JPH04104942A - Oxide superconductor and production thereof - Google Patents

Abstract

PURPOSE:To provide the subject superconductor improved in magnetic field dependency by mixing the respective raw materials of Tl, Ba, Sr, Ca, Cu, Ag and pt so as to form a composition containing the Ag and Pt and represented by a specific formula, and firing the composition. CONSTITUTION:The respective powdery raw materials of Ba, Sr, Ca and Cu are weighed in prescribed amounts, mixed with each other, preliminarily fired and ground. The ground product is mixed with a prescribed amount of the raw material powder of Tl and ground to prepare a composition force superconductors. The composition is press-molded and fired in a lidded ceramic container to form a material for oxide superconductors. The material is ground, homogeneously mixed with prescribed amounts of Ar powder and Pt powder, press-molded and fired at 800 to 900 deg.C to provide an oxide superconductor containing 1-25wt.% of Ag and 0.1-5wt.% of Pt, having a composition represented by the formula [A=1.2 to 1.9; B<=1; (A+B)<=2.2; C=1,8 to 2.4; the numbers are each an atomic ratio] and improved in the dependency of the superconductive characteristics on magnetic field.

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) Tj-Ba-8r-Ca-Cu-0 system (Dll compound st
The a-forms are generally thallium (T7), barium (Ba),
Strontium (Sr), Calcium (Ca), Copper (C
u) Simultaneously mixing the starting materials containing Ba-
8r-Ca-Cu-0, Ba-8r-Cu-0, Ca-
It can be obtained by mixing a compound such as 0°Cu-0 and a T/compound to prepare a raw material for a superconductor, and then molding and firing this.

The Tl-Ba-8r-Ca-Cu-0 based OS compound superconductor is known to be a material having a high critical temperature (hereinafter referred to as Tc) of about 120°C.

(Problem to be Solved by the Invention) However, the TI produced by the above method! -Ba-
8r-Ca-Cu-0 based oxide superconductor (hereinafter referred to as TI!
superconductors) have many voids and are difficult to obtain with high density. For this reason, the connections between crystal grains are poor <,T
Superconducting properties such as c and critical current density (hereinafter referred to as Jc) are reduced, and mechanical strength and the like are also reduced.

In addition to the heat treatment process, as a method to improve the above drawbacks,
A generally known method is to introduce processes such as rolling, crushing, and press forming, combine these processes, and repeat the process several times. If this method is used, the superconducting properties of Tc and J can be improved to some extent, but this method increases the number of manufacturing steps.

The problem is that it is complicated.

Furthermore, Tj compounds easily evaporate and are expensive.

Therefore, it is important to suppress the evaporation of TE, but as the number of heat treatment steps increases, it becomes difficult to suppress the evaporation of Tl, and a shift in composition due to the evaporation of T7 is likely to occur.

Generally TI! It is said that the Jc of Y-Ba-Cu-0 based superconductors is more likely to decrease when a magnetic field is applied than Y-Ba-Cu-0 based oxide superconductors. It is essential to improve these problems and introduce a magnetic flux binding point.

An object of the present invention is to provide an oxide superconductor in which +TC, Jc, etc. do not decrease or decrease only slightly, and the magnetic field dependence of Jc is improved, and a method for manufacturing the same.

(l!Means for solving the problem) As a result of various studies on the above-mentioned drawbacks, the inventors discovered that by adding silver and platinum to the conventional T/based superconductor, improvements in TCHJC, etc., magnetic field properties, etc. It was discovered that it was effective in improving the invention, and it was scattered to complete the invention.

The present invention contains 1 to 25% by weight of silver and 0.1 to 5% by weight of platinum.
% by weight, and general formula T11.4-2BaAS rB
caOcu7B-3,60x (A = 1.2~L
, 9, B≦1. (A1B)≦Z2. C=1.8～
2. ．． 4. After weighing the oxide superconductor having the composition shown by the number Fi (representing the atomic ratio) and the raw materials including silver, platinum, thallium, barium, strontium, calcium, and at to have the above composition, and then mixing them,
The present invention relates to a method for producing an oxide superconductor to be fired.

In the present invention, the raw materials (starting raw materials) containing thallium, barium, strontium, calcium, and copper, which are the main components constituting the oxide superconductor, are not particularly limited; One or more of the following may be used.

General formula T/1;,, -2Ba*5rnCaoCul@~
At 3,60x.

Thallium has an atomic ratio in the range of 1.4 to 2, and if it is outside this range, the Tc is high (TI!) of 120 or more.
zBazcatcuscho phase, 2223 phase) production amount decreases.

Barium (5) has an atomic ratio in the range of 1.2 to 1.9.

If it deviates from this range, crystal phases other than the superconductor phase are likely to be formed, and the superconductor content decreases.

Strontium (Bl) is kept at an atomic ratio of 1 or less, and if it exceeds 1, Tc will drop significantly.

Calcium TC) has an atomic ratio in the range of 1.8 to 2.4, and if it is less than 1.8, the amount of high temperature phase produced decreases.

If z4 is exceeded, crystal phases other than the superconductor phase are likely to be formed, and the superconductor content decreases.

Steel has an atomic ratio in the range of 28 to 3.6, and if it is less than 28, the amount of high temperature phase produced decreases, and if it exceeds 3.6, the superconductor content decreases.

