JP6187711B1 - Oxide superconducting wire - Google Patents

Abstract

The oxide superconducting wire (1) includes a substrate (10) and an oxide superconducting layer (30) formed on the substrate (10). The oxide superconducting layer (30) includes an oxide superconducting phase and a non-superconducting phase. The non-superconducting phase constitutes a plurality of particles dispersedly arranged in the oxide superconducting phase. At least some of the plurality of particles have one or more irregularities. The oxide superconducting phase has a spinodal decomposition type structure configured to surround a plurality of particles.

Description

  The present invention relates to an oxide superconducting wire, and more particularly, to an oxide superconducting wire including an oxide superconducting layer formed on a substrate.

  Since the discovery of high-temperature superconductors that have superconductivity at the temperature of liquid nitrogen, development of high-temperature superconducting wires aimed at application to power equipment such as cables, current limiters, and magnets has been actively conducted. In particular, an oxide superconducting wire in which a thin film layer (oxide superconducting layer) made of an oxide superconductor is formed on a substrate has attracted attention.

One method for producing such an oxide superconducting wire is a coating pyrolysis method (Metal Organic Deposition, abbreviated as MOD method). In the MOD method, a raw material solution (MOD solution) produced by dissolving each organic metal compound of RE (rare earth element), Ba (barium), and Cu (copper) in a solvent was applied to a substrate to form a coating film. Thereafter, for example, a calcined heat treatment is performed at around 500 ° C., the organometallic compound is thermally decomposed, and the thermally decomposed organic components are removed to prepare a calcined film that is a precursor of the oxide superconducting layer. The calcined film is crystallized by subjecting it to a heat treatment at a higher temperature (for example, around 750 to 800 ° C.) to form a RE123-based superconducting layer represented by REBa ₂ Cu ₃ O _X to form an oxide superconducting wire. Is to be manufactured.

  The MOD method is simpler than the gas phase method (evaporation method, sputtering method, pulsed laser deposition method, etc.) manufactured mainly in vacuum, and can handle large areas and complex shapes. Since it has features such as being easy, it is widely used.

  However, in recent years, there has been a strong demand for oxide superconducting thin film wires with improved critical current density Jc and critical current Ic. As a countermeasure, nano-sized quantized magnetic flux that penetrates RE123-based oxide superconductors under a magnetic field. For the purpose of hindering the movement of the magnetic field, a nano-sized magnetic flux pinning point (hereinafter referred to as “pin”) is artificially introduced (for example, JP-T-2007-526199 (Patent Document 1). )reference).

  Also in the MOD method described above, an oxide superconducting layer into which a pin is introduced is formed by adding an element that is a pin raw material, for example, a metal complex (salt) of Zr, to the raw material solution. (For example, refer to JP 2009-164010 A (Patent Document 2)).

Special Table 2007-526199 JP 2009-164010 A

  In the MOD method described above, development of a technique for increasing Ic by increasing the thickness of the oxide superconducting layer is required. As a method for producing a thick oxide superconducting layer, a thick oxide superconducting layer is generally formed by producing a thick calcined film and then subjecting it to a main heat treatment. ing.

  However, in the above method, although the oxide superconductor crystal grows in the c-axis orientation, the pins cannot be properly dispersed in the thick oxide superconductor layer. The effect of pinning to was not fully demonstrated. Further, when crystallization is performed by the main annealing heat treatment, it has been difficult to sufficiently introduce oxygen into the thick oxide superconducting layer. As a result, there is a problem that Jc is lowered and Ic is not sufficiently increased even when the film thickness is increased.

  An object of one embodiment of the present invention is to provide an oxide superconducting wire capable of obtaining a sufficiently high Ic in proportion to the increase in thickness.

  An oxide superconducting wire according to one embodiment of the present invention includes a substrate and an oxide superconducting layer formed over the substrate. The oxide superconducting layer includes an oxide superconducting phase and a non-superconducting phase. The non-superconducting phase constitutes a plurality of particles dispersedly arranged in the oxide superconducting phase. At least some of the plurality of particles have one or more irregularities. The oxide superconducting phase has a spinodal decomposition structure configured to surround the plurality of particles.

  According to the above, it is possible to provide an oxide superconducting wire capable of obtaining a sufficiently high Ic in proportion to the increase in thickness.

It is a cross-sectional schematic diagram which shows the structure of the oxide superconducting wire which concerns on embodiment. It is a flowchart for demonstrating the manufacturing method of the oxide superconducting wire which concerns on this embodiment. It is a figure explaining the outline | summary of the manufacturing method of the oxide superconducting wire which concerns on this embodiment. It is a figure explaining the outline | summary of the manufacturing method of the oxide superconducting wire which concerns on this embodiment. It is a figure explaining the outline | summary of the manufacturing method of the oxide superconducting wire which concerns on this embodiment. It is a schematic diagram which shows the structure of the oxide superconducting layer in the oxide superconducting wire which concerns on this embodiment. It is the elements on larger scale which looked at the superconducting material layer of FIG. 6 from the arrow VII direction. It is a schematic diagram which shows the two-dimensional structure of the oxide superconducting layer which can be confirmed by cross-sectional observation.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  (1) The oxide superconducting wire 1 (see FIG. 1) according to one aspect of the present invention includes a substrate 10 and an oxide superconducting layer 30 formed on the substrate 10. The oxide superconducting layer 30 (see FIGS. 6 and 7) includes an oxide superconducting phase 32 and a non-superconducting phase 34. The non-superconducting phase 34 is composed of a plurality of particles dispersed in the oxide superconducting phase 32. At least some of the plurality of particles have one or more irregularities. The oxide superconducting phase 32 has a spinodal decomposition structure configured to surround the plurality of particles. In the present specification, the “spinodal decomposition type structure” is a structure formed by spinodal decomposition. “Spinodal decomposition” refers to a phase separation phenomenon that does not require nucleation and occurs due to composition fluctuations in a binary or multicomponent solid solution. However, the formation process of the structure of the oxide superconducting phase 32 is not limited to the one including spinodal decomposition.

