. The vertical axis is the critical current density of the superconducting wire.

In both Example 1 and Comparative Example 1, the critical current density was improved compared to Comparative Example 2 in which no artificial pin was added. Further, when comparing Example 1 and Comparative Example 1, it can be seen that the critical current density of Example 1 is improved compared to Comparative Example 1 at any angle. The superconducting wire of Example 1 has a critical current density of 0.6×10 ⁶ A/cm ² or more at any angle.

Further, FIG. 6 is a graph showing the critical current density of the superconducting wires of Example 1 and Comparative Example 2 in a state where the measurement temperature was 65 K and an external magnetic field of 5 T was applied. The horizontal axis is the direction in which the external magnetic field is applied, with the z direction being 0 degrees and the inclination angle in the y direction being θ. θ=90° coincides with the y direction. The vertical axis is the critical current density of the superconducting wire.

In both Example 1 and Comparative Example 1, the critical current density was improved compared to Comparative Example 2 in which no artificial pin was 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.

<Consideration 2>
Study 2 investigated the behavior of critical current density when varying the oxygen annealing temperature. Study 2 was conducted when the concentration of the artificial pin was 5.0 mol% (series of Example 1) and when it was 3.5 mol% (series of Comparative Example 1). In each case, the maintenance temperature during oxygen annealing was 250°C, 300°C, 350°C, 400°C, and 450°C. The critical current density was measured in a self-magnetic field with no external magnetic field applied. The other conditions were produced and evaluated in the same manner as in Example 1.

FIG. 7 is a diagram showing the relationship between the oxygen annealing maintenance temperature and the critical current density in the self-magnetic field. The horizontal axis is the oxygen annealing maintenance temperature, and the vertical axis is the critical current density in the self-magnetic field. As shown in FIG. 7, when the concentration of the artificial pin is 5.0 mol% and the oxygen annealing temperature is set to 350°C or less, the critical current density in the self-magnetic field is 5.0 × 10 ⁶ A/cm ² That's all. Note that when the oxygen annealing temperature exceeds 400° C., even if the oxygen annealing time is sufficiently long, the critical current density does not reach 5.0×10 ⁶ A/cm ² .

<Consideration 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 investigated when the film formation temperature during film formation was varied.

In Study 3, the concentration of the artificial pin was 10 mol%. Film formation temperatures of 1040°C, 1060°C, 1080°C, 1100°C, 1120°C, 1140°C, and 1160°C were investigated, respectively.

FIG. 8 is a diagram showing the relationship between the film formation temperature, the critical transition temperature, and the c-axis length of the superconducting layer. The horizontal axis is the film formation temperature, the left column of 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 in X-ray diffraction (XRD). The results shown in FIG. 8 are the results before oxygen annealing.

The critical transition temperature increased as the film formation temperature increased. This is thought to be because the Young's modulus of the superconducting layer became smaller as the film-forming temperature became higher, and the spread width of the strained region became narrower. The critical transition temperature is improved when a destrained region is formed between adjacent strained regions, creating a conduction path for electrons.

Furthermore, the c-axis length of the superconducting layer became narrower as the film-forming temperature increased. This is thought to be because the spread width of the strained region became narrower, and the c-axis length determined as the average value of the superconducting layer became narrower. When the c-axis length becomes narrower, the difference in lattice constant between the artificial pin and the superconducting layer becomes smaller, and strain is suppressed.

In addition, in Study 3, since oxygen annealing was not performed, the critical transition temperature was improved, but a sufficient critical current density was not obtained. That is, the critical current density could not be improved unless sufficient oxygen was introduced through oxygen annealing.

<Consideration 4>
Study 4 investigated the relationship between the concentration of artificial pins and the critical current density 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 oxygen annealing profile was maintained at 500° C. for 1 hour and then slowly cooled to room temperature. The time required for film formation was 7 hours or more, and the time required for passing through the temperature range of 250° C. or less was 3 hours.

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

1 Artificial pins 2, 2' Strain regions 10, 10' Superconducting layer 20 Base material 100 Superconducting wire

Claims (2)

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 the compositional formula BaMO ₃ (M is at least one selected from the group consisting of Hf, Zr, Sn, Nb, and Ti);
The concentration of the artificial pin added to the precursor material of the superconducting layer is 5.0 mol% or more and 10.0 mol% or less,
The c-axis direction of the artificial pin and the c-axis direction of the superconducting layer match,
The distance d (005) between adjacent planes of the (005) plane in the superconducting layer is 100% or more and 101% or less of the theoretical value,
The theoretical value of the distance d (005) between adjacent surfaces of the (005) plane in the superconducting layer is 1/5 of the theoretical value of the c-axis length of the (005) plane in the superconducting layer,
The theoretical value of the c-axis length of the (005) plane in the superconducting layer is 11.650 Å when the rare earth element is Yb, 11.659 Å when the rare earth element is Er, 11.670 Å when the rare earth element is Ho, and 11 when the rare earth element is Y. .657 Å, 11.668 Å for Dy, 11.703 Å for Gd, 11.704 Å for Eu, 11.721 Å for Sm, 11.736 Å for Nd, 11.783 Å for La. A method for manufacturing a superconducting wire ,
a film forming step of forming a superconducting layer having artificial pins by pulsed laser deposition;
an annealing step of annealing the superconducting layer in an oxygen atmosphere,
The film forming step is performed at a temperature that is 200 degrees lower than the peritectic temperature of the superconducting layer or higher,
The method for manufacturing a superconducting wire, wherein the annealing step is performed at a temperature of 450° C. or lower for 2 hours or more. The method for manufacturing a superconducting wire according to claim 1 , wherein in the annealing step, the oxygen partial pressure is 1 atm or more.

Images