JPH04119968A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having high critical current density by heating a mixture of source powders for RE-Ba-Cu-O oxide superconductor (RE is a rare earth element including Y) under specified conditions and cooling, then pulverizing and mixing the obtd. solidified material, molding, and again heating this molded body under specified conditions. CONSTITUTION:A mixture of source powders for RE-Ba-Cu-O oxide superconductor (RE is a rare earth element including Y) is heated in a high temp. region where the mixture partly changes into a liquid phase, and then cooled to obtain a solidified material. This solidified material is pulverized and mixed to uniformly disperse the structure. Then the mixture powder is compacted into a specified shape and then again heated in a high temp. region where the body partly changes into a liquid phase to grow the superconductor phase.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing an oxide superconductor with a high critical current density, and in particular, to
The present invention relates to a method for producing an oxide superconductor in which O5 is uniformly dispersed.

(Prior Art) The discovery of a YBaCuO-based oxide superconductor with a critical temperature (Tc) exceeding 90K has made it possible to use liquid nitrogen as a coolant. As a result, research into practical application is being carried out worldwide.

However, to date, it has not been put to practical use in a liquid nitrogen atmosphere because the critical current density (J c ), which is most important in practice, is low.

However, recently, by generating a superconducting phase from a molten state, it has become possible to obtain a critical group fi density exceeding l[)00 (IA/cj) even in a magnetic field as high as 1 Tesla (T). Ori (M.

Murakashi et al., Japan
se Journal or Applied Phys.
ics, vol, 29.1989. pH89),
It is becoming possible to obtain critical current densities close to practical levels.

This method uses a superconducting phase (Y Ba 2 Cu 30
Focusing on the fact that 211
By devising a method to finely and uniformly disperse the phase in the liquid phase, we not only promoted the growth of the superconducting phase, but also succeeded in dispersing the 211 phase, which can serve as a pinning center, in the superconducting phase. In order to uniformly and finely disperse the 211 phase, a process of rapidly heating to a high temperature of 1200° C. or higher and then rapidly cooling is performed in order to finely disperse the Y2O phase, which is the nucleus of the 211 phase.

However, with the above-mentioned conventional technical means, when heated to 1200°C or higher, Y2O tends to aggregate and coarsen, and it also sinks because it is more fluffy than the liquid phase, so there was a problem that it was difficult to uniformly disperse Y2O3. . Furthermore, it has been difficult to manufacture molded bodies of arbitrary shapes due to limitations on the shape of the rapidly cooled material.

(Question 8) The present invention has been made to solve the above-mentioned problems, and the purpose is to create a fine R inside the superconducting phase.
An object of the present invention is to provide a technology for manufacturing an oxide superconductor in which E2BaCuOs is uniformly dispersed.

Furthermore, it is an object of the present invention to produce an oxide superconductor having a high critical current density, uniformity, and an arbitrary shape having excellent mechanical properties and thermal stability.

(Means for solving the problem) In order to achieve the above object, the present invention provides REBa-Cu
- Raw material powder for producing 0-based oxide superconductor (RE is a rare earth element containing Y) or a material made by normal sintering method is heated to high temperature and then cooled to solidify the heated material. When the solidified material is crushed and the REBaCuO raw material powder mixture is reheated to 1050°C or higher, RE2O3 or RE2 Ba Cu
The pulverized material mixture is molded into a desired shape so that the O% phase is finely and uniformly dispersed in the liquid phase, the pulverized material is sufficiently stirred and mixed, and the molded product is reheated to form a superconductor. It is characterized by growing a phase.

Furthermore, the present invention provides a step in which only the raw material of the RE-Ba-Cu-0 based oxide superconductor is heated, the heated material is cooled and solidified, the solidified material is pulverized, and the powder is mixed. Silver or silver oxide is added to create a finely dispersed precursor of silver or silver oxide, this mixture (precursor) is molded into a predetermined shape, and this molded body is reheated to create superconductivity. It is characterized by growing a phase.

