JPH0492852A - Oxide superconductor and production thereof - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having durable superconducting property and exhibiting small lowering of the critical current density by the application of magnetic field by specifying the composition composed of Tl, Ba, Sr, Ca, Cu and O and adding specific amounts of Ag and Pd to the composition. CONSTITUTION:The objective oxide superconductor contains 1-25wt.% of Ag and 0.1-5wt.% of Pd and is expressed by the general formula Tl1.4-2 BaASrBCaCCu2.8-3.6OX (A is 1.2-1-9; B<=1; A+B<=2.2; C is 1.8-2.4). The superconductor exhibits no or, if any, extremely little lowering of superconducting properties such as critical temperature and critical current density and has improved magnetic field dependency of the critical current density. The oxide superconductor can be easily produced by weighing and mixing the materials containing Ag, Pd, Tl, Ba, Sr, Ca and Cu at ratios to satisfy the above composition and baking the mixture.

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) Tz-Ba-8r-Ca-Cu-0-based oxide superconductors generally include thallium (TI), barium (Ba),
Strontium (Sr), Calcium (C), Steel (C
u) etc., or by simultaneously mixing the starting materials including Ba-
8r-Ca-Cu-0, Ba-8r-Cu-0, Ca-
K can be obtained by mixing a compound such as 0°Cu-0 with a T/compound to prepare a raw material for a superconductor, and then molding and firing this.

The T/-Ba-8r-Ca-Cu-0-based oxide superconductor is known to be a material having a critical temperature (hereinafter referred to as Tc) as high as 120°C.

(Problem to be solved by the invention) However, T/-Ba- produced by the above method
An 8r -Ca-Cu- width oxide superconductor (hereinafter referred to as a Tr-based superconductor) has many voids and is difficult to obtain with high density. For this reason, the bond between the crystal particles is poor <, Tc
Superconducting properties such as 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, superconducting properties such as T%ero and JC can be improved to some extent, but this method increases the number of manufacturing steps.

The problem is that it is complex.

Furthermore, T/compounds easily evaporate and are expensive.

Therefore, it is important to suppress the evaporation of T2O, but as the number of heat treatment steps increases, it becomes difficult to suppress the evaporation of T2O, and a shift in composition due to the evaporation of T2 is likely to occur.

In general, it is said that Je is more likely to decrease when a magnetic field is applied than T/based superconductors and aY-Ba -Cu-0 based oxide superconductors. Improve problems such as.

It is essential to introduce a stop point for magnetic flux.

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

(Means for Solving the Problem) As a result of various studies in view of the above-mentioned drawbacks, the inventors of the present invention found that trapping silver and palladium were added to the conventional T/based superconductor, resulting in +1% improvement in erO, JC, etc. , the magnetic property invention contains 1 to 25% by weight of silver and 0.1 to 5% by weight of palladium, and has the general formula 'rza-z BaASrBCJL□Cu
ts −1@Ox (However, λ”4.2~1.9.B≦
1゜(A+B)≦12. C=18~z4. Number FiX
An oxide superconductor having the composition shown by (representing the particle ratio) and each raw material containing silver, palladium, thallium, barium, strontium, calcium, and copper so as to have the above composition are weighed, mixed, and then fired. The present invention relates to a method for producing an oxide superconductor.

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 type or 2s or more of the following are used.

General formula T/ m-z BAA SrB Ca (, Cut
s-龜s OX K k i"C, fi, I sea urchin has an atomic ratio of -cJ~2° range, and is □.

Outside this range, high-temperature phases with Te of 120 or higher (TZIBJC11CusOjll phase, 2223 phase)
The amount of O produced decreases.

The barium prison #'i atomic ratio is in the range of L2 to L9.

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

Strontium (B) has an atomic ratio of 1 or less, and when it exceeds 1, THero decreases significantly.

Calcium (C) has an atomic ratio of L8 to Z4,
When it is less than 18, the amount of high temperature phase produced decreases.

When it exceeds 24, crystal phases other than the superconductor phase tend to be formed, and the superconductor content decreases.

Copper has an atomic ratio in the range of 28 to λ6. If the atomic ratio is less than 28, the amount of high-temperature phase produced decreases, and if it exceeds λ6, the superconductor content decreases.

Silver is required to be contained in the oxide superconductor in an amount of 1 to 25% by weight, and if it is less than 1% by weight, it has the effect of improving the bonds between crystal grains 5 The effect of improving mechanical strength etc. If it exceeds 25% by weight, the effect will be diminished, but the superconductor content will decrease.

On the other hand, palladium is required to be contained in the oxide superconductor in an amount of 0.1 to 5% by weight.

When α is less than 1 weight, palladium has little effect of improving magnetic field characteristics, and when it exceeds 5 weight S, there is an effect of improving magnetic field characteristics Fi, but there is a drawback that *TC*JC, etc. are decreased.

The chains include silver powder, 9M silver chloride, and silver chloride.

There is no particular restriction as long as silver nitrate or the like is used and the material becomes pure silver after firing.

Palladium is also available in addition to palladium powder.

There is no particular restriction as long as palladium oxide or the like is used and the material becomes pure palladium after firing.

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

There are no particular restrictions on the mixing method, for example.

Dry mixing method using a molding machine 1 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.

Firing is preferably performed in a closed container.

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

The firing temperature is appropriately selected depending on the blending ratio of each raw material, etc., but it is preferably fired in the range of 800 to 900°C, and the firing atmosphere F! It is preferable to carry out firing in the atmosphere, in an air stream, or in a low oxygen pressure atmosphere at a Ca content of 1 to 20 volume cm, preferably 2 to 20 volume cm.

The amount of O (oxygen) in the composition of the present invention is determined by the amount of CuO and the oxidation state of Cu. However, since it is not possible to precisely and accurately measure the oxidation state, 9 is expressed by X in the present invention.

(Example) The following li! of the present invention! An example will be explained.

Example 1 BaO (manufactured by Kojundo Kagaku Kenkyushin, purity 99- or higher) was prepared such that the ratios of barium, stro/tium, calcium, and steel were as shown in Table 1 in terms of atomic ratio.

8rO (manufactured by Kojun Kinugaku Institute, pure denaturation 99 or higher).

Cab (Kojundo Kagaku Kenkyushin, pure 11:99.911)
and CuO (Kojundo Kagaku Kenkyushin Co., Ltd., pure 5H9.9g) were weighed and used as starting materials.

After this, 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 K Tl! Ol C High Purity Chemical Research New Product, Pure [99
9) T-The compositions shown in Table 1 were weighed and added to the above-mentioned pulverized material, mixed uniformly in a mortar, and pulverized to obtain a composition for an oxide superconductor.

The obtained composition for oxide superconductor was molded with a mold press for 100%
A molded product having a thickness of 2 mm was obtained by molding at a pressure of MPa. Next, this molded body was placed in an alumina container with a lid.
The material for oxide superconductors was obtained by baking at ℃ for 3 hours.

After grinding the obtained oxide superconductor material into powder in a mortar, silver powder (manufactured by Tokuriki Honten, purity 99.C1) and palladium powder (manufactured by Tokuriki Honten, pure [99.9%)] were added to 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 pellets with a diameter of 20 m and a thickness of 1 cm using a Venus press at a pressure of 150 MPm, and then heated at 870 m in the atmosphere.
An oxide superconductor was obtained by firing at ℃ for 5 hours.

Next, the length of the oxide superconductor obtained above is 20a! ×Width 1m
It was processed into a rectangular parallelepiped with a thickness of 1 cm, and the change in electrical resistance with temperature was measured using the four-terminal method to determine Tc.

In addition, using the same sample as above, liquid nitrogen was heated at m degrees (77K).
JC, was measured at 1 g of liquid nitrogen at a temperature of 1 g, and the crystalline oxide superconductor according to the present invention was determined based on the conventional oxide superconductor shown in Fig. 13.

There is little decrease in Jc, and there is almost no decrease in Jc.

Even if it decreases, it is very small, and the J
It is shown that the decrease in e is small.

(Effect of the invention) The oxide superconductor of the present invention is zero, JC
The oxide superconductor does not have a decrease in Jc, and even if it does decrease, it is only a small amount, and the decrease in Jc due to the application of a magnetic field is also small, making it an industrially extremely suitable oxide superconductor and having the above-mentioned effects. A manufacturing method can be provided.

Claims (2)

[Claims] 1. It contains 1 to 25% by weight of silver and 0.1 to 5% by weight of palladium, and has the general formula Tl_1_. ＿４＿～＿２Ba＿
ASr_BCa_OCu_2_. ＿８＿～＿３＿． ＿４
OX (However, A=1.2~1.9, B≦1, (A+B)≦
2.2, C=1.8-2.4, numbers represent atomic ratios)
An oxide superconductor with the composition shown. 2. Silver, palladium,
A method for producing an oxide superconductor, which comprises weighing raw materials containing thallium, barium, strontium, calcium, and copper, mixing them, and then firing them.