JPH04124015A - Oxide superconductor and its production - Google Patents

Abstract

PURPOSE:To obtain a superconductor showing a higher critical temperature than 90 deg.K without passing through a quenching process by blending Bi with Sc, Sr, Ca, Mg, Ba and Cu in a specific ratio, calcining, grinding, molding and burning in a nitrogen atmosphere. CONSTITUTION:Raw materials containing bismuth, scandium, strontium, calcium, magnesium, barium and copper are weighed so as to give a composition shown by the formula. Then the raw materials are mixed, calcined, ground, molded and burnt in a nitrogen atmosphere or a nitrogen atmosphere containing <10vol.% oxygen to give the objective oxide superconductor. The calcination temperature is properly selected depending upon the blending ratio of the raw materials and is preferably in a range of 780-870 deg.C. The burning temperature is properly selected depending upon the blending ratio of the raw materials and a temperature <= approximately a temperature to melt a specimen, such as 780-950 deg.C is preferable.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an oxide superconductor and a method for producing the same.

(Prior art) As a conventional oxide superconductor, B1-3r-Ca-, which has bismuth, strontium, calcium, and copper as its main components, was discovered in 1988 by the above-mentioned general researcher of the Institute of Metals and Materials Technology. There is a Cu-0-based (hereinafter referred to as Bj-based) oxide superconductor, but this Bi-based oxide superconductor has a critical temperature (hereinafter referred to as TC2erO) at which the electrical resistance becomes zero at a temperature of 2223 around 110. There was a problem in that it was difficult to form a phase. For this reason, attempts have been made to utilize the 2212 phase, which has a low Tc2@r0 but a wide generation temperature flI range.

(Problem to be solved by the invention) However, the 2212 phase of Bi-based oxide superconductor is
Since T c Z″r0 is around 80, the difference from Tczaro is small when cooled with liquid nitrogen (77 K), and the superconducting properties are unstable and there is a possibility that it cannot be used.

As a method to increase the T clro of the 2212 phase, Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)
plied Physics) Vo127.9 (1
Published in September 1988), L1626 page L1628 page and same page V
o127, No. 12 (December 1988), L2327
←L2329 and Atopances, In, Superconductivity U (Advances in
5upper-△ conductj vj tyff) + 149~i5
As shown on page 2, a method has been reported in which the material is heat treated at a temperature of 500 to 880°C and then rapidly cooled in liquid nitrogen or air.

Since this method includes a step of rapid cooling, it has the disadvantage that although it is possible to produce a small molded body, it is difficult to produce a large molded body.

The present invention has a high temperature of 90% without going through a quenching process.
The object of the present invention is to provide a 22 ]-2 phase Bi-based oxide superconductor exhibiting c2 e r O and a method for producing the same.

(Means for Solving the Problems) The present invention contains bismuth, scandium, strontium, calcium, magnesium, barium, and copper as main components.

General formula B1. +-vS cyS r ACa BM
gcB a DCu+, o+-o20X (However, LA, = 0.6-1.2.B = 0.35-0.7°C = 0.05-0.2.D = 0.05-0.2. Y=0
．． An oxide superconductor having a composition shown by 05 to 0.3 (numbers represent atomic ratios), and bismuth and scandium so as to have the above composition.

Each raw material including strontium, calcium, magnesium, barium, and steel is weighed, mixed, calcined, pulverized, and molded in a nitrogen atmosphere or with 10% oxygen by volume.
A method for producing an oxide superconductor by firing in a nitrogen atmosphere containing less than bismuth, scandium, strontium, calcium, magnesium,
Each raw material containing barium and copper is weighed, mixed, calcined and fired first, further crushed, shaped, and then fired again in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen. The present invention relates to a method for producing an oxide superconductor.

Bismuth, scandium, and strontium are the main components constituting the oxide superconductor in the present invention.

There are no particular restrictions on raw materials containing calcium, magnesium, barium, and copper, but for example, oxides, charcoal*@,
One or more types of saccharides, oxalates, etc. are used.

The mixing ratio of bismuth, scandium, strontium, calcium, magnesium, barium, and copper is such that the sum of bismuth and scandium is 1.0 in atomic ratio, and the ratio of scandium to the sum of bismuth and scandium is 0.05 to 1.
0.3. Strontium is 0.6-1.2. Calcium is 0.35-0.77, magnesium is 0.05-0.
2. Barium is 0.05-0.2 and copper is 1.0±0.
2, and outside this range, it is difficult to obtain a 2212-phase (7) Bi-based sulfide superconductor with a Tczero of 9CJK without a quenching process.

Especially about the mixing method! For example, a ball mill made of synthetic wood is filled with balls coated with synthetic resin, a solvent such as ethanol or methanol, and raw materials.
Wet mixing is preferred.

Regarding the calcination conditions, the calcination temperature is appropriately selected depending on the blending ratio of each raw material, etc., but it is preferable to calcinate in the range of 780 to 870°C, and the calcination atmosphere is air, i!
Calcination can be performed in an elementary atmosphere, a vacuum, a reducing atmosphere, a neutral atmosphere, etc.

There are no particular restrictions on the pulverization and molding methods, and conventionally known methods can be used.

Regarding the firing conditions, the firing temperature is appropriately selected depending on the blending temperature of each raw material, etc., but it is preferable to perform firing at a temperature in the vicinity of the melting temperature of the sample, for example in the range of 780 to 950 °C, and 810 to 900 °C. It is more preferable to perform the firing at a temperature within the range of °C.

