JPH046147A - Oxide superconductor and production thereof - Google Patents

Abstract

PURPOSE:To suppress the lowering of critical temp. at which electric resistance becomes zero and the lowering of critical current density by the application of a magnetic field by rendering a specified compsn. and incorporating Ag and Pt. CONSTITUTION:Powdery starting materials contg. Ag, Pt, Bi, Pb, Sr, Ca, Mg, Ba and Cu are weighed in a prescribed ratio, mixed, optionally calcined at 835+ or -20 deg.C for 20-200 hr and then sintered at 820-870 deg.C to obtain an oxide superconductor having a compsn. represented by the formula (where A is 0.15-0.35, B is 0.8-1.1, B' is 0.8-1.2, C is 0.05-0.3, D is < 0.2 and the numerals show atomic ratio) and contg. 10-35 wt.% Ag and 0.1-2 wt.% Pt.

Description

[Detailed description of the invention] (Industrial application field) The present invention ii relates to an oxide superconductor and its manufacturing method.

(Conventional technology) As a conventional oxide superconductor, in 1988.

There is a Bi-Sr-Ca-Cu-0 system oxide superconductor whose main components are bismuth, strontium, calcium, and copper, which was discovered by the above-mentioned general research staff of the Institute of Metals and Materials Technology. Sr-Ca-
The Cu-0 based oxide superconductor is 1! The critical temperature at which the air resistance becomes zero (hereinafter referred to as T: erO) is around 110, and the Tl-Ba-Ca-Cu-0 system oxide superconductor has thallium, barium, calcium, and copper as its main components. It is known to be the second highest in the body.

Bi-Sr-Ca-Cu-0 based oxide superconductor.

It is characterized by being less toxic than the Tl-Ba-Ca-Cu-0-based oxide superconductor, but more so than the 2223 phase in which Tg0 is 110 in the crystal phase.

T: ero force 80K (D2212 phase or 1; tT:”0
There is a drawback that the 2201 phase in the phase 20 is likely to be generated.

Later, the Japanese Journal of Applied Physics
of Applied Physics) Vol.
, No. 27.6 (June 1988), L1041-L
As shown on page 1043, lead-doped Bi-P
It has been revealed that a large amount of 2223 phase can be obtained in a b-8r-Ca-Cu-0-based oxide superconductor (hereinafter referred to as a layered superconductor).

(Problem to be Solved by the Invention) However, the above-mentioned Bi-based superconductor has the problem that the temperature range for producing the 2223 phase is narrow, and
For a long time to generate many phases.

For example, 100 hours of firing is required.

On the other hand, Bi-based superconductors contain Ca2P b in addition to the 2223 phase.
o4.

Different phases such as PbCuOz tend to remain. Ca2Pb04.
If a different phase such as PbCuOz coexists in the 2223 phase, there is a problem in that the superconductor content decreases and the critical current density (hereinafter referred to as Jc) decreases.

In addition, there is a problem that Jc is more likely to decrease when a magnetic field is applied than Bi-based superconductors and YBa-Cu-0-based superconductors, which is disadvantageous in terms of application to superconducting electromagnets and superconducting magnetic shielding materials. Furthermore, it is difficult to increase the density of the sintered body, and there has been a strong demand for improvement in the connection between two particles.

An object of the present invention is to provide an oxide superconductor and a method for producing the same that are free from the above-mentioned problems.

(Means for Solving the Problems) The present invention uses silver in the range of 10 to 351. Quantity and platinum 0.1-2
and general formula Bib-APbASrBCaBr Mgof3a
Dcu1.7tO, 30x (A=0.15~0.3
5. B=0.8-1.1. B'20, 8-1.2. C=
0.05-0.3. D=less than 0.2.

(Numbers represent atomic ratios) Weigh each raw material containing silver, platinum, bismuth, lead, strontium, calcium, magnesium, barium, and copper so as to have the composition shown above and the composition shown above, The present invention relates to a method for producing an oxide superconductor which is then mixed and then fired.

In the present invention, as silver, in addition to silver powder, 2. There are no particular restrictions if oxide, silver chloride, silver nitrate, etc. are used and the material will be made into a pot unit after firing.

In addition to platinum powder, platinum oxide or the like may be used as the platinum, and there is no particular restriction as long as it becomes a simple platinum substance after firing.

Steel is required to be contained in the oxide superconductor in a range of 10 to 35% by weight, and if it is less than 10% by weight, the effect as an auxiliary agent for uniformizing the effect of platinum addition is low; If it exceeds this, although this effect is achieved, the volume fraction of the superconductor decreases.

On the other hand, platinum is required to be contained in the oxide superconductor in an amount of 0.1 to 2% by weight, and if it is less than 0.1'ijl, platinum's effect of increasing Jc and improving magnetic field properties will be small. , if it exceeds 2% by weight, the disadvantage is that it becomes expensive.

In addition to the above ingredients, it also contains bismuth, lead, and strontium.

There are no particular restrictions on the raw materials containing calcium, magnesium, barium, and copper; for example, oxides, carbonates,
One or more types of nitrates are used.

General formula Bib-APbASrIICa, +MgoHaD
Cul, 7 ± 6, 30x, the Alum atomic ratio is in the range of 0.15 to 0.35, and if it is less than 0.15, a meso-temperature phase near Tg 0 of 80 is likely to be generated.
The amount of high-temperature phase produced near 10 is small, and when it exceeds 0.35, Ca2P, which is an oxide of lead and calcium, is produced.
A foreign phase such as bo4 is generated in the lines, and the critical temperature is lowered.

The atomic ratio of B is in the range of 0.8 to 1.1, and when it is less than 0.8, the range of firing conditions in which a high temperature phase is generated is narrow, and the electrical resistance is stabilized at around 110 and becomes zero. 5. If it exceeds 1.1, foreign phases other than superconductors are likely to be generated, resulting in a decrease in T%eTo.

B' is in the range of 0.8 to 1.2 in terms of atomic ratio, and if it is less than 0.8, no significant effect will be observed, and if it exceeds 1.2, different phases other than superconductors are likely to be produced.

The CFi atomic ratio is in the range of 0.05 to 0.3, and 0.0
If it is less than 5, no significant effect will be observed, and if it exceeds 0.3, a different phase other than the superconductor is likely to be generated.

The DIII ratio is less than 0.2, and when it is 0.2 or more, a different phase other than the superconductor is likely to be generated.

There are no particular restrictions on the method of mixing the raw materials.

For example, a method of filling a ball mill made of synthetic resin with balls coated with synthetic resin, a solvent such as ethanol or methanol, and raw materials and wet mixing, and a coprecipitation method of obtaining a coprecipitated product after dissolving the raw materials in a solvent. A sol-gel method or the like can be used in which a sol is prepared by hydrolyzing raw materials such as , alkoxides, etc., and the sol is turned into a gel.

In the present invention, calcining is performed as necessary after mixing.

Under the calcination conditions, the calcination temperature and time are appropriately selected depending on the blending ratio of each raw material, etc.
Preferably, calcination is carried out at 835°C ± 10°C for 20 to 200 hours, and the calcination atmosphere can be air, oxygen atmosphere, vacuum, reducing atmosphere, etc., and there are no particular restrictions. do not have.

There are no particular restrictions on crushing and molding, and conventionally known methods may be used.

Regarding the firing conditions, 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 820 to 870°C, and the firing atmosphere is air, air current, or low oxygen pressure. In the atmosphere (oxygen content is 1
It is preferable to fire in a range of 20 to 20 volumes, preferably 2 to 20 volumes.

The amount of O (oxygen) in the composition of the present invention is determined by the oxidation state of Cu and the oxidation state of Cu. However, it is not possible to measure the oxidation state strictly and accurately, so it is represented by X in the present invention.

(Example) Hereinafter, nine aspects of the present invention will be described in detail.

Examples 1-6 Bismuth, lead, strontium, magnesium.

Bismuth trioxide (manufactured by Kojun Kagaku Kenkyushin, purity 99.9%) and strontium carbonate (manufactured by Rare Metallic, purity 99.9) were prepared so that the ratio of barium, calcium and copper was as shown in Table 1 in atomic ratio. %) Magnesium oxide (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%), barium carbonate (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%), calcium carbonate (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9) %) and oxidized second
Copper (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) was weighed and used as a starting material.

Next, the above starting materials were filled in a synthetic resin ball mill together with steel balls coated with synthetic resin and methanol, and mixed for 72 hours at 50 revolutions per minute. After drying, place it in an alumina sagger and heat it in the air at 800°C using an electric furnace.
Calcined for 0 hours, then coarsely ground in a mortar, placed in a synthetic resin ball mill with zirconia balls and ethyl acetate so that lead monoxide (yellow) has the composition shown in Table 1 in terms of atomic ratio.

(manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) was weighed and filled, mixed 24 hours a day at 50 rotations per minute, and then dried to obtain a composition for an oxide superconductor.

Thereafter, the composition for oxide superconductor was press-molded at a pressure of 147 MPa, and the volume ratio was 02:Nz =1:1.
The material was fired at 835° C. for 100 hours in a low oxygen pressure atmosphere of 0.0° C. to obtain a material for an oxide superconductor with a thickness of one inch.

After that, the above-mentioned material for oxide superconductor was coarsely ground in a mortar, then filled in a synthetic resin ball mill with zirconia balls and ethyl acetate, and ground at 50 revolutions per minute for 48 hours, followed by silver powder and platinum. The powder was added to the composition shown in Table 1 and mixed for an additional 5 hours to make it homogeneous. The silver powder and platinum powder used were powders manufactured by Nichia Precious Metals, which had a purity of 99.9 cm or more and an average particle size of 1 to 5 μm.

The powder obtained after drying was heated to a diameter of 30 m under a pressure of 147 MPa.
After forming the pellet into a pellet having a thickness of Im and a thickness of Im, it was fired in the atmosphere at 840° C. for 10 hours to obtain an oxidized conductor.

Comparative examples 1 to 6 Weigh each raw material so that it has the composition shown in Table 1.

An oxide superconductor was obtained by following the same steps as in the example.

Next, the oxide superconductor obtained in each example and comparative example was
It was processed into a rectangular parallelepiped with dimensions of 0 body x 3 width x 1 thickness, and the temperature change in resistance was measured using the four-terminal method to determine Tg 0. Also, using the same sample as above, Jc at liquid nitrogen temperature (77.3K)
6 and JCO8 in a magnetic field of 0.05 Tesla in liquid nitrogen. These measurement results and J
The ratios of CO,05 and JcO are shown in Table 1.

From Table 1, the oxide superconductors that are examples of the present invention are T
: It is shown that erO is high and the decrease in Jc due to the application of a magnetic field is small. On the other hand, the oxide superconductor of the comparative example TZerO is not much different from the oxide superconductor of the example, but it is shown that the Jc decreases significantly when a magnetic field is applied.

(Effects of the Invention) The oxide superconductor of the present invention has a small decrease in T:erO, and also a decrease in Jc due to the application of a magnetic field.
It is an industrially very suitable oxide superconductor.

Claims (1)

[Claims] 1. 10 to 35% by weight of silver and 0.1 to 2% by weight of platinum
and the general formula Bi_1_-_APb_ASr_BC
a_B^´Mg_CBa_DCu_1.7_±_0_.
_3O_X (A=0.15-0.35, B=0.8
~1.1, B'=0.8~1.2, C=0.05~0.
3, D=less than 0.2, the number represents an atomic ratio). 2. Silver, platinum, bismuth, lead, strontium, calcium, magnesium,
A method for producing an oxide superconductor, which comprises weighing raw materials containing barium and copper, mixing them, and then firing them.