JPH0543205A - Production of oxide superconductive film - Google Patents

Abstract

PURPOSE:To obtain a stabilized-quality oxide superconductive film by the sol-gel method which is low in inflammability. CONSTITUTION:An aq. soln. contg. a complexing agent consisting of the oxidation or reduction product of monosaccharides and a raw compd. for forming an oxide superconductor is spread over a substrate, and the spread layer is heated to thermally decompose the raw compd. The process is repeated plural times to form the superimposed layers of the thermally decomposed raw compd. on the substrate, and the superimposed layers are sintered to produce an oxide superconductive layer. Consequently, the spreading liq. is prepared as the aq. soln., a good-quality gel film is formed, a homogeneous superconductive film excellent in superconductivity is stably obtained, the spreading liq, is difficult to ignite, and the production equipment and process are simplified.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an oxide superconducting film having excellent superconducting properties by a sol-gel method.

[0002]

2. Description of the Related Art Conventionally, as a method for producing an oxide superconducting film by a sol-gel method, alcohols, propionic acid,
Alternatively, there has been known a method in which a developing solution obtained by dissolving a raw material compound in acetic acid is spread on a substrate, the developed layer is heat-treated to thermally decompose the raw material compound, and then sintered.

However, there has been a problem that the viscosity of the developing solution changes with time and the superconducting properties of the resulting oxide superconducting film are not stable, resulting in large variations. In addition, the developing solution easily ignites, and there is a problem that manufacturing facilities or manufacturing processes are complicated to prevent ignition.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to obtain an oxide superconducting film having stable quality by a sol-gel method having low flammability.

[0005]

The present invention develops an aqueous solution containing a complexing agent composed of an oxide or reduced product of a monosaccharide and a raw material compound for forming an oxide superconductor on a substrate, The operation of thermally treating the spreading layer to thermally decompose the raw material compound is repeated a plurality of times to form a superposed layer of the pyrolytically treated layer of the raw material compound on the substrate, and then the superposed layer is sintered. The present invention provides a method for producing an oxide superconducting film.

[0006]

[Function] By using a complexing agent composed of an oxide or reduced product of a monosaccharide, an aqueous solution of a raw material compound for forming an oxide superconductor can be obtained, which is hard to catch fire, and solvent evaporation and solute polymerization. It is possible to obtain a developing solution in which the liquid quality such as viscosity does not easily change. As a result, it is possible to form a film with stable quality for a long time, and it is possible to perform a continuous film forming process of an oxide superconducting film by a sol-gel method.

[0007]

The present invention is intended to produce an oxide superconducting film by a sol-gel method. As a developing solution for the oxide superconducting film, a complexing agent composed of an oxide or a reduced product of a monosaccharide and an oxide superconducting film are used. An aqueous solution containing a raw material compound for body formation is used.

The developing solution can be prepared by mixing the complexing agent, the raw material compound and water. The preferred method of preparing the developing solution from the viewpoint of mixing efficiency is a method of adding the raw material compound to an aqueous solution to which the complexing agent has been added in advance.

As the complexing agent, oxides or reduced products of monosaccharides are used. Examples thereof include heptonic acid, gluconic acid, sorbit, ammonium salts thereof, and the like. The amount of the complexing agent used can be appropriately determined depending on the stability of the developing solution and the like, but is generally 5 to 60 parts by weight, and preferably 20 to 40 parts by weight, per 100 parts by weight of water.

As a raw material compound for forming an oxide superconductor, a compound which reacts with a complexing agent to form a water-soluble compound such as a chelate is used. Examples thereof include oxides such as yttrium, barium, copper, bismuth, strontium, calcium, etc., such as nitrates of elements forming oxide superconductors, chlorides, fluorides, and the like. The raw material compound that can be preferably used is one having a compound form in which constituent elements other than the element forming the oxide superconductor are easily gasified as an oxide or the like and volatilized. The raw material compound to be used does not need to be in the form of a compound containing oxygen because it can replenish the oxygen component in the sintering step and the like.

The amount of each raw material compound used is usually the composition ratio for forming an oxide superconductor, that is, for example, YBa ₂ Cu ₃ O.
_{For the} purpose of forming _y, the use ratio is such that Y, Ba, and Cu are contained in a molar ratio of 1: 2: 3, respectively. In addition, for the purpose of further improving the magnetic characteristics of the critical current density, the usage rate at which the pinning center is formed can be set.

The concentration of the raw material compound in the developing solution may be appropriately determined within the range where it can be dissolved. Generally 0.1 mmo
L / l to 2 mol / l, especially 0.01 to 1 mol / l.
When preparing the developing solution, raw material compounds having different compound forms may be used in combination.

The formation of the oxide superconducting film is carried out by expanding the developing solution on the base material and subjecting the developed layer to heat treatment to thermally decompose the raw material compound a plurality of times. This is performed by forming a superposed layer of the decomposition treatment layer and then sintering the superposed layer.

As the base material, any suitable material that can withstand the sintering temperature may be used. In general, silver or silver alloys, among others,
High melting point alloys such as silver / platinum alloys, silver / palladium alloys,
Alternatively, those made of various ceramics are used.

The developing solution may be spread by an appropriate method such as a spin coating method. The thickness of the spread layer to be formed is preferably 20 μm or less, and more preferably 10 μm or less from the viewpoint of obtaining a homogeneous oxide superconducting film. If the thickness is too thick, the surface texture between the layers to be superimposed tends to vary,
The formed oxide superconducting film is likely to be inhomogeneous.

The spreading layer formed on the substrate is heat-treated to thermally decompose the raw material compound. At that time, a step of drying the spreading layer may be separately provided. The drying treatment is preferably performed at a high temperature, for example, about 150 ° C., and a vacuum drying method or the like may be used together.

The thermal decomposition of the raw material compound can be carried out at an appropriate temperature depending on the kind of the compound. The conditions for general thermal decomposition treatment are 200 to 1500 ° C., especially 350 to 12
00 ° C., 10 minutes to 2 hours, especially 20 minutes to 1 hour. The thermal decomposition may be performed in an appropriate atmosphere such as the atmosphere or an inert gas atmosphere.

In the present invention, the spreading of the developing solution and the thermal decomposition of the developing layer are repeated a plurality of times to form a superposed layer of the pyrolysis-treated layer of the raw material compound on the base material. The number of repetitions is determined by the intended thickness of the superimposed layer, and is generally about 5 to 15 times.

Next, the superposed layer of the pyrolysis-treated layer is subjected to a sintering treatment to form an oxide superconducting film. The sintering process may be performed in series with the pyrolysis process of the final spreading layer. Sintering is performed at an appropriate temperature according to the type of oxide superconductor to be formed. The general condition is a treatment at 500 to 1800 ° C. for 10 minutes to 30 hours. The sintering process is generally performed in an atmosphere containing oxygen.

The oxide superconducting film formed by the sintering process is subjected to an oxygen annealing process as necessary to adjust the oxygen content. The treatment operation is generally performed by heating at 300 to 600 ° C. for 30 minutes to 10 hours in an atmosphere containing oxygen.

There is no particular limitation on the type of oxide superconductor that can be formed by the present invention. An example is YB
Y-based oxide superconductors such as a ₂ Cu ₃ O _y and YBa ₂ Cu ₄ O _y ,
Ba _- based oxide superconductors such as Ba _1-x K _x BiO ₃ , Nd _2-x C
Nd-based oxide superconductor such as e _x CuO _y , Bi ₂ Sr ₂ CaCu _{2
O y, Bi 2-x Pb} x Sr 2 Ca 2 Cu 3 O y such Bi-based oxide superconductor, other La-based oxide superconductor, Tl-based oxide superconductors, and Pb-based oxide superconductor mentioned Be done.

Also, the above-mentioned components such as Y are substituted with other rare earth elements, the components such as Ba are substituted with other alkaline earth metals, and the O components are substituted with F and the like. can give. Furthermore, the thing containing the pinning center etc. is mentioned.

[0023]

【Example】

Example 1 200 g of heptonic acid was added to 1000 ml of water heated to 80 ° C.
Was added and dissolved, and then an aqueous solution (developing solution) obtained by dissolving and cooling yttrium nitrate 0.07 mol, barium carbonate 0.14 mol, and copper nitrate 0.21 mol, was prepared by spin coating to a thickness of 50 μm. It is spread on a silver foil to form a spread layer having a thickness of about 5 μm, and the spread layer is naturally dried for 1 hour and then to a thickness of 0.
Dry at 1 Torr and 150 ° C for 1 hour, then at 480 ° C for 1 hour
It was pyrolyzed for an hour (in air).

Next, in accordance with the above, the operation of forming a new spreading layer on the above pyrolysis layer and pyrolyzing it is repeated 9 times to form a superposed layer of a total of 10 pyrolysis layers, It is sintered in an oxygen atmosphere at 900 ° C. for 2 hours and then oxygen-annealed at 400 ° C. for 5 hours to obtain a silver foil having a thickness of about 4 μm and having a YBa ₂ Cu ₃ O _y oxide superconducting film with good adhesion. Obtained.

