JP2550253B2 - Method for producing oxide high temperature 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 producing an oxide superconductor.

[0002]

_2. Description of the Related Art A YBa ₂ Cu ₃ O _7-y type superconductor is manufactured under the conditions of 77K and 1T by a QMG (Quench and Melt Growth) method, which is a kind of melting method.
It has been revealed that it has a critical current density (Jc) of 0 ⁴ A / cm ² or more, and has characteristics to withstand practical use (New Superconducting Materials Foram News No.10.
(1988) P15). In addition, the size of these QMG materials is increased, and R
Studies on combinations of E elements have also been conducted. (Ph
yica C162-164 (1989) PP1217-1
218). These are one type of Y element or various RE
The crystal is enlarged by unidirectionally growing it in a temperature gradient of a QMG material containing an element.

[0003]

The above-mentioned prior art is a superconducting substance, that is, a single crystal in which 211 phases are finely dispersed.
The formation of the 23 phase is determined by the contingency caused by cooling such as slow cooling. Therefore, the crystal orientation and crystal growth could not be controlled. Controlling the crystal orientation is technically important for producing a large single crystal material. In view of this problem, the present invention controls the nucleation, crystal orientation and growth by using a seed crystal having a composition of RE element having a high formation temperature to obtain a large REBa ₂ Cu ₃ O _7-x crystal. Is provided.

[0004]

The present invention is characterized by the following method for producing a superconducting material. That is, RE ₂ O having RE (one rare earth element including Y or a combination thereof) in an oxide body containing Ba and Cu elements in which the ratio of Ba element is 25 mol% to 75 mol% in terms of metal element ratio. Precursor in which ₃ is dispersed 5% to 50% by volume
A precursor having the same RE composition throughout the body is once heated in an oxidizing atmosphere to a temperature range of 950 ° C. to 1350 ° C. to bring the precursor into a semi-molten state, and then a temperature range of 900 ° C. to 1100 ° C. REBa ₂ Cu in the precursor after cooling to
₃ O _7-x phase of the production temperature of the single crystalline seed crystals of REBa ₂ Cu ₃ O _7-x phase of RE composition having a high product temperatures than RE composition is contacted with the precursor, the same optional seed crystal Is characterized in that REBa ₂ Cu ₃ O _7-x is continuously grown by gradually cooling or retaining a superconducting phase having an orientation in the temperature range of 800 ° C. to 1060 ° C. in a uniform temperature or a temperature gradient. .

The ratio of Ba element to metal element is 25
RE ₂ O ₃ having RE (one kind of rare earth element including Y or a combination thereof) in an oxide body containing Ba element and Cu element in an amount of 5% to 5% by volume.
The REBa ₂ Cu ₃ O _{7- x} in the precursor M is interposed between the precursor M in which 0% is dispersed and the support material that supports the precursor M.
REBa ₂ Cu ₃ O in another precursor H having the RE composition having a higher crystal formation temperature than the RE composition of the phase and the precursor M
Another precursor L having a RE composition having a lower crystal formation temperature than the RE composition of _7-x , precursor M-precursor L-precursor H
-A high-temperature oxide superconductor is produced by the method of performing the above heat treatment after the support materials are arranged in this order.

Further, the ratio of Ba element to the metal element ratio is 2
Precursor of RE ₂ O ₃ having RE (one kind of rare earth element including Y or a combination thereof) of 5% to 50% by volume in an oxide body containing 5 mol% to 75 mol% of Ba and Cu elements REBa in the precursor on the surface of the body
After applying the powder containing RE having the RE composition of the low crystalline product temperature than the crystalline product temperature of ₂ Cu 3 O _7-x phase, characterized by forming the oxide high-temperature superconductor according to the method of applying the heat treatment And

[0007]

When the liquid phase component obtained by reheating the precursor is extremely biased to the Ba or Cu component, the liquid phase component after the 211 phase is generated is further biased, and the liquid phase component in the subsequent superconducting phase is This adversely affects the crystal growth of a certain 123 phase, and crystal growth with stable facets does not occur. Therefore, the proportion of Ba element in the oxide body containing Ba and Cu elements is limited to 25% to 75%. Also, RE ₂
If the proportion of O ₃ is lower than 5%, the amount of 211 phase produced is small, and the shape cannot be maintained. On the other hand, if it exceeds 50%, the liquid phase component becomes small, and the growth of the 123 phase does not proceed sufficiently, so that a large crystal cannot be obtained. For these reasons, it is limited to 5% to 50%.

The precursor satisfying the above-mentioned conditions may be produced by lap quenching (a method for producing a precursor in which a melt is repeatedly rapidly cooled with a copper plate or the like to obtain a thick precursor successively), and Y, Ba, Cu It may be obtained by pressure molding a powder containing.

