JP2828396B2 - Oxide superconductor and manufacturing method thereof - 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 having a high critical temperature and a high critical current and a method for producing the same, and more particularly to a technology effective when applied to a magnetic levitation, a magnetic shield, a superconducting bulk magnet, and the like. is there.

[0002]

2. Description of the Related Art With the discovery of superconductors whose critical temperature exceeds the temperature of liquid nitrogen, superconducting applications are being studied worldwide. Among them, 123 represented by Y-Ba-Cu-O
For system materials, the development of melting methods such as MPMG
Fine Y ₂ BaCuO ₅ (2
11) A large critical current has been successfully achieved by dispersing the phases. Such a superconductor can generate a large electromagnetic force by interaction with a magnetic field,
Applications of this force to bearings, flywheels, conveyors, etc., have been actively studied. For example, "Melt ProcessedHigh Temperature Superconducto
rs ", ed. M. Murakami (World Scientific, 1993).

[0003] It has also been clarified that a superconductor having a large critical current shields a strong magnetic field or conversely functions as a permanent magnet by capturing a strong magnetic field. When considering such various applications, it is necessary to produce a material having as large a crystal grain as possible, to increase the size by superconducting bonding, and to deal with complicated shapes by precision processing.

[0004] Since the oxide superconductor is a material having a large anisotropy, it is important to control the crystal orientation. Furthermore, if a material having a larger critical current can be manufactured, the generated electromagnetic force can be improved.

At present, a combination of a seed crystal and a temperature gradient is generally used as a technique for controlling the crystal orientation and increasing the crystal size. At this time, as a seed crystal, for example, La, Nd, Sm1 having a higher melting point is used for growth of Y123 system.
23 superconductors are used.

On the other hand, when considering a superconducting junction, Nd12
3 and Sm123 superconductors are manufactured and heated near the melting point of Y123, which has a lower melting point, so that the Y123 phase is sandwiched between the Nd123 plates, and the
It is also conceivable to melt 3 and join. For the above-mentioned applications, it is necessary to synthesize high-quality Nd123 and Sm123 superconductors.

[0007]

However, when these superconductors are manufactured by a commonly used sintering method or melting method, they are easily replaced with Ba sites due to the large ionic radius of the rare earth element, and the critical temperature is lowered. However, there has been a problem that is greatly reduced. For example, H. Uwe et al .: Physica
C vol.153-155 (1988) P.930-931 describes related technologies.

Further, RE123 (RE: Y, Ho, E
In the (r, Dr) superconductor, a high critical current is achieved by finely dispersing 211 phases.
There is a limit to the pinning effect of the eleven phases, and studies are underway to investigate the possibility of other pinning points.

The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a semiconductor device having a critical temperature of 90K.
And to provide a method for producing the same.

Another object of the present invention is to provide a superconductor having a large critical current even in a high magnetic field and a method for manufacturing the same.

[0011]

In order to achieve the above object, the present invention is characterized by the following configuration or method.

(1) RE-Ba-Cu-O (RE is La,
Nd, Sm, Eu, high a composition of those containing at least one element selected from the group consisting of Gd)
An oxide superconductor having a current density , wherein (RE _1-x , Ba _x )
Ba ₂ Cu ₃ O _d is represented by the chemical formula (0 <x <0.5, 6.8 <d <7.2), the critical temperature is equal to or more than 90 K.

(2) RE-Ba-Cu-O (RE is La,
(RE _1-x , Ba _x ) Ba ₂ Cu ₃ O comprising an oxide superconductor comprising at least one element selected from the group consisting of Nd, Sm, Eu and Gd).
_The phase represented by the chemical formula of _d ( 0 ≦ x <0.5 , 6.8 <d <7.2) is defined as a mother phase, and (RE _1−x , Ba _x ) (Ba _1−y , RE _y ) _Two
Cu ₃ O _d ( 0 ≦ x <0.5 , 0 <y < 0.5 , 6.8 <d
It has a dispersed phase represented by a chemical formula of <7.2).

(3) RE-Ba-Cu-O (RE is La,
(RE _1-x , Ba _x ) Ba ₂ Cu ₃ O comprising an oxide superconductor comprising at least one element selected from the group consisting of Nd, Sm, Eu and Gd).
_The phase represented by the chemical formula of _d ( 0 ≦ x <0.5 , 6.8 <d <7.2) is used as a mother phase, and (RE _4-x , Ba _{2 + x} ) Cu ₂ O _10-y ( R
E includes at least one of the elements La and Nd, and a phase represented by a chemical formula of 0 <x <0.2, 0 <y <0.5) and / or RE ₂ BaCuO ₅ (RE includes at least one element selected from the group consisting of Sm, Y, Eu, Gd, Ho, Er, and Yb) in an amount of 40% or less.

(4) (RE _1-x , Ba _x ) Ba ₂ Cu ₃ O _d (R
E contains at least one element selected from the group consisting of La, Nd, Sm, Eu and Gd, and 0 ≦ x <
0.5 , 6.8 <d <7.2), and a phase represented by a chemical formula of (RE _1−x , Ba _x ) (Ba _1−y , RE _y ) ₂ Cu ₃
O _d ( 0 ≦ x <0.5 , 0 <y < 0.5 , 6.8 <d <7.
An oxide superconductor having a composition in which the phase represented by the chemical formula 2) is a dispersed phase, wherein (RE _4-x , Ba _{2 + x} ) Cu ₂ O
_10-y (RE includes at least one element of La and Nd, and 0 <x <0.2, 0 <y <0.5) A phase represented by a chemical formula and / or RE ₂ BaCuO ₅
(RE includes at least one element selected from the group consisting of Sm, Y, Eu, Gd, Ho, Er, and Yb) in an amount of 40% or less.

[0016]

( 5 ) In the oxide superconductor of (2) or (4), the size of the dispersed phase is 1 μm or less.

(6) RE-Ba-Cu-O (RE is La,
And at least one element selected from the group consisting of Nd, Sm, Eu and Gd). (RE _1-x , Ba _x ) (Ba
_1-y , RE _y ) ₂ Cu ₃ O _d ( 0 ≦ x <0.5 , 0 <y <0.
In order to generate the phase represented by the chemical formula of 5,6.8 <d <7.2), when the superconducting phase is solidified from the molten state, the oxygen partial pressure of the generating atmosphere is set to be equal to or more than 0.0001 atm.
It is characterized in that it is performed in a range of not more than 05 atm.

( 7 ) In the method for manufacturing an oxide superconductor according to the above ( 6 ), the temperature in a molten state is from 1000 ° C. to 130 ° C.
It is characterized by a temperature of 0 ° C.

( 8 ) The method for producing an oxide superconductor according to the above (6) or (7) , wherein a rate of solidification from a molten state is 5 ° C./hour or less.

( 9 ) In the method for producing an oxide superconductor according to any one of the above (6) to (8) , when solidifying from a molten state, the crystal is grown under a temperature gradient of 5 ° C./cm or more. .

That is, the present invention is to obtain a 123 crystal having a high critical temperature and a high critical current by controlling the atmosphere in which the 123 phase is generated from a molten state.

FIG. 1 is a ternary phase diagram of RE ₂ O ₃ —BaO—CuO of a sample having a large ionic radius. In the present invention, as shown in FIG. 1, there is a solid solution zone along a line extending from the 123 phase to the upper right. This solid solution region is defined as RE _{1 + x} Ba _2-x Cu ₃ O shifted from the 123 phase in the air.
_{This is because the y} (x> 0, 6.8 <y <7.2) phase becomes stable. However, this solid solution region differs depending on the type of RE. Also, Sm, Eu, in the case of Gd rather than 422 phase, Ru 211 Sodea.

In normal air, La, Nd, Sm, Eu,
When a RE123 crystal having a large ionic radius such as Gd is grown, as shown in FIG. 1, a solid solution region exists between RE and Ba, and Nd ions replace Ba ions. I will.

This is because under the partial pressure of oxygen such as air, RE
(Ba _{2 -x} , RE _x ) Cu ₃ O _y
This is because (x> 0,6.8 <y <7.2) is more stable. In such a solid solution phase, since the trivalent ions replace the divalent ions, the carrier concentration tends to decrease, and it is considered that the critical temperature decreases.

In order to solve this, a sintering method or the like
Once a superconductor is formed in a nitrogen atmosphere, a relatively good critical temperature is achieved by oxidation (for example, T. Wada et al .: J. Am. Ceram. Soc., Vol. 72. (1989)
p.2000-2003).

However, the change in magnetic susceptibility indicates that the transition width is wide and good superconducting characteristics cannot be obtained. This is considered to be because the sintering method is a solid-phase reaction, so that it is inevitably affected by the solid solution region, and many phases in which Nd ions replace Ba ions are generated. Therefore, the volume ratio of the superconducting phase is low and cannot be put to practical use.

Therefore, in the method of solidifying from a molten state, if the replacement of Nd ions with Ba sites can be suppressed at the stage of nucleation and growth, it is expected that a high-quality RE123 phase can be synthesized. Moreover, it has been reported that at a high temperature of 1050 ° C. or higher, a 123 phase that does not form a solid solution becomes stable, and there is a possibility that a high-quality superconducting phase can be synthesized by synthesizing by a melting process (for example, SIYoo & R.W. McCall).
um: Physica C vol.210 (1933) P.147-156).

However, although the melting process was attempted under various conditions, it was found that a good superconductor could not be easily obtained. Then, the present inventor tried to control the oxygen partial pressure in order to suppress the mutual substitution at the stage of nucleation and growth. This is because, under a low oxygen partial pressure, Ba substitution of divalent ions by RE, which is a trivalent ion, is considered to be suppressed.

As a result of conducting experiments under various conditions, when the oxygen partial pressure was in the range of 0.0001 to 0.05 atm,
It was clear from the measurement by the X-ray photoelectron spectroscopy shown in FIG. 2 that not only the replacement of the RE ion with the Ba site was suppressed, but also the Ba ion replaced the RE ion.

FIG. 2 shows BaO by X-ray photoelectron spectroscopy and Ba of the Nd—Ba—Cu—O superconductor of Example 1 of the present invention.
It is a measurement result of the binding energy of a 3d nucleus. In FIG. 2, the upper curve is the result of BaO, that is, it corresponds to a divalent Ba ion. On the other hand, the lower curve is the result of the superconductor of the present invention, and shows that the binding energy of the Ba3d nucleus has shifted to the lower energy side, and that the Nd site has been replaced by about 10% of Ba ions. ing. When the composition of the oxide superconductor of the present invention was analyzed by an electron beam microanalyzer, it was found that Nd _0.9 Ba _2.1 Cu _3.0
A result of O _7.0 was obtained, and it was confirmed that the Ba ion replaced the Nd site.

As a result of various measurements, the oxygen partial pressure became 0.000.
When a RE123 (RE is at least one element selected from the group consisting of La, Nd, Sm, Eu and Gd) -based material is solidified and grown in a range of 01 atm to 0.05 atm, a chemical formula (RE _{1− x} , Ba _x ) Ba ₂ Cu _{3 Od} , x was found to vary from 0 to 0.5. Analysis by iodometry showed that the range of d was 6.8 to 7.2. FIG. 3 corresponds to the crystal structure of the oxide superconductor of the present invention.

As described above, a divalent Ba ion is converted to a trivalent R
When the E ions are replaced, new carriers are injected, and the critical temperature increases. FIG. 4 shows the temperature change of the electric resistance of the Nd—Ba—Cu—O superconductor manufactured in Example 1 of the present invention. Nd-Ba-Cu prepared in Example 1 of the present invention
It can be seen from FIG. 4 that the superconducting transition of the -O superconductor occurs at a very high temperature, which has not been reported in the past.

In other words, according to the present invention, the atmosphere for crystal growth from the molten state is formed by partial pressure of oxygen within a certain range.
A superconductor having a new crystal structure and a high critical temperature having a new crystal structure as shown in FIG. 3 in which divalent Ba replaced trivalent RE sites was successfully synthesized. Thus, the previously reported 12
A critical temperature higher than three materials is achieved. At this time, the lower limit of the oxygen partial pressure is defined below that the superconducting phase is decomposed. On the other hand, when the oxygen partial pressure exceeds 0.05 atm, substitution of the Ba element for the RE site is suppressed, and conversely, R
The E ion replaces the Ba site.

As described above, according to the present invention, a superconductor having a new composition and a high critical temperature can be synthesized, but it has also become clear that the structure is not 100% composed of this phase.