(Function) As shown in Figure 1 (quasi-binary system phase diagram), the superconducting phase is
11 phase and liquid phase (Bad, or BaCuO2 and Cub
) is known to be produced by the reaction of (M,
Murakami et at.

Japanese Journal orApplie
d Physjcs, vol, 2g.

1989, l, 399).

In order to continuously grow the superconducting phase, both the 211 phase and the liquid phase need to be supplied. Therefore, it is necessary that the 211 phase is finely and uniformly dispersed in the liquid phase.

One way to achieve this uniform dispersion is to cool a structure in which RE2O3, which is the nucleus for the production of the 211 phase, is uniformly dispersed in the liquid phase to bring it to the solid phase, and then reheat the structure to bring the 211 It is possible to generate a phase. In the conventional technology, such a structure was obtained by rapidly heating to a stable region of liquid phase with RE2O3 as shown in FIG. 1, and then rapidly solidifying it. However, as mentioned above, Y2O tends to aggregate and coarsen, making it difficult to obtain a uniformly dispersed structure, and while products made using conventional technology are partially uniform, they are non-uniform as a whole. there were.

However, research by the present inventor revealed that even if the quenched state contains non-uniform regions, the RE2O is lower than that in the quenched state.
It has been found that it is possible to obtain a more uniformly dispersed state.

In other words, when a rapidly solidified solidified body in which RE20
It was found that a more uniformly developed superconducting structure could be obtained by reheating the sample to a temperature of ~1200°C. It has also been found that it is unnecessary to rapidly cool the high-temperature structure of a material that has been heated to a high-temperature region where it partially exhibits a liquid phase and solidify it as it is. In other words, for example, even if heated materials in a solid-liquid coexistence state are placed in a crucible and left to cool in the atmosphere, pulverization and mechanical mixing for the purpose of uniform dispersion of RE2O3 are not performed after solidification. As long as this is done, the same structure as in the case of rapid solidification can be obtained.

Therefore, the coexistence region of RE2O3 and liquid phase, that is, 1200
After heating to a temperature above ℃, the product is rapidly cooled or left to cool, then crushed to a particle size of 0.1μ to 50μ, stirred and mixed well until RE2O3 is finely and uniformly dispersed, and molded bodies of any shape are formed. After fabrication, if the material is reheated to a temperature range where the 211 phase is generated, that is, 1050 to 1200°C, a structure that is much more uniformly dispersed in the 211 phase or liquid phase can be obtained than when it is not crushed. . By slowly cooling this state to a temperature range of 950 to 1000°C where a superconducting phase is generated, an oxide superconductor with a well-developed superconducting phase and fine 211 phases uniformly dispersed inside it can be produced. .

In addition, when cooling after heating to the coexistence region of 211 phase and liquid phase as shown in Fig. 1, the structure that remains rapidly cooled or air-cooled has R
Although the result is more non-uniform than when cooling from a region where the E2O3 phase and liquid phase coexist, a structure in which the 211 phase is uniformly dispersed can be obtained by subsequently crushing and mechanically mixing. When this mixed powder is reheated to grow a superconducting phase,
An oxide superconductor in which the superconducting phase is well developed and the fine 211 phase is uniformly dispersed therein can be produced in the same manner as in the above-described method. In either case (RE203 phase use or RE211 phase use), an extremely high critical current density (J c ) of 30000 A/c- or more can be obtained.

As described above, according to the present invention, a uniformly dispersed 211-phase precursor can be obtained relatively easily, and various molded bodies can be produced by the two-phase region method.

Next, the steps of the manufacturing method according to the present invention will be specifically explained.