The growth temperature of REBa ₂ Cu ₃ O _7-x is determined by the types of REs contained and their contents. In the atmosphere, the highest Sm system is about 1060 ° C., Y and Ho are about 1000 ° C., The lower one is about 900 ° C. of Yb. The smaller the atomic number and the larger the ion radius, the higher the production temperature. When a plurality of RE elements are mixed, the molar fraction of RE _{1 in} all RE elements is m ₁ , RE
Generating _second mole fraction of crystals having the composition _m 2 · · · temperature _{Tg [RE 1 (m 1)} , RE 2 (m 2), ···]
Can be expressed by the following equation.

Tg = Tg (RE ₁ ) × m ₁ + Tg (RE ₂ ) × Tg (RE ₂ ) × m ₂ ··· However, at this time RE is Sm, Eu, Gd, Tb, D
y, Ho, Er, Yb, Lu, Y. Further, the primary crystal with respect to La system becomes _{(La 1-x Ba x)} 2 CuO 4, with respect to Nd-based _{Nd 1-x Ba 2-x} Cu 3 O
_7-x . However, La and Nd have a function of increasing the production temperature by adding them to other RE system. Therefore, REBa ₂ C having a composition having a higher generation temperature Tg is used.
It can be seen that the crystal of u ₃ O _7-x is effective as a seed crystal of the precursor in a semi-molten state having a lower formation temperature Tg.

The single crystal temperature of the precursor is 950 ° C. or higher at which the Lu-based 123 phase is sufficiently decomposed, and the Sm-based 21 is used.
Below the temperature at which one phase decomposes and the shape cannot be maintained 1350
Limited to ℃. The seeding temperature is 900 ° C. to 1 as a temperature range in which the Yb-based 123 phase and the Sm-based 123 crystal added with La and Nd can be used as a seed crystal.
It was 100 ° C.

Further, since 123 crystal has a complicated structure, entropy changes greatly during crystallization, it is difficult for nucleation even in a relatively large supercooled state, and growth is not completed sufficiently. is there. Therefore, the retention or gradual cooling end temperature is from 1060 ° C at which the Sm-based 123 phase grows to L
The temperature was limited to 800 ° C. at which the 123 phase of the u system was completely finished. The slow cooling rate is preferably 5 ° C./h or less.

The inventor applied these findings to the crystal growth, and increased the size of the QMG crystal by seeding and temperature control. The first item is a method for obtaining a large-sized QMG crystal by controlling a nucleation and orientation of a crystal of a superconductor by making a seed crystal by using a superconductor containing a 123 phase having a relatively high generation temperature and contacting with a precursor. Is to give. The second item is that the precursor H is a barrier between the precursor and the support material to prevent the liquid phase component of the precursor from flowing out to the support material, and the precursor L is a QMG crystal made of the precursor H. The present invention provides a method for obtaining a large-sized QMG crystal by arranging a barrier that prevents the growth of a crystal grown and growing from a seed crystal. The third item is to provide a method for suppressing the nucleation on the surface of the precursor and allowing more stable crystal growth from the seed crystal.

[0014]

【Example】

(Example 1) 20 wt% of Y type 211 phase was added to Y type 123 phase powder.
% (Tg: 1000 ° C.), heated and melted at 1400 ° C., and repeatedly quenched with a copper plate to prepare a 10-layer precursor. After reheating the precursor to 1200 ° C. again,
Hold at 1040 ° C. While holding at 1040 ° C., Sm-based seed crystal (Tg: 1060 ° C.) was placed on the semi-molten precursor to perform seeding. Then, the system was gradually cooled to 950 ° C. at 1 ° C./h to grow a Y-based 123 phase. FIG. 1 shows a crystal state of the obtained sample. Although a crystal having a slightly different crystal orientation was located away from the seeded crystal, a crystal having a size of about 40 cm ³ having the same orientation as the seed crystal was obtained.

(Embodiment 2) Er ₂ O ₃ , BaCuO ₂ and CuO powders were mixed at an element ratio of Er: Ba: Cu of 4: 5: 7.
After kneading so that it becomes uniform, it is molded and has a diameter of 5 cm and a thickness of 2.5 cm.
A precursor (Tg: 980 ° C.) was obtained. 500 of this precursor
C./h to 1150.degree. C., hold for 20 minutes, then
After cooling to 040 ° C., an Sm-based seed crystal (Tg: 1060
Seeding was carried out according to (.degree. C.). Then 1 ℃ up to 910 ℃
/ H was gradually cooled to grow an Er-based 123 phase. The appearance of crystals of the obtained sample is shown in FIG. Large nucleation of about 40 cm ³ was obtained, although nucleation was slightly generated at a distance from the seeded place.

(Example 3) After adding 211 wt% of 211 phase powder to 123 phase powder containing 20 mol% of Yb with respect to Y,
After heating and melting at 1400 ° C, repeatedly quenching with a copper plate,
A 10-layer precursor (Tg: 980 ° C.) was prepared. A Yb-based one-layer precursor (Tg: 900 ° C.) produced by hammer quench is placed under this precursor, and Sm is placed under the precursor.
The system precursor (Tg: 1060 ° C.) was placed and placed on a platinum support. After that, it was rapidly heated again to 1200 ° C. and then kept at 1025 ° C. Seed crystal (Tg: 10) containing 20 mol% of Nd in Sm while holding at 1025 ° C.
(70 ° C.) was placed on the semi-molten precursor to perform seeding. Then, it was gradually cooled to 920 ° C. at 1 ° C./h to grow 123 phase. FIG. 3 shows the crystal state of the obtained sample.
Crystals grew from the seeding, and large crystals of about 60 cm ³ were obtained.

(Embodiment 4) Ho ₂ O ₃ , BaCuO ₂ and CuO powders are mixed in a Ho: Ba: Cu element ratio of 4: 5: 7.
After kneading so that it becomes, it is molded and has a diameter of 5 cm and a thickness of 4 cm.
To obtain a precursor (Tg: 990 ° C.). A Yb-based single layer precursor (Tg: 900 ° C.) produced by hammer quench is placed under this precursor, and an Sm-based precursor (Tg: 1060 ° C.) is placed under the precursor, and a platinum support material is provided. Put it on. Furthermore, YbBa ₂ Cu ₃ O is formed on the surface of the precursor.
After applying _7-x powder (Tg: 900 ° C.), the precursor was heated to 1150 ° C. at 500 ° C./h and held for 20 minutes, and then cooled to 1040 ° C. to obtain a Sm-based seed crystal (Tm).
(g: 1060 ° C.). Then 9
It was gradually cooled to 10 ° C. at 1 ° C./h, and a Ho-based 123 phase was grown. The appearance of crystals of the obtained sample is shown in FIG. From seeding, a large crystal of about 80 cm ³ was obtained.

[0018]

INDUSTRIAL APPLICABILITY As described above, the present invention facilitates the enlargement of a bulk material having a high critical current density, can be applied in various fields, and has a great industrial effect. As a specific example, a superconducting magnet, a superconducting magnetic shield,
Examples include superconducting bearings.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and appearance sketch of a large Y-type crystal produced using an Sm-based seed crystal.

FIG. 2 is a cross-sectional view and a sketch of the appearance of a large Er-based crystal produced using an Sm-based seed crystal.

FIG. 3 is a cross-sectional view and appearance sketch of a large Yb-Y-based crystal produced by using a Sm-Nd-based seed crystal and Yb and Sm-based precursors as a barrier.

FIG. 4 uses a Sm-based seed crystal and a Yb and Sm-based precursor as a barrier, and further uses a Yb-based 1 as a Ho-based precursor.
23 is a cross-sectional view and appearance sketch of a Ho-based large-sized crystal produced by applying 23 powders.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C30B 17/00 ZAA C30B 17/00 ZAA H01B 12/00 ZAA H01B 12/00 ZAA H01L 39/24 ZAA H01L 39/24 ZAAB (72) Inventor Kiyoshi Sawano 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Shin Nippon Steel Co., Ltd. Technical Research Institute No. 1 (56) Reference JP-A-2-208286 (JP, A)

Claims (3)

(57) [Claims] 1. The ratio of Ba element to metal element is 25 mol.
% -75 mol% Ba and Cu elemental oxidation
RE (Y containing one kind of rare earth element or its
RE ₂ O ₃ having a volume ratio of 5% to 5%
Before having the same RE composition throughout the precursor, 0% dispersed
Once the precursor is in an oxidizing atmosphere, once at 950 ° C to 1350 ° C
To a semi-molten state by heating to a temperature range up to
After cooled from 900 ° C. in the region of 1100 ℃, REBa ₂ Cu ₃ O of RE composition having a forming temperature higher than the RE composition of the product temperature of REBa ₂ Cu ₃ O _7-x phase in the precursor
_{A 7-x} phase single crystal seed crystal is brought into contact with a precursor to form a superconducting phase having an arbitrary orientation same as that of the seed crystal from 800 ° C. to 10 ° C.
REBa ₂ Cu ₃ O can be obtained by gradually cooling or retaining the temperature within a temperature range of 60 ° C. in a uniform temperature or a temperature gradient.
_A method for manufacturing an oxide high temperature superconductor, which comprises continuously growing _7-x . _2. The REBa ₂ Cu ₃ O having the RE composition in the precursor M between the precursor M and a support material that supports the precursor M.
RE composition precursor H having higher _7-x phase formation temperature REBa ₂ Cu ₃ O _7-x phase formation temperature and said precursor M
RE with lower REBa ₂ Cu ₃ O _7-x phase formation temperature of REBa ₂ Cu ₃ O _7-x phase formation temperature of the RE composition in
The composition of the precursor L, precursor M-precursor L-precursor H-
The manufacturing method according to claim 1, wherein the supporting materials are arranged in this order. 3. REBa ₂ Cu ₃ O _7-x having a RE composition in the precursor or in the precursor M on the surface of the precursor or the precursor M.
The method according to claim 2, wherein a powder of RE composition having a REBa ₂ Cu ₃ O _7-x phase formation temperature having a lower phase formation temperature is applied.