JP3217727B2 - Manufacturing method of oxide superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting member, and in particular, has excellent electrical characteristics, magnetic characteristics, mechanical strength, and environmental resistance used for current leads, magnetic bearings, magnetic shields, bulk magnets, and the like. And a method for manufacturing an oxide superconductor.

[0002]

2. Description of the Related Art A raw material mixture containing an RE compound (RE is one or more rare earth metal elements), a Ba compound and a Cu compound is heated and melted to a temperature not lower than the melting point of the raw material mixture, and then a slow cooling step is performed. To grow the crystal, and RE-B
As a method for producing an a-Cu-O-based oxide superconductor, for example, a method described in JP-A-4-119968 is known.

[0003] The method described in this publication discloses an RE compound, B
After a compound and a Cu compound are mixed at a predetermined ratio and melt-quenched, the obtained solidified product is pulverized again, molded and melted again, and then subjected to a slow cooling process to crystallize to obtain a high criticality. This is a method for producing a RE-Ba-Cu-O-based oxide superconductor having a current density.

[0004]

However, in the above-mentioned conventional method, there was a problem that a phenomenon that cracks occurred in the molded body in the slow cooling step occurred more or less.

According to the study of the present inventors, in the above-mentioned conventional method, a raw material for a molded body to be crystallized by performing a slow cooling step after melting is manufactured by performing a melting and quenching step. Reduction occurs and the amount of oxygen in the raw material becomes extremely low. Therefore, it was found that the absorption of oxygen occurred in the subsequent melting and slow cooling step.

SUMMARY OF THE INVENTION The present invention has been made under the above-mentioned background, and an object of the present invention is to provide an oxide superconductor having a large oriented superconductor crystal having high electric and magnetic characteristics with good reproducibility. It is an object of the present invention to provide a manufacturing method and an oxide superconductor having such characteristics.

[0007]

Means for Solving the Problems In order to solve the above problems, the invention of claim 1 is directed to an RE compound (RE is a compound containing Y
Or two or more rare earth metal elements) and a Ba compound
Mixing a raw material mixture containing a Cu compound,
After the mixed raw material mixture is melted, it is rapidly cooled and solidified.
Degree and, pulverized powder by pulverizing a raw material mixture obtained by the rapid solidification
And firing this pulverized powder at 880 to 940 ° C.
And firing the crushed powder to form a compact.
That the step to melt the molded body, Tanezuke the molded body melted
And the molded body that has been melted and seeded,
Cooling and crystallizing, and crystallizing the molded body
Oxygen annealing step .

[0008] The invention according to claim 2 is characterized in that REBa ₂ Cu _30
In an oxide superconductor in which a RE ₂ BaCuO ₅ phase is finely dispersed in a _7-x phase (RE is one or more rare earth metal elements containing Y), the oxygen content is 15 to 20 wt.
% Of the oxide superconductor.

According to a third aspect of the present invention, there is provided an oxide superconductor characterized in that a magnetic flux density that can be captured over a continuous area of 30 cm ² or more in an arbitrary region of the surface is 0.1 T or more.

[0010] The invention of claim 4 is characterized in that REBa ₂ Cu _30
In an oxide superconductor in which a RE ₂ BaCuO ₅ phase is finely dispersed in a _7-x phase (RE is one or more rare earth metal elements containing Y), the oxygen content is 15 to 20 wt.
% And 30 cm ² in any area of the surface
The magnetic flux density that can be captured over the above sequence is 0.1T
An oxide superconductor characterized by the above.

A raw material mixture containing an RE compound (RE is one or more rare earth metal elements containing Y), a Ba compound and a Cu compound is subjected to a firing step at least in a temperature range higher than the melting point of the raw material mixture. In the method for producing an oxide superconductor in which a RE-Ba-Cu-O-based oxide superconductor is produced by performing a treatment including the above, the oxygen content in the raw material mixture before the firing step is set to 15 to 20 wt%. Accordingly, a large oxide superconductor having excellent magnetic properties can be manufactured with good reproducibility without causing cracks in the compact during the annealing step. In particular, in this method, the superconductor phase is REB
When an oxide superconductor that is a ₂ Cu ₃ O _7-x phase (123 phase) is manufactured, about 0.1 to 30 μm of R
An E ₂ BaCuO ₅ phase (211 phase) is finely dispersed, and a material having a high critical current density can be obtained.