  In the oxide superconducting layer 30, the surface of the particles that are the non-superconducting phase 34 acts as a pin. Since the particles have one or more irregularities, pins having all three-dimensional angles can be efficiently distributed in the oxide superconducting phase 32. In addition, since the oxide superconducting phase 32 surrounding the particles has a spinodal decomposition structure, the oxide superconducting phase 32 is not interrupted by the particles. Thereby, since pins can be appropriately dispersed in the oxide superconducting phase 32, a high pinning function can be obtained even in a thick oxide superconducting layer. Therefore, an oxide superconducting wire having a high Ic in proportion to the increase in thickness can be realized.

  The portion where the oxide superconducting phase 32 has a spinodal decomposition structure is at least a part of the oxide superconducting layer 30 in the direction in which the oxide superconducting wire 1 extends, or the width direction of the oxide superconducting wire 1. If it exists at least in part, a high pinning function can be obtained.

  (2) In the oxide superconducting wire 1 according to the above (1), the spinodal decomposition structure is preferably continuous at least in the extending direction of the oxide superconducting wire. In this way, in the oxide superconducting phase 32, the flow of the superconducting current is not hindered by the non-superconducting phase 34. Therefore, the oxide superconducting layer 30 has stable superconducting characteristics over the entire length.

  (3) Preferably, in the oxide superconducting wire 1 according to the above (1) or (2), the volume ratio of the oxide superconducting phase 32 in the oxide superconducting layer 30 is 48% or more and 83% or less. By setting it as such a volume ratio, the particle | grains which comprise the non-superconducting phase 34 can fully exhibit the function of pinning, without interrupting the spinodal decomposition | disassembly type | mold structure in the oxide superconducting phase 32. In the present specification, the volume ratio of the oxide superconducting phase 32 in the oxide superconducting layer 30 refers to the ratio of the volume of the oxide superconducting phase 32 to the volume of the oxide superconducting layer 30.

  (4) In the oxide superconducting wire according to any one of (1) to (3), preferably, at least some of the plurality of particles have a plurality of inflection points in cross-sectional shape. In this way, since the curved surface acting as a pin increases on the surface of the particle, the function of pinning can be enhanced. In the present specification, the inflection point refers to a point at which the curvature changes in a curve forming the cross-sectional shape of one particle.

(5) Preferably, in the oxide superconducting wire 1 according to (4) above, the ratio of the circumference of the at least some of the particles to the area of the cross-sectional shape is 20 μm ⁻¹ or more and 50 μm ⁻¹ or less. The ratio of the perimeter to the area of the cross-sectional shape of the particles is one of the indices indicating the distortion of the cross-sectional shape of the particles, and the cross-sectional shape of the particles becomes distorted as the ratio increases. By setting the ratio in the above range, the curved surface acting as a pin on the surface of the particle increases, so that the pinning function can be enhanced.

Preferably in the oxide superconducting wire 1 according to any one of (6) above (1) to (5), the plurality of particles, the cross-sectional area per particle is 0.005 .mu.m ² or more 1 [mu] m ² or less. By setting it as such a cross-sectional area, particle | grains can fully exhibit the function as a pin, without having a bad influence on the superconducting characteristic of the oxide superconducting wire 1. FIG.

(7) In the oxide superconducting wire 1 according to any one of the above (1) to (6), preferably, the oxide superconducting layer 30 is formed of REBa ₂ Cu ₃ O _X (wherein RE is one of rare earth elements). A RE123-based superconductor represented by a composition formula of a seed or two or more. The non-superconducting phase 34 includes RE ₂ O ₃ . When the peak intensity of the RE ₂ O ₃ (222) plane by X-ray diffraction measurement is IRE ₂ O ₃ (222) and the peak intensity of the REBa ₂ Cu ₃ O _x (003) plane is IREBa ₂ Cu ₃ Ox (003). The peak intensity ratio IRE ₂ O ₃ (222) / (IRE ₂ O ₃ (222) + IREBa ₂ Cu ₃ O _x (003)) is 0.05 or more. With such a peak intensity ratio, it can be said that the RE ₂ O ₃ particles are large enough to function as pins. Therefore, a high pinning function can be obtained.

(8) In the oxide superconducting wire 1 according to any one of the above (1) to (7), the area ratio of the non-superconducting phase 34 per unit cross-sectional area of the oxide superconducting layer 30 is preferably 40% or more. By setting such an area ratio, a sufficient amount of particles can be obtained, so that a high pinning function can be obtained. In this specification, the area ratio of the non-superconducting phase per unit cross-sectional area refers to the ratio of the area of the non-superconducting phase to the area of the observation region of 1 μm square (1 μm ² ). The area of the non-superconducting phase refers to the total value of the cross-sectional areas of all particles detected in the observation region.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

(Configuration of oxide superconducting wire)
FIG. 1 is a schematic cross-sectional view illustrating a configuration of an oxide superconducting wire according to an embodiment.

  FIG. 1 shows a cross section cut in a direction crossing the extending direction of the oxide superconducting wire 1 according to the present embodiment. For this reason, the direction intersecting the paper surface is the longitudinal direction of the oxide superconducting wire 1, and the superconducting current of the oxide superconducting layer 30 flows along the direction intersecting the paper surface. Further, in FIG. 1 and the subsequent schematic sectional views, in order to make the drawing easier to see, the vertical direction (hereinafter also referred to as “thickness direction”) and the left-right direction (hereinafter also referred to as “width direction”) in the rectangular cross section. However, in fact, the length in the thickness direction of the cross section is sufficiently smaller than the length in the width direction.

  Referring to FIG. 1, oxide superconducting wire 1 has a long shape (tape shape) having a rectangular cross section. Here, a relatively large surface extending in the longitudinal direction of the long shape is defined as a main surface. To do. Superconducting wire 1 includes substrate 10, intermediate layer 20, and oxide superconducting layer 30.

  The substrate 10 is preferably made of, for example, metal and has a long shape (tape shape) with a rectangular cross section. The substrate 10 is more preferably an oriented metal substrate. The oriented metal substrate means a substrate having a uniform crystal orientation with respect to the biaxial direction in the plane of the substrate surface. Examples of the oriented metal substrate include Ni (nickel), Cu (copper), Cr (chromium), Mn (manganese), Co (cobalt), Fe (iron), Pd (palladium), Ag (silver), and Au ( An alloy composed of two or more metals among (gold) is preferably used. These metals can be laminated with other metals or alloys. For example, an alloy such as SUS, which is a high-strength material, can be used. In addition, the material of the board | substrate 10 is not specifically limited to this, For example, you may use materials other than a metal.

  The intermediate layer 20 is formed on one main surface of the substrate 10. The oxide superconducting layer 30 is formed on the main surface of the intermediate layer 20 opposite to the main surface facing the substrate 10 (upper main surface in FIG. 1).

The material constituting the intermediate layer 20 is preferably YSZ (yttria stabilized zirconia), CeO ₂ (cerium oxide), MgO (magnesium oxide), Y ₂ O ₃ (yttrium oxide), SrTiO ₃ (strontium titanate), or the like. . These materials have extremely low reactivity with the oxide superconducting layer 30 and do not deteriorate the superconducting characteristics of the oxide superconducting layer 30 even at the interface in contact with the oxide superconducting layer 30. In particular, when a metal is used as the material constituting the substrate 10, the difference in orientation between the substrate 10 having crystal orientation on the surface and the oxide superconducting layer 30 is alleviated, and the oxide superconducting layer 30 is heated at a high temperature. When formed, it can play a role of preventing the outflow of metal atoms from the substrate 10 to the oxide superconducting layer 30. In addition, the material which comprises the intermediate | middle layer 20 is not specifically limited to this.

  The intermediate layer 20 may be composed of a plurality of layers. When the intermediate layer 20 is composed of a plurality of layers, each layer constituting the intermediate layer 20 may be composed of a different material or a part of the same material.

  The oxide superconducting layer 30 is a thin film through which a superconducting current flows in the oxide superconducting wire 1. The oxide superconducting layer 30 has a first main surface 30a located on the substrate 10 side and a second main surface 30b located on the opposite side to the first main surface 30a.

The superconducting material is not particularly limited. For example, it is preferable to use a RE123-based oxide superconductor. The RE123-based oxide superconductor means a superconductor represented by a composition formula of REBa ₂ Cu ₃ O _X. In the above composition formula, RE represents one or more of rare earth elements such as Y (yttrium), Gd (gadolinium), Sm (samarium), and Ho (holmium). X is 6 to 8, more preferably 6.8 to 7. In order to improve Ic, the thickness of the oxide superconducting layer 30 is preferably 1 to 4 μm.

  Although illustration is omitted, in the oxide superconducting wire 1, a protective layer for protecting the oxide superconducting layer 30 may be formed on the second main surface 30 b of the oxide superconducting layer 30. The material constituting the protective layer is preferably, for example, silver (Ag) or a silver alloy.

  The oxide superconducting wire 1 may further include a stabilization layer so as to cover the periphery of the laminate composed of the substrate 10, the intermediate layer 20, and the oxide superconducting layer 30 (and the protective layer). The stabilization layer is made of a foil or plating layer of a highly conductive metal material, and for example, copper (Cu) or a copper alloy is preferable. The stabilization layer may be disposed so as to cover almost the entire outer periphery of the laminate, or may be disposed so as to cover at least the upper main surface of the laminate.

(Manufacturing method of oxide superconducting wire)
Next, with reference to FIGS. 2-4, the manufacturing method of the oxide superconducting wire which concerns on this embodiment is demonstrated.

  FIG. 2 is a flowchart for explaining the manufacturing method of the oxide superconducting wire according to the present embodiment. Referring to FIG. 2, first, a substrate preparation process is performed. Specifically, an oriented metal substrate biaxially oriented to the c axis is prepared as the substrate 10. As the oriented metal substrate, an IBAD (Ion Beam Assisted Deposition) base material, a Ni—W alloy base material, a clad type metal substrate using SUS or the like as a base metal, or the like can be used.

Next, an intermediate layer forming step is performed. Specifically, the intermediate layer 20 is formed on the substrate 10 (aligned metal substrate). For example, a Y ₂ O ₃ layer, a YSZ layer, and a CeO ₂ layer are sequentially formed on the substrate 10. These layers can be formed by a vapor phase method such as sputtering, but may be formed by a MOD method.

  Next, a superconducting layer forming step is performed. In this embodiment, the oxide superconducting layer 30 is formed on the intermediate layer 20 using the MOD method. The MOD method includes a TFA-MOD method (Metal Organic Deposition using TrifluoroAcetates) using an organic metal salt containing fluorine in a raw material solution and a fluorine-free MOD method (FF-MOD method) using an organic metal salt not containing fluorine. is there. In this embodiment, the FF-MOD method is used.

  Specifically, the superconducting layer forming step mainly includes a coating film forming step, a temporary baking step, a main baking step, and an oxygen introduction step. Hereinafter, each process will be described.

(1) Coating film formation process First, a coating film formation process is implemented. In this coating film forming step, a fluorine-free raw material solution is applied to the surface of the intermediate layer 20 and then dried to form a coating film having a predetermined thickness.

  The fluorine-free raw material solution is a fluorine-free organometallic salt solution of RE, Ba, and Cu. As the organic metal salt solution, for example, a metal acetylacetonate solution or a naphthenic acid solution can be used.

  The raw material solution is prepared by dissolving each acetylacetonate complex of RE, Ba, and Cu so that the composition ratio of RE, Ba, and Cu (RE: Ba: Cu) is a: 2: b and dissolving in the solvent. To make. In the present specification, the composition ratio (RE: Ba: Cu) refers to an atomic concentration ratio (molar ratio) of RE, Ba, and Cu. In the MOD method, the composition ratio of the oxide superconducting layer 30 to be formed can be controlled by adjusting the composition ratio of the raw material solution.

In the composition ratio (a: 2: b), in order to obtain a high pinning function, a is preferably selected within a range satisfying 1 ≦ a ≦ 2, and a range of 1.5 ≦ a ≦ 2 It is more preferable to select within the range. In the above composition ratio, b is preferably selected within a range satisfying 3 ≦ b ≦ 3.7, and more preferably selected within a range satisfying 3.2 ≦ b ≦ 3.7. In this embodiment, the total cation concentration of RE ³⁺ , Ba ²⁺ and Cu ²⁺ in the raw material solution is 1 mol / L.

  The prepared raw material solution is applied to the surface of the intermediate layer 20. As a method for applying the raw material solution, a dipping method, a die coating method, or the like can be selected. A coating film is formed by drying the applied raw material solution. The thickness of the coating film is preferably 5 to 30 μm.

  For example, by setting the drying temperature to 100 ° C. or more and 150 ° C. or less, a heat treatment (drying treatment) for removing water and alcohol from the applied raw material solution is performed. In this drying process, for example, the material coated with the raw material solution is placed inside the drying furnace and heated.

  In addition, the said drying process can be implemented continuously with the application | coating process of said raw material solution. For example, the processing apparatus may be configured such that after the tape-shaped substrate is passed through the processing unit for applying the raw material solution, the substrate passes through the drying furnace as it is.

(2) Temporary baking process Next, a temporary baking process is implemented. In this temporary baking step, the solvent component and the like are removed from the coating film that is the precursor. Specifically, the substrate 10 on which the coating film has been formed is heated up to a temperature range of 400 ° C. to 600 ° C., for example, 500 ° C. in an air atmosphere, and is maintained for a certain period of time. The holding temperature is, for example, about 90 minutes. The applied organometallic salt solution is pyrolyzed. At this time, the solvent component and the like are removed from the organometallic salt solution by the separation of CO ₂ (carbon dioxide) and H ₂ O (water). Thereby, as shown in FIG. 3, the calcined film 40a which is a precursor is formed. The calcined film 40a is amorphous.

(3) Main baking process Next, a main baking process is implemented. In the main firing step, the calcined film 40a is crystallized to form the main fired film 40 shown in FIG.

Specifically, the substrate 10 on which the calcined film 40a is formed is heated to a temperature range of 800 ° C. or higher and 850 ° C. or lower, for example, 830 ° C., in a mixed atmosphere of Ar (argon) and O ₂ (oxygen). For the atmosphere at this time, the oxygen concentration can be less than 100 ppm and the carbon dioxide concentration can be 10 ppm or less. This heat treatment is intended to decompose the carbonate in the object to be treated.

When the ambient temperature reaches 830 ° C., the temperature is maintained for a predetermined time. For the atmosphere at this time, the oxygen concentration can be increased to, for example, 500 to 1500 ppm. The predetermined time can be set according to the thickness of the oxide superconducting layer 30 to be formed, for example, at a rate of 2 minutes per 1 μm thickness of the crystallized oxide superconducting layer 30. A crystal is epitaxially grown from the calcined film 40a, thereby forming a main-fired film 40 in which a c-axis oriented oxide superconducting phase is formed.
(4) Oxygen introduction process Next, an oxygen introduction process is carried out. In this oxygen introduction process, a heat treatment for introducing oxygen into the formed film 40 is performed. Specifically, for example, the atmospheric gas is switched to 1 atm and the oxygen concentration is changed to 100%, and while maintaining this oxygen concentration, the maximum heating temperature is set to 550 ° C., and then gradually cooled to 200 ° C. over 3 hours. In this way, the oxide superconducting layer 30 shown in FIG. 1 is formed.

  In addition, by repeatedly performing the above-described coating film forming step, provisional baking step, main baking step and oxygen introduction step, a plurality of main baking films 40 are laminated as shown in FIG. 5 (three layers in FIG. 5). By doing so, the oxide superconducting layer 30 can be formed. In this case, a defective layer that acts as a pin is formed at the interface between the laminated main baking films 40 during the main baking step. The number of stacked layers is appropriately set based on the specifications of the oxide superconducting wire to be manufactured.

(Basic structure of oxide superconducting wire)
Next, the basic structure of the oxide superconducting wire according to this embodiment will be described.

(Three-dimensional structure of oxide superconducting layer)
FIG. 6 is a schematic diagram showing the configuration of the oxide superconducting layer 30 in the oxide superconducting wire 1 according to the present embodiment. FIG. 7 is a partially enlarged view of the superconducting material layer 30 of FIG. 6 as viewed from the direction of arrow VII.

Referring to FIGS. 6 and 7, oxide superconducting layer 30 includes an oxide superconducting phase 32 and a non-superconducting phase 34. The non-superconducting phase 34 includes precipitates (oxide particles) precipitated from the crystal, such as RE ₂ O ₃ (RE oxide) and CuO (copper oxide).

  The non-superconducting phase 34 constitutes a plurality of particles arranged dispersed in the oxide superconducting phase 32. These plural particles include those having one or more irregularities. The shape of the particles will be described later.

  Referring to FIG. 7, the oxide superconducting phase 32 has a spinodal decomposition type structure configured to surround the particles. Specifically, the oxide superconducting phases 32a and 32b, which are network layers, are connected to form a substantially three-dimensional network structure. The spinodal decomposition type structure is continuous at least in the extending direction of the oxide superconducting wire 1. Therefore, in the oxide superconducting phase 32, the flow of the superconducting current is not hindered by the non-superconducting phase 34. Therefore, the oxide superconducting layer 30 has stable superconducting characteristics over the entire length.

  The non-superconducting phase 34 has a function of capturing and fixing (pinning) the magnetic flux lines that have penetrated into the oxide superconducting phase 32. For this reason, the non-superconducting phase 34 dispersed in the oxide superconducting phase 32 has a role of improving the magnetic field dependence of the superconducting current flowing in the oxide superconducting phase 32.

  In the present embodiment, the precipitate that is the non-superconducting phase 34 is a particle having one or more irregularities. Therefore, the particle has a curved surface having all three-dimensional angles on the surface, and the curved surface acts as a pin. Since the particles are dispersed in the oxide superconducting phase 32, pins having various angles can be efficiently distributed in the oxide superconducting phase 32. As a result, the pinning function can be enhanced.

  In the conventional oxide superconducting wire, precipitates formed in the oxide superconducting layer are exclusively spherical or columnar particles. Even a spherical or columnar particle has a curved surface with various angles three-dimensionally on its surface, but one particle has as compared with an uneven particle as in this embodiment. It is thought that the function as a pin is inferior due to the lack of variations in the curved surface. Therefore, as in this embodiment, even if the structure is such that particles are dispersed in the oxide superconducting phase, it is difficult to say that the pins are efficiently distributed. Therefore, it is not easy to obtain a high pinning function.

  As a result of examining the composition of the raw material solution and the heat treatment conditions in the main firing step in the superconducting layer forming step using the MOD method, the present inventors have found that one in the oxide superconducting phase 32 having a spinodal decomposition type structure. It was confirmed that the oxide superconducting layer 30 in which the non-superconducting phase 34 made of particles having the above irregularities is dispersedly arranged can be produced. This makes it possible to obtain the oxide superconducting layer 30 in which the non-superconducting phase 34 sufficiently functioning as a pin is appropriately dispersed without interrupting the oxide superconducting phase 32, so that the oxidation with improved Jc and Ic is improved. Superconducting wire can be realized.

  Here, the spinodal decomposition type structure shown in FIG. 6 and FIG. 7 is confirmed by, for example, performing three-dimensional observation of the oxide superconducting wire 1 using an X-ray micro computerized tomography (X-ray). be able to. In recent years, an X-ray micro CT apparatus having an analysis capability with a resolution of the order of μm has been developed (for example, 4 Yasuda et al., “3 of solidification / crystal growth structure using X-ray micro tomography”). Dimensional observation ", synchrotron radiation, Vol. 16, No. 2 (2003)). According to this, the crystal growth and solidification structure of metals and ceramics is tertiary by using synchrotron radiation (SPring-8) that can obtain high-intensity monochromatic light in the hard X-ray region and SP-μCT using a high-resolution detector. It can be observed in the original.

  In the present embodiment, a sample having a cubic shape of 1.5 μm square was prepared from the oxide superconducting layer 30, and this sample was three-dimensionally observed using the X-ray micro CT apparatus. Based on the obtained three-dimensional data, the volume of the oxide superconducting phase 32 present in the oxide superconducting layer 30 and the volume of the non-superconducting phase 34 present in the oxide superconducting layer 30 were calculated. In this specification, the volume of the non-superconducting phase 34 refers to the total volume of all particles that can be detected by three-dimensional observation using an X-ray micro CT apparatus.

  As a result of three-dimensional observation, in order to obtain a spinodal decomposition type structure in which the non-superconducting phase 34 sufficiently functioning as a pin is appropriately dispersed, the volume ratio of the oxide superconducting phase 32 in the oxide superconducting layer 30 is 48%. It was confirmed that the content is preferably 83% or less. In the present specification, the volume ratio of the oxide superconducting phase 32 in the oxide superconducting layer 30 refers to the ratio of the volume of the oxide superconducting phase 32 to the volume of the oxide superconducting layer 30.

  Note that the structure in which the volume fraction of the oxide superconducting phase 32 is 48% or more and 83% or less is the volume ratio of the non-superconducting phase 34 to the oxide superconducting phase 32 (volume of non-superconducting phase 34 / oxide superconducting phase). 32), the volume ratio is 0.2 or more and 1.1 or less.

  The volume fraction of the oxide superconducting phase 32 is preferably 48% or more. When the volume fraction of the oxide superconducting phase 32 is lower than 48%, in other words, the non-superconducting phase 34 of the oxide superconducting phase 32 is reduced. When the volume ratio is higher than 1.1, it is considered that the non-superconducting phase 34 becomes excessive and partial discontinuity occurs in the spinodal decomposition type structure. This is because the discontinuity of the spinodal decomposition structure may cause discontinuity in the extending direction of the oxide superconducting wire 1 and make it difficult for the superconducting current to flow.

  On the other hand, the volume fraction of the oxide superconducting phase 32 is preferably 83% or less. When the volume fraction of the oxide superconducting phase 32 is higher than 83%, in other words, the non-superconducting phase relative to the oxide superconducting phase 32. When the volume ratio of 34 is lower than 0.2, it is considered that the non-superconducting phase 34 becomes too small to sufficiently exhibit the pinning function.

(Cross-sectional structure of oxide superconducting layer)
The cross-sectional structure of the oxide superconducting layer 30 is determined by a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM). This can be confirmed by observing the cross section of the sample.

  As the SEM, for example, SU3500 manufactured by Hitachi High-Technologies Corporation can be used. The sample analysis area is 2 μm × 2 μm, for example. The acceleration voltage is 15 kV, for example. The probe current is 0.5 pA, for example. As the TEM, for example, HT7700 manufactured by Hitachi High-Technologies Corporation can be used. The sample analysis area is, for example, 2 μm × 2 μm × 0.1 μm. The acceleration voltage is 200 kV, for example. As the STEM, for example, JEM-ARM200F manufactured by JEOL Ltd. can be used. The sample analysis area is 2 μm × 2 μm, for example. The acceleration voltage is 100 kV, for example.

  FIG. 8 is a schematic diagram showing a two-dimensional structure of the oxide superconducting layer 30 that can be confirmed by cross-sectional observation. As shown in FIG. 8, particles having various sizes constituting the non-superconducting phase 34 are dispersed in the oxide superconducting phase 32. The oxide superconducting phase 32 forms a spinodal decomposition structure (see FIGS. 6 and 7) so as to surround these particles. The area and perimeter of the cross-sectional shape of each particle can be calculated by actually measuring an image (two-dimensional planar projection image) obtained with an electron microscope.

In the oxide superconducting wire 1 according to this embodiment, the cross-sectional area per particle contained in the oxide superconducting phase 32 is preferably 0.005 .mu.m ² or more 1 [mu] m ² or less. If the size of the particles is too small, the function as a pin cannot be exhibited sufficiently. On the other hand, if the size of the particles is too large, the superconducting properties of the oxide superconducting wire 1 may be adversely affected.

The area ratio of the non-superconducting phase 34 per unit cross-sectional area of the oxide superconducting layer 30 is preferably 40% or more. If the area ratio of the non-superconducting phase 34 is too low, a sufficient amount of particles cannot be obtained, and the function as a pin cannot be sufficiently exhibited. In this specification, the area ratio of the non-superconducting phase 34 per unit cross-sectional area of the oxide superconducting layer 30 refers to the ratio of the area of the non-superconducting phase 34 to the area (1 μm ² ) of the 1 μm square observation region. . The area of the non-superconducting phase 34 refers to the total value of the cross-sectional areas of all particles detected in the observation region.

  Here, in the cross-sectional observation of the oxide superconducting layer 30, it was confirmed that at least some of the particles had a plurality of inflection points in the cross-sectional shape. In the present specification, the inflection point refers to a point at which the curvature changes in a curve forming the cross-sectional shape of one particle. Particles having a plurality of inflection points in such a cross-sectional shape occupy 50% or more of the total area when the total area of the region occupied by the plurality of particles is calculated in the 1.5 μm square observation region. It was confirmed that

With respect to the particles having a plurality of inflection points in the cross-sectional shape, assuming that the area of the cross-sectional shape of one particle is S (unit: μm ² ) and the circumference is L (unit: μm), L / S is The ratio of the circumference L with respect to the area S of the cross-sectional shape in one particle is represented. This L / S is one of the indices indicating the distortion of the cross-sectional shape of the particles. For example, when the cross-sectional shape of the particle is a perfect circle with a radius of 1 μm, that is, when the cross-sectional shape does not have an inflection point, L / S = 2 μm ⁻¹ . On the other hand, when an inflection point appears in the cross-sectional shape, the value of L / S increases and the cross-sectional shape of the particles becomes distorted.

In the oxide superconducting wire 1 according to this embodiment, L / S is preferably 20 μm ⁻¹ or more and 50 μm ⁻¹ or less. This is because, since the cross-sectional shape of the particles becomes distorted, the curved surface acting as a pin increases on the surface of the particle, and thus the pinning function is enhanced.

(X-ray diffraction)
The oxide superconducting layer 30 included in the oxide superconducting wire 1 according to this embodiment has a peak intensity of the RE ₂ O ₃ (222) plane of IRE ₂ O _{3 in} X-ray diffraction (XRD) measurement. (222), and the peak intensity of the REBa ₂ Cu ₃ O _x (003) plane is IREBa ₂ Cu ₃ O _x (003), the peak intensity ratio IRE ₂ O ₃ (222) / (IRE ₂ O ₃ (222) + IREBa ₂ Cu ₃ O _x (003)) is preferably 0.05 or more.

The peak intensity IRE ₂ O ₃ (222) of the RE ₂ O ₃ (222) plane is affected by the particle size of RE ₂ O ₃ . When the particle size of RE ₂ O ₃ is small, the peak intensity IRE ₂ O ₃ (222) is low, and as a result, the peak intensity ratio is small. On the other hand, when the particle size of RE ₂ O ₃ is large, the peak intensity IRE ₂ O ₃ (222) increases, and as a result, the peak intensity ratio increases. If the peak intensity ratio is 0.05 or more, the RE ₂ O ₃ particles are considered to have a sufficient size to function as a pin.

  In the XRD measurement, for example, D8 manufactured by Bruker can be used as the X-ray generator. As the X-ray source, Cu Kα ray is used. X-rays are generated with an output of 40 kV and 40 mA. The scan method is a θ-2θ continuous method, and the scan range 2θ is 15 ° to 48 °. Set the measurement time to 60 sec.

  The peak intensity can be calculated by subtracting a background component excluding a clear diffraction peak component from the obtained X-ray diffraction profile and then performing curve fitting on the peak component belonging to each substance. The maximum value of the curve obtained at this time is defined as the peak intensity.

For example, when RE is Gd, the peak intensity IGd ₂ O ₃ (222) is calculated by curve fitting with respect to the peak component (2θ = 28.6 °) belonging to Gd ₂ O ₃ . _Further, the curve fitting for the peak component attributable to _{GdBa 2 Cu 3 O x (2θ} = 22.8 °), to calculate a peak intensity _{IREBa 2 Cu 3 O x (003} ). Then, based on the calculated peak intensity, a peak intensity ratio IGd ₂ O ₃ (222) / (IGD ₂ O ₃ (222) + IGdBa ₂ Cu ₃ O _x (003)) is calculated.

(Composition ratio of oxide superconducting layer)
In the oxide superconducting wire 1 according to the present embodiment, when the composition ratio (RE: Ba) of RE and Ba in the oxide superconducting layer 30 is a: 2, a is preferably 1 or more and 2 or less. In this specification, the composition ratio of RE and Ba refers to the atomic concentration ratio (molar ratio) of RE and Ba.

  The composition ratio of RE and Ba (RE: Ba) can be calculated, for example, by element mapping using energy dispersive X-ray spectroscopy (EDX).

Specifically, the cross-sectional observation sample is manufactured using, for example, a focused ion beam system (FIB). Using a SEM (device name: SU3500, manufactured by Hitachi High-Technologies Corporation) with an EDX device (device name: X-Max ^N , manufactured by Oxford), the distribution state of RE and Ba in the cross section of the sample is measured. To do. The measurement conditions are an acceleration voltage of 10 to 15 kV and a measurement area of 2 μm × 2 μm. Based on the distribution of the RE atom concentration in the thickness direction of the oxide superconducting layer 30 and the distribution of the RE atom concentration in the direction perpendicular to the thickness direction, the average RE atom concentration in the oxide superconducting layer 30 is calculated. Similarly, the average Ba atom concentration in the oxide superconducting layer 30 is calculated based on the Ba atom concentration distribution in the thickness direction of the oxide superconducting layer 30 and the Ba atom concentration distribution in the direction perpendicular to the thickness direction. Then, the ratio between the average RE atom concentration and the average Ba concentration is calculated as the composition ratio of RE and Ba (RE: Ba).

Here, in a general RE123-based oxide superconductor, the composition ratio (RE: Ba) of RE and Ba is 1: 2. In this embodiment, the RE atom concentration can be made higher than that of this general RE123-based oxide superconductor. By increasing the RE atom concentration, the precipitates RE ₂ O ₃ can be formed into the shape of particles having one or more irregularities as described above.

  Furthermore, when the oxide superconducting layer 30 is thickened, a is more preferably 1.5 or more and 2 or less. As a method of increasing the thickness of the oxide superconducting layer 30 in order to improve Ic, in general, a thick calcined film is prepared and then subjected to a main baking treatment to thereby form a thick oxide superconducting layer. It is performed to form. However, oxygen cannot be sufficiently introduced into the formed thick film of the fired film, resulting in a decrease in Jc and an increase in Ic proportional to the increase in film thickness. .

In this embodiment, since the RE atom concentration is higher than that of a general RE123-based oxide superconductor, more precipitates (RE ₂ O ₃ ) can be introduced into the oxide superconducting layer 30. .

  In the oxide superconducting layer 30, the interface between the precipitate (oxide particles) and the oxide superconducting phase 32 becomes an oxygen diffusion path. Therefore, by increasing the precipitates introduced into the oxide superconducting layer 30, the oxygen diffused into the oxide superconducting phase 32 can be increased. Thereby, oxygen can be efficiently introduced into the thick oxide superconducting layer 30. As a result, the oxide superconducting layer 30 having a sufficiently high Ic can be formed in proportion to the increase in thickness.

