JPH05279033A - Production of oxide superconductor having high critical current density - Google Patents

Abstract

PURPOSE:To improve the critical current density by mixing and molding the compd. expressed by specific formula, Ba oxide and Cu oxide, then subjecting the molding to a heat treatment, thereby growing a superconducting phase. CONSTITUTION:Raw material powders of the compd., such as Y2Cu2O5, expressed by the formula (RE is a rare earth element, such as Y, Sm, Eu or Gd), BaCO3, CuO, etc., are so mixed that Y/B/Cu attain prescribed atomic ratios. Pt or a Pt compd. is added and mixed at 0.1 to 2wt.% (hereafter %) in terms of Pt to and with this mixture or a Ce oxide at 0.1 to 2% in terms of CeO2. The mixture is then press molded and the molding is heated to 950 to 1250 deg.C and is held for a prescribed period of time, by which the molding is partially melted to allow an REBa2CuO5 phase and a liquid phase to coexist. The molding is cooled until REBa2Cu3Ox grows from the liquid phase and is then slowly cooled down to 850 to 950'C at 0.2 to 20 deg.C/hour to allow the crystal to grow. The molding is then heat treated at 650 to 300 deg.C in an oxygen enriched atmosphere and is cooled, by which the REBaCuO oxide superconductor having the high critical current density is obtd.

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 novel REBaCuO-based oxide superconductor, and more particularly to a method for producing an oxide superconductor having a high critical current density. Where RE is Y,
Represents a rare earth element selected from the group of Sm, Eu, Gd, Dy, Ho, Er, and Yb.

[0002]

REBaCuO-based oxide bulk superconductors have been conventionally manufactured by the MTG (Melt Textured Growth) method (S. Jin et al. Appl. Phys. Lett. Vol 52 No. 207 1988 P297.
4) etc. were manufactured. An example of manufacturing by the MTG method will be shown. First, the raw material powders are blended so as to have the REBa ₂ Cu ₃ O _x composition and molded. The molded body is partially melted, and then gradually cooled under a temperature gradient to grow a superconducting phase. afterwards,
Annealing is performed in an oxygen-rich atmosphere to add oxygen to the superconducting phase. In this method, the RE ₂ BaCuO ₅ phase (hereinafter referred to as the 211 phase) is not intentionally dispersed, and the critical current density is about 4,000 A / cm ² at 77K, 1T (Tesla). Is not high enough.

On the other hand, recently MPMP (Melt Powder Melt G
rowth) method (H. Fujimoto et al. Proc. of ISS'89 Springer-V
erlag 1990 P285) etc. were developed and the critical current density was 77K, 1
It has exceeded 10,000 A / cm ² at T. Below, M
An example of manufacturing with PMG is shown. First, the raw material powder, for example Y ₂
O ₃ , BaCO ₃ , and CuO are mixed in a predetermined ratio. This may be calcined and crushed. Further, this powder is heated to a temperature at which the RE ₂ O ₃ phase and the liquid phase coexist, for example, 1400 ° C. to partially melt (M) the mixed powder. Further, it is solidified by cooling. After that, it is crushed (P) mixed and pressure molded. The molded body is heated to a temperature at which the 211 phase and the liquid phase coexist, for example, 1100 ° C. to partially melt (M). Thereafter, the 123 phase which is the superconducting phase is cooled to a temperature at which the 123 phase is generated, and the 123 phase is generated by cooling the temperature from that temperature, for example, at 1 ° C./h.
A superconductor is manufactured by growing (G).

The high critical current density is YBa ₂ Cu ₃ O _x
It was achieved by finely dispersing the 211 phase in the phase (hereinafter 123 phase). Furthermore, it has been reported that the critical current density improves as the size of the 211 phase decreases (M. Murakami et al. Proc. Of M ² S HTSC III Confere.
nce 1991). Therefore, as one means for obtaining a high critical current density, it is important to disperse the 211 phase in the 123 phase and further reduce the size of the 211 phase.

On the other hand, the magnetic levitation force exhibited by the superconductor is
The higher the critical current density and the larger the superconducting crystal, the higher (M. Murakami et al. Japanese Journal of Applie
d Physics Vol.29 No.11 1990 L1991), it is important to have a high critical current density in order to obtain a high magnetic levitation force.

However, as described above, according to the MTG method, although the superconductor can be manufactured in a relatively simple and small number of steps, the critical current density is relatively low. Further, although the MPMG method has a high critical current density, it has a drawback that the manufacturing process is complicated.

Thus, the present invention has a critical current density higher than that of the superconductor obtained by the MTG method.
It is intended to provide a method capable of manufacturing a REBaCuO-based oxide superconductor with a simpler and fewer manufacturing process than the MPMG method.

[0008]

The present inventors have SUMMARY OF THE INVENTION may, RE ₂ Cu ₂
Using O ₅ , Ba oxide, and Cu oxide as raw materials,
After molding, the molded body is heated to a temperature at which the 211 phase and the liquid phase coexist, is partially melted, and is a superconducting phase 123.
A superconductor produced by a method of producing and growing 123 phases by cooling to a temperature at which a phase is produced and then cooling from that temperature is a conventional combination of other raw materials, that is, RE ₂
O ₃ , BaO ₂ CuO or RE ₂ BaCuO ₅ , REBa ₂ Cu ₃ Ox
Alternatively, the size of the 211 phase dispersed in the 123 phase is smaller than that of the superconductor manufactured in the same manner as above using RE ₂ O ₃ , BaCuO ₂ , CuO, etc., and the critical current density and the magnetic levitation force are further improved. The inventors have found that they can be improved and have completed the present invention.

Further, in the preparation of the above raw materials, 0.1 to 2% by weight of platinum or a platinum compound is added as platinum, or 0.01 to ₂ % by weight of rhodium is added, or cerium oxide is added as CeO ₂ of 0%. If 1 to 2 wt% is added and a superconductor is manufactured by the above method, the size of the 211 phase dispersed in the 123 phase is smaller than that of the superconductor manufactured without adding the additive, and the critical current It has also been found that the density is even higher.

Therefore, the present invention is characterized in that the superconducting phase is generated and grown by mixing and molding RE ₂ Cu ₂ O ₅ , Ba oxide and Cu oxide as raw materials and further subjecting to heat treatment. The present invention provides a method for producing a REBaCuO-based oxide superconductor.

An example of the procedure of the method for producing a superconductor according to the present invention is shown below. The present invention will be described in detail along with this.

(Process) First, as a first step of manufacturing a REBaCuO-based superconductor, a molded body before partial melting is manufactured. At least one kind of RE is selected from Y, Sm, Eu, Gd, Dy, Ho, Er, and Yb. As raw material powder, RE ₂ Cu ₂ O
₅ , a combination of Ba oxide and Cu oxide or R
A combination of E ₂ Cu ₂ O ₅ and BaCu oxide is used. These raw material powders are mixed in a predetermined ratio to prepare a mixed powder made of REBaCuO 2.

At this time, as a method for further improving the critical current density, 0.1 to 2 of platinum or a platinum compound is added.
It is also possible to add 0.01% to 2% by weight of rhodium or 0.1 to 2% by weight of cerium oxide. Examples of platinum compounds include Pt ₂ Ba ₄
CuO ₉ is used. Further, as the cerium oxide, for example, CeO ₂ or CeBaO ₃ is used.

(Step) Further, this mixed powder is molded into a desired shape to prepare a molded body.

