JP2001335322A - Method for manufacturing triaxial orientation oxide superconducting complex and triaxial orientation bismuth oxide superconducting complex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a triaxially oriented organization of oxide superconducting complexes, having an excellent critical current density, by employing a remarkably simple process. SOLUTION: A composite comprising a precursor and a substrate of an oxide superconductor is baked in a furnace with a temperature gradient of 0.5-10 deg.C/cm, allowing at least one part of the precursor to melt. Thereafter, the composite is slowly cooled and solidified with the above temperature gradient being maintained, and transformed into a triaxial orientation oxide superconductor having a triaxially oriented organization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a triaxially oriented oxide superconducting composite and a triaxially oriented bismuth-based oxide superconducting composite. More specifically, the invention of this application provides a method for producing a triaxially oriented oxide superconducting composite suitable as a practical application technique, which realizes a triaxially oriented structure excellent in critical current density by a very simple process,
The present invention relates to a novel triaxially oriented bismuth-based oxide superconducting composite having a triaxially oriented structure.

[0002]

2. Description of the Related Art Research and development of oxide superconductors are proceeding for practical use. For example, the use of wires has been studied for use in various electrical devices, energy storage devices, magnetic separation devices, NMR analysis devices, high energy accelerators, superconducting devices such as fusion reactors, and the like.

In general, superconductors are expected to transport large currents due to their characteristics. In addition, realization of a high critical current density is also required to promote the miniaturization of superconducting equipment and the accompanying reduction in cooling costs. Is indispensable. For this reason, formation of an oriented structure is considered for the oxide superconductor.

[0004]

However, the oriented structure of the oxide superconductor provided so far is mainly a uniaxially oriented structure, particularly a c-axis oriented structure. The critical current density obtained is not very high because the bonds between them are not strong enough. In order to realize a high critical current density, the orientation of the crystal grains of the oxide superconductor is aligned not only in the c-axis but also in the ab plane of the crystal, that is, by forming a triaxially oriented structure, Make the bond stronger,
It is conceivable that the superconducting current easily flows.

At present, as a technique for obtaining a three-axis texture, it has been proposed to epitaxially grow an oxide superconductor on a textured substrate by a vapor phase method.

However, epitaxial growth of an oxide superconductor using an oriented substrate is not a simple process, and there is a problem in terms of cost as a practical application technique. As for a so-called bismuth-based oxide superconductor, one having a triaxial orientation structure is not known.

The invention of this application has been made in view of the above circumstances, and a method for producing a triaxially oriented oxide superconducting composite suitable as a practical application technique and a new method having a triaxially oriented structure. It is an object of the present invention to provide a triaxially oriented bismuth-based oxide superconducting composite.

[0008]

Means for Solving the Problems The present invention solves the above-mentioned problems by providing a composite comprising a precursor of an oxide superconductor and a substrate with a temperature gradient of 0.5 to 10 ° C./cm. After melting at least a part of the precursor of the oxide superconductor in the furnace having the above, the solid is slowly cooled and solidified while maintaining the temperature gradient to form a triaxially oriented oxide superconductor having a triaxially oriented structure. A method for producing a triaxially oriented oxide superconducting composite (claim 1) is provided.

With respect to the invention according to claim 1, the invention of this application provides, as a preferred embodiment, slow solidification at a cooling rate of 10 ° C./hour or less (claim 2).

[0010] The invention of this application is a composite of a bismuth-based oxide superconductor having a triaxially oriented structure and a base material, characterized in that it is a triaxially oriented bismuth-based oxide superconductor composite. 3) is provided.

In a preferred embodiment, the invention according to claim 3 is characterized in that the invention of this application is a bismuth-based oxide superconductor represented by the general formula Bi ₂ Sr ₂ CaCu ₂ O _x (claim 4). provide.

