JP2010123433A - Method of manufacturing re123 superconducting thin film wire rod, and re123 superconducting thin film wire rod - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an RE123 superconducting thin film wire rod by which even if the RE123 superconducting thin film wire rod has a large thickness, no cracks are formed on an RE123 superconducting thin film after introduction of oxygen thereto to provide the RE123 superconducting thin film wire rod having a high critical current value. <P>SOLUTION: The manufacturing method includes a precursor forming step of applying a raw material to a substrate to form a precursor wire rod, a thin film forming step of subjecting the precursor wire rod to heat treatment in an oxygen-containing atmosphere to form an RE123 superconducting thin film, a first heat treatment step of subjecting the superconducting thin film to heat treatment, after the thin film forming step in an atmosphere with oxygen concentration lower than oxygen concentration at the thin film forming step, and a second heat treatment step of subjecting the superconducting thin film to heat treatment after the first heat treatment step in an atmosphere with oxygen concentration higher than oxygen concentration at the thin film forming step. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing RE123 superconducting thin film wire and a superconducting thin film wire, and more particularly, a method of manufacturing RE123 superconducting thin film wire having a high critical current value, and a superconducting thin film wire having a high critical current value obtained by the manufacturing method. About.

Currently, there is a RE123 superconducting thin film wire as one of superconducting wires using an oxide superconducting material. The RE123 superconducting thin film wire is a superconducting wire in which a superconducting layer is formed on a metal substrate by a vapor phase method or a liquid phase method. The oxide superconducting material used here is an oxide superconducting material represented by a chemical formula of RE ₁ Ba ₂ Cu ₃ O _x (x is a number close to 7: hereinafter referred to as RE123), and RE (Rare Earth) is a rare earth. ) Is one of rare earth elements such as Y, Ho, Nd, Sm, Dy, Eu, La, Tm, and Gd, or a mixture thereof. In order to further spread the superconducting wire using the RE123 superconducting thin film, research on the RE123 superconducting thin film wire with higher critical current density (Jc) and critical current value (Ic) has been conducted.

  In order to obtain the RE123 superconducting thin film wire having a high critical current value, a process of introducing oxygen into the superconducting layer after forming the RE123 superconducting thin film on the substrate is necessary in the production of the RE123 superconducting thin film wire.

In such an oxygen introduction process, conventionally, oxygen is introduced into the RE123 superconducting layer by performing heat treatment in an atmosphere of 100% oxygen (for example, Patent Document 1).
JP 2001-357730 A

  However, in the conventional method, particularly when the film thickness of the RE123 superconducting thin film is thick, the RE123 superconducting thin film after the introduction of oxygen cracks, resulting in a problem that the critical current value remains low.

  Therefore, the present invention provides a method for producing the RE123 superconducting thin film wire, even if it is a thick RE123 superconducting thin film wire, cracks do not occur in the RE123 superconducting thin film after the introduction of oxygen, and as a result, it has a high critical current value. It is an object of the present invention to provide a method for producing a RE123 superconducting thin film wire and to provide a RE123 superconducting thin film wire having a high critical current value.

  The manufacturing method of the RE123 superconducting thin film wire of the present invention includes a precursor forming step of forming a precursor wire by applying a raw material to a base material, and a heat treatment of the precursor wire in an oxygen-containing atmosphere to form a RE123 superconducting thin film. A first heat treatment step in which heat treatment is performed at a lower oxygen concentration than in the thin film formation step after the thin film formation step; and a first heat treatment step in which heat treatment is performed at a higher oxygen concentration after the first heat treatment step than in the thin film formation step. It includes two heat treatment steps.

In the present invention, a superconducting layer having a thickness of 0.2 μm or more is adopted by applying a coating pyrolysis method (hereinafter also referred to as “MOD method”) in which a raw material is applied to a substrate and heat-treated to form a superconducting layer. To obtain a large critical current value. When a heat treatment for introducing oxygen is performed on a superconducting layer having a thickness of 0.2 μm or more, cracks are likely to occur in the superconducting layer. Therefore, the oxygen introducing heat treatment as described above is performed. The first heat treatment is intended to reduce oxygen contained in the superconducting layer after the thin film formation step. That is, in the chemical formula of RE ₁ Ba ₂ Cu ₃ O _x , if x immediately after the thin film formation step is x0 (about 6.5), it is an operation to make x1 smaller than that. The second heat treatment is intended to increase the oxygen contained in the superconducting layer. That is, this is an operation for making the oxygen content x2 after the second heat treatment larger than x0. RE123 superconducting thin film wire having a high critical current value without cracking in the superconducting layer if oxygen is introduced into the superconducting layer following the oxygen content change path such as x0 → x1 → x2 (x1 <x0 <x2) Is obtained.

  In the present invention, the first heat treatment is preferably performed so that the c-axis length of RE123 superconductivity is longer than that after the thin film formation step. It is effective to reduce the oxygen content to such an extent that the c-axis length can be confirmed to be long in the first heat treatment.

  Furthermore, it is preferable to change the crystal structure of RE123 superconductivity to tetragonal by performing the first heat treatment. It is more effective to further reduce the oxygen content to the extent that it can be confirmed that the crystals are tetragonal. The oxygen content, crystal axis length, crystal structure and crack generation mechanism will be described in detail later.

  In the present invention, it is preferable to make the c-axis length of RE123 superconductivity shorter than after the thin film formation step by performing a second heat treatment. It is effective to increase the oxygen content so that it can be confirmed that the c-axis length is shortened in the second heat treatment.

  In the present invention, the first heat treatment is preferably performed in an atmosphere having an oxygen concentration of 10 ppm or less. If heat treatment is performed at such an oxygen concentration, the amount of oxygen in the superconducting layer can be reliably reduced.

  In the present invention, the second heat treatment is preferably performed in an atmosphere having an oxygen concentration of 1000 ppm or more. If heat treatment is performed at such an oxygen concentration, the amount of oxygen in the superconducting layer can be reliably increased.

  The RE123 superconducting thin film wire of the present invention is manufactured by the above manufacturing method. Thereby, the RE123 superconducting thin film wire having a high critical current value is obtained.

  According to the present invention, even if the RE123 superconducting thin film wire having a thickness of 0.2 μm or more is not cracked during the oxygen introduction process, an RE123 superconducting thin film wire having a high critical current value can be obtained.

  Hereinafter, the present invention will be described based on the best mode. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(Configuration of RE123 superconducting thin film wire)
FIG. 1 is a partial cross-sectional perspective view schematically showing the configuration of the RE123 superconducting thin film wire that is the subject of the present invention. An example of a typical RE123 superconducting thin film wire will be described with reference to FIG. The RE123 superconducting thin film wire 10 protects the oriented metal substrate 11, the intermediate layer 12 formed on the oriented metal substrate 11, the superconducting thin film layer 13 formed on the intermediate layer 12, and the superconducting thin film layer 13. It consists of a stabilizing layer 14 and protective layers 15 and 16 for protecting the whole and enhancing conductivity. As a basic configuration, it consists of an oriented metal substrate 11, an intermediate layer 12, and a superconducting layer 13, and a stabilization layer 14 and protective layers 15 and 16 are optionally provided depending on the application.

As the alignment metal substrate 11, for example, a Ni alignment substrate, a Ni alloy-based alignment substrate, or the like can be adopted. The intermediate layer 12 can employ an oxide such as CeO ₂ or YSZ (yttrium stabilized zirconia). As the superconducting thin film layer 13, a RE123-based superconducting material such as YBa ₂ Cu ₃ O _x (x is a number close to 7) is selected. As the stabilization layer 14 and the protective layers 15 and 16, Ag (silver) or Cu (copper) is used.

(Preparation of RE123 superconducting thin film wire before oxygen introduction treatment)
First, an oriented metal substrate such as a Ni alloy is prepared as a base material. An intermediate layer made of CeO ₂ , YSZ, or the like is laminated on the oriented metal substrate by physical vapor deposition or the like. This laminate is used as a base material. The structure of the substrate, for example, _{CeO 2 / YSZ / CeO 2 /} Ni alloy is preferable. On this substrate, for example, fluorine-free acetylacetonate complex of each element of RE, Ba, and Cu is adjusted so that the molar ratio of RE: Ba: Cu is 1: 2: 3. A dissolved raw material solution is used. This raw material solution is applied so that the thickness when the superconducting layer is formed is 0.2 to 1.0 μm. The solution applied body is calcined to remove the solvent. The calcination is performed in an air atmosphere at 400 to 500 ° C. for about 1-2 hours.

  An intermediate heat treatment may be applied to the calcined solution application body. This is performed in order to decompose and remove the carbonate generated in advance before the subsequent calcination, because the carbonate generated during calcination inhibits the growth of the superconducting layer. This intermediate heat treatment is performed in an atmosphere having an oxygen concentration of about 100 ppm under conditions of a temperature of 600 to 700 ° C. and a time of 1 to 3 hours. The above is the precursor wire forming step.

  Subsequently, the precursor wire obtained above is subjected to heat treatment (main firing) for forming a superconducting thin film. By this firing, the applied raw material is transformed into the intended RE123 superconducting phase. What is obtained after this step is the RE123 superconducting thin film wire. The main firing is performed in an atmosphere having an oxygen concentration of about 100 ppm under conditions of a temperature of 750 to 800 ° C. and a time of 1-2 hours. The RE123 superconducting thin film wire is subjected to the following oxygen introduction treatment.

(Oxygen introduction treatment)
First, the oxygen content, the crystal axis length, the crystal structure, and the mechanism of crack generation will be described with reference to FIG. FIG. 2 is a graph showing the relationship between the oxygen content (x) in the superconducting layer, the crystal structure, the axial length of the crystal, and the superconducting characteristics. In the RE123 superconductor, the superconducting characteristics, the crystal axial length, and the crystal structure change depending on the oxygen content (x). The closer x is to 7, the better the superconducting properties and the shorter the c-axis length. The RE123 superconducting crystal is orthorhombic, and the difference between the a-axis length and the b-axis length increases.

  Since the superconducting layer in the superconducting thin film forming step is heat-treated and formed under the condition of an oxygen concentration of about 100 ppm, x is about 6.5. In FIG. 2, it is in the state of a rectangular area indicated by x0. In other words, the c-axis length is about 11.73 mm, the orthorhombic a-axis length is about 3.83 mm, the b-axis length is about 3.87 mm, and the superconducting characteristics are medium. In the conventional oxygen introduction method, in order to increase the oxygen content from this state, heat treatment is performed immediately after the superconducting thin film formation step in an atmosphere having a high oxygen concentration, for example, 100% oxygen, and oxygen is introduced into the superconducting layer. It was. In FIG. 2, this is a route (x0 → x2) represented by a dashed arrow. In this case, the performance of each superconducting crystal constituting the superconducting layer is improved, but as described above, cracks (the superconducting crystals are separated from each other) are likely to enter the layer. That is, although individual superconducting crystals have high performance, they are not connected, resulting in low performance.

  The mechanism for generating the crack is as follows. In the superconducting layer after the superconducting thin film is formed, a large number of crystals are orthorhombic with a small difference between the a-axis length and the b-axis length, and these crystals are arranged in the best fit (energy stable state). Although there are a few tetragonal crystals in the superconducting layer, a large amount of crystal structure appears as an observation result. When oxygen is introduced into these crystals, the a-axis becomes shorter and the b-axis becomes longer without changing the direction and position of the axis. From the best fit state, it shrinks in a certain part to form a gap, or cracks to prevent the crystals from pressing each other and lengthening the axis. These are cracks. This is a phenomenon that occurs because oxygen is introduced without changing the crystal structure. This phenomenon is likely to appear in a superconducting layer having a thickness of 0.2 μm or more, and becomes prominent when the thickness is 0.5 μm or more.

  On the other hand, when oxygen is introduced into a superconducting layer in which all crystals are tetragonal, the a and b axis directions are not determined before the introduction of oxygen, and are stable in terms of energy during the oxygen introduction process, in other words, the crystals become orthorhombic. The a- and b-axis directions of each crystal are selected in the direction in which the obstacle is small for the transition. In other words, the crystals change so that they fit well. As a result, cracks are unlikely to occur.

  Accordingly, in the present invention, after the superconducting thin film is formed, the oxygen is extracted from the superconducting layer by heat treatment at a lower oxygen concentration (for example, 10 ppm) than in the superconducting thin film forming step (about 100 ppm). Thereby, tetragonal superconducting crystals are increased. After that, heat treatment is performed at a higher oxygen concentration (for example, 1000 ppm) than in the superconducting thin film formation step (for example, 1000 ppm), and when oxygen is introduced, tetragonal crystals increase and cracks are less likely to occur.

  Since the change in oxygen content (x) cannot be measured by nondestructive inspection, the change in oxygen content is determined by looking at the change in c-axis length. If the c-axis length in the first heat treatment is longer than after the formation of the superconducting thin film (initial state), the oxygen content is reduced. If the c-axis length is shorter than the initial state after the second heat treatment, the oxygen content is reduced. Can be confirmed.

  Further, after the first heat treatment, if the crystal structure that can be observed macroscopically is a tetragonal crystal (a state in the vicinity of the rectangular region indicated by x1 in FIG. 2), the tetragonal crystal is mainly used. In addition, the occurrence of cracks can be prevented. In FIG. 2, the route (x0 → x1 → x2) represented by the solid line arrow is the most preferable oxygen introduction route.

  The first heat treatment is performed under the conditions of a temperature of 500 to 600 ° C. and a time of 30 to 120 minutes in an atmosphere having an oxygen concentration lower than that of the superconducting thin film forming step (for example, 50 ppm). The second heat treatment is performed under conditions of a temperature of 500 to 600 ° C. and a time of 30 to 120 minutes in an atmosphere in which the oxygen concentration is higher (for example, 500 ppm) than in the superconducting thin film forming step.

  The present invention will be specifically described below with reference to examples and comparative examples. In the following Examples and Comparative Examples, the fluorine-free MOD method that does not cause harmful HF or the like among the MOD methods was used to form the RE123 superconducting thin film.

A substrate of CeO ₂ / YSZ / CeO ₂ / Ni alloy having a width of 1 cm is used as a base material, and each acetylacetonate complex of Y, Ba, and Cu is formed on this base material with a molar ratio of Y: Ba: Cu. It adjusted so that it might become 1: 2: 3, and it melt | dissolved in the solvent. The solution was applied to the substrate. Two types of coated bodies were prepared so that the thickness after forming the superconducting layer was 0.3 μm and 0.6 μm. These were heated to 500 ° C. at a temperature rising rate of 20 ° C./min in an air atmosphere, held for 2 hours, and then cooled in a furnace and subjected to a calcining heat treatment.

Next, in an argon / oxygen mixed gas atmosphere (oxygen concentration: 100 ppm, CO ₂ concentration: 1 ppm or less), the temperature was increased to 680 ° C. at a temperature increase rate of 20 ° C./min, and maintained for 180 minutes to perform an intermediate heat treatment. This intermediate treatment is performed in order to decompose and remove the carbonate generated in advance before the main heat treatment because the carbonate produced during the calcining heat treatment inhibits the crystal growth of the superconducting layer.

After the intermediate heat treatment, the temperature is increased to 780 ° C. at a temperature increase rate of 20 ° C./min in an argon / oxygen mixed gas (oxygen concentration: 100 ppm, CO ₂ concentration: 1 ppm or less) atmosphere, and maintained for 90 minutes. Heat treatment was performed, and the applied raw material was transformed into a superconductor to obtain a Y123 superconducting thin film wire. There are two types of film thickness of the superconducting layer: 0.3 μm and 0.6 μm.

Thereafter, each Y123 superconducting thin film wire obtained was heat-treated under the following conditions.
Comparative Example 1: Superconducting layer thickness 0.3 μm
No first heat treatment
Second heat treatment None Comparative example 2: Superconducting layer thickness 0.6 μm
No first heat treatment
Second heat treatment None Comparative example 3: Superconducting layer thickness 0.3 μm
First heat treatment in 100% oxygen at 550 ° C. for 60 minutes
No second heat treatment
In FIG. 2, x0 → x2 path Comparative Example 4: Superconducting layer thickness 0.6 μm
First heat treatment in 100% oxygen at 550 ° C. for 60 minutes
No second heat treatment
In FIG. 2, x0 → x2 path Comparative Example 5: Superconducting layer thickness 0.3 μm
First heat treatment 550 ° C., 60 minutes in 10 ppm oxygen
No second heat treatment
In FIG. 2, the path from x0 to x1 Comparative Example 6: Superconducting layer thickness 0.6 μm
First heat treatment 550 ° C., 60 minutes in 10 ppm oxygen
No second heat treatment
In FIG. 2, x0 → x1 path Example 1: Superconducting layer thickness 0.3 μm
First heat treatment 550 ° C., 60 minutes in 10 ppm oxygen
Second heat treatment in 100% oxygen at 550 ° C. for 60 minutes
In FIG. 2, the path of x0 → x1 → x2 Example 2: Superconducting layer thickness 0.6 μm
First heat treatment 550 ° C., 60 minutes in 10 ppm oxygen
Second heat treatment in 100% oxygen at 550 ° C. for 60 minutes
The route x0 → x1 → x2 in FIG.

  The critical current values (Ic) of the above Examples and Comparative Examples were measured at a temperature of 77K and a self magnetic field. Further, the crystal structure of the superconducting layer and the length of the c-axis length were measured by XRD. In addition, the presence or absence of cracks in each wire was visually observed. The measurement results are also shown in Table 1.

  In Comparative Examples 1 and 2 where the first and second heat treatments were not performed, the crystal structure was orthorhombic and the c-axis length was 11.73 mm, which was in the vicinity of x0 in FIG. Although no crack is generated, the superconducting properties are not so good and Ic is zero.

  Comparative examples 3 and 4 in which the first heat treatment was performed at a higher oxygen concentration than the main firing conditions immediately after the main firing were orthorhombic and had a shorter c-axis length than the comparative examples 1 and 2. These have good superconducting properties, but cracks occur and Ic is not so high.

  In Comparative Examples 5 and 6 in which only the first heat treatment was performed at an oxygen concentration lower than that in the main baking conditions immediately after the main baking, the comparative examples 5 and 6 are tetragonal and have a longer c-axis length than the comparative examples 1 and 2. These have poor superconducting properties and Ic is 0. However, no cracks have occurred.

  Examples 1 and 2, which were subjected to the first heat treatment at an oxygen concentration lower than the firing conditions and the second heat treatment at an oxygen concentration higher than the firing conditions, are orthorhombic and have a shorter c-axis length than the comparative examples 1 and 2. It has become. These have good superconducting properties and have high Ic because no cracks are generated.

  Further, the influence of the superconducting layer thickness will be examined in Comparative Examples 3 and 4 and Examples 1 and 2. The ratio of Ic in Comparative Example 3 and Example 1 having a thickness of 0.3 μm is 65A / 40A = 1.63. On the other hand, the ratio of Ic in Comparative Example 4 and Example 2 having a thickness of 0.6 μm is 107A / 55A = 1.95, and the effect of the present invention becomes more remarkable as the thickness of the superconducting layer increases. I understand.

  Next, several test materials were produced using a wire having a superconducting layer thickness of 0.6 μm, heat-treated at a temperature of 550 ° C. in the first and second heat treatments, and changing the oxygen concentration. Table 2 shows the heat treatment conditions and the measurement results of Ic, crystal structure, and c-axis length.

  Comparing Examples 6 and 7, in Example 7 in which the oxygen concentration in the first heat treatment is 20 ppm, the crystal structure is not tetragonal after the first heat treatment, and oxygen is not much from the superconducting layer. It is not missing. Therefore, Ic after the second heat treatment is lower than that in Example 6.

  The influence of the oxygen concentration in the second heat treatment can be seen by comparing Examples 6, 8, and 9. In Examples 6 and 9, in which the oxygen concentration of the second heat treatment is 1000 ppm or more, Ic exceeding 100 A is obtained. From this, it can be said that the oxygen concentration during the second heat treatment is preferably 1000 ppm or more.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a partial section perspective view showing typically composition of RE123 superconducting thin film wire. It is a figure showing the relationship between oxygen content (x) in a superconducting layer, crystal structure, crystal axial length, and superconducting characteristics.

Explanation of symbols

10 RE123 superconducting thin film wire 11 oriented metal substrate 12 intermediate layer 13 superconducting thin film layer 14 stabilization layer 15 16 protective layer

Claims (7)

A manufacturing method of RE123 superconducting thin film wire,
A precursor forming step of forming a precursor wire by applying a raw material to a base material; and a thin film forming step of heat-treating the precursor wire in an oxygen-containing atmosphere to form a RE123 superconducting thin film;
After the thin film formation step, a first heat treatment step for heat treatment at a lower oxygen concentration than during the thin film formation step,
A method for producing a RE123 superconducting thin film wire, comprising a second heat treatment step after the first heat treatment step, wherein the second heat treatment step is performed at a higher oxygen concentration than during the thin film formation step.   2. The method of manufacturing an RE123 superconducting thin film wire according to claim 1, wherein the first heat treatment is performed to make the RE123 superconducting c-axis length longer than after the thin film forming step.   3. The method of manufacturing a RE123 superconducting thin film wire according to claim 1 or 2, wherein the first heat treatment is performed to change the RE123 superconducting crystal structure into a tetragonal crystal.   4. The method of manufacturing a RE123 superconducting thin film wire according to claim 1, wherein the second heat treatment is performed to shorten the c-axis length of RE123 superconductivity after the thin film forming step. 5. .   5. The method of manufacturing a RE123 superconducting thin film wire according to claim 1, wherein the first heat treatment is performed in an atmosphere having an oxygen concentration of 10 ppm or less.   6. The method of manufacturing an RE123 superconducting thin film wire according to claim 1, wherein the second heat treatment is performed in an atmosphere having an oxygen concentration of 1000 ppm or more.   An RE123 superconducting thin film wire produced by the method for producing an RE123 superconducting thin film wire according to any one of claims 1 to 6.

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