JP2001342020A - Method of preparing rare earth oxide super-conductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of preparing a rare earth oxide super-conductor having high density and high strength. SOLUTION: This method comprises the steps of preparing a rare earth oxide super-conductor preparatively heat treated under oxygen atmosphere or under vacuum, and melting it to grow. More specifically, this method comprises the steps of mixing the materials containing the constituting elements of the rare earth oxide super-conductor in a prescribed ratio, forming the mixture to obtain a preparative formed body, heat treating the preparative formed body in vacuum or in an atmosphere consisting of oxygen only to obtain a preparative sintered compact, pyrolyzing the preparative sintered compact at a temperature below the foaming threshold value of oxygen, and melting to grow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bulk rare earth (RE) -based oxide superconductor manufactured by a melt growth method, and more particularly to a method for improving the density of an oxide superconductor by improving the density thereof. Regarding the technology for increasing the strength, the oxide superconductor obtained in the present invention can be applied to a superconducting bearing, a superconducting magnetic carrier, a superconducting permanent magnet, a superconducting magnetic shield, and the like.

[0002]

2. Description of the Related Art In recent years, in order to realize application of a bulk oxide superconductor to a flywheel, a linear motor car, and the like, a bulk superconductor having higher performance is desired.
As this bulk superconductor, a REBa ₂ Cu ₃ O _y -based superconductor (may be abbreviated as RE123) is considered promising. The repulsion between the oxide superconductor and the permanent magnet required for these applications is proportional to the critical current density (Jc) and the size of the shielding current loop (R) flowing in the oxide superconductor, so that a higher performance is obtained. To produce a bulk oxide superconductor, it is necessary to increase the critical current density and the shielding current loop.

Hitherto, as a method of improving the critical current density of an oxide superconductor, a factor that causes a weak coupling such as a grain boundary or a crack that hinders a current flow has been removed as much as possible. Furthermore, it is known that the critical current density of an oxide superconductor generally has a crystal orientation dependency, and that in a low magnetic field, the critical current density becomes maximum in an orientation parallel to the c-axis of the crystal of the REBa ₂ Cu ₃ O _y -based oxide superconductor. Have been. on the other hand,
It is said that in order to increase the shielding current loop, it is necessary to increase the particle size of the crystal of the oxide superconductor.

[0004] In addition, the technology for controlling the crystal orientation of an oxide superconductor has been advanced, and a large single-domain bulk material has come to be obtained by the development of a method of performing melt growth using a seed crystal under a temperature gradient. ing.

[0005] In principle, these large bulk oxide superconductors can capture a magnetic field exceeding 5 T (tesla) at the temperature of liquid nitrogen (77 K). Further, as a method for realizing these, the MPMG method
(Melt-Powder-Melt-Growth) [H. Fujimoto et.al .: ADV.
In Supercond. II65 (1990) 285], OCMG method (Oxgen-Co
ntrolled-Melt-Growth) [SIYoo et al .: Appl, Phys.
Lett. 65 (1994) 633]. The melt growth method is a method in which a raw material powder is molded into a predetermined shape by a uniaxial molding press or a cold isostatic press using a metal mold, and a precursor (molded body) of a rare earth oxide superconductor is formed. Is obtained, the precursor of the rare-earth oxide superconductor is temporarily converted to the thermal decomposition temperature (R
This is a method of heating to a temperature higher than the melting point according to the composition of the E123 composition) and then cooling it to a temperature lower than the thermal decomposition temperature to crystallize it. This is a large bulk rare earth oxide superconducting crystal in which weak bonds are eliminated. It is known as a method by which the body can be obtained.

In the above-described melt growth method, it is necessary to change the oxygen partial pressure in accordance with the composition of the rare earth oxide superconductor to be used. Tend to be processed inside. However, an RE123-based material (for example, L
a, Nd, Sm, Eu, and Gd), when a sample is prepared in an atmosphere having a high oxygen partial pressure, rare-earth element ions replace Ba ions to form a solid solution and deteriorate the superconducting properties. When a rare earth oxide superconductor sample is prepared using an element, formation of a solid solution is performed by performing melt growth under a low oxygen partial pressure. In addition, in order to improve the mechanical properties of the rare-earth oxide superconductor, the second phase (RE
It has been reported that mechanical properties such as fracture toughness can be improved by adding about 10% by weight of silver and 211 phase or RE422 phase). [For example, JP.Sh
igh et al. J. Appl. Phys. 66 (1989) 3154]

[0007]

In order for the bulk rare earth oxide superconductor to capture a high magnetic field, the critical current density must be improved, the oxide superconductor itself must be increased in size, Strengthening is considered essential. For example, in order to increase the strength of a rare-earth oxide superconductor, the above-mentioned second phase, silver, and the like are excessively added. There are a large number of vacancies inside the rare-earth oxide superconductor, and these large vacancies are likely to be a source of destruction and cause a decrease in strength, which is lower than the trapped magnetic field predicted from electromagnetic force calculations There was a problem that a tensile stress due to the Lorentz force acts on the trapped magnetic field, and the oxide superconductor is broken.

[0008] The main causes of the formation of such vacancies are, in addition to the residual atmospheric gas such as nitrogen or argon which does not diffuse inside the oxide superconductor, a large amount of the voids are generated during the thermal decomposition of the rare-earth oxide superconductor. It is considered that foaming due to the generated oxygen gas is the cause. Therefore, it is necessary to increase the density of the bulk oxide superconductor and to increase the strength by minimizing vacancies generated to eliminate these causes as much as possible.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method capable of manufacturing a rare earth oxide superconductor having a high density and a high strength. I do.

[0010]

SUMMARY OF THE INVENTION The production method of the present invention has been made in view of the above-mentioned circumstances, and in a method of producing a rare earth (RE) -based oxide superconductor by a melt growth method, it has been previously conducted under an oxygen atmosphere or a vacuum. A pre-sintered body of the rare-earth-based oxide superconductor preliminarily heat-treated in step (1), and then melt-grown. Unnecessary element gas inside the pre-sintered body by heat-treating the pre-formed body in a vacuum atmosphere or an atmosphere containing only oxygen to form a pre-sintered body,
For example, a pre-sintered body can be obtained without nitrogen gas or the like. By performing melt growth on the basis of this pre-sintered body, it is possible to obtain a rare-earth oxide superconductor in a state in which foaming by gas other than oxygen and foaming by oxygen gas are suppressed. The rare-earth-based oxide superconductor manufactured in this manner has few pores inside, or is sufficiently fine even if there are pores, and has a high density and a high strength. You. In addition, the production method of the present invention has been made in view of the above circumstances, and a material containing a constituent element of a rare-earth (RE) -based oxide superconductor is mixed at a predetermined ratio and molded to obtain a preformed body. After heat-treating the pre-formed body in a vacuum atmosphere or an atmosphere containing only oxygen to obtain a pre-sintered body, the pre-sintered body is thermally decomposed at a temperature equal to or lower than a foaming threshold, and then melted. It is characterized by growing.

[0011] In the present invention, the threshold value of the oxygen foaming is determined by adding the thermal decomposition temperature of the rare earth oxide superconductor in pure oxygen +
It can be set to 50 ° C. By performing the thermal decomposition at the temperature set in this way and then performing the melt growth, it is possible to obtain a high-strength rare earth-based oxide superconductor having no large holes or having only fine holes.

The preparation process of the present invention has been made in view of the above circumstances, as the rare earth-based oxide superconductor, the composition formula _{RE 1 + x1 Ba 2-x1} Cu 3 O y ( provided that shows the composition ratio x1
Satisfies the relationship of 0.1 ≦ x1 ≦ 0.3) as a mother phase, and a RE ₂ BaCuO ₅ phase or RE ′ _{4-2 × 2} B
a _{2 + 2x2} Cu _2-x2 O _10-2x2 phase (where RE 'is La, N
x2 indicating either one or both of d and indicating the composition ratio
Which satisfies the relationship of 0 ≦ x2 ≦ 0.8). RE _{1 + x1} Ba
_The matrix represented by _2-x1 Cu ₃ O _y is used as the RE ₂ BaC
uO ₅ phase or RE ' _4-2x2 Ba _{2 + 2x2} Cu _2-x2 O _10-2x2
The strength is improved by containing an appropriate amount of the phase.

[0013] The production method of the present invention has been made in view of the above circumstances.
d, Sm, Eu, Gd, Dy, Ho, Y, Er, Yb,
It is characterized by using a rare earth oxide superconductor containing one or more rare earth elements of Tm and Lu. If it is an oxide superconductor containing these rare earth elements, it can be brought into a superconducting state by cooling with liquid nitrogen, and an oxide superconductor having excellent superconducting state stability and a high trapping magnetic field can be obtained. .

The production method of the present invention has been made in view of the above circumstances, and is characterized in that in the production method described above, a material having a density of 90% or more of the theoretical density is used as the pre-sintered body. I do. If the pre-sintered body has a theoretical density of more than 90%, the number of pores and gas in the pre-sintered body is sufficiently reduced. Therefore, when a rare earth oxide superconductor is produced from this pre-sintered body by melt growth, A high-density, high-strength rare-earth-based oxide superconductor having few voids therein can be obtained.

The production method of the present invention has been made in view of the above-mentioned circumstances. In the above-mentioned production method, the preliminary sintered body has no voids or a preliminary air-filled void filled with only oxygen. It is characterized by using a sintered body. If there is no void in the pre-sintered body, or if a pre-sintered body in which only the enclosed voids are filled with oxygen is used, a gas such as nitrogen or argon is used to melt the rare-earth oxide superconductor. While gas components having low solubility in the liquid portion can be eliminated as much as possible, only oxygen that can be easily dissolved in the melt portion of the rare earth oxide superconductor and can diffuse inside can be contained in the pre-sintered body. Therefore, when the pre-sintered body is melt-grown, there is little possibility that voids are generated due to the presence of unnecessary gas.

The production method of the present invention has been made in view of the above circumstances, and in the above-mentioned production method, the temperature at the time of the melt growth is not lower than the thermal decomposition temperature of the rare earth oxide superconductor used. The temperature is set within a range not exceeding the threshold value for foaming. By performing the melt growth at a temperature not lower than the thermal decomposition temperature and not exceeding 50 ° C. from the foaming threshold value during the melt growth, the melt growth is smoothly performed.

The production method of the present invention has been made in view of the above circumstances, and is characterized in that, in the production method described above, the melt growth is performed using a seed crystal. Making the whole pre-sintered body into a high-density, high-strength bulk rare-earth oxide superconductor by bringing the seed crystal into contact with the pre-sintered body and performing melt growth from the contact portion in the previous manufacturing method Can be.

The production method of the present invention has been made in view of the above circumstances. In the above-mentioned production method, the material containing the constituent elements of the rare earth (RE) -based oxide superconductor is made of Ag and Au as dispersed phases. Characterized in that one or both of them are added in an amount of 30% by weight or less. The manufacturing method of the present invention has been made in view of the above circumstances, and in the above-described manufacturing method, the material containing the constituent element of the rare earth (RE) -based oxide superconductor is one of Pt and CeO ₂ or It is characterized in that both are added in an amount of 2% by weight or less. The manufacturing method of the present invention has been made in view of the above circumstances, and in the manufacturing method described above, the material containing the constituent elements of the rare earth (RE) -based oxide superconductor is made of Zr, Sn, Ti, Z
One or more of the n Ba compounds are added in an amount of 30% by weight or less. Ag or A described above
u, or Pt or CeO ₂ , or Zr, S
By adding a predetermined amount of at least one of Ba compounds of n, Ti and Zn, the strength of the rare earth oxide superconductor is improved.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
However, the present invention is limited to the embodiments described below.
It is not specified. Obtain in the production method of the present invention
Bulk rare earth oxide superconductors are rare earth
When the class element is expressed as RE, it is represented by the following composition formula.
The main phase is the main phase. RE_{1 + x1}Ba_2-x1Cu
_ThreeO_y(However, x1 indicating the composition ratio is a relation of 0.1 ≦ x1 ≦ 0.3.
Satisfy RE, La is Nd, Sm, Eu, Gd, D
one of y, Ho, Y, Er, Yb, Tm, and Lu
Or two or more types. In addition, in addition to the matrix component represented by the above composition formula, a second phase and
RE_TwoBa₁Cu ₁O_FivePhase (R211 phase) or
Is RE 'as the second phase_4-2x2Ba_{2 + 2x2}Cu_{2-x Two}O
_10-2x2Phase (R422 phase) (However, RE 'is La, Nd
And either or both of them, and 0 ≦ x ≦ 0.3)
It may contain 50% or less and 0% or more. Above
RE_{1 + x1}Ba_2-x1Cu_ThreeO_yAnd a second phase having the following composition:
RE_TwoBa₁Cu₁O_FiveAs a mixture of phases
Rare earth-based oxide superconductors have RE as the second phase._TwoB
a₁Cu₁O_FiveMagnetic phase pinning due to phase dispersion and miniaturization
Function to increase the trapped magnetic field by functioning as a center
Play.

Further, in addition to these components, one or both of Ag and Au are used as a dispersed phase in an amount of 30% by weight.
The following may be used. These elements penetrate into defects such as vacancies and cracks during melt growth and block the vacancies and cracks, and contribute to improving the strength of the resulting rare earth oxide superconductor. Is an element having low reactivity with, but if the added amount exceeds 30% by weight, the magnetic properties may be deteriorated. Further, in addition to the above components, one or both of Pt and CeO ₂ may be added in an amount of 0.5% by weight or more and 2% by weight or less. These elements are added to the R phase prior to being added as a second phase to improve the strength.
E ₂ BaCuO ₅ phase (R211 phase) or RE ′ _{4
-2x2 Ba2 + 2x2 Cu2 - x2O10-2x2} phase (R422 phase) is added in order to suppress the grain growth, but if the added amount exceeds 2% by weight, the magnetic properties may be deteriorated. There is. In addition to the above components, Zr, Sn, Ti, Zn
Compounds in which one or more of the a compounds are added in an amount of 30% by weight or less may be used. Addition of these elements has a smaller particle size as a powder to be added, which has an effect on stress relaxation, and contributes to an improvement in the strength of the bulk rare earth oxide superconductor obtained.

Next, an example of a method for producing a rare earth oxide superconductor having these compositions will be described. "Raw material powder adjusting step" To manufacture a rare earth-based oxide superconductor, first, raw material powders of elements necessary for a target composition are prepared. Specifically, an oxide powder of an individual element constituting the target rare earth oxide superconductor, a carbonate powder, or the like, more specifically, an oxide powder of a rare earth element and Ba
Oxide powder or carbonate powder, and Cu oxide powder. Once these raw material powders are prepared, some of the necessary elements are excessively added so as to have the above-mentioned composition ratio, or in consideration of the disappearance during melting or the precipitation state of components during melt diffusion. The raw material powders are mixed so as to have a composition ratio that is slightly or slightly added.

For example, when manufacturing a rare earth-based oxide superconductor having a composition ratio of Y _1.8 Ba _2.4 Cu _3.4 O _y , Y: B
It is preferable to mix at a ratio of a: Cu = 1.8: 2.4: 3.4, and when producing a rare earth oxide superconductor having a composition ratio of (SmGd) _1.2 Ba _2.1 Cu _3.1 O _y , (S
It is preferable to use a mixture of (m, Gd): Ba: Cu = 1: 2: 3. In addition, when adding an element as a dispersed phase to the rare-earth oxide superconductor or when adding an element for improving strength or the like, a powder of the added element is mixed in this raw material powder mixing stage. For example, Ag
When Au or Au is added, these elemental element powders or Ag ₂
O powder may be added in an amount of 30% by weight or less. For example, one or both of Pt powder and CeO ₂ powder may be added in an amount of 2% by weight.
It is sufficient to add at least 30% by weight of one or more of a single powder, an alloy powder and an oxide powder among Ba compounds of Zr, Sn, Ti and Zn.

"Pre-sintered body production step" Once the mixed powder is obtained, the mixed powder is formed into a desired shape by a molding device such as a uniaxial pressing device or an isostatic pressing device.
For example, a preform such as a bar, a disk, or a block is formed. When the pressurizing condition of the preform is ideally set by the molding apparatus, the relative density of the compact in which the solid spherical particles are closest packed is up to about 66%, and a large number of pores existing inside the preform. Since holes are adjacent to each other, the following preliminary heat treatment step is performed in order to make these adjacent holes closed as much as possible to the outside. This pre-heat treatment step is performed by using RE ₂ BaCuO _5, which is the second phase component of the rare earth oxide superconductor having the desired composition.
Alternatively, at a temperature lower than the thermal decomposition temperature (about 1200 ° C. to 1250 ° C.) of the RE ′ _4-2X Ba _{2 + 2X} Cu _2-X O _10-2X phase,
In an oxygen atmosphere containing only oxygen or in a vacuum atmosphere containing no gas, several tens of minutes to several tens
It is applied for 0 hours.

FIG. 1 and Table 1 show the thermal decomposition temperatures of various rare earth oxide superconductors.

[0025]

[Table 1]

As shown in FIG. 1 and Table 1, the thermal decomposition temperature (T _p BULK) of the rare earth oxide superconductor varies depending on the composition and the oxygen partial pressure. Set the preliminary heat treatment temperature.

Next, FIG. 2 shows a state in a 1% oxygen atmosphere and 0.1% oxygen atmosphere.
3 shows the thermal decomposition temperature of a rare earth oxide superconductor in an oxygen atmosphere. From this figure, it is clear that lowering the oxygen concentration by one digit lowers the thermal decomposition temperature by about 30 ° C., a binary mixed EuY system using two types of rare earths,
SmY system, EuGd system, SmGd system, SmEu system, Nd
It is clear that any of the Gd-based, NdEu-based, and NdSm-based systems has an intermediate thermal decomposition temperature of the single-phase thermal decomposition temperature of each system.

In the above situation, FIG. 1, Table 1 and FIG.
The preliminary heat treatment temperature is set with reference to the oxygen partial pressure and the thermal decomposition temperature shown in (1), and the heat treatment temperature described later is set.

At the time of the above heat treatment, a part of a large number of pores existing inside the preform can be made closed pores which are closed to the outside, so that the relative density of the presintered body becomes 90% or more. be able to. In addition, there are no holes inside the pre-sintered body, or the inside of the holes is filled with no gas as in vacuum sintering, or in the case of sintering in an oxygen atmosphere. Thus, only oxygen is charged. The relationship between the heating temperature and the heating time in the pre-sintered body manufacturing process is shown by the area a1 in FIG.

[Melting Growth Step] Next, a melting growth step is performed using the preliminary sintered body. Here, for example, when a disc-shaped pre-sintered body 1 is used as shown in FIG. 4, a small disc-shaped seed crystal 2 is placed at the center of the upper surface of the pre-sintered body 1, and from this state, melt growth is performed. Let it. Further, a method in which a seed crystal is placed on the upper portion of the sintered body under high-temperature melting is also possible. The seed crystal is a single crystal of the target rare earth oxide superconductor or a material that is not the target composition system but belongs to the rare earth oxide superconductor of the various compositions described above, and is appropriately selected and used. Can be. For example, an Nd ₁ Ba ₂ Cu ₃ O _x -based seed crystal (for example, a seed crystal having a size of several tenths of a pre-sintered body) can be used.

The pressure at the time of performing the melt growth step using the seed crystal is preferably in a positive pressure atmosphere of not less than 0.0001 atm and not more than 100 atm. In this case, the partial pressure of oxygen is preferably at least 0.0001%. , 100% or less. The oxygen atmosphere here can be controlled by mixing an inert gas such as Ar and a pure oxygen gas.

Next, FIG. 3 shows an example of heat treatment temperature conditions for performing the melt growth step. Foaming hold threshold _{(T max = (T 'p} BULK) + 50 ℃) for several hours to several ten hours at that temperature and heated to a temperature slightly lower than as shown in FIG. 3, a state where there is no foaming At the thermal decomposition temperature (T _p BUL) of the bulk rare earth oxide superconductor.
K) After cooling to the vicinity, 0.1 ° C./hr.
C./hour, for example, slowly cooling at a cooling rate of about 1.degree. C./hour, melt-growing under the temperature gradient shown in FIG. 3, and then allowing to cool to room temperature.

Here, the threshold value for foaming is a value calculated based on the equation of the thermal decomposition temperature (T ' _p BULK) of the rare earth oxide superconductor in pure oxygen (100%) + 50 ° C. From this, it is preferable to heat-treat the material containing the constituent elements of the RE-based oxide superconductor shown in Table 1 in a temperature range of a thermal decomposition temperature in pure oxygen + 50 ° C or lower. Note that, within this range, a temperature range of not more than the thermal decomposition temperature + 20 ° C is preferable. For example, in the case of a composition of NdBa ₂ Cu ₃ O _y , Table 1
Since the thermal decomposition temperature in pure oxygen (100%) is 1108 ° C., sintering is preferably performed at a temperature of 1108 ° C. or higher and 1108 ° C. + 50 ° C. (1158 ° C.) or lower. .

Next, the bulk rare earth oxide superconductor cooled to room temperature is subjected to a heat treatment in a pure oxygen atmosphere at a temperature of about 400 ° C. for several tens to hundreds of hours, if necessary, so that the final purpose is obtained. In the form of a bulk rare earth oxide superconductor.

The rare earth-based oxide superconductor obtained by the above steps is formed by melting and growing a pre-sintered body having a relative density of 90% or more with a seed crystal. Is not filled, or even if it is filled with gas, it is filled only with oxygen gas that can melt and diffuse into the oxide superconductor with high solubility during melt generation, so it is unnecessary during melt growth. Void formation due to discharge of gas components can be suppressed. As a result, vacancies generated in the rare earth oxide superconductor obtained from the seed crystal by melt growth can be suppressed, and as a result of suppressing vacancies, the relative density can be increased, and the strength can be improved. Can be higher. For example, even if the relative density of the rare-earth-based oxide superconductor obtained by the conventional manufacturing method is about 85%, the relative density of the rare-earth-based oxide superconductor is about 97% by implementing the manufacturing method of the present invention.
% Relative density can be increased.
Further, the strength of the rare-earth-based oxide superconductor obtained thereby can be increased.

Further, in the melt growth step, the heat treatment is performed at a temperature lower than the threshold value of oxygen foaming, and the material is thermally decomposed and then melt-grown. A high-strength rare earth oxide superconductor free from defects and cracks can be obtained. From the above, it is possible to provide a rare-earth-based oxide superconductor having excellent superconducting characteristics with a high trapping magnetic field due to high density and few defects and vacancies.

[0037]

EXAMPLE 1 Y ₂ Ba ₃ powder, BaCO ₃ powder and CuO powder were mixed with Y: Ba: Cu = 1.8: 2.4: 3.
The mixture was mixed at a ratio of 4 and uniaxially formed into a rod shape, and then calcined at 920 ° C. for 30 hours in an electric furnace in which air was circulated on an alumina boat. Thereafter, the powder obtained by the pulverization was heated to 1400 ° C. in a platinum crucible to be rapidly melted, and rapidly cooled to room temperature using a copper plate. The quenched plate was pulverized to 200 mesh or less and formed into a disk having a diameter of 6 cm and a thickness of 1.5 cm by a uniaxial pressing machine and an isotropic isostatic press machine. After replacing the inside of the furnace with this disc-shaped sample at 1040 ° C. in an oxygen atmosphere, it was subjected to a heat treatment for 24 hours while being evacuated by a rotary pump to prepare a pre-sintered body.

Next, this disc-shaped pre-sintered body was placed in air (2
(Under 0% oxygen atmosphere) in an electric furnace provided with a temperature gradient at 1050 ° C. (1030 + 20 ° C.) for 20 minutes and then Nd ₁ Ba ₂ Cu _{3 at} 1020 ° C.
After the seed crystal having the composition of O _y was placed at the center of the upper surface of the disk, the temperature was lowered to 900 ° C. at a cooling rate of 1 ° C./hour so that the growth start portion became 1010 ° C., and then the furnace was cooled to room temperature.
In the crystal of the rare earth-based oxide superconductor sample obtained at this stage, almost the c-axis is perpendicular to the radial direction of the disk-shaped sample. Oxygen was further introduced into this rare earth-based oxide superconductor sample at 400 ° C. for 100 hours in a pure oxygen atmosphere to obtain a bulk rare earth-based oxide superconductor finally obtained.

This rare earth oxide superconductor sample was 1 T
After cooling to the temperature of liquid nitrogen while applying the magnetic field of (Tesla), the applied magnetic field was removed. The rare earth oxide superconductor sample was measured by a magnetic field distribution measuring device using a Hall element. As a result, it was confirmed that the magnetic field was uniformly trapped inside. The maximum trapping magnetic field of the rare earth oxide superconductor sample was 0.75 T with a gap of 0.5 mm. Furthermore, from this rare earth oxide superconductor sample,
Cut out a prism of 3 mm x 4 mm x 20 mm in size,
The bending strength of the rare earth oxide superconductor sample was 155 MPa as measured by a three-point bending tester.

Example 2 As starting materials, (Sm, G
d) 0.5% by weight of Pt powder and 10% by weight of Ag ₂ O powder were added to a material mixed in a molar ratio of the composition of ₁ Ba ₂ Cu ₃ O _{y and} the composition of RE ₂ Ba ₁ Cu ₁ O ₅ . Thereafter, the mixed powder was compacted into a disc having a diameter of 60 mm and a height of 20 mm to obtain a preform. Next, the preform is placed in an oxygen stream for 1 hour.
Heat treatment was performed at 027 ° C. for 10 hours to produce a preliminary sintered body.
Then, the Nd123-based seed crystal is placed on the upper part of the pre-sintered body, thermally decomposed at 1025 ° C. for 10 hours in a 1% oxygen-Ar atmosphere, and then 0.5 ° C./hour from 990 ° C. to 950 ° C. To obtain a rare earth oxide superconductor. Oxygen was further introduced into this rare earth-based oxide superconductor sample at 400 ° C. for 100 hours in a pure oxygen atmosphere to obtain a bulk rare earth-based oxide superconductor finally obtained.

This rare earth oxide superconductor sample was 10 T
After cooling to liquid nitrogen temperature with the applied magnetic field, the applied magnetic field was removed. The rare earth oxide superconductor sample was measured by a magnetic field distribution measuring device using a Hall element. As a result, the maximum trapping magnetic field of the sample was 2.67 T with a gap of 0.5 mm. Further, a prism having a size of 3 mm × 4 mm × 20 mm was cut out from the rare earth-based oxide superconductor sample and measured by a three-point bending tester. The bending strength of the rare earth-based oxide superconductor sample was 147 MPa.
a. FIG. 5 shows a photograph of a cross-sectional structure of the rare-earth oxide superconductor sample. In this picture, the white particles are Ag
No particles were present around the Ag particles, and no vacancies could be confirmed.

Comparative Example 1 A rare earth oxide superconductor sample was prepared under the same conditions as in Example 2 except that the preform was not pre-sintered in pure oxygen. Oxygen was introduced into this sample at 400 ° C. for 100 hours in a pure oxygen atmosphere to obtain a bulk rare earth oxide superconductor finally obtained. After cooling the rare earth oxide superconductor sample to the temperature of liquid nitrogen while applying a magnetic field of 10 T, the applied magnetic field was removed. As a result, the sample was split into two from the center. When a prism having a size of 3 mm × 4 mm × 20 mm was cut out from a part of the undamaged rare earth-based oxide superconductor sample and measured using a three-point bending tester,
The bending strength of the rare earth oxide superconductor sample was 46MP.
a. In addition, the density measurement of this sample revealed that the relative density was 85%. FIG. 6 shows a photograph of a cross-sectional structure of the rare earth oxide superconductor sample of this comparative example. In this photograph, white particles indicate Ag particles, and phases of other constituent elements are present around the Ag particles, but black circle-shaped pattern portions existing around the Ag particles form voids. Show. From FIG. 6, the size of the generated pore is 10
It is more than 0 μm, and since there are a plurality of these, it is considered that the mechanical strength was reduced and the material was damaged by the applied magnetic field.

[0043]

As described above, according to the present invention, the pre-formed body is heat-treated in a vacuum atmosphere or an atmosphere containing only oxygen to form a pre-sintered body. A pre-sintered body can be obtained without incorporating a gas of any element, for example, nitrogen gas or the like. Based on this pre-sintered body, it is thermally decomposed below the threshold temperature where oxygen foaming possibility is low, and then melt-grown, so that foaming of gases other than oxygen as well as foaming by oxygen gas is suppressed. Thus, a rare earth oxide superconductor can be obtained.
The rare earth-based oxide superconductor manufactured in this manner is:
There are few pores inside, or even if there are pores, they are sufficiently miniaturized, and a high-density and high-strength bulk rare earth-based oxide superconductor can be obtained.

Further, in the present invention, the foaming threshold value of oxygen is calculated by calculating the thermal decomposition temperature of the rare earth oxide superconductor in pure oxygen +
By setting the temperature to 50 ° C., and performing the thermal decomposition and then the melt growth, it is possible to obtain a bulky rare-earth-based oxide superconductor having no fine pores and having only fine pores.

In the present invention, the RE_{1 + x1}Ba_2-x1Cu_Three
O_yIs the mother phase, RE _TwoBaCuO_FiveCompanion
Or RE '_4-2x2Ba_{2 + 2x2}Cu_2-x2O_10-2x2The right phase
Bulk rare earth with improved strength by containing
A kind of oxide superconductor can be obtained.

In the present invention, La, Nd, Sm, E
If a rare-earth oxide superconductor containing one or more rare-earth elements among u, Gd, Dy, Ho, Y, Er, Yb, Tm, and Lu is used, the superconductor is cooled by liquid nitrogen. A bulk oxide superconductor having excellent superconducting state stability and a high trapping magnetic field can be obtained.

In the present invention, if a pre-sintered body having a theoretical density of more than 90% is used, the number of pores and gas in the pre-sintered body is sufficiently reduced. A high-density, high-strength bulk rare-earth-based oxide superconductor having few vacancies can be obtained.

In the production method of the present invention, if there is no void in the pre-sintered body or if a pre-sintered body in which only the enclosed voids are filled with oxygen is used, a gas such as nitrogen or argon is used. As a result, gas components having low solubility in the melt portion of the rare-earth oxide superconductor can be eliminated as much as possible, while oxygen that is easily dissolved in the melt portion of the rare-earth oxide superconductor and can diffuse into the inside can be eliminated. Since only the pre-sintered body is included in the pre-sintered body, it is possible to obtain a bulk rare-earth-based oxide superconductor in which pores due to the presence of unnecessary gas are suppressed when the pre-sintered body is melt-grown. it can.

In the production method of the present invention, one or both of Ag and Au, one or both of Pt and CeO ₂ , or Zr, Sn, T
By adding one or two or more of the Ba compounds of i and Zn in specified amounts, a bulk rare-earth oxide superconductor with improved strength can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the ionic radius and the thermal decomposition temperature of a rare-earth oxide superconductor.

FIG. 2 is a diagram showing a relationship between an average ionic radius of a rare-earth oxide superconductor and a thermal decomposition temperature.

FIG. 3 is a diagram showing a relationship between a processing temperature and a time in a pre-sintered body production step and a melt growth step according to the present invention.

FIG. 4 is a diagram showing a positional relationship between a pre-sintered rare earth oxide superconductor to be produced in an embodiment of the present invention and a seed crystal.

FIG. 5 is a photograph of the structure of the rare earth oxide superconductor obtained in the example.

FIG. 6 is a structural photograph of a rare earth oxide superconductor obtained in a comparative example.

[Explanation of symbols]

 1 ... pre-sintered body, 2 ... seed crystal.

Continued on the front page (72) Inventor Naomichi Sakai 1-14-1 Shinonome, Koto-ku, Tokyo Inside the Superconductivity Engineering Research Center, International Superconducting Technology Research Institute (72) Inventor Masato Murakami 1-14-1, Shinonome, Koto-ku, Tokyo In the Superconductivity Engineering Research Center, International Superconducting Technology Research Center (72) The inventor Kei Ogasawara 1-14-3 Shinonome, Koto-ku, Tokyo, Japan 1-14-3 Shinonome, Koto-ku F-term in the Superconducting Engineering Research Institute, International Superconducting Technology Research Center 4G047 JB03 JB04 JB06 JC02 KC05 KC06 LA02 LB01 4G077 AA02 BC53 CD10 EA01 EC05 EC08 HA08

Claims (12)

[Claims] In a method for producing a rare earth (RE) -based oxide superconductor by a melt growth method, a pre-sintered body of a rare earth-based oxide superconductor which has been preliminarily heat-treated in an oxygen atmosphere or in a vacuum is prepared. A method for producing an oxide superconductor, which is performed by melt growth. 2. A preform is obtained by mixing and molding a material containing a constituent element of a rare earth (RE) -based oxide superconductor at a predetermined ratio, and obtaining the preform, which is in a vacuum atmosphere or an atmosphere containing only oxygen. A rare earth-based oxide superconductor, characterized in that after being subjected to a heat treatment in air to obtain a pre-sintered body, the pre-sintered body is thermally decomposed at a temperature equal to or lower than an oxygen foaming threshold value and then melt-grown. Manufacturing method. 3. The production of a rare earth oxide superconductor according to claim 2, wherein the oxygen foaming threshold value is set to the thermal decomposition temperature of the rare earth oxide superconductor in pure oxygen + 50 ° C. Method. 4. The rare earth-based oxide superconductor has a composition formula of RE _{1 + x1} Ba _{2− x1} Cu ₃ O _y (wherein the composition ratio indicates
x1 satisfies the relationship of 0.1 ≦ x1 ≦ 0.3) as a mother phase, and a RE ₂ BaCuO ₅ phase or RE ′ _4-2x2
Ba _{2 + 2x2} Cu _2-x2 O _10-2x2 phase (where RE ′ is La,
Indicates one or both of Nd and indicates the composition ratio
x2 which satisfies the relation of 0 ≦ x2 ≦ 0.8) is used in an amount of 50% or less.
Or the method for producing a rare earth oxide superconductor according to 3. 5. La, Nd, Sm, Eu, Gd, Dy,
The rare earth element according to any one of claims 1 to 4, wherein a rare earth oxide superconductor containing one or more rare earth elements among Ho, Y, Er, Yb, Tm, and Lu is used. A method for producing a system oxide superconductor. 6. The pre-sintered body has a 90% theoretical density.
The method for producing a rare-earth oxide superconductor according to any one of claims 1 to 5, wherein a material having the above density is used. 7. The presence or absence of voids in the pre-sintered body,
7. The method for producing a rare earth-based oxide superconductor according to claim 1, wherein a pre-sintered body in which only voids are filled with oxygen is used. 8. The method according to claim 1, wherein the temperature during the melt growth is set to a temperature not lower than the thermal decomposition temperature of the rare earth oxide superconductor to be used and not exceeding the threshold value for foaming. 8. The method for producing a rare earth oxide superconductor according to any one of 1 to 7. 9. The method for producing a rare earth oxide superconductor according to claim 1, wherein the melt growth is performed using a seed crystal. 10. A material containing a constituent element of the rare-earth (RE) -based oxide superconductor, wherein one or both of Ag and Au are added as a dispersed phase in an amount of 30% by weight or less. 10. The method for producing a rare-earth oxide oxide superconductor according to any one of the above items 9. 11. The method according to claim 1, wherein one or both of Pt and CeO ₂ are added in an amount of 2% by weight or less to the material containing the constituent elements of the rare earth (RE) -based oxide superconductor. A method for producing a rare-earth oxide oxide superconductor according to any one of the above. 12. A material containing a constituent element of the rare earth (RE) -based oxide superconductor is made of Ba of Zr, Sn, Ti, Zn.
The method for producing a rare earth oxide oxide superconductor according to claim 1, wherein one or more compounds are added in an amount of 30% by weight or less.