FIG. 5 is a schematic tres diagram of an electron beam microanalyzer photograph showing a result of analysis of a minute region of the Nd—Ba—Cu—O superconductor of Example 1 by an electron beam microanalyzer. Although the parent phase had Nd _0.9 Ba _2.1 Cu _3.0 O _7.0 , it was found that phases having different compositions were dispersed in a region smaller than 1 μm. These phases show that some Nd ions are B
(Nd _1-x , Ba _x ) (Ba _1-y , Nd _y ) ₂ substituted for a site
Cu ₃ O _d ( 0 ≦ x <0.5 , 0 <y < 0.5 , 6.8 <d
It was found that the phase having the chemical formula of <7.2) was dispersed. This is considered to be due to the fact that the temperature at which the 123 phase is formed is high and that this system originally has a solid solution region, so that a certain statistical distribution occurs in RE and Ba.

These dispersed phases are slightly different from the parent phase in properties such as critical temperature and critical current. Under a strong magnetic field, superconductivity is broken and transition to normal conduction occurs. Since the applied magnetic fields are different, it is possible to act as a pinning point from a low magnetic field to a high magnetic field depending on the degree of replacement of the dispersed phase.

[0038] Consequently, as shown in FIG. 6, the irreversible magnetic field much higher as compared with the previously reported in that the material is obtained. This magnetic field is the upper limit at which the superconductor can be used, and is very important in practical use.

FIG. 6 shows an Nd—Ba—Cu—O material grown under a partial pressure of oxygen of 0.01 atm according to an embodiment of the present invention and a MPMG method which is a kind of a conventional melting method. Y
It is a figure which shows temperature dependence of the irreversible curve of -Ba-Cu-O material.

The present invention is characterized by an atmosphere adjustment when growing a crystal from a molten state, and is applicable to all so-called melting methods and to growing a single crystal from a molten state. However, in order to manufacture a high-quality superconductor, some conditions are defined. The temperature in the molten state is in the range of 1000 ° C to 1300 ° C. The lower limit is the temperature at which the material becomes a molten state, and the upper limit is that at a temperature higher than this, the reaction with the supporting material is severe, and a large composition deviation occurs from the molten state to the solidification. Also,
The speed at the time of solidification is desirably 5 ° C./hour or less. This is because if the speed is exceeded, stable crystal growth becomes difficult. Furthermore, in order to control the crystal orientation, it is necessary to grow under a temperature gradient of 5 ° C./cm or more.

Further, in the melting method, a so-called 21
One phase and 422 phase can be distributed in the parent phase, but even with such a structure, the above-described pinning effect can be obtained. Here, the 422 phase means that the RE element is L
It is generated at the time of a and Nd. From the analysis of the electron beam microanalyzer, in the chemical formula of RE _4-x , Ba _{2 + x} Cu ₂ O _10-y , 0 <x <0.2, 0 <y <0.5. It is known to be in the range. However, the volume ratio of these phases is 4
If it exceeds 0%, the ratio of the superconducting phase itself decreases,
The superconducting properties, especially the critical current density, deteriorate.

The 422 phase and the 211 phase have a crack suppressing effect, and if the phases are miniaturized, the pinning effect due to these phases can be reduced as in the case of the Y—Ba—Cu—O material produced by the MPMG method. It is possible to synergize.

[0043]

According to the means described above, L having a large ionic radius is used.
RE element 123 which contains at least one element selected from the group consisting of a, Nd, Sm, Eu and Gd
In the synthesis of a system-based oxide superconductor, the replacement of RE ions with Ba sites is suppressed at the stage of nucleation and growth, so that an oxide superconductor having a critical temperature exceeding 90 K can be provided.

Further, since the dispersed phase in which RE and Ba are slightly substituted is finely dispersed in the matrix and acts as a pinning point in a wide magnetic field range, the oxide superconductor having a large critical current even in a high magnetic field can be used. Synthesis can be possible.

[0045]

Embodiments of the present invention will be described below in detail.

Example 1 An oxide superconductor according to Example 1 of the present invention and a method for manufacturing the same will be described.

First, Nd ₂ O ₃ , BaCO ₃ , and CuO powders are mixed so that the ratio of Nd: Ba: Cu is 1: 2: 3. This is calcined at 900 ° C. for 24 hours, placed in a platinum crucible, heated and melted at 1400 ° C. for 20 minutes, and then rapidly cooled with a copper hammer. Pulverize the quenching plate, 50 × 50 × 2
Mold to 0 mm ³ . Two such samples are prepared.
After heating these samples at 1120 ° C for 20 minutes, 1080 ° C
Cool down to 950 ° C in 20 minutes, then 1 ° C / hour
Cool slowly at the speed of (h). At this time, the sample was heat-treated under an oxygen partial pressure of 0.01 atm. Then, at 500 ° C, 1
Treated in 1 atmosphere of oxygen for 00 hours.

When this sample was analyzed by an electron beam microanalyzer, a composition ratio of Nd _0.9 Ba _2.1 Cu _3.0 O _7.0 was obtained. For comparison, analysis of data grown in air yielded Nd _1.1 Ba _1.9 Cu _3.0 O _6.9 .

FIG. 4 shows the temperature dependence of the electrical resistance of the sample obtained in the first embodiment. The sample prepared in Example 1 under an oxygen partial pressure of 0.01 atm has a critical temperature of 95 K or more, has a very narrow transition width, and is a good superconductor.

Embodiment 2 Next, an oxide superconductor according to Embodiment 2 of the present invention and a method for manufacturing the same will be described.

First, powders of Nd ₂ O ₃ , BaCO ₃ and CuO are mixed so that the ratio of Nd: Ba: Cu is 1: 2: 3. This is calcined at 900 ° C. for 24 hours, placed in a platinum crucible, heated and melted at 1400 ° C. for 20 minutes, and then rapidly cooled with a copper hammer. Crush the quenching plate, 50x50x
Molded into 20mm ^3. Two such samples are prepared. After heating these samples at 1120 ° C. for 20 minutes, 108
The mixture is cooled to 0 ° C. in 20 minutes, and then gradually cooled to 950 ° C. at a rate of 1 ° C./hour (h). At this time, the sample was heat-treated under an oxygen partial pressure of 0.01 atm. Thereafter, the substrate was treated at 500 ° C. for 100 hours in oxygen at 1 atm.

As a comparative example, a Y—Ba—Cu—O-based material was prepared. Powders of Y ₂ O ₃ , BaCO ₃ and CuO are mixed so that the ratio of Y: Ba: Cu is 1.8: 2.4: 3.4. This is calcined at 900 ° C. for 24 hours, placed in a platinum crucible, heated and melted at 1400 ° C. for 20 minutes, and then rapidly cooled with a copper hammer. Crush the quenching plate, 50 × 5
Mold to 0 × 20 mm ³ . Two such samples are prepared. After heating these samples at 1100 ° C. for 20 minutes, 10
Cool to 10 ° C in 20 minutes, then to 950 ° C at 1 ° C /
Cool slowly at the speed of time (h). Thereafter, at 500 ° C. for 100
Treated in oxygen at 1 atmosphere for 1 hour.

When these irreversible curves are measured, as shown in FIG. 6, the superconductor of Example 2 shows a much higher value.

When the critical temperature of these superconductors is measured at a temperature of 77 K with a sample vibrating magnetometer and the relationship between the magnetic flux pinning force and the magnetic field is obtained, the results shown in FIG. 7 are obtained. FIG. 7 shows an Nd—Ba—Cu—O material grown in an oxygen partial pressure of 0.01 atm according to an embodiment of the present invention, and a Y—Mn produced by an MPMG method, which is a kind of a conventional melting method. Ba-C
It is a figure which shows the magnetic field dependence of the pinning force at 77K of u-O material.

As described above, the Nd123-based material is
The phase is finely dispersed, and the pinning force is much larger than that of a Y-Ba-Cu-O-based material which has conventionally exhibited the highest value as a bulk material.

Embodiment 3 Next, an oxide superconductor according to Embodiment 3 of the present invention and a method for manufacturing the same will be described.

First, powders of Nd ₂ O ₃ , BaCO ₃ , and CuO were mixed at a ratio of Nd: Ba: Cu of 1.2: 2.1: 3.1, 1.N.
4: 2.2: 3.2, 1.8: 2.4: 3.4, and the mixture was prepared in the same manner as in Example 1, and then gradually cooled from 1080 ° C. to 0. It is performed in an oxygen partial pressure of 0.001 atm. Nd 422 phase is about 9% each in the matrix,
Although dispersed at volume fractions of 16% and 29%, the zero resistance temperatures are 93K, 95K, and 94K, indicating that high-quality superconductors are all synthesized.

Further, 42
As a result of the two-phase separation, Nd _3.9 Ba _2.1 Cu ₂
O _9.6 , Nd _3.85 Ba _2.15 Cu ₂ O _9.7 , Nd _3.95 Ba
A value of _2.05 Cu ₂ O _9.6 was obtained.

Embodiment 4 Next, an oxide superconductor according to Embodiment 4 of the present invention and a method for manufacturing the same will be described.

First, La ₂ O ₃ , Sm
₂ O ₃ , Eu ₂ O ₃ , and Gd ₂ O ₃ powder were prepared, and RE: Ba:
Mixing so that the ratio of Cu is 1.2: 2.1: 3.1,
Hereinafter, after being manufactured in the same manner as in Example 1, the slow cooling start temperatures were set to 1080 ° C., 1060 ° C., and 1040 ° C., respectively.
And 1020 ° C., and gradually cooled to 900 ° C. in air and at a partial pressure of oxygen of 0.01 at a rate of 1 ° C./hour (h).
Then, after cooling to room temperature, the substrate was treated at 400 ° C. for 100 hours in 1 atmosphere of oxygen. Those processed in air have zero resistance temperatures of 10K, 65K, 75K,
Those treated at 50K but under an oxygen partial pressure of 0.001 atm were 90K, 92K, 92K and 93K. X-ray photoelectron spectroscopy measurements indicated that in all of these, Ba ions replaced the RE sites.

Embodiment 5 Next, an oxide superconductor according to Embodiment 5 of the present invention and a method for manufacturing the same will be described.

First, powders of Sm ₂ O ₃ , BaCO ₃ , and CuO were mixed so that the ratio of Sm: Ba: Cu was 1: 2: 3, and the powder was produced in the same manner as in Example 1 above. ,
Cooling from 1080 ° C. at 10 ° C./hour (h) and 5 ° C./h
When the test was performed at a speed of time (h), the zero resistance temperature was 80K in the former case and 92K in the latter case.

As described above, if the cooling rate is high, a high-quality superconductor cannot be obtained.

Embodiment 6 Next, an oxide superconductor of Embodiment 6 of the present invention and a method for manufacturing the same will be described.

First, powders of Nd ₂ O ₃ , BaCO ₃ , and CuO were mixed so that the ratio of Nd: Ba: Cu was 1: 2: 3, and calcined at 950 ° C. for 24 hours (h). Diameter 2c
m, molded into pellets 1 cm high. This is placed in an electric furnace having an oxygen partial pressure of 0.01 atm, heated to 1100 ° C for 1 hour (h), and then gradually cooled from 1080 ° C to 900 ° C at a rate of 1 ° C / hour (h). Then, it is cooled in a furnace to room temperature. The zero resistance temperature of this sample was 95K.

Embodiment 7 Next, an oxide superconductor according to Embodiment 7 of the present invention and a method for manufacturing the same will be described.

First, powders of Sm ₂ O ₃ , BaCO ₃ , and CuO were mixed so that the ratio of Sm: Ba: Cu was 1: 2: 3, and calcined at 950 ° C. for 24 hours (h). Diameter 2c
m, molded into pellets 1 cm high. This is placed in an electric furnace having an oxygen partial pressure of 0.01 atm, heated to 1100 ° C for 1 hour (h), and then gradually cooled from 1080 ° C to 900 ° C at a rate of 1 ° C / hour (h). At this time, a temperature gradient of 5 ° C. /
cm, 10 ° C./cm, and 30 ° C./cm. As a result, in each of the samples, 92K was obtained as zero resistance. In addition, a sample in which the (001) plane of the crystal was oriented perpendicular to the direction of the temperature gradient from the measurement of X-ray diffraction was obtained.
Even without a temperature gradient, a critical temperature of 92 K is obtained, but the crystals are not oriented.

Embodiment 8 Next, an oxide superconductor of Embodiment 8 of the present invention and a method for manufacturing the same will be described.

First, powders of Sm ₂ O ₃ , BaCO ₃ , and CuO were mixed such that the ratio of Sm: Ba: Cu was 1: 2: 3, and calcined at 950 ° C. for 24 hours (h). 1400 ° C
After heating and melting for 20 minutes, the mixture is quenched with a copper hammer. This quenched material is pulverized to a diameter of 2 cm and a height of 1.
Mold into cm pellets. The oxygen partial pressure is 0.00
Put into an electric furnace of 1 atm and 0.05 atm, 1100 ° C
, And gradually cooled from 1060 ° C. to 900 ° C. at a rate of 1 ° C./hour (h), and cooled to room temperature in a furnace.
Thereafter, a treatment is performed at 500 ° C. for 100 hours in oxygen at 1 atm. All of these samples exhibited a critical temperature of 93K.

Next, when the critical current density of this sample at 77 K was measured using a sample vibrating magnetometer in a direction in which the magnetic field was parallel to the c-axis, as shown in FIG.
Very high critical currents were obtained for samples grown under 1 atmosphere of oxygen partial pressure. Although a relatively high value can be obtained with the sample at 0.05 atm, it is understood that the characteristics are considerably lower than in the case of the oxygen partial pressure of 0.001 atm. FIG. 8
FIG. 9 is a diagram showing the magnetic field dependence of the critical current density in the direction parallel to the c-axis with the magnetic field at 77 K of the Sm material manufactured in Example 8 of the present invention. Under partial pressure, the lower curve corresponds to a sample grown under an oxygen partial pressure of 0.05 atm.

As can be seen from the above description, according to the above embodiment, RE-Ba-Cu-O (RE is La, Nd, S
m) at least one element selected from the group consisting of Eu, Gd.) When the oxide superconductor is solidified from a molten state, by controlling the oxygen partial pressure, the oxide superconductor having a high critical temperature and a high critical current is obtained. Can be obtained.

Although the present invention has been described in detail with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments and can be variously modified without departing from the gist thereof. Absent.

[0073]

As described above, according to the present invention, RE contains at least one element selected from the group consisting of La, Nd, Sm, Eu and Gd.) When the oxygen partial pressure is controlled during the solidification from the solid, an oxide superconductor having a high critical temperature and a high critical current can be obtained.

That is, La, Nd,
In the synthesis of 123-based oxide superconductors of the elements Sm, Eu, and Gd, the substitution of these elements for Ba sites during the nucleation and growth stage is suppressed, and Ba ions are generated by these REs.
Since the element is substituted, an oxide superconductor having a critical temperature exceeding 90 K can be provided.

Further, since the dispersed phase in which RE and Ba are slightly substituted is finely dispersed in the matrix and functions as a pinning point in a wide magnetic field range, the oxide superconductor having a large critical current even in a high magnetic field can be used. Synthesis can be possible.

[Brief description of the drawings]

FIG. 1 shows the RE of a sample of the present invention having a large ionic radius.
FIG. 3 is a ternary phase diagram of ₂ O ₃ —BaO—CuO.

FIG. 2 BaO and Nd-Ba-Cu by X-ray photoelectron analysis
It is a figure which shows the analysis result of Ba3d nucleus in a -O superconductor.

FIG. 3 is a view showing a crystal structure of an oxide superconductor of the present invention.

FIG. 4 is a diagram showing the temperature dependence of the electric resistance of the sample of Example 1 of the present invention.

FIG. 5 is a diagram showing a result of a micro area analysis of the sample of Example 1 by an electron beam analyzer.

FIG. 6 shows a Nd—Ba—Cu—O material grown in an oxygen partial pressure of 0.01 atm in Example 1 and a Y—Ba— produced by an MPMG method, which is a kind of a conventional melting method. It is a figure which shows the temperature dependence of the irreversible curve of Cu-O material.

FIG. 7 shows a Nd—Ba—Cu—O material grown in an oxygen partial pressure of 0.01 atm in Example 1 and a Y—Ba— produced by an MPMG method, which is a kind of conventional melting method. It is a figure which shows the magnetic field dependence of the pinning force in 77K of Cu-O material.

FIG. 8 shows 77K of Sm material produced in Example 8 of the present invention.
FIG. 4 is a diagram showing the magnetic field dependence of a critical current density in a direction in which the magnetic field is parallel to the c-axis.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masato Murakami 1-14-3 Shinonome, Koto-ku, Tokyo Foundation International Superconductivity Research Institute, Japan (72) Inventor Yu Sang Im, Shinonome, Koto-ku, Tokyo 1-14-3 Foundation, International Superconducting Technology Research Center, Superconductivity Engineering Research Laboratory (72) Inventor Naomichi Sakai 1-1-14, Shinonome, Koto-ku, Tokyo Foundation, International Superconducting Technology Research Center, Superconducting Engineering Research Laboratory (72 ) Inventor Hiroshi Takaichi 1-14-3 Shinonome, Koto-ku, Tokyo Foundation International Research Institute for Superconducting Technology, Superconductivity Engineering Laboratory (72) Inventor Tenmitsu Higuchi 1-14-2 Shinonome, Koto-ku, Tokyo Foundation International Superconductivity Technology Research Center, Superconductivity Engineering Laboratory (72) Invention Shoji Tanaka 1-14-3 Shinonome, Koto-ku, Tokyo Foundation, International Superconducting Technology Research Center, Superconducting Engineering Laboratory (56) References JP-A-64-41120 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1/00-57/00 C04B 35/45 C04B 35/653 H01B 12/00 H01L 39/00-39/24

Claims (9)

(57) [Claims] 1. RE-Ba-Cu-O (RE is La, N
an oxide superconductor having a composition of (RE _1-x , Ba _x ) Ba ₂ Cu ₃ O _d ( 0
<X <0.5, 6.8 <represented by the chemical formula of d <7.2), an oxide superconductor critical temperature is equal to or more than 90 K. 2. RE-Ba-Cu-O (RE is La, N
an oxide superconductor having a composition of (RE _1-x , Ba _x ) Ba ₂ Cu ₃ O _d ( 0
A phase represented by a chemical formula of ≦ x <0.5 , 6.8 <d <7.2) is defined as a mother phase, and (RE _{1 -x} , Ba _x ) (Ba _{1 -y} , RE _y ) ₂ Cu ₃
O _d ( 0 ≦ x <0.5 , 0 <y < 0.5 , 6.8 <d <7.
An oxide superconductor having a dispersed phase represented by the chemical formula of 2). 3. RE-Ba-Cu-O (RE is La, N
an oxide superconductor having a composition of (RE _1-x , Ba _x ) Ba ₂ Cu ₃ O _d ( 0
The phase represented by the chemical formula of ≦ x <0.5 , 6.8 <d <7.2) is used as a mother phase, and (RE _4-x , Ba _{2 + x} ) Cu ₂ O _10-y (RE is La And at least one of the elements of Nd and a phase represented by a chemical formula of 0 <x <0.2, 0 <y <0.5) and / or RE ₂ BaCuO ₅ (RE is S
m, Y, Eu, Gd, Ho, Er, and Yb).
An oxide superconductor containing 0% or less. 4. (RE _1-x , Ba _x ) Ba ₂ Cu ₃ O _d (RE is at least one element selected from the group consisting of La, Nd, Sm, Eu and Gd, and 0 ≦ x <0.
5 , 6.8 <d <7.2), and a phase represented by a chemical formula of (RE _1−x , Ba _x ) (Ba _1−y , RE _y ) ₂ Cu ₃ O _d
( 0 ≦ x <0.5 , 0 <y <0.5 , 6.8 <d <7.2)
An oxide superconductor having a composition in which the phase represented by the chemical formula is a dispersed phase, wherein (RE _4-x , Ba _{2 + x} ) Cu ₂ O
_10-y (RE includes at least one element of La and Nd, and 0 <x <0.2, 0 <y <0.5) A phase represented by a chemical formula and / or RE ₂ BaCuO ₅
(RE is at least one element selected from the group consisting of Sm, Y, Eu, Gd, Ho, Er, and Yb) in an amount of 40% or less. 5. The oxide superconductor according to claim 2, wherein the size of the dispersed phase is 1 μm or less. 6. RE-Ba-Cu-O (RE is La, N
d, Sm, Eu, and Gd), which comprises at least one element selected from the group consisting of: (RE _1-x , Ba _x ) (Ba
_1-y , RE _y ) ₂ Cu ₃ O _d ( 0 ≦ x <0.5 , 0 <y <0.
In order to generate the phase represented by the chemical formula of 5,6.8 <d <7.2), when the superconducting phase is solidified from the molten state, the oxygen partial pressure of the generating atmosphere is set to be equal to or more than 0.0001 atm.
A method for producing an oxide superconductor, which is performed in a range of not more than 05 atm. 7. The method for producing an oxide superconductor according to claim 6 , wherein the temperature in a molten state is from 1000 ° C. to 130 ° C.
A method for producing an oxide superconductor, which is performed at 0 ° C. 8. The method for producing an oxide superconductor according to claim 6 , wherein the speed of solidification from a molten state is 5 or less.
C./hour or less. 9. The method for producing an oxide superconductor according to any one of claims 6 to 8 , wherein when solidifying from a molten state, the crystal is grown under a temperature gradient of 5 ° C./cm or more. A method for producing an oxide superconductor, comprising: