JPH0570135A - Oxide superconductor and its production - Google Patents

Abstract

PURPOSE:To suppress lowering of critical electric current density by magnetic application by a specific amount of Ru to a composition consisting of oxides of Bi, Sr, Ca and Cu. CONSTITUTION:Raw material powder of Bi2O3, SrCO3, CaCO3 and Cub, etc., is weighted and these powder is mixed in moisten state using a ball mill, etc. and dried to prepare mixed powder having prescribed weight ratio. Then Ru powder is blended so as to become 0.1-2wt.% based on the total composition and ethyl acetate, etc., is added thereto and these components are mixed in moisten state and dried and then molded under pressure. Then the resultant molding is heated and calcined in atmosphere at about 800-900 deg.C to provide the oxide superconductor reduced in lowering of critical temperature and hardly causing lowering of critical electric current density by the application of magnetic field.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide superconductor and a method for producing the same.

[0002]

2. Description of the Related Art As a conventional oxide superconductor, 198
Bi-Sr-Ca-Cu- containing bismuth, strontium, calcium and copper as the main components, which was discovered by Dr. Maeda of the Research Institute for Metals, January 20, 8
O-based oxide superconductors are generally known, and the critical temperature (hereinafter referred to as T _C ) at which the electric resistance of the Bi-Sr-Ca-Cu-O-based oxide superconductor becomes zero is 110K.
It is known that it is the second highest in the Tl-Ba-Ca-Cu-O system containing thallium, barium, calcium and copper as main components.

On the other hand, the Bi-Sr-Ca-Cu-O-based oxide superconductor has a characteristic that it is less toxic than the Tl-Ba-Ca-Cu-O-based oxide superconductor, but in the crystalline phase. T _C 2223 than the phase composed is a 110K, T _C
However, there is a drawback that a 2212 phase of 80K or a 2201 phase of T _C of 20K is easily generated.

Then, the Japanese Journal of Applied Physics
urn of of Applied Physics)
Vol. 27, 6 (June 1988), L1041
~ L1043, as shown on page 104
22 in Pb-Sr-Ca-Cu-O-based oxide superconductor
It became clear that many 23 phases were obtained.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the i-Pb-Sr-Ca-Cu-O-based oxide superconductor (hereinafter referred to as bismuth-based superconductor), a small amount of a different phase such as 2212 phase, Ca ₂ PbO _{4 and the} like easily remain, In order to increase the content of the 2223 phase, long-time firing is necessary.

Of the different phases, 2212 phase has a T _C of 8
Although it is as low as 0K, it can be easily produced and can be applied at liquid nitrogen temperature (77K) for the time being. However, if a large amount of Ca ₂ PbO _{4 that} is not a superconductor remains, there is a problem that the content rate of the superconductor decreases and the critical current density (hereinafter referred to as Jc) decreases.

Further, there is a problem that Jc tends to be lowered by applying a magnetic field, and it is difficult to increase the density of the sintered body, and improvement of connection between particles has been strongly demanded.

An object of the present invention is to provide an oxide superconductor which does not have the above problems and a method for producing the same.

[0009]

The present invention relates to an oxide containing bismuth, strontium, calcium and copper as main components, and an oxide superconductor containing 0.1 to 2% by weight of rhenium in the total composition. The present invention relates to a method for producing an oxide superconductor in which the above-mentioned amount of rhenium is added to a mixed powder of bismuth, strontium, calcium and copper, the mixture is uniformly mixed, and then fired.

In the present invention, the blending ratio of bismuth, strontium, calcium and copper is not particularly limited, but Bi: Sr: Ca: Cu is 2: 2: in atomic ratio.
If it is 1: 2 or 2: 2: 2: 3, it is easy to become a superconductor, and in particular, in the case of 2: 2: 2: 3, if 10 to 30 mol% of bismuth is replaced with lead, T _C It is preferable because a high oxide superconductor can be obtained. When used at a temperature below the liquid nitrogen temperature, the superconductor has 2212 phases and 22
It may be a mixture with 23 phases.

The amount of rhenium added is 0.1 to 0.1% based on the total composition.
It is set to a range of 2% by weight, and if it is less than 0.1% by weight, the effect of increasing the Jc and improving the magnetic field characteristics due to the lenium is small.
If it exceeds 5% by weight, there is a drawback that it becomes expensive.

Among the raw materials constituting the oxide superconductor, rhenium may be rhenium powder, rhenium oxide, or the like, and is not particularly limited as long as it is a substance that becomes a simple substance of rhenium after firing.

In addition to the above raw materials, raw materials containing bismuth, lead, strontium, calcium and copper (starting raw materials)
There is no particular limitation about, for example, oxides, carbonates,
Oxalates, acetates, nitrates, metal alkoxides, etc. 1
One kind or two or more kinds are used.

There are no particular restrictions on the method of mixing the above-mentioned raw materials, but for example, a ball mill made of synthetic resin is filled with a synthetic resin-coated ball, a solvent such as ethanol or ethyl acetate, and raw materials, and wet-mixed. A method, a coprecipitation method in which a raw material is dissolved in a solvent to obtain a coprecipitated product, a sol-gel method in which a raw material such as an alkoxide is hydrolyzed to prepare a sol, and the sol is gelated can be used.

The firing temperature and firing time are appropriately selected depending on the blending ratio of each raw material and the atmosphere, but Bi: Sr: C
When the atomic ratio of a: Cu is 2: 2: 1: 2, it is 810.
Bi: Sr: Ca: C at a temperature of 900 ° C. for 5 to 50 hours
When u is approximately 2: 2: 2: 3 and part of the bismuth is replaced by lead, 845 ± 20 ° C., preferably 845 ±
It is preferable to bake at a temperature of 10 ° C. for 20 to 200 hours.

The method of adding rhenium is not particularly limited, but, for example, fine powder of a raw material containing rhenium is used together with a mixed powder of raw materials containing bismuth, strontium, calcium and copper together with a ball mill, a mortar or the like to dry or wet. The method of mixing and homogenizing can be mentioned. In addition to this, there is a method of adding an aqueous solution of rhenium heptaoxide, an alcohol solution, an acetone solution, etc. to a mixed powder of raw materials containing bismuth, strontium, calcium and copper, and then uniformly heating this.

The oxide superconductor in the present invention is prepared by mixing the above composition with a composition obtained by adding rhenium to an oxide containing strontium, an alkaline earth metal other than calcium, bismuth and copper as a main component. There is no problem, and there is no problem even if a hetero phase composed of these elements is contained. If the rhenium is contained in the phase of the superconductor, the object of the present invention can be achieved.

[0018]

EXAMPLES Examples of the present invention will be described below. Examples 1 to 5 Bismuth trioxide (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%), strontium carbonate (rare) so that the ratio of bismuth, strontium, calcium and copper in atomic ratio is as shown in Table 1. Made by Metallic, purity 99.9%), calcium carbonate (made by Kojundo Chemical Laboratory, purity 99.9%)
And cupric oxide (manufactured by Kojundo Chemical Laboratory, purity 99.9)
%) Was weighed and used as the starting material.

Next, the above starting materials were filled in a ball mill made of synthetic resin together with a steel ball covered with the synthetic resin and methanol, and wet-mixed and pulverized for 72 hours under the condition of 50 rpm. Then, the crushed product is taken out of the ball mill and dried at 100 ° C. for 24 hours, then placed in an alumina sagger and placed in an electric furnace at 800 ° C. for 10 hours in the air.
After calcination for a while, and then coarsely crushing it in a mortar, lead monoxide (yellow, manufactured by High Purity Chemical Laboratory Co., Ltd.) is mixed with a zirconia ball and ethyl acetate in a synthetic resin ball mill so as to have the composition shown in Table 1. , Purity 99.9%) was weighed and filled, wet-ground for 24 hours under the condition of 50 rpm, and dried to obtain a powder for synthesis.

Thereafter, the powder for synthesis was press-molded at a pressure of 147 MPa, and then the volume ratio of O ₂ : N ₂ = using an electric furnace.
100 at a temperature of 835 ° C in a low oxygen pressure atmosphere of 1:10.
After firing for a period of time, it was cooled to synthesize a bismuth-based superconductor. Then, after roughly crushing with a mortar, fill a synthetic resin ball mill with zirconia balls and ethyl acetate,
Wet pulverization was performed for 48 hours under the condition of 50 rpm to obtain a pulverized product. Rhenium powder was added to the pulverized product so as to have the composition shown in Table 1, and the mixture was further mixed for 5 hours to make the mixture uniform. The rhenium powder used was a powder made of Tanaka Kikinzoku, which has a purity of 99.9% or more and an average particle size of 1 to 5 μm.

The powder obtained after drying was molded into pellets having a diameter of 30 mm and a thickness of 1 mm at a pressure of 147 MPa, and then fired at 835 ° C. for 10 hours in the air to obtain an oxide superconductor.

Comparative Examples 1 to 5 The respective raw materials were weighed so that the compositions shown in Table 1 were obtained, and the oxide superconductor was obtained through the same steps as in the following Examples.

Next, the oxide superconductors obtained in each of the examples and comparative examples were processed into a rectangular parallelepiped having a length of 20 mm, a width of 3 mm and a thickness of 1 mm, and the temperature variation of the resistance was measured by the four-terminal method. I asked for _c . In addition, J _c0 at the liquid nitrogen temperature (77.3 K) was measured using the same sample as described above, and J _c0.05 was measured in a magnetic field of 0.05 Tesla in liquid nitrogen. The results of these measurements and the ratio of J _c0.05 and J _c0 are shown in Table 1.
Shown in.

In Example 1, Example 2, Comparative Example 1 and Comparative Example 2, 30 mol% of bismuth was replaced with lead, and Example 3, Example 4, Comparative Example 3 and Comparative Example 4 were in bismuth. Of 2
The composition was such that 0 mol% was replaced with lead.

[0025]

[Table 1]

Table 1 shows that the oxide superconductors according to the examples of the present invention have a high T _{c and} a small decrease in J _c due to the application of a magnetic field. On the other hand, the oxide superconductor of the comparative example has a T _{c that} is not much different from that of the oxide superconductors of the examples, but it is shown that the application of a magnetic field causes a large decrease in J _c .

[0027]

INDUSTRIAL APPLICABILITY The superconductor according to the present invention is an oxide superconductor industrially extremely suitable because it has a small decrease in T _{c and} a small decrease in J _c due to the application of a magnetic field.

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[Procedure amendment]

[Submission date] March 9, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

[0025]

[Table 1]

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Claims (3)

[Claims] 1. An oxide superconductor containing bismuth, strontium, calcium and copper as main components, and 0.1 to 2% by weight of rhenium in the entire composition. 2. The oxide superconductor according to claim 1, wherein part of bismuth is replaced with lead. 3. A method for producing an oxide superconductor, which comprises adding the amount of rhenium shown in claim 1 to a mixed powder of bismuth, strontium, calcium and copper, mixing the mixture uniformly, and then firing the mixture.