Here, the reason why the oxygen content in the raw material mixture before the firing step is set to 15 to 20% by weight is that when the content is 15% or less, the absorption of oxygen occurs sharply in the melting and slow cooling step, so that the molded article is cracked. When the content is 20 wt% or more, the release of oxygen occurs sharply in the melting and slow cooling step, so that the molded product is also likely to crack.

[0013] REBa ₂ Cu ₃ 0 _7-x phase (RE is one or more rare earth metal elements including Y) RE ₂ in
In the oxide superconductor in which the BaCuO ₅ phase is finely dispersed, when the oxygen content is adjusted to 15 to 20 wt%, the magnetic flux density that can be captured over a continuous area of 30 cm ² or more in an arbitrary region of the surface is 0.1 T or more. A large oxide superconductor excellent in certain magnetic properties can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing an oxide superconductor according to an embodiment of the present invention will be described with reference to examples, and embodiments of the oxide superconductor according to the present invention will be described.

(Example 1) Y ₂ O ₃ , BaCO ₃ , Cu
Each raw material powder of O was weighed so that Y: Ba: Cu = 18: 24: 34, melted in a Pt crucible at 1400 ° C. for 30 minutes, poured into a copper plate and rapidly cooled to solidify.

The amount of oxygen in the coagulated body was measured by a combination of a high-temperature extraction method using an impulse furnace and an infrared absorption method (the same measurement method was used hereinafter) to be 14.5% by weight.

Next, this coagulated material was pulverized to an average particle size of 2 μm by a pot mill, and calcined at 900 ° C. for 10 hours to adjust the amount of oxygen. The amount of oxygen after firing is 15.
It was 6 wt%.

Next, this was press-molded into a disk having an outer diameter of 83 mm and a thickness of 25 mm to produce a molded body.

Next, the molded body is placed on an alumina substrate to be in a semi-molten state at 1130 ° C. in the atmosphere, and then a temperature gradient of 5 ° C./cm is applied vertically so that the upper part of the molded body is on the low temperature side. Te was cooled at 10 ° C. / min up to 1000 ° C., as previously prepared in advance was _{Y (Ba 1-y Sr y} ) 2 Cu 3 0 7-x based growth direction seed crystals of is parallel to the c-axis It is brought into contact with the upper part of the molded body.

Next, crystallization was performed by gradually cooling to 850 ° C. at a rate of 1 ° C./hr and then lowering the temperature to room temperature at 10 ° C./hr.

The crystallized molded body is placed in a furnace capable of gas replacement. First, 0.1To with a rotary pump
After exhausting the inside of the furnace to rr, an oxygen gas is introduced to make an atmospheric oxygen atmosphere having an oxygen partial pressure of 95% or more. Thereafter, while flowing oxygen gas into the furnace at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 600 ° C. in 10 hours.
Slowly cool from 0 ° C to 300 ° C over 200 hours,
The temperature was lowered from ° C. to room temperature in 10 hours.

In the obtained material, the entire material was oriented along the c-axis reflecting the seed crystal, and a substantially single-crystal material with few cracks was obtained. The amount of oxygen in the material is 16.1 wt%
Met. Outer diameter is 65mm and thickness is 22mm due to shrinkage
Had become.

The critical temperature (Tc) of the obtained disc-shaped material was 90 K, the critical current density was 77 K, and 3.2 × 10 ⁴ A / cm ² under an external magnetic field of 0 T.

The disk-shaped material obtained from room temperature to a temperature of 77 K was cooled while applying an external magnetic field of 0.45 T, and then the magnetic field was removed to measure the amount of magnetic flux held by the material. The measurement was performed by measuring the magnetic flux density distribution in the vertical direction on the material surface using a Hall element.

FIG. 1 is a plan view of the retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of the first embodiment. FIG. 2 is a retained magnetic flux density of the oxide superconductor manufactured by the manufacturing method of the first embodiment. It is a three-dimensional diagram of a distribution.

The oxide superconductor manufactured by the manufacturing method of Example 1 has cracks suppressed, exhibits a uniform convex magnetic flux density distribution, and has a magnetic flux density that can be maintained over a surface area of approximately 33 cm ^{2 of the} material of 0.1 T or more. Met.

The oxide superconductor obtained in this manner can be used in a system such as a flywheel or a magnetic transfer device utilizing the magnetic repulsion between the permanent magnet and the oxide superconductor. That is, when a superconductor is used in these devices, a magnetic field of about 0.1 to 0.2 T is applied to the surface of the superconductor, but if the magnetic flux density that the superconductor can hold is 0.1 T or more, This is because a sufficient magnetic repulsion can be obtained. Further, since the magnetic flux density that can be held over an area of 30 cm ² or more is 0.1 T or more, it can be used for a practical magnet core, a rotor of a motor, and the like.

Example 2 Y ₂ O ₃ , BaCO ₃ , Cu
After weighing each raw material powder of O so that Y: Ba: Cu = 18: 24: 34, only BaCO ₃ and CuO are fired at 880 ° C. for 30 hours in the air to obtain BaCuO ₂ and CuO.
(A molar ratio of BaCuO ₂ : CuO = 2) was obtained.
4:10).

Next, this calcined powder was weighed in advance using a hot mill to obtain Y _{2 having} an average particle size of about 1 μm.
Adding a 0 ₃ and 0.5 wt% of Pt and mix. At this time, the amount of oxygen in the raw material was 20.1 wt%. further,
By firing this mixed powder at 920 ° C. for 10 hours, Y
The _{2 0 3 + BaCuO 2 + CuO} → 123 phase Tasu211 phase reaction moderately advanced the amount of oxygen was adjusted to 17.1wt%.

Next, this was added to an outer diameter of 115 mm and a thickness of 25 mm.
Was pressed into a disk shape to produce a molded body. After placing the compact on an alumina substrate to make it in a semi-molten state at 1130 ° C. in the atmosphere, a temperature gradient of 5 ° C./cm is applied up and down so that the upper part of the compact is on the low temperature side, and 1 °
The temperature was lowered at 0 ° C./min, and Y (Ba
_{1-y Sr y) 2 Cu} 3 0 7-x, the direction of growth of seed crystals of the system is brought into contact with the upper portion of the molded body so as to be parallel to the c axis.

Next, crystallization was performed by gradually cooling to 850 ° C. at a rate of 1 ° C./hr, and then cooling to room temperature at 10 ° C./hr.

The crystallized molded body is placed in a furnace capable of gas replacement. First, 0.1To with a rotary pump
After exhausting the inside of the furnace to rr, an oxygen gas is introduced to make an atmospheric oxygen atmosphere having an oxygen partial pressure of 95% or more. Thereafter, while flowing oxygen gas into the furnace at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 600 ° C. in 10 hours.
Slowly cool from 0 ° C to 300 ° C over 200 hours,
Let the temperature drop from ℃ to room temperature in 10 hours.

In the obtained material, the entire material was oriented along the c-axis reflecting the seed crystal, and a substantially single-crystal material with few cracks was obtained. The amount of oxygen in the material is 17.3 wt%
Met. Outer diameter is 100mm and thickness is 22m due to shrinkage
m.

The critical temperature (Tc) of the obtained disk-shaped material was 90 K, and the critical current density was 3.5 × 10 ⁴ A / cm ² under a temperature of 77 K and an external magnetic field of 0 T.

The disk-shaped material obtained from room temperature to a temperature of 77 K was cooled while applying an external magnetic field of 0.45 T, and then the magnetic field was removed to measure the amount of magnetic flux held by the material. The measurement was performed by measuring the magnetic east density distribution in the vertical direction of the material surface using a Hall element.

FIG. 3 is a plan view of the retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of the second embodiment, and FIG. 4 is a retained magnetic flux density of the oxide superconductor manufactured by the manufacturing method of the second embodiment. It is a three-dimensional diagram of a distribution.

The oxide superconductor produced by the production method of Example 2 has cracks suppressed, exhibits a uniform convex magnetic flux density distribution, and has a magnetic flux density that can be maintained over a surface area of approximately 78 cm ^{2 of the} material of 0.1 T or more. Met.

Example 3 Sm ₂ O ₃ , BaCO ₃ , C
Each raw material powder of uO was prepared as Sm: Ba: Cu = 20: 25: 3.
After weighing to 5 and mixing, in a Pt whirlpool, add 14
The mixture was melted at 00 ° C. for 30 minutes, poured into a copper die, rapidly cooled, and solidified.

Ag powder was added to the coagulated material in an amount of 10 wt%, and the mixture was pulverized by a pot mill to an average particle size of 2 μm and mixed. At this time, the amount of oxygen in the raw material was 14.2% by weight. Further, this mixed powder was baked at 900 ° C. for 10 hours to adjust the oxygen content to 16.8 wt%. next,
This was breath-formed into a disk shape having an outer diameter of 83 mm and a thickness of 25 mm to produce a molded body.

After placing the compact on an alumina substrate to make it in a semi-molten state at 1150 ° C. in the air, a temperature gradient of 5 ° C./cm was applied up and down so that the upper part of the compact was on the low temperature side, and the temperature was 1018 ° C. The temperature was lowered at a rate of 10 ° C./min until the seed crystal of Nd _{1 + y} Ba _2-y Cu ₃ O _7-x prepared in advance was placed on top of the compact so that the growth direction was parallel to the c-axis. Contacted.

Next, crystallization was performed by gradually cooling to 850 ° C. at a rate of 1 ° C./hr and then lowering the temperature to room temperature at 10 ° C./hr.

The crystallized molded body is placed in a furnace capable of gas replacement. First, use a rotary pump for 0.1 To
After exhausting the inside of the furnace to rr, an oxygen gas is introduced to make an atmospheric oxygen atmosphere having an oxygen partial pressure of 95% or more. Thereafter, while flowing oxygen gas into the furnace at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 600 ° C. in 10 hours.
Slowly cool from 0 ° C to 300 ° C over 200 hours,
Let the temperature drop from ℃ to room temperature in 10 hours.

In the obtained material, the entire material was oriented along the c-axis reflecting the seed crystal, and a substantially single-crystal material with few cracks was obtained. The amount of oxygen in the material is 17.5 wt%
Met. Outer diameter is 65mm and thickness is 22mm due to shrinkage
It was.

The critical temperature (T
c) is 92K, critical current density is temperature 77K, external magnetic field is 0
Under T, it was 3.1 × 10 ⁴ A / cm ² .

The disk-shaped material obtained from room temperature to a temperature of 77 K was cooled while applying an external magnetic field of 0.45 T, and then the magnetic field was removed to measure the amount of magnetic flux held by the material. The measurement was performed by measuring the magnetic flux density distribution in the vertical direction on the material surface using a Hall element.

FIG. 5 is a plan view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of the third embodiment, and FIG. 6 is a retained magnetic flux density of the oxide superconductor manufactured by the manufacturing method of the third embodiment. It is a three-dimensional diagram of a distribution.

The oxide superconductor manufactured by the manufacturing method of Example 3 has cracks suppressed, exhibits a uniform convex magnetic flux density distribution, and has a magnetic flux density that can be maintained over a surface area of approximately 33 cm ^{2 of the} material of 0.1 T or more. Met.

Comparative Example 1 Y ₂ O ₃ , BaCO ₃ , Cu
Each raw material powder of O was weighed so that Y: Ba: Cu = 18: 24: 34, melted in a Pt crucible at 1400 ° C. for 30 minutes, poured into a copper plate and rapidly cooled to solidify. When the oxygen content of this coagulated body was measured, it was 14.0 wt%.

The coagulated material was subjected to an average particle size of 2 using a pot mill.
After grinding to μm, the outer diameter is 83 mm without oxygen adjustment treatment.
A molded body was produced by breath molding into a disk having a thickness of 25 mm.

After placing this compact on an alumina substrate and making it in a semi-molten state at 1130 ° C. in the air, a temperature gradient of 5 ° C./cm is applied up and down so that the upper part of the compact is on the low temperature side and 1000 ° C. until the temperature was decreased at l0 ℃ / min, Y (Ba 1-y Sr y) 2 Cu 3 0 7-x based growth direction seed crystals of the molded body so as to be parallel to the c-axis that has been previously prepared Contact top.

Next, the solution was gradually cooled to 850 ° C. at a rate of 1 ° C./hr, and then cooled to room temperature at 10 ° C./hr for crystallization.

The crystallized molded body is placed in a furnace capable of gas replacement. First, use a rotary pump. lTo
After exhausting the inside of the furnace to rr, an oxygen gas is introduced to make an atmospheric oxygen atmosphere having an oxygen partial pressure of 95% or more. Thereafter, while flowing oxygen gas into the furnace at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 600 ° C. in 10 hours.
Slowly cool from 0 ° C to 300 ° C over 200 hours,
Let the temperature drop from ℃ to room temperature in 10 hours.

In the obtained material, the entire material was oriented along the c-axis reflecting the seed crystal, but a long microcrack was generated from the end of the material toward the center.

The critical temperature (T
c) is 90K, critical current density is 77K, external magnetic field is 0.
Under T, it was 3.2 × 10 ⁴ A / cm ² .

The disk-shaped material obtained from room temperature to a temperature of 77 K was cooled while applying an external magnetic field of 0.45 T, and then the magnetic field was removed to measure the amount of magnetic flux held in the material. The measurement was performed by measuring the magnetic flux density distribution in the vertical direction on the material surface using a Hall element.

FIG. 7 is a plan view of the holding magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Comparative Example 1, and FIG. 8 is a holding magnetic flux density of the oxide superconductor manufactured by the manufacturing method of Comparative Example 1. It is a three-dimensional diagram of a distribution.

In the oxide superconductor manufactured by the manufacturing method of Comparative Example 1, magnetic flux leaks from a portion where a defect such as a crack is present, and shows an uneven magnetic flux density distribution. The area of 1 T or more was about 30 cm ² or less.

In the above-described embodiment, Y and Sm are shown as examples of RE, however, it has been confirmed that similar effects can be obtained with other rare metal elements.

Furthermore, in Example 2, Pt was used, but it has been confirmed that Pd, Ru, Rh, Ir, 0s and Re show the same effect.

In the raw material firing step for adjusting the amount of oxygen, firing was performed at 900 ° C. in Example 1, 920 ° C. in Example 2, and 900 ° C. in Example 3, respectively, for 10 hours. It has been confirmed that the oxygen amount can be set to approximately 14 to 18 wt% when the temperature is in the range of ９940 ° C. and the time is 1 hour or more.

[0061]

As described above in detail, the method for producing an oxide superconductor according to the present invention comprises subjecting a raw material mixture to a treatment including a firing step at least in a temperature range higher than the melting point of the raw material mixture. In producing a -Ba-Cu-O-based oxide superconductor, the oxygen content in the raw material mixture before the firing step is adjusted to 15 to 20 wt%,
Further, the oxide superconductor of the present invention is made of REBa ₂ Cu _30
The oxide superconductor in which the RE ₂ BaCuO ₅ phase is finely dispersed in the _7-x phase has an oxygen content of 15 to 20 wt%, and the magnetic flux density which can be maintained over 30 cm ² or more in an arbitrary region of the surface is 0%. And a method for producing an oxide superconductor having a large oriented superconductor crystal having high electric and magnetic characteristics with good reproducibility, and a method for producing such an oxide superconductor. An oxide superconductor having characteristics is obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a retained magnetic flux density distribution of an oxide superconductor manufactured by a manufacturing method of Example 1.

FIG. 2 is a three-dimensional diagram of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Example 1.

FIG. 3 is a plan view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Example 2.

FIG. 4 is a three-dimensional view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Example 2.

FIG. 5 is a plan view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Example 3.

FIG. 6 is a three-dimensional view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Example 3.

FIG. 7 is a plan view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Comparative Example 1.

FIG. 8 is a three-dimensional view of a retained magnetic flux density distribution of the oxide superconductor manufactured by the manufacturing method of Comparative Example 1.

──────────────────────────────────────────────────続 き Continued on the front page (72) Shuji Yoshizawa, Inventor 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. 20-1 Chubu Electric Power Co., Inc. Power Technology Laboratory (56) References JP-A-5-254834 (JP, A) JP-A-5-17205 (JP, A) JP-A-6-183730 (JP, A A) JP-A-8-198624 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 1/00, 3/00 C30B 29/22

Claims (1)

(57) [Claims] 1. RE compounds (RE is one or more compounds containing Y
Are two or more rare earth metal elements), a Ba compound, and Cu
A step of mixing a raw material mixture containing the compound and a step of melting and then rapidly solidifying the mixed raw material mixture.
And extent, and pulverized powder by pulverizing a raw material mixture obtained by the rapid solidification
A step of firing the crushed powder at 880 to 940 ° C., a step of forming the fired crushed powder into a molded body, and a step of melting the molded body and seeding the melted molded body.
And extent, the molded body subjected to the molten seeded, crystallization gradually cooled
And oxygen annealing the crystallized compact.
Method of manufacturing an oxide superconductor, characterized in that that.