JPH0873264A - Production of bismuth based 2212 phase superconductor - Google Patents

Abstract

PURPOSE: To provide a producing method of a Bi based 2212 phase superconductor free from the generation of thermal decomposition by controlling the quantity of oxygen by heat treatment for a short time even when the film thickness of the Bi based 2212 phase semiconductor is increased. CONSTITUTION: A precursor which becomes a superconductor by firing or the superconductor is heat-treated at >=750 deg.C to <=860 deg.C in the midst of cooling in an atmosphere of <=0.2atm oxygen partial pressure after fired and cooled to <=200 deg.C at the rate of <=500 deg.C/hr while keeping the oxygen partial pressure.

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 Bi-based 2212 phase superconductor which can obtain a high critical current.

[0002]

2. Description of the Related Art Bi-based 2212 phase superconductors are expected to be put to practical use as magnetic shields, power transmission cables, current leads, etc., and aim to improve superconducting characteristics such as critical current density (hereinafter referred to as Jc). Research is being conducted.

In the conventional Bi-based 2212 phase superconductor, starting materials are mixed, calcined and crushed to prepare a precursor, and a binder and the like are further mixed according to the manufacturing method, and then shaped into a desired shape and fired. Was manufactured.

In order to improve the superconducting characteristics, Bi system 2
The Y-based oxide superconductor discovered before the 212-phase superconductor is generally used to improve Tc because the temperature at which the electric resistance becomes zero (hereinafter referred to as Tc) also changes when the oxygen amount is changed. After firing, heat treatment was performed.

From the above, also in the Bi type 2212 phase superconductor, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2-199057, after the Bi type 2212 phase superconductor or its precursor is fired, it is cooled under a specific condition. Alternatively, a method has been proposed in which heat treatment is performed again to remove excess oxygen to improve Tc and Jc. Further, in Japanese Patent Application Laid-Open No. 5-145267, when the divided bodies are joined, heat treatment is performed at a temperature of preferably 450 to 750 ° C. in an atmosphere having an oxygen concentration of 15% by volume (oxygen partial pressure of 0.15 atm) or less to obtain superconducting characteristics. A way to improve is proposed.

However, since the heat treatment temperature is low in both methods, the oxygen amount can be controlled in a short time when the film thickness of the Bi-based 2212 phase superconductor is thin, but when the film thickness becomes thick, it is necessary to perform heat treatment for a long time. There is a problem that it is difficult to control the uniform oxygen content in the entire thick film. Further, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2-199057, if the heat treatment atmosphere is 0.1 atm or less and the temperature exceeds 700 ° C., the amount of oxygen in the Bi-based 2212 phase superconductor crystal does not become an appropriate amount, which is an object. Superconductor characteristics cannot be obtained. On the other hand, in the method disclosed in Japanese Patent Laid-Open No. 5-145267, 780 ° C.
When the Bi-based 2212 phase superconductor is heat-treated in an atmosphere having an oxygen concentration of 15% by volume (oxygen partial pressure of 0.15 atm) or less at the above temperature, thermal decomposition starts, and at 750 ° C. or less, such thermal decomposition is less likely to occur. Preferably, heat treatment at a temperature exceeding 750 ° C. and an oxygen partial pressure of 0.15 atm or less causes thermal decomposition, which is not preferable.

According to the present invention, even if the film thickness of the Bi-based 2212 phase superconductor is increased, the amount of oxygen is controlled by a short time heat treatment,
Bi system 221 that improves superconducting properties and does not cause thermal decomposition
A method for manufacturing a two-phase superconductor is provided.

[0008]

Means for Solving the Problems In order to improve superconducting characteristics by removing excess oxygen of Bi-based 2212 phase superconductor crystal in the cooling process after firing, the present inventors have conducted heat treatment and cooling after firing under various conditions. As a result of performing Tc, Jc measurement, X-ray diffraction, SEM (scanning electron microanalyzer) observation, etc., the superconductor does not undergo thermal decomposition even in the above-mentioned high temperature and low oxygen partial pressure atmosphere. Moreover, heat treatment and cooling conditions exhibiting excellent superconducting properties have been found. It has also been found that even when a thicker superconducting film is formed, it is possible to control to an appropriate amount of oxygen in a short time.

