JPH09255335A - Production of bulk-oxide superconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxide superconductor having satisfactory superconducting characteristics by using an atmosphere of oxygen as an atmosphere at the time of growing a crystal when an RE-Ba-Cu-O bulky superconductor is produced by a half melting method. SOLUTION: An atmosphere of oxygen is used as an atmosphere at the time of growing a crystal of REBa2 Cu3 O7-x [(x) is the deficiency of oxygen and is 0-0.5 and RE is lanthanoids including Y] when an REBa2 Cu3 O7-x bulk superconductor is produced by a half melting method (melt processing method). A powdery material mixture is heated to 1,010-1,050 deg.C to form RE2 BaCuO5 and a liq. phase and then slow cooling to 1,000-930 deg.C is carried out at 0.1-10 deg.C/hr cooling rate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a REBa ₂ Cu ₃ O _7-x (x is an oxygen deficiency amount of 0 to 0.5, RE is a lanthanoid element containing yttrium) system by a semi-melting method (melt process method). The present invention relates to a manufacturing method for manufacturing a bulk oxide superconductor, and particularly to a technology effectively applied to a manufacturing technology of a magnetic levitation device, a magnetic shield, and a superconducting bulk magnet using a bulk body of an oxide superconductor.

[0002]

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

A bulk oxide superconducting material in which a fine normal-conducting phase is dispersed in a superconducting phase as a RE123-based bulk oxide superconducting material exhibiting excellent characteristics is obtained by a semi-melting method (melt process method). Manufactured. This semi-melting method includes MTG (Melt-Txture-Growth processes)
s) method, MPMG (Melt-Powder-Melt-Growth process)
Law (“Melt processed high-temperature superconducto
rs ", World Scientific, Editor. Masato Murakami), OCMG (Oxygen-Controlled-Melt-Growthpro)
cess) method (Applied Physics, Volume 64, No. 4, 1995, p368-371) and the like are known.

The crystal growth atmosphere of the conventional semi-melting method is based on the atmosphere (MTG method, MPMG method) or low oxygen partial pressure (OCMG method).

Particularly, in the latter method, it is said that a high-quality superconductor cannot be obtained by the semi-melting method in pure oxygen.
(See Applied Physics, Volume 64, No. 4, 1995, p368-371).

On the other hand, in a method of synthesizing Yb123 having a low melting point, a method of synthesizing a polycrystalline wire by heat-treating it in an atmosphere having an oxygen partial pressure of 0.01 to 0.2 atm (Japanese Patent Laid-Open No. 6-18784).
No. 8), the polycrystal is heat treated in oxygen, and Yb12
A method for obtaining a single phase of No. 3 (refer to Japanese Patent Laid-Open No. 64-14149) is known. However, these methods do not produce the above-mentioned bulk oxide superconductor.

[0007]

The present inventor has found the following problems as a result of examining the conventional semi-melting method.

The above-mentioned conventional semi-melting method uses R having a low melting point.
Bulk superconductor of E123 (Yb123, Tm123,
Er123 etc.) was not effective. actually,
When the semi-melting method of Yb123 was carried out, the Yb123 bulk did not grow easily and its size was several hundreds μm or less.

When the crystals were observed carefully, Yb123 and BaCuO ₂ were precipitated as twins, suggesting that both were precipitated at the same time (FIG. 5).

In addition, TG-DTA (Thermo Gravimetry)
-Differential Thermal Analysis: Thermogravimetric and differential calorimetry studies show that Yb123 and BaCuO
_{It was found that} the crystallization temperatures of ₂ were very close to 930 ° C. and 910 ° C., respectively, and the temperature difference between the two crystallization temperatures was insufficient for preferentially growing only Yb123.

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 manufacturing a bulk oxide superconductor which can generate a strong magnetic field.

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

[0014]

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

As a result of daily research, the inventor has found that the crystallization temperatures of YbBa ₂ Cu ₃ O _7-x and BaCuO ₂ are 980 ° C. and 940 ° C., respectively, in a pure oxygen atmosphere, and the temperature difference between the two is relatively large. It has been found that the size of the crystal is large and that crystal growth is easier than in the atmosphere.

