JPH11329118A - Oxide superconducting composite material and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve critical current density (Jc), by regulating a state of the surface of a metal material such as silver, etc., contacting with an oxide superconductor and a state of crystals of the superconductor. SOLUTION: This oxide superconducting composite material is composed of a metal material and an oxide superconductor. Here, the average surface roughness of the metal material contacting with the oxide superconductor is set to be less than 0.5 μm. And the half-width of a locking curve of a (001) main peak in the time of X-ray diffraction the oxide superconductor contacting with the metal material is set to be less than 4 degrees. The manufacture for the oxide superconducting composite material composed of the metal material and the oxide superconductor includes a process in which an oxide superconductive precursor is formed by contacting with the metal material having the average surface roughness of less than 0.5 μm, and a superconducting heat treatment process generating a liquid phase in at least a part of the oxide superconductive precursor. The half-width of the rocking curve of the (001) main peak of the oxide superconductor contacting with the metal material after the heat treatment process is set to be less than 4 degrees when evaluated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting composite material in which the critical current density of an oxide superconductor is improved, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, an oxide superconducting composite material in which a metal material such as silver or a silver alloy is combined with an oxide superconductor has been known. For example, when the oxide superconducting composite material is used as a tape or round wire, the oxide superconductor is covered with a metal substrate or a metal sheath material such as silver or a silver alloy (for example, the 53rd 1995 fiscal year). (Summary of Spring Low Temperature Engineering and Superconductivity Society P77, 57th 1997 Autumn Meeting of Low Temperature Engineering and Superconductivity Society P82). The reason is that an oriented structure of the oxide superconductor is obtained at the interface with silver or a silver alloy, and as a result, the critical current density (Jc)
(For example, the 56th 1997 Spring Low Temperature Engineering and Superconductivity Conference Abstracts P22).

[0003]

However, even in the case of a wire or a material similarly coated or composited with silver or a silver alloy, the critical current density (Jc) is often low or varies.

Accordingly, an object of the present invention is to specify the critical current density (Jc) by defining the surface state of a metal material such as silver in contact with the oxide superconductor and the crystal state of the oxide superconductor.
It is an object of the present invention to provide an oxide superconducting composite material having an improved resistance and a method for producing the same.

[0005]

According to the present invention, there is provided an oxide superconducting composite material comprising a metal material and an oxide superconductor, wherein an average of the metal material in contact with the oxide superconductor is provided. The surface roughness is 0.5 μm or less, and
(0000) during X-ray diffraction of an oxide superconductor in contact with a metal material
1) An oxide superconducting composite material characterized in that the half width at the time of evaluating the rocking curve of the main peak is 4 degrees or less.

According to the present invention, the oxide superconductor is Bi-2212 containing at least Bi, Sr, Ca and Cu.
It is preferably a phase oxide superconductor or a Bi-2223 phase oxide superconductor. In the former case, at least B
Bi-2212 containing i, Sr, Ca, Cu and Pb
It can be a phase oxide superconductor.

Further, the present invention provides a method for producing an oxide superconducting composite material comprising a metal material and an oxide superconductor, wherein the oxide superconducting precursor is brought into contact with a metal material having an average surface roughness of 0.5 μm or less. And a superconducting heat treatment step of generating a liquid phase in at least a portion of the oxide superconducting precursor. Provided is a manufacturing method in which the half width is 4 degrees or less when evaluated.

At this time, the superconducting heat treatment step is preferably performed in an atmosphere at a temperature of 700 to 950 ° C. and an oxygen partial pressure of 0.01 to 10 atm.

[0009]

Embodiments of the present invention will be described below.

[0010] The oxide superconducting composite material according to the present invention is obtained by adjusting the average surface roughness of a metal material which is in contact with at least the oxide superconductor to 0.5 μm or less. In order to obtain such an oxide superconducting composite material, it is desirable to use silver or a silver-based alloy as the metal material that comes into contact with the oxide superconductor. An example of the metal material is a silver substrate or a silver coating, and can be manufactured by adjusting the average surface roughness by machining or the like including, for example, polishing, grinding, and rolling. The production of the composite material of the present invention desirably includes a heat treatment step for superconducting the precursor of the oxide superconductor composited with the metal material. In this case, at least the metal material immediately before the superconductivity heat treatment is performed. Must have an average surface roughness of 0.5 μm or less. The superconducting heat treatment is performed under the condition that at least a part of the superconducting precursor forms a liquid phase, that is, a temperature of 700 to 700.
It is desirable to carry out in an atmosphere at 950 ° C. and an oxygen partial pressure of 0.01 to 10 atm. The reason is that, when the oxide superconductor and its precursor generate a liquid phase, nucleation and growth occur from a contact portion with the silver substrate, and the surface of the oxide superconductor grows from the substrate, and a structure with a high degree of orientation is obtained. . The degree of orientation is evaluated by the rocking curve of the (00l) main peak to determine how parallel the ab plane, which is the conductive surface of the oxide superconductor, to the silver substrate, that is, how easily the superconducting current flows. Can be evaluated.

The limitation of the half width of the rocking curve is defined by the following phenomena. When the angle is 4 degrees or less, since the ab plane of the crystal of each oxide superconductor is arranged substantially parallel to the silver substrate, the superconducting current at the crystal grain boundary on the ab plane is likely to flow, or Since the contact area of the crystal in the c-axis direction increases, current easily flows, and as a result, the critical current density (Jc) increases. On the other hand, if the angle is larger than 4 degrees, the supercurrent does not easily flow at the crystal grain boundary on the ab plane, or the current does not easily flow because the contact area of the crystal in the c-axis direction is geometrically small. ,
As a result, the critical current density (Jc) decreases.

As a material for the coating or the substrate, a silver-based alloy can be used instead of silver. In this case, the main component is silver, and Cd,
A silver-based alloy containing at least one of Hf, Mg, Mn, Ni, Sn, Ti, and Zr in a total amount of 0.01 to 5 atomic% and the remainder being inevitable impurities can be obtained.
The main purpose of containing these elements in a predetermined amount is to improve the strength, for example, 0.2% proof stress and tensile strength of the obtained oxide superconducting composite material. This is because the superconducting characteristics are not degraded due to the reaction with, for example.

[0013]

EXAMPLE 1 A silver substrate having a purity of 99.99%, a width of 5 mm and a thickness of 0.0 was used.
5 mm, 30 mm in length and 0.23 μm and 0.72 μm average surface roughness (Ra) were prepared.
After keeping the silver substrate at 1 atm in the atmosphere at 880 ° C for 10 minutes,
The mixture was gradually cooled to 830 ° C. at a cooling rate of 5 ° C./hour, held for 1 hour, and cooled in a furnace. When the average surface roughness of the obtained silver substrate was measured, the former was 0.28 μm and the latter was 0.88 μm.
μm.

On the other hand, the composition is Bi ₂ Sr ₁ Ca ₂ Cu
₂ O _x is Bi ₂ O ₃ so as to obtain, SrCO _3, Ca
₂ CO ₃ and CuO powders are mixed and mixed in the atmosphere for 8 hours.
After heat treatment at 20 ° C. for 20 hours, it is pulverized into B
A precursor powder of the i-2212 phase was prepared. This powder is suspended in alcohol, and about 50 μm
m on one side. 1atm, 880 ℃ -1 in air
After holding for 0 minutes, the sample was gradually cooled to 830 ° C. at a cooling rate of 5 ° C./hour, further held for 1 hour, and cooled in a furnace to obtain a sample.

The critical current of each sample was measured in liquid helium in an external magnetic field of 10 T under the definition of 1 μV / cm.
As a result, the former was 1500 A / mm ² , and the latter was 700 A / mm ² .
It was Jc of mm ² . Note that these Jc are values obtained by dividing the critical current value Ic by the cross-sectional area of the oxide superconductor layer formed on the silver substrate, and the same applies to the following examples.

After the measurement of Jc, both samples were immersed in an etching solution (a mixed solution of 80 cc of water, 20 cc of 35% hydrogen peroxide solution and 60 cc of ammonia water) to remove silver. The oxide superconductor on the side that was in contact with the silver material was changed to θ by CuKα radiation.
X-ray diffraction at -2θ was performed. The X-ray tube voltage is 35 kV and the tube current is 300 mA. In each case, the results were as shown in FIG. 1. The (00l) main peak (the peak having the highest intensity) was the (00 10 ) plane. Where 2θ =
28. Fix θ and change θ. That is, the method of moving the sample while keeping the optical system as it is (00
1) The rocking curve of the (00 10 ) plane, which is the main peak, was evaluated. The result is shown in FIG. The full width at half maximum was 3.5 degrees for the former and 5.3 degrees for the latter. That is, it was found that the former half width was smaller and the ab planes perpendicular to the c-axis were arranged more parallel to silver.

That is, the oxide superconducting composite using a silver substrate having a small surface roughness had a good degree of orientation at a contact portion with the substrate, and as a result, Jc was high.

Example 2 The same Bi-2212 phase precursor powder as in Example 1 was prepared. On the other hand, as a silver pipe, outer diameter 15mm, inner diameter 11mm,
Two pieces each having a length of 1000 mm were prepared, and the inner surface of each pipe was polished, and the average surface roughness (Ra) was 0.3 each.
μm and 1.2 μm were prepared. Each of the pipes was tap-filled with the powder to form a composite billet. These composite billets were drawn to a diameter of 1.2 mm. The obtained composite wire is cut into a predetermined length, and each is cut into a pipe similar to that described above.
The core was assembled, and further drawn to an outer diameter of 1 mm, and further rolled to a thickness of 0.20 mm. Each of the obtained composite materials was cut into a length of about 30 mm, and was cut at 1 atm and 880 in the atmosphere.
After holding at 10 ° C. for 10 minutes, the mixture was gradually cooled to 830 ° C. at a cooling rate of 5 ° C./hour, further held for 1 hour and cooled in a furnace to obtain a 61-core composite sample.

The critical current of each sample was measured in liquid helium in an external magnetic field of 10 T under the definition of 1 μV / cm.
As a result, the former was 2000 A / mm ² and the latter was 900 A / mm ² .
It was Jc of mm ² .

As in Example 1, after the measurement of Jc, a part of silver was removed from both samples by etching to expose the oxide superconductor. As in Example 1, the rocking curve of the (00 10 ) plane of the oxide superconductor in contact with the silver material was evaluated. As a result, the half width was 3.6 degrees for the former and 5.8 degrees for the latter. That is, it was found that the former half width was smaller, the ab plane perpendicular to the c-axis was more parallel to silver, and Jc was higher.

Example 3 A silver substrate was 99.99% pure, 10 mm wide and 0.1 mm thick.
05mm, 1000mm long sheet with average surface roughness (R
a) of 0.23 μm and 1.35 μm, respectively. On the other hand, Bi-2212 phase main phase Bi _1.84
A precursor powder having a composition of Pb _0.34 Sr _1.9 Ca _2.2 Cu _3.1 O _x was prepared. The powder was sandwiched between the silver sheets and further processed by rolling to a thickness of 0.25 mm. After baking the obtained tape-shaped material in air at 845 ° C. for 50 hours, the width is 4 m.
m, rolled to a thickness of 0.20 mm, and then 845 in air.
The resultant was fired at 50 ° C. for 50 hours to produce a Bi-2223 wire.
The wire was wound around a bobbin having an inner diameter of 30 mm while inserting a mylar tape as an insulating material to obtain a single pancake coil. The critical current Jc of this coil was measured in liquid helium with no external magnetic field and a definition of 1 μV / cm. As a result, the former 570A / mm ^2, the latter of 300A / mm ² J
c.

After the measurement of Jc, silver was removed from both samples in the same manner as in Example 1. The oxide superconductor on the side in contact with the silver material was subjected to X-ray diffraction of θ-2θ by CuKα radiation. The X-ray tube voltage is 35 kV and the tube current is 300 mA. The main phase was Bi-2223, and the (00l) main peak was on the (00 12 ) plane. As a result of evaluating the rocking curve of the (00 12 ) plane, the half width of the former was 3.3.
Degree, and the latter was 6.1 degrees. That is, it was found that the former half width was smaller, the ab plane perpendicular to the c-axis was more parallel to silver, and Jc was higher.

Example 4 A pure silver pipe having an outer diameter of 8 mm, an inner diameter of 6 mm, and a length of 500 mm was used.
This preparation was polished or ground to prepare pipes having an average surface roughness of 0.3 μm and 1.5 μm, respectively.

Also, TlO _1.5 , PbO, SrO, Ba
O, CaO, and CuO are 0.5: 0.5: 1.6: 0.
A powder mixed at a ratio of 4: 2: 3 is heated at 820 ° C. in air.
After repeating the heat treatment for −10 h twice, it was pulverized to prepare a precursor powder. This powder was tap-filled into the above pipe to form a composite billet. This composite billet was drawn until the diameter became 1 mm. Thereafter, the rolling process and the heat treatment at 845 ° C. for 50 hours in the atmosphere at 1 atm were repeated twice to obtain a width of 4 mm and a thickness of 0.12.
mm Tl-1223 wire was produced. Both samples were measured in liquid nitrogen with no external magnetic field and a critical current of 1 μV / cm. As a result, the former was 180 A / mm ² and the latter was 80 A / mm ² Jc. The average surface roughness of the silver portion of the obtained composite wire which was in contact with the oxide superconductor was 0.48 μm and 1.6 μm, respectively.

After the measurement of Jc, silver was removed from both samples in the same manner as in Example 1. The oxide superconductor on the side in contact with the silver material was subjected to X-ray diffraction of θ-2θ by CuKα radiation. The X-ray tube voltage is 35 kV and the tube current is 300 mA. The main phase was Tl-1223, and the (00l) main peak was on the (005) plane. As a result of evaluating the rocking curve of the (005) plane, the half value width of the former was 3.8.
Degree, and the latter was 6.1 degrees. That is, it was found that the former half width was smaller, the ab plane perpendicular to the c-axis was more parallel to silver, and Jc was higher.

The present invention is not limited to the above embodiments, and the method for producing a composite material of a metal material and an oxide superconductor includes a dip coating method, a doctor blade method,
The coating method, organic acid salt method, powder-in-tube method, jelly roll method, thermal spraying method, plasma spraying method, screen printing method, vapor deposition method, CVD method, sputtering method, laser ablation method, etc. Is not limited to a combination of one oxide superconductor and one metal, and may be a combination of a plurality of materials and other materials.

As the type of the oxide superconductor, at least 2212 and 2223 phases containing Bi, at least Tl
2212, 2223, 1201, 1212, 12 including
23, 1234, ReBa ₂ Cu ₃ O _y phase (Re
= Y, La, Nd, Eu, Dy, Gd, Ho, Er, T
m, Yb, Lu) or 221 containing at least Hg
2,2223,1201,1212,1223,123
It may be four-phase or the like. Among these, a material suitable for a manufacturing process in which a part or the whole of the superconductor is in a molten state, particularly during the superconducting heat treatment, is desirable. The reason is that, when the oxide superconductor and its precursor generate a liquid phase, nucleation and growth occur from a contact portion with the silver substrate, and the surface of the oxide superconductor grows from the substrate, and a structure with a high degree of orientation is obtained. .

In the present invention, the composite material is a wire,
Includes conductors or members obtained by assembling or combining them. Examples of its application include magnets, coils, cables, bus bars, current leads, magnetic shields, current limiters, and permanent current switches. When used in these applications, the fabrication method is the React & Wind method or Wind & React method.
Any of the methods may be used.

When used as a wire, the shape thereof may be any of a round wire, a flat wire, a tape wire, a single core wire, a multiple core wire, a straight wire, a spiral wire, a stranded wire, and the like.

As a secondary effect of the present invention, since the surface roughness of the interface between the metal material and the superconductor is small, for example, when applied to a multifilamentary superconducting wire, the relative distance between adjacent oxide superconductors becomes larger. Therefore, there is an advantage that AC loss is reduced. Further, in general, when applied to a metal-coated superconducting wire, there is an advantage that the relative distance between the surface portion and the oxide becomes larger and the surface defects are reduced.

[0031]

As described above, according to the present invention,
An oxide superconducting composite material comprising a metal material and an oxide superconductor, wherein the metal material in contact with the oxide superconductor has an average surface roughness of 0.5 μm or less, and an oxide in contact with the metal material. When the rocking curve of the (00l) main peak at the time of X-ray diffraction of the superconductor was evaluated, the half width of the superconductor was 4 degrees or less. The degree is improved, and as a result, Jc is improved.

[Brief description of the drawings]

FIG. 1 is a grab showing the result of X-ray diffraction of θ-2θ by CuKα ray of the oxide superconductor in the present invention.

FIG. 2 is a graph showing an example of a rocking curve when a (001) main peak is a (00 10 ) plane.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Jin Kitaguchi 1-2-1 Sengen, Tsukuba-city, Ibaraki Pref., National Institute of Metals Science and Technology (72) Inventor Junichi Sato 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Electric Wire Co., Ltd. Advanced Research Center Co., Ltd. (72) Inventor Takemi Muroka 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Co., Ltd. Advanced Research Center Co., Ltd.

Claims (8)

[Claims] An oxide superconducting composite material comprising a metal material and an oxide superconductor, wherein the metal material in contact with the oxide superconductor has an average surface roughness of 0.5 μm or less, and When the rocking curve of the (00l) main peak at the time of X-ray diffraction of the oxide superconductor in contact with the metal material is evaluated, the half value width thereof is 4 degrees or less. 2. The oxide superconducting composite according to claim 1, wherein said metal material is silver or a silver-based alloy. 3. The method according to claim 1, wherein the metal material is mainly composed of silver, and Cd, H
A silver-based alloy containing at least one of f, Mg, Mn, Ni, Sn, Ti, and Zr in a total amount of 0.01 to 5 atomic%, with the balance being inevitable impurities. Item 3. The oxide superconducting composite according to Item 2. 4. The method according to claim 1, wherein the oxide superconductor comprises at least Bi,
The oxide superconducting composite according to claim 2, which is a Bi-2212 phase oxide superconductor or Bi-2223 phase oxide superconductor containing Sr, Ca and Cu. 5. An oxide superconductor comprising at least Bi,
The oxide superconducting composite according to claim 2, which is a Bi-2212 phase oxide superconductor containing Sr, Ca, Cu and Pb. 6. The oxide superconductor according to claim 1, wherein at least a portion of the oxide superconductor precursor has been subjected to a superconducting heat treatment for generating a liquid phase. An oxide superconducting composite according to the above. 7. A method for producing an oxide superconducting composite material comprising a metal material and an oxide superconductor, wherein the average surface roughness is not more than 0.
A step of providing an oxide superconducting precursor in contact with the metal material of 5 μm or less, and a superconducting heat treatment step of generating a liquid phase in at least a part of the oxide superconducting precursor,
(E) When the rocking curve of the (00l) main peak of the oxide superconductor in contact with the metal material after the heat treatment step is evaluated, the half value width thereof is 4 degrees or less. Method. 8. The superconducting heat treatment step is carried out at a temperature of 700-700.
The method for producing an oxide superconducting composite according to claim 7, wherein the method is performed in an atmosphere at 950 ° C and an oxygen partial pressure of 0.01 to 10 atm.