JPH04124025A - Oxide superconductor and its production - Google Patents

Abstract

PURPOSE:To readily obtain a Bi-based superconductor of 2,212 phase having a high critical temperature by blending raw materials containing Bi, Sr, Ca, Be, Ba and copper in a specific ratio, calcining, grinding, molding and burning in a nitrogen atmosphere. CONSTITUTION:Raw materials containing bismuth, strontium, calcium, beryllium, barium and copper are weighed and blended to give a composition shown by the formula (A is 0.6-1.2; B is 0.35-0.7; C is 0.05-0.2; D is 0.05-0.2; figure shows atomic ratio). Then the mixture is calcined, ground, molded and burnt in a nitrogen atmosphere or a nitrogen atmosphere containing <10vol.% oxygen to give an oxide superconductor shown by the formula. Consequently, a Bi-based oxide superconductor of 2,212 phase showing >=90K critical temperature can be produced without requiring a quenching process. Therefore a large-sized molded article can readily be prepared.

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) As a conventional oxide superconductor, B1-8r-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-〇-based (hereinafter referred to as Bi-based) oxide superconductor, but this Bi-based oxide superconductor has a critical temperature (hereinafter referred to as Tczero) 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 T 02ero but a wide temperature range of formation.

(Problem to be solved by the invention) However, the 2212 phase of the B-based oxide superconductor is
Since T02ero is around 80, the difference from T02@to is small when cooling with liquid nitrogen (77K), and the superconducting properties are unstable and there is a possibility that it cannot be used.

2212 phase Tc2e'. Japanese Journal of Applied Physics (Japanese Journal of App)
Lied Physics) Vo127.9 (19
Published September 1988), L1626γL 1628 pages and the same V
o127, No. 12 (December 1988), L2327
L2329 and Atopances, In, Superconductivity II (Advances in
As shown on pages 149 to IF 52 of 5uper conductivity U), 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 it in air in nitrogen.

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 achieves a higher T than 90 without going through a quenching process.
The object of the present invention is to provide a 2212-phase Bi-based oxide superconductor exhibiting czero and a method for producing the same.

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

General formula B i +, oS rAc aBB ecB a
r+cut,.

Thick Q, 20X (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 consisting of M shown in the following, and bismuth and strontium so as to have the above composition.

Oxide superconductors are manufactured by weighing and mixing raw materials containing calcium, beryllium, barium, and copper, then calcining and pulverizing them, forming them, and then firing them in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 10% by volume of oxygen. The raw materials containing bismuth, strontium, calcium, beryllium, barium, and copper are weighed and mixed, then calcined and fired, and then pulverized so as to have the above-mentioned composition.

The present invention relates to a method for producing an oxide superconductor, which is formed and then fired again in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen.

In the present invention, there are no particular restrictions on the raw materials containing bismuth, strontium, calcium, beryllium, barium, and copper, which are the main components constituting the oxide superconductor. A species or two or more species may be used.

Bismuth, strontium, calcium, beryllium,
The blending ratio of barium and copper is bismuth in atomic ratio of 1.0.
．． Strontium: 0.6-1.2° Calcium: 0.
35-0.77, beryllium 0.05-0.2. Barium is in the range of 0.05-0.2 and copper is in the range of 1.0 + 0.2, and outside this range T
It is difficult to obtain a 2212-phase Bi-based oxide superconductor with a czero value on the order of 90.

Although there is no particular limit 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 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, 1$
Calcination can be performed in a single element atmosphere, vacuum, reducing atmosphere, 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 sample9, for example in the range of 780 to 950 °C, and preferably in the range of 810 to 900 °C. It is even more preferable to bake it with

On the other hand, the firing atmosphere requires firing on a platform for one-time firing, in a nitrogen atmosphere, or in a nitrogen atmosphere containing less than 10% by volume of oxygen, and when firing is performed twice, the first firing is in the air. , in an 11-element atmosphere, in a vacuum, in a reducing atmosphere,
Although there are no particular restrictions such as a neutral atmosphere, the secondary firing must be performed in a nitrogen atmosphere or in a nitrogen atmosphere containing less than 7% by volume of oxygen, and if firing is performed under conditions other than the above, there will be no quenching step. So TC211rO is 2 in the 90s.
It is difficult to obtain a 212-phase Bi-based oxide superconductor. In the present invention, after calcination, pulverization and molding may be carried out if necessary, and then primary calcination may be performed.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 (*element) is determined by the amount of Cu and the oxidation state of Cu. However, it is not possible to precisely and accurately measure 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 1-2 Bismuth dioxide (manufactured by Koujun Kagaku Kenkyushin, purity 99.9%) and strontium carbonate were mixed so that the ratios of bismuth, strontium, beryllium, barium, calcium, and copper were as shown in Table II1 in atomic ratio. (Made by Rare Metallic, purity 99.9%), l! ! Beryllium chloride (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 Kenkyu Shin, purity 99.9%), Cupric oxide (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) was weighed and used as a starting material.

Next, the above starting materials were filled into 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 pot and heat it in the air at 800℃ using an electric furnace.
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 press-molded into a pellet with a diameter of 30 mm and a thickness of 1 mm at a pressure of 147 MPa, and then baked at 840°C for 100 hours in a low oxygen atmosphere with a volume ratio of 02:N2 = 1 = 20. A Bi-based oxide superconductor was obtained.

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

Thereafter, a composition for oxide superconductor was obtained through the same steps as in Examples 1 and 2. This composition for a hindlimb oxide superconductor was calcined by volume at 900°C for 15 hours in an oxygen atmosphere, and then crushed, and then crushed into powders with a diameter of 30 mm at a pressure of 147 MPa.
After press molding into pellets with a thickness of 1 mm, the volume ratio of 0.02
:N2=1. : 10 at 830℃ in a low oxygen atmosphere of 20
Secondary firing was performed for 0 hours to obtain an oxide superconductor in Bi.

(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 (manufactured by Kojundo Kagaku Kenkyushin, purity 99
．． 9%) and cupric oxide (purity 99 manufactured by Kojundo Kagaku Kenkyusho)
．． 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 Y to 2) were weighed and used as starting materials so that the atomic ratios were as shown in Table 4.

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

Next, T cZ''ro 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, the oxide superconductors according to the embodiments of the present invention have Tc2er0 of 90 or more. Further, when the crystal phase was examined, it was confirmed that it was a 2212 phase.

(Effects of the Invention) According to the present invention, a 2212-phase oxide superconductor exhibiting a T Czero of 90 or more can be obtained without going through a quenching step.

Claims (3)

[Claims] 1. The main components are bismuth, strontium, calcium, beryllium, barium and copper, and the general formula is Bi_1_
．． _0Sr_ACa_BBe_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, beryllium, 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, beryllium, barium, and copper is weighed so as to have the composition described in claim 1, and then mixed, calcined, and fired for the first time, and then 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.