JP4153651B2 - Seed crystal of oxide superconducting material and manufacturing method of oxide superconducting material using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seed crystal of a rare earth oxide superconductor having a critical temperature of 90K class and a method for producing an oxide superconductor using the seed crystal.
[0002]
[Prior art]
A rare earth oxide superconductor in which RE ₂ BaCuO ₅ phase is finely dispersed in REBa ₂ Cu ₃ O _7-x (where RE is one or a combination of rare earth elements including Y) is another oxide superconductor. Compared to the above, the magnetic flux pinning force is large, and the critical current density is high even at high temperatures close to the liquid nitrogen temperature (77K). A bulk material usually produced by the melting method is added with a small amount of Pt, Rh, Ce, etc., and the RE ₂ BaCuO ₅ phase of about 1 μm is refined. However, this superconductor requires crystal grains to be highly oriented because crystal grain boundaries significantly reduce the critical current density.
[0003]
The melting method represented by the QMG (Quench and Melt Growth) method (Japanese Patent Laid-Open No. 2-153803, Japanese Patent Laid-Open No. 5-93938, etc.) is used once for RE ₂ BaCuO ₅ phase or RE ₄ Ba ₂ Cu ₂ O _10. The temperature is raised to the temperature range where the phase and the liquid phase containing Ba-Cu-O as the main component coexist, and this is cooled to just above the peritectic temperature where REBa ₂ Cu ₃ O _7-x is formed, and then gradually cooled from that temperature. Is a method for obtaining a large bulk material composed of a single crystal grain by performing crystal growth to control nucleation and crystal orientation.
[0004]
In the seeding method for crystal growth using a seed crystal having a high peritectic temperature disclosed in Japanese Patent Application Laid-Open No. 5-193938, the RE ^I Ba ₂ Cu ₃ O _7-x oxide superconductivity to be produced is to be produced. A RE ^II Ba ₂ Cu ₃ O _7-x single crystal sample having a higher melting point (peritectic temperature) than the body is used. The raw material precursor of the RE ^I Ba ₂ Cu ₃ O _7-x oxide superconductor is changed to the peritectic temperature of RE ^I Ba ₂ Cu ₃ O _{7-x and} the peritectic temperature of RE ^II Ba ₂ Cu ₃ O _7-x . To the intermediate temperature of RE ^I Ba ₂ Cu ₃ O _7-x decomposes and the liquid is composed mainly of RE ^I ₂ BaCuO ₅ phase or RE ^I ₄ Ba ₂ Cu ₂ O ₁₀ phase and Ba-Cu-O. The phase is made to coexist, and one surface of the RE ^II Ba ₂ Cu ₃ O _7-x crystal is brought into contact with the precursor. Thereafter, RE ^I Ba ₂ Cu ₃ O _7-x is cooled to the peritectic temperature to produce RE ^I Ba ₂ Cu ₃ O _7-x. By slowly cooling near the peritectic temperature, RE ^II Ba ₂ In this method, crystals are grown in the same orientation as the crystal orientation of the contact surface of Cu ₃ O _7-x .
[0005]
The manufacturing method of JP-A-RE-Ba-Cu-O system No. disclosed in Japanese 9-156925 oxide superconductor, the _{RE (Ba 1-y Sr y} ) 2 Cu 3 O 7-x phase (here y 0.01 The ratio of RE: Ba + Sr: Cu is 1: 2: 3, except that the Ba element is replaced by the Sr element. Yes, the composition ratio is the same as that of the oxide superconducting phase REBa ₂ Cu ₃ O _7-x .
[0006]
In addition, the manufacturing method of an oxide superconducting bulk material disclosed in Japanese Patent Application Laid-Open No. 10-310498 discloses a material (gold, silver, rare earth) that lowers the peritectic temperature of REBa ₂ Cu ₃ O _{7-x on} the surface of a raw material compact. After coating with elements, etc., the seeding operation is performed in the cooling process after heating and melting.
[0007]
As described above, in the conventional melting method, a slight difference in melting point between the raw material molded body (precursor) and the seed crystal is used, and a rare-earth oxide superconductor crystal having a high melting point is used for the seed crystal. By lowering the melting point of the raw material molded body, a temperature difference between the melting points of the raw material molded body and the seed crystal is ensured to perform seeding.
