JP2001233696A - Seed crystal of oxide superconductive material and method for producing oxide superconductive material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seed crystal for producing a high quality oxide superconductive bulk material in a large amount at a low cost, and to provide a method for producing the oxide superconductive bulk material using the seed crystal. SOLUTION: This seed crystal for the oxide superconductive material, characterized in that the seed for producing a REBa2Cu3O7-x-based superconductor (RE is one or more of rare earth elements including Y) is a crystal having a K2NiF4 or Sr3Ti2O7 type crystal structure. By the method for producing the oxide superconductive material using the seed crystal, the oxide superconductive material can be produced in a large amount in an improved production yield in high workability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seed crystal of a rare-earth oxide superconductor having a critical temperature of 90 K class and a method for producing an oxide superconductor using the same.

[0002]

BACKGROUND ART RE ₂ BaCuO ₅ phase is REBa ₂ Cu ₃ O _7-x (where RE is
The rare earth-based oxide superconductor finely dispersed in the rare earth element containing Y (or a combination thereof) has a higher magnetic flux pinning force than other oxide superconductors, and is particularly close to liquid nitrogen temperature (77K). Since the critical current density is high even at high temperatures, its use is expected. A small amount of Pt, Rh, Ce, etc. is added to the bulk material usually produced by the melting method,
Refinement of the RE ₂ BaCuO ₅ phase of about 1 μm has been performed. However, in this superconductor, the crystal grain boundaries must be highly oriented because the crystal grain boundaries significantly lower the critical current density.

The melting method represented by the QMG (Quench and Melt Growth) method (Japanese Patent Application Laid-Open No. 2-153803, Japanese Patent Application Laid-Open No. 5-139938, etc.) is a method of once using RE ₂ BaCuO ₅ phase or RE ₄ Ba ₂ Cu _The temperature was raised to the temperature range where the ₂ O ₁₀ phase and the liquid phase mainly composed of Ba-Cu-O coexisted, and this was cooled to just above the peritectic temperature at which REBa ₂ Cu ₃ O _7-x was formed. In this method, crystal growth is performed by performing slow cooling from the substrate to control nucleation and crystal orientation to obtain a large bulk material including a single crystal grain.

[0004] Peritectic temperature disclosed in JP-A-5-93938
Seeding method for growing crystals using seed crystals with high
Now, the seed that we are going to produce is RE^IBa_TwoCu_ThreeO_7-xSystem oxidation
RE with higher melting point (peritectic temperature) than superconductor^IIBa_TwoCu_ThreeO_7-xsingle
Use a crystalline sample. RE^IBa_TwoCu_ThreeO_7-xOxide superconductivity
Raw material precursor^IBa_TwoCu_ThreeO_7-xPeritectic temperature and RE^IIBa _Two
Cu_ThreeO_7-xHeated to an intermediate temperature of the peritectic temperature of RE^IBa_TwoCu_ThreeO
_7-xIs disassembled and RE^I _TwoBaCuO _FivePhase or RE^I _FourBa_TwoCu_TwoO_TenPhase and Ba-C
The liquid phase containing u-O as the main component is coexisted, and the precursor is R
E^IIBa_TwoCu_ThreeO_7-xOne side of the crystal is brought into contact. Then RE^IBa
_TwoCu_ThreeO_7-xCool to the peritectic temperature of RE^IBa_TwoCu_ThreeO_7-xGenerated
However, by slow cooling near the peritectic temperature, the RE
^IIBa_TwoCu_ThreeO_7-xCrystal growth in the same orientation as the crystal orientation of the contact surface of
It is a way to make it.

[0005] RE-Ba-Cu disclosed in Japanese Patent Application Laid-Open No. Hei 9-156925
Method for producing -O type oxide _{superconductor, RE (Ba 1-y Sr} y) 2 Cu 3 O
_This is a method using an oriented seed crystal containing a _7-x phase (here, y takes a value of 0.01 to 1), except that the Ba element is replaced with the Sr element, but RE: Ba + Sr: The ratio of Cu is 1: 2: 3,
It has the same composition ratio as the oxide superconducting phase REBa ₂ Cu ₃ O _7-x .

[0006] In addition, the method of manufacturing an oxide superconducting bulk material disclosed in Japanese Patent Application Laid-Open No. 10-310498 discloses a method of reducing the peritectic temperature of REBa ₂ Cu ₃ O _7-x (gold,
After coating with silver, a rare earth element, etc.), heating and melting, and then performing a seeding operation in a cooling process.

As described above, the conventional melting method utilizes a slight difference in melting point between the raw material compact (precursor) and the seed crystal, and uses a rare earth oxide superconductor crystal having a high melting point as the seed crystal. By using or lowering the melting point of the raw material molded body, the temperature difference between the melting points of the raw material molded body and the seed crystal is secured to perform seeding.

However, the relatively high melting point of rare earths (N
(d, Sm, Eu) -based oxide superconductor bulk material is produced by using Nd-based or Nd-Sm-based oxide superconductor crystals with the highest melting point, and further adding silver or the like to the bulk material. Although the melting point of the bulk material is lowered to ensure a temperature difference between the melting point of the seed crystal and that of the bulk material, the temperature difference is only a few tens of degrees Celsius. Due to the slight inhomogeneity, the seed crystal was often melted or polycrystallized from the seed crystal, and it was difficult to stably produce a good bulk material.

In the production of bulk materials of rare-earth (Dy, Y, Ho, Er) -based oxide superconductors having a relatively low melting point of about 1000 ° C., a large number of heating furnaces are required for mass production. Mass production is achieved by arranging and heat-treating raw material compacts, but it is difficult to control the entire furnace interior to a temperature distribution within tens of degrees Celsius in a large furnace heated to about 1000 degrees Celsius. Despite processing in the same batch, depending on the arrangement position in the furnace, the seed crystal may be melted, or the raw material compact may not be melted, resulting in a low product yield. Was. In addition, inoculation of seed crystals at a high temperature of 1000 ° C. had to be repeated many times, and workability was not always good.

On the other hand, in the production of a relatively small oxide superconductor, a single crystal of MgO is used as a seed crystal. However, in this case, the probability of controlling the crystal orientation of the oxide superconductor is about 1/3, and the product yield is extremely low. As described above, the conventional method for manufacturing an oxide superconductor has a problem in that mass production of a superconducting material with good yield and stability cannot be performed.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a seed crystal having a sufficiently high melting point and capable of reliably controlling the crystal orientation of a bulk material, and having high workability using the seed crystal. An object is to provide a method for manufacturing an oxide superconducting material.

[0012]

As a result of intensive studies to solve the above problems, it has been found that even if a crystal having a crystal structure similar to that of a rare earth oxide superconductor is used as a seed crystal, a rare earth oxide The inventors have found that the crystal orientation of an oxide superconducting material can be controlled, and have completed the present invention.

That is, the present invention relates to (1) REBa_TwoCu_ThreeO_7-xsystem
Superconductor (where RE is one of the rare earth elements including Y or
The seed crystal for producing the combination is K_TwoNiF_FourType
Oxide characterized by having a crystal structure of
Seed crystal of superconducting material, (2) RE¹Ba_TwoCu_ThreeO_7-xSuperconductivity
Body (here RE¹Is one of the rare earth elements containing Y or
The seed crystal for producing the combination^Two _TwoCuO_Four(This
RE^TwoIs one or a combination of rare earth elements including Y
Seeding of oxide superconducting material, characterized in that
Akira, (3) RE¹Ba_TwoCu_ThreeO_7-xSystem superconductor (here, RE¹Is Y
One or a combination of rare earth elements containing
The seed crystal to make (RE^Two _1-yM_y)_TwoCuO_4-z(Here RE
^TwoIs one or a combination of rare earth elements containing Y, or
M is one or a group selected from alkaline earth metals
(0 <y <1.0, 0.9y <z <1.1y)
Seed crystal of oxide superconducting material, (4) RE¹Ba_Two
Cu_ThreeO_7-xSystem superconductor (here, RE¹Is a rare earth element containing Y
Seed crystal for producing one or a combination thereof)
But (Nd_1-ySr_y)_TwoCuO_4-z(Where 0 <y <0.75, 0.9y <z <
1.1y) a kind of oxide superconducting material, characterized in that
Crystal, (5) RE¹Ba_TwoCu_ThreeO_7-xSystem superconductor (here, RE¹Is
One or a combination of rare earth elements containing Y)
The seed crystal to make is Sr_ThreeTi_TwoO₇Has a type crystal structure
(6) a seed crystal of an oxide superconducting material, characterized in that:
RE¹Ba_TwoCu_ThreeO_7-xSystem superconductor (here, RE¹Is a rare earth containing Y
One or a combination of elements)
The seed crystal is (RE^Two _1-yM_y)_ThreeCu_TwoO_6-z(RE^TwoIs a rare earth containing Y
One or a combination of elements, and M is alkali
One or a combination of earth metals)
(However, 0 <y <1.0, 1.35y-0.45 <z <1.65y-0.55)
Seed crystal of oxide superconducting material characterized by (7) RE¹B
a_TwoCu_ThreeO_7-xSystem superconductor (here, RE¹Is a rare earth element containing Y
Or a combination thereof)
A crystal is (Nd_1-ySr_y)_ThreeCu_TwoO_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)
A seed crystal of an oxide superconducting material,
(8) REBa_TwoCu_ThreeO_7-xSuperconductor (where RE includes Y
Raw material molding of one or a combination of rare earth elements
The body is melted and heat-treated,
_TwoCu_ThreeO_7-xRE during the phase_TwoBaCuO_FivePhase or RE_FourBa_TwoCu_TwoO_TenPhase dispersed
In the method for producing a oxidized oxide superconductor, (1)
Characterized in that the seed crystal according to any one of (1) to (7) is used.
(9) A method for producing an oxide superconducting material,
Melt heat treatment after placing seed crystal on form
(8) A method for producing an oxide superconducting material according to (8).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS REBa_TwoCu_ThreeO_7-xPhase (where RE is Y
One or a combination of rare earth elements
_TwoBaCuO_FiveOr RE_FourBa_TwoCu_TwoO_TenOxide superconducting
In the manufacture of conductive materials, these materials are
It has a crystal growth temperature of about 900C to 900C. to this
On the other hand, La_TwoCuO_FourAnd (La_1-yBa_y)_TwoCuO_4-zEtc. K_TwoNiF_FourType tie
Materials with a crystalline structure have a crystal growth temperature of about 1300 ° C.
And (Nd_1-ySr_y)_ThreeCu_TwoO_6-zEtc. Sr _ThreeTi_TwoO₇Type crystal structure
The material has a crystal growth temperature of about 1160 ° C.
_TwoCu_ThreeO_7-xCrystal growth temperature difference of 100-200 ° C or more compared to phase
Having. This means that the seed crystals of these systems
REBa_TwoCu_ThreeO_7-x100-200 ° C or higher than the seed crystal of the system
Means endurance.

_{Further, La 2 CuO 4, (La} 1-y Ba y) 2 CuO 4-z and _{(Nd 1-y Sr y)} 3 Cu 2 O 6-z also constituent elements and rare earth oxide superconductor In addition to being almost the same, each crystal structure has a Cu-O plane formed by enclosing one Cu with four oxygens, similar to REBa ₂ Cu ₃ O _7-x . This allows
The lattice constant of the a-axis is about 3.8 °, which is very close to REBa ₂ Cu ₃ O _7-x . The crystal structure of la ₂ CuO ₄ in FIG. _{1, (Nd 1-y Sr} y) 3
Figure 2 shows the crystal structure of Cu ₂ O _6-z .

Further, (Nd, Ce) ₂ CuO _4-z and (Nd, Sr, C
e) ₂ CuO _4-z is a pyramid-like block in which octahedral blocks with 6 oxygens coordinated around Cu in La ₂ CuO ₄ are each formed with 5 oxygens coordinated around Cu, It also has a crystal structure in which four oxygen atoms coordinate around Cu and are replaced by planar blocks (Y. Tokura et al, Nature 337, P
345 and F. Izumi et at, Physica C 158, P440). In these crystal structures, as in REBa ₂ Cu ₃ O _7-x , one
There is a Cu-O plane formed by surrounding four oxygen atoms with Cu, and the lattice constant of the a-axis is about 3.8 °. Here, it is assumed that such a crystal structure is also included as a K ₂ NiF ₄ type crystal structure.

K ₂ such as RE ₂ CuO ₄ or (RE _1-y Ba _y ) ₂ CuO _4-z (where RE is a rare earth element such as Nd, Sm, Eu, Pr, and Gd)
Materials with a NiF type ₄ crystal structure are also
It is known that it does not decompose even at temperatures as high as about 1250C. Similarly _{also, (RE 1-y Sr y} ) 3 Cu 2 O 6-z ( where RE is
It is known that materials having a Sr ₃ Ti ₂ O ₇ type crystal structure such as La, Sm, Eu, Pr, and Gd) do not decompose even at a high temperature of about 1100 ° C. in the atmosphere.

For the above reasons, RE¹Ba_TwoCu_ThreeO_7-xPhase (here
RE¹Is one or a combination of rare earth elements including Y
During the RE¹ _TwoBaCuO_FiveOr RE¹ _FourBa_TwoCu_TwoO_TenAre dispersed
In the production of certain oxide superconducting materials, RE^Two _TwoCuO_Four, (R
E^Two _1-yBa_y)_TwoCuO_4-z, (RE^Two _1-ySr _y)_ThreeCu_TwoO_6-z(Here RE
^TwoIs one or a combination of rare earth elements containing Y)
Relatively high crystal growth by using
Production yield of bulk materials for systems with temperature (Nd, Sm, Eu)
Greatly improved, and also for the production of other systems,
Mass production becomes easy. Where RE¹And RE^TwoAre the same
It may be another rare earth element.

_{Further, RE 2 CuO 4, (RE} 1-y Ba y) 2 CuO 4-z and ^{_{(RE 2 1-y Sr y}} ) 3 Cu 2 O 6-z Besides, the Ba Sr, Ca, the Mg and the like, those obtained by partly or completely replacing Sr Ba, Ca, an element such as Mg, about what further was partially substituted with other elements Cu and O even, K ₂ NiF comprise essentially Cu Type ₄ and Sr ₃ Ti ₂ O
Those having a _7- type crystal structure are also effective as seed crystals.

Here, (RE^Two _1-yM_y)_TwoCuO_4-zOr (R
E^Two _1-yM_y)_ThreeCu_TwoO_6-z(Here RE^TwoIs a rare earth element containing Y
One or a combination thereof, and M is an alkaline earth metal
0 <y <
The value of 1.0 is for rare earth elements and alkaline earth metal ions.
Because the radius of the fan has almost the same size depending on the selection,
Being able to maintain a stable crystal structure even when widely substituted
According to Also, (RE^Two _1-yM _y)_TwoCuO_4-zThen 0.9y <z <1.1y, if
Kuha (RE^Two _1-yM_y)_ThreeCu_TwoO_6-zThen 1.35y-0.45 <z <1.65y-0.55
The reason is that if it exceeds this range, stable crystal structure
Can not be held.

Further, the _{(Nd 1-y Sr y)} 2 CuO 4-z 0 <y <
The reason for the 0.75, and the _{(Nd 1-y Sr y)} 3 Cu 2 O 6-z
The reason for setting 0.3 ≦ y ≦ 0.4 or 0.5 ≦ y ≦ 0.7 is that if the range is exceeded, the crystal structure cannot be stably maintained. For the same reason, the _{(Nd 1-y Sr y)} 2 CuO 4-z 0.9
y <z <1.1y or _{(Nd 1-y Sr y)} 3 Cu 2 O in _{6-z 1.35y-0.45,}
<z <1.65y-0.55.

Further, the fact that these elements are Nd and Sr will be 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 vicinity of the seed crystal. Even if such a phenomenon occurs, if the element is Nd or Sr, the REBa
_{Even if} the peritectic temperature (crystal growth starting temperature) of ₂ Cu ₃ O _7-x is raised, it does not decrease (the highest peritectic temperature among REBa ₂ Cu ₃ O _7-x Is NdBa ₂ Cu ₃ O _7-x , and the peritectic temperature hardly changes even if the Sr element is added to or replaced with NdBa ₂ Cu ₃ O _7-x ). In other words, if the seed crystal is composed of Nd and Sr elements, even if the constituent elements diffuse into REBa ₂ Cu ₃ O _7-x , the peritectic temperature near the crystal is high, and the REBa ₂ Since the peritectic temperature of Cu ₃ O _7-x is lowered as a lower limit, crystal growth can be progressed stably sequentially from the seed crystal, and the seed crystal is more preferable.

The REBa ₂ Cu ₃ O _7-x phase contains RE ₂ BaCuO ₅ phase or RE ₄ Ba
_In the method of manufacturing an oxide superconductor in which ₂ Cu ₂ O ₁₀ phase is dispersed, the raw material compact is melt-heat treated, and the seed crystal is grown at a relatively high temperature by performing crystal growth using the above-described seed crystal. , And mass production of a stable superconducting material with good yield becomes easy. Since the seed crystal withstands high temperatures, it is possible to perform the melting heat treatment after placing the seed crystal on the raw material compact, and the workability of mass production is further improved. It should be noted that R in the REBa ₂ Cu ₃ O _7-x phase
To further disperse the E ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase, add Pt, Rh, Ce, or the like, or to lower the peritectic temperature of REBa ₂ Cu ₃ O _7-x , Ag or the like may be added.

[0024]

EXAMPLES Example 1 Raw material powders of Sm ₂ O ₃ , BaO ₂ and CuO were mixed so that the molar ratio of each metal element (Sm: Ba: Cu) was (13:17:24). Further, 0.5% by mass of Pt was added to the mixed powder to prepare a mixed raw material powder. 900 of this raw material powder
Calcination was performed in an oxygen stream at ℃. This calcined powder was formed into a disc-shaped compact having a diameter of 30 mm and a thickness of 20 mm using a rubber press at a pressure of ² ton / cm ² .

This was heated in the air to 1150 ° C. in 8 hours and kept for 1 hour. Thereafter, a seed crystal of La ₂ CuO ₄ was used at 1080 ° C., and the seed crystal was arranged such that the normal to the board surface substantially coincided with the c-axis. Thereafter, the temperature was lowered to 1060 ° C. in 30 minutes, and then gradually cooled to 1040 ° C. over 120 hours to grow crystals. Subsequently, it was cooled to room temperature in 24 hours. With respect to the obtained cylindrical bulk material, both board surfaces were cut, and the surface layer was removed to obtain a bulk having a thickness of about 15 mm. Subsequently, an oxygen enrichment treatment was performed. Oxygen enrichment treatment is 500 ℃ in oxygen stream
, And gradually cooled from 400 ° C. to 250 ° C. over 100 hours. The temperature was further lowered from 250 ° C. to room temperature over 10 hours.

The obtained crystal was a single crystal in which the c-axis coincided with the normal of the board surface, similarly to the seed crystal.
After cooling in a magnetic field at 77K and removing the external magnetic field,
When the trapped magnetic flux density was measured, a good value of 0.7 T at the maximum was obtained.

(Example 2) Gd ₂ O ₃ , Sm ₂ O ₃ , BaO ₂ and CuO were mixed in a raw material powder having a molar ratio of each metal element (Gd: Sm: Ba: Cu) of (7: 7:
17:24), and 0.5% by mass of Pt and 10% by mass of Ag were added to the mixed powder to prepare a mixed raw material powder. This raw material powder was calcined at 880 ° C. in an oxygen stream. The calcined powder was converted to ² ton / cm ² using a rubber press.
At a pressure of 40 mm to form a disc-shaped molded body having a diameter of 40 mm and a thickness of 20 mm.

This was heated to 1150 ° C. in nitrogen of 1 mol% of oxygen for 8 hours and kept for 1 hour. Then, at 1060 ° C, several mm
A seed crystal of (Sm _0.95 Ba _0.05 ) ₂ CuO _{3.95 at} the corner was used, and the seed crystal was arranged such that the normal of the board surface almost coincided with the c-axis. Thereafter, the temperature was lowered to 1010 ° C. in 30 minutes, and then gradually cooled to 970 ° C. over 110 hours to grow crystals. Then 24 hours to room temperature
Cooled in time. With respect to the obtained cylindrical bulk material, both board surfaces were cut, and the surface layer was removed to obtain a bulk having a thickness of about 15 mm. Subsequently, an 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 gradually cooled from 400 ° C. to 300 ° C. over 100 hours. Further, the temperature was lowered from 300 ° C. to room temperature over 10 hours.

The obtained crystal was a single crystal in which the c-axis coincided with the normal of the board surface, similarly to the seed crystal.
After cooling in a magnetic field at 77K and removing the external magnetic field,
When the trapped magnetic flux density was measured, a good value of up to 1.2 T was obtained.

(Example 3) Each raw material powder of Y ₂ O ₃ , BaO ₂ and CuO was mixed so that the molar ratio of each metal element (Y: Ba: Cu) became (13:17:24). Further, 0.2% by mass of Rh was added to the mixed powder to prepare a mixed raw material powder. 870
Calcination was performed in an oxygen stream at ℃. Using a rubber press machine, 50 pieces of the calcined powder were formed into a disk-shaped formed body having a diameter of 50 mm and a thickness of 20 mm at a pressure of ² ton / cm ² .

These were placed in a furnace at room temperature, and a seed crystal was placed on a disk-shaped compact using a Nd _0.67 Sr _1.33 CuO _3.33 seed crystal so that the normal of the board face almost coincided with the c-axis. did.
Thereafter, the temperature was raised to 1120 ° C. in the air in 8 hours and maintained for 1 hour. Thereafter, the temperature was lowered to 1010 ° C in 30 minutes, and further 960 ° C.
The solution was gradually cooled to 110 ° C. over 110 hours to grow a crystal. During the 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. Got
For 50 cylindrical bulk materials, cut both panels
The surface layer was removed to obtain a bulk having a thickness of about 15 mm. continue,
An oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature is raised to 500 ° C in 24 hours in an oxygen stream, and from 450 ° C to 400 ° C in 1 hour.
The solution was slowly cooled over 00 hours. The temperature was further lowered from 400 ° C. to room temperature over 10 hours.

As with the seed crystal, all of the obtained 50 crystals were single crystals in which the c-axis coincided with the normal of the board surface. After cooling in a magnetic field at 77K and removing the external magnetic field, the trapped magnetic flux density was measured. As a result, a good material having an average maximum value of 1.2T was obtained.

As a comparative example, the following experiment was conducted.
According to the method described above, 50 disk-shaped molded bodies were formed and similarly placed in a furnace. Thereafter, the temperature was raised to 1120 ° C. in the air in 8 hours and maintained for 1 hour. The temperature was further lowered to 1040 ° C. in 30 minutes, and the temperature was maintained for 30 minutes. During that time, a NdBa ₂ Cu ₃ O _7-x type seed crystal was arranged such that the normal line of the board surface almost coincided with the c-axis. The temperature was further lowered to 1010 ° C. in 30 minutes, and then gradually cooled to 960 ° C. over 110 hours to grow crystals. It was further cooled to room temperature in 24 hours.

Thirteen of the 50 obtained materials had evidence of melting of seed crystals and were polycrystalline. The remaining 37
As in the case of the seed crystal, a single crystal in which the c-axis coincided with the normal of the board surface was obtained. When the trapped magnetic flux density was similarly measured for these, the average of the maximum values was 1.0T.

(Example 4) Each raw material powder of Sm ₂ O ₃ , BaO ₂ and CuO was mixed so that the molar ratio of each metal element (Sm: Ba: Cu) became (12:18:26), Further, 0.5 mass% of Pt was added to the mixed powder to prepare a mixed raw material powder. 900 of this raw material powder
Calcination was performed in an oxygen stream at ℃. This calcined powder is hydrostatic pressure 2ton
It was molded at a pressure of / cm ² into a disc-shaped compact having a diameter of 30 mm and a thickness of 20 mm.

The temperature was raised to 1150 ° C. in the air in 8 hours and maintained for 1 hour. Then, at 1080 ° C, Nd _1.92 Sr _1.08 Cu ₂
A seed crystal of O _5.96 was used, and the seed crystal was arranged such that the normal of the board surface substantially coincided with the c-axis. Thereafter, the temperature was lowered to 1070 ° C. in 60 minutes, and then gradually cooled to 1045 ° C. over 120 hours to grow crystals. Then, it cooled to room temperature in 24 hours. With respect to the obtained cylindrical bulk material, both board surfaces were cut, and the surface layer was removed to obtain a bulk having a thickness of about 10 mm. Subsequently, an oxygen enrichment treatment was performed. Oxygen enrichment treatment is performed in an oxygen stream.
The temperature was raised to 400 ° C. in 24 hours, and gradually cooled from 400 ° C. to 280 ° C. over 100 hours. Further, the temperature was lowered from 280 ° C. to room temperature over 10 hours.

The obtained crystal was a single crystal in which the c-axis coincided with the normal of the board, similarly to the seed crystal.
After cooling in a magnetic field at 77K and removing the external magnetic field,
When the trapped magnetic flux density was measured, a good value of up to 0.75T was obtained.

Example 5 Each raw material powder of Gd ₂ O ₃ , Sm ₂ O ₃ , BaO ₂ and CuO was mixed with a metal element at a molar ratio (Gd: Sm: Ba: Cu) of (7: 7:
17:24), and 0.5% by mass of Pt and 10% by mass of Ag were added to the mixed powder to prepare a mixed raw material powder. This raw material powder was calcined at 880 ° C. in an oxygen stream. Diameter 45m The calcined powder at a pressure of hydrostatic pressure 2 ton / cm ²
m, and formed into a disk-shaped molded body having a thickness of 30 mm.

This was heated in nitrogen of 1 mol% of oxygen to 1150 ° C. for 8 hours and kept for 1 hour. Then, using a seed crystal of Nd _1.3 Sr _1.7 Cu ₂ O _5.65 of several mm square at 1080 ° C., the normal of the board surface is c
The seed crystal was arranged so as to substantially coincide with the axis. After 10
The temperature was lowered to 10 ° C. in 120 minutes, and then gradually cooled to 970 ° C. over 110 hours to grow crystals. Subsequently, it was cooled to room temperature in 24 hours. With respect to the obtained cylindrical bulk material, both board surfaces were cut, and the surface layer was removed to obtain a bulk having a thickness of 12 mm.
Subsequently, an oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature is raised to 500 ° C in 24 hours in an oxygen stream,
The mixture was gradually cooled to 200 ° C over 200 hours. The temperature was further lowered from 300 ° C. to room temperature over 10 hours.

The obtained crystal was a single crystal in which the c-axis coincided with the normal of the board surface, similarly to the seed crystal.
After cooling in a magnetic field at 77K and removing the external magnetic field,
When the trapped magnetic flux density was measured, a good value of up to 1.1 T was obtained.

(Example 6) Each raw material powder of Y ₂ O ₃ , BaO ₂ and CuO was mixed so that the molar ratio of each metal element (Y: Ba: Cu) became (13:17:24). Further, 0.2% by mass of Rh was added to the mixed powder to prepare a mixed raw material powder. 870
Calcination was performed in an oxygen stream at ℃. This calcined powder is hydrostatic pressure 2ton
At a pressure of / cm ² , 12 disc-shaped compacts having a diameter of 50 mm and a thickness of 30 mm were formed.

[0042] These were placed in a furnace at room temperature, using a _{Nd 1.9 Sr 1.05 Ba 0.05 Cu 2} O 5 .9 5 based seed crystal on the shaped product, the normal of the disk surface substantially coincides with the c-axis The seed crystals were arranged as follows. Thereafter, the temperature was raised to 1120 ° C. in the air in 8 hours and maintained for 1 hour. After that, the temperature dropped to 1010 ° C in 30 minutes,
Further, the crystal was gradually cooled to 960 ° C. over 110 hours to grow a crystal. During this slow cooling, the difference between the maximum and minimum temperature in the furnace is 40
° C. Subsequently, it was cooled to room temperature in 24 hours.
With respect to the obtained 12 columnar bulk materials, both board surfaces were cut, and the surface layer was removed to obtain a bulk having a thickness of about 15 mm.
Subsequently, an oxygen enrichment treatment was performed. In the oxygen enrichment treatment, the temperature is raised to 500 ° C in 24 hours in an oxygen stream, and from 450 ° C.
The mixture was gradually cooled to 400 ° C. over 100 hours. The temperature was further lowered from 400 ° C. to room temperature over 10 hours.

As with the seed crystal, all of the obtained twelve crystals were obtained as single crystals in which the c-axis coincided with the normal of the board surface. After cooling in a magnetic field at 77K and removing the external magnetic field, the trapped magnetic flux density was measured. As a result, a good material having an average maximum value of 1.28T was obtained.

Example 7 Dy ₂ O ₃ , Er ₂ O ₃ , BaO ₂ and CuO were mixed with each other at a molar ratio of each metal element (Y: Ba: Cu) of (7: 7: 17: 2
4) and further added to this mixed powder at 1.0% by mass.
Ce was added and a mixed raw material powder was produced. This raw material powder was calcined at 870 ° C. in an oxygen stream. Fifteen pieces of this calcined powder were formed into a disk-shaped formed body 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, using _{La 1.79 Sr 1.19 Ba 0.02 Cu 2} O 5. 9 based seed crystal on the shaped product, the normal of the disk surface substantially coincides with the c-axis The seed crystals were arranged as follows. Thereafter, the temperature was raised to 1120 ° C. in the air in 8 hours and maintained for 1 hour. After that, the temperature dropped to 1005 ° C in 30 minutes,
Further, it was gradually cooled to 970 ° C. over 110 hours to grow a crystal. Subsequently, it was cooled to room temperature in 24 hours. With respect to the obtained fifteen cylindrical bulk materials, both board surfaces were cut, and the surface layer was removed to obtain a bulk having a thickness of about 15 mm. Subsequently, an oxygen enrichment treatment was performed. In the oxygen enrichment treatment, in an oxygen stream, the temperature is raised to 500 ° C. in 24 hours, and from 450 ° C. to 400 ° C.
Slowly cooled over time. The temperature was further lowered from 400 ° C. to room temperature over 10 hours.

As with the seed crystal, all of the obtained fifteen crystals were single crystals in which the c-axis coincided with the normal of the board surface. After cooling in a magnetic field at 77K and removing the external magnetic field, the trapped magnetic flux density was measured. As a result, a good material having an average maximum value of 1.2T was obtained.

Example 8 Each of the raw material powders of Dy ₂ O ₃ , Er ₂ O ₃ , BaO ₂ and CuO was mixed with each other at a molar ratio of each metal element (Y: Ba: Cu) of (7: 7: 17: 2).
4) and further added to this mixed powder at 1.0% by mass.
Ce was added and a mixed raw material powder was produced. This raw material powder was calcined at 870 ° C. in an oxygen stream. This calcined powder was dried at a pressure of ² ton / cm2 using a rubber press machine to a diameter of 50 mm and a thickness of 50 mm.
50 pieces were molded into a 20 mm disc-shaped molded body.

These were placed in a furnace at room temperature, and Nd _0.05 La _0.95 SrCuO _3.5 series seed crystal was used on the disc-shaped molded body, and the seed crystal was placed so that the normal line of the board surface almost coincided with the c-axis. . Thereafter, the temperature was raised to 1120 ° C. in the air in 8 hours and maintained for 1 hour. Thereafter, the temperature was lowered to 1005 ° C. in 30 minutes, and then gradually cooled to 970 ° C. over 110 hours to grow crystals. continue,
Cooled to room temperature in 24 hours. For the obtained 50 cylindrical bulk materials, both board surfaces were cut and the surface layer was removed.
The bulk was about 15 mm thick. Subsequently, an oxygen enrichment treatment was performed. Oxygen enrichment treatment is up to 500 ° C in oxygen stream.
The temperature was raised in 4 hours and 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.

All of the 50 obtained crystals were single crystals in which the c-axis coincided with the normal of the board surface, like the seed crystal. After cooling in a magnetic field at 77K and removing the external magnetic field, the trapped magnetic flux density was measured. As a result, a good material having an average maximum value of 1.2T was obtained.

[0050]

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.) bulk material production yield is greatly improved, and also for the production of other systems,
This facilitates mass production of high-quality superconducting bulk material in a large furnace where it is relatively difficult to make the temperature distribution uniform, and its industrial effect is enormous.

[Brief description of the drawings]

Fig. 1 Crystal structure of La ₂ CuO ₄

[2] _{(Nd 1-y Sr y)} 3 Cu 2 O 6-z crystal structure

[Explanation of symbols]

1 An octahedral block with six oxygens coordinated around La or Ba 2 Cu 3 Five oxygens coordinated around Nd 5 Cu partially substituted with Sr 4 Sr partially substituted with Nd Pyramid block

Claims (9)

[Claims] 1. A seed crystal for producing a REBa ₂ Cu ₃ O _7-x- based superconductor (here, RE is one of rare earth elements including Y or a combination thereof) has a K ₂ NiF ₄ type crystal structure. A seed crystal of an oxide superconducting material, which is a crystal having the following. 2. RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is Y
The seed crystal for producing the rare earth element containing one or a combination thereof is RE ² ₂ CuO ₄ (where RE ² is one or a combination of rare earth elements including Y). Seed crystal of oxide superconducting material. 3. An RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is Y
One or seed crystal for producing the combination) _{^{is, (RE 2 1-y M}} y) 2 CuO 4-z ( wherein RE ² of the rare earth elements including Y-
One or a combination of rare earth elements containing
Is a kind selected from an alkaline earth metal or a combination thereof (provided that 0 <y <1.0, 0.9y <z <1.1y), wherein the seed crystal is a seed crystal of an oxide superconducting material. 4. RE ¹ Ba ₂ Cu ₃ O _7-x- based superconductor (where RE ¹ is Y
Seed crystals for the manufacture of one or a combination thereof) of rare earth elements including _{the, (Nd 1-y Sr y} ) 2 CuO 4-z ( where 0 <y <0.
75, a seed crystal of an oxide superconducting material, wherein 0.9y <z <1.1y). 5. An RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is Y
). A seed crystal of an oxide superconducting material, characterized in that the seed crystal for producing (a) a rare earth element or a combination thereof contains a Sr ₃ Ti ₂ O ₇ type crystal structure. 6. An RE ¹ Ba ₂ Cu ₃ O _7-x- based superconductor (where RE ¹ is Y
(RE ² _{1- y My} ) ₃ Cu ₂ O _6-z (RE ² is a rare earth element containing Y or one of the rare earth elements containing Y). A combination, or M is one or a combination of alkaline earth metals or a combination thereof (where 0 <y <1.0, 1.35y-0.45 <z <1.65y-0.55), and the oxide superconducting material is characterized in that: Seed crystal. 7. An RE ¹ Ba ₂ Cu ₃ O _7-x superconductor (where RE ¹ is Y
Seed crystals for the manufacture of one or a combination thereof) of rare earth elements including _{the, (Nd 1-y Sr y} ) 3 Cu 2 O 6-z ( where the range of y is 0.3 ≦ y ≦ 0.4 or 0.5 ≦ y ≤0.7, 1.35y-0.45 <z <1.6
5y-0.55) A seed crystal of an oxide superconducting material, characterized in that: 8. A raw material molded body of a REBa ₂ Cu ₃ O _7-x- based superconductor (here, RE is one or a combination of rare earth elements including Y) is subjected to a melting and heat treatment and cooled to obtain a R
The 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 an EBa ₂ Cu ₃ O _7-x phase, according to any one of claims 1 to 7, A method for producing an oxide superconducting material, comprising using a seed crystal. 9. The method for producing an oxide superconducting material according to claim 8, wherein a melt heat treatment is performed after placing a seed crystal on the raw material compact.