JPH04124029A - Oxide superconductor and its production - Google Patents

Abstract

PURPOSE:To obtain a Bi-based oxide superconductor showing a high critical temperature without passing through a quenching process, comprising an oxide compound containing Bi, Sr, Ca, K Ba and Cu in a specific ratio. CONSTITUTION:An oxide compound shown by the formula Bi1.0 SrACaBKCBaDCu1.0+ or -0.2OX (A is 0.6-1.2; B is 0.3-0.5; C is 0.05-0.2; D is 0.05-0.2) is made into a Bi-based oxide superconductor of 2,212 phase showing TC<zero> higher than 90K. The superconductor is obtained by weighing raw materials containing each metal, blending, calcining, grinding, molding and calcining in a nitrogen atmosphere or a nitrogen atmosphere containing <10V& oxygen at 780-950 deg.C, preferably 810-900 deg.C. In the case of burning twice, after the first burning, the burnt material is burnt in a nitrogen atmosphere or a nitrogen atmosphere containing <7V% oxygen.

Description

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

(Prior art) Conventional oxide superconductors include B i, -S r -, which has bismuth, strontium, calcium, and copper as its main components, and was discovered in 1988 by general research staff of the Institute of Metals and Materials Technology. Ca-Cu-0 system (hereinafter referred to as Bi
This Bi-based oxide superconductor has a critical temperature at which its electrical resistance becomes zero (currently T
There was a problem in that the 2223 phase near 110 (referred to as czero) was difficult to generate. For this reason Tczllr
Attempts have been made to utilize the 2212 phase, which has a low o but a wide temperature range.

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

As a method to increase the T cz@ro of the 2212 phase, Japanese Journal of Applied Physics (Japanese Journal of Ap
pliecl Physics) Vol. 127.9 (published in September 1988), page L1626 and volume 27.12% (published in December 1988),
L2327 valve L2329 and Atopances, Inn.
Super Conductivity II (Advance
s in 5upper conductivity II) t 149-152
As shown on page 1, a method has been reported in which the material is obtained by heat treatment at a temperature of 500 to 880° C. and then quenching 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 provides a Tc higher than 90 without going through a quenching step.
The purpose of this study is to provide a 2212-phase Bi-based oxide superconductor exhibiting zero and its IEL production process.

(Means for Solving Problem 1) The present invention contains bismuth, strontium, calcium, potassium, barium and copper as main components.

General formula E l i, oS rACa eKcB a o
CL+.

±0.2Ox (However, A=0.6~1.2.B=0.35~0.7°C
=0.05~0.2. D=0.05-0.2. (Numbers represent atomic ratios) An oxide superconductor with the composition shown below, and bismuth and strontium so as to have the above composition.

Oxide superconductors are produced by weighing and mixing raw materials containing calcium, potassium, barium, and copper, then calcining and pulverizing them, shaping them, and then firing them in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 10% by volume of oxygen. Bismuth, strontium, calcium, potassium as well as the above composition.

Each raw material including barium and steel is weighed, mixed, calcined, primary fired, further pulverized, molded, and then re-baked in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen. This invention relates to a method for producing oxide superconductors to be fired.

In the present invention, there are no particular restrictions on the raw materials containing bismuth, strontium, calcium, potassium, barium, and copper, which are the main components constituting the oxide superconductor; for example, oxides, carbonyl salts, nitrates, oxalates, etc. One or more of these are used.

The atomic ratio of bismuth, strontium, calcium, potassium, barium, and copper is 1.0 for bismuth.
Strontium: 0.6-1.2° Calcium: 0.3
5-0. /7. Potassium is 0.05-0.2. Barium is in the range of 0.05 to 0.2 and steel is in the range of 1.0±0.2, and if it is out of this range, it will be TC without the quenching process! er
It is difficult to obtain a Bi-based oxide superconductor with a 2212 phase on the order of 6 to 90.

Although there are no particular restrictions on the mixing method, it is preferable, for example, to fill a ball mill made of synthetic resin with balls coated with synthetic resin, a solvent such as ethanol or methanol, and raw materials, and perform wet mixing.