Example 2 According to Example 1, except that 200 g of gluconic acid was used in place of heptonic acid, and 0.07 mol of yttrium chloride, 0.14 mol of barium chloride and 0.21 mol of copper chloride were used. A silver foil having a YBa ₂ Cu ₃ O _y based oxide superconducting film with good adhesion was obtained.

Example 3 Instead of heptonic acid, 200 g of sorbit was used, and 0.07 mol of yttrium fluoride and 0.1 barium fluoride were used.
Example 1 except that 4 mol and 0.21 mol of copper fluoride were used.
According to the above, a silver foil having a YBa ₂ Cu ₃ O _y based oxide superconducting film with good adhesion was obtained.

Example 4 Instead of heptonic acid, ammonium salt of heptonic acid 20
YBa ₂ Cu ₃ O _y according to Example 1 except that 0 g was used.
A silver foil having a system oxide superconducting film with good adhesion was obtained.

Example 5 200 g of heptonic acid was added to 1000 ml of water heated to 80 ° C.
After adding and dissolving, 0.14 mol of bismuth nitrate,
Strontium nitrate 0.14 mol, calcium nitrate 0.0
An aqueous solution obtained by dissolving and cooling 7 mol and 014 mol of copper nitrate was spread on a silver foil having a thickness of 50 μm by a spin coating method to form a spread layer having a thickness of about 5 μm, and the spread layer was naturally dried for 1 hour. After that, it was dried at 0.1 Torr and 150 ° C. for 1 hour and then thermally decomposed at 400 ° C. for 1 hour (in air).

Then, in accordance with the above, the operation of forming a new spreading layer on the previous pyrolysis layer and pyrolyzing it is repeated 9 times to form a superposed layer consisting of 10 pyrolysis layers in total. It was sintered in an oxygen atmosphere at 845 ° C. for 2 hours to obtain a silver foil having a thickness of about 4 μm and having a Bi ₂ Sr ₂ CaCu ₂ O _y based oxide superconducting film with good adhesion.

Comparative Example 1 A silver foil having a YBa ₂ Cu ₃ O _y type oxide superconducting film was obtained in the same manner as in Example 1 except that EDTA ammonium salt was used as a complexing agent.

Comparative Example 2 A silver foil having a YBa ₂ Cu ₃ O _y based oxide superconducting film was obtained in the same manner as in Example 1 except that triethanolamine was used as the complexing agent.

Evaluation Test Viscosity Change The developing solutions used in Examples and Comparative Examples were allowed to stand at room temperature, and the viscosity after a predetermined time was examined.

Critical Temperature The oxide superconducting films obtained in Examples and Comparative Examples were found to have 0.1
The temperature change of the electric resistance was measured by the four-terminal method while cooling with liquid nitrogen under a current density of A / cm ² , and the temperature when the generated voltage between the voltage terminals became 0 was investigated.

Critical Current Density With respect to the oxide superconducting films obtained in Examples and Comparative Examples, the current value was gradually increased while cooling with liquid nitrogen together with the power leads, and the four terminals method was applied to the voltage applied between the voltage terminals. The change was measured, and a value obtained by dividing the current value when a voltage of 1 μv / cm appeared in the XY recorder by the cross-sectional area of the superconducting film was obtained.

The above results are shown in Table 1.

[Table 1]

[0036]

EFFECTS OF THE INVENTION According to the present invention, the quality of the developing solution consisting of an aqueous solution is unlikely to change, and a stable quality oxide superconducting film can be formed by the sol-gel method. It is possible to stably obtain an oxide superconducting film that can be formed, is homogeneous, and has excellent superconducting properties. Further, since the developing solution is an aqueous solution, it is difficult to catch fire and has the advantage of simplifying manufacturing equipment or manufacturing process.

Claims (1)

[Claims] 1. A raw material obtained by spreading an aqueous solution containing a complexing agent composed of an oxide or reduced product of a monosaccharide and a raw material compound for forming an oxide superconductor on a substrate and heat-treating the developed layer. After repeating the operation of thermally decomposing the compound a plurality of times, after forming a superposed layer of the thermally decomposed layer of the raw material compound on the substrate,
A method for manufacturing an oxide superconducting film, which comprises subjecting the superposed layer to a sintering treatment.