JP2556401B2 - Oxide superconductor and method for manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconductor and a method for manufacturing the same.

[0002]

_2. Description of the Related Art YBa ₂ Cu ₃ O _7-X type (123 phase type) superconductor is a type of melting method, QMG (Quench).
h and Melt Growth) method, 77
Under the conditions of K and 1T, it has a critical current density (Jc) of 10 ⁴ A / cm 2 or more, and it has been clarified that it has characteristics for practical use (New.
Superconducting Materials
Forum News NO. 10. (1988) P1
5). In addition, research into increasing the size of these QMG materials and combining RE elements is also being conducted (Physica
C 162-164 (1989) PP1217-12
18 or Proceedings of the 50th Annual Meeting of the Applied Physics Society of Japan (Autumn 1989) 39a-P-10). These are ones in which an oxide superconducting material containing one type of Y element or various RE elements is grown in one direction in a temperature gradient to enlarge the crystal.

The study on the enlargement of such a crystal has been made to solve such a problem because the crystal grain boundary acts as a weak bond in the polycrystalline structure to inhibit the superconducting property. However, in the above-mentioned prior art, only a single crystal material having a size of 0.3 cubic centimeters was obtained at most, and it was extremely difficult to grow the structure of 123 phase in one direction to form a large single crystal. That is, the prior art has not solved the crystal nucleus generation means, the crystal growth control method, and the like.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides RE (one or a combination of rare earth elements including Y), Ba and C.
It is an object of the present invention to provide a material composed of a large single crystal REBa ₂ Cu ₃ O _7-X phase (hereinafter referred to as 123 phase) in an oxide superconductor which is a composite oxide of u. Further, the present invention has a RE ₂ BaCuO ₅ phase (hereinafter referred to as 211 phase) having a very fine grain size in a large 123 phase.
The purpose of the present invention is to provide a tissue material in which is dispersed.

[0005]

In order to achieve the above object, the present invention provides R by changing the kind of RE element or the kind and mixing ratio thereof (hereinafter referred to as RE composition).
The present invention provides a technique for controlling crystal growth by utilizing the difference in crystal formation temperature peculiar to each component of E, and further provides a method for inoculating a seed crystal to produce a large crystal body. .

That is, according to the present invention, among rare earth elements, Y and S
m, Eu, Gd, Dy, Ho, Br, Tm, Yb and an element consisting of two or more kinds selected from the group of Lu (hereinafter referred to as RE), a superconductor which is a composite oxide of Ba and Cu, The superconductor is a single crystal 123
The phase consists of a structure in which 211 phases are finely dispersed, and the 123 phases are multi-layered according to the composition of RE and 12 of each layer.
An oxide high-temperature superconductor composed of three-phase generation temperatures in order, and the present invention is a method for producing the oxide high-temperature superconductor, comprising the oxide of RE, Ba and Cu (complex oxide). The powder contains mol% (R
E, Ba, Cu) is (10, 60, 30), (10,
20, 70), and (50, 20, 30) are mixed so as to have a composition in a region connected to each other, and then a mixed powder of another RE composition different from the 123 phase formation temperature of the RE composition in the mixed powder. Are mixed so as to have a composition within the above-mentioned region, and further, a plurality of such mixed powders are laminated in a multilayer and in order of 123 phase generation temperature of the RE composition of each layer, and then pressure molding is performed to form a precursor, Next, the precursor is heated to a temperature region (solid-liquid coexistence region) in which a solid phase (211 phase) determined by the RE composition and a liquid phase determined by the oxides of Ba and Cu coexist, and then, in a semi-molten state, The 123-phase formation temperature region determined by the RE composition is gradually cooled or stepwise-cooled under predetermined conditions, or cooled from the solid-liquid coexistence region to the seed crystal inoculation temperature, and the seed crystal (in the RE composition of the precursor Higher than the highest 123-phase formation temperature of 1 After inoculation of a single crystal) of the 123 phase of the RE composition having a three-phase formation temperature, and wherein the gradual cooling or steps retention cooling the precursor at the same conditions. The oxide superconductor having the above-mentioned characteristics is manufactured by controlling the generation of the 123 phase and increasing the growth thereof by such a method.

