JPH02221149A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having a high critical temp. and a high critical current density by melting oxides as starting materials for an Sr-Ca-Cu-O type oxide superconductor by heating, solidifying the molten oxides by cooling, bringing a Bi-Pb-O type oxide into contact with the resulting solid body and carrying out heat treatment. CONSTITUTION:Starting materials such as SrCO3, CaCO3 and CuO are mixed in such a ratio as to give an Sr-Ca-Cu-O type oxide superconductor. They are melted by heating in the air and solidified by cooling. Bi2O3 and PbO are brought into contact with the resulting solid body in such a ratio as to give a Bi-Pb-Sr-Ca-Cu-O type oxide superconductor and they are held at a temp. at which a superconducting phase is formed for a certain time to diffuse a Bi-Pb-O type oxide in the Sr-Ca-Cu-O type oxide. A Bi-Pb-Sr-Ca-Cu-O type oxide superconductor having a high critical temp. and a high critical current density is obtd.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to Bl-Pb-3r-Ca-Cu-0
The present invention relates to a method for manufacturing a superconductor based on oxides, and particularly to a method for manufacturing a superconductor with a high critical current density (Jc).

[Conventional technology]

A method for producing an oxide superconductor consisting of Bi-Pb-5r-Ca-Cu-0 is described in B 1203. PbO.

Compound powder 3' such as SrcOCaCO3 and CuO is mixed and first pre-calcined at 700 to 800°C to react. This is pulverized, molded, and fired at 830 to 840°C in an atmosphere with an oxygen concentration of 4 to 8% to form a sintered body. Furthermore, since Jc is low in the sintering method, a method is also used in which after preliminary firing, the material is melted at a temperature above the melting point, approximately 1100°C, and then heat treated at 750 to 850°C.

[Problem to be solved by the invention]

In practical terms, it is desirable that the critical temperature (Tc) and Jc of the superconductor are both high. In order to obtain a superconductor with a high Jc, it is preferable that the porosity is small and the bulk density is high.

Furthermore, it is preferable that the particles are oriented in a certain crystal axis direction. For this reason, a method of melting has generally been attempted as a method of increasing the density of the gas.

However, Bl -Pb -8r -Ca -Cu
-0 has a melting point of around 860°C, whereas Bi2O3 has a low melting point of 820°C and a high vapor pressure at 860°C. Therefore, when the superconductor is held in a molten state, Bl becomes bubbles and evaporates, causing a composition shift and generation of pores in the liquid phase. Since these pores remain in the solid during solidification, the key density does not increase. Therefore, Jc does not become high.

The present invention provides Bi-Pb-8r-Ca-Cu-0
The purpose of this invention is to provide a method for producing a high-density superconductor, and furthermore, a high Jc superconductor, by preventing compositional deviation and porosity, which are disadvantages of the melting method, in a method for producing a oxide superconductor. .

[Means to solve the problem]

As a result of intensive research to achieve the above object, the present inventors found that only Sr-Ca-Cu-0-based oxides, excluding Bi-Pb-0-based oxides with relatively low melting points, were heated above their melting temperature. After melting and solidifying, B
It was discovered that the superconductivity could be improved by diffusion by bringing i-Pb-0 type oxide into contact with the oxide, and the present invention was completed.

That is, the gist of the present invention is Bi-Pb-Sr-C
In the method for producing an a-Cu-0 based oxide superconductor, S
The raw material oxide for the r -Ca -Cu -0 superconductor is heated above its melting temperature to melt it, then cooled and solidified, and the Blpb-o oxide is brought into contact with this solid to form a superconductor. The B
A method for producing an oxide superconductor, characterized by producing a high-density superconductor with a high critical temperature by diffusion of l-Pb-0-based oxides.

Here, the melting temperature of the raw material oxide for Sr-Ca-Cu-0 superconductor is Bl-Pb-3r-Ca-
1000, which is the same as the melting temperature of Cu-0 based oxide superconductor.
~1200°C is preferred. However, since it does not contain low-melting-point substances such as Bi2O3, which has a melting point at about 820°C, and a composite oxide of Bi2O3 and PB, no bubbles are generated due to the evaporation of these substances. Therefore, when the melt is cooled, a dense superconducting material with no pores in the solid can be produced.

Thereafter, a Bi-Pb-0 based oxide is brought into contact with this dense superconducting material made of Sr-Ca-Cu-0. Bl -Pb -0 series oxide has Bl 203゜P
A mixture of bO powder may be used, but BizO3゜P
It may also be made by sintering bO powder.

After contacting, they are heated for a certain period of time at a temperature that allows the formation of a superconducting phase. The heating temperature is 830℃ in an atmosphere with an oxygen concentration of 4 to 8%.
~840°C is preferred. This heating includes two or more stages of heating: heating at a temperature below the temperature at which a superconducting phase can be generated, and then heating at a temperature at which a superconducting phase can be generated.

During this heating, the Bi-Pb-0 component, which is a contact substance, diffuses into the Sr-Ca-Cu-0 material and becomes dense l-Pb-3r-Ca-Cu-
A zero-based oxide superconductor is obtained.

Although the composition ratio of the Bl -Pb -8r -Ca -Cu -0 system oxide is not limited, it is generally Bi
:Pb :Sr :Ca :Cu-1,8:0.3
Since a mixing ratio in the vicinity of :1.9 :2.0 :3.0 is desirable, it is preferable to set the mixing ratio after contact and diffusion to the above ratio.

As a method of contacting, when a molten material of Sr--Ca--Cu-0 is formed into a thick film by a spin cord or the like, contact can be made by coating or vapor depositing a Bi-Pb-0 based oxide on both sides or one side. Furthermore, it is also possible to process it into a linear shape by coating it or filling it together in a metal sheath material.

〔Example〕

Next, the present invention will be explained in more detail by giving examples of the present invention and conventional comparative examples.

The critical temperature Tc of superconductors obtained by these methods
and critical current density Jc were determined by the following method.

First, Tc was measured by cutting out a sample piece to a length of 10 m and a width of 3 mm and measuring it by a DC 4-terminal method. Lower the temperature of the sample piece to about 1' at a rate of 7 minutes, introduce a current of 3 from both terminals approximately every other layer, and lower the lower limit of the voltage appearing at the inner two terminals (1, O
When X IO'V ) was cut off, the resistance was set to 0, and the temperature was set as Tc.

Next, the n1 constant of Jc was determined as follows. The center part of the sample piece mentioned above was further processed to a width of 0.5 mm and a thickness of 0.3 mm, immersed in liquid nitrogen, and heated to the inner two terminals while increasing the current introduced from both terminals in a temperature of 77 mm. The voltage appearing was measured, and the value of the introduced current at the point where the voltage value became larger than the measurement lower limit (1.0 x 10'V) was divided by the cross-sectional area, and was determined as Jc.

[Example 1] An oxide superconductor raw material composition made of 5rCOCaCO5, CuO and having a ratio of S'23'Ca: Cu -1,9: 2.0: 3.0 was heated at 1100°C in air.
Heat to melt. After quenching the melt once, Bi2O3
゜PbO powder with final composition Bl:Pb:Sr
:Ca:Cu”1.8:0.3:1.9
:2.0 :3. They were added so as to have the same ratio as O, brought into good contact, and heat-treated at 830° C. for 100 hours in an atmosphere with an oxygen concentration of 8%.

Table 1 shows the values of Tc and Jc of the produced superconductor.

[Comparative Example 1] B iOP b O, S r COa , Ca COa
.

23″ CuO is used as raw material, Bi:Pb:Sr:Ca
:Cu-1,8: 0.3: 1.9: 2.0
: An oxide superconductor raw material composition having a ratio of 3.0 is heated and melted at 1100° C. in air. After the melt was once rapidly cooled, it was heat-treated at 830° C. for 100 hours in an atmosphere with an oxygen concentration of 8%.

Table 1 shows the values of Tc and Jc of the produced superconductor.

Table [Effect] The superconductor with few pores according to the present invention can be obtained by melting a high melting point element and then bringing it into contact with a low melting point element and annealing to obtain a superconductor having both high Tc and high Je. can.

Note that although the values of Jc and Tc have been announced in various places, it is not appropriate to compare them in terms of absolute values, as they vary somewhat depending on the preparation conditions of the sample. It is important to make relative comparisons while keeping other conditions as constant as possible.

Claims (1)

[Claims] 1. In a method for producing a Bi-Pb-Sr-Ca-Cu-O based oxide superconductor, a raw material oxide for the Sr-Ca-Cu-O based superconductor is heated to a temperature higher than its melting temperature to melt it. After that, it is cooled and solidified, and Bi-Pb is added to this solid.
-O-based oxides are brought into contact and held at a temperature at which a superconducting phase is formed for a certain period of time, and a high-density superconductor with a high critical temperature is produced by diffusion of the Bi-Pb-O-based oxides. A method for producing an oxide superconductor.