The present invention is a manufacturing method for synthesizing a bulk oxide superconductor of RE123 having a low melting point (for example, Yb123, Tm123, Er123, etc.) by performing a semi-melting method in a pure oxygen atmosphere. That is, (1) REBa ₂ Cu _{3 by the} semi-melting method (melt process method)
A method for producing a bulk oxide superconductor for producing an O _7-x (x is an oxygen deficiency amount of 0 to 0.5, RE is a lanthanoid element containing yttrium) -based bulk superconductor, comprising:
The atmosphere during crystal growth of EBa ₂ Cu ₃ O _7-x was an oxygen atmosphere.

(2) In the method for manufacturing a bulk oxide superconductor according to (1), Yb is used as RE.

(3) In the method for producing a bulk oxide superconductor according to (1) or (2) above, YbBa ₂ Cu ₃ O _{7-x is used.}
And Yb ₂ BaCuO _{5 in} the mixing ratio of 1.0: 0.0 to 1.
It is set to 0: 0.4.

(4) Any one of (1) to (3) above
In one method for manufacturing a bulk oxide superconductor, the material powder mixture is heated to a temperature range of 1010 ° C to 1050 ° C to form RE ₂ BaCuO ₅ and a liquid phase, and then 100
The temperature is gradually cooled from 0 ° C to 930 ° C.

(5) Any one of (1) to (4) above
In one method for manufacturing a bulk oxide superconductor, the slow cooling rate is 0.1 ° C./hour to 10 ° C./hour.

(6) Any one of (1) to (5) above
In one method for manufacturing a bulk oxide superconductor, a seed crystal is placed on the surface of a material powder mixture to grow crystals.

The processing procedure of the method for producing a bulk oxide superconductor according to the present invention will be described below.

Step 1 (mixing of Yb123 raw material powder) Yb ₂ O ₃ , BaCO ₃ , and CuO are used as starting materials, and these 3
The two raw materials are mixed in a molar ratio of 1: 4: 6 and mixed well in a mortar. For this mixing time, use an automatic mortar to mix the raw material powders for 3 hours, and mix with YbBa ₂ Cu ₃ O _7-x.
The raw material powder of (Yb123) is used.

Step 2 (synthesis of Yb123 calcined powder) 20 to 30 g of the raw material powder obtained in the above step 1
After being formed into φ pellets, it is fired at 880 ° C. for 48 hours in the atmosphere (first temporary firing). The pellets after the calcination are crushed, mixed in an automatic mortar for 3 hours to form pellets, and then calcinated in the air at 890 ° C. for 48 hours (second calcination). Further, the pellets are crushed and mixed in an automatic mortar for 3 hours to form pellets, and then the pellets are placed in air at 890 ° C.
Calcination is performed for 24 hours (third calcination). By these treatments, the raw material powder of Yb123 is Yb123, Yb ₂ BaC.
uO ₅ (hereinafter referred to as Yb211), BaCuO ₂ , C
It is a mixture of four uO. The powder (pellet) thus obtained is hereinafter referred to as a Yb123 calcined powder (pellet).

Step 3 (Synthesis of Yb123 Single Phase) The calcined powder of Yb123 obtained in the above Step 2 is crushed, mixed in an automatic mortar for 1 hour, and formed into pellets, and then at 960 ° C. in a pure oxygen atmosphere. Bake for 48 hours (first main firing). The mixing time in the automatic mortar was set to 1 hour in order to prevent decomposition of Yb123 due to water contained in the atmosphere. Also, firing in a pure oxygen atmosphere is Yb12.
This is to obtain 3 single phases.

The pellets after the above firing (first firing) are crushed and mixed in an automatic mortar for 1 hour to form pellets, which are then fired in a pure oxygen atmosphere at 960 ° C. for 48 hours (second firing). . Further, the pellets are crushed and mixed in an automatic mortar for 1 hour to form pellets, which are then fired in a pure oxygen atmosphere at 960 ° C. for 24 hours (third main firing). By these treatments, the calcined powder of Yb123 becomes Y.
It becomes a single phase of b123. The powder (pellet) obtained in this step 3 is hereinafter referred to as Yb123 single-phase powder (pellet).