[0007]

[Function] The temperature T at which the 123 phase is generated in the oxide superconductor
g is determined by the composition of the contained rare earth element (including Y).
In the atmosphere, the formation temperature of the 123 phase of the element (RE) shown in Table 1 among the rare earth elements is almost the temperature shown in this table.

[0008]

[Table 1]

The RE element having a smaller atomic number, that is, a larger ionic radius has a higher production temperature. When a plurality of RE elements are mixed, the formation temperature Tg [RE ₁ (m ₁ ) of a crystal having a composition in which the molar fraction of RE ₁ occupies all the RE elements is m ₁ , the molar fraction of RE ₂ is m ₂ , ... ₁ ), RE
₂ (m ₂ ), ...] can be expressed by the following equation. Tg = (Tg (RE ₁ ) × m ₁ + Tg (RE ₂ ) × m ₂ + ...)

Among the rare earth elements, Ce, Pr, Tb
Since each element does not form a 123 phase structure by itself, it is not used as the rare earth element of the present invention. Further, regarding La, the primary crystal from the molten state becomes (La _1-X Ba _X ) ₂ CuO ₄ , and regarding Nd, Nd _{1 + Y} Ba _2-Y Cu ₃ O _7-X.
Therefore, the genuine type 123 phase targeted by the present invention is not generated. Therefore, although not used alone in the present invention, La, N
Since d can be added in a small amount to another RE system, the temperature at which the 123 phase is formed can be increased, so that the temperature range can be widened when RE is selected.
It can also be used to increase the phase formation temperature.

The method for producing the superconductor of the present invention based on these findings will be described below. RE, Ba and C
The molar ratios (RE, Ba, Cu) of the respective metal elements of the oxide of u and / or the composite oxide are points A: (10, 60, 30) and B: in the ternary equilibrium diagram shown in FIG. (10,
20, 70) and C: (50, 20, 30) to form a layer by mixing so as to have a composition in a region connected by (50, 20, 30). The composition outside this region does not retain the shape of the precursor described later during heating to the solid-liquid coexistence region, and the 123 phase does not proceed smoothly in the cooling process after heating. The preferable range of the above molar ratio is D: (30,33,3) shown in FIG.
7), E: (15, 38, 47), F (15, 30, 5)
5), G: (30, 25, 45) is the composition in the region connected by the points.

In this case, the starting material is RE ₂ O ₃ ,
BaCuO ₃ , BaO, CuO, CuO ₂ , BaCuO
_{2, RE 2 BaCuO 5, REBa} 2 Cu 3 O 7-X or the like. Next, the RE element in the mixed powder is 12
Another RE element having a different three-phase generation temperature, that is, an RE element having a temperature lower than or higher than the 123-phase generation temperature of the powder mixing layer is mixed to have a composition within the above range, and the mixed powder is mixed. Laminated on top of the layers to form multiple layers.

By repeating this operation, the mixed powders having a plurality of RE compositions are piled up in multiple layers.
The layers are laminated so that the 123 phase generation temperature of the E composition is continuous to the high temperature side. The thickness of the above layer is preferably about 2 cm or less in consideration of the effects obtained by the present invention and work efficiency. After laminating each layer in this manner, pressure is applied to form a precursor.

The precursor may be manufactured by the stack quenching method. That is, the mixed powder layer is heated to 1200 ° C.
A molten body is formed by heating to the above temperature, and the molten body is pressed against a lump made of a cooled metal such as a metal having high thermal conductivity to be rapidly cooled (hammer quench method) to form a molded body, Next, a mixed powder layer containing another RE element having a different 123 phase formation temperature in the compact is formed into a compact by the same operation as described above, and these plural compacts are formed into 123 phases of each compact. The precursors are formed by stacking them so that the temperature continues to the high temperature side.

The composition of the precursor thus produced by the powder lamination method or the overlap quench method has a composition in which the RE oxide is finely dispersed in the Ba and Cu oxides.

Next, a method for producing a superconductor using the above precursor will be described. First, the temperature range of the precursor in the solid-liquid coexistence region, that is, the 123 phase formation temperature (Tg)
A temperature range exceeding the 211 phase melting temperature (Td) (that is, the lower limit is a temperature at which the Lu-based 123 phase is sufficiently decomposed,
The upper limit is a temperature (about 900 to 1300 ° C.) at which the Sm-based 211 phase decomposes and cannot maintain its shape, and is heated for 15 to 45 minutes to a semi-molten state, and 21 in the liquid phase (Ba, Cu oxide).
Generate one phase (solid phase).

Next, the temperature is cooled from the above temperature range to a temperature of (Tg (H) +10) ° C. at an arbitrary cooling rate, and (Tg (H))
The temperature range of +10) ° C to (Tg (L) -40) ° C is gradually cooled, or stepwise-cooled substantially equivalent thereto to obtain 123.
The phase is grown at a growth rate of 5 mm / hr or less. Here, Tg (H) represents the highest temperature of the 123-phase production temperatures of each RE composition of the precursor, and Tg (L) represents the lowest temperature of the production temperatures.

Since the 123-phase crystal has a complicated structure, entropy changes greatly during crystallization, and it is difficult for nucleation to occur even in a relatively large supercooled state, and the growth is not completed sufficiently. is there. Therefore, the gradual cooling or the stepwise cooling is an essential work within a range from 1070 ° C. in which the Sm-based 123 phase enters the production process to 840 ° C. (see Table 1) at which the Lu-based 123 phase finishes growing sufficiently. .

The substantial average cooling rate R (° C./hr) in the above slow cooling or staged cooling is determined by the following equation. R ≦ k · ΔTg / D where k: target grain growth rate (mm / hr) ΔTg: maximum Tg deviation where ΔTg = (Tg (H) +10) ° C .- (Tg (L) -40) ° C. D: total Thickness (mm)

By gradually cooling or stepwise holding cooling at the cooling rate of the above formula, the layers are sequentially cooled according to the 123-phase formation temperature of each layer. It is possible to produce a single crystal 123 phase. The slow cooling may be performed in an atmosphere having a temperature gradient of 2 ° C./cm or more, or the precursor may be moved so that this temperature gradient is achieved.

The treatment at the 123-phase formation temperature described above causes nuclei to be generated from the layer having the highest 123-phase formation temperature Tg (H) in the precursor, and the crystal growth orientations are sequentially formed in the layer having the lower temperature. Grow crystals while inheriting. With such a multilayer structure, it is possible to extremely effectively suppress the generation of other crystal nuclei as compared with a single layer having the same size.

Next, in order to further exert the effects of the present invention, a single crystal seed crystal containing a 123 phase having a 123 phase formation temperature higher than the maximum 123 phase formation temperature Tg (H) in the precursor is prepared. The technique of inoculating the body will be explained.

First, the precursor is heated to a solid-liquid coexistence temperature range to be in a semi-molten state. Next, the seed crystals are cooled from the above temperature range to a seed crystal inoculation temperature, that is, a temperature range of 900 to 1100 ° C., and seed crystals are inoculated in this temperature range. The lower limit of the temperature range is limited to the Yb-based 123 phase, and the upper limit is limited to the point that a crystal of the Sm-based 123 phase added with La and Nd can be used as a seed crystal.

The seed crystal has a RE composition having a 123 phase formation temperature higher than the 123 phase formation temperature of the RE composition in the precursor, and is a crystal body having a single crystal structure at least on the surface in contact with the precursor. is there. After the seed crystal was inoculated in this manner, the precursor was added at (Tg (L) -40) ° C. to (Tg (H)).
Gradually cool or stage-hold cooling in the temperature range of +10) ° C.

As described above, when the seed crystal (a single crystal or a polycrystal in which the contact surface is a single crystal state) is inoculated into a precursor in a semi-molten state close to the temperature at which the 123 phase is produced, 1
Since it is possible to reliably generate the 23-phase crystal nuclei and grow the 123-phase in the same arbitrary direction as that of the seed crystal, the crystal orientation of the 123-phase can be more strictly controlled to the high current density direction. An extremely high critical current density can be obtained in combination with an increase in the size of the phase crystals.

Further, at least one of Pt and Rh may be added to the precursor component. As a result, the grain size of the 211 phase in the 123 phase can be made fine. The addition amount is Pt: 0.2 to 2.0 wt%, Rh: 0.005 to
It is in the range of 1.0 wt%, whereby the effects of the present invention can be sufficiently exhibited.

When heat treating the precursor, it is necessary to support the precursor with some substance. At present, platinum is mainly used as a support material, but the liquid phase components (oxides of Ba and Cu) in the semi-molten state are extremely reactive, and if they are kept in contact with the support material for a long time, the liquid phase components will become The crystallinity and superconducting properties are impaired due to the inclusion of impurities and impurity elements.

The inventors have found that a stable support material should use the 123 phase itself. That is, another RE composition having a higher crystal formation temperature than the RE composition of the 123 phase in the precursor M is provided between the precursor (hereinafter referred to as the precursor M) and the support material that supports the precursor M. Precursor H and another precursor L having a RE composition having a lower crystal formation temperature than the RE composition of the 123 phase in the precursor M in the order of precursor M-precursor L-precursor H-support material. It is arranged and such a precursor is used as a barrier to the support material. The precursor H serves as a barrier for preventing the liquid phase portion of the precursor M from flowing out to the support material, and the precursor L prevents the 123-phase crystal made of the precursor H from growing to prevent the crystal growth of the precursor M. It is used as a barrier to prevent If the 123 phase of the lowermost layer of the precursor M has the same function as the precursor L, the precursor L may be omitted. By arranging such a barrier, crystals can be grown more efficiently.

The present inventors conducted an experiment in which the precursor of the present invention was inoculated with a seed crystal as follows. Table 2 shows the ratio of Y and Yb
, Y (Yb) Ba ₂ C varied by 10% as shown in FIG.
u ₃ O _7-X powder and Y (Yb) ₂ BaCuO ₅ powder were prepared, and Y (Yb) Ba ₂ Cu ₅ O _7-X powder was prepared so that RE: Ba: Cu became (6: 9: 13). To Y (Yb)
After adding ₂ BaCuO ₅ powder in 20 mol% increments, 140
A precursor was prepared by heating and melting at 0 ° C., and rapidly cooling it by lap hammer quenching nine times so that the Y component was sequentially replaced by Yb. The temperature of 123-phase formation due to the difference in RE component of this precursor is shown in Table 2 below.

[0030]

[Table 2]

After heating such a precursor to 1100 ° C.,
One end of the precursor was cooled to 1020 ° C., and the Sm-based single crystal prepared in advance was placed as a seed crystal on one end of the semi-molten precursor. Next, it was gradually cooled at 3 ° C./hr until one end thereof reached 910 ° C. FIG. 2 shows the crystal structure of the junction between the seed crystal and the obtained crystal. It can be seen that the crystal orientation of the seed crystal is inherited.

Next, the following experiment was conducted using the above precursor. The precursor was placed on a quench material having RE of Sm with the Y side facing up, heated to 1100 ° C., and then a temperature gradient of 5 ° C./cm was created in the furnace to make the precursor Y After cooling the side to 1020 ° C., a Sm-based single crystal prepared in advance was used as a seed crystal and placed on the Y side of the semi-molten precursor. Next, 5 until one end reaches 910 ° C
The mixture was gradually cooled at 3 ° C / hr while maintaining the temperature gradient of ° C / cm.

FIG. 3 shows a crystal structure near the surface of the obtained superconductor. It can be seen that nucleation is suppressed even on the surface. Further, FIG. 4 shows the structure of the Sm barrier inserted between the precursor and the support, that is, the crystal of the precursor contact portion. It can be seen that the Sm-based superconductor is in a polycrystalline state, whereas the Y-Yb system is a single-crystal superconductor.

The superconductor manufactured by the seed metal inoculation method as described above has a structure in which 211 phases are finely dispersed in 123 phases of a single crystal, and the 123 phases have a plurality of Rs.
Each of the 123 phases of the E composition has a multilayer structure and is stacked so that the 123 phase generation temperature of each layer is continuous on the high temperature side.

The obtained single crystal superconductor is a columnar material having an average diameter of 50 mm and a height of about 30 mm, which is 30 to 30% higher than that of the conventional material announced in Physica C. It is 50 times larger.

The 211 phase in the superconductor is 123
Volume ratio in the phase is in the range of 5 to 50%, preferably 10 to 3
The particles are dispersed in the range of 0%, and the particle size is fine at 20 μm or less, and particularly when Pt or Rh is added, the average particle size becomes 2 μm or less (about 5 μm at maximum).

The superconductor having the above structure is in the state of stacking 123 phases different for each RE composition, but since there is no grain boundary between the layers, the superconductor is not cut into a superconducting state and an extremely large amount of current flows. Can be drained.

Further, the 211 phase has toughness to the 123 phase and has an action of retaining the magnetic force lines passing through the superconductor (pinning action). In the present invention, the 211 phase is extremely finely dispersed throughout the entire structure. Since the magnetic lines of force can be reliably held, the lines of magnetic force are pinned even when the superconductor is placed in a magnetic field, and a large current density can be obtained. Due to such an effect, the material of the present invention can exhibit excellent superconducting properties.

[0039]

EXAMPLES Example 1 The Dy: Er ratio was changed by 20% (100: 0),
(80:20), (60:40), (40:60),
Six types of RE compositions of (20:80) and (0: 100) were prepared by kneading Dy ₂ O ₃ and Er ₂ O _3, and R
B so that E: Ba: Cu becomes (25:35:40)
Six kinds of mixed powders were obtained by mixing aCuO ₂ and CuO.
Using a die having a diameter of 30 mm, the Dy layer was sequentially laminated to the Er layer to have a thickness of about 6 mm to prepare a columnar precursor having a height of about 35 mm. This is shown in FIG.

The precursor was supported by a Pt plate with the Er side facing down, heated from room temperature to 1180 ° C. in the atmosphere for 2 hours, then held for 30 minutes and kept at 1020 ° C. for 1 hour.
Cooling at 00 ℃ / hr and 0.5 ℃ / h till 940 ℃
Cooled at r. Then, it was cooled to room temperature in the furnace, reheated to 800 ° C. in an oxygen stream, and gradually cooled to 200 ° C. at a cooling rate of 8 ° C./hr.

The obtained sample was composed of three large crystal grains, and the largest sample had a volume of about 15 cubic centimeters, and an extremely large superconducting material could be obtained.

Example 2 The ratio of Dy: Ho: Er was (100: 0: 0), (50:
5: 0), (0: 100: 0), (0: 50: 5)
0), (0: 0: 100), and 5 types of RE compositions with Dy ₂
It was prepared by kneading O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ and the like, and further mixed with BaCuO ₂ and BaCu ₂ O ₃ so that RE: Ba: Cu becomes (25:28:47). 5
A mixed powder was obtained. Using a die having a diameter of 50 mm, the Dy layer and the Er layer were laminated in the above order to make the thickness of one layer about 6 mm, and a columnar precursor having a height of 30 mm was produced.

This precursor was supported by a Pt plate with the Er side facing down, heated from room temperature to 1180 ° C. in the atmosphere for 2 hours, then held for 30 minutes and kept at 1040 ° C. for 1 hour.
Cooled at 00 ° C./hr and at 1040 ° C. Sm: Nd
Using a seed crystal having a RE composition of 7: 3. The cleavage was placed on the semi-molten precursor and seeded. 1 more
Cooled from 020 to 940 ° C at 0.5 ° C / hr. Then, it was cooled to room temperature in the furnace, reheated to 800 ° C. in an oxygen stream, and gradually cooled to 200 ° C. at a cooling rate of 8 ° C./hr.

The obtained sample has a diameter of about 4 as shown in FIG.
Two small crystals with a different orientation from the seed crystal were formed in the vicinity of platinum of the support material on a cylindrical body of 3 mm and a height of about 27 mm, but most of them consisted of a single crystal grain with the same orientation as the seed crystal. And a superconducting material having a size of about 35 cubic centimeters could be obtained.

Example 3 The ratio of Y: Er was changed by 20% (100: 0),
(80:20), (60:40), (40:60),
After preparing RE ₂ BaCuO ₅ having 6 types of RE compositions of (20:80) and (0: 100), RE: Ba:
BaCuO ₂ so that Cu becomes (18:35:47)
And BaCu ₂ O ₂ are mixed, and 0.5 wt% of Pt is further added.
The powder was added to obtain 6 kinds of mixed powder. Using a mold having a diameter of 50 mm, the Y layer to the Er layer were laminated in the above order to have a thickness of one layer of about 5 mm and a columnar precursor having a height of about 30 mm was produced.

This precursor was supported by a Pt plate with the Er side facing down, heated from room temperature to 1150 ° C. in the atmosphere for 2 hours, then held for 30 minutes and kept at 1030 ° C. for 1 hour.
Cooled at 00 ° C./hr and at 1030 ° C. Sm: Nd
Using a seed crystal having an RE composition of 7: 3, the cleavage plane was placed on the semi-molten precursor to perform seeding. 1 more
Cooled from 010 to 940 ° C at 0.5 ° C / hr. Then, it was cooled to room temperature in the furnace, reheated to 700 ° C. in an oxygen stream, and gradually cooled to 250 ° C. at a cooling rate of 5 ° C./hr.

As shown in FIG. 7, the obtained sample was a cylindrical body having a diameter of about 46 mm and a height of about 28 mm, and two small crystals having different orientations from the seed crystal were formed in the vicinity of platinum of the support material. Most of them consisted of a single crystal grain having the same orientation as the seed crystal, and a superconducting material having a size of about 40 cubic centimeters could be obtained. Further, from the measurement of the magnetic susceptibility by the sample vibration type magnetometer, this sample was 1.
A Jc of 2 × 10 ⁴ A / cm ² was obtained.

Example 4 The Y: Er ratio was changed by 20% (100: 0),
(80:20), (60:40), (40:60),
After preparing RE ₂ BaCuO ₅ having 6 types of RE compositions of (20:80) and (0: 100), RE: Ba:
BaCuO ₂ so that Cu becomes (18:30:52)
And BaCu ₂ O ₂ are mixed, and R of 0.02 wt% is further added.
h powder was added to obtain 6 kinds of mixed powder. 50 mm diameter
Using the mold described in (1), the Y layer was stacked in this order on the Er layer in the above order to have a thickness of about 5 mm, and a columnar precursor having a height of about 30 mm was produced.

This precursor is Er-side down, and using a precursor of Sm and Yb of RE composition having a thickness of 1.5 mm prepared by a hammer quench method, a precursor of Y-Er composition-Yb composition is prepared. Precursor-precursor of Sm composition-Pt plate, stacked and supported in this order from room temperature to 115
After heating to 0 ° C for 2 hours, hold for 30 minutes,
Cooled to 100 ° C / hr at 100 ° C and S at 1030 ° C
Using a seed crystal having a RE composition of m: Nd of 7: 3, the cleaved surface was placed on the semi-molten precursor to perform seeding.
Further, it was cooled from 1010 to 940 ° C at 0.5 ° C / hr. After that, cool to room temperature in the furnace, and in an oxygen stream 70
It was reheated to 0 ° C. and gradually cooled to 250 ° C. at a cooling rate of 5 ° C./hr.

The obtained sample has a diameter of about 4 as shown in FIG.
A cylindrical body of 6 mm and a height of about 28 mm was formed by a single crystal grain in the same orientation as the seed crystal, and an extremely large superconducting material of about 45 cubic centimeters could be obtained. Further, this sample was 1.5 × 10 5 under the same conditions as in Example 3.
A Jc of ⁴ A / cubic centimeter was obtained.

Example 5 Y (Yb) Ba ₂ Cu ₃ O _7-X powder and Y (Yb) in which the ratio of Y and Yb was changed by 10% as shown in Table 2.
b) ₂ BaCuO ₅ powder was prepared, and Y (Yb) Ba ₂ Cu ₃ was prepared so that RE, Ba, and Cu were (6: 9: 13).
After adding Y (Yb) ₂ BaCuO ₅ to O _7-X by 20 mol%, each was heated to 1400 ° C., and 9 times of repeated quenching was performed so that the Y composition was sequentially changed to the Yb composition.
A molded body having a thickness of one layer of about 2 mm and a total thickness of about 20 mm was obtained. From this, a precursor was prepared by cutting into a size of 20 mm square. Table 2 shows the 123-phase formation temperature in the atmosphere due to the difference in RE composition of this precursor.

This precursor was once heated at 1100 ° C. for 20 minutes to be partially melted, and then Y in a temperature gradient of 30 ° C./cm.
Composition side is high temperature side, Y side is 1010 ℃ to 850 ℃
The temperature of the entire furnace was cooled to 6 ° C./hr and unidirectionally grown to obtain a superconductor. At this time, the average crystal growth rate is about 0.
It was 8 mm / hr. Oxygen annealing was performed by gradually cooling from 700 ° C. to 300 ° C. at 10 ° C./hr in an oxygen stream. As a result, a sample consisting of three crystal grains was obtained, as shown in FIG.
It was a cubic centimeter.

Example 6 The RE composition was changed to Sm, Eu, Gd, Dy, Ho, Er, T.
REBa ₂ Cu ₃ O _7-X powder and RE ₂ BaCuO ₅ powder which were changed in the order of m and Yb were prepared, and RE, B
a, Cu (6: 9: 13) so that REBa ₂ Cu
After adding RE ₂ BaCuO ₅ to ₃ O _7-X by 20 mol%, each was heated to 1450 ° C., and repeated quenching was repeated eight times so that the Sm composition was changed to the Yb composition in order.
A molded body having a thickness of one layer of about 2 mm and a total thickness of about 17 mm was obtained, from which a precursor was cut out to a size of 20 mm square. Next, this precursor was heated to 1150 ° C., then cooled to 1060 ° C. at 50 ° C./hr, and further 9
It was cooled to 10 ° C at 2 ° C / hr and unidirectionally grown. The average growth rate at this time was 0.2 mm / hr.

FIG. 10 is a sketch of an EPMA image showing the distribution of Dy, Ho and Er elements. It can be seen that they are distributed in layers. In addition, a material with uniform orientation was obtained over the entire sample.

[0055]

INDUSTRIAL APPLICABILITY As described in detail above, the present invention can easily increase the size of a bulk material having a high critical current density, can be applied in various fields, and has an extremely large industrial effect.
Specific examples include a superconducting coil, a superconducting magnetic shield material, and a substrate of a superconducting device.

[Brief description of drawings]

FIG. 1 is a diagram showing a range of components of RE, Ba, and Cu in the present invention.

FIG. 2 is a photograph showing a structure of a crystal in the vicinity of an interface with a seed crystal of a Y-based superconductor produced using an Sm-based seed crystal.

FIG. 3 is a photograph showing the structure of crystals in the vicinity of the surface of a unidirectionally grown Y superconductor.

FIG. 4 is a photograph showing a crystal structure of an Sm barrier phase when an Sm superconductor is used as a barrier with a support.

5 is a perspective view of a precursor in Example 1. FIG.

FIG. 6 is a partial cutaway perspective view of a sample in Example 2 after the method of the present invention is applied.

FIG. 7 is a partial cutaway perspective view of a sample in Example 3 after the method of the present invention is applied.

FIG. 8 is a partially cutaway perspective view of a sample in Example 4 after being subjected to the method of the present invention.

FIG. 9 is a perspective view of a sample in Example 5 after being subjected to the method of the present invention.

10 is an EP showing the distribution of Ho, Dy, and Er elements in the sample after the method of the present invention was applied in Example 6. FIG.
It is a sketch figure of MA image.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01L 39/24 ZAA H01L 39/24 ZAZZ (72) Inventor Kiyoshi Sawano 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Address Nippon Steel Co., Ltd., First Technology Research Institute (72) Inventor, Shoki Takebayashi, 1618, Ida, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Nippon Steel Co., Ltd., First Technology Research Laboratory (72) Inventor, Masamoto Tanaka, Kanagawa Prefecture 1618 Ida, Nakahara-ku, Kawasaki-shi, Nippon Steel Corporation (56) References JP-A-2-204322 (JP, A) JP-A-2-153803 (JP, A) JP-A-2- 204358 (JP, A) International publication 90/13517 (WO, A) APPL. PHYS. LETT. 52 (24) (1988) P. 2074-2076

Claims (15)

(57) [Claims] 1. Y, Sm, Eu, Gd, Dy, Ho, E
An element consisting of two or more kinds selected from the group of r, Tm, Yb and Lu (hereinafter referred to as RE), Ba and Cu
In the superconductor which is a composite oxide of the above, the superconductor has a RE ₂ BaCuO ₅ phase (hereinafter referred to as 211 phase) in a single crystalline REBa ₂ Cu ₃ O _7-X phase (hereinafter referred to as 123 phase). It is composed of a finely dispersed structure.
An oxide superconductor characterized in that the phases are formed in multiple layers for each composition of RE and in order of the 123 phase generation temperature of each layer. 2. The 211 phase is finely dispersed in the 123 phase in a volume ratio of 5 to 50%.
The superconductor according to. 3. The superconductor according to claim 4, wherein the grain size of the 211 phase is 20 μm or less. 4. The superconductor according to claim 1, wherein one kind or two kinds of Pt or Rh is added to the superconductor. 5. A powder containing at least one of oxides of RE, Ba and Cu, or at least one of composite oxides, wherein the mol% (RE, Ba, Cu) of each metal element is (10, 60, 3).
0), (10, 20, 70), and (50, 20, 30) to form a layer by mixing so as to have a composition in a region connected to each other, and a 123 phase generation temperature is different from RE. A layer containing other RE elements is formed, and these plural layers are formed in each layer.
23. Stacking so that the phase formation temperature is continuous to the high temperature side or the low temperature side, and then pressure forming to form a precursor, and then supporting the layer having the maximum 123 phase formation temperature in the precursor as the uppermost layer. After being placed on a material, the precursor is heated in the temperature range of the solid-liquid coexistence region to be in a semi-molten state, and then the precursor is gradually cooled in the 123 phase generation temperature range to give crystals of 123 phase at 5 mm / A method for producing an oxide high-temperature superconductor characterized by growing at a growth rate of hr or less. 6. The precursor is heated to a temperature range of a solid-liquid coexistence region so as to be in a semi-molten state, then cooled from the temperature range to a seed crystal inoculation temperature range, and then in the precursor range in the temperature range. Of the maximum 123 phase formation temperature, a seed crystal having a RE composition having a formation temperature higher than that of the above is inoculated into the precursor, and then the precursor is gradually cooled in the 123 phase formation temperature range to continuously form the 123 phase. The manufacturing method according to claim 5, wherein the growth is carried out. 7. The temperature of the solid-liquid coexisting region is 900 to 1350.
The method according to claim 5 or 6, wherein the temperature is ° C. 8. The 123-phase production temperature range is from 1070 to 84.
Within the temperature range of 0 ° C., and (Tg (H) +10)
6. The temperature range is from ℃ to (Tg (L) -40) ℃.
Or the manufacturing method according to 6. However, Tg (H) ... maximum 123-phase generation temperature Tg (L) ... minimum 123-phase generation temperature 9. The seed crystal inoculation temperature range is 900 to 1100.
The method according to claim 6, wherein the temperature is ° C. 10. The production method according to claim 5, wherein the cooling rate R of the slow cooling in the 123-phase production temperature range is performed by the following formula. R ≦ K · ΔTg / D (° C./hr) where k: target grain growth rate (mm / hr) ΔTg: maximum Tg deviation where ΔTg = (Tg (H) +10) ° C .− (Tg (L)
-40) ° C D: Total thickness (mm) 11. The production method according to claim 5, wherein the 123-phase production temperature range is controlled by stepwise cooling. 12. A stepwise holding cooling rate is set to the cooling rate R.
The production method according to claim 10, wherein the production is performed at (° C / hr). 13. The mixed powder layer is heated to a temperature of 1200 ° C. or higher to form a melt, and the melt is rapidly cooled to form a molded body, and then a 123 phase formation temperature in the molded body is changed. A mixed powder layer containing other RE element is formed into a molded body by the same process as above, and the plurality of molded bodies are stacked so that the 123-phase generation temperature of each molded body is continuous on the high temperature side to form a precursor. The manufacturing method according to claim 5 or 6, which is formed. 14. A RE composition having a higher crystal formation temperature than the RE composition of the 123 phase in the precursor M between the precursor (hereinafter referred to as the precursor M) and a support material supporting the precursor M. With another precursor H and R of 123 phase in said precursor M
Another precursor L having a RE composition having a lower crystal formation temperature than the E composition is arranged in the order of precursor M-precursor L-precursor H-support material, and then heated to a temperature range of 950 to 1350 ° C. The manufacturing method according to claim 5 or 13. 15. Pt: 0.2 to 2.0 in the precursor.
wt% and / or Rh: 0.005-1.0 wt
% Is added, The manufacturing method of the oxide superconductor of Claim 5 characterized by the above-mentioned.