JPH0543233A - Oxide superconductor and production thereof - Google Patents

Abstract

PURPOSE:To produce an oxide superconductor which undergoes very slight or the no lowering of the Tc, Jc, etc., and undergoes slight lowering of the Jc when a magnetic field is applied. CONSTITUTION:Starting materials contg. Tl, Ba, Ca, Cu and Mg are weighed so as to obtain a compsn. represented by a general formula Tl1.4-2 BaACABCU2.8-3.6MG0.05-2Ox (where 1.6<=A<=2.3, 1.8<=B<=2.6, 0.9<=B/A<=1.62 and the numbers show atomic ratio). They are mixed and fired to produce an oxide superconductor having the above-mentioned compsn.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxide superconductor and a method for producing the same.

[0002]

2. Description of the Related Art Tl-Ba-Ca-Cu-O-based oxide superconductors are generally thallium (Tl) and barium (B).
a), calcium (Ca), copper (Cu), and other starting materials are mixed at the same time, or Ba-Ca-Cu-O, Ba
It can be obtained by mixing a compound such as —Cu—O, Ca—O or Cu—O and a Tl compound as a raw material for a superconductor, and molding and firing this. Tl-Ba-Ca-
It is known that a Cu-O-based oxide superconductor is a material having a high critical temperature (hereinafter referred to as Tc) of 120K or higher.

[0003]

Generally, Tl-Ba-C is used.
It is said that Jc of an a-Cu-O-based superconductor is more likely to be lowered by application of a magnetic field than that of an Y-Ba-Cu-O-based oxide superconductor. It is essential to improve the above problems and introduce pinning points for magnetic flux.

It is an object of the present invention to provide an oxide superconductor and a method for producing the same, in which Tc, Jc, etc. are not lowered, are slight even if they are lowered, and improve the magnetic field dependence of Jc. Is.

[0005]

As a result of various studies on the above-mentioned drawbacks, the present inventors have found that the conventional Tl-Ba-Ca-
When magnesia was added to a Cu—O-based oxide superconductor, the inventors found that it was effective in improving the magnetic field characteristics of Jc, and completed the present invention.

The present invention has the general formula Tl _1.4-2 Ba _A Ca _B Cu.
_2.8-3.6 Mg _0.05-2 O _x (where A = 1.6-2.
3, B = 1.8 to 2.6, 0.9 ≦ B / A ≦ 1.62
5, numbers represent atomic ratios) and oxide superconductors having a composition shown by the formula (1), and each raw material containing thallium, barium, calcium, copper and magnesium is weighed so as to have the above composition, and then mixed and baked. The present invention relates to a method for producing an oxide superconductor.

In the present invention, the raw material (starting raw material) containing thallium, barium, calcium, copper and magnesium, which are the main components of the oxide superconductor, is not particularly limited. For example, these oxides, carbonates and nitrates can be used. One or more of oxalate and the like are used.

General formula Tl _1.4-2 Ba _A Ca _B Cu _2.8-3.6
In mg _{0.05 to 2} O _X, thallium 1.4 in atomic ratio
It is set to the range of 2, and when it deviates from this range, Tc is 120K
The above high temperature phase (Tl ₂ Ba ₂ Ca ₂ Cu ₃ O ₁₀ phase, 2223
The amount of phase) produced is reduced.

Barium (A) has an atomic ratio of 1.6 to 2.3.
If it deviates from this range, a crystal phase other than the superconductor phase is likely to be generated, and the content rate of the superconductor is lowered.

Calcium (B) has an atomic ratio of 1.8-2.
When it is within the range of 6, the amount of the high temperature phase produced is reduced when it is less than 1.8, and when it exceeds 2.4, the crystal phase other than the superconductor phase is easily produced and the content rate of the superconductor is reduced.

The atomic ratio of copper is in the range of 2.8 to 3.6, and if it is less than 2.8, the amount of high-temperature phase produced decreases,
If it exceeds 3.6, the content rate of the superconductor decreases.

[0012] Magnesium has an atomic ratio in the range of 0.05 to 2. When it is less than 0.05, the effect of improving the magnetic field characteristics of Jc is small, and when it exceeds 2, Tc is greatly reduced.

The method of adding magnesium is not particularly limited, but for example, a starting material containing barium, strontium, calcium and copper together with a material containing magnesium can be used in a ball mill, a raker machine (automatic kneader), a mortar or the like. There are methods such as wet or dry mixing and homogenizing.

The mixing method is also not particularly limited, for example, a method of dry mixing with a raker machine, a ball coated with a synthetic resin in a ball mill made of a synthetic resin, and ethanol,
It is preferable to fill a solvent such as methanol and raw materials and wet mix.

The 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 mixing ratio of each raw material and the like, but it is preferable to perform firing in the range of 750 to 1000 ° C., and the firing atmosphere is not particularly limited, and may be in an oxygen atmosphere, air, or air. Firing is possible in an air stream or in an atmosphere of low oxygen pressure (oxygen content is in the range of 1 to 20% by volume, preferably 2 to 20% by volume).

In the composition of the present invention, the amount of O (oxygen) is
It depends on the amount of Cu and the oxidation state of Cu. However, it is not possible to measure exactly how the oxidation state is, so that it is represented by X in the present invention.

[0018]

EXAMPLES Examples of the present invention will be described below. Example 1 BaO (manufactured by Kojundo Chemical Laboratory, purity 99% or more), CaO (manufactured by Kojundo Chemical Laboratory, purity 99.) so that the ratios of barium, calcium and magnesium in atomic ratio are as shown in Table 1. 9%), CuO (manufactured by Kojundo Chemical Laboratory,
Purity 99.9%) and MgO (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were weighed and used as starting materials.

After that, the above starting materials were mixed for 30 minutes by using a raker. The obtained mixed powder was pre-baked at 900 ° C. for 10 hours in the air using an electric furnace, and then pulverized for 30 minutes using a raider machine.

Next, the preliminary fired powder was re-fired at 1300 ° C., then coarsely crushed in a mortar and then crushed for 30 minutes by a raker machine, and further, Tl ₂ O ₃ (manufactured by Kojundo Chemical Laboratory, purity 99.
9%) was weighed so as to have the composition shown in Table 1 and added to the above pulverized product, and uniformly mixed and pulverized in a mortar to obtain a composition for oxide superconductor.

The resulting composition for oxide superconductor was molded with a die press at a pressure of 100 MPa to obtain a molded body having a thickness of 2 mm. Then, this molded body was baked at 870 ° C. for 10 hours in an alumina container with a lid to obtain an oxide superconductor.

Next, the oxide superconductor obtained above was made to have a length of 20.
A rectangular parallelepiped having a size of mm × width 1 mm × thickness 1 mm was processed, and a temperature change of electric resistance was measured by a four-terminal method to obtain Tc. Also, using a sample similar to the above, the liquid helium temperature (4.2
K) was used to measure Jc ₀ and the liquid helium temperature was set to 10
Jc ₁₀ was measured in a Tesla magnetic field. The results and the ratio of Jc ₁₀ to Jc ₀ are shown in Table 1.

[0023]

[Table 1]

From Table 1, the oxide superconductor according to the present invention is
It is shown that the decrease in Tc is small with respect to the conventional oxide superconductor of trial number 1, the Jc does not decrease, and the decrease in Jc due to the application of the magnetic field is small.

[0025]

INDUSTRIAL APPLICABILITY In the superconductor according to the present invention, Tc, Jc, etc. do not decrease, the decrease is negligible, and the decrease in Jc due to the application of a magnetic field is small. It is a superconductor.

Claims (2)

[Claims] 1. The general formula Tl _{1.4 to 2} Ba _A Ca _B Cu
_2.8-3.6 Mg _0.05-2 O _x (where A = 1.6-2.
3, B = 1.8 to 2.6, 0.9 ≦ B / A ≦ 1.62
5, the numbers represent atomic ratios), which are oxide superconductors having a composition shown in FIG. 2. A method for producing an oxide superconductor, characterized in that raw materials containing thallium, barium, calcium, copper and magnesium are weighed so as to have the composition according to claim 1, then mixed and fired. Law.