JPH06219742A - Production of bi oxide superconductor membrane - Google Patents

Abstract

PURPOSE:To produce a Bi series oxide superconductor thick membrane having a high density and excellent characteristics. CONSTITUTION:Each organic salt of Bi, Sr, Ca and Cu is dissolved in xylene so as to have a given molar ratio of each metal. To this solution are added 10-200wt.% oxide powders having the same composition, based on the solution to prepare a paste. The paste is coated on an Ag substrate plate by applicator coating method, heated over a partially melted point after pyrolysis and then slowly cooled under the coagulation point to form a thick membrane. Critical current density (Jc: 77K, OT) of the electric conductive membrane thus obtained and having >=50mum thickness shows >=(1-2)X10<4>A/cm<2> and its degree of orientation along the C axis is 95%.

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 superconducting film, and more particularly to a Bi-based oxide superconductor which can be easily made long and can easily form a thick film having a uniform thickness. The present invention relates to improvement of manufacturing method.

[0002]

2. Description of the Related Art Bi-based (Bi-Sr-Ca-Cu-O
System) has a high critical temperature (Tc), Y-
It is expected to be a practical material for oxide superconductors because it is superior in stability and workability to Ba—Cu—O (Y) superconductors. In this Bi-based superconductor, there are phases having three kinds of Tc depending on the composition, and in particular, an 80K-class (2212) phase (Bi: Sr: Ca: Cu molar ratio = 2: 2: 1: (2, the same below) and 1102K (2223) phase are being studied for practical use as materials that can be used at liquid nitrogen temperatures or higher.

As an application field of the above Bi-based superconductors, there are firstly wire rods and elements. In addition to these, application to a large-area molded article having a large area such as a magnetic shield or a resonator is under study. . In particular, as a method for applying to the latter, (a) a method in which a binder is mixed with an oxide superconducting powder and a slurry whose viscosity is adjusted to a predetermined value is applied onto a substrate, dried, and then baked is generally performed. , And others (b)
A method of applying a solution in which a metal organic acid salt is dissolved onto a substrate and then thermally decomposing it is also under study.

[0004]

However, in the method (a), there is a problem that a high density film cannot be obtained because the binder is thermally decomposed by the desolvation treatment, and the method (b) is also used. On the other hand, while a dense film can be easily obtained, it is difficult to obtain a thick film. The present invention has been made to solve the above problems, and an object thereof is to provide a method for easily producing a thick film made of a high-density Bi-based oxide superconductor.

[0005]

In order to achieve the above object, the method for producing a Bi-based oxide superconducting film according to the present invention comprises:
A metal organic acid salt or organic metal compound containing Bi, Sr, Ca or Cu was dissolved in an organic solvent at a predetermined metal molar ratio, and an oxide powder having substantially the same composition as the metal component of the solution was added to the solution. 10 to 200 parts by weight of the mixed paste is applied to the base material and then heat-treated.

As the solution in the present invention, for example, a metal organic acid salt such as octylic acid, neodecanoic acid or naphthenic acid, or an organic metal compound such as metal alkoxide or metal acetylacetonate, which is soluble in a solvent, is a hydrocarbon. A solvent completely dissolved in an organic solvent such as an organic solvent, an ether solvent, an alcohol solvent, or a mixed solvent of an organic solvent and water is used.

The oxide powder to be mixed with this solution has almost the same composition as the metal component of the solution and has a superconducting composition produced by a solid phase method, a coprecipitation method, a sol-gel method or the like, more preferably a superconducting powder. Is used. The above powder preferably has a particle size of 0.1 to 10 μm,
If a powder having a particle size of more than 10 μm is used, the film thickness and the film quality are uniform, and the smoothness of the film surface is lost. A more preferable range of particle size is 0.3 to 3 μm.

If the amount of the oxide powder mixed in the solution is less than 10 parts by weight with respect to the solution, it becomes difficult to increase the film thickness, and if it exceeds 200 parts by weight, the viscosity of the slurry cannot be adjusted. Therefore, the range is 10 to 200 parts by weight. In the present invention, the molar ratio of the metal component in the solution constituting the Bi-based oxide superconductor is B in the case of 110K phase.
i: Pb: Sr: Ca: Cu = (1.8 to 2.2):
(0 to 0.5): (1.8 to 2.0): (1.8 to 2.
2): (3.0 to 3.5) is preferable, and in the case of 80K phase, Bi: Sr: Ca: Cu = (2.0 to 2.
2): (1.8 to 2.0): (0.9 to 1.1):
It is preferably in the range of (2.0 to 2.5). When the composition is out of these ranges, a non-superconducting phase is likely to be generated and the characteristics thereof are deteriorated.

The base material is a metal such as Ag, Au, Pt, or an alloy thereof, or a ceramic such as SrTiO ₃ or YSZ, which has excellent oxidation resistance in the heat treatment temperature range.
In addition, those which do not cause a reaction with the superconductor or those which do not deteriorate the superconductivity even when a reaction with the superconductor occurs are preferable. As a method for applying the paste onto the substrate, a method generally used for coating a paint can be used, and examples thereof include dip coating and applicator coating.

After the paste is applied on the base material, a heat treatment for thermally decomposing and burning the organic component is applied. For this heat treatment, a generally used sintering method or partial melting method is adopted. You can In particular, since the (2212) phase improves the crystal orientation by gradually cooling from a partially molten state in which a solid phase and a liquid phase coexist to a temperature below the solidification temperature, it is heated to a temperature in the partially molten region after thermal decomposition. The characteristics can be improved by cooling from this temperature to the crystallization temperature or lower in an oxidizing atmosphere.

