JPH01308602A - Manufacture of oxide super conductor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing an oxide superconductor having an excellent critical current density value.

(Prior Art) In recent years, since it was announced that layered perovskite-type oxides based on La-Ba-Cu-0 may have a high critical temperature, research on oxide superconductors has been carried out in various places. (z, Phys, B Condensed Mat
ter64.189-193 (1988)), among which defective perovskite type ((ABa2Cus O□-8
type) (δ represents an oxygen defect and is usually 1 or less, A is Y 5
Las Scs Nds S1% Eus Gd5Dy
The oxide superconductor of SHO%ErSTm, yb, and at least one element selected from Lu, and a part of Ba can be replaced with S, etc.) has a critical temperature of 90 or higher, which is higher than the boiling point of liquid nitrogen. It is attracting attention as a very promising material because it exhibits high temperatures (Phys, Rev, Lett.

Vol. 58 No. 9.908-910).

However, this oxide superconductor is obtained as a sintered body of crystalline oxide or its powder, and when these are used, for example, as wire rods, the oxide superconductor powder is filled into a metal tube or the like and a long length of the oxide superconductor is obtained. However, in the oxide superconductor described above, superconducting current flows along the zero plane of the crystal, so simply increasing the length of this oxide superconductor powder will not change the orientation direction of the crystal. There is a problem that the current density becomes random and it is difficult to obtain the desired current density.

Further, similar problems arise when this oxide superconductor is formed into a block shape or a film shape.

(Problems to be Solved by the Invention) As described above, oxide superconductors are sintered bodies or powder thereof, and since superconducting current flows along the zero plane of the crystal, it is difficult to simply sinter them or to make them into long pieces. However, there is a problem in that the current density obtained is small if the oxide superconductor is simply converted into a oxide, and it is difficult to obtain an oxide superconductor having a sufficient current density for practical use.

The present invention was made in order to cope with such conventional circumstances, and an object of the present invention is to provide a method for manufacturing an oxide superconductor that allows superconducting current to flow at a practical current density.

[Structure of the Invention] (Means for Solving the Problems) The method for producing an oxide superconductor of the present invention comprises forming an oxide superconductor powder into a predetermined shape and then heating and baking it. The manufacturing method is characterized in that the molding is performed by pressing in a magnetic field.

Many oxide superconductors are known, but
It is practically preferable to use a rare earth element-containing perovskite-type oxide superconductor that has a high critical temperature. The oxide superconductor containing a rare earth element and having a perovskite structure may be one that can realize a superconducting state, and may be LnBa Cu O-based 237-δ (Ln is YbS Tms Ers DYS HO%
Y S La, ScS Nds Sm.

at least one element selected from Eu and Gd,
δ represents an oxygen defect and usually represents a number of 1 or less, and a part of Ba can be replaced with Sr or the like. Examples include oxides having a perovskite type in a broad sense, such as a defective perovskite type having oxygen defects such as ), and a layered perovskite type such as La-3r-Cu-0 type.

In the present invention, rare earth elements are defined in a broad sense and include Sc, Y, and La elements.

Typical systems include, in addition to the Y-Ba-Cu-0 system,
All or part of Y as Yl)s Tm, Ers Dy,
) to, systems substituted with rare earth elements such as Eu, 5e-Ba
Examples include -Cu-0 series, La-8r-Cu-○ series, and systems in which Sr is replaced with Ba5Ca.

In particular, in the present invention, Yb, Yb,
Tm, Er, Dy, HOSNd, S1% Eu
s LnBa Cu substituted with magnetic elements such as Gd
An O-based layered pe237-δ lobskite type oxide superconductor is suitable.

The oxide superconductor powder used in the present invention is manufactured, for example, by the following method.

First, the constituent elements of the perovskite oxide superconductor, such as Ho and Ba5Cu, are thoroughly mixed. When mixing)
Oxides such as io203 and BaO5CuO can be used as raw materials. In addition to these oxides,
Compounds such as carbonates, nitrates, hydroxides, etc. that are converted to oxides after calcination may be used. Furthermore, oxalate obtained by a coprecipitation method or the like may be used. The elements constituting the perovskite-type oxide superconductor are basically mixed so as to have a stoichiometric composition, but there may be a slight deviation depending on the manufacturing conditions, etc. For example, in the Ho-Ba-Cu-0 system, Ba 2sol, C
The standard composition is u 3sol, but in practice it is llo 1
sol, Ba 2 ± 0.6 sol, Cu 3
A deviation of approximately ±0.2 sol is not a problem.

After thoroughly mixing the above-mentioned raw materials, 850 to 98
Fire at around 0°C. This firing is preferably performed in an oxygen-containing atmosphere where oxygen can be sufficiently supplied. Next, by heat treatment in an oxygen-containing atmosphere, preferably in an oxygen stream, or by slow cooling to about 300° C. in a similar atmosphere, oxygen can be introduced into the oxygen defects δ and the superconducting properties can be improved. This heat treatment is usually 300~
It is carried out at about 700℃. Next, this baked product is ball milled,
0.5~ by sand grinder or other known means
Grind to about 2 μm. At this time, the perovskite-type oxide superconductor is split from the cleavage plane and becomes fine powder. This pulverization is based on the average particle size (length of the largest axis on the C-plane)
It is preferable to carry out the process so that the uniaxial ratio (ratio of grain size to thickness) is about 3 to 5.

The oxide superconductor powder thus obtained has an oxygen defect δ, for example, an oxygen-deficient perovskite structure (LnBa Cu O (δ is usually a number of 1 or more and 237−δ or less)). In addition, in this type of oxide superconductor, it is also possible to replace Ba with Sr, Ca, etc., and further replace a part of Cu with Ti5V SCr1Mn5Pe.
It can also be replaced with sCo, old, Zn, etc. The amount of this substitution can be set as appropriate within a range that does not reduce the superconducting properties, but too large a substitution will reduce the superconducting properties, so it should be kept at 8011o1% or less, and in practical terms, 20mo1% or less. .

To explain in more detail the method for producing an oxide superconductor of the present invention, first, the oxide superconductor powder produced by the method described above is molded into a predetermined shape. Examples of this molding process include the following method.

■ Filling oxide superconductor powder into a tube-shaped base material,
After compacting the powder from outside the tube-shaped base material using a swaging machine or the like while applying a magnetic field in the longitudinal direction, draw a wire so that the outer diameter of the tube is 1110 or less of the original outer diameter, preferably The diameter is reduced to about 1/20 or less, and the length is lengthened so that the powder filling rate is 50 to 70%.

At this time, annealing may be performed in the middle if necessary.

■ Oxide superconductor powder is pressed into a block shape while applying a vertical magnetic field.

Molded bodies of various shapes such as linear, tubular, and membrane shapes are produced.

In this case as well, before the oxide superconductor powder is compressed during press molding and the movement of individual powders is restrained, the powder is compressed while applying a magnetic field in a direction perpendicular to the electric path. The magnitude of the magnetic field at this time is preferably 1.0 T or more. The magnitude of this magnetic field is 1. Below OT, crystal rearrangement by the magnetic field becomes insufficient.

By pressing in this magnetic field, the crystalline structure within the oxide superconductor is rearranged in a direction that facilitates current flow under the influence of the magnetic field, improving current density.

In addition, the material of the tube-shaped base material used in the method (2) above includes metals such as Ag, Nb, ^gSPds Cu, etc., and glass, etc. In particular, metal tubes such as Ag5Pd, etc.
Since it does not oxidize even at high temperatures, a wire with a desired outer diameter is produced by wire drawing, and then annealed in an oxygen-containing atmosphere. This is preferable because it can be introduced.

Next, the compact of the oxide superconductor powder is subjected to a sintering treatment in an oxygen-containing atmosphere. The sintering temperature is preferably 700°C to less than the melting point, usually in the range of about 800 to 950°C.

Thereafter, it is slowly cooled in an oxygen atmosphere, or heat treatment is performed in an oxygen atmosphere at a temperature of 700 to 200° C. to introduce oxygen into the oxygen vacancies.

Note that the same magnetic field as during molding may be applied during the above-mentioned sintering and annealing stages.

(Function) In the method for producing an oxide superconductor of the present invention, the compact made of oxide superconductor powder is pressed in a magnetic field and then sintered. Tissues are rearranged in the direction in which current can easily flow, and current density is significantly improved.

(Example) Next, examples of the present invention will be described.

Example 1 2 mo1% BaC03 powder, Ho2 with a particle size of 2 to 5 μm
O3 powder 0.5mo1%, CuO powder 3no1%,
After thoroughly mixing and firing in the atmosphere at 900°C for 48 hours to react, this fired product was further fired in oxygen at 800°C for 24 hours to react, and then slowly cooled to introduce oxygen into the oxygen vacancies. .

This sintered body is crushed using a ball mill, classified, and
A perovskite-type oxide superconductor powder having an average particle size of 0.85 μm and a diameter-to-thickness ratio of 3 to 5 was obtained.

Next, this oxide superconductor powder was placed in a press mold and press-molded at 2t/cd while applying a 7.0T magnetic field in the vertical direction.

Thereafter, heat treatment was performed at 940° C. for 7 hours while flowing oxygen, and then slowly cooled at 3° C.

When we measured the superconducting properties of the superconductor block obtained in this way, we found that the critical temperature was 90°C, as shown in the figure.
Good results were obtained with a critical current density of 400 to 800 A/c.

Comparative Example 1 For comparison with the present invention, YBa2Cu30 containing no magnetic ions produced in the same manner as in Example 1 was pressed without applying a magnetic field, and then sintered to produce a superconductor block.

The critical current density of this superconductor block was 60 to 200 A/c (as shown in the figure).

Example 2 The I(oBa CuO bulk produced in Example 1 was pulverized in the same manner as in Example 1, and one end of this oxide superconductor powder was 20 mm in outer diameter x 18 sm in inner diameter x 70 sn in length. After filling a chain tube sealed with a silver material and welding it with a silver stopper at the other end leaving a ventilation hole, it was cold-heated to an outer diameter of 3 mm while applying a 7.0 T magnetic field in the longitudinal direction. The wire was then drawn at 940° C. for 7 hours in an oxygen flow.The critical current density of this superconductor wire was also 830 A/c7, which was a good result.

[Effects of the Invention] As is clear from the above examples, in the manufacturing method of the present invention, the oxide superconductor powder is bus-molded in a magnetic field and then sintered. The crystalline structure within the physical superconductor rearranges itself in the direction where current flows easily,
The critical current density is significantly improved, and an oxide superconductor having a practical current density can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing a comparison between the critical current density of an oxide superconductor containing magnetic ions and the critical current density of an oxide superconductor not containing magnetic ions in an example of the present invention.

Claims (1)

[Claims] (1) After molding the oxide superconductor powder into a predetermined shape,
A method for producing an oxide superconductor comprising heating and firing, characterized in that the shaping is performed by pressing in a magnetic field.