[0008]
However, for the production of bulk materials of relatively high melting point rare earth (Nd, Sm, Eu) based oxide superconductors, the highest melting point Nd based or Nd-Sm based oxide superconductor crystals are used. Although silver or the like is added to the bulk material to lower the melting point of the bulk material to ensure a temperature difference between the melting point of the seed crystal and the bulk material, the temperature difference is only a few dozen degrees Celsius, so 1000 degrees Celsius Due to the slight non-uniformity of the temperature distribution in the heating furnace, many seed crystals are melted or polycrystallized from the seed crystals, and a good bulk material can be produced stably. was difficult.
[0009]
Also, in the production of bulk materials of rare earth (Dy, Y, Ho, Er) oxide superconductors with a relatively low melting point of about 1000 ° C, many raw material compacts are placed in a large heating furnace for mass production. However, it is difficult to control the entire furnace to a temperature distribution within several tens of degrees centigrade in a large furnace heated to about 1000 degrees centigrade, by heat treating this. In spite of processing in the same batch, depending on the arrangement position in the furnace, seed crystals may be melted, or raw material compacts may not be mixed, resulting in a low product yield. In addition, seed crystal inoculation at a high temperature of 1000 ° C. had to be repeated many times, and workability was not always good.
[0010]
On the other hand, for the production of relatively small oxide superconductors, MgO single crystals are used as seed crystals. However, in this case, the probability that the crystal orientation of the oxide superconductor can be controlled is about 1/3, and the product yield is very low.
As described above, the conventional oxide superconductor manufacturing method has a problem that it is impossible to mass-produce a superconducting material which is stable with a high yield.
[0011]
[Problems to be solved by the invention]
Therefore, the present invention provides a seed crystal having a sufficiently high melting point and capable of reliably controlling the crystal orientation of the bulk material, and a method for producing an oxide superconducting material having high workability using the seed crystal. The purpose is to do.
[0012]
[Means for Solving the Problems]
As a result of diligent studies to solve the above problems, the crystal orientation of the rare earth oxide superconducting material can be controlled even if a crystal having a crystal structure similar to that of the rare earth oxide superconductor is used as a seed crystal. The present invention has been completed by finding that it can be achieved.
[0013]
That is, the present invention
(1) RE ¹ Ba ₂ Cu ₃ O _7-x series superconductor (where RE ¹ is one or a combination of rare earth elements including Y) is a Sr ₃ Ti ₂ O ₇ type A seed crystal of an oxide superconducting material characterized by having a crystal structure of
(2) RE ¹ Ba ₂ Cu ₃ O _7-x- based superconductor (where RE ¹ is one or a combination of rare earth elements including Y) is used as a seed crystal (RE ² _1-y M _y ) ₃ Cu ₂ O _6-z (RE ² is one or a combination of rare earth elements including Y, and M is one or a combination selected from alkaline earth metals) (where 0 <y <1.0, 1.35y-0.45 <z <1.65y-0.55), a seed crystal of an oxide superconducting material,
(3) A seed crystal for producing RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is one or a combination of rare earth elements including Y) is (Nd _1-y Sr _y ) ₃ Cu ₂ O _6-z (however, the range of y is 0.3 ≦ y ≦ 0.4 or 0.5 ≦ y ≦ 0.7, 1.35y-0.45 <z <1.65y-0.55) Seed crystals,
(4) REBa ₂ Cu ₃ O _7-x based superconductor (where RE is one or a combination of rare earth elements including Y) is melt-heated and cooled to cool the REBa ₂ Cu _In the method for producing an oxide superconductor in which the RE ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase is dispersed in the ₃ O _7-x phase, the seed according to any one of (1) to (3) (5) Oxidation according to (4), characterized in that a seed crystal is placed on the raw material compact and then melt heat treatment is performed. This is a manufacturing method of a superconducting material.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Oxide superconductivity in which RE ₂ BaCuO ₅ or RE ₄ Ba ₂ Cu ₂ O ₁₀ is dispersed in the REBa ₂ Cu ₃ O _7-x phase (where RE is one or a combination of rare earth elements including Y) In the production of materials, these materials have a crystal growth temperature of about 1070 ° C. to 900 ° C. in the atmosphere. In contrast, a material having a crystal structure of Sr ₃ Ti ₂ O ₇ type such as (Nd _1-y Sr _y ) ₃ Cu ₂ O _6-z has a crystal growth temperature of about 1160 ° C., and REBa ₂ Cu _It has a crystal growth temperature difference of 100-200 ° C or more compared to ₃ O _7-x phase. This means that the seed crystals of these systems can withstand higher temperatures of 100 to 200 ° C. or more than the conventional REBa ₂ Cu ₃ O _7-x system seed crystals.