(Step) This molded body is heated to a temperature range of 950 to 1250 ° C. at which the 211 phase is formed, and kept at that temperature for 15 to 90 minutes, from that temperature to the 211 phase and from the liquid phase to the 123 phase. The temperature at which the
When RE is Y and in air 10 to 1000 ℃ up to 1000 ℃
It is cooled at a cooling rate of / h, and is gradually cooled to a temperature of 850 to 950 ° C at a cooling rate of 0.2 to 20 ° C / h. During this slow cooling, for example, to maximize the temperature at one end of the molded body,
It is possible to gradually cool under a temperature gradient of ℃ / cm or more.

(Step) After that, it is possible to cool from 850 to 950 ° C. to room temperature at an arbitrary cooling rate.

If necessary, 65% in an oxygen-enriched atmosphere in order to add sufficient oxygen to the manufactured superconductor.
Hold for 2 to 500 hours in the temperature range of 0 to 300 ° C,
Or the temperature range of maximum 650 ℃, minimum 300 ℃ 2
Cool for 500 hours. After that, it is possible to cool at an arbitrary cooling rate.

As described above, by using RE ₂ Cu ₂ O ₅ , Ba oxide and Cu oxide as raw materials, REBa with high critical current density is obtained.
We were able to manufacture CuO-based oxide superconductors.

FIG. 1 shows RE ₂ Cu ₂ O ₅ (where RE = Y), Ba
O ₂ and CuO were used as raw materials and were produced according to the present invention.
2 is a polarization microscope photograph of a superconductor structure, and FIGS. 2 to 4 are all polarized light of a superconductor structure produced by a conventional raw material other than the above-mentioned examples for comparison and not manufactured by the present invention. It is a micrograph. It is clear that the size of the 211 phase dispersed in the 123 phase shown in FIG. 1 is smaller than that dispersed in the 123 phase of the superconductor manufactured from the conventional raw material shown in FIGS. Is.

5 to 7 show the above Y ₂ Cu ₂ O ₅ , BaO ₂ and Cu.
2 is a polarization micrograph of a superconductor structure produced according to the present invention by adding platinum, rhodium and cerium oxide at 0.5% by weight to O 2 raw material powder. Superconductor 123 manufactured by adding each of the additives shown in FIGS.
It is clear that the size of the 211 phase dispersed in the phase is as small as that dispersed in the superconductor 123 phase produced without addition of the additive found in FIG.

Therefore, the superconductor obtained according to the present invention disperses in 123 phases more than those not according to the present invention.
The size of 11 phases is small. Therefore, it is clear that the critical current density and the magnetic levitation force are also increased. Moreover, the superconductor can be obtained by a simple manufacturing process, and the present invention is effective.

[0022]

【Example】

Example 1 Using Y ₂ Cu ₂ O ₅ , BaO ₂ and CuO as starting materials, Y: Ba: Cu
Are mixed in a ratio of 1.8: 2.4: 3.4.
Mold further, then heat at 1030 ℃ for 20 minutes,
After cooling to 00 ° C. in 2 minutes, it is gradually cooled to 890 ° C. at a rate of 1 ° C./h and then furnace cooled. Further, a superconductor was manufactured by heating at 600 ° C. for 1 hour in an oxygen stream of 1 atm and then cooling the furnace.

FIG. 1 is a polarization microscope photograph of the crystal of the superconductor thus obtained. Separately, as conventional starting materials, Y ₂ BaCuO ₅ and Y Ba ₂ Cu ₃ O _x , Y ₂ BaCuO ₅
A superconductor was manufactured in the same manner using BaCuO ₂ and CuO, Y ₂ O ₃ , BaCuO ₂ and CuO. 2 to 4 are polarization microscope photographs of the structures of three superconductors from which the conventional starting materials were obtained in this order.

As is clear from comparing these, as shown in FIG.
Y dispersed in the crystal of the superconductor according to the present invention shown in
The size of ₂ BaCuO ₅ was smaller than that of the superconductor manufactured from the conventional starting materials shown in FIGS. Example 2 A superconductor was manufactured in the same manner as in Example 1. The starting materials are the same as in Example 1. As shown in Table 1, Y ₂ Cu ₂ O ₅ , Ba
The critical current densities of the superconductors made from O ₂ and CuO as starting materials at 77K, 1T (Tesla) were higher than those of the superconductors made from conventional starting materials. Example 3 A superconductor pellet was produced in the same manner as in Example 1. The pellet size is about 16 mm in diameter and about 7 mm in height. The magnetic levitation force of these pellets was measured using a permanent magnet with a diameter of 12 mm and a surface magnetic flux density of 0.4 T. As shown in Table 2, pellets using Y ₂ Cu ₂ O ₅ , BaO ₂ , and CuO as starting materials were obtained. Magnetic levitation force was higher than that of pellets made from other conventional starting materials. Example 4 Sm ₂ Cu ₂ O containing RE other than Y in place of Y ₂ Cu ₂ O _5
5 , Eu ₂ Cu ₂ O ₅ , Gd ₂ Cu ₂ O ₅ , Dy ₂ Cu ₂ O ₅ , Ho ₂
A superconductor was produced in the same manner as in Example 1 using Cu ₂ O ₅ , Er ₂ Cu ₂ O ₅ , and Yb ₂ Cu ₂ O ₅ . Table 3 shows the critical current densities obtained by measuring the magnetization of the obtained superconductors at 77K and 1T.
Shown in. The effect was recognized in all RE systems. Example 5 A superconductor was produced in the same manner as in Example 1 except that 0.5% by weight of platinum, rhodium and cerium oxide were added to the raw materials.
Table 4 shows the results of measuring the critical current density of the obtained superconductor by the same method as in Example 4. It is clear that the critical current density is considerably improved when these are added as compared with the case where they are not added. Example 6 Using Y ₂ Cu ₂ O ₅ , BaO ₂ and BaCuO ₂ as starting materials, Y: Ba: Cu
Are mixed in a ratio of 1.8: 2.4: 3.4.
Mold further, then heat at 1030 ℃ for 20 minutes,
After cooling to 10 ° C for 20 minutes, the pellet bottom surface was cooled to 1 ° C /
A temperature gradient of 5 ° C./cm, 9 ° C./cm, 9 ° C./cm is applied, and the temperature is gradually cooled to 880 ° C. at a rate of 1 ° C./h and then furnace cooled.

Further, at 1 ° C in an oxygen stream at 600 ° C, 1
After heating for h, the furnace was cooled to produce a superconductor.

The magnetic levitation force of these superconductors was measured in the same manner as in Example 3. As the result is shown in Table 5, a high magnetic levitation force was exhibited.

Table 1 Starting Material and Critical Current Density Starting Material Critical Current Density (77K, 1T) (A / cm ² ) Y ₂ Cu ₂ O ₅ + BaO ₂ + CuO 11,500 Y ₂ BaCuO ₅ + YBa ₂ Cu ₃ O _x 8 2,000 Y ₂ BaCuO ₅ ＋ BaCuO ₂ ＋ CuO 7,800 Y ₂ O ₃ ＋ BaCuO ₂ ＋ CuO 6,000 Table 2 Starting materials and magnetic levitation Starting materials Magnetic levitation (Kgf) Y ₂ Cu ₂ O ₅ ＋ BaO ₂ ＋ CuO 0.72 Y ₂ BaCuO ₅ ＋ YBa ₂ Cu ₃ O _x 0.28 Y ₂ BaCuO ₅ ＋ BaCuO ₂ ＋ CuO 0.26 Y ₂ O ₃ ＋ BaCuO ₂ ＋ CuO 0.27 Table 3 Substituents and critical current density Y 77K, 1T) (A / cm ² ) Sm 11,000 Eu 10,500 Gd 10,000 Dy 10,500 Ho 11,000 Er 10,000 Yb 9,500 Table 4 Additives and critical current density additives (additions 0.5% by weight) Critical current density (77K, 1T) (A / cm ² ) Platinum 17,500 18,000 cerium oxide 16,500 Table 5 Temperature gradient and magnetic levitation force Temperature gradient (℃ / cm) Magnetic levitation force (kgf) 1 1.10 5 1.05 9 0.91

[0028]

As is apparent from the above, according to the present invention, an oxide superconductor having a small crystal size and a high critical current density and a high magnetic levitation force can be manufactured by a simple manufacturing process.

[Brief description of drawings]

FIG. 1 is a micrograph of a crystal of a superconductor made of Y ₂ Cu ₂ O ₅ , Ba and Cu oxides according to the present invention.

FIG. 2 is a photomicrograph of a crystal of a superconductor made of Y ₂ BaCuO ₅ and YBa ₂ Cu ₃ O _x .

FIG. 3 is a photomicrograph of a crystal of a superconductor made of Y ₂ BaCuO ₅ , BaCuO ₂ and CuO.

FIG. 4 is a micrograph of a crystal of a superconductor made of Y ₂ O ₃ , BaCuO ₂ and CuO.

FIG. 5 is a micrograph of a crystal of a superconductor obtained by adding platinum to the raw material according to the present invention.

FIG. 6 is a micrograph of a crystal of a superconductor obtained by adding rhodium to the raw material according to the present invention.

FIG. 7 is a micrograph of a crystal of a superconductor obtained by adding cerium oxide to the raw material according to the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 000006655 Nippon Steel Co., Ltd. 2-3-6 Otemachi, Chiyoda-ku, Tokyo (72) Inventor Akihiro Kondo 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Industrial Technology Research Center Superconductivity Institute of Technology (72) Inventor Hiroyuki Fujimoto 1-14-3 Shinonome, Koto-ku, Tokyo Inside Superconductivity Research Institute (72) Inventor Masato Murakami 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Industrial Technology Research Center Superconductivity Institute of Technology (72) Inventor Naoki Koshizuka 1-14-3 Shinonome, Koto-ku, Tokyo Foundation Corporation International Superconductivity Industrial Technology Research Center Superconductivity Research Institute (72) Inventor Shoji Tanaka 1-14-3 Shinonome Foundation, Koto-ku, Tokyo When people Country Superconductivity Technology Center superconducting Engineering Institute in

Claims (10)

[Claims] 1. RE ₂ Cu ₂ O ₅ (RE is Y, Sm, Eu, Gd, Dy,
A rare earth element selected from the group of Ho, Er, and Yb), Ba oxide, and Cu oxide are used as raw materials and mixed.
A method for producing a REBaCuO-based oxide superconductor, which comprises molding and further heat treatment to grow a superconducting phase. 2. The method according to claim 1, wherein BaCu oxide is used as a raw material instead of Ba oxide or Cu oxide. 3. The method according to claim 1, wherein the heat treatment is a partial heat treatment followed by slow cooling to grow a superconducting phase. 4. The method according to claim 3, wherein the partial melting temperature is 950 to 1250 ° C. 5. The method according to claim 3, wherein the slow cooling rate is 0.2 to 20 ° C./h. 6. The method according to claim 3, wherein the slow cooling is performed under a temperature gradient of 1 ° C./cm or more. 7. The method according to claim 1, wherein 0.1 to 2% by weight of platinum or a platinum compound is added to the raw material as platinum. 8. The method according to claim 1, wherein 0.01 to 2% by weight of rhodium is added to the raw material. 9. A cerium oxide (Cerium oxide (C
The method according to claim 1, wherein 0.1 to ₂ % by weight is added as eO ₂ ). 10. After growing the superconducting phase, it is held in an oxygen-enriched atmosphere at a temperature range of 650 to 300 ° C. for 2 to 500 hours, or at a temperature range of 650 ° C. maximum and 300 ° C. minimum for 2 to 500 hours. By cooling over
The method according to claim 1, wherein oxygen is added to the superconducting phase.