JP2001114518A - Oxide superconductor and manufacturing method thereof - Google Patents

Abstract

(57) [Problem] To provide a novel oxide superconductor which can easily provide a required pinning effect during production. SOLUTION: Ln _{1 + x} Ba _2-x Cu ₃ O _7-y (where -0.1 ≦ x ≦ 0.5, y ≒ (1-x) / 2, and an element at a crystallographic atomic position is An oxide superconductor having a crystal structure of the type (including those partially or entirely substituted with other elements). A pinning center is introduced by containing 0.001 to 2 at% of carbon atoms.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an oxide superconductor and a method for producing the same. In particular, the present invention relates to a Y123-based oxide superconductor suitable for using a large current, a high frequency, or a magnetic field.

Here, the Y123 system means Ln _{1 + x} Ba
_2-x Cu ₃ O _7-y (however, -0.1 ≦ x ≦ 0.5, y
≒ (1-x) / 2, including those in which the element at the crystallographic atom position is partially or entirely replaced with another element. ) Type. Ln is Y, La, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb
And one or more selected from the group

[0003] "at%" means "atomic%".

[0004]

2. Description of the Related Art A Y123 type superconductor (oxide superconductor), when the magnetic field is increased and placed in the region of an upper critical magnetic field, the Lorentz force acts on the magnetic flux when an electric current is applied, and the magnetic flux is generated. It moves. As a result, a voltage is induced in the same direction as the current, and a resistance appears, so that the superconductor is no longer used. For this reason, it is necessary to introduce a pinning center that has the effect of capturing quantum flux lines and hindering movement in the Y123-based superconductor. Dislocations, normal precipitates,
Any defects or inhomogeneities, such as voids and grain boundaries, can act as pinning centers.

As a method of introducing a pinning center in a Y123-based superconductor, for example, there is a method of introducing a non-superconducting phase such as the Y211 phase as a pinning center in a liquid phase growth method.

In this method, it is practically impossible to grow the solution from a homogeneous solution phase, and an operation step for mixing and dispersing the non-superconducting phase in the precursor is required.

In addition, as typified by the Nd123 superconductor, the introduction of a pinning center by a method of dispersing a region in which atoms of a rare earth site and atoms of a Ba site are substituted with each other involves dispersing the region with mutual substitution. In addition to the annealing treatment step of the invention, a further post heat treatment step was required.

[0008]

SUMMARY OF THE INVENTION In view of the above, the present invention has been developed to introduce a pinning center.
It is an object of the present invention to provide an oxide superconductor in which an operation step for mixing and dispersing a non-superconducting phase in a precursor and a post heat treatment step for dispersing an intersubstituted region are not indispensable, and a method for producing the same.

[0009] That is, an object of the present invention is to provide a novel oxide superconductor in which a pinning center can be easily introduced at the time of manufacturing, and a method of manufacturing the same.

[0010]

The oxide-based superconductor of the present invention solves the above-mentioned problems by the following constitution.

Ln _{1 + x} Ba _2-x Cu ₃ O _7-y (however,
−0.1 ≦ x ≦ 0.5, y ≒ (1-x) / 2, including those in which the element at the crystallographic atomic position is partially or entirely substituted with another element. The oxide superconductor having the (ii) type crystal structure is characterized by containing 0.001 to 2 at%, preferably 0.1 to 0.4 at%, of carbon atoms.

One of the methods for producing an oxide superconductor according to the present invention is a method for producing an oxide superconductor by controlling a carbon atom content of the oxide superconductor in the liquid phase growth method. The method is characterized by adjusting the concentration of the carbon-containing component in the liquid phase, and further by adjusting the concentration of the carbon-containing component in the gas phase in contact with the liquid phase.

Another method for producing an oxide superconductor is a method for producing an oxide superconductor by a vapor phase growth method, wherein the control of the amount of carbon atoms of the oxide superconductor is performed by controlling the carbon-containing component in the vapor phase. Is adjusted by adjusting the density of

Still another method of manufacturing an oxide-based superconductor is a method of manufacturing by a solid-phase growth method, wherein the amount of carbon atoms contained in the oxide superconductor is controlled by controlling the carbon content of the solid phase in the solid-phase growth method. It is characterized by performing by adjusting the concentration of the component.

[0015]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, each constitution of the present invention will be described.
This will be described in detail.

Y123 type, that is, Ln _{1 + x} Ba _2-x C
u ₃ O _7-y (-0.1 ≦ x ≦ 0.5, y ≒ (1
-X) / 2, including those obtained by partially or entirely substituting the element at the crystallographic atomic position with another element. The present invention relates to an oxide superconductor having a crystal structure of the type (1) wherein the number of carbon atoms is 0.001 to _{2 at} % (0.00125 to 0.125 in the unit cell of the LnBa ₂ Cu ₃ O _7-y type crystal). ), Desirably 0.1 to 0.4 at% (LnBa ₂ C
u ₃ O _7-y type 0.0125 to 0.0 in the unit cell of the crystal of
(Equivalent to 5).

That is, by adding an appropriate amount of carbon to the above Y123-based oxide superconductor, the present inventors introduce a pinning center into the oxide superconductor material, thereby improving the magnetic flux pinning force and the irreversible magnetic field. It was found that.

It has been reported that the added carbon is substituted with Cu of the Cu—O bond of the Ln _{1 + x} Ba _2-x Cu ₃ O _7-y type crystal structure in a form bonded to an extra oxygen atom. (Reference: J. Wang et al., Supercond. Sci. Technol. 9 (1996)
P.69 and B. Grevin et al., Physica C 289 (1997) P.7
7). Alternatively, it has been reported that the added carbon exists as an interstitial type in the crystal lattice in a state of forming a CO ₃ group (Reference: FJ Gotor et al., Physica C 218).
(1993) P.429).

The detailed position and whether or not an atomic group such as a CO ₃ group is formed are not necessarily clear. Whatever the state, it is presumed that the superconducting state around the carbon atoms taken into the crystal changes and contributes to the improvement of the pinning force.

In the above, the carbon atom weight: 0.001 at
%, The effect of improving the magnetic flux pinning force and the irreversible magnetic field in the Y123-based superconductor, that is, it is difficult to obtain an effective pinning center. On the other hand, when the carbon atom content exceeds 2 at%, the critical temperature T _C is lowered, and no superconductivity is exhibited. And Y
It is not preferable because it greatly disturbs the 123 type crystal structure.

And Y123 containing the carbon atom.
The control of the amount of carbon atoms in the system superconductor is performed as follows according to each manufacturing method.

(1) In the case of the liquid phase growth method (liquid phase reaction method), the amount of carbon atoms in the oxide superconductor is controlled by adjusting the concentration of the carbon-containing component (carbon compound) in the liquid phase in the liquid phase growth method. It is done by doing.

Here, the liquid phase growth method is referred to as a melt solidification method, and includes a kilopros method (kyropoulus method) belonging to the whole melt solidification type, a rotation pulling method (CZ method) belonging to the crystal drawing type, In addition, various partial melting types are included (Reference: RALaudise "The growth of sin
gle crystal '' in solid state physical electronicsse
ries 1970 by Prentice-Hall, Inc., Englewood Criffs,
NJP306).

Among these, a top-seed solution (TSSG) which is a kind of the following kilopros method is used.
growth) (also known as the improved Chocolarski method) and a partial melting method (MPMG: melt-p
An owder-melt-growth process is preferred because it can produce crystals of practically advantageous size.

TSSG method: A seed crystal is attached to a seed holder, and this is heated by heating a crucible to bring the seed crystal into contact with the liquid surface in a molten flux to grow the crystal. A schematic diagram of the apparatus is shown below. Usually, the seed crystal is made of various substrates (M
A film formed on a gO substrate or the like by a PLD (pulse laser deposition) method is used.

MPMG method: This is basically the same method as the above-mentioned TSSG method. However, while the TSSG method is performed within the primary crystal growth temperature of Y123 crystal (about 970 to 1000 ° C.), the partial melting method is a partial melting region (solid-liquid coexistence region) at a higher temperature (1000 ° C. or higher). By gradually lowering the temperature from the above), Y123 is precipitated from the insulator phase.

As the above-mentioned carbon-containing component, a carbon compound which can be dissolved in various solution phases can be usually used. Usually, a carbonate such as barium carbonate (BaCO ₃ ) is used. Furthermore, carbon compounds can be used.

When a solvent of BaO: CuO = 3: 5 was used as the solution phase, the concentration (addition amount) of the above barium carbonate was used.
Is usually 0.004 to 0.4% by weight, preferably 0.04% by weight.
2 to 0.08 wt%.

At this time, as described above, the control of the carbon atom content of the Y123-based superconductor is not only directly controlled by adjusting the concentration of the carbon-containing component in the liquid phase in the liquid phase growth method, but also controlled by the liquid phase. It can also be achieved by indirectly controlling the concentration of the carbon-containing component (carbon compound) in the gas phase in contact. Here, as the carbon compound, carbon dioxide gas (C
O ₂ ), but other carbon compounds, such as carbon monoxide (CO), may be used.

The concentration of carbon dioxide at this time is usually 5 to 2
000 ppm, preferably 50 to 700 ppm.

(2) In the case of vapor phase growth (vapor phase reaction), the amount of carbon atoms in the oxide superconductor is controlled by adjusting the concentration of the carbon-containing component in the gas phase.

Here, the vapor phase growth method includes a laser tabulation method, a sputtering method, a reactive vacuum deposition method, a chemical vapor deposition method (CVD method) and the like.

Among them, metal organic chemical vapor deposition (MOC)
VD method) is preferable in terms of production cost and carbon addition.

As the carbon-containing component in the gas phase, carbon dioxide or carbon dioxide accompanying the decomposition of the raw material by the MOCVD method is usually used.

The concentration of carbon dioxide is 10 to 3500 ppm, preferably 100 to 1000 ppm.

(3) In the case of the solid-phase growth method (solid-state reaction method), the amount of carbon atoms in the oxide superconductor is controlled by adjusting the concentration of the carbon dioxide component in the atmosphere in the solid-phase growth method.

Here, the manufacturing process by a general solid phase growth method (solid phase reaction method) is as follows.

Selection of raw materials: Powders of oxides and carbonates of various metals are usually used as raw materials for the oxide superconductor. For example, Y ₂ O ₃ , BaCO ₃ , or CuO powder is used.

Weighing / mixing process: Since the solid-phase reaction occurs from the contact point of the powder particles, they are sufficiently mixed to improve the contact between different kinds of particles. For example, mixing in a ball mill is performed.

Calcination process: firing this mixed powder,
Decompose the carbonate and react the raw material powder. For example, the firing temperature is about 850 ° C.

Molding process: repeated grinding and calcination,
Mix well. Thereafter, the calcined sample is pulverized sufficiently finely and pressure-formed.

Firing process: 900-950
Main firing and sintering at ℃ for a sufficient time.

Process for controlling oxygen amount: Heat treatment is performed because the superconductivity changes greatly depending on the nonstoichiometric amount of oxygen. For example, the heat treatment conditions are as follows.
C. for at least 40 hours.

The concentration of the carbon dioxide component used for controlling the carbon atom content of the present oxide superconductor is usually 5 to 2,000.
ppm, preferably 50 to 700 ppm.

[0045]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment performed to confirm the effects of the present invention will be described below with reference to the drawings.

Example 1 YBa ₂ Cu ₃ O _{6 + x} (Y1
23) 100 g, BaO: CuO = 3: 5 (mol ratio)
100 g of a mixture of BaCuO ₂ and CuO weighed so as to fill a crucible made of yttria and heated to 1000 ° C. in an electric furnace to obtain a solution (melt) 200 for crystal growth.
g was obtained.

20 g of barium carbonate (BaCO ₃ ) and 13.4 g of copper oxide (CuO) were added to the solution, and a Y123 crystal thin film formed on a magnesia single crystal substrate was used as a seed crystal.

By the upper seeding liquid phase method (TSSG method),
A thick film crystal of Y123 was grown.

The crystal growth conditions were as follows: growth temperature: 970
1000 ° C, atmosphere: air (1 atm), crystal rotation speed: 1
0 to 30 rotations / min, growth time: 10 to 30 min.

The concentration of carbon contained in the solution (liquid phase) and the concentration of carbon contained in the film grown from the solution were measured by a combustion / infrared absorption method and a secondary ion mass spectrometry, respectively.

FIG. 1 shows the time-dependent changes in the solution after the addition of BaCO ₃ and the carbon concentration in the film. From FIG. 1, it can be seen that the carbon concentration in the solution and in the film decreases over time and approaches a finite value.

FIG. 2 shows the ratio between the solution (melt: Flux) and the amount of carbon atoms taken into the crystal. From this, it was found that half of the carbon atoms in the solution (that is, the partition coefficient was 0.5) were taken into the crystal.

These facts indicate that BaCO added to the solution
It is shown that a method of controlling the amount of carbon atoms added to the superconductor material can be obtained by controlling the amount of ₃ and the elapsed time.

<Example 2> In Example 1, the atmosphere (carbon dioxide (CO ₂ ) concentration was about 350 pp) for 144 hours.
m) The carbon atom weight of the superconductor after leaving the solution is 0.13a
t%.

On the other hand, the same film formation was carried out while maintaining the concentration of carbon dioxide (CO ₂ ) in the atmosphere at about three times as high as 1000 ppm. As a result, 0.4 at% of carbon atoms were incorporated into the crystal. By this, by controlling the atmosphere,
It has been found that the amount of carbon atoms in the crystal can be controlled.

This is because CO ₂ in the atmosphere and carbon contained in the solution (in the solution, it exists in the form of a carbonate group and is considered to be easily equilibrium with CO ₂ ) are in an equilibrium state. In order to maintain, the concentration of carbon-containing components in the liquid phase is kept constant,
As a result, the amount of carbon atoms in the superconductor material is kept constant and can be controlled.

<Example 3> In Example 1, the solution forming temperature condition was set to 1050 ° C. (partially molten state: not less than the peritectic temperature of Ln123 phase) × 600 min, and then to the growth temperature of Example 1 up to 970-1000 ° C. The Y123 superconductor of this example was prepared in the same manner except that the temperature was lowered for 60 minutes and then the crystal was grown for 30 minutes.

At the time of the primary crystal growth, as in Example 2, the superconductor of this example was prepared by being left in the air atmosphere (gas phase) for 144 hours. The carbon atom weight of the superconductor was 0.13 at%. On the other hand, with the CO ₂ concentration in the atmosphere set to 1000 ppm, the carbon amount of the superconductor after standing for a sufficient time was 0.4 at%.

<Embodiment 4> In the above-mentioned solid-phase reaction method, the conditions of the sintering step (firing process) were 950 ° C. × 48 hours,
Atmosphere: A superconductor was prepared as air. The carbon atom weight of the superconductor was 0.13 at%. On the other hand, when the CO ₂ concentration in the atmosphere of the sintering step was 1000 ppm, the carbon atom weight of the superconductor was 0.4 at%.

Example 5 Y prepared by the method of Example 2
Of 123 superconductor materials, carbon content is 0.5at%
Was changed to a temperature slightly below the peritectic temperature of 9
At 90 ° C, CO _Two In an atmosphere with a concentration of 5 ppm or less
Annealed for 100 hours. Superconductor material after this operation
Had a carbon content of 0.1 at%. That is,
After the superconductor material is formed, a suitable amount of CO_Two In the atmosphere
Controllable by annealing
Was.

<Test Example> The solution growth method (T
The irreversible magnetic field of a superconductor (sample) having various carbon contents prepared by annealing the material obtained by the SSG method at 400 to 500 ° C. in an oxygen stream was measured by a DC four-terminal method.

In FIG. 3 showing the results, when the carbon content is about 0.25 at%, the irreversible magnetic field at 77 K is large. This indicates that the pinning force was improved by the addition of carbon.

FIG. 4 shows the critical current density at 50 K evaluated by the Bean model from the magnetization hysteresis curve. It can be seen that the critical current density is improved when the carbon content of the superconductor is about 0.2 at%. It can also be seen that the pinning characteristics change depending on the amount of carbon added.

That is, in a sample having a relatively low carbon content, the characteristics at a high magnetic field are improved, and in a sample having a relatively high carbon content, the characteristics at a low magnetic field are improved.

Therefore, by adjusting the carbon content so as to have preferable characteristics according to the magnetic field to be used, it is possible to provide a material capable of exhibiting pinning characteristics most effectively.

[0066]

As described above, the oxide superconductor according to the present invention has a carbon atom content within a predetermined range (0.001 to 2 at%).
Which is a novel oxide superconductor having an effective pinning effect.

The superconductor material is used in each of the manufacturing methods (liquid phase, gas phase, solid phase growth method) in the liquid phase / solid phase growth method.
By adjusting the concentration of the gas phase, the solid phase, and the concentration of the carbon-containing component in the gas phase in contact with them, the amount of carbon atoms can be easily controlled.

Accordingly, the oxide superconductor of the present invention
In order to introduce a pinning center, a work process for mixing and dispersing the non-superconducting phase in the precursor and a post-heat treatment process for dispersing the inter-substituted region are not indispensable as in the conventional case. Can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the solution after adding BaCO ₃ and the change over time in the carbon concentration in a film in Example 1.

FIG. 2 is a graph showing the ratio between the solution (Flux) and the amount of carbon atoms taken into crystals in Example 1.

FIG. 3 is a graph showing the results of measuring the irreversible magnetic field by a DC four-terminal method for the superconductor (sample) having each carbon atom weight prepared in Example 1.

FIG. 4 is a graph showing a critical current density at 50 K evaluated using a Bean model from a magnetization hysteresis curve.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoji Yamada 2-4-1 Rokuno, Atsuta-ku, Nagoya City, Aichi Pref. International Superconducting Technology Research Center Inside the Superconducting Engineering Laboratory (72) Inventor Hiroshi Ikuta Aichi Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan (72) Inventor: Uichiro Mizutani Nagoya University, Furo-cho, Chikusa-ku, Aichi, Japan (72) Inventor: Tadamasa Miura Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, Japan (72) ) Inventor Yoshihiro Koike 20-1, Kita-Sekiyama, Odaka-cho, Midori-ku, Nagoya-shi, Aichi F-term (Reference) 4C047 JA03 JB01 JC03 KB04 KC01 KC10 KD09 KE02 KE04 KF01

Claims (7)

[Claims] 1. Ln _{1 + x} Ba _2-x Cu ₃ O _7-y (where -0.1 ≦ x ≦ 0.5, y ≒ (1-x) / 2, element at crystallographic atomic position) ). An oxide superconductor having a crystal structure of the type wherein the carbon atom is contained in an amount of 0.001 to 2 at%. . 2. The oxide superconductor according to claim 1, containing 0.1 to 0.4 at% of carbon atoms. 3. The method for producing an oxide superconductor according to claim 1 or 2, wherein the control of the amount of carbon atoms of the oxide superconductor is performed by using a liquid phase carbon in the liquid phase growth method. A method for producing an oxide superconductor, which is carried out by adjusting the concentration of a component. 4. The oxide superconductor according to claim 3, wherein the concentration of the carbon-containing component in the gas phase in contact with the liquid phase is adjusted when controlling the carbon atomic weight of the oxide superconductor. Manufacturing method. 5. The method for producing the oxide superconductor according to claim 1 or 2 by a vapor phase growth method, wherein the control of the amount of carbon atoms of the oxide superconductor is performed by using a vapor phase in the vapor phase growth method. A method for producing an oxide superconductor, which is performed by adjusting the concentration of a carbon-containing component. 6. A method for producing the oxide superconductor according to claim 1 or 2 by a solid phase growth method, wherein the carbon atom content of the oxide superconductor is controlled by a carbon-containing component in the solid phase growth method. A method for producing an oxide superconductor, which is performed by adjusting the concentration of the oxide superconductor. 7. The oxide superconductor according to claim 3, wherein the control of the amount of carbon atoms in the oxide superconductor is further performed by a production temperature and a time. Manufacturing method.