JPH02102166A - Production of oxide superconducting material - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having a critical temperature of >=100K by sintering a mixture comprising BiO, SrO, CaO and CuO at specified proportion within the range from the melting point minus 10 deg.C to the melting point. CONSTITUTION:The objective oxide superconductor can be obtained by sintering a mixture comprising BiO, SrO, CaO and CuO at the molar ratio 2:2:n:m (3<n<=10, 4<m<=11, n+1<m) within the range from the melting point minus 10 deg.C to the melting point. This superconducting material, which has a Tc of >=100K, is of such main structure that four Cu-O layers are present between Bi layers.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing an oxide superconducting material used in superconducting magnets and Josephson junction devices.

Conventional technology superconducting materials: (1) have zero electrical resistance; (2)
It has properties not found in other materials, such as being completely diamagnetic and (3) having the Josephson effect, making it useful for power transportation, generators, plasma confinement in nuclear fusion reactors, magnetic levitation trains, magnetic shields, ultra-high-speed computers, etc. A wide range of applications are being considered. Metal-based superconducting materials, which have been put into practical use in the past, require cooling with expensive liquid helium and large-scale insulation equipment, which has been a major industrial problem.

For this reason, researchers have been searching for materials that become superconducting at higher temperatures.

In February 1987, YBa2c showed superconductivity at 90
uao7-y was discovered, and then Y was replaced by other rare earth elements (
LalNdlSms Eu1GcL Dy1HCh
It was confirmed that substitution is possible with E rlT ms Y blL u ). Because this material can use inexpensive liquid nitrogen for cooling, it is expected to have a wider range of applications than conventional metal-based materials.

In January 1988, a Bi-based oxide superconductor was discovered that exhibits superconductivity at even higher temperatures of 100°C or higher. This material can be said to be an even more superior material in that it does not contain expensive rare earth elements, which are ubiquitous in terms of resources and can be considered strategic materials. For this reason, a lot of research is currently underway regarding the production, physical properties, applications, etc. of this material.

Problems to be solved by the invention Recent research has shown that Bi-based superconductors are layered compounds.
It has been revealed that those having a critical temperature of 100 or more have three or more layers of Cu and O between the Bi and Bi layers. However, it is very difficult to obtain such a compound, and in many cases there are less than two Cu-0 layers between the Bi layers.
Only a mixture of layers and layers could be obtained.

In this case, by replacing Bi with Pb, we succeeded in producing a Bi-based superconductor with three Cu-0 layers between the Bi layers (U, Endo(Indo-) +
s, Koyama and T,
Kawal (Kawai L Jpn, J, Ap
p+, phys,
Of Affirmed Fish) 2! (+9
88) 1147G-LI479) However, PB is extremely harmful to the human body, and special equipment is required for actual industrialization.

Means for solving the problem B101S r OlCa Ol and CuO 2
:2: n: m (3<n≦LO14<m≦11,
An oxide superconducting material is produced by mixing in a ratio of n+1<m) and firing in a temperature range from 10° C. below the melting point to the melting point.

Function The Bi-based superconducting oxide produced as described above contains Bi and B.
There are at least three or more layers of Cu and 0 between the layers of i, and has a critical temperature of 100°C or more. Depending on the manufacturing conditions, a Bi-based superconducting oxide having a main structure of four layers can also be obtained.

Example The present invention will be specifically described with reference to Examples.

99% purity B t20s S rcO3, CaCO
3. Weigh each CuO powder so that it has a predetermined composition ratio, and mix it with ethanol in an agate ball mill for 20 minutes.
Mixed time-wise. After drying the mixture at 120″C,
It was placed in an alumina crucible and calcined in air at 750°C for 6 hours. The calcined powder was coarsely ground, milled using ethanol in an agate ball mill for 20 hours, and dried at 120°C.

To the thus obtained powder was added 5% by weight of an impropatul solution in which polyvinyl butyral was dissolved at a concentration of 5% by weight and granulated.

Pour 0.8g of this granulated powder into a mold of 18mm x 5mm,
Uniaxial pressure molding was performed at a pressure of 0 kg/cm2.

These molded bodies were heat treated at 600°C for 2 hours to remove the binder, heated at a heating rate of 300″C/hour, and fired at 750°C to 90°C.
It was fired at 0°C for 5 hours to 30 days at a temperature drop rate of 300'C/hour. However, the atmosphere was airy.

Blending composition 11m (Br OlS roi Car
The respective ratios of tCuO were 2: 2: n: m
), firing temperature ('C), firing time (h), number of Cu-0 layers between Bi layers, superconducting transition temperature (K), and magnetic susceptibility are shown in Table 1. However, the "Number of Cu-0 layers between BiJti" is 7.3゛ in 2θ according to the X-ray diffraction pattern.
5.7° was treated as 2 layers, 4.7° was treated as 3 layers, and when there was a peak at an angle lower than 4.7°, it was treated as 3 layers. The ``transition temperature'' is the temperature Tc at which the resistance value begins to rapidly decrease and the temperature TlI at which the resistance value becomes zero, and the ``magnetic susceptibility'' is the magnetic susceptibility -M (emu/g) at 100K.

Table 1 (Part 1) Table 1 (Part 2) Table 1 (Part 4) Table 1 (Part 3) Table 1 (Part 5) Transmission electron microscopy of samples fired for 720 hours at n=4, m=6.5 When the lattice images were observed, 3 to 7 Cu-0 layers were observed between the Bi layers.

The most commonly observed layer was 4 layers, and there were almost no areas with 2 layers or less. The X-ray diffraction pattern also has a strong peak at 4.2° in 2θ, supporting the fact that the main structure is 4 layers.

In the example, 1 is used only when the firing time is 3 days or more.
Samples showing zero resistance at temperatures above 00 were obtained, indicating that firing for a long time is effective in improving the characteristics.

Effects of the Invention According to the present invention, an oxide superconducting material having at least three or more Cu-0 layers between Bi layers and having a critical temperature of 100 or higher can be easily produced without using Pb. .

Claims (1)

[Claims] BiO, SrO, CaO, and CuO in 2:2:n
:m (3<n≦10, 4<m≦11, n+1<m) and is fired in a temperature range from 10°C lower than the melting point to the melting point. manufacturing method.