  Further, in the oxide superconducting wire 1 according to the present embodiment, when the composition ratio of Ba and Cu (Ba: Cu) in the oxide superconducting layer 30 is 2: b, b is preferably 3 or more and 3.7 or less. . In the present specification, the composition ratio of Ba and Cu refers to the atomic concentration ratio (molar ratio) of Ba and Cu. The composition ratio (Ba: Cu) of Ba and Cu in the oxide superconducting layer 30 can be calculated using the same method as the composition ratio of RE and Ba described above.

  In a general RE123-based oxide superconductor, the composition ratio of Ba and Cu (Ba: Cu) is 2: 3. In the present embodiment, the Cu atom concentration can be increased as compared with this general RE123-based oxide superconductor. By increasing the Cu atom concentration, the precipitate CuO can be made into the shape of the particles having one or more irregularities described above. In addition, in order to fully exhibit the function as a pin, it is more preferable that b is 3.2 or more and 3.7 or less.

  Further, by increasing the Cu atom concentration, the amount of precipitates introduced into the oxide superconducting layer 30 can be increased as in the case of increasing the RE atom concentration described above. For this reason, oxygen can be efficiently introduced into the thick oxide superconducting layer. Therefore, an oxide superconducting layer having a sufficiently high Ic can be formed in proportion to the increase in thickness.

  Here, regarding the Cu atom concentration in the oxide superconducting layer 30, the Cu atom concentration on the second main surface 30b side is preferably higher than the Cu atom concentration on the first main surface 30a side.

  As described above, by increasing the Cu atom concentration, oxygen can be efficiently introduced into the oxide superconducting layer 30, but on the other hand, if too much precipitate (CuO) is formed, Since the volume fraction of the oxide superconducting phase 32 in the oxide superconducting layer 30 is decreased, the superconducting characteristics may be deteriorated.

  In the present embodiment, by setting the Cu atom concentration on the second main surface 30b side higher than the Cu atom concentration on the first main surface 30a side, the second main surface 30b side, that is, the oxide superconducting layer 30. The precipitates (CuO) formed on the surface side of the oxide are increased more than the precipitates formed inside the oxide superconducting layer 30. Thereby, it is possible to suppress a decrease in the volume ratio of the oxide superconducting phase 32 inside the oxide superconducting layer 30 while efficiently introducing oxygen from the surface side. Therefore, oxygen can be efficiently introduced without degrading the superconducting characteristics.

  The above-mentioned composition ratio of RE and Ba (RE: Ba) and the composition ratio of Ba and Cu (Ba: Cu) are both those of RE, Ba, and Cu when the raw material solution is prepared in the coating film forming step. It can be realized by adjusting the composition ratio.

  The above-described configuration in which the Cu atom concentration on the second main surface 30b side is made higher than the Cu atom concentration on the first main surface 30a side is, for example, as shown in FIG. In the configuration in which the oxide superconducting layer 30 is formed by laminating 40, the Cu atom concentration in the raw material solution for forming the uppermost main-fired film 40 is set as the raw material solution for forming the lower main-fired film 40. This can be realized by making the Cu atom concentration higher than the above.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 1 Oxide superconducting wire, 10 board | substrate, 20 intermediate | middle layer, 30 oxide superconducting layer, 32, 32a, 32b oxide superconducting phase, 34 non-superconducting phase, 40 this fired film 40a calcined film.

Claims (7)

A substrate,
An oxide superconducting layer formed on the substrate,
The oxide superconducting layer includes an oxide superconducting phase and a non-superconducting phase,
The non-superconducting phase constitutes a plurality of particles dispersedly arranged in the oxide superconducting phase,
At least some of the plurality of particles have one or more irregularities,
The oxide superconducting phase, have a configured spinodal decomposition structure so as to surround the particles,
The oxide superconducting wire, wherein the spinodal decomposition structure is continuous at least in the extending direction of the oxide superconducting wire. The oxide superconducting wire according to claim 1 , wherein a volume ratio of the oxide superconducting phase in the oxide superconducting layer is 48% or more and 83% or less. The oxide superconducting wire according to claim 1 or 2 , wherein the at least some of the particles have a plurality of inflection points in a cross-sectional shape. 4. The oxide superconducting wire according to claim 3 , wherein the at least some of the particles have a ratio of a circumference to an area of the cross-sectional shape of 20 μm ⁻¹ or more and 50 μm ⁻¹ or less. Wherein the plurality of particles, the cross-sectional area per particle is 0.005 .mu.m ² or more 1 [mu] m ² or less, the oxide superconducting wire according to any one of claims 1 to 4. The oxide superconducting layer comprises a RE123-based superconductor represented by a composition formula of REBa ₂ Cu ₃ O _X (wherein RE represents one or more of rare earth elements),
The non-superconducting phase comprises RE ₂ O ₃ ;
The peak intensity of the RE ₂ O ₃ (222) plane by X-ray diffraction measurement is IRE ₂ O ₃ (222), and the peak intensity of the REBa ₂ Cu ₃ O _X (003) plane is IREBa ₂ Cu ₃ O _X (003). Then, the peak intensity ratio IRE ₂ O ₃ (222) / (IRE ₂ O ₃ (222) + IREBa ₂ Cu ₃ O _X (003)) is 0.05 or more, and any one of claims 1 to 5 The oxide superconducting wire according to Item. The oxide superconducting wire according to any one of claims 1 to 6 , wherein an area ratio of the non-superconducting phase per unit cross-sectional area of the oxide superconducting layer is 40% or more.

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