Hereinafter, the method for producing a triaxially oriented oxide superconducting composite and the triaxially oriented bismuth-based oxide superconducting composite of the present invention will be described in more detail with reference to examples.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a triaxially oriented oxide superconducting composite according to the present invention, as described above, a composite comprising a precursor of an oxide superconductor and a base material is formed in an amount of 0.5 to 10 In an electric furnace having a temperature gradient of ° C./cm, at least a part of the precursor of the oxide superconductor is melted, and then gradually cooled and solidified while maintaining the temperature gradient. The melt-solidification heat treatment of slowly cooling and solidifying after at least part of the precursor of the oxide superconductor is melted is a heat treatment usually used for manufacturing an oxide superconductor. 0.5-1
By performing the process in a furnace having a temperature gradient of 0 ° C./cm, the produced oxide superconductor has uniform crystal orientation in the ab plane of the crystal as well as in the c-axis. It becomes a triaxially oriented oxide superconductor having an axially oriented structure. As a method for obtaining a triaxially oriented structure, there is no example of such a very simple process of only heat treatment, and attention is paid to a technique for practical use.

As described above, the temperature gradient in the furnace for performing the melt-solidification heat treatment is limited to 0.5 to 10 ° C./cm. If the temperature gradient is smaller than 0.5 ° C./cm or larger than 10 ° C./cm, a triaxially oriented structure cannot be obtained. For example, as shown in FIG. 1, a tubular furnace is used as a furnace, a heater (2) is arranged on the outer periphery of a tube (1), and the heating of the heater (2) is adjusted. Can be formed. In this case, the sample (3) is kept at 0.5-10 ° C /
It can be placed at the site where the temperature gradient of cm is formed.

As a condition for slow cooling solidification, maintaining a temperature gradient of 0.5 to 10 ° C./cm is indispensable for obtaining a triaxially oriented structure, but for obtaining a sufficiently high oriented structure, cooling is required. Preferably, the rate is 10 ° C./hour or less. Cooling rate is 1
When the temperature exceeds 0 ° C./hour, the degree of orientation of the oriented structure tends to decrease.

The method for producing the triaxially oriented oxide superconductor composite of the invention of this application is not particularly limited as to the type of the target oxide superconductor. So-called yttrium-based, bismuth-based,
The present invention can be applied to the production of composites of various oxide superconductors such as thallium and the like, which have been confirmed so far, and substrates. Also, even if only one type of superconducting phase is developed,
Alternatively, two or more types can be mixed.

There is no particular limitation on the type of substrate used together with the oxide superconductor precursor. Various materials such as silver can be widely used.

The triaxially oriented bismuth-based oxide superconducting composite of the invention of this application has a triaxially oriented structure in which the crystal grains of the oxide superconductor are aligned in the ab plane of the crystal together with the c-axis. It is a composite of a bismuth-based oxide superconductor and a substrate. Due to the triaxial orientation structure, the bond between the particles of the bismuth-based oxide superconductor is sufficiently strong. For example, as shown in the examples described below, 400,000 amps / cm
A high critical current density of ² is obtained.

The triaxially oriented bismuth-based oxide superconducting composite can be produced by the above-described method for producing a triaxially oriented oxide superconducting composite of the present invention. At present, no example has been found in which a triaxially oriented bismuth-based oxide superconducting composite has been produced by a technique of epitaxial growth on an oriented substrate.

The form of the oxide superconductor is not particularly limited in the method for producing a triaxially oriented oxide superconducting composite and the triaxially oriented bismuth-based oxide superconducting composite of the present invention. Bulk materials are also possible, including wires and tapes.

[0021]

EXAMPLE A bismuth-based oxide superconductor represented by the general formula Bi ₂ Sr ₂ CaCu ₂ O _x by a solid-state reaction method (Bi-2212 superconductor)
Was prepared, and an organic binder, a solvent, and a dispersant were added to the precursor powder to form a suspension (slurry). A silver tape having a width of 10 mm and a thickness of 50 μm was used as a base material, and one surface thereof was masked with an adhesive tape, immersed in the slurry, and the slurry was uniformly applied to the silver tape. After drying sufficiently, remove the mask and fold the silver tape in the longitudinal direction to remove the Bi-221
Several samples were prepared so as to enclose the precursor of the two superconductors.

Some of them are 0.5, 1.5, 10 ° C./c
Each of the tubular electric furnaces having a temperature gradient of m was placed in a tubular electric furnace and heat-treated in an atmosphere of 100% oxygen. In the heat treatment, first, the temperature is kept at 500 ° C. for 2 hours to remove organic substances, and then the temperature is raised to 880 ° C. to bring the Bi-2212 superconductor precursor into a partially molten state, and the temperature gradient is maintained at 880 ° C. To 830 ° C. at a cooling rate of 2 ° C./hour. And 100 to room temperature
Cooling was performed at a cooling rate of ° C / hour.