[Process　■]

RE20h raw material powder such as Y2O, HO20, etc. and Ba
RE-Ba -C made of raw material powder such as CO3 and CuO
Raw material powder for u-0 type superconducting material is heated to 1200°C or higher 15
Hold at a temperature range of 00℃ or less for 1 to 60 minutes to release RE2O.
Three phases and liquid phase (Bad.

(consisting of BaCuO2 + CuO, etc.) or
Hold for 5 to 60 minutes to generate 211 phase and liquid phase.

[Process　■]

The material in the solid-liquid coexistence region is solidified by air cooling or cooling at a cooling rate equal to or higher than air cooling.

[Process　■]

Each of the coagulated materials obtained in this way is crushed to give a 0.1 to 5
The particle size is 01tm, and after reheating, RE2O3 phase or 2
The components of the 11th phase and the liquid phase are sufficiently stirred and mixed to uniformly disperse them to form a fine mixed powder, and this powder is molded into a desired shape.

[Process　■]

Next, the above molded body is processed into 1050-1 in which 211 phase is generated.
Heat to a temperature range of 200°C, hold at that temperature for 15-60 minutes, and from that temperature 1000°C/hr, IO ~ 1
Cooled at a cooling rate of 000℃/hr, and further cooled to 950℃/hr.
hr, 0.2 to b [Step (1)] Thereafter, cooling is performed from 950° C. to room temperature using any cooling conditions and method. If necessary, the material is heated to 600 to 20
Either hold in a temperature range of 0°C for 2 to 200 hours, or substantially slowly cool in a temperature range of 600°C to 200°C for 2 to 200 hours, and then cool at any cooling rate. Heat treatment may be performed.

Practical applications of superconducting materials often require not only critical current density but also mechanical properties and stability. Oxide superconductors essentially have a characteristic of low toughness, similar to ceramics, and it has been reported that even their single crystals are susceptible to cleavage. The dispersion of the 211 phase in the liquid phase also has the effect of suppressing the occurrence of racks, but since the material is a type of ceramic, there is a limit to this effect, and the material as a whole Its crack prevention effect is extremely unsatisfactory.

On the other hand, thermal stability is often a problem with superconducting materials.

In other words, when a part of a superconductor becomes normal conductor for some reason and generates heat, if the heat is not quickly removed by a coolant, the normal conductor will spread throughout the superconductor and break the superconducting state. It is.

Conventional superconducting wires (metallic superconductors) solve this problem by incorporating a composite with copper, which has excellent thermal conductivity.

Since ceramics alone have problems with thermal stability, it is being considered to create composites with metals in order to improve the mechanical properties and thermal stability of oxide superconductors. For example, a method of filling a silver sheath with superconducting powder and drawing it is used, or if the wire diameter is sufficiently small, the strength of the silver can maintain the shape of the wire.

Furthermore, since silver has excellent thermal conductivity, it also has the effect of improving thermal stability.

On the other hand, it is possible to add silver directly into the oxide superconductor, for example by adding it by a dissolution method.
IRGICAL TRANSACTION A (v
ol, 21A, Jan.

1990, pp. 257-260), and there are reports that sintering methods have also been attempted, but in these methods, silver is coarsely segregated in the matrix (as shown in the above literature). In the microphotograph of Pig 5, approximately 50 to 100 lIA of silver is segregated.)
Sufficient superconducting properties cannot be obtained.

The present inventors focused on the fact that silver has the advantage of not deteriorating the superconducting properties of the matrix and also has excellent thermal conductivity, and if silver can be successfully dispersed within the superconductor, thermal stability will be improved. Furthermore, we have discovered that if silver is finely dispersed within a matrix, it is possible to alleviate strain by deformation of the dispersed silver, thereby improving mechanical properties. That is, the present inventors discovered that during the above-mentioned heating-cooling/solidification-pulverization/mixing-reheating process in the solid-liquid coexistence region, 2.
By finely dispersing silver in the matrix while maintaining the dispersion of the 11 phases, they succeeded in improving the mechanical properties and thermal stability of the oxide superconductor.

Next, the process will be specifically explained.

After preparing the raw material powder of REBaCuO in an appropriate ratio, 1
The material is heated to 200°C or higher, cooled and solidified, and the solidified material is pulverized, and Ag2O or Ag is added to this powder and mixed. Then, mold this mixture to 1050
Reheat to ~1200℃, then 1000℃/h from that temperature
cooling at 1000°C and then slow cooling at 950°C/hr.

According to the above method, as shown in Fig. 2, it is possible to produce a REBa-Cu-0 based oxide superconductor finely dispersed in a silver or superconducting matrix, and moreover, it is possible to produce a molded body in a desired shape. can be created.

Figure 2(a) shows the structure under an optical microscope, with 2
It can be seen that 11 phases are finely dispersed.

Figure (b) shows a similar microscopic structure, but shows that silver is finely dispersed (average grain size is approximately 5 mm) within the superconducting phase. It can be seen that the silver dispersion of the present invention is much finer than that in the conventional structure, which is 50 to 100 za+a (therefore, the generation of cracks cannot be effectively prevented). Such fine dispersion of silver suppresses the generation of cracks and also improves the thermal conductivity of the superconductor, resulting in improved thermal stability. Furthermore, the effect that finely dispersed silver acts as a new pinning point can also be imparted.

The present inventors have also found that it is possible to form a superconducting phase by later adding RE2O3 or 211 phase to the molten liquid phase (FIG. 1). It can be seen from FIG. 3 that a liquid phase can be obtained at about 900° C. by using the eutectic of BaCuO2 and Cub. The temperature range (1000 to 9
When the superconducting phase is slowly cooled to 50° C., the superconducting phase is well developed, and an oxide superconductor in which the 211 phase is dispersed can be produced.

That is, after mixing raw material powders such as BaCO3 and CuO, they are calcined at around 900°C, and then heated at 950 to 1200°C.
The melt is heated to a temperature range of
O3 powder is added, held for a predetermined period of time, and then cooled, making it suitable for forming continuous long objects such as wire rods at low temperatures. Even in this case, a high critical current density (J o ) of 2000 OA/cd can be obtained (see Example 5.6).

Alternatively, a rough REBaCuO-based raw material powder is mixed, the mixture is pre-sintered, and this sintered body is made into a 1050
The 211 phase is formed by reheating to a temperature range of ~1200°C, and separately, raw material powders of BaCO3 and CuO are mixed and calcined, and the mixture is melted by heating to a temperature of around 1100°C. It is also possible to adopt a procedure in which the 211 phase is added to the obtained melt, held for a predetermined period of time, and then cooled (see Example 7).

(Example 1) The oxide superconductor of Example 1 was produced by the method shown in FIG. 4 (schematic diagram of the process). That is, Y2O
, BaCO3 and CuO were mixed as raw material powders so that the ratio of cations was approximately 1:2:3, and heated at 900℃ for 24 hours.
After calcining for an hour, it was heated to 1400° C. for 10 minutes and rapidly cooled using a copper hammer. The quenched material was pulverized to a particle size of 0.1μ to 50μ, stirred and mixed well until RE2O3 was finely and uniformly dispersed, then formed into a pellet with a diameter of 30m and a height of 3011, and heated again to 1100℃ for 30 minutes. After reheating for minutes, 100℃ of 1000℃/hr
/ hour (hr) and then 5℃/hr to 950℃/h
The mixture was slowly cooled to 100 ml and then cooled in a furnace.

Furthermore, in order to sufficiently enrich oxygen, 6
It was held at 00°C for 1 hour.

This sample has zero resistance temperature of 93 and magnetization #J constant of 77 and 30000 A at 1 Tesla (T).
/c showed a high critical current density. This is a much higher critical current density than 100OOA/c- when produced without grinding and mixing.

(Example 2) The sample of this Example 2 was prepared in the same manner as in Example 1 (mixing raw material powder and calcining), placed in a platinum crucible, heated to 1300°C for 20 minutes, taken out from the furnace, and left as is. Allow to cool in air, crush the cooled mass, thoroughly mix this powder, form into pellets with a diameter of 10 mm, reheat the pellets to 1150°C, and heat at 50°C at a rate of 1000°C/hr. /h
After cooling at 2° C./hr and slow cooling at 950° C./hr, the sample was cooled in a furnace. This sample has a zero resistance temperature of 9
3TC, 77 according to magnetization measurements, 250 in IT
It showed a high critical current density of 00A/cd.

(Example 3) The oxide superconductor of this Example 3 was produced by the method shown in FIG. 5 (schematic diagram of the process). That is, Ho2
0*, BaCO3, CuO powder as Ho:Ba:Cu
The mixture was kept at 1150°C for 1 hour, then air cooled, and the cooled material was pulverized with a jet mill, mixed, and then heated under isostatic pressure. (CIP)Diameter 10!11+Length 5 depending on the device
It was molded into a rod-shaped sample of 0I+m, reheated to 1100℃ for 30 minutes, cooled at 50℃/hr of 1000℃/hr, and heated to 1000℃ in a temperature gradient of 20℃/cm.
It was slowly cooled while moving a bar at 950°C/hr. As a result, the superconducting phase grew in one direction.The critical current density CJ)6) of this material was measured by the four-terminal method using a pulsed current power supply77, and was found to be 33000 A/
A value of c was obtained.

In addition, after thoroughly mixing the powder obtained by pulverization using the jet mill, it is filled into a flexible tube made of rubber, copper, silver, etc., and the flexible tube is shaped into a predetermined shape such as a rod shape or a coil shape. It is then shaped into a rod using an isostatic pressure (CI P) device.
It was possible to mold the sample into a predetermined shape such as a coil shape.

Note that even when the Ho site was replaced with another lanthanide element, a higher Jc value than that of conventional superconductors was obtained. The results are shown in Table 1.

As can be seen from the explanations in Table 1 and above, according to Examples 1 to 3, in the RE-Ba-Cu-0 based oxide superconductor (RE is a rare earth element containing Y), there are fine particles inside the superconducting phase. Since RE2BaCuO1 is uniformly dispersed, an oxide superconductor with a high critical current density can be obtained.

(Example 4) Each powder of RE2O3, BaCO3, and CuO was
:Cu ratio was 1.4:2:3, and preliminary sintering was performed in air at 950° C. for 24 hours. In addition, as RE, Y, Ho, SIl as shown in Table 2 are used.
, Er, Eu, Gd, Dy, NdT+a, and Yb were selected at an appropriate mixing ratio. The preliminary sintered body is an aluminum crucible of 130
After heating for 20 ml at 0° C., it was sandwiched between copper plates and rapidly cooled.

Next, the cooled material is pulverized and A by 0.1 in weight ratio is
g and mixed well. Then this mixture was added to 108
80℃/h of 1000℃/hr after heating 30ml at 0℃
After cooling at a rate of r, 950℃/hr is 2℃/h
It was cooled at a rate of r and then taken out into the air and left to cool. The cooled material was heated in a stream of oxygen at 550° C. for 1 hr and then furnace cooled.

According to magnetization measurements, all samples had a value of 77, and IT had a value of 270.
It showed a critical current density Jc of 00 A/cd or more.

When a drop test was performed on bricks from 1 m above ground, no damage was observed in any of the samples. We also measured heat conduction by immersion in liquid nitrogen.

Bubbling occurs when immersed in liquid nitrogen, but by measuring the time from immersion until bubbling stops (bubbling stops when the superconductor reaches the temperature of liquid nitrogen), it is possible to make a relative comparison of heat conduction. In the sample with silver addition, this time is 3/4 compared to the sample without silver addition,
In addition, when the sample was taken out from the liquid nitrogen temperature and the floating time was measured on a magnet, as in the immersion experiment, the holding time was 3/4 that of the sample with silver added, and the thermal conductivity of both samples was improved. It is shown that.

(Example 5) BaCO3 and CuO were prepared as raw material powder so that the ratio of cations was approximately 2:3, BaCO3 and CuO were mixed, pre-sintered at 900°C for 12 hours, and then heated to 1100°C.
After being reheated to ℃, powder of Y2O, as raw material was added, and the mixture was kept at that temperature for 20 minutes.
5℃ after cooling at 100℃/hr of 1000℃/hr
After slow cooling at 950°C/hr, the mixture was cooled in a furnace. Further, in order to sufficiently enrich the material with oxygen, the material was heated at 600° C. for 1 hour in oxygen at 1 atm and then cooled in a furnace. This sample has a zero resistance temperature of 93, and magnetization measurements indicate an IT of 77.
te 220 (t.

The critical current density of A/c- is shown.

(Example 6) Create B a CO3 and CuO, mix them as raw material powder so that the mass ratio of both is approximately 3.8,
Place this mixed powder on a silver (Ag> tape and heat it at 950°C.
The mixed powder was heated for 1 hour at
While maintaining the temperature at 0°C, Y2O and powder were added to the molten material, followed by slow cooling at 50°C/hr and 300°C/hr.
From 00℃, the superconducting phase (YBa2CLI30
X) was generated. This silver tape superconductor sample showed a critical current density of 77 and 2100 OA/c at zero magnetic field when measured by the four-probe method.

(Example 7) Y203, BaCO3 and CuO were mixed as raw material powder so that the ratio of cations was approximately 1:2:3, and 900
After pre-sintering at 1050°C for 24 hours, the 211 phase was prepared by rapidly heating to 1050°C and then quenching, and then BaCO5 and CuO were mixed as raw material powders at a ratio of approximately 3:5 to 900°C. After pre-sintering at 12 hours at ℃, the prepared 211 phase was added to the 211 phase, which was reheated to 1100 ℃.
After the temperature was maintained for 10 minutes, it was cooled at 100'C/hr at 1000°C/hr, then cooled at 950°C/hr at 5°C/hr, and then cooled in a furnace. Furthermore, in order to sufficiently enrich oxygen, the mixture was heated in oxygen at 1 atm at 600° C. for 1 hour and then cooled in a furnace.

This sample had a zero resistance temperature of 93°C and a critical current density of 23000 A/cd at 77°C according to magnetization measurements.

(Effects) As described above, according to the present invention, an oxide superconductor with a high critical current density and an oxide superconductor with excellent mechanical properties and thermal stability can be manufactured. It is expected that this will make a significant contribution to the development of industry.

[Brief explanation of drawings]

Figure 1 is a pseudo-binary phase diagram of the RE-Ba-Cu-0 based oxide superconductor (RE is a rare earth element containing Y), and a micrograph is shown in Figure 3. The phase diagram, FIG. 4 is a schematic diagram showing the manufacturing process of the Y-Ba-Cu-0 based oxide superconductor of Example 1, and FIG. 5 is the R phase diagram of Example 3.
FIG. 2 is a schematic diagram showing a manufacturing process of an E-Ba-Cu-0 based oxide superconductor. Applicant sub-agent Nippon Steel Corporation

Claims (12)

[Claims] (1) A raw material powder mixture for forming an RE-Ba-Cu-O-based oxide superconductor (RE is a rare earth element containing Y) is heated to a high temperature region where it partially exhibits a liquid phase, and this heated The solidified material is cooled to form a solidified material, the solidified material is crushed and mixed to uniformly disperse the structure, the mixed powder is molded into a predetermined shape, and the molded body is partially liquefied. 1. A method for producing an oxide superconductor, which comprises growing a superconducting phase by reheating in a high-temperature region where a superconducting phase is formed. (2) The method for producing an oxide superconductor according to claim 1, characterized in that the raw material powder mixture is heated to 1200° C. or higher to form a RE_2O_3 phase and a liquid phase, and then cooled. (3) Heat the raw material powder mixture above from 1050°C to 1200°C.
2. The method for manufacturing an oxide superconductor according to claim 1, wherein the RE_2BaCuO_5 phase and the liquid phase are formed by heating to a temperature range of 0.degree. (4) After the heated material consisting of the RE_2O_3 phase and the liquid phase is cooled and solidified, the solidified material is crushed and mixed, the mixed powder is molded into a predetermined shape, and the molded object is is reheated to a temperature range of 1050°C to 1200°C to form a RE_2BaCuO_5 phase and a liquid phase, and this reheated material is cooled to 1000°C at a cooling rate of 10 to 1000°C/hr, and then 3. The method for producing an oxide superconductor according to claim 2, wherein the oxide superconductor is cooled to 950° C. at a cooling rate of 20° C./hr, and then cooled to room temperature at an arbitrary cooling rate. (5) After the heated material consisting of the RE_2BaCuO_5 phase and the liquid phase is cooled and solidified, the solidified material is pulverized and mixed, and the mixed powder is molded into a predetermined shape. is reheated to a temperature range of 1050°C to 1200°C to form the RE_2BaCuO_5 phase and liquid phase again, and the reheated material is heated at 10 to 1000°C/hr.
Cool to 1000℃ at a cooling rate of 0.2 to 20℃/
4. The method for producing an oxide superconductor according to claim 3, wherein the oxide superconductor is cooled to 950° C. at a cooling rate of hr, and then cooled to room temperature at an arbitrary cooling rate. (6) The method for manufacturing an oxide superconductor according to claim 1, characterized in that the RE-Ba-Cu-O-based raw material powder mixture is heated to a high temperature range after preliminary calcination. (7) The oxide superconductor according to claim 4, wherein after cooling to room temperature, the manufactured product is held in an oxygen-enriched atmosphere in a temperature range of 600°C to 200°C for 2 to 200 hours. Production method. (8) The oxide superconductor according to claim 5, wherein after cooling to room temperature, the manufactured product is held in an oxygen-enriched atmosphere in a temperature range of 600°C to 200°C for 2 to 200 hours. Production method. (9) The above RE-Ba-Cu-O based raw material powder is RE
2. The method for producing an oxide superconductor according to claim 1, wherein the superconductor is made of powder of _2O_3, BaCO_3, and CuO. (10) The RE-Ba-Cu-O raw material powder mixture described above is heated to 1050°C or higher, cooled and solidified, pulverized, mixed with silver oxide or silver, molded, and then reheated. The method for producing an oxide superconductor according to claim 1, characterized in that: (11) B of RE-Ba-Cu-O based raw material powder
Mix aCO_3 and CuO powder, and add this mixture to about 9
The mixture was calcined at 1000°C to 1200°C.
It is heated to a temperature range of ℃ to melt it, and this melt is given RE_2
Add powder of O_3 or RE_2BaCuO_5, hold this mixture at the above temperature for a predetermined time, cool the material to 1000°C at a cooling rate of 10-1000°C/hr, and cool it at a cooling rate of 0.2-20°C/hr. 1. A method for producing an oxide superconductor, which comprises cooling to 950° C. at a cooling rate, and then cooling to room temperature at an arbitrary cooling rate. (12) The powder of RE_2BaCuO_5 is
-Ba-Cu-O based raw material powders are mixed, this mixture is pre-sintered, this sintered body is reheated to a temperature range of 1050°C to 1200°C to form a 211 phase, and this material is 12. The method for producing an oxide superconductor according to claim 11, wherein the oxide superconductor is produced by cooling and solidifying the material and pulverizing the solidified material.