Silver is required to be contained in the LT-ride superconductor in an amount of 1 to 25% by weight, and if it is less than 1% by weight, it improves the effect of improving connections between crystal grains and improves mechanical strength. effect becomes smaller.

If it exceeds 25% by weight, the superconductor content decreases.

Platinum is required to be contained in the oxide superconductor in an amount of 0.1 to 5% by weight, and if it is less than 0.1% by weight, platinum has little effect on improving magnetic field characteristics, If the value exceeds 1, the disadvantage is that it becomes expensive.

In addition to silver powder, silver oxide and silver chloride can be used as silver.

There is no particular restriction as long as silver nitrate or the like is used and the material becomes a single pot 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.

There are no particular restrictions on the method of adding silver and platinum, but for example, a method of mixing and homogenizing silver and platinum with powder of an oxide superconductor material in a dry or wet method using a ball mill, miller (automatic kneader), mortar, etc. There is a method in which an aqueous solution of silver and platinum is added to an oxide superconductor material and then uniformly heated.

There are no particular restrictions on the mixing method, and examples include 9.

Method 9: Dry mixing in a molding machine 9 Fill balls coated with synthetic resin with solvents such as ethanol, methanol, etc. and raw materials in a synthetic resin ball mill.

Wet mixing is preferred.

The firing is preferably performed in a closed can container.

As the closed container, it is preferable to use a container made of ceramics such as alumina or magnesia.

The firing temperature can be selected as appropriate depending on the blending ratio of each raw material, but it is preferable to perform firing in the range of 800 to 900°C, and the firing atmosphere can be in the atmosphere, in an air stream, or in a low oxygen pressure atmosphere ( It is preferable to carry out the firing in such a manner that the content of element a is in the range of 1 to 20 volume units, preferably 2 to 20 volume units.

In the composition of the present invention, the amount of Of element is determined by the amount of CuO and the oxidation state of Cu. However, it was not possible to precisely and precisely measure the oxidation state of the oxidation state, so in the present invention, it was expressed as X.

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

Example 1 Badf high-purity (high-purity chemical research laboratory produced 99% or higher) so that the ratio of barium, strontium, calcium, and copper becomes the composition shown in Table 1 in terms of atomic ratio.

8rO (manufactured by Kojundo Kagaku Kenkyusho, purity 99% or more).

Cab (Kojundo Kagaku Kenkyushin, purity 99.9%) and C
uO (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) was weighed and used as a starting material.

Thereafter, the above starting materials were mixed for 30 minutes using a strainer. The obtained mixed powder was preliminarily calcined at 900° C. for 10 hours in the air using an electric furnace.

The mixture was ground for 30 minutes using a grinder.

Next, Th1s (manufactured by Kojundo Kagaku Kenkyushin, purity 99.9%) was weighed to have the composition shown in Table 1, added to the above pulverized material, mixed uniformly in a mortar, pulverized, and oxidized. A composition for a physical superconductor was obtained.

The obtained composition for oxide superconductor was pressed with a mold press to 100%
Molded with a pressure of MPa and has a thickness of 21! A molded body of Ill was obtained. Next, this molded body was fired at 870° C. for 3 hours in an alumina container with a lid to obtain a material for an oxide superconductor.

After grinding the obtained oxide superconductor material into powder in a mortar, silver powder (manufactured by Tokuriki Honten, purity 99.9chi) and platinum powder (manufactured by Tokuriki Honten, purity 99.9chi) were added as shown in Table 1. It was weighed so as to have the composition shown, added to the above-mentioned pulverized powder, and mixed uniformly in a mortar.

The obtained powder was molded into a pellet with a diameter of 30 m and a thickness of 1 m using a die press at a pressure of 150 MPa, and then molded into a pellet with a diameter of 30 m and a thickness of 1 m.
An oxide superconductor was obtained by firing at 0° C. for 5 hours.

Next, the oxide superconductor obtained above is 20 m long x 1 m wide.
It was processed into a rectangular parallelepiped with a thickness of 1 cm, and the temperature change in electrical resistance was measured using the four-terminal method to determine +TC.

Also, using the same sample as above, liquid nitrogen temperature (77K)
At the same time, the liquid phoneme temperature and JCo, 1 were measured in a magnetic field of 0.1 Tesla. These results and J
Table 1 shows the ratio between co,1 and Jc(,).

From Table 1, the oxide superconductor of the present invention has a small decrease in T:erO and a decrease in Jc when compared with the conventional oxide superconductor of Fragrance 13, and J
It is shown that the decrease in c is small.

(Effects of the Invention) The oxide superconductor of the present invention does not have a decrease in + TC + Jc, etc., and even if it does, the decrease in Jc is small, and it is extremely suitable for industrial use. It is an oxide superconductor.

Claims (2)

[Claims] 1. It contains 1 to 25% by weight of silver and 0.1 to 5% by weight of platinum, and has the general formula Tl_1_. ＿４＿〜＿２Ba_ASr
_BCa_CCu_2_. ＿８＿～＿３＿． _6O_X
(However, A=1.2-1.9, B≦1, (A+B)≦2.
2, C=1.8 to 2.4, numbers represent atomic ratios). 2. A method for producing an oxide superconductor, which comprises weighing each raw material containing silver, platinum, thallium, barium, strontium, calcium, and copper so as to have the composition according to claim 1, and then mixing and firing.