According to the present invention, after the precursor or superconductor which becomes the superconductor after firing is fired, the temperature exceeds 750 ° C. and 860 ° C. during cooling.
Heat treatment is performed in a temperature range of ℃ or less and an oxygen partial pressure of less than 0.2 atm, and then a rate of 500 ℃ / hour or less while maintaining the above oxygen partial pressure until reaching a temperature of 200 ℃ or less. The present invention relates to a method for manufacturing a Bi-based 2212 phase superconductor that is cooled by.

The heat treatment atmosphere in the present invention is required to have an oxygen partial pressure of less than 0.2 atm, and 0.005
To 0.1 atm is more preferable, and 0.01 to
More preferably, it is in the range of 0.05 atm. When the oxygen partial pressure of the heat treatment atmosphere is 0.2 atm or more, even if the optimum oxygen amount is obtained at a high temperature, the oxygen amount is excessive during the cooling, so that the oxygen amount becomes excessive and the superconducting property is deteriorated.

The temperature of the heat treatment process exceeds 750 ° C. and is 86
The temperature is set to 0 ° C. or less, more preferably 760 to 840 ° C., further preferably 780 to 820 ° C. When the temperature is 750 ° C. or lower, long-time heat treatment is required when the film thickness of the Bi-based 2212 phase superconductor is large, and when the temperature exceeds 860 ° C., the Bi-based 2212 phase superconductor is likely to be thermally decomposed.

In the cooling process, it is necessary to keep the oxygen partial pressure of the heat treatment atmosphere below 0.2 atm until the temperature reaches 200 ° C. or lower, and the oxygen partial pressure of the heat treatment atmosphere before the temperature reaches 200 ° C. or lower. Is 0.2 atm or more, Bi
2212-phase superconductor crystal becomes easy to absorb oxygen,
This causes deterioration of superconducting properties.

The cooling rate in the heat treatment step is required to be 500 ° C./hour or less until it becomes 200 ° C. or less, preferably 30 to 300 ° C./hour. 500 ° C
If cooling is performed at a rate exceeding / hour, micro cracks are likely to occur in the superconductor or the like due to thermal stress during cooling.

Although the present invention relates to a Bi-based 2212 phase superconductor, it can be applied to a composition deviated from the stoichiometric composition, a composition in which a part of the main elements is replaced with an element such as Pb or Sb, and the like. .

There are no particular restrictions on the raw materials containing bismuth, strontium, calcium and copper which compose the Bi-based 2212 phase superconductor of the present invention. For example, carbonates, oxides, oxalates, nitrates, metal alkoxides, etc. One kind or two or more kinds can be used.

The firing temperature is appropriately selected depending on the blending ratio of each raw material, etc., but it is preferable to perform firing in the range of 800 to 980 ° C., and the firing atmosphere is in the air.
The firing can be performed in an oxygen atmosphere, an air stream, or the like.

[0017]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to the examples. Note that% is weight%
Means Examples 1 to 8 and Comparative Examples 1 to 5 Bismuth trioxide (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity: 99) so that the composition ratio of bismuth, strontium, calcium and copper is 2: 2: 1: 2 in atomic ratio. 9.9%) 228.
3 g, strontium carbonate (manufactured by Kojundo Chemical Laboratory, purity 99.9%) 144.7 g, calcium carbonate (manufactured by Kojundo Chemical Laboratory, purity 99.9%) 49.0 g and cupric oxide 77.9 g ( Made by Kojundo Chemical Research Institute, purity 99.9%)
Was weighed and used as the starting material.

The above starting materials were filled in a synthetic resin container together with a steel ball covered with the synthetic resin and 300 cc of water, and after wet mixing for 24 hours, the slurry was taken out of the container and dried at 100 ° C. for 24 hours. A mixed powder was prepared.
This mixed powder was placed in an alumina mortar, calcined at 830 ° C. for 5 hours in the air using an electric furnace, coarsely crushed, and then filled in a synthetic resin container with zirconia balls and 300 cc of ethyl acetate. The powder was wet pulverized for an hour to obtain a calcined powder having an average particle size of 5 μm.

To 100 parts by weight of the above calcined powder, 8 parts by weight of polyvinyl butyral resin (manufactured by Wako Pure Chemical Industries, reagent grade 1), 3 parts by weight of phthalate ester (made by Wako Pure Chemical Industries, reagent grade 1) and 50 parts by weight of butanol (Wako Pure Chemical Industries, Ltd.) A medicinal product, first-grade reagent) was added and mixed, and then deaeration was performed to obtain a slurry having a viscosity of 15 Pa · s. This slurry is supplied onto a polyester film (manufactured by Toray) having a thickness of 180 μm, and a green sheet for a superconductor having a thickness of 0.1 mm (hereinafter referred to as a green sheet) is formed by a doctor blade method. Is made into a precursor, cut into a shape with a width of 3 mm and a length of 25 mm, and then the cut green sheet has a thickness of 0.1 mm.
One is placed on each side of the silver substrate, and the temperature is 60 ° C and the pressure is 10
A green sheet pressure-bonded substrate was obtained by pressure bonding under the condition of MPa for 15 minutes.

This green sheet pressure-bonded substrate was put in an electric furnace and heated to 300 ° C. in air at 50 ° C./hour, 300 ° C.
To 880 ° C, the temperature is raised at a rate of 150 ° C / hour,
After holding (calcining) at 82 ° C. for 0.5 hour, it was cooled down to 850 ° C. at a rate of 2 ° C./hour, then cooled to a temperature shown in Table 1 at a rate of 100 ° C./hour, and After holding (heat treatment) in the time and atmosphere shown in 1, the atmosphere was cooled at a rate of 100 ° C./hour to 200 ° C. or less, and the thickness of one layer on one side of the superconductor layer was 35.
A Bi-based 2212 phase superconductor having a thickness of μm was obtained.

Regarding the obtained Bi-based 2212 phase superconductor, Jc at Tc and liquid nitrogen temperature (77.3K) at zero magnetic field was obtained.
c was measured by the four-terminal method. The results are shown in Table 1 together with the comparative example.

[0022]

[Table 1] * Comparative example 1 has no heat treatment

As shown in Table 1, it is shown that the Bi-based 2212 phase superconductor according to the embodiment of the present invention is excellent in Tc and Jc. On the other hand, the Bi-based 2212 phase superconductor of the comparative example has lower Tc and Jc than the Bi-based 2212 phase superconductor according to the embodiment of the present invention.

Example 9 Except for changing the number of pressure-bonded green sheets to 4 sheets each to obtain a green-sheet pressure-bonded substrate, thermocompression bonding, firing, heat treatment and cooling were performed under the same conditions as in Example 4 to form a superconductor layer. A Bi-based 2212 phase superconductor having a thickness of 140 μm on one side was obtained. Tc and Jc of the obtained Bi-based 2212 phase superconductor were measured under the same conditions as in Examples 1 to 8
c was 89.6 K and Jc was 1,840 A / cm ² .

Comparative Example 6 The green sheet pressure-bonded substrate obtained in Example 9 was placed in an electric furnace and heated in the air at a rate of 50 ° C./hour up to 300 ° C. and from 150 to 300 ° C. at a rate of 150 ° C./hour. Warm, 88
After holding at 2 ° C for 0.5 hours, the temperature in the electric furnace was cooled at a rate of 2 ° C / hour up to 850 ° C and 100 ° C / hour up to 600 ° C. And hold for 1 hour, then 200 at the rate of 200 ℃ / hour
It was cooled to ℃ or less, to obtain a Bi-based 2212 phase superconductor in which the thickness of the four layers on one side of the superconductor layer was 0.2 mm. Examples 1 to 8 of the obtained Bi-based 2212 phase superconductor
As a result of measuring Tc and Jc under the same conditions as above, Tc was 8
The 4.9 K and Jc were 630 A / cm ² .

Five samples were prepared for each of the above Examples and Comparative Examples according to each condition, and Tc and Jc are represented by an average value of five samples.

[0027]

[Effect of the invention] Bi system 2212 obtained by the present invention
The phase superconductor is a Bi-based 2212 phase superconductor industrially extremely suitable because the superconducting property can be improved by heat treatment for a short time even if the film thickness is large without causing thermal decomposition.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 39/24 ZAA B

Claims (1)

[Claims] 1. After firing a precursor or a superconductor to be a superconductor after firing, heat treatment is performed in a temperature range of more than 750 ° C. and less than 860 ° C. and an oxygen partial pressure of less than 0.2 atm during cooling. A method for producing a Bi-based 2212 phase superconductor, which is performed and then cooled at a rate of 500 ° C./hour or less while maintaining the above oxygen partial pressure until the temperature reaches 200 ° C. or less.