On the other hand, in the case of one-time firing, firing is required in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 104 t-vol% oxygen;
There are no particular restrictions on the secondary firing, such as in the air, oxygen atmosphere, vacuum, reducing atmosphere, or neutral atmosphere, but the secondary firing may be performed in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen. However, if firing is performed under conditions other than the above, the Tc2erQ will be on the order of 90 without the rapid cooling process.
It is difficult to obtain a 212-phase Bi-based oxide superconductor. In the present invention, after calcination, pulverization and molding may be performed as necessary, and then primary firing may be performed. Although 10 hours is acceptable, it is preferable to carry out the heating for 20 to 100 hours in order to improve the homogeneity of the crystals.

In the composition of the present invention, the amount of ○ (oxygen) is determined by the amount of +Cu and the oxidation state of Cu. However, it is not possible to precisely and precisely measure the oxidation state of the oxidation state, so it is designated as X in the present invention.

(Example) The present invention will be explained in detail below.

Bismuth dioxide (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%), scandium oxide (manufactured by Kojundo Kagaku Kenkyu Shin, purity 99%) and scandium oxide (manufactured by Kojundo Kagaku Kenkyushin, purity 99%) were prepared so that the proportions of barium, calcium and copper were as shown in Table 1 in atomic ratio. .9%).

Strontium carbonate (manufactured by Rare Metallic, purity 99.9
%), Magnesium Iflide (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%), barium carbonate (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%),
Weighed calcium carbonate (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) and cupric oxide (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) and added them to the starting I'JK material. did.

Next, the above starting materials were charged into a synthetic resin ball mill together with copper balls coated with synthetic resin and methanol, and mixed for 72 hours at 50 revolutions per minute. After drying, place it in an alumina pot and heat it in an electric furnace at 800°C.
Bake for 10 hours.

The mixture was then coarsely ground in a mortar to obtain a composition for an oxide superconductor. This composition for hindlimb oxide superconductor was heated to 147 M P
After press molding into pellets with a diameter of 30 mm + thickness of 1 mm at a pressure of 1 volume ratio Oe:N2 = 1:20
Bi
A system oxide superconductor was obtained.

Examples 3-4 Bismuth, scandium, strontium, magnesium, barium, calcium and copper (all of Examples 1-4)
The same raw materials as those used in Example 2 were weighed so as to have the composition shown in Table 2 in terms of atomic ratio, and used as starting materials.

Thereafter, the same steps as in Examples 1 and 2 were carried out to obtain a converted product for an oxide superconductor. This composition for a hindlimb oxide superconductor was calcined by volume at 900'C in an oxygen atmosphere for 15 hours, and then crushed, and then heated to a diameter of 30 m at a pressure of 147 MPa.
m, 2 volume ratio after press molding into pellets with a thickness of 1 mm,
02: N2; 830' in a low oxygen atmosphere of 1:20
A Bi-based oxide superconductor was obtained by secondary firing with C for 100 hours.

(Comparative Examples) Comparative Examples 1 and 2 Bismuth dioxide (manufactured by Kojun Kagaku Kenkyushin, purity 99.9%) was prepared so that the ratios of bismuth, strontium, calcium, and copper were as shown in Table 3.

Strontium carbonate (manufactured by Rare Metallic, purity 99.9
%), calcium carbonate (manufactured by Kojundo Kagaku Kenkyushin, purity 99
．． 9%) and oxidation No. 2 #4 (Kojundo Kagaku Kenkyusho purity 9)
9.9%) was weighed and the same steps as in Examples 1 and 2 were carried out to obtain a Bi-based oxide superconductor.

Comparative Examples 3-4 Starting materials were weighed on a scale so that the ratios of bismuth, strontium, calcium, and copper (all using the same raw materials as in Comparative Examples 1-2) were as shown in Table 4 in terms of atomic ratio. And so.

Thereafter, a Bi-based oxide superconductor was obtained through the same steps as in Examples 3 and 4.

Next, Tczero of the Bi-based oxide superconductors obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was measured by a four-probe method. The results are shown in Table 5.

As shown in Table 5, it can be seen that the oxide superconductors according to the examples of the present invention have Tcff1er0 of 90 or more. Further, when the crystal phase was examined, it was confirmed that it was a 2212 phase.

(Effect of the invention)

Claims (3)

[Claims] 1. Main ingredients are bismuth, scandium, strontium, calcium, magnesium, barium and copper, with the general formula Bi_1_-_YSc_YSr_ACa_BMg
_CBa_DCu_1_. ＿0＿±＿0＿． _2O_x (However, A=0.6~1.2, B=0.35~0.7, C
=0.05-0.2, D=0.05-0.2, Y=0.
An oxide superconductor having a composition of 05 to 0.3 (numbers represent atomic ratios). 2. Bismuth, scandium, strontium, calcium, magnesium,
Each raw material including barium and copper is weighed, mixed, calcined, crushed, and molded in a nitrogen atmosphere or heated with oxygen for 10 minutes.
A method for producing an oxide superconductor, characterized by firing in an atmosphere containing nitrogen in an amount less than % by volume. 3. Bismuth, scandium, strontium, calcium, magnesium,
Each raw material containing barium and copper is weighed, mixed, calcined, primary fired, further crushed and shaped, and then secondary fired again in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen. A method for producing an oxide superconductor characterized by: