JPH09255334A - Production of bulk-oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve superconducting characteristics by finely dividing a 2nd phase (ordinary conductor) dispersed in a superconductor.

SOLUTION: When a bulky REBa₂Cu₃O_7-x [RE is a rare earth element and (x) is deficiency] superconductor is produced by a half melting method (melt processing method), powder of a previously crystallized REBa₂Cu₃O_7-x. superconductor and powder obtd. by making the particle diameter of a 2nd phase ordinary conductor as small as possible are used as starting materials. The conductor is an RE₂BaCuO₅ or RE₄Ba₂Cu₂O₅ conductor.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to REBa ₂ Cu ₃ O _7-x (x is a loss amount, a semi-melting method).
RE relates to a manufacturing method for manufacturing a bulk oxide superconductor of a rare earth element type, and particularly relates to a technology effectively applied to a manufacturing technology of a magnetic levitation device, a magnetic shield, and a superconducting bulk magnet using the bulk oxide superconductor. It is a thing.

[0002]

2. Description of the Related Art As described in JP-A-7-111213, pinning in a superconducting bulk body of REBa ₂ Cu ₃ O _7-x (x is a deficient amount) (hereinafter referred to as RE123) system by a melting method. A superconducting magnet using a bulk oxide superconductor that captures a magnetic field at the center is disclosed.

When these superconductors are manufactured by a commonly used melting method, there is a problem that the ionic radius of the rare earth element is large, so that the Ba site is easily replaced and the critical temperature is greatly lowered. For example, H.Uwe et a
l .: Physica C vol.153-155 (1988) P.930-931 discloses the related art.

RE123 is mainly composed of (a) polycrystal, (b) single crystal, (c) bulk (having a pinning point in the superconducting phase, and having excellent superconducting characteristics, because of its structure in the order of μm. Are shown).

The RE123 bulk superconductor is manufactured by the semi-melting method (melt process method). This semi-melting method includes MTG (Melt-Txture-Growth process) method, M
PMG (Melt-Powder-Txture-Growth process) method
(“Melt processed high-temperature superconductor
s ”World Scientific, Editor. Masato Murakami),
QMG (Quench and Melt Growth process) method, PD
MG method (Platinum Doped Melt Growth process: platinum addition melting method, solid-state physics Vol.26 No12 1991 p11-17 reference) etc. are known.

Particularly, the QMG method and the MPMG method are shown in FIG.
As shown in FIG. 5, the raw material is melted at 1400 ° C. and then rapidly cooled to form an intermediate, which is a two-step heat treatment process including a melt quenching process and a melt growth process. According to this method, it is known that the sample has a structure in which the 211 phase is finely dispersed, a crack is reduced, and a strong pinning force is obtained, as compared with the usual melting method.

Further, the PDMG method (platinum addition melting method)
Is a calcined powder of Y123 superconductor and platinum powder (0.
5% by weight) and then molded into pellets. After this molded body was put in a semi-molten state at 1100 ° C. for 1 hour, 1
The temperature is slowly lowered from 000 ° C to 940 ° C at 1 ° C / hour (h) to grow crystals. Then anneal. As described above, when a Y123-based superconductor is produced by the melting method in which platinum is added, the Y211 phase has a finely dispersed structure and a superconducting bulk body having a high critical current density Jc can be obtained.

[0008]

SUMMARY OF THE INVENTION The present inventor has found the following problems as a result of studying the above conventional technology.

In order to improve the critical current density in a low magnetic field, it is essential to miniaturize the second phase (normal conductor) dispersed in the superconductor. However, when the conventional method is used as it is for the RE123-based superconductor, there is a problem that the RE211 phase and the second phase of the RE411 become coarse. The reason for this will be examined below.

When the conventional MPMG method is applied to the YBCO system, the structure obtained after the melt quenching is YBCO.
In the case of a system, only Y ₂ O ₃ and an amorphous phase (including a BaCu ₂ O ₂ phase) are not included, and a phase such as Y123 or Y211 is not included.

On the other hand, in the case of a rare earth-based superconductor, the phase obtained after melt quenching is different from that of the Y-based RE123 and RE2.
The phase 11 (or RE422) can be combined with RE ₂ O ₃ and the amorphous phase. Since this RE211 (or RE422) has grown to several tens of microns, even if it is crushed and mixed after that, a coarse RE211 (or R
E422) remains as it is.

The reason why a second phase of 123 phase, 211 phase or 422 phase is formed after melting and quenching in a rare earth superconductor is as shown in FIG. 3 (RE123 system pseudo binary system phase diagram). This is because the liquid phase line indicated by a thick line in the state diagram of the superconductor has a steeper slope than that of the Y system. This indicates that the temperature change of the solubility of the rare earth element in the liquid phase is larger than that of the Y system. In the case of the Y system, since the temperature change of the solubility is small, the growth rate of the phase due to the temperature change is small, and the Y ₂ O ₃ + liquid phase remains as Y ₂ O ₃ + amorphous even after being rapidly cooled.

On the other hand, in the case of a rare earth element, for example, Nd, a large amount of Nd is supplied from the liquid phase since Nd ₂ O ₃ is supplied with a large amount of Nd because the solubility rapidly changes during the rapid cooling.
Since d422 also grows rapidly, N after melting and quenching
As a result, in addition to d ₂ O ₃ and the amorphous phase, the 123 phase and the second phase remain.

An object of the present invention is to provide a method for producing a bulk oxide superconductor having good superconducting properties.

Another object of the present invention is to provide a method for producing a bulk oxide superconductor which miniaturizes the second phase (normal conductor) dispersed in the superconductor.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0017]

The following is a brief description of an outline of a typical invention among the inventions disclosed by the present application.

(1) R by the semi-melt method (melt process method)
EBa ₂ Cu ₃ O _7-x (x: deficiency, RE: rare earth element)
The oxide superconductor for producing the system superconductor is a bulk production method, and the previously crystallized REBa ₂ Cu ₃ O is used.
A powder of _7-x type superconductor and a powder of RE ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ type second phase normal conductor with the smallest possible particle size were used as starting materials. It is a thing.

(2) In the method for producing a bulk oxide superconductor according to the above (1), RE ₂ BaCuO ₅ or RE _{4 is used.}
As a powder of a Ba ₂ Cu ₂ O ₅ -based second-phase normal conductor, RE ₂
BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ type second-phase normal conductor crystals are pulverized and then classified, or fine particles having a particle size of 3 μm or less obtained by a spray dry method, a coprecipitation method, a metal alkoxide, or the like. It uses a powder.

(3) In the method for producing a bulk oxide superconductor according to (1) above, REBa ₂ Cu ₃ O precrystallized.
Instead of the powder of _7-x type superconductor powder and the RE ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ type second phase normal conductor powder with the smallest possible particle size, pre-crystallized Transformed RE
Ba ₂ Cu ₃ O _7-x based superconductor powder coated with a RE ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ based second phase normal conductor having a thickness of 3 μm or less is used. is there.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

The method for producing the bulk oxide superconductor according to the present embodiment uses the pre-crystallized NdBa ₂ C as the starting material.
u ₃ O _7-x (Nd123) -based superconductor powder and Nd ₄
Ba ₂ Cu ₂ O ₅ (Nd422) or Nd ₂ BaCuO
_{A 5} (Nd211) -based second-phase normal conductor was pulverized and classified to obtain a fine powder having a particle size of 1 μm or less. The particle size of the powder of the second-phase normal conductor is ideally a powder that is as small as possible in view of the superconducting property, but a fine powder having a particle size of 1 μm or less is preferable from the viewpoint of labor and cost of production.

Nd123 crystal powder and Nd422
A fine powder having a crystal grain size of 1 μm or less is weighed and mixed so as to have a target composition, and is pressed into a diameter of 20 mm and a height of 7 mm to produce pellets. This molded body (pellet) is heated to 1080 ° C. in an atmosphere of 1% oxygen partial pressure in argon.
After melting for 30 minutes and quenching to 1030 ℃, 960 ℃
To -1 ° C./hour (-1 ° C./h) to obtain an Nd123-based bulk oxide superconductor. As a result, Nd123
The average particle size of the second phase of Nd422 dispersed therein is MPMG
Whereas the thickness produced by the method was 10 μm or more,
It became about 2 μm.

FIG. 1 is a scanning electron microscope (SEM) photograph of a cross section of the Nd123-based bulk oxide superconductor obtained by the MPMG method and the Nd123-based bulk oxide superconductor obtained by the method of the present embodiment. is there. In FIG. 1, (a)
Is a scanning electron microscope (SEM) photograph of the Nd123-based bulk oxide superconductor obtained by the MPMG method, and (b) is a cross-sectional scan of the Nd123-based bulk oxide superconductor obtained by the method of the present embodiment. Scanning electron microscope (SEM) photograph, the white part is the second phase of Nd422, and the black part is the Nd123 phase.

Further, Nd1 obtained by the method of the present embodiment
The 23-type bulk oxide superconductor has a critical current density at 0 Tesla (T) of 20000 A / cm ² to 5000.
It was improved to 0 A / cm ² . As a result, it is possible to put the superconducting magnet using the Nd123-based bulk oxide superconductor into practical use.

In the above embodiment, Nd ₄ Ba ₂ Cu _{2 is used.}
O ₅ (Nd422) or Nd ₂ BaCuO ₅ (Nd2
11) The second phase normal conductor of the system is crushed and classified to have a particle size of 1
A fine powder of less than μm was used, but the particle size was 3
Nd4 dispersed in Nd123 even when a fine powder having a size of less than or equal to 2 μm is used.
The average particle size of the second phase of No. 22 could be made smaller than that of the one prepared by the MPMG method.

Although the invention made by the present inventor has been specifically described based on the embodiments (examples), the present invention is not limited to the above-described embodiments (examples), and the gist thereof is not limited. It goes without saying that various changes can be made without departing from the scope.

[0028]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

Since a bulk oxide superconductor in which the average particle diameter of the second phase such as RE422 or RE211 dispersed in RE123 is made fine is obtained, a bulk oxide superconductor having good superconducting properties can be produced. . Further, it was possible to synthesize a RE123-based bulk oxide superconductor having a high critical current density.

[Brief description of drawings]

FIG. 1 is an Nd123-based bulk oxide superconductor obtained by MPMG method and Nd obtained by a method according to an embodiment of the present invention.
It is a scanning electron microscope (SEM) photograph of a cross section of a 123-based bulk oxide superconductor.

FIG. 2 is a diagram for explaining a QMG method and an MPMG method.

FIG. 3 is a pseudo-2 of RE123 (RE = Nd, Sm, Y) system.
It is an original phase diagram.

Front page continued (72) Inventor Hiroki Ogi 1-14-3 Shinonome, Koto-ku, Tokyo Inside the Institute for Superconductivity Engineering, International Superconductivity Research Center (72) Inventor Naomichi Sakai 1-14 Shinonome, Koto-ku, Tokyo No. 3 International Superconducting Industrial Technology Research Center, Superconducting Engineering Laboratory (72) Inventor Masato Murakami 1-14-3 Shinonome, Koto-ku, Tokyo International Superconducting Industrial Technology Center, Superconducting Engineering Laboratory

Claims (3)

[Claims] 1. A semi-melt method (melt process method: Melt pr
The method for producing a bulk oxide superconductor for producing a REBa ₂ Cu ₃ O _7-x (x is a deficiency amount, RE is a rare earth element) -based bulk superconductor according to the above
EBa ₂ Cu ₃ O _7-x based superconductor powder and RE ₂ BaC
uO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ type second-phase normal conductor powder having the smallest possible particle size used as a starting material. . 2. The method for producing a bulk oxide superconductor according to claim 1, wherein RE ₂ BaCuO ₅ or R is used.
As a powder of the E ₄ Ba ₂ Cu ₂ O ₅ system second-phase normal conductor, R
E ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ type second-phase normal conductor crystals pulverized and then classified, or obtained by spray-drying method, coprecipitation method, metal alkoxide, etc., particle size of 3 μm or less A method for producing a bulk oxide superconductor characterized by using the fine powder of. 3. The method for producing a bulk oxide superconductor according to claim 1, wherein REBa ₂ C precrystallized is used.
Instead of the powder of u ₃ O _7-x system superconductor and the powder of RE ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ system second phase normal conductor with the smallest possible particle size. , Pre-crystallized REBa ₂ Cu ₃ O _7-x based superconductor powder with a thickness of 3 μm
A method for producing a bulk oxide superconductor, characterized by using the following RE ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₅ -based second-phase normal conductor.