[0015]
In addition, (Nd _1-y Sr _y ) ₃ Cu ₂ O _6-z has almost the same constituent elements as the rare earth oxide superconductor, and each crystal structure contains REBa ₂ Cu ₃ O _7-x Similar to, there is a Cu-O plane formed by four Cu surrounding one Cu. As a result, the lattice constant is about 3.8 mm on the a-axis, which is very close to REBa ₂ Cu ₃ O _7-x . The crystal structure of _{(Nd 1-y Sr y)} 3 Cu 2 O 6-z shown in Figure 1.
[0017]
Also, it has Sr ₃ Ti ₂ O ₇ type crystal structure such as (RE _1-y Sr _y ) ₃ Cu ₂ O _6-z (where RE is a rare earth element such as La, Sm, Eu, Pr, Gd) It is known that the material does not decompose even at a high temperature of about 1100 ° C. in the atmosphere.
[0018]
For the above reasons, in the RE ¹ Ba ₂ Cu ₃ O _7-x phase (where RE ¹ is one or a combination of rare earth elements including Y), RE ¹ ₂ BaCuO ₅ or RE ¹ ₄ Ba ₂ Cu ₂ In the production of an oxide superconducting material in which O ₁₀ is dispersed, (RE ² _1-y Sr _y ) ₃ Cu ₂ O _6-z (where RE ² is one or a combination of rare earth elements including Y) By using it as a seed crystal, the bulk material production yield of a system (Nd, Sm, Eu) having a relatively high crystal growth temperature is greatly improved, and mass production is facilitated for the production of other systems. Here, RE ¹ and RE ² may be the same or different rare earth elements.
[0019]
In addition to (RE ² _1-y Sr _y ) ₃ Cu ₂ O _6-z , Ba is partially or completely substituted with elements such as Sr, Ca, Mg, etc., and Sr with Ba, Ca, Mg, etc. Furthermore, with respect to those in which Cu and O are partially substituted with other elements, those having a crystal structure of Sr ₃ Ti ₂ O ₇ type containing Cu are also effective as seed crystals.
[0020]
Where (RE ² _1-y M _y ) ₃ Cu ₂ O _6-z (where RE ² is one or a combination of rare earth elements including Y, and M is one selected from alkaline earth metals) (Or a combination thereof) 0 <y <1.0 because the ionic radii of the rare earth element and the alkaline earth metal have almost the same size depending on the selection, so that the crystal structure can be stably maintained even when widely substituted. by. In addition, (RE ² _1-y M _y ) ₃ Cu ₂ O _6-z has 1.35y-0.45 <z <1.65y-0.55 because the crystal structure cannot be stably maintained beyond this range. by.
[0021]
Further, due to the reason that the _{(Nd 1-y Sr y)} 3 Cu 2 O 6-z 0.3 ≦ y ≦ 0.4 or 0.5 ≦ y ≦ 0.7 for, if it exceeds this range, which can not be stably crystal structure held . For the same reason, and the _{(Nd 1-y Sr y)} 3 Cu 2 O 6-z In 1.35y-0.45 <z <1.65y- 0.55.
[0022]
Furthermore, the point which made these elements Nd and Sr is described below. During crystal growth, the constituent elements of the seed crystal may partially diffuse into REBa ₂ Cu ₃ O _7-x in the very vicinity of the seed crystal. Even if such a phenomenon occurs, if it is an element of Nd or Sr, even if the peritectic temperature (crystal growth start temperature) of REBa ₂ Cu ₃ O _7-x is raised in the vicinity of the seed crystal, NdBa ₂ Cu ₃ O _{7-x has} the highest peritectic temperature among REBa ₂ Cu ₃ O _7-x. This is because the crystal temperature does not change). That is, if the Nd and Sr elements in composed a seed crystal, the constituent elements REBa ₂ Cu ₃ O _7-x as diffused in high peritectic temperature of the crystal near, REBa ₂ with distance from the seed crystal Since the peritectic temperature of Cu ₃ O _7-x is lowered with the lower limit, crystal growth can proceed stably and sequentially from the seed crystal, and the seed crystal is more preferable.
[0023]
In the method for producing an oxide superconductor in which the RE ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase is dispersed in the REBa ₂ Cu ₃ O _7-x phase, the raw material compact is melt-heat treated, and the above-mentioned By crystal growth using a seed crystal, seed crystal seeding at a relatively high temperature is possible, and mass production of a stable superconducting material with a high yield is facilitated. Since the seed crystal can withstand high temperatures, it becomes possible to perform the melt heat treatment after placing the seed crystal on the raw material compact, and further improve the workability of mass production.
In addition, in order to disperse the RE ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase in the REBa ₂ Cu ₃ O _7-x phase in the raw material molded body, Pt, Rh, Ce, etc. are added. In order to lower the peritectic temperature of REBa ₂ Cu ₃ O _7-x , Ag or the like may be added.
[0024]
【Example】
(Comparative example)
Each raw material powder of Y ₂ O ₃ , BaO ₂ and CuO is mixed so that the molar ratio of each metal element (Y: Ba: Cu) is (13:17:24), and further 0.2 mass% in this mixed powder Rh was added to prepare a mixed raw material powder. This raw material powder was calcined in an oxygen stream at 870 ° C. Using a rubber press, 50 calcined powders were molded into a disk-shaped compact having a diameter of 50 mm and a thickness of 20 mm at a pressure of ² ton / cm ² .
[0033]
These were placed in a furnace at room temperature. Thereafter, the temperature was raised to 1120 ° C. in the atmosphere over 8 hours and held for 1 hour. Further, the temperature was lowered to 1040 ° C. in 30 minutes and held for 30 minutes, during which NdBa ₂ Cu ₃ O _7-x seed crystals were placed so that the normal of the board surface substantially coincided with the c axis. Further, the temperature was lowered to 1010 ° C. in 30 minutes, and then gradually cooled to 960 ° C. over 110 hours for crystal growth. Furthermore, it cooled to room temperature in 24 hours.
[0034]
Of the 50 materials obtained, 13 had evidence that the seed crystals had melted and were polycrystallized. The remaining 37 were obtained as single crystals in which the c-axis coincided with the normal of the board surface in the same manner as the seed crystal. When these were cooled in a magnetic field at 77 K and the external magnetic field was removed, and the trapped magnetic flux density was measured, the average of the maximum values was 1.0 T.
[0035]
(Example 1)
Each raw material powder of Sm ₂ O ₃ , BaO ₂ and CuO is mixed so that the molar ratio of each metal element (Sm: Ba: Cu) is (12:18:26), and further 0.5% by mass in this mixed powder Pt was added to prepare a mixed raw material powder. This raw material powder was calcined at 900 ° C. in an oxygen stream. This calcined powder was molded into a disk-shaped molded body having a diameter of 30 mm and a thickness of 20 mm at a hydrostatic pressure of ² ton / cm ² .
[0036]
This was heated up to 1150 ° C. in the atmosphere over 8 hours and held for 1 hour. Thereafter, a seed crystal of Nd _1.92 Sr _1.08 Cu ₂ O _5.96 was used at 1080 ° C., and the seed crystal was arranged so that the normal of the board surface substantially coincided with the c-axis. Thereafter, the temperature was lowered to 1070 ° C. over 60 minutes, and further cooled gradually to 1045 ° C. over 120 hours for crystal growth. Subsequently, it was cooled to room temperature in 24 hours.
About the obtained cylindrical bulk material, both board surfaces were cut | disconnected, the surface layer was removed, and it was set as the bulk of about 10 mm in thickness. Subsequently, oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature was raised to 400 ° C. in 24 hours in an oxygen stream, and then gradually cooled from 400 ° C. to 280 ° C. over 100 hours. The temperature was further lowered from 280 ° C. to room temperature over 10 hours.
[0037]
The obtained crystal was a single crystal having a c-axis coincident with the normal of the board surface, similar to the seed crystal. When the trapped magnetic flux density was measured after cooling in a magnetic field at 77K and removing the external magnetic field, a good value of up to 0.75T was obtained.
[0038]
(Example 2)
Gd ₂ O ₃ , Sm ₂ O ₃ , BaO ₂ and CuO raw material powders are mixed so that the molar ratio of each metal element (Gd: Sm: Ba: Cu) is (7: 7: 17: 24). Further, 0.5% by mass of Pt and 10% by mass of Ag were added to this mixed powder to produce a mixed raw material powder. This raw material powder was calcined at 880 ° C. in an oxygen stream. This calcined powder was molded into a disk-shaped compact having a diameter of 45 mm and a thickness of 30 mm at a hydrostatic pressure of ² ton / cm ² .
[0039]
This was heated in 1 mol% nitrogen to 1150 ° C. over 8 hours and held for 1 hour. Thereafter, a seed crystal of Nd _1.3 Sr _1.7 Cu ₂ O _5.65 of several mm square at 1080 ° C. was used, and the seed crystal was arranged so that the normal line of the board surface substantially coincided with the c-axis. Thereafter, the temperature was lowered to 1010 ° C. in 120 minutes and further cooled gradually to 970 ° C. over 110 hours for crystal growth. Subsequently, it was cooled to room temperature in 24 hours. About the obtained cylindrical bulk material, both board surfaces were cut | disconnected, the surface layer was removed, and it was set as the bulk of 12 mm in thickness. Subsequently, oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature was raised to 500 ° C. in 24 hours in an oxygen stream, and then gradually cooled from 500 ° C. to 300 ° C. over 200 hours. The temperature was further lowered from 300 ° C. to room temperature over 10 hours.
[0040]
The obtained crystal was a single crystal having a c-axis coincident with the normal of the board surface, similar to the seed crystal. When the trapped magnetic flux density was measured after cooling in a magnetic field at 77K and removing the external magnetic field, a good value of up to 1.1T was obtained.
[0041]
(Example 3)
Each raw material powder of Y ₂ O ₃ , BaO ₂ and CuO is mixed so that the molar ratio of each metal element (Y: Ba: Cu) is (13:17:24), and further 0.2 mass% in this mixed powder Rh was added to prepare a mixed raw material powder. This raw material powder was calcined in an oxygen stream at 870 ° C. Twelve of the calcined powders were molded into a disk-shaped compact having a diameter of 50 mm and a thickness of 30 mm at a hydrostatic pressure of ² ton / cm ² .
[0042]
These are placed in a furnace at room temperature, and a seed crystal of Nd _1.9 Sr _1.05 Ba _0.05 Cu ₂ O _5.95 is used on the disk-shaped compact, and the seed crystal is aligned so that the normal of the surface of the disk approximately matches the c-axis. Arranged. Thereafter, the temperature was raised to 1120 ° C. in the atmosphere over 8 hours and held for 1 hour. Thereafter, the temperature was lowered to 1010 ° C. in 30 minutes, and further cooled gradually to 960 ° C. over 110 hours to carry out crystal growth. During this slow cooling, the difference between the maximum temperature and the minimum temperature in the furnace was about 40 ° C. Subsequently, it was cooled to room temperature in 24 hours. About the obtained 12 cylindrical bulk materials, both board surfaces were cut | disconnected, the surface layer was removed, and it was set as the bulk of thickness about 15mm. Subsequently, oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature was raised to 500 ° C. in 24 hours in an oxygen stream, and then gradually cooled from 450 ° C. to 400 ° C. over 100 hours. The temperature was further lowered from 400 ° C. to room temperature over 10 hours.
[0043]
All of the 12 crystals obtained were in the form of a single crystal having the c-axis coincident with the normal of the board surface, similar to the seed crystal. When the trapped magnetic flux density was measured after cooling in a magnetic field at 77K and removing the external magnetic field, a good material with an average maximum value of 1.28T was obtained.
[0044]
Example 4
Each raw material powder of Dy ₂ O ₃ , Er ₂ O ₃ , BaO ₂ and CuO is mixed so that the molar ratio of each metal element (Y: Ba: Cu) is (7: 7: 17: 24). 1.0% by mass of Ce was added to this mixed powder to produce a mixed raw material powder. This raw material powder was calcined in an oxygen stream at 870 ° C. Fifteen of the calcined powders were molded into a disk-shaped compact having a diameter of 50 mm and a thickness of 20 mm at a hydrostatic pressure of ² ton / cm ² .
[0045]
These were placed in a furnace at room temperature, and a seed crystal of La _1.79 Sr _1.19 Ba _0.02 Cu ₂ O _5.9 system was used on the disk-shaped compact, and the seed crystal was aligned so that the normal of the surface of the disk almost coincided with the c-axis. Arranged. Thereafter, the temperature was raised to 1120 ° C. in the atmosphere over 8 hours and held for 1 hour. Thereafter, the temperature was lowered to 1005 ° C. over 30 minutes, and further cooled gradually to 970 ° C. over 110 hours to carry out crystal growth. Subsequently, it was cooled to room temperature in 24 hours. About the obtained 15 cylindrical bulk materials, both board surfaces were cut | disconnected, the surface layer was removed, and it was set as the bulk of thickness about 15mm. Subsequently, oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature was raised to 500 ° C. in 24 hours in an oxygen stream, and then gradually cooled from 450 ° C. to 400 ° C. over 100 hours. The temperature was further lowered from 400 ° C. to room temperature over 10 hours.
[0046]
All of the 15 crystals obtained were in the form of single crystals having the c-axis coincident with the normal of the board surface, similar to the seed crystal. When the trapped magnetic flux density was measured after cooling in a magnetic field at 77K and removing the external magnetic field, a good material with an average maximum value of 1.2 T was obtained.
[0050]
【The invention's effect】
The present invention provides a seed crystal having a high melting point and a production method using the seed crystal having a high melting point, and a system having a relatively high crystal growth temperature (Nd, Sm, Eu system, etc.) The bulk material production yield is greatly improved, and the mass production of high-quality superconducting bulk materials in large furnaces, where temperature distribution is relatively difficult, is also facilitated for the production of other systems. The industrial effect is enormous.
[Brief description of the drawings]
FIG. 1 is a view showing a crystal structure of (Nd _1-y Sr _y ) ₃ Cu ₂ O _6-z .
[Explanation of symbols]
3 Sr partially substituted with Nd
4 Nd partially substituted with Sr
5 Pyramid block with 5 oxygens coordinated around Cu

Claims (5)

The seed crystal for producing RE ¹ Ba ₂ Cu ₃ O _7-x based superconductor (where RE ¹ is one or a combination of rare earth elements including Y) has a crystal structure of Sr ₃ Ti ₂ O ₇ type A seed crystal of an oxide superconducting material, comprising: A seed crystal for producing a RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is one or a combination of rare earth elements including Y) is (RE ² _{1- y My} ) _{3 Cu 2 O 6-z (RE} 2 is one or a combination of one or a combination of rare earth elements, and M is selected from alkaline earth metals including Y) (where 0 <y <1.0,1.35y- 0.45 <z <1.65y-0.55), a seed crystal of an oxide superconducting material. A seed crystal for producing a RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is one or a combination of rare earth elements including Y) is (Nd _1-y Sr _y ) ₃ Cu ₂ O _6-z (wherein y is in the range 0.3 ≦ y ≦ 0.4 or 0.5 ≦ y ≦ 0.7, 1.35y-0.45 <z <1.65y-0.55). REBa ₂ Cu ₃ O _7-x based superconductor (where RE is one or a combination of rare earth elements including Y) is melt-heated and cooled to cool the REBa ₂ Cu ₃ O _{7 Use} of the seed crystal according to any one of claims 1 to 3 in a method for producing an oxide superconductor in which a RE ₂ BaCuO ₅ phase or a RE ₄ Ba ₂ Cu ₂ O ₁₀ phase is dispersed in a _-x phase A method for producing an oxide superconducting material.   The method for producing an oxide superconducting material according to claim 4, wherein a melt heat treatment is performed after placing a seed crystal on the raw material compact.

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