Regarding the calcination conditions, the calcination salinity 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 9W1 in the air.
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 ratio of each raw material, etc., but it is preferable to perform firing at a temperature near the melting temperature of the sample, for example in the range of 780 to 950 °C, and in the range of 810 to 900 °C. It is even more preferable to bake it with

On the other hand, when firing once, it is necessary to fire in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 10% by volume of oxygen; when firing twice, the first firing is in the air, There are no particular restrictions such as in an oxygen atmosphere, in a vacuum, in a reducing atmosphere, in a neutral atmosphere, etc., but the secondary firing is required to be performed in a nitrogen atmosphere or a nitrogen atmosphere containing 7% by volume of oxygen, If firing is performed under conditions other than the above, without the rapid cooling process, the ``1+czero'' will be 22, which is 90.
It is difficult to obtain a 12-phase B4-based oxide superconductor. Note that in the present invention, after calcination, pulverization and molding may be performed as necessary, and then primary calcination may be performed.) 4) The calcination time may be 5 to 10 hours, but in order to improve the homogeneity of the crystals, It is preferable to carry out the treatment for 20 to 100 hours.

In the composition of the present invention, the amount of O (11! element) is determined by the amount of Cu and the oxidation state of Cu. However, it is not possible to precisely and precisely determine the oxidation state. Therefore, it has been decided to be represented by X in the present invention.

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

Examples 1 to 2 Bismuth dioxide (manufactured by Koujun Kagaku Kenkyushin, purity 99
．． 9%), strontium carbonate (manufactured by Rare Metallic, purity 99.9%), potassium carbonate (manufactured by Kojundo Kagaku Kenkyu Shin, purity 99.9%), barium carbonate (manufactured by Kojundo Kagaku Kenkyu Shin, purity 99.9) %), calcium carbonate (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) and cupric oxide (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) were weighed and used as starting materials.

Next, the above-mentioned XB starting material was charged into a ball mill made of synthetic resin MI together with a #1 ball coated with a 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 the air using an electric furnace.
Calcinate at 00℃ for 10 hours.

The mixture was then coarsely ground in a mortar to obtain a composition for an oxide superconductor. After this, the composition for oxide superconductor was heated to 147 M P.
After press forming into pellets with a diameter of 30 mm and a thickness of 1 mm at a pressure of 9, the volume ratio is 02: N2 = 1: 20 (7)
A Bi-based oxide superconductor was obtained by firing in a low oxygen atmosphere for 840"Cl00 hours.

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

Thereafter, a composition for oxide superconductor was obtained through the same steps as in Examples 1 and 2. The after-refined oxide superconductor composition was calcined by volume at 900° C. for 15 hours in an oxygen atmosphere, then crushed, and then crushed 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 = 1. :83 in a low oxygen atmosphere of 20
Secondary firing was performed at 0° C. for 100 hours to obtain a Bi-based oxide superconductor.

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

Strontium carbonate (manufactured by Rare Metallic, purity 99.9
%), Calcium Carbonate C High Purity Chemical Research Institute, purity 99
, 9% fu and oxidation No. 2 #J (purity 9 manufactured by Kojundo Chemical Research Institute
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 to 4 Bismuth, strontium, calcium, and copper (all using the same raw materials as in Comparative Examples 1 to 2) were weighed and used as starting materials such that the ratio of the atomic ratio was 1114 as shown in the table.

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

Next, T czsro 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 T cZero of 90 or more. Further, when the crystal phase was examined, it was confirmed that it was the 2212 phase in Table 2.

(Effects of the Invention) According to the present invention, it is possible to obtain a 2212-phase oxide superconductor exhibiting T Cze ro of 90 or more without going through a quenching step.

c=z, H, knee main Enemy country:

Claims (3)

[Claims] 1. The main components are bismuth, strontium, calcium, potassium, barium and copper, and have the general formula Bi_1_. _0Sr_ACa_BK_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, numbers represent atomic ratios). 2. Each raw material containing bismuth, strontium, calcium, potassium, barium, and copper is weighed so as to have the composition described in claim 1, then mixed, calcined, pulverized, molded, and then heated in a nitrogen atmosphere or with 10 volumes of oxygen. A method for producing an oxide superconductor, the method comprising firing in an atmosphere containing less than % nitrogen. 3. Each raw material containing bismuth, strontium, calcium, potassium, barium, and copper is weighed so as to have the composition described in claim 1, then mixed, calcined, primary fired, further crushed, shaped, and heated again with nitrogen. A method for producing an oxide superconductor, comprising performing secondary firing in an atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen.