JPH0733434A - Production of re1ba2cu3o7-x type oxide superconductor - Google Patents

Abstract

PURPOSE:To increase critical current density by mixing a Ba compd. with a Cu compd., calcining this mixture, mixing the resulting calcined powder with an RE compd. and carrying out calcining, compacting, heating and slow cooling. CONSTITUTION:An RE compd. (RE is one or more kinds of elements selected among Y and rare earth elements), a Ba compd. and a Cu compd. are weighed so that the ratio of RE:Ba:Cu is contained in a region defined by (55:10:35), (40:40:20), (10:60:30) and (10:25:65). The Ba compd. is mixed with the Cu compd. and calcined at 800-930 deg.C. The resulting calcined powder is mixed with the RE compd. and press-compacted into a lump shape to form a compact of >=6mm thickness. This compact is half melted by heating to 1,060-1,200 deg.C and slowly cooled at 0.1-10 deg.C/hr rate to obtain the objective RE1Ba2Cu3O7-x type oxide superconductor having a structure contg. an RE2Ba1Cu1O5 phase of <=50mum diameter dispersed in an RE1Ba2Cu3O7-x phase.

Description

Detailed Description of the Invention

[0001]

The present invention relates to RE ₁ Ba ₂ which exhibits superconducting characteristics with a high critical current density even under a strong magnetic field.
The present invention relates to a method for producing a Cu ₃ O 7- _x oxide superconductor.

[0002]

_2. Description of the Related Art The general formula RE ₁ Ba ₂ Cu ₃ O _7-x (where RE is one element selected from the group consisting of Y and rare earth metal elements or a mixture of two or more elements). As a method for producing an oxide superconductor containing a substance represented by (4) as a main component, the following methods have been conventionally used.

(1) First, the so-called QMG method (Quench and Mel) disclosed in Japanese Patent Laid-Open No. 2-153803.
t Growth method). This is a mixture of RE ₂ O ₃ (RE: Y-containing rare earth element) and BaCu oxide, and a plate-shaped or linear molded body having a thickness of 5 mm or less
It is a method of heating to a high temperature of ℃ to 1350 ℃ to make a semi-molten state, and then gradually cooling at a rate of 200 ℃ / hr or less.

(2) Secondly, the so-called MPMG method (Melt Powder) disclosed in Japanese Patent Application Laid-Open No. 4-119998.
Melt Growth method). This is RE-Ba-Cu-O
BaCO ₃ and CuO powders among the raw material powders of the system are mixed, and the mixture is calcined at about 900 ° C.
The mixture is heated to a temperature range of 000 ° C to 1200 ° C to be melted, RE ₂ O ₃ or RE ₂ BaCuO ₅ powder is added to this melt, and this mixture is kept at the above temperature for a predetermined time, 1 at a cooling rate of 10 to 1000 ° C./hr
It is a method of cooling to 000 ° C., cooling at 950 ° C. at a cooling rate of 0.2 to 20 ° C./hr, and then cooling to room temperature at an arbitrary cooling rate.

(3) Third, there is a method proposed in Japanese Patent Laid-Open No. 4-231364.

In this method, a mixture of the compositions shown in (a) to (e) is semi-molten and then slowly cooled to obtain RE-B.
An a-Cu-O-based oxide superconductor (wherein RE means one element selected from the group consisting of Y and rare earth metal elements or a mixture of two or more elements) is prepared. is there.

(A) RE, Ba, Cu element molar ratio (R
E: Ba: Cu) is (50:20:30), (10:60:30),
Be in the area surrounded by (20:20:60).

(B) RE exists substantially as RE ₂ O ₃ .

(C) Ba exists substantially as a Ba oxide and / or a Ba-Cu composite oxide.

(D) Cu substantially exists as Cu oxide and / or Ba-Cu composite oxide.

(E) At least one element of Ba and Cu exists as BaCu ₂ O ₂ in an amount of 20% or more and BaCuO _{2 in an} amount of 20% or more, and 70% or more of the element is (BaCu ₂ O _2). Exists as O ₂ + BaCuO ₂ ).

[0012]

However, it has been found that the above-described conventional method has the following drawbacks.

Method (1) This method can produce an oxide superconducting bulk material having a relatively high critical current density, but it is a plate-shaped or linear material obtained by mixing RE ₂ O ₃ and BaCu oxide. The molded body of thickness 5
Since it is less than or equal to mm, when it is heated to a high temperature of 1000 ° C. to 1350 ° C. to be in a semi-molten state, the reaction with the substrate (Al ₂ O ₃ , MgO, Pt, ZrO) on which the sample is placed is violent. Element may diffuse as an impurity throughout the sample, and a large amount of liquid phase component of the sample may flow out to deteriorate the critical current density.

Method (2) This method can also produce a superconductor having a relatively high critical current density, but the mixture is heated to a temperature range of 100 ° C. to 1200 ° C. to be melted and solidified into a lump, Subsequent crushing and molding steps are required to substantially adjust the shape, which requires time and effort and makes mass production very difficult.

Method (3) This method also gives a superconductor having a relatively high critical current density, but it is substantially difficult to obtain single-phase BaCu ₂ O ₂ , and the composition is BaCu ₂ O. To produce a powder having many _two phases, it is necessary to perform a melting process or to produce in an atmosphere with a very strong reducing power, which is very expensive. 2 more
When 0% or more of BaCu ₂ O ₂ phase is present, the reactivity is excessively increased, and the shape cannot be maintained when the semi-melting step is performed using a large superconductor.

The present invention was made in the context of the above background and is a large RE ₁ having a higher critical current density.
Ba ₂ Cu ₃ O _7-x based oxide superconductor may more easily reproducible and can be produced _{RE 1 Ba 2 Cu 3 O 7} -x
An object of the present invention is to provide a method for producing a system oxide superconductor.

[0017]

[MEANS FOR SOLVING THE PROBLEMS] In order to solve the above-mentioned problems, a method for producing an RE ₁ Ba ₂ Cu ₃ O _7-x oxide superconductor according to the present invention is as follows: (Structure 1) General formula RE ₁ Ba ₂ Cu ₃ O _7-x (However, RE is one or a mixture of two or more elements selected from the group consisting of Y and rare earth metal elements.)
RE ₁ Ba ₂ Cu ₃ O containing the substance represented by
_A method for producing a _7-x- based oxide superconductor, wherein (RE: Ba: Cu) is (55: 10: 3) in a molar ratio of RE, Ba and Cu compounds.
5), (40:40:20), (10:60:30), (10: 25: 6)
5) A weighing step of weighing so as to be included in a region surrounded by 5), a Ba compound and a Cu compound among the weighed compounds are taken out and mixed, and calcined at 800 to 930 ° C. to form BaCuO ₂ and CuO. Calcining step for obtaining a calcined powder of, and mixing the calcined powder and the RE compound with a thickness of 6 m
The molding step of press-molding into a lump of m or more to obtain a molded body, the heating step of heating the molded body to a temperature of 1060 to 1200 ° C. to bring it into a semi-molten state, and the molded body in the semi-molten state of 0. And a gradual cooling step of gradual cooling at a rate of 1 ° C. to 10 ° C./hr, with a diameter of 5 in the RE ₁ Ba ₂ Cu ₃ O _7-x phase.
A structure characterized by obtaining a RE ₁ Ba ₂ Cu ₃ O _7-x oxide superconductor having a structure in which a RE ₂ Ba ₁ Cu ₁ O ₅ phase of 0 micron or less is dispersed. (Structure 2) In the method for manufacturing an RE ₁ Ba ₂ Cu ₃ O _7-x oxide superconductor according to Structure 1, the calcination step is Ba
BaCuO ₂ and C in which a mixed powder of a compound and a Cu compound is pre-baked at 930 to 960 ° C. on a Pt, MgO or ZrO substrate so that a carbon content is 1.0 wt% or less.
The constitution is characterized in that a calcined powder of uO is obtained.

[0018]

According to the above-mentioned structure 1, RE ₂ Ba ₁ Cu ₁ O
_{5 RE 1 Ba 2 Cu 3 O 7} -x phase consisting finely dispersed crystals in (hereinafter, referred to as the 123 phase) R ₁ Ba ₂ Cu
It has become possible to more easily and reproducibly manufacture a ₃ O _7-x- based large-sized oxide superconductor having a higher critical current density.

Here, RE, Ba, Cu in the starting raw material powder
The ratio of elements needs to have a value within the range specified in Configuration 1 for the following reason.

That is, (RE: Ba: Cu) is (55:
If the RE is larger or the Ba is smaller than 10:35), the 123 phase does not grow. (40:40:20)
If RE is higher or Ba is higher, 1
The growth of the 23rd phase does not progress. Ba from (10:60:30)
If the amount is large, the precipitation of impurities is large and the characteristics are deteriorated. When the amount of Cu is more than (10:25:65), the liquid phase component increases and the shape cannot be maintained when melted. For this reason, (R: Ba: Cu) is (55:10:35), (40:
40:20), (10:60:30), and (10:25:65).

Further, when the calcination temperature of the Ba compound and the Cu compound is 800 ° C. or lower, unreacted substances remain. In this case, it is preferable to set the temperature to 930 ° C. or higher as in the constitution 2, because the content of the residual carbon that significantly deteriorates the superconducting property is reduced, and the firing time can be shortened. At that time, Pt, which has relatively little reaction as a substrate for firing,
When MgO or ZrO is used, the mixing of impurities due to the reaction with the substrate is reduced, and the characteristics are further improved. 9
If the temperature is set to 30 ° C. or lower, Al ₂ O ₃ can be used as the substrate, which has the advantage of cost reduction.

However, if the temperature is higher than 960 ° C., the BaCu compound melts and solidifies into a lump and sticks to the substrate, which substantially deteriorates the recovery rate. In addition, a crushing process is required after that, which is expensive.

Further, the thickness of the molded body is set to 6 mm or more because the substrate (Al) on which the sample is placed in the semi-molten state is used.
_This is because a large amount of the upper end portion that does not deteriorate due to the reaction with ₂ O ₃ , MgO, Pt, ZrO, etc. is prepared.

The semi-melting temperature is 1060 to 1200 ° C.
The reason is that the melting point is insufficient at 1060 ° C. to form a polycrystalline body, and at 1200 ° C. or higher, R ₂ Ba ₁ Cu is formed.
_{This is because the 1} O ₅ phase is coarsened and the characteristics are significantly deteriorated.

Further, the slow cooling rate is 0.1 to 10 ° C./hr.
The reason is that if the temperature is 0.1 ° C./hr or less, crystallization takes a very long time and the cost increases, and if the temperature is 10 ° C./hr or more, impurities are taken into the crystal.

[0026]

EXAMPLES Example 1 Y: B was used as a raw material powder of Y ₂ O ₃ , BaCO ₃ , and CuO.
a: Cu = 18:24:34 and then BaCO
₃ , CuO only 3 at 850 ℃ on alumina substrate
It was calcined for 0 hour to obtain a calcined powder of BaCuO ₂ and CuO (molar ratio of BaCuO ₂ : CuO = 24: 10). When the carbon content of this calcined powder was measured, it was 1.05.
% By weight. The calcined powder and Y ₂ O ₃ are mixed and press-molded into a disk shape having an outer diameter of 75 mm and a thickness of 30 mm,
It was placed on an alumina substrate, brought into a semi-molten state at 1150 ° C., and then gradually cooled to room temperature at a rate of 1 ° C./hr.

The obtained sample maintained its shape and had almost no cracks. The amount of residual carbon after melting is 0.
It was 07% by weight.

The obtained sample was divided into 5 areas A, B, C, D, and E from the upper end portion downwardly at intervals of 6 mm, and in each area, a temperature of 77 [K], the outside The results of measuring the critical current density (Jc) in the magnetic field of 1 [T] and the results of analyzing the diffused Al in each region are as follows.

ABCD E Jc (× 10 ⁴ A / cm) 1.0 1.0 0.9 0.8 0.3 Diffused Al (wt%) 0.01 or less 0.01 or less 0.02 0.05 0.13 As is clear from the above results, the lower 6 mm (region E) is Although the alumina of the substrate was diffused and the characteristics were largely deteriorated, the upper part (regions A, B, C, D) was almost uniform and had a sufficiently high critical current density.

Example 2 Each raw material powder of Sm ₂ O ₃ , BaO ₂ and CuO was mixed with Sm: B.
a: Cu = 18:24:34, and then weighed BaO
₂ and CuO only on an alumina substrate at 850 ° C for 3
It was calcined for 0 hour to obtain a calcined powder of BaCuO ₂ and CuO (molar ratio of BaCuO ₂ : CuO = 24: 10). When the carbon content of this calcined powder was measured, it was 1.20.
% By weight. The calcined powder and Sm ₂ O ₃ are mixed and press-molded into a disk shape having an outer diameter of 75 mm and a thickness of 30 mm, placed on an alumina substrate and put in a semi-molten state at 1150 ° C., and then at a rate of 1 ° C./hr. It was gradually cooled to room temperature.

The obtained sample had no cracks and the carbon content after melting was 0.09% by weight.

The obtained sample was divided into 5 areas A, B, C, D, and E from the upper end portion downwardly at intervals of 6 mm, and in each area, the temperature was 77 [K] and the outside The results of measuring the critical current density (Jc) in the magnetic field of 1 [T] and the results of analyzing the diffused Al in each region are as follows.

ABCD E Jc (× 10 ⁴ A / cm) 0.9 1.0 0.9 0.6 0.3 Diffused Al (wt%) 0.01 or less 0.01 or less 0.02 0.02 0.12 As is clear from the above results, the lower 6 mm (region E) is Although the alumina of the substrate was diffused and the characteristics were largely deteriorated, the upper part (regions A, B, C, D) was almost uniform and had a sufficiently high critical current density.

Example 3 Each raw material powder of Y ₂ O ₃ , BaCO ₃ , and CuO was mixed with Y: B.
a: Cu = 18: 24: 34, then weighed, and then BaC
Only O ₃ and CuO were baked on a Pt substrate at 950 ° C. for 2 hours to obtain a calcined powder of BaCuO ₂ and CuO (in molar ratio,
BaCuO ₂ : CuO = 24: 10). When the carbon content of this calcined powder was measured, it was 0.40% by weight. The calcined powder and Y ₂ O ₃ are mixed and press-molded into a disk shape having an outer diameter of 75 mm and a thickness of 30 mm, placed on an alumina substrate and put in a semi-molten state at 1150 ° C.
It was gradually cooled to room temperature at a rate of r.

The obtained sample had no cracks, and the carbon content after melting was very low at 0.02% by weight.

The obtained sample was divided into 5 areas A, B, C, D, and E from the upper end portion downwardly at intervals of 6 mm, and in each area, the temperature was 77 [K], and the outside The results of measuring the critical current density (Jc) in the magnetic field of 1 [T] and the results of analyzing the diffused Al in each region are as follows.

ABCD E Jc (× 10 ⁴ A / cm) 1.4 1.5 1.3 1.2 0.8 Diffused Al (wt%) 0.01 or less 0.01 or less 0.01 0.04 0.11 As is clear from the above results, the lower 6 mm (region E) is Alumina of the substrate diffuses and the characteristics are slightly degraded, but
The upper part (regions A, B, C, D) was almost uniform and had a higher critical current density as compared with Examples 1-2.

Example 4 Each raw material powder of Y ₂ O ₃ , BaCO ₃ and CuO was mixed with Y: B.
a: Cu = 18: 24: 34, then weighed, and then BaC
Only O ₃ and CuO were calcined on a ZrO substrate at 950 ° C. for 2 hours to obtain a calcined powder of BaCuO ₂ and CuO (in molar ratio, BaCuO ₂ : CuO = 24: 10). When the carbon content of this calcined powder was measured, it was 0.40% by weight. The calcined powder and Y ₂ O ₃ are mixed to give an outer diameter of 75 m.
m, press-molded into a disk with a thickness of 30 mm, placed on an alumina substrate, and semi-molten at 1150 ° C., then 1 ° C.
It was gradually cooled to room temperature at a rate of / hr.

The obtained sample had no cracks, and the carbon content after melting was very low at 0.02% by weight.

The obtained sample was divided into 5 areas A, B, C, D, and E from the upper end portion downwardly at intervals of 6 mm, and in each area, a temperature of 77 [K], the outside The results of measuring the critical current density (Jc) in the magnetic field of 1 [T] and the results of analyzing the diffused Al in each region are as follows.

ABCD E Jc (× 10 ⁴ A / cm) 1.3 1.3 1.2 1.0 0.6 Diffused Al (wt%) 0.01 or less 0.01 or less 0.02 0.05 0.15 As is clear from the above results, the lower 6 mm (region E) is Alumina of the substrate diffuses and the characteristics are slightly degraded, but
The upper part (regions A, B, C, D) was almost uniform and had a higher critical current density as compared with Examples 1-2.

Comparative Example 1 Y ₂ O ₃ , BaCO ₃ , and CuO raw material powders were mixed with Y: B.
a: Cu = 18:24:34 and then BaCO
₃ 、 Place CuO only on the alumina substrate at 850 ℃ for 3
It was calcined for 0 hour to obtain a calcined powder of BaCuO ₂ and CuO.
When the carbon content of this calcined powder was measured, it was 1.0
It was 5% by weight. The calcined powder and Y ₂ O ₃ are mixed and press-formed into a disk shape having an outer diameter of 75 mm and a thickness of 5 mm,
It was placed on an alumina substrate, brought into a semi-molten state at 1150 ° C., and then gradually cooled to room temperature at a rate of 1 ° C./hr.

The obtained pellets had no cracks, but the carbon content after melting was as high as 0.05% by weight, and
The diffusion amount of Jc and aluminum in the thickness direction of the sample was as follows, which was extremely insufficient as compared with the examples.

Area from top to bottom 1 mm from top to bottom 1 to 5 mm area Jc (× 10 ⁴ A / cm) 1.1 0.4 Diffused Al (wt%) 0.03 0.15 Comparative Example 2 Y ₂ O ₃ , BaCO ₃ , CuO raw material powder Y: B
a: Cu = 18:24:34 and then BaCO
₃ , CuO alone was baked in nitrogen at 900 ° C. for 30 hours, and about 20% of BaCu ₂ O ₂ was present.
A calcined powder of O ₂ and CuO was obtained. When the carbon content of this calcined powder was measured, it was 0.50% by weight.
The calcined powder and Y ₂ O ₃ are mixed to give an outer diameter of 75 mm and a thickness of 3
It was press-formed into a disk shape of 0 mm, placed on an alumina substrate, brought into a semi-molten state at 1150 ° C., and then gradually cooled to room temperature at a rate of 1 ° C./hr.

The pellets obtained had a deformed shape and the liquid phase flowed out violently. In addition, the obtained sample was divided into 6 mm intervals from the upper end downward, and A, B, C, D, and
It is divided into 5 areas of E, and the temperature is 77 in each area.
[K], critical current density in external magnetic field 1 [T] (J
c) measurement result and diffused Al in each region
The results of the analysis were as follows.

A B C D E Jc (× 10 ⁴ A / cm) 0.9 0.9 0.8 0.4 0.2 Diffused Al (wt%) 0.03 0.05 0.04 0.11 0.18 Although a near sea current density was obtained, the characteristics began to deteriorate from the middle part to the lower part, and the shape collapsed remarkably, so there were very few parts that could be used as superconductors compared to the examples. It was poor in practicality.

[0047]

As described above in detail, the present invention uses the so-called melting method, which is one of the methods for producing oxide superconductors, and measures the RE compound, the Ba compound and the Cu compound in a predetermined ratio. Among them, the Ba compound and the Cu compound are taken out, mixed, and calcined at 800 to 930 ° C. to form BaC.
A calcined powder of uO ₂ and CuO was obtained, and the calcined powder was mixed with an RE compound and press-molded to a thickness of 6 mm or more.
After being heated to a temperature of 060 to 1200 ° C. to be in a semi-molten state and then gradually cooled at a rate of 0.1 ° C. to 10 ° C./hr, a diameter of 50 in the RE ₁ Ba ₂ Cu ₃ O _7-x phase is obtained. RE ₁ B having a structure in which sub-micron RE ₂ Ba ₁ Cu ₁ O ₅ phases are dispersed and having a large and higher critical current density
It is possible to obtain an a ₂ Cu ₃ O _7-x oxide superconductor.

Claims (2)

[Claims] 1. A general formula RE ₁ Ba ₂ Cu ₃ O _7-x (where RE is one or a mixture of two or more elements selected from the group consisting of Y and rare earth metal elements).
RE ₁ Ba ₂ Cu ₃ O containing the substance represented by
_A method for producing a _7-x- based oxide superconductor, comprising: adding a RE compound, a Ba compound and a Cu compound to RE, B
In the molar ratio of a and Cu, (RE: Ba: Cu) is (55:10:35), (40:40:20), (10:60:30),
(10:25:65) Weighing step for weighing so as to be included in a region surrounded by (10:25:65), Ba compound and Cu compound among the weighed compounds are taken out and mixed, and calcined at 800 to 930 ° C. B
a calcination step of obtaining a calcinated powder of aCuO ₂ and CuO, a molding step of mixing the calcination powder and the RE compound and press-molding into a lump having a thickness of 6 mm or more to obtain a molded body, Is heated to a temperature of 1060 to 1200 ° C. to bring it into a semi-molten state, and a slow cooling step of gradually cooling the semi-molten compact at a rate of 0.1 ° C. to 10 ° C./hr. , RE ₁ Ba ₂ Cu ₃ O _7-x phase having a structure in which a RE ₂ Ba ₁ Cu ₁ O ₅ phase having a diameter of 50 μm or less is dispersed
A method for producing a RE ₁ Ba ₂ Cu ₃ O _7-x based oxide superconductor characterized by obtaining an E ₁ Ba ₂ Cu ₃ O _7-x based oxide superconductor. 2. The RE ₁ Ba ₂ Cu ₃ O according to claim 1.
_{In the} method for manufacturing a _7-x oxide superconductor, in the calcination step, a mixed powder of a Ba compound and a Cu compound is mixed with 930 to 96 on a Pt, MgO or ZrO substrate.
RE ₁ Ba ₂ Cu ₃ O _7-x- based oxidation characterized by obtaining a calcined powder of BaCuO ₂ and CuO having a carbon content of 1.0 wt% or less by calcination at 0 ° C. Method for manufacturing superconductors.