On the other hand, some samples were subjected to the same heat treatment as above in an electric furnace having no temperature gradient.

After the heat treatment, the silver tape was removed from the sample to confirm the structure, and the structure of the Bi-2212 superconductor was observed by X-ray diffraction. The critical current density Jc was measured under a magnetic field of 4.2 K and 10 T by a four-terminal resistance method.

FIG. 2 is a (115) pole figure of a sample heat-treated in a furnace having a temperature gradient of 1.5 ° C./cm. FIG. 3 is a (115) pole figure of a sample heat-treated in a furnace having no temperature gradient.

The sample that had been heat-treated in a furnace having a temperature gradient of 1.5 ° C./cm had clear four-fold symmetry and was confirmed to be triaxially oriented. On the other hand, a sample heat-treated in a furnace without a temperature gradient has a normal uniaxial orientation (c-axis orientation).
Was only confirmed.

As for Jc, the sample heat-treated in a furnace having a temperature gradient of 1.5 ° C./cm was 400,000 A / cm ² , whereas the sample heat-treated in a furnace having no temperature gradient was at most 20 J / cm ^2. 10,000 amps / cm ² . Jc due to triaxial texture
Was confirmed to improve.

For the remaining samples, a temperature gradient of 0.4, 1
Each was placed in each tubular electric furnace at 1 ° C./cm, and subjected to the same heat treatment as described above. Samples heat-treated in a furnace with a temperature gradient of 0.5 and 10 ° C./cm showed triaxial orientation as a result of X-ray diffraction.
In each case, only uniaxial orientation (c-axis orientation) was confirmed as in the sample heat-treated in a furnace having no temperature gradient.

In the heat treatment in a tubular electric furnace having a temperature gradient of 1.5 ° C./cm, cooling and solidification were performed by changing the cooling rate from 880 ° C. to 830 ° C. to 5, 10 ° C./hour. As a result, as the cooling rate increased, the degree of orientation of the Bi-2212 superconductor decreased, and Jc also decreased. When the cooling rate was further increased, Jc no longer reached the practical level.

Of course, the invention of this application is not limited by the above embodiments and examples. It goes without saying that various aspects are possible for details such as the type and form of the oxide superconductor.

[0031]

As described in detail above, according to the invention of this application, it is possible to realize a triaxially oriented structure having an excellent critical current density in an oxide superconducting composite by a very simple process. It becomes suitable as technology.

Further, according to the invention of this application, a completely new triaxially oriented bismuth-based oxide superconducting composite having a triaxially oriented structure is provided. This triaxially oriented bismuth-based oxide superconducting composite has a sufficiently high critical current density, and
Further, it can be applied to various superconducting devices as a bulk material, and is effective in reducing the size of superconducting devices and, in turn, reducing cooling costs.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a furnace having a temperature gradient and a temperature gradient.

FIG. 2 is a (115) pole figure of a sample heat-treated in a furnace having a temperature gradient of 1.5 ° C./cm.

FIG. 3 shows a sample (1) heat-treated in a furnace having no temperature gradient.
15) It is a pole figure.

[Explanation of symbols]

 1 tube 2 heater section 3 sample

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazumasa Toba 1-2-1, Sengen, Tsukuba, Ibaraki Pref. 5G321 AA01 AA05 DB30

Claims (4)

[Claims] In a furnace having a temperature gradient of 0.5 to 10 ° C./cm, at least a part of a precursor of an oxide superconductor is mixed with a composite comprising a precursor of an oxide superconductor and a substrate. A method for producing a triaxially oriented oxide superconductor composite, comprising: gradually melting and solidifying the melt while maintaining the temperature gradient to form a triaxially oriented oxide superconductor having a triaxially oriented structure. . 2. The method for producing a triaxially oriented oxide superconducting composite according to claim 1, wherein the solid is slowly cooled and solidified at a cooling rate of 10 ° C./hour or less. 3. A triaxially oriented bismuth-based oxide superconductor composite, which is a composite of a bismuth-based oxide superconductor having a triaxially oriented structure and a substrate. 4. The triaxially oriented bismuth-based oxide superconductor composite according to claim 3, which is a bismuth-based oxide superconductor represented by the general formula Bi ₂ Sr ₂ CaCu ₂ O _x .