This constitutes the second invention of the method for producing a Bi-based oxide superconducting film. That is, Bi, Sr, Ca
Alternatively, a metal organic acid salt or an organometallic compound containing Cu is dissolved in an organic solvent in an approximate molar ratio of Bi: Sr: Ca: Cu = 2: 2: 1: 2, and the solution is almost mixed with the metal component of the solution. Oxide powder of the same composition is 10-2 for the solution
After applying a paste mixed with 100 parts by weight on a base material, a heat treatment is performed including a heating step of heating above the partial melting point after thermal decomposition and a cooling step of gradually cooling from this heating temperature to below the freezing point.

In the above cooling step, the cooling rate is 1 to 30 ° C. /
It is preferable to carry out by slow cooling in the range of hr. If the cooling rate is less than 1 ° C./hr, the film damage due to the evaporation of elements from the liquid phase becomes large, while if it exceeds 30 ° C./hr, the crystal orientation tends to deteriorate. Further, the partial melting point and the freezing point, that is, the crystallization temperature depends on the composition of the raw material solution, so it is desirable to determine it by means such as thermal analysis, and for example, from the partial melting point to + 10 ° C. Be heated.

[0013]

In the present invention, the paste containing the oxide powder mixed with the solution containing the metal elements constituting the Bi-based oxide superconductor in a predetermined metal molar ratio is applied on the base material and then heat-treated. As a result, the pores of the organic component generated by thermal decomposition are filled with the superconducting powder of fine particles generated from the metal organic acid salt or the metal content of the organometallic compound, and the superconducting film is formed integrally with the oxide powder. Will increase. Further, since the oxide powder is mixed in the solution as compared with the case where heat treatment is performed after applying the metal organic acid salt solution, the film thickness can be easily increased.

[0014]

EXAMPLES Examples and comparative examples of the present invention will be described below. Examples 1-3 Each octylate salt of Bi, Sr, Ca and Cu was added to xylene at 50 wt% so that the metal content thereof had a molar ratio of Bi: Sr: Ca: Cu = 2: 2: 1: 2. Was dissolved at a concentration of, and oxide powder was added to this solution to prepare a paste.

The above oxide powder is Bi: Sr: Ca:
The coprecipitated powder having a molar ratio of Cu = 2: 2: 1: 2 was 85
It was made by firing at 0 ° C. for 20 hours. This paste is Ag
500 on the substrate by the applicator coating method
After pyrolyzing at ℃, heat to 890 ℃ in the partial melting zone,
Then slowly cool to 800 ° C at a cooling rate of 10 ° C / hr,
Further, it was cooled to room temperature at a cooling rate of 100 ° C./hr to form a thick film.

The critical current density (Jc: 77K, 0T) and C-axis orientation of the superconducting film thus obtained are shown in Table 1 together with the film thickness and paste composition (parts by weight).

[0017]

[Table 1]

Comparative Example 1 A thick film was formed in the same manner as in Example except that the paste composition was changed, and the Jc and C-axis orientation of this superconducting film are shown in Table 1 together with the film thickness and paste composition (parts by weight). It was Comparative Example 2 Bi, Sr, Ca and Cu octylates were added in xylene at a concentration of 50 wt% so that the metal content of the octylates was Bi: Sr: Ca: Cu = 2: 2: 1: 2. Then, the solution was applied onto an Ag substrate by an applicator coating method to form a superconducting film in the same manner as in the following examples.

The Jc of the superconducting film thus obtained,
The C-axis orientation degree is shown in Table 1 together with the film thickness. Comparative Example 3 A coprecipitated powder having a molar ratio of Bi: Sr: Ca: Cu = 2: 2: 1: 2 was fired at 850 ° C. for 20 hours to prepare an oxide powder.

This oxide powder was mixed with ethanol to form a slurry, which was then coated on an Ag substrate to form a superconducting film in the same manner as in the following examples. The Jc and C-axis orientation degrees of the superconducting film thus obtained are shown in Table 1 together with the film thickness.

[0021]

As described above, according to the method of the present invention, a paste prepared by mixing a solution of a metal organic acid salt or an organometallic compound with an oxide powder having substantially the same composition as the metal component of the solution is prepared. A thick film made of a Bi-based oxide superconductor with high density and excellent characteristics can be easily obtained by applying heat treatment to the base material and then heat-treating it, especially by gradually cooling it from the partial melting point after pyrolysis to below the freezing point. Can be manufactured.

Claims (3)

[Claims] 1. A solution of a metal organic acid salt or organic metal compound containing Bi, Sr, Ca or Cu dissolved in an organic solvent at a predetermined metal molar ratio, and an oxide having substantially the same composition as the metal component of the solution. 10-200 powder to the solution
A method for producing a Bi-based oxide superconducting film, which comprises applying a paste mixed with parts by weight onto a substrate and then performing a heat treatment. 2. A metal organic acid salt or an organometallic compound containing Bi, Sr, Ca or Cu is added to Bi: Sr: Ca:
A paste prepared by mixing 10 to 200 parts by weight of an oxide powder having substantially the same composition as the metal component of the solution with a solution dissolved in an organic solvent at an approximate molar ratio of Cu = 2: 2: 1: 2. After being applied to a base material, a heat treatment including a heating step of heating above the partial melting point after thermal decomposition and a cooling step of gradually cooling from this heating temperature to below the freezing point is performed, and the Bi-based oxide superconductivity is characterized. Membrane manufacturing method. 3. The oxide powder comprises a superconducting material.
Alternatively, the method for producing the Bi-based oxide superconducting film according to 2 above.