JPH111320A - Oxide superconductor and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide superconductor having excellent properties and large crystal particles in a La123-system oxide superconductor, and a method for producing the superconductor. SOLUTION: This oxide superconductor having excellent properties and large crystal granules comprises La-Ba-Cu-O containing La1+x Ba2-x Cu3 O(7+x/2-d) -0.1<=(x)<=0.3 and 0<=(d)<=0.3} as a matrix phase and 0 <(the content)<=50 mol.% of the phases of La2-x Ba1+x Cu2 O6-x/2 0<=(x)<=0.8} and/or La4-x Ba2+2x Cu2-x O10-2x 0<=(x)<=0.8} and is obtained by using La2-x Ba1+x Cu2 O6-x/2 0<=(x)<=0.8} and/or La4-x Ba2+2x Cu2-x O10-2x 0<=(x)<=0.8} as one of the starting materials in generating a La123ss phase from a molten state.

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 ( _Tc ) and a high critical current and a method for producing the same, and more particularly to a superconducting bearing, a superconducting magnetic carrier, a magnetic shield, a superconducting magnet, and the like. And effective technology.

[0002]

BACKGROUND OF THE INVENTION T _c is the discovery of superconductors exceeding the liquid nitrogen temperature (77K), worldwide superconducting applications is being studied. Above all, in the case of 123-based materials represented by Y-Ba-Cu-O, MPMG (Melt-Powder-Melt-Growt
h) With the development of melting methods such as the method, YBa ₂ Cu ₃ O
_y (Y123) Fine Y ₂ BaC in superconducting matrix
By dispersing the uO ₅ (Y211) phase, a large critical current density (J _c ) has been successfully achieved.
Such a superconductor can generate a large electromagnetic force by interaction with a magnetic field, and application research to a bearing, a flywheel, a transfer device, and the like using this force has been active. For example, "Melt Processed High Te
mperature Superconductors ”, ed.M.Murakami (World Sc
ientific, 1993).

It has 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.

[0005] Y is replaced with another rare earth element (RE; La, Nd,
Sm, Eu, Gd, Dy, Ho, Er, Yb , etc.) it is known that a superconductor showing a T _c of similarly 90K class and RE123-based material obtained by substitutions Y123 at. Also,
The melting point (peritectic decomposition temperature) of RE123 is directly proportional to the ionic radius of RE to be used, and L has a larger ionic radius than Y.
RE123 replaced with a, Nd, Sm, etc.
° C higher. Taking advantage of this, for example, for growth of Y123 system, Nd123 or Sm
A large crystal with a controlled crystal orientation has been obtained by combining a 123 crystal or the like with a temperature gradient as a seed crystal. Since La has a larger ionic radius than Nd, if a high-quality La123 crystal can be produced, it is possible to further widen the melting point difference between the seed crystal and the bulk material to be grown.
Control of the fabrication process becomes easier.

In the case of superconducting bonding, a La123 superconductor having a high melting point is manufactured, and a Y123 superconductor is placed between the La123 plates.
By heating to the melting point of Y123 or more and the melting point of La123 or less with the 123 phase interposed, La123 remains in a solid phase and Y
It is also conceivable to melt and join 123. For the above-mentioned applications, it is necessary to synthesize a high-quality La123 superconductor.

[0007]

However, when an RE123-based superconductor substituted with RE having an ionic radius larger than Gd is manufactured by a commonly used sintering or melting method, the ionic radius of the rare earth element becomes Ba. In this case, there is a problem that the ionic radius is close to the ionic radius, and therefore, it is easily replaced with a Ba site, and T _c is greatly reduced. For example, H. Uwe et
al .: Physica Cvol. 153-155 (1988) P.930-931 describes the related art. La123 substituted with La is particularly easy to substitute with Ba, and it is difficult to produce a material having a high _Tc . Further, the replacement of the rare earth element with the Ba site lowers the melting point. Good quality La123 is N
Although the melting point is expected to be higher than d123, the substitution actually lowers the melting point of La123.

In order to solve the above-mentioned problem, the oxygen partial pressure of the generation atmosphere in the melting process of the oxide superconductor is set to 0.1.
When performed in the range from 00001 atmospheres to 0.1 atmospheres, T _c
It has been clarified that an oxide superconductor exceeding 90K can be obtained. For example, it is described in JP-A-7-187671, Wada, et al., Phys. Rev. B 39 (1989) 9126.

However, in the La123 system,
No bulk materials with high _Tc have been reported in the melt process. This is because La123 has a complex phase relationship with Nd123 or Sm123-based material after peritectic decomposition (partially melted state), which seems to make the production difficult. When La123ss is manufactured by a conventional melting method, La422ss, La21
To generate many solid phases such as 2ss and La214ss,
It is considered that the finally obtained La123ss phase becomes a polyphase having a different substitution amount, which causes a deterioration in characteristics.

[0010] In the partial melting method, the 123 material is once heated to the peritectic decomposition temperature of 123 (about 1 in the case of the Y123 system).
(000 ° C.) or more, and after partially melting, a bulk material is grown by a method of cooling to a peritectic temperature or less. La1
At 23, in the partial melting temperature range, the La123 phase decomposes into a solid phase and a liquid phase rich in Ba. Here, in the partial melting temperature range, the decomposed liquid phase easily separates and flows out, resulting in a composition deviation, and as a result, La in La123 obtained after melt growth has an excessive composition, thereby lowering _Tc. was there.

As one method for solving this problem, it has been reported that it is effective to add Ba excessively in the initial composition [Japanese Patent Application No. 9-46607].
issue].

The RE123-based bulk superconductor is subjected to oxygen treatment at a temperature in the range of 250 ° C. to 550 ° C. after crystal growth, and oxygen is introduced into the 123 material to form a superconductor. At this time, a structural phase transition occurs from the tetragonal system to the orthorhombic system, and defects such as cracks are generated due to a volume change caused by the phase transition. Further, the RE123-based bulk superconductor contains a second phase such as the RE211 phase or the RE422 phase, and since the second phase and the 123 phase have different coefficients of thermal expansion, cracks may occur during cooling after crystal growth. Are known. Cracks reduce the critical current and cause a decrease in mechanical strength.

An object of the present invention is to provide a technique capable of obtaining large crystal grains having good characteristics of a La123-based oxide superconductor.

[0014] It is another object of the present invention, high-T _c La12
It is an object of the present invention to provide a technique capable of obtaining a ternary oxide superconductor.

The above and other objects and novel features of the present invention will become apparent from the description and the drawings of the present specification.

[0016]

The outline of a typical invention among the inventions disclosed in the present application will be briefly described as follows.

(1) In an oxide superconductor composed of the element La-Ba-Cu-O, La _{1 + x} Ba _2-x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _2−x Ba _{1 + x} Cu ₂ O _{6− x / 2}
A phase (having a composition range of 0 ≦ x ≦ 0.8) containing not more than 50 mol% and more than 0 mol% (content> 0).

(2) In an oxide superconductor comprising an element of La-Ba-Cu-O, La _{1 + x} Ba _2-x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _2−x Ba _{1 + x} Cu ₂ O _{6− x / 2}
Phase (in the composition range of 0 ≦ x ≦ 0.8) and La _4-2x B
a _{2 + 2x} Cu _2-x O _10-2x (having a composition range of 0 ≦ x ≦ 0.8) less than 50 mol% and more than 0 mol% (content>
0) It is contained.

(3) In an oxide superconductor made of the element La-Ba-Cu-O, La _{1 + x} Ba _2-x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _4-2x Ba _{2 + 2x} Cu _2-x O
_10-2x (0.25 <x ≦ 0.8 in composition range) is 50
It contains less than 0 mol% and more than 0 mol% (content> 0).

(4) In the oxide superconductor of any one of the above (1) to (3), La is contained in the superconducting matrix.
_{1 + x} Ba _2-x Cu ₃ O _{7 + x / 2-d} (-0.1 ≦ x ≦ 0.5, 0 ≦
(in the composition range of d ≦ 1) is contained in 30 mol% or less and more than 0 mol% (content> 0).

(5) In the oxide superconductor according to any one of the above (1) to (4), silver as a disperse phase is 30% by weight or less and more than 0% by weight (content> 0).
It is contained.

(6) In an oxide superconductor composed of the element La-Ba-Cu-O, La _{1 + x} Ba _2-x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _4-2x Ba _{2 + 2x} Cu _2-x O
_10-2x (in the composition range of 0 <x ≦ 0.25) is contained in an amount of 50 mol% or less and more than 0 mol% (content ratio> 0), and silver as a dispersed phase is contained in an amount of 30 wt% or less and containing It is contained in an amount of more than% by weight (content> 0).

(7) In the oxide superconductor according to (6), La _{1 + x} Ba _2-x Cu ₃ O is contained in the superconducting matrix.
Contains _{7 + x / 2-d} (-0.1 ≦ x ≦ 0.5, 0 ≦ y ≦ 1) dispersed phase not more than 30 mol% and more than 0 mol% (content> 0) Is what is being done.

(8) In the melting process of the oxide superconductor composed of the element La—Ba—Cu—O, when the superconducting phase is solidified from the molten state, La _2−x Ba _{1 + x} Cu ₂
O _{6-x / 2} (having a composition in the range of 0 ≦ x ≦ 0.8)
Is used as a part of the precursor.

(9) In the process of melting an oxide superconductor composed of an element of La—Ba—Cu—O, when a superconducting phase is solidified from a molten state, La _2−x Ba _{1 + x} Cu ₂
O _{6-x / 2} (having a composition in the range of 0 ≦ x ≦ 0.8)
And La _4-2x Ba _{2 + 2x} Cu _2-x O _10-2x (0 ≦ x ≦ 0.8
Is used as a part of the precursor.

(10) In the melting process of an oxide superconductor composed of the element La-Ba-Cu-O, when solidifying and forming a superconducting phase from a molten state, La _4-2x Ba _{2 + 2x} C
_{u 2- x} O 10-2x (0.25 <in the composition range of x ≦ 0.8)
Is used as a part of the precursor.

(11) In the method for producing an oxide superconductor according to any one of the above (8) to (10), silver is added to the precursor in an amount of 30% by weight or less and more than 0% by weight. The manufacturing method of the oxide superconductor characterized by the above.

(12) In the melting process of the oxide superconductor composed of the element La-Ba-Cu-O, when the superconducting phase is solidified from the molten state, La _4-2x Ba _{2 + 2x} C
u _{2- x} O _10-2x (having a composition range of 0 <x ≦ 0.25) is used as a part of the precursor, and silver is used as a dispersed phase.
% Or less and more than 0% by weight.

FIGS. 1, 2 and 3 show LaO-BaO in pure oxygen (oxygen concentration 100%), air (oxygen concentration about 20%), and low oxygen partial pressure (oxygen concentration about 1%), respectively.
1 shows a ternary system diagram of a CuO system.

FIG. 1 shows a phase diagram in LaO-BaO-CuO-based pure oxygen (oxygen concentration 100%). As a typical phase, La _{1 + x} Ba _2-x Cu ₃ O _{7 + x / 2-d} (La
123ss; -0.1 ≦ x ≦ 0.7, 0 ≦ d ≦ 1), La _2-x Ba _{1 + x} Cu ₂ O _{6-x / 2} (La212s
s; in the composition range of 0 ≦ x ≦ 0.8), and La _4-2x
Ba _{2 + 2x} Cu _2-x O _10-2x (La422ss; 0 ≦ x ≦
0.8 in the composition range).

La212ss phase is LaO-BaO-Cu
A phase characteristic of the O system, and other REO-BaO-CuO
This is a phase not generated in the system (RE; Nd, Sm, Y, etc.). The La123ss phase is a solid solution generated in RE (La, Nd, Sm, Eu, Gd) having an ionic radius larger than Gd, but the solid solution limit x is proportional to the ionic radius of RE, and in La system, A considerably large substitution type solid solution is produced. The La422ss phase is a phase obtained only in the La-based and Nd-based phases, and the solid solubility limit x of the La-based phase is larger than that of the Nd-based phase.

Generally, RE _{1 + x} Ba _2-x Cu ₃ O _{7 + x / 2-d}
When the solid solution amount x in (RE123ss) increases,
Since T _c decreases, if one wants to obtain a high T _c material,
The solid solution amount x must be kept small. However, in oxygen, the solid solution limit in La123ss is large, so that _Tc is low (x in La123ss).
Phase is likely to precipitate. Here, a solid phase component (La212 or La422ss) in a partially molten state
Is made to be Ba excess, so that the crystallized La1
It is possible to keep the value of x at 23 ss small. In RE123ss, d has a non-stoichiometric property in the range of 0 ≦ d ≦ 1, but in the case of La123ss type, a high T _c cannot be obtained unless d ≦ 0.3.

In the production of a 123-series bulk superconductor by the melting method, the material is once thermally decomposed (partially melted) by heating to a temperature equal to or higher than the melting point of 123, and then, in a cooling process, the 123 phase is crystallized. A large crystal with few grain boundaries that obstructs the flow of superconducting current is produced. In the case of the Y123-based material, it becomes a (Y211 + liquid-phase) state when partially melted, and a Y123-based bulk superconductor is produced through a reaction of (Y211 + liquid-phase) → Y123 in a cooling process. However, in the case of the La123 system, the La123ss phase changes La12s with increasing temperature.
3ss → (La212s + liquid phase 1) → (La422s
s + liquid phase 2) and pyrolyzed. Also, with the temperature drop, (La422ss + liquid phase 2) → (La2
12ss + liquid phase 1) → La123ss, La12
The 3ss phase crystallizes.

Therefore, initially, an excessive amount of La212ss is added and thermally decomposed in a region above the melting point of La123ss and below the melting point of La212. Can be manufactured. Also, initially, L
a212ss and La422ss are added in excess, and La
After being thermally decomposed in a region having a melting point of 123 ss or more and a melting point of La212 or less, the crystal is grown to obtain La1.
A material in which La212ss and La422ss are included inside 23ss can be manufactured. Further, at an initial stage, La212ss and / or La422ss are excessively added and thermally decomposed in a region having a melting point of La212ss or more and a melting point of La422 or less.
A material including a422ss can also be manufactured.
Further, initially, an excessive amount of La422ss was added, and
After being thermally decomposed in a region having a melting point of 123 ss or more and a melting point of La212 or less, the crystal is grown to obtain La1.
A material in which La212ss and La422ss are included inside 23ss can also be manufactured. However, 123
When the amount of the second phase included in the mother phase is 50 mol% or more,
It is not preferable because the continuity of the 123 superconducting mother phase is hindered and the critical current is reduced.

FIG. 2 shows LaO—BaO—CuO based air.
The phase diagram in the middle (oxygen concentration about 20%) is shown. Typical
La phase_{1 + x}Ba_2-xCu_ThreeO_{7 + x / 2-d}(La12
3ss; in the range of -0.1≤x≤0.5, 0≤d≤1
), La_2-xBa_{1 + x}Cu_TwoO_{6 -x / 2}(La212ss;
0 ≦ x ≦ 0.5 in the composition range), and La_4-2xBa<sub>Two
+ 2x</sub>Cu_2-xO_10-2x(La422ss; 0 ≦ x ≦ 0.5
In the composition range).

As shown in FIG. 2, when the oxygen partial pressure is reduced, La123ss, La212ss, La422ss
In both cases, the solid solution amount x tends to be smaller than that in pure oxygen. La123ss is thermally decomposed and crystallized in the same manner as in pure oxygen.
a123ss → (La212ss + liquid phase 1) → (La4
22s + liquid phase 2) and pyrolyzed. In addition, while lowering the temperature, (La422ss + liquid phase 2) → (L
a212ss + liquid phase 1) → La123ss, and La
123ss crystallizes.

As in pure oxygen, La212s
s in excess of the melting point of La123ss, La2
After being thermally decomposed in a region having a melting point of 12 or less, the crystal is grown, so that La212s is contained inside La123ss.
The material containing s can be manufactured. In addition, La212ss and La422ss are excessively added at an early stage, and thermally decomposed in a region having a melting point of La123ss or more and a melting point of La212 or less, and then growing a crystal, thereby forming La212ss and La4 inside La123ss.
A material containing 22ss can be manufactured. Furthermore, initially, La212ss and / or La422s
s is added in excess, the melting point of La212ss or higher, La4
After being thermally decomposed in a region having a melting point of 22 or less, the crystal is grown, so that La212s is contained inside La123ss.
A material containing s and La422ss can also be manufactured. Furthermore, La422ss is excessively added at an early stage, and thermally decomposed in a region having a melting point of La123ss or more and a melting point of La212 or less, and then growing a crystal, thereby forming La212ss and La4 inside La123ss.
A material containing 22ss can also be manufactured. However, when the content of the second phase included in the 123 parent phase is 50 mol% or more, the continuity of the 123 superconducting parent phase is hindered, and J _c
This is not preferable because it causes a decrease in

FIG. 3 is a phase diagram of the LaO-BaO-CuO system under a low oxygen partial pressure (oxygen concentration of about 1% or less). As a typical phase, La _{1 + x} Ba _2-x Cu ₃ O _{7 + x / 2-d}
(La123ss; -0.1 ≦ x ≦ 0.25, 0 ≦ d ≦ 1
), La _2-x Ba _{1 + x} Cu ₂ O _{6-x / 2} (La ₂
12ss; _x- 0), and La 4-2x Ba _{2 + 2x} Cu _2-x O _1
0-2x (La422ss; in the composition range of 0 ≦ x ≦ 0.25).

As shown in FIG. 3, when the oxygen partial pressure is further reduced, the solid solution amount of each phase is further reduced.
In La212ss, there is almost no solid solution. La123ss is directly decomposed into La422ss.
That is, La123ss increases in temperature and La1ss
23s → (La422ss + liquid phase) and pyrolyzed. Also, while lowering the temperature, (La422ss)
(+ Liquid phase) → La123ss, La123ss is crystallized, and a material in which La422 phase is included in the 123 phase can be produced.

La _{1 + x} Ba _2-x Cu ₃ O is contained in the superconducting matrix.
_{7 + x / 2-d} (La123ss, -0.1 ≦ x ≦ 0.5, 0 ≦
By dispersed phase of a) the composition range of d ≦ 1 is to contain more than zero mole% in 30 mol% or less (content> 0), it is possible to improve the J _c in high magnetic field. here,
La123ss phase is -0.1≤x≤0.5, 0≤d≤1
Has a composition of, T _c than 123 superconducting matrix phase is a phase which does not show low or superconducting. La123s
In the s phase, if 0.2 ≦ x, the phase is a phase where T _c is low or does not show superconductivity regardless of the value of d. Also, if d ≦ 0.7, the phase does not exhibit T _c is low or superconducting regardless of the value of x. When these dispersed phases are included in the 123 superconducting matrix having a high T _c, they act as pinning centers of magnetic flux lines, and as a result, J _c is improved. The dispersed phase is generated in the 123 superconducting matrix due to temperature fluctuation, composition fluctuation, and the like during crystal growth.

In the RE123-based bulk superconductor,
Volume change due to structural phase transition due to oxygen introduction, or
Cracks occur due to the difference in thermal expansion coefficient between the second phase and the 123 phase included in the 123 matrix. The resulting crack thus reduces the J _c, and causes a reduction in mechanical strength. Here, silver (Ag) is converted to Ag powder or Ag ₂ O.
Ag particles can be finely included inside by adding in advance to the precursor before the melting treatment in the form of powder or the like. Due to the presence of the Ag particles, the stress inside the 123 phase is relaxed, and the generation of cracks can be suppressed. However, excessive addition of more than 30% by weight, causes that prevent the continuity of the 123 superconducting matrix, to reduce the J _c,
Not preferred. Further, it is known that the addition of silver of several weight% or more lowers the melting point of the 123 phase by about 30 ° C., and has an advantage that the process temperature can be lowered.

As can be seen from the above description, in the present invention, by controlling the oxygen partial pressure and the decomposition temperature, it is possible to produce a bulk superconductor having a La123ss superconductor and a La212ss phase and / or a La422ss phase. Become. Further, the use of a composition containing excessive Ba leads to an increase in T _c , and therefore, the use of a composition material containing excessive Ba (La422ss and / or La212ss having a large solid solution amount x) as a precursor. It is valid.

In order to increase the amount of solid solution x in La422ss and La212ss, it is effective to prepare La422ss and La212ss in advance under an oxygen partial pressure of 0 atm or more, but preferably to a high pressure of 0.1 atm or more. La422ss and La212s under oxygen partial pressure
Make s.

In the present invention, La123s
s, La212ss, and La422ss are individually calcined and mixed to form a precursor.
From the experimental results of the present invention to be described later, it has been found that it is effective to produce La123ss at a partial pressure of oxygen of 0 to 0.1 atm.

[0045] In the present invention, for further improvement in the size and T _c the crystal grains of the oxide superconductor, when solidifying an oxide superconductor from the molten state, the partial pressure of oxygen generated atmosphere Is preferably performed in the range of 0.00001 to 1 atm.

[0046] In the present invention, for further improvement in the size and T _c the crystal grains of the oxide superconductor, when solidifying an oxide superconductor from the molten state, the cooling rate 10 ° C. / It is preferable to carry out in less than time.

Further, in the present invention, in order to enlarge the crystal grains of the oxide superconductor and further improve T _c , the temperature gradient is set to 1 ° C./sec when the oxide superconductor is solidified from a molten state. cm or more.

[0048]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments (examples) of the present invention will be described in detail.

(Embodiment 1) The method of manufacturing an oxide superconductor according to Embodiment 1 of the present invention has a ratio of La: Ba: Cu of 1:
Weigh and mix to make 2: 3. The mixed powder is formed by a uniaxial press, and the formed body is heated at 880 ° C. in air.
For 30 hours. This calcined powder is crushed and mixed,
After forming by a uniaxial press, calcination is performed at 940 ° C. for 50 hours in an atmosphere of 0.1% O ₂ + Ar gas. This is repeated twice.

The ratio of La: Ba: Cu is 2.4: 3.
6: 1.2 and 4: 2: 2 (La _{4 -2x} Ba _{2 + 2x} Cu _2-x
Weigh and mix so that O _10-2x , x = 0.8 and 0). The mixed powder is formed by a uniaxial press and calcined at 880 ° C. for 30 hours in an air atmosphere. Grind the calcined powder
After mixing and molding with a uniaxial press, in a pure oxygen atmosphere,
Calcination is performed at 950 ° C. for 50 hours.

Each of the individually calcined powders was LaBa ₂
La _4-2x Ba _{2 + 2 x} Cu _2-x O with respect to Cu ₃ O _y
10-2x (x = 0.8 and 0) were mixed to give a composition containing 20 mol%. In FIG. 4A, x = 0.8
The results obtained by examining the thermogravimetric change of the powder in a 1% oxygen gas flow using a thermobalance are shown. Combined with the results of differential thermal analysis (DTA) and the analysis of oxygen concentration, it was confirmed that this decomposition behavior was the release of oxygen gas accompanying the thermal decomposition of the sample.
In a 1% oxygen gas flow, one kind of melting peak was shown, and X-ray diffraction of a sample quenched from each temperature showed
The thermal decomposition behavior at 1025 ° C. was the melting point of La123, and it was confirmed that the La422 + liquid phase was a stable phase at higher temperatures.

The mixed powder was formed into pellets by a uniaxial press and a cold isostatic press (CIP),
And then cooled to 1025 ° C in 5 minutes,
Thereafter, it is cooled to 925 ° C. at a rate of 0.5 ° C./hour (h). At this time, the sample was heat-treated in a 1% oxygen stream. Then, from 500 ° C to 400 ° C for 24 hours (h), from 400 ° C to 250 ° C for 100 hours (h),
Treated in one atmosphere of pure oxygen.

The obtained sample had a La123 crystal of 5 mm.
It has grown to above
It was found that there was a structure in which the La422 phase was finely dispersed.

FIG. 5 shows the temperature dependence of the magnetization of the obtained sample. Those manufactured by the conventional method (x = 0) have a low _{Tc and a} wide transition width. On the other hand, the sample of the present invention has a _Tc of 90K or more, has a very narrow transition width, and is a good superconductor.

[0055] Also, when measuring the J _c of the superconductor in the SQUID magnetometers, it is observed a so-called peak effect as shown in FIG. 6, moreover, a high J _c can be obtained to a high magnetic field side. This suggests the existence of a pinning point operating under a high magnetic field. As this kind of pinning point, Y-
Oxygen deficiency has been reported in Ba-Cu-O-based materials,
In that case, a large change is shown under a slight oxygen annealing condition. However, such a change is not observed in the sample of the first embodiment. This is because the pinning is not due to oxygen deficiency and La _{1 + x} Ba _2-x C
_{u 3 O 7 + x / 2} -d (La123ss, -0.1 ≦ x ≦ 0.5,
(In the composition range of 0 ≦ d ≦ 1).

Further, as a result of cutting out several types of sample pieces from a sample having a _Tc of 90 K or more and performing elemental analysis,
The ratio of La: Ba: Cu was approximately 1: 2: 3, indicating that O was distributed between 6.8 and 7.2.

(Embodiment 2) In the method of manufacturing an oxide superconductor according to Embodiment 2 of the present invention, the ratio of La: Ba: Cu is 1:
Weigh and mix to make 2: 3. The mixed powder is formed by a uniaxial press, and the formed body is heated at 880 ° C. in air.
For 30 hours. This calcined powder is crushed and mixed,
After forming by a uniaxial press, calcination is performed at 940 ° C. for 50 hours in an atmosphere of 0.1% O ₂ + Ar gas. This is repeated twice.

The ratio of La: Ba: Cu is 1.2: 1.
8: 2 (La _2-x Ba _{1 + x} Cu ₂ O _{6-x / 2} , x = 0.8) and weigh and mix. The mixed powder is formed by a uniaxial press and calcined at 880 ° C. for 30 hours in an air atmosphere. After the calcined powder is pulverized and mixed and formed by a uniaxial press, calcining is performed at 950 ° C. for 50 hours in a pure oxygen atmosphere.

Each of the individually calcined powders was LaBa ₂
La _2−x Ba _{1 + x} Cu ₂ O _{6−x / 2} is added to Cu ₃ O _y for 20 times.
Mixing was performed so as to obtain a composition in which mol% was added.

FIG. 4B shows the result of examining the thermogravimetric change of this powder using a thermobalance. In the air,
It shows two melting peaks, and the X-ray diffraction of the sample quenched from each temperature shows that the thermal decomposition behavior at 1065 ° C. is L
The melting point of a123 and the thermal decomposition behavior at 1095 ° C. are La212.
It was confirmed that at a temperature higher than the melting point, the La422 + liquid phase was a stable phase.

The mixed powder is formed into pellets by a uniaxial press and a cold isostatic press (CIP),
And then cooled to 1065 ° C in 5 minutes,
Thereafter, the mixture is cooled to 965 ° C. at a rate of 0.5 ° C./hour (h). At this time, the sample was heat-treated in air. Thereafter, from 500 ° C. to 400 ° C. for 24 hours (h), 400
It was treated in pure oxygen at 1 atm from 100 ° C to 250 ° C for 100 hours (h).

The obtained sample had a La123 crystal of 5 mm.
It has grown to above
It was found that La212 phase had a finely dispersed structure inside.

From the measurement of the temperature dependence of the magnetization of the obtained sample, _Tc of this sample was 90 K or more, the transition width was very narrow, and the sample was a good superconductor.

(Embodiment 3) In the method of manufacturing an oxide superconductor according to Embodiment 3 of the present invention, weighing and mixing are performed so that the ratio of La: Ba: Cu becomes 1: 2: 3. The mixed powder is formed by a uniaxial press, and the formed body is heated to 88 mm in air.
Perform calcination at 0 ° C. for 30 hours. The calcined powder is pulverized and mixed, molded by a uniaxial press, and calcined at 940 ° C. for 50 hours in a 0.1% O ₂ + Ar gas atmosphere. This is 2
Repeat several times.

The ratio of La: Ba: Cu is 1.6: 1.
_{4: 2 (La 2x Ba 1} + x Cu 2 O 6-x / 2, x = 0.4) and _{3.2: 2.8: 1.6 (La 4-2x} Ba 2 + 2x Cu 2 _-x O
Weigh and mix so that _10-2x , x = 0.4). After the mixed powder is formed by a uniaxial press, it is calcined at 880 ° C. for 20 hours in an air atmosphere. After the calcined powder is pulverized and mixed, and formed by a uniaxial press, it is calcined at 950 ° C. for 50 hours in a pure oxygen atmosphere.

The individually calcined powders were separated from LaBa ₂
Against _{Cu 3 O y, La 2-} x Ba 1 + x Cu 2 O 6-x / 2 and La
_4-2x Ba _{2 + 2x} Cu _2-x O _10-2x is mixed to have a composition to which 20 mol% is added. Silver oxide is added to the mixture at 10% by weight and mixed, and the mixture is formed into pellets by a uniaxial press and an isostatic press. According to the measurement of TG and DTA, the melting point of the 123 phase was higher than that of the sample containing no silver.
It was confirmed that the temperature had dropped by about 30 ° C. After heating these samples at 1050 ° C. for 30 minutes, they are cooled to 1035 ° C. in 5 minutes, and then cooled to 935 ° C. at a rate of 0.5 ° C./hour (h). At this time, the sample was heat-treated in air. Then, from 500 ° C to 400 ° C for 24 hours (h), from 400 ° C to 250 ° C for 100 hours (h),
Treated in 1 atmosphere of oxygen.

The obtained sample had a La123 crystal of 5 mm.
It grows as described above.
It was found that the a212 phase, the La422 phase and the Ag particles had a finely dispersed structure.

From the measurement of the temperature dependence of the magnetization of the obtained sample, it was found that the sample had a _Tc of 90K or more, a very narrow transition width, and was a good superconductor.

Further, when the initial raw material contains 10% by weight or less of silver, the 123
Ag particles of several tens of microns could be included.
It was confirmed that the generation of cracks was significantly suppressed in the 123 phase of the obtained sample as compared with the sample to which Ag was not added.

In the first, second and third embodiments, Ba
Use of a composition containing an excessive amount of T leads to an increase in T _c , and therefore, it is effective to use a composition material containing an excessive amount of Ba as a precursor (La422ss and / or La212ss having a large solid solution amount x). .

Further, La422ss and / or La2s
In order to increase the solid solution amount x at 12 ss, 0
Under an oxygen partial pressure higher than atmospheric pressure, La422ss and L
Although it is effective to produce a212ss, it is preferable to produce La422ss and La212ss under a high oxygen partial pressure of 0.1 atm or more.

Although the present invention has been specifically described based on the embodiments (examples), the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

[0073]

The effects obtained by typical aspects of the invention disclosed in the present application will be briefly described as follows.

According to the present invention, when the La123ss phase is generated from the molten state, La212ss and / or
Alternatively, by adding La422ss in excess, L
La212ss and / or La inside a123ss
422ss can be produced, and T
Large crystal grains having good characteristics of the La123-based oxide superconductor having a high _c can be obtained.

According to the present invention, when the La123ss phase is generated from a molten state, La212ss and / or L
By setting the initial composition of a422ss to an excess composition of Ba, the mutual replacement of La and Ba is suppressed as much as possible, and T _c
And large crystal grains having good characteristics of a La123-based oxide superconductor having a high density can be obtained.

According to the present invention, cracks in the block body can be prevented by containing 30% by weight or less and more than 0% by weight of silver (content rate> 0) as a dispersed phase. The mechanical strength of the superconductor can be improved.

[Brief description of the drawings]

FIG. 1 shows ＬLa ₂ in a pure oxygen atmosphere of the present invention.
FIG. 3 is a ternary phase diagram of O ₃ —BaO—CuO.

FIG. 2 shows １ ／ La ₂ O ₃ in an air atmosphere of the present invention.
It is a -BaO-CuO ternary phase diagram.

FIG. 3 shows １ ／ La ₂ in a low oxygen atmosphere of the present invention.
FIG. 3 is a ternary phase diagram of O ₃ —BaO—CuO.

FIG. 4 is a diagram showing a thermogravimetric change of a sample used in Embodiments 1 and 2 of the present invention.

FIG. 5 shows a sample of Embodiment 1 of the present invention (open circle, x = 0.
8) is a diagram showing the temperature dependence of the magnetization of a sample (solid circle, x = 0) manufactured by the conventional method.

FIG. 6 is a diagram showing the magnetic field dependence of the critical current density of the sample of Embodiment 1 (open circles, x = 0.8) and a sample manufactured by a conventional method (black circles, x = 0).

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Shingo Gojima 1-16-25 Shibaura, Minato-ku, Tokyo International Superconducting Technology Research Center, Superconductivity Engineering Laboratory, Tamachi Research Institute (72) Inventor Sakai Straight path 1-16-25 Shibaura, Minato-ku, Tokyo International Research Institute for Superconducting Technology, Superconductivity Engineering Laboratory, Tamachi Research Institute (72) Inventor Liu Aitaku 1-16-25 Shibaura, Minato-ku, Tokyo Foundation International Superconducting Technology Research Center Tamachi Research Laboratory (72) Inventor Masato Murakami 1-16-25 Shibaura, Minato-ku, Tokyo International Superconducting Technology Research Center Superconducting Engineering Research Laboratory Tamachi Research Laboratory

Claims (12)

[Claims] 1. An oxide superconductor comprising an element of La—Ba—Cu—O, wherein La _{1 + x} Ba _2−x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _2−x Ba _{1 + x} Cu ₂ O _{6− x / 2}
An oxide superconductor comprising a phase (having a composition range of 0 ≦ x ≦ 0.8) of 50 mol% or less and more than 0 mol% (content> 0). 2. An oxide superconductor comprising an element of La—Ba—Cu—O, wherein La _{1 + x} Ba _2−x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _2−x Ba _{1 + x} Cu ₂ O _{6− x / 2}
Phase (in the composition range of 0 ≦ x ≦ 0.8) and La _4-2x B
a _{2 + 2x} Cu _2-x O _10-2x (having a composition range of 0 ≦ x ≦ 0.8) less than 50 mol% and more than 0 mol% (content>
0) An oxide superconductor characterized by being contained. 3. An oxide superconductor comprising an element of La—Ba—Cu—O, wherein La _{1 + x} Ba _2−x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _4-2x Ba _{2 + 2x} Cu _2-x O
_10-2x (0.25 <x ≦ 0.8 in composition range) is 50
An oxide superconductor containing less than 0 mol% and more than 0 mol% (content> 0). 4. The oxide superconductor according to claim 1, wherein La _{1 + x} is contained in the superconducting matrix.
Ba _2-x Cu ₃ O _{7 + x / 2-d} (−0.1 ≦ x ≦ 0.5, 0 ≦ d
≦ 1) (a composition range of ≦ 1) in an amount of not more than 30 mol% and more than 0 mol% (content> 0). 5. The oxide superconductor according to claim 1, wherein silver is contained as a dispersed phase in an amount of 30% by weight or less and more than 0% by weight (content> 0). An oxide superconductor characterized by the above-mentioned. 6. An oxide superconductor comprising an element of La—Ba—Cu—O, wherein La _{1 + x} Ba _2−x Cu ₃ O
_{7 + x / 2-d} (having a composition range of -0.1 ≦ x ≦ 0.3, 0 ≦ d ≦ 0.3) as a mother phase, and La _4-2x Ba _{2 + 2x} Cu _2-x O
_10-2x (in the composition range of 0 <x ≦ 0.25) is contained in an amount of 50 mol% or less and more than 0 mol% (content ratio> 0), and silver as a disperse phase is contained in an amount of 30 wt% or less. An oxide superconductor characterized by containing more than 1% by weight (content> 0). 7. The oxide superconductor according to claim 6, wherein La _{1 + x} Ba _2-x Cu ₃ O _{7 + x / 2-d} (−
0.1 ≦ x ≦ 0.5, 0 ≦ d ≦ 1) in an amount of 30 mol% or less and more than 0 mol% (content> 0). Superconductor. 8. In a melting process of an oxide superconductor composed of an element of La—Ba—Cu—O, when a superconducting phase is solidified from a molten state, La _2−x Ba _{1 + x} Cu ₂ O
_A method for producing an oxide superconductor, comprising using _{6-x / 2} (having a composition in the range of 0 ≦ x ≦ 0.8) as a part of a precursor. 9. In a process of melting an oxide superconductor composed of an element of La—Ba—Cu—O, when a superconducting phase is solidified from a molten state, La _2−x Ba _{1 + x} Cu ₂ O
_{6-x / 2} (having a composition of 0 ≦ x ≦ 0.8) and La _4-2x Ba _{2 + 2x} Cu _2-x O _10-2x (composition of 0 ≦ x ≦ 0.8) ) Is used as a part of the precursor. 10. In a melting process of an oxide superconductor having a composition of La—Ba—Cu—O, when solidifying a superconducting phase from a molten state, La _4-2x Ba _{2 + 2x} Cu
_A method for producing an oxide superconductor, comprising using _{2- xO 10-2x} (having a composition range of 0.25 <x ≦ 0.8) as a part of a precursor. 11. The method for producing an oxide superconductor according to claim 8, wherein 30% by weight or less and more than 0% by weight of silver are added to the precursor. An oxide superconductor manufacturing method. 12. In a melting process of an oxide superconductor composed of an element of La—Ba—Cu—O, when solidifying and forming a superconducting phase from a molten state, La _4-2x Ba _{2 + 2x} Cu
_{Using 2- xO 10-2x} (having a composition range of 0 <x ≦ 0.25) as a part of a precursor, and adding silver as a dispersed phase in an amount of 30% by weight or less and more than 0% by weight. A method for producing an oxide superconductor, comprising: