JP3330962B2 - Manufacturing method of oxide superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a strong even under a magnetic field indicate superconductivity with high critical current densities R ₁ Ba ₂ Cu
_{The present} invention relates to a method for producing an oxide superconductor for producing a ₃ O _7-δ oxide superconductor.

[0002]

_2. Description of the Related Art A general formula R ₁ Ba ₂ Cu ₃ O _7-δ (where R is at least one element selected from Y, Sc and lanthanoids, and δ = 0.1 to 0.5) The following method has been conventionally known as a method for producing an oxide superconductor represented by

(1) First, Y ₁ Ba _{2 is used} as a seed crystal.
Sm ₁ Ba ₂ Cu ₃ O having a higher decomposition temperature than Cu ₃ O _7-δ
Prepare a _7-δ single crystal in advance.

[0004] Next, a powder of Y ₁ Ba ₂ Cu ₃ O _7-δ containing an excess of Y ₂ Ba ₁ Cu ₁ O ₅ is melted at about 1450 ° C., and then flown on a copper plate to be quenched, whereby the Y is cooled. _A precursor consisting of a ₂ O ₃ phase and a liquid phase is produced.

Then, the precursor is again brought into a semi-molten state at 1100 ° C.

After that, Sm ₁ B created in advance
The cleavage plane of a single crystal of a ₂ Cu ₃ O _7-δ is brought into contact with the precursor, is unidirectionally grown by slow cooling, Y ₁ Ba
₂ Obtain relatively large crystals of Cu ₃ O _7-δ .

(2) First, Y ₁ Ba _{2 is used} as a seed crystal.
M ₁ Ba ₂ Cu ₃ O having a higher decomposition temperature than Cu ₃ O _{7-δ
A 7-δ} (M is any one of Sm, Eu, Gd, and Dy) single crystals is prepared in advance.

[0008] Next, after melting the powder of Y ₂ Ba ₁ Cu ₁ O ₅ excessively comprises _{Y 1 Ba 2 Cu 3 O 7} -δ at about 1450 ° C, Y by flowing the copperplate, quenching ₂ A precursor consisting of an O ₃ phase and a liquid phase is produced.

Next, after keeping the precursor at 1100 ° C. for 20 minutes, the precursor is cooled to a temperature lower than the decomposition temperature of the seed crystal, and the cleavage plane of the seed crystal is brought into contact with the precursor, and the temperature is reduced to 1 ° at 1000 ° C. The temperature was gradually increased from the seed crystal side at a rate of C to 5 ° C./hour, and the temperature was gradually decreased to obtain R _{2 from the} seed crystal as a base point.
A relatively large crystal in which Ba ₁ Cu ₁ O ₅ is finely dispersed in R ₁ Ba ₂ Cu ₃ O _7-δ is obtained.

[0010]

However, each of the above-mentioned conventional manufacturing methods has the following disadvantages.

That is, in order to obtain a larger crystal of Y ₁ Ba ₂ Cu ₃ O _7-δ , the seed crystal M ₁ Ba ₂ Cu
_It is necessary to use a larger ₃ O _7-δ single crystal.
However, since it is extremely difficult to make a large seed crystal of M ₁ Ba ₂ Cu ₃ O _7-δ , after all, Y ₁ Ba ₂ Cu ₃ O _7-δ obtained by the size of this seed crystal The size of the crystal is also limited.

In addition, when the precursor becomes lower than the melting point of the seed crystal, the heating furnace must be opened to bring the seed crystal into contact with the precursor.

[0013] The present invention provides a method for producing R ₁ B comprising larger crystals.
It is an object of the present invention to provide a method for producing an oxide superconductor that can obtain an oxide superconductor of a ₂ Cu ₃ O _7-δ and can simplify the production process.

[0014]

In order to solve the above-mentioned problems, the present invention provides (1) a compound represented by the following general formula: R ₁ Ba ₂ Cu ₃ O _7-δ
(Where R is at least one element selected from among Y, Sc and lanthanoids, and δ = 0.1 to 0.5).
Compound, Ba compound and Cu compound are represented by R _{1 + 2K} Ba _{2 + K} Cu
After mixing with a composition of _{3 + K} (where K = 0 to 0.6), pellets are formed, and then the above R ₁ Ba ₂ Cu ₃ O
A single crystal having a perovskite structure having a decomposition temperature higher than _7-δ is brought into contact with the pellet as a seed crystal, and then
The pellet is heated to 1050 to 1300 ° C. to form an R ₂ BaCuO ₅ phase and a liquid phase in the pellet, and then the temperature of the seed crystal side is increased to 960 to 1050 ° C.
And a temperature gradient of 5 to 20 ° C./cm is applied from the seed crystal side to the pellet side.
By slow cooling at a temperature lowering rate of ° C / hour, R ₂ BaCuO ₅ becomes R ₁ Ba ₂ Cu ₃ O starting from the seed crystal.
_{According to} another aspect of the present invention, there is provided (2) a method for manufacturing an oxide superconductor according to the above (1), wherein the seeds are finely dispersed in _7-δ. As a configuration characterized in that the crystal is a single crystal of SrTiO ₂ , and as another aspect of Configuration 1,
(3) In the method for manufacturing an oxide superconductor according to the first aspect,
A structure characterized in that a single crystal having a cubic structure is used as the seed crystal. Further, as a third aspect of the present invention, (4) In the method for manufacturing an oxide superconductor of the third aspect, the seed crystal may be a single crystal of MgO. (5) The method for producing an oxide superconductor according to any one of the constitutions (1) to (4), wherein the R compound and the Ba compound are any one of the constitutions 1 to 4. , Cu compound is mixed at a ratio according to the composition of the oxide superconductor, and then pelletized, the R compound, B compound
At least one or more of the compound a and the Cu compound are taken out and mixed, and then the mixture is heated to 800 to 900 ° C.
And then forming a pellet by mixing the fired product with the remaining compound.

[0015]

According to the above configuration 1, R ₂ BaCuO ₅ is converted to R
It made it possible to obtain an oxide superconductor consisting of larger crystals than finely dispersed _{R 1 Ba 2 Cu 3 O 7} -δ relatively easily in _{1 Ba 2 Cu 3 O 7-} δ. This is because a single crystal having a perovskite structure having a decomposition temperature higher than that of R ₁ Ba ₂ Cu ₃ O _7-δ is used as the seed crystal. This is because a large single crystal can be obtained and a single crystal such as SrTiO ₂ having a sufficiently high decomposition temperature can be used. That is, the present invention is, as a seed crystal close to the lattice constant of the lattice constant is _{Y 1 Ba 2 Cu 3 O 7} -δ, with a large single crystal can be easily obtained, SrTiO having a perovskite structure having a high decomposition temperature ₂ Is based on the fact that the present inventors have found that such single crystals can be used. Incidentally, conventionally, since it was necessary to use a seed crystal having a composition and a structure close to R ₁ Ba ₂ Cu ₃ O _7-δ , it was extremely difficult to obtain a large seed crystal, This made it difficult to obtain an R ₁ Ba ₂ Cu ₃ O _7-δ oxide superconductor consisting of larger crystals, and because the decomposition temperature of the seed crystal was low, the seed temperature was increased in advance from the high processing temperature stage. The crystal could not be set, and a complicated operation of inserting the seed crystal when the treatment temperature became lower than the decomposition temperature of the seed crystal during the heat treatment was required. According to Configuration 1, since the seed crystal has a sufficiently high decomposition temperature, the seed crystal can be set in advance, so that such a complicated operation is not required. The oxide superconductor of R ₁ Ba ₂ Cu ₃ O _7-δ obtained by the method of Configuration 1 is R ₁ B 2
R ₂ BaCuO finely dispersed in a ₂ Cu ₃ O _{7-δ
Since 5 functions} as a magnetic flux pinning center (pinning center), a high critical current density can be obtained.

The seed crystal may be a single crystal having a cubic structure as in Structure 3, for example, Mg as in Structure 4.
It has been confirmed that the same operation and effect as in Configuration 1 can be obtained even when an O single crystal is used.

Further, by forming the pellet forming step as in the configuration 5, the R ₂ BaCuO ₅ is more uniformly and finely dispersed in the R ₁ Ba ₂ Cu ₃ O _7-δ to provide a better pinning center. It becomes possible to obtain an oxide superconductor having better superconductor properties.

[0018]

EXAMPLE 1 First, Y ₂ O ₃ , BaCO ₃ , having a particle size of 0.01 to ₃ μm,
Each raw material powder of CuO was prepared by mixing Y: Ba: Cu at a ratio of 1.8:
Weighed to 2.4: 3.4.

Next, only BaCO ₃ and CuO are mixed,
The powder was fired at 850 to 900 ° C. for 24 hours to obtain a fired powder .

Next, after mixing the calcined powder and the raw material powder of Y ₂ O ₃ , it was formed into pellets having a diameter of 1 inch φ.

Next, 5 mm square Sr was placed on the pellet.
A TiO ₃ single crystal is placed with its (100) plane in contact with the pellet, and is placed at 110 ° C. at 1 ° C. to 20 ° C./min.
The temperature was raised to 0 to 1150 ° C and kept at that temperature for 20 minutes.

Next, the pellets are placed at 5 ° C to 20 ° C /
The temperature was lowered to 1000 ° C in min.

Next, the seed crystal side is set to a low temperature side by blowing oxygen from the seed crystal side, and a temperature gradient of 5 to 15 ° C./cm is applied from the seed crystal side to the pellet side to give 1 ° C./hour. And slowly cooled.

1 inch φ × (thickness) 5 thus obtained
15 mm square x 3
mm. The crystal grains are formed of Y ₁ Ba ₂ Cu ₃
Y ₂ BaCuO ₅ was finely dispersed in O _{7- δ} and exhibited superconducting properties. Its critical current density was measured to be 1.7 × 10 ⁴ A / cm ² . .

Example 2 First, Y ₂ O ₃ , BaCO ₃ having a particle size of 0.01 to ₃ μm,
Each of the raw material powders of CuO has a ratio of Y: Ba: Cu of 1.8:
It mixed so that it might become 2.4: 3.4.

Next, the mixture was heated to 1450 ° C. at a heating rate of 20 ° C./min to melt it, poured into a copper plate, rapidly cooled to room temperature, and solidified.

Next, the quenched solidified product is treated with a particle size of 0.5 to 0.5.
After pulverizing to 3 μm and forming into a 1-inch pellet, an MgO single crystal was placed on the pellet so that the (100) plane was in contact with the pellet.

Next, the pellets were placed in a crucible, which was suspended in the center of a vertical tubular furnace with a platinum wire.

Next, in the vertical tube furnace, the pellets
The temperature was raised to 1100 ° C. at a temperature of 20 ° C./min to 20 ° C./min and kept at that temperature for 20 minutes. Cooled down.

The crystal grains grown in the obtained 1-inch φ × (thickness) 5 mm pellet were 20 mm × 3 mm. Further, these crystal grains are those in which Y ₂ BaCuO ₅ is finely dispersed in Y ₁ Ba ₂ Cu ₃ O _7-δ and show superconducting properties, and the critical current density was measured. It was 1.7 × 10 ⁴ A / cm ² .

Next, an example manufactured by a conventional method will be described as a comparative example.

Comparative Example Y ₂ O ₃ , BaCO ₃ , and CuO were weighed so that the ratio of Y: Ba: Cu was 1.8: 2.4: 3.4.
Only aCO ₃ and CuO were mixed and fired at 850 ° C. for 24 hours. This was mixed with Y ₂ O ₃ , formed into a 1-inch pellet, heated to 1100 ° C. at 20 ° C./min, kept for 20 minutes, and kept at 100 ° C. at 20 ° C./min.
A 2 mm square of Sm and Ba ₂ Cu ₃ O _7-δ single crystal prepared in advance at 1030 ° C. on the way to lower the temperature to 0 ° C. is placed on the pellet, and a temperature gradient of 10 ° C./cm is applied. It was gradually cooled at a rate of ° C / hour.

The crystal grains grown in the obtained 1-inch φ × (thickness) 5 mm pellets are 10 mm × 3 mm and exhibit superconducting properties. 0.0 × 10 ⁴ A / cm.

In each of the above embodiments, Y ₁ Ba ₂ C
Although an example of producing an oxide superconductor of u ₃ O _7-δ was described, the present invention relates to the general formula R ₁ Ba ₂ Cu ₃ O _7-δ (where R is a group of Y, Sc and lanthanoids). It is confirmed that the present invention can be similarly applied to the production of another oxide superconductor represented by the following formula (one or more selected elements, δ = 0.1 to 0.5).

Further, the examples using a single crystal of SrTiO ₃ (perovskite structure) and a single crystal of MgO (cubic) as the seed crystal have been described.
lO _3, a single crystal and having a perovskite structure such as LaGaO _3, YSZ, it has been confirmed that it is possible to use a single crystal of cubic structure of Si or the like.

[0036]

As described above in detail, according to the present invention, a crystal having a crystal structure similar to that of a superconductor to be manufactured is obtained by using a so-called melting method which is one of the methods for manufacturing an oxide superconductor. In a method in which a crystal is grown as a seed crystal, a single crystal having a perovskite structure having a high decomposition temperature or a single crystal having a cubic crystal structure having a high decomposition temperature is used as the seed crystal. As a result, R ₁ Ba ₂ Cu ₃ O composed of larger crystals
An oxide superconductor of _7-δ is obtained, and a method of manufacturing an oxide superconductor that can simplify the manufacturing process has been obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 1/00, 3/00 C30B 29/22

Claims (5)

(57) [Claims] 1. A general formula R ₁ Ba ₂ Cu ₃ O _7-δ (where R is one or more elements selected from Y, Sc and lanthanoids, and δ = 0.1 to 0.5) The method for producing an oxide superconductor represented by the following formula: wherein the R compound, the Ba compound, and the Cu compound are represented by R _{1 + 2K} Ba _{2 + K} C
After mixing with a composition of u _{3 + K} (where K = 0 to 0.6), the mixture is pelletized, and then has a perovskite structure having a decomposition temperature higher than that of R ₁ Ba ₂ Cu ₃ O _7-δ. The single crystal is brought into contact with the pellet as a seed crystal, and then the pellet is heated to 1050 to 1300 ° C. to form a R ₂ BaCuO ₅ phase and a liquid phase in the pellet. 960 to 1050 °
C, a temperature gradient of 5 to 20 ° C./cm is applied from the seed crystal side to the pellet side, and the temperature is set to 1 ° C.
By slow cooling at a temperature lowering rate of 5 ° C./hour, R ₂ BaCuO ₅ becomes R ₁ Ba ₂ Cu ₃ starting from the seed crystal.
A method for producing an oxide superconducting sintered body, wherein a crystal finely dispersed in O _7-δ is grown. 2. The method for manufacturing an oxide superconductor according to claim 1, wherein said seed crystal is a single crystal of SrTiO ₂ . 3. The method for manufacturing an oxide superconductor according to claim 1, wherein a single crystal having a cubic structure is used as the seed crystal. 4. The method for producing an oxide superconductor according to claim 3, wherein the seed crystal is a single crystal of MgO. 5. The method for producing an oxide superconductor according to claim 1, wherein the R compound, the Ba compound, and the Cu compound are R _{1 + 2K} Ba.
After mixing with a composition of _{2 + K} Cu _{3 + K} (where K = 0 to 0.6), the step of forming a pellet comprises at least one of an R compound, a Ba compound, and a Cu compound.
Remove one or more and mix, then mix this mixture with 800
A process of firing at about 900 ° C., and then mixing the fired product with the remaining compound to form pellets.