This Yb123 single-phase powder (pellet)
Since is easily decomposed by moisture in the air, it must be stored in a desiccator or in a vacuum pack.

Step 4 (Mixing of Yb211 raw material powder) Yb ₂ O ₃ , BaCO ₃ and CuO were used as starting materials, and these 3
The two raw materials are mixed at a molar ratio of 1: 1: 1, and thereafter, the same operation as in step 1 is performed to obtain a raw material powder of Yb211.

Step 5 (Synthesis of Yb211 Single Phase) The raw powder of Yb211 obtained in the above Step 4 is used in an amount of 10 to 30.
After molding g into pellets of 20 to 30φ, 88 in air
Bake at 0 ° C. for 24 hours (first main firing). Crush the baked pellets and mix in an automatic mortar for 3 hours,
After forming into pellets, it is fired in the air at 890 ° C. for 24 hours (second firing). By these operations, Yb211
A single phase is obtained.

Step 6 (Mixing of pellets for crystal growth) Using the Yb123 single phase and the Yb211 single phase thus obtained, the raw materials for the semi-melting method are blended. The compounding was performed in a molar ratio, and Yb123: Yb211 was 1.0: 0.0 (= Y
b1.0), 1.0: 0.2 (= Yb1.4), 1.0: 0.
4 (= Yb1.8), 1.0: 0.6 (= Yb2.2),
1.0: 0.8 (= Yb2.6), 1.0: 1.0 (= Yb
3.0) etc. can be considered.

After mixing in a mortar made of agate for 1 hour, about 10 g is uniaxially formed with a 20φ mold and isotropically pressurized (CIP) to give pellets for crystal growth.

Step 7 (Seed Crystal) Next, a seed crystal is placed on the surface of the pellet. This seed crystal may be a single crystal of REBa ₂ Cu ₃ O ₇ having a melting point higher than that of Yb123, but is preferably NdBa ₂ having the highest melting point.
A single crystal of Cu ₃ O ₇ (Nd123) is most suitable because there is no risk of contamination with Yb123. At this time, the orientation of the seed crystal is not particularly limited, but it is easy to place it so that the ab plane is in contact.

Step 8 (Control of Atmosphere) The pellet on which the seed crystal is placed is placed in an airtight annular furnace, and pure oxygen is circulated to obtain a pure oxygen atmosphere. The oxygen purity at this time may be 99% or more, but it is realistic to use the industrially-preferred purity.
A purity of 9.9995% is used. The flow rate is not limited as long as the temperature of the furnace can be controlled and the atmosphere in the furnace can be maintained as a pure oxygen atmosphere, but from the balance of both, it is preferably about 300 cc / min (min).

It is also possible to use a method in which the oxygen partial pressure is higher than atmospheric pressure within a range that the furnace can handle. At this time, if the pressure is 10 atm or more, the design of the furnace is significantly changed, so that the synthesis can be performed under the condition of 1 to 10 atm.

Step 9 (Crystal Growth) The temperature pattern of crystal growth by the semi-melting method is shown below.
The crystal growth shown below is performed under pure oxygen flow.

First, up to 900 ° C., 300 ° C./h (hour)
Then, the temperature is raised at 100 ° C./h until the temperature range (980 to 1050 ° C.) in which the Yb211 phase + liquid phase is reached. However, the temperature rising rate up to the temperature (980 ° C.) at which Yb123 decomposes and the liquid phase begins to appear is not particularly limited, and if the pellet does not crack or foam, the temperature is raised faster than this. May be.

On the contrary, the temperature at which the liquid phase begins to emerge is several degrees Celsius to 2
It is also possible to increase the density of pellets by holding at a temperature of 0 ° C. lower for 1 to 24 hours. If the rate of temperature increase above the temperature at which the liquid phase begins to appear is lower than the above, crystal growth may be hindered due to coarsening of the Yb211 phase, flow-out of the liquid phase, and the like.

Next, the temperature range of Yb211 phase + liquid phase is maintained for 10 to 60 minutes (min). This is because the raw material contained in the pellets is completely Yb211 + liquid phase. That is, the reason is to complete the reaction represented by the following formula (1).

[0039]

[Formula 1] YbBa ₂ Cu ₃ O ₇ (solid phase) → Yb ₂ BaCuO
₅ (solid phase) + BaCuO ₂ (liquid phase) + CuO (liquid phase) If the holding time at this time is too short, the above reaction becomes incomplete. On the other hand, if it is too long, crystal growth may be hindered due to coarsening of the Yb211 phase, loss of the liquid phase, and the like.

After the pellet becomes the Yb211 phase + liquid phase, the cooling rate is preferably as high as possible within the range where the furnace does not undergo supercooling up to the temperature (1000 ° C.) at which crystal growth is started. If the cooling rate at this time is slow, the Yb211 phase may become coarse and the liquid phase may be washed away. Preferably 1
It is about 00 ° C / h.

Crystal growth is from 1000 ° C. to 930
Slowly cool down to ℃. This is because a temperature margin for safety was added to the crystallization temperature of Yb123 (980 ° C.) and the crystallization temperature of BaCuO ₂ (940 ° C.). The cooling rate is 10 to 0.1 ° C./h. This slow cooling rate is 1
It is better to be slower than 0 ° C / h, but it is unrealistic at 0.1 ° C / h or less because it takes too much time.

Finally, at 930 to 900 ° C, 10 ° C /
h, cooling from 900 ° C. to room temperature by furnace cooling. In addition, pure oxygen continues to flow until the furnace cools to room temperature.

According to the above process, Yb is formed under the seed crystal.
123 bulk superconductor grows. This size is about 3 × 3 × 0.5 mm, though it varies depending on the synthesis conditions.

Step 10 (Cutting of Yb123 Bulk Superconductor) The synthesized Yb123 bulk superconductor is cut into a predetermined size with a wire saw or the like.

Step 11 (oxygen anneal) The Yb123 bulk superconductor cut out in the step 10 is 300 ° C. in a pure oxygen stream (300 cc / min).
After holding for 48 hours, oxygen annealing was performed. It should be noted that this oxygen annealing can be performed in the room temperature cooling process of the step 9.

As can be seen from the above description, according to the method for manufacturing a bulk oxide superconductor of the present invention, fine RE2
It is possible to synthesize an RE123 bulk superconductor in which 11 phases are dispersed and which has a high critical current density.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below along with its embodiments (examples).

(Embodiment 1) Yb123 and Yb211 synthesized through the above steps 1 to 6 were used, and Yb was used in a molar ratio.
123: Yb211 1.0:... Raw materials blended at a ratio of _{0.4 (= Yb 1 8 Ba 2} 4 Cu 3 4 O 9 ( hereinafter, referred to as Yb1.8) with 10 g, of Step 7 10mm after processing
A φ crystal growth pellet was formed. A single crystal of Nd123 was placed on the surface of this pellet to form a seed crystal.

After placing the pellets in the furnace, 99.9% pure oxygen was flowed at a flow rate of 300 cc / min to create a pure oxygen atmosphere. Atmospheric pressure is slightly higher than atmospheric pressure (20 mm
H ₂ O). The temperature pattern of crystal growth was as shown below.

First, up to 900 ° C., 300 ° C./h, 90
The temperature was raised at 100 ° C / h from 0 to 1030 ° C. 103
It was kept at 0 ° C. for 30 minutes (min) to be in a state of Yb211 + liquid phase. Next, 60 ° C / up to 1030-1010 ° C
It cooled at 20 degreeC / h to 1010-1000 degreeC by h. Next, the crystal was grown by gradually cooling from 1000 to 930 ° C. at 1 ° C./h. Then 10 up to 930-900 ℃
After 900 ° C./h and 900 ° C., the furnace was cooled.

By the above processing, 3 × 3 × is formed under the seed crystal.
A 0.5 mm-sized Yb123 bulk superconductor grew.
In addition, from the observation with a scanning electron microscope (SEM), Yb1
It was confirmed that 1 to 10 μm of Yb211 phase was dispersed in 23 phases (FIG. 1: Scanning electron microscope (SEM)).
(A schematic diagram tracing the outline of the photograph).

The grown Yb123 bulk superconductor was cut into a size of 1.0 × 3.0 × 0.3 mm and subjected to oxygen annealing (300 ° C. for 48 hours).

When the characteristics of the superconductor obtained as described above were evaluated by a SQUID (superconducting quantum interferometer) magnetometer, Tc (zero resistance starting temperature) was 91.5K (FIGS. 2 and 3). , Critical current density is 77k, 0 Tesla (T)
It showed high values of 50,000 A / cm ² (without external magnetic field) and 10,000 A / cm ² at 1 Tesla (T) (FIG. 4).

(Embodiment 2) Yb123 and Yb211 synthesized through the above steps 1 to 6 were used, and Yb was used in a molar ratio.
123: Yb211 1.0:.... Raw materials blended at a ratio of _{0.2 (= Yb 1 4 Ba 2} 2 Cu 3 2 O 8 0, below, Yb1.4
10g through 10g after using the process of step 7
A pellet for crystal growth of mφ was formed. As a result of crystal growth using the pellets in the same process as in the first embodiment, Yb1 of 2.5 × 2.5 × 0.5 mm is formed under the seed crystal.
23 bulk superconductors have grown.

(Comparative Example 1) Yb123 and Yb211 synthesized through the above steps 1 to 6 were used, and Yb was used in a molar ratio.
Y: 123: Yb211 mixed in a ratio of 1.0: 0.4
Using 10g of b1.8, 10mm after step 7
A φ crystal growth pellet was formed. A single crystal of Nd123 was placed on the surface of this pellet to form a seed crystal.

For comparison of the pellet with the first embodiment, crystal growth was tried in the atmosphere. However, in the atmosphere Y
The crystallization temperatures of b123 and BaCuO ₂ are 930, respectively.
And 910 ° C. Therefore, the temperature of Yb211 + liquid phase was set to 980 ° C, and the slow cooling temperature range for crystal growth was set to 950 to 900 ° C and 1 ° C / h. Other steps and parameters were performed according to the first embodiment. As a result, the growth of the Yb123 bulk superconductor did not occur.

That is, the fine structure of the Yb123 bulk growth attempted in air is as shown in FIG. This is because the crystallization temperatures of Yb123 and BaCuO ₂ are close to each other,
Both grow. Therefore, Yb ₂ BaC that cannot react completely
The uO ₅ (Yb211) phase and the CuO phase also precipitate (Equation 2).

[0058]

[Formula 2] Yb ₂ BaCuO ₅ (solid phase) + BaCuO ₂ (liquid phase) + CuO (liquid phase) → Yb ₂ BaCuO ₅ (solid phase) + Y
bBa ₂ Cu ₃ O _7-x (solid phase) + BaCuO ₂ (solid phase) + C
uO (solid phase) On the other hand, the microstructure when attempting to grow the Yb123 bulk in the pure oxygen atmosphere as in Embodiment 1 is as shown in FIG. This is because the crystallization temperature difference between Yb123 and BaCuO ₂ becomes large, so that Yb123 is preferentially grown. That is, the peritectic reaction represented by the equation of Formula 3 proceeds, and a bulk superconductor in which Yb211 is finely dispersed in Yb123 is formed.

[0059]

[Formula 3] Yb ₂ BaCuO ₅ (solid phase) + BaCuO ₂ (liquid phase) + CuO (liquid phase) → YbBa ₂ Cu ₃ O _7-x (solid phase) (Comparative form 2) Synthesized through steps 1 to 6 described above. Yb1
23 and Yb211 in a molar ratio of Yb123: Yb
Yb1.8 containing 211 in a ratio of 1.0: 0.4 is 1
0 g was used to go through the treatment of step 7 to form a 10 mmφ crystal growth pellet.

For comparison with the first embodiment, a crystal growth was tried without placing a seed crystal. As a result, a Yb123 bulk superconductor having a size of about 0.4 × 0.4 × 0.05 mm grew near the surface of the pellet, but no crystal having the size as in Embodiment 1 was observed.

(Embodiment 3) When the amount of RE 123 is changed in accordance with Embodiments 1 and 2 described above, or when RE is Tm, E
An attempt was made to grow crystals of the RE123-based bulk oxide superconductor when changing to r and Ho. As a result, 1.0 x 1.0 x
The success or failure of the results of 0.1 mm or more is shown in Table 1 below.

[0062]

[Table 1]

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-mentioned embodiments (examples), and its gist is not limited. It goes without saying that various changes can be made without departing from the scope.

[0064]

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

(1) It is possible to synthesize an RE123 bulk superconductor having a high critical current density in which fine RE211 phases are dispersed without BaCuO ₂ inhibiting the crystal growth of RE123.

(2) Crystal growth of RE123 bulk is 10
It is possible even at a low temperature of 00 ° C or less.

(3) According to the above (1) and (2), it is possible to manufacture a bulk superconductor having a superconducting characteristic and a strong magnetic field.

[Brief description of drawings]

FIG. 1 is a diagram tracing a schematic configuration of a scanning electron microscope (SEM) photograph of a bulk oxide superconductor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing magnetization temperature characteristics of the bulk oxide superconductor according to the first embodiment.

FIG. 3 is an enlarged view of a main part of FIG. 2;

FIG. 4 is a diagram showing the critical current density of the bulk oxide superconductor of the first embodiment.

FIG. 5 is a diagram tracing a schematic configuration of a scanning electron microscope (SEM) photograph of a conventional bulk oxide superconductor.

[Explanation of symbols]

1 ... Yb123, ₂ ... Yb211, 3 ... BaCuO ₂ ,
4 ... CuO.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Mochida 1-14-3 Shinonome, Koto-ku, Tokyo Inside the Institute for Superconductivity Engineering, International Superconductivity Research Center (72) Inventor Liu, Koto-ku, Tokyo 1-14-3 Shinonome International Superconductivity Industrial Technology Research Center Superconductivity Engineering Laboratory (72) Inventor Naomichi Sakai 1-14-3 Shinonome Koto-ku Tokyo Metropolitan Superconductivity Engineering Research Center Superconductivity Engineering Research In-house (72) Inventor Masato Murakami 1-14-3 Shinonome, Koto-ku, Tokyo International Superconducting Industrial Technology Research Center Superconducting Engineering Laboratory

Claims (6)

[Claims] 1. REB by a semi-melting method (melt process method)
A method for producing a bulk oxide superconductor for producing an a ₂ Cu ₃ O _7-x (x is an oxygen deficiency amount of 0 to 0.5, RE is a lanthanoid element containing yttrium) -based bulk superconductor, comprising: A method for producing a bulk oxide superconductor, characterized in that an oxygen atmosphere is used as an atmosphere during crystal growth of REBa ₂ Cu ₃ O _7-x . 2. The method for manufacturing a bulk oxide superconductor according to claim 1, wherein Yb is used as the RE. 3. The method for producing a bulk oxide superconductor according to claim 1, wherein YbBa ₂ Cu ₃ O _{7-x is used.}
And Yb ₂ BaCuO _{5 in} the mixing ratio of 1.0: 0.0 to 1.
A method for producing a bulk oxide superconductor, characterized in that it is set to 0: 0.4. 4. The method for manufacturing a bulk oxide superconductor according to claim 1, wherein the raw material powder mixture is heated to a temperature range of 1010 ° C. to 1050 ° C. and RE ₂ BaCuO _{5 is} added. And a liquid phase are formed, and then 100
A method for producing a bulk oxide superconductor, which comprises gradually cooling from 0 ° C to 930 ° C. 5. The bulk oxide superconductor manufacturing method according to claim 1, wherein the slow cooling rate is 0.1 ° C./hour to 10 ° C./hour. Manufacturing method of oxide superconductor. 6. The bulk oxidation method according to claim 1, wherein a seed crystal is placed on the surface of the material powder mixture and the crystal is grown. Method for manufacturing superconductors.