JP2003300726A - Tape-like oxide superconductor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a thick tape-like oxide superconductor by a non- vacuum process. <P>SOLUTION: An oxide superconductive film is obtained by applying to a substrate a mixed solution containing metal elements composing an RE-based oxide superconductor at a prescribed molar ratio; heat treating it by calcinations at a heat-up rate of 0.1-0.6°C/min in the range of 200-250°C to form a precursor of the oxide superconductor; and performing crystallization heat treatment to the precursor. The oxide superconductive film has a characteristic of [t]×[Jc]≥0.8, when a thickness of the superconductive film after crystallization is [t] μm, and a critical current density is [Jc]MA/cm<SP>2</SP>at 77K. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tape-shaped oxide superconductor suitable for use in superconducting equipment such as superconducting cables and superconducting magnets, and a method for producing the same, and particularly to a high critical current density (Jc) and a thick film. TECHNICAL FIELD The present invention relates to a tape-shaped oxide superconductor that can be easily formed and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a method of manufacturing a non-vacuum process of an oxide superconducting wire that can be used for superconducting cables and magnets that require high critical current density (Jc),
The MOD method (Metal Organic Deposition Processes) is known.

In this MOD method, a solution of a metal organic acid salt such as trifluoroacetate containing each metal element constituting an oxide superconductor in a predetermined molar ratio is applied onto a substrate, and calcination heat treatment is applied thereto. Is applied to form an amorphous precursor, and then crystallization heat treatment is applied to crystallize the precursor to form an oxide superconductor.

In the calcination heat treatment in the MOD method, for example, the partial pressure of water vapor of the gas introduced in the calcination heat treatment is 4.
Since 2 vol% and an oxygen partial pressure of 95.8 vol% require a heat treatment time of 15 hours or more, productivity is low and there is a practical problem.

In order to solve this problem, the steam partial pressure of the gas introduced in the calcination heat treatment is set to 19.7 vol% and the oxygen partial pressure is set to 2 vol%, so that 190 to 31 during the calcination heat treatment are set.
It has been recently reported that the heating rate during heating to 0 ° C can be increased to 1.0 ° C / min and the heat treatment time can be shortened to about 3 hours. The film thickness of the superconductor at that time is 0.3 μm.
And its Jc value is about 1.1 MA / cm ² (M. Paranthaman
at. el.:Proc. of Applied Superconductivity 2000,
Paper 2MH06).

[0006]

However, when the film thickness is thin, the critical current value (Ic) required for use in a superconducting cable or a superconducting magnet cannot be secured unless the Jc value is increased. , To increase the Ic value, it is necessary to further increase the film thickness.

In the prior art, the TFA is
Decomposition of metal organic acid salts including salts is insufficient and tends to remain in the film. For this reason, the fluorine that remains when the temperature is raised during the crystallization heat treatment is rapidly decomposed, and cracks and pores are generated in the film. This tendency becomes remarkable when the coating and the calcination heat treatment are repeated to form an oxide superconducting precursor film having a multi-layered structure to increase the film thickness. As a result, epitaxial growth during crystallization of the superconductor becomes difficult, the crystal orientation is disturbed, and the critical density characteristics rapidly deteriorate as the film thickness increases, making it difficult to shorten the calcination time for thickening the film. Met.

The present invention has been made in order to solve the above problems, and relates to a tape-shaped oxide superconductor which has a high Jc value and is easy to form a thick film, and a method for producing the same.

The present invention focuses on the rate of temperature increase during the calcination heat treatment that affects the decomposition rate of the oxide superconducting precursor containing a metal organic acid salt, and optimizes the rate of temperature increase and the partial pressure of water vapor. This was done by finding out the conditions for calcination heat treatment to sufficiently decompose the metal organic acid salt.

[0010]

In order to solve the above problems, the invention according to claim 1 of the present invention is a metal-organic compound containing, on a substrate, each metal element forming an oxide superconductor in a predetermined molar ratio. After applying a mixed solution of acid salt, in the oxide superconductor obtained by subjecting the oxide superconducting precursor that has been subjected to the calcination heat treatment to the crystallization heat treatment, the heating rate during the calcination heat treatment is 0.1 to 0.6 ° C / min. It is characterized by including.

Further, the invention according to claim 2 of the present application is that after applying a mixed solution of a metal organic acid salt containing each metal element constituting the oxide superconductor in a predetermined molar ratio on the substrate, calcination heat treatment is performed. In the oxide superconductor obtained by subjecting the oxide superconducting precursor that has been subjected to the crystallization heat treatment, the temperature rising rate during the calcination heat treatment is 0.1
Including the process of ~ 0.6 ℃ / min, the thickness of superconducting film after crystallization is [t] μm and the critical current density at 77K is [Jc] MA / cm ² [t] × [Jc] ≧ It has a characteristic of 0.8.

The above oxide superconductor is an invention according to claim 13 of the present application, that is, a mixed solution of a metal organic acid salt containing each metal element constituting the oxide superconductor in a predetermined molar ratio is coated on a substrate. Then, the temperature range of 200-250 ℃ is 0.1-0.6 ℃ / min.
The oxide superconducting precursor is formed by performing calcination heat treatment at a heating rate of, and then the oxide superconducting precursor is subjected to crystallization heat treatment to reduce the thickness of the superconducting film after crystallization to [t] μ
When the critical current density at m and 77K is [Jc] MA / cm ² , a tape-shaped oxide superconducting film having a characteristic of [t] × [Jc] ≧ 0.8 can be formed on the substrate.

Further, the invention according to claim 14 of the present application, that is, after applying a mixed solution of a metal organic acid salt containing each metal element constituting the oxide superconductor in a predetermined molar ratio on the substrate, water vapor content In a temperature range of 200 to 250 ° C in an atmosphere with a pressure of 4.0 vol%
The oxide superconducting precursor is formed by performing calcination heat treatment at a temperature rising rate of 0.1 to 0.6 ° C / min, and then this oxide superconducting precursor is subjected to crystallization heat treatment in an atmosphere with a water vapor partial pressure of 1.0 to 3.2 vol%. It can also be achieved by applying.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As the substrate used in the present invention, either a single crystal substrate or a polycrystalline substrate can be used.

A LaAlO ₃ (100) single crystal substrate (hereinafter referred to as LAO