JP3031448B2 - Crystal growth method for oxide superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a large crystal of an oxide superconductor for use in a magnetic bearing or a high magnetic field shield using a superconductor. The present invention relates to a method for growing an oxide superconductor crystal having a directional orientation.

[0002]

2. Description of the Related Art Conventionally, methods for growing oxide superconductor crystals include self-flux method, flux method, and TSFZ.
Methods, the FZ method, the Bridgeman method, and the like are known, and it has been experimentally studied to grow a 123-phase oxide superconductor crystal by these methods.

[0003] Among these methods, in the flux method, a single crystal having no impurities in the 123 phase is grown, and a crystal of several mm square has been reported. There is also known an example in which a crystal of about 1 cm square was successfully grown by holding a crystal and bringing it into contact with a liquid, growing a crystal in its seed crystal orientation, and replenishing a raw material having a crystal composition into the solution as needed during the crystal growth stage. Have been. At present, there are few examples in which a 123-phase single crystal has been grown by other methods.

In the crystal grown by the above method, 1
Since the 23 phases do not contain an impurity phase, there are no pinning sites required for application, and thus they cannot be used as a magnetic bearing or a magnetic shield. This is because in these applications, the basic characteristic mechanism is that the invasion of the external magnetic field is shielded by stopping the magnetic flux in the impurity phase that becomes the pinning site, thereby shielding the magnetic field.

[0005] Therefore, even if a 123-phase single crystal is produced by the above method, the desired crystal cannot be obtained. Therefore, a partial melting method is used as a method for solving these problems.
A method of growing crystals of 123 phases in which 11 phases are finely dispersed has come to be generally used.

According to this method, a large crystal or a crystal oriented sample is prepared by controlling crystal growth while generating a 123 phase from a peritectic reaction of a 211 phase and a liquid phase component.

[0007] The structure produced by this method is such that 211 phases remaining as unreacted substances of the peritectic reaction have 1 to 10
It is dispersed in a size of about a micron,
In general, the composition of this sample is such that 211 phases are added by several tens mol% to 123 phases.

[0008] The superconducting characteristics of the sample produced by this method are as follows. At an applied magnetic field of 1 T (tesla), the magnetic field current density is 2 ×
More than 10 ⁴ A / cm ² and repulsion force is also 1 kgf / cm ²
As described above, the characteristics are approaching the range in which practicality is sufficient.

On the other hand, as a problem, application to a magnetic bearing or a magnetic shield requires uniformity of the characteristics of the entire sample. In a normal manufacturing method, the crystal size is 1 cm.
The corners had an agglomerated structure, and the grain boundaries of each crystal were weakly bound or in a non-superconducting phase.

As a method conventionally developed to solve these problems, a production method in which a seed crystal is placed and the orientation of the crystal is improved using a temperature gradient furnace such as a two-zone furnace or a one-zone furnace is employed. Have been. However, even in these methods, as the diameter of the crystal increases to 3 to 4 inches,
The generation of unoriented structure at the edge of the sample was not suppressed.

[0011]

As described above, the conventional manufacturing methods include a method suitable for increasing the size of an oriented sample of a 123-phase crystal in which 211 impurity phases are dispersed and a method for mass-producing a large-oriented sample. There was no suitable recipe.

Therefore, an object of the present invention is to develop a novel manufacturing method capable of simultaneously increasing the size of an oriented sample and mass-producing it.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve the above-mentioned problems. As a result, the seed crystal is sequentially enlarged, and a crystal orientation sample is produced using the seed crystal. By this, larger than the seed crystal size,
Alternatively, they have found that a sample of the same size can be produced stably, and have provided the present invention.

That is, the present invention provides a compound represented by the general formula RE ₁ RA ₂
Cu ₃ O _x (RE is 1 selected from the group consisting of rare earth elements)
Or a mixture of two or more elements, and RA is a mixture of one or more elements selected from the group consisting of alkaline earth elements).
In the method for growing a 123-phase crystal including the 211 phase, a 123-phase seed crystal having a crystal structure of the above general formula is prepared in advance, and a 123-phase seed crystal having a size larger than the seed crystal is formed.
A molded body for producing a crystal having a phase crystal structure is produced, and then the molded body is maintained at 1050 to 1200 ° C. to be in a semi-molten state.
A crystal having the same crystal orientation as the seed crystal is obtained by a heat treatment step of gradually cooling at a rate of 0.5 to 2 ° C./hr while growing the phase crystal, and then the obtained crystal is sliced, By using the obtained sliced piece as a seed crystal, the above-described heat treatment step is repeated to produce a second seed crystal having a size larger than that of the first seed crystal. Wherein said shaped body for producing a 123 phase crystal has a size ratio of less than 72.6 / 5 to said seed crystal in contact with said shaped body. It relates to the breeding method.

[0015]

In the present invention, a 123-phase crystal including 211 phases is called a single crystal (formally referred to as a pseudo-single crystal). As in the present invention, the 123 phase single crystal or crystal orientation is uniform. Increasing the size of a crystal oriented body requires a crystal growing process starting from a seed crystal.

In this case, the seed crystals are Y, Sm, Nd
A rare earth element such as that having a 123 phase structure and having a high melting point is used. Also, as the seed crystal production conditions, the stoichiometric composition of the 123 phase causes too much liquid phase seepage,
Instead, it is desirable to use a composition containing a small amount of 211 phase by a partial melting method. This is the same when the seed crystal is produced by another crystal growing method such as a flux method.

When a seed crystal of Sm _{1 + 2X} Ba _{2 + x} Cu _{3 + x} O _Y is prepared as a specific preparation method in the above partial melting method, Sm ₂ O ₃ , BaO ₂ , CuO or the like is used. The oxide raw materials are mixed and fired at 950 to 900 ° C. to produce a molding powder.

In this case, the same effect can be obtained by using a raw material powder such as a nitrate or a carbonate. In addition, the molding powder may be used simply as a mixed powder of an oxide raw material powder.

As another method, Ba _{2 + x} Cu
There is also a method of synthesizing a powder of _{3 + x} O ₂ and mixing it with a powder of Sm ₂ O ₃ to obtain a powder for molding. In this case, the same result can be obtained by replacing Sm of the Sm powder with another rare earth element such as Y or Nd.

Next, using these molding powders, a compact having an appropriate size is produced by pressing. In this case, the size of the formed body needs to be a size that can easily cut out a seed crystal of several mm square, and is desirably 1 inch or more.

Next, the formed product was subjected to 1050 to 120
After the temperature was raised to 0 ° C. and held, it was cooled to a temperature slightly higher than the crystal growth temperature of each of the 123 phases according to the type of rare earth such as Sm, Y, Nd, and Yb, and then 0.5 to 2 ° C. / hr
Cool slowly. As a result, the entire sample grows as a crystal of several mm square or more. This is cut out to form a seed crystal.

When this seed crystal is used, it is desirable that the crystal decomposition temperature of the compact for enlarging the crystal is equal to or higher than the crystal decomposition temperature of the seed crystal. This is because, if not so, the seed crystal is melted and decomposed first in the crystal growth stage of the formed body (hereinafter, referred to as a precursor), and does not serve as a seed crystal.

For example, when producing a large crystal of the Y-based 123 phase, the Sm-based 123 phase is used as a seed crystal. Yb
In the case of a large crystal of the system 123 phase, a seed crystal of the Y system 123 phase is preferable. Furthermore, in the case of a large crystal of the Y-based 123 phase, a seed crystal of the Y-based 123 phase having the same composition can be used.

Next, the precursor to be grown is set in a one-zone or two-zone temperature gradient furnace, heated to a partial melting temperature of 1000 to 1200 ° C.
One phase and a liquid phase state are generated. After the generation, the furnace temperature is lowered to a temperature higher than the crystal growth temperature or the crystal growth temperature, and the seed crystal prepared as described above is brought into contact with the furnace so as to have a temperature of 0.5%.
Move at ~ 2 mm / hr. In this case, the temperature gradient in the furnace is 100 ° C./cm or less, preferably several tens ° C./cm.
Is desirable.

As a moving method, the sample itself is moved while the center temperature in the furnace is kept constant, or the temperature gradient is added to the sample by using the temperature gradient in the furnace by fixing the sample without moving it. There is a method of growing crystals, and equivalent results can be obtained by either method.

Based on the crystal growth sample thus obtained,
By using the same as a new large seed crystal and repeating the same steps as above, a larger crystal and a sample having crystal orientation could be produced.

As a method of further increasing the mass productivity of the production,
The crystal once produced is sliced and used as a large number of seed crystals, and mass production can be promoted by the above steps.

Hereinafter, the present invention will be described in detail with reference to examples, but the scope of the present invention is not limited thereto.

[0029]

EXAMPLE 1 First, raw material powders of Y ₂ O ₃ , BaO ₂ , and CuO were mixed at a molar ratio of Y: Ba: Cu = 1.8: 2.4: 3.4, and then fired at 900 ° C. for 20 hours. did. Next, the fired product was sufficiently pulverized with an automatic mortar, and further pulverized with a ball mill using an acetone solvent to prepare a powder having an average particle diameter of about 3 μm.

Next, 1 ton / cm 2 was obtained using the obtained powder.
Pressed at ² of pressure, to prepare a molded product having a thickness of 1cm in 2 inch diameter was held for one hour at 1100 ° C. in a furnace, at 1 ° C. / hr from gradually cooled 1000 ° C. to 900 ° C. After cooling, crystallization was carried out, followed by furnace cooling to obtain a sample having a diameter of 2 inches, and then a 5 mm square crystal was taken out from the sample and used as a seed crystal.

Next, 2 having the same composition as the seed crystal described above
After preparing a molded body having an inch diameter, using the precursor as a precursor and setting it at the center of a one-zone temperature gradient furnace, setting the center temperature in the furnace to 1100 ° C., holding the sample for about one hour,
The sample was moved to a temperature range of about 1000 ° C., where the seed crystal was set on the precursor.

Next, when the seed crystal was moved from the side where the seed crystal was placed to the outside of the furnace at a speed of 1 mm / hr, a sample having the entire 2-inch diameter aligned with the crystal orientation of the seed crystal was produced. A 1 cm thick seed crystal was cut from the sample.

Next, a molded product having a diameter of 3 inches was separately prepared by the above-mentioned method and used as a precursor. A seed crystal obtained from the sample having a diameter of 2 inches was set under the same conditions and subjected to the same treatment. 3 having the same crystal orientation as the seed crystal
An inch diameter sample was obtained, and a 1 cm thick seed crystal was cut from the sample.

Next, a molded article having a diameter of 4 inches was separately prepared by the above-mentioned method and used as a precursor. A seed crystal obtained from the sample having a diameter of 3 inches was set under the same conditions and subjected to the same treatment. 4 having the same crystal orientation as the seed crystal
An inch diameter sample was obtained.

[0035]

Example 2 First, raw material powders of Sm ₂ O ₃ , BaO ₂ and CuO were mixed at a molar ratio of Sm: Ba: Cu = 1: 2: 3, and then fired at 900 ° C. for 20 hours. Next, the fired product was sufficiently pulverized with an automatic mortar, and further pulverized with a ball mill using an acetone solvent to prepare a powder having an average particle diameter of about 3 μm.

Then, 1 ton / cm
Pressed at ² of pressure, to prepare a molded product having a thickness of 1cm in 2 inch diameter was held for one hour at 1150 ° C. in a furnace, at 1 ° C. / hr from gradually cooled 1080 ° C. to 900 ° C. After cooling, crystallization was carried out, followed by furnace cooling to obtain a sample having a diameter of 2 inches, and then a 5 mm square crystal was taken out from the sample and used as a seed crystal.

Then, Y ₂ O ₃ , BaO ₂ , and CuO raw material powders were separately mixed at a molar ratio of Y: Ba: Cu = 1.8: 2.4: 3.4, and then fired at 900 ° C. for 20 hours. . Next, the fired product was sufficiently pulverized with an automatic mortar, and further pulverized with a ball mill using an acetone solvent to prepare a powder having an average particle size of about 3 μm.

Next, 1 ton / cm 2 was obtained using the obtained powder.
Pressed at ² of pressure, to prepare a molded product having a thickness of 1cm in 2 inch diameter and a precursor was set in the center of the temperature gradient furnace zone 1, after the central temperature in the furnace to 1100 ° C., After holding the sample for about 1 hour, the sample was moved to a temperature range of about 1000 ° C., where the seed crystal was set on the precursor.

Next, when the seed crystal was moved from the side where the seed crystal was placed to the outside of the furnace at a speed of 1 mm / hr, a sample having an entire 2-inch diameter aligned with the crystal orientation of the seed crystal was produced. Further, a seed crystal having a thickness of 1 cm was cut out from this sample.

Next, a molded product having a diameter of 3 inches was separately prepared by the above-mentioned method and used as a precursor. A seed crystal obtained from the sample having a diameter of 2 inches was set under the same conditions and subjected to the same treatment. 3 having the same crystal orientation as the seed crystal
An inch diameter sample was obtained.

[0041]

Example 3 First, raw material powders of Sm ₂ O ₃ , BaO ₂ and CuO were mixed at a molar ratio of Sm: Ba: Cu = 1.4: 2.2: 3.2 and then fired at 900 ° C. for 20 hours. did. Next, the fired product was sufficiently pulverized with an automatic mortar, and further pulverized with a ball mill using an acetone solvent to prepare a powder having an average particle diameter of about 3 μm.

Next, the obtained powder was pressed under a pressure of 1 ton / cm ² to form a molded body having a diameter of 2 cm and a thickness of 1 cm, and was kept in a furnace at 1150 ° C. for 1 hour. It was cooled and cooled at a rate of 1 ° C./hr from 1080 ° C. to 900 ° C. to perform crystallization, and then cooled in a furnace to obtain a sample having a diameter of 2 inches.
Next, a 5 mm square crystal was taken out from the sample and used as a seed crystal.

Next, raw material powders of Y ₂ O ₃ , BaO ₂ , and CuO were separately mixed in a molar ratio of Y: Ba: Cu = 1.8: 2.4: 3.4, and then fired at 900 ° C. for 20 hours. . The obtained calcined product was sufficiently pulverized with an automatic mortar, and further pulverized with a ball mill using an acetone solvent to prepare a powder having an average diameter of about 3 μm.

Then, the obtained powder was pressed under a pressure of 1 ton / cm ² to form a 2 inch-diameter compact, which was used as a precursor, and was set at the center of a one-zone temperature gradient furnace. After setting the center temperature of the sample to 1100 ° C., holding the sample for about 1 hour, moving the sample to a temperature range of about 1000 ° C.
Here, the seed crystal was set on the precursor.

Next, when the seed crystal was moved from the side where the seed crystal was placed to the outside of the furnace at a speed of 1 mm / hr, a sample in which the entire 2-inch diameter was aligned with the crystal orientation of the seed crystal was produced. A seed crystal having a thickness of 5 mm was cut out.

Next, Yb ₂ O ₃ , BaO ₂ , CuO
Of the raw material powder of Yb: Ba: Cu = 1.8: 2.4: 3.4
And then calcined at 900 ° C for 20 hours,
A 3 inch diameter molded body produced using the powder having an average particle diameter of about 3 μm obtained by the above method was used as a precursor,
The zone was set at the center of the temperature gradient furnace.

After the central temperature in the furnace was set at 1100 ° C., the sample was held for about 1 hour, and then moved to a temperature range of about 980 ° C. where the seed crystal was set on the precursor. 1 mm from the side where the seed crystal is placed to the outside of the furnace
When the sample was moved at a speed of / hr, a sample having the entire 3-inch diameter aligned with the crystal orientation of the seed crystal was produced.

[0048]

Comparative Example 1 A 5 mm square seed crystal obtained by the method shown in Example 1 was used. In this case, Y was used as a precursor for depositing the seed crystal.
The raw material powder of ₂ O ₃ , BaO ₂ , and CuO is Y: Ba: Cu =
Using a powder having an average diameter of about 3 μm obtained from a mixture of 1.8: 2.4: 3.4 in a molar ratio of 1.8: 2.4: 3.4, a molded body having a diameter of 3 inches instead of a diameter of 2 inches was directly used as a precursor. And

Next, the precursor was set in the center of a one-zone temperature gradient furnace, the center temperature in the furnace was set to 1100 ° C., and the sample was held for about 1 hour. After moving the sample and setting the above 5 mm square seed crystal, move 1 mm from the side where the seed crystal is placed to the outside of the furnace.
When the seed crystal is moved at a speed of / hr, the seed crystal grows in a direction different from the seed crystal direction at the edge part away from the place where the seed crystal is placed. A sample having the same crystal orientation could not be produced.

Similarly, a molded product having a diameter of 4 inches was prepared using the above-mentioned powder as a precursor, and a 5 mm square seed crystal was treated in the same manner. It was not possible to grow in the same orientation as the seed crystal.

As a result, it was found that it is possible to obtain an oxide superconductor having a desired size by sequentially increasing the size of the seed crystal in contact between the seed crystal and the precursor and adjusting the crystal decomposition temperature. did.

[0052]

As described above, the present invention is a method utilizing the principle that the size of a seed crystal can be adjusted to the size of a precursor so that crystals having successively larger diameters can be formed. Since the seed crystal can be sliced and used, the mass productivity is high and the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of how to place a seed crystal.

FIG. 2 is a schematic diagram showing another example of how to place a seed crystal.

[Explanation of symbols]

 1 seed crystal 2 precursor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keizo Takeuchi 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Shigeo Nagaya 20 Kita-Sekiyama, Otakacho, Midori-ku, Nagoya-shi, Aichi Prefecture Address No. 1 Chubu Electric Power Co., Inc. Power Technology Research Institute (72) Inventor Naoki Hirano 20-1 Kita-Sekiyama, Odaka-cho, Midori-ku, Nagoya-shi, Aichi Prefecture No. 1 Chubu Electric Power Co. Power Technology Research Institute (56) Reference Document JP-A-5-170598 (JP, A)

Claims (1)

(57) [Claims] 1. The general formula RE ₁ RA ₂ Cu ₃ O _x (RE is a mixture of one or more elements selected from the group consisting of rare earth elements, and RA is selected from the group consisting of alkaline earth elements. in one or has a crystal structure represented by a mixture of two or more elements in a), and method for growing a 123 phase crystal containing 211 phases, in advance of the general formula
While producing a seed crystal of 123 phase having a crystal structure ,
To prepare a molded body for producing a sintered <br/> crystal having a 123 phase crystal structure larger dimensions than seed crystals, then, the molded article
After the semi-molten state maintained at 1050 to 1200 ° C., while growing the seed crystals the contacted with 123 phase crystal, a heat treatment step of gradually cooling at a rate of 0.5~2 ℃ / hr <br / To obtain a crystal having the same crystal orientation as the seed crystal,
Next, the obtained crystal is sliced, and the obtained slice is
By repeating the previous heat treatment step by using a single as seed crystals to prepare large second seed crystal dimensions than the initial seed crystals, further method for accomplishing the same thing increasingly large crystals by repeating sequentially the A, 123 phase crystal production
The molded body for
A method for growing an oxide superconductor, wherein the ratio of the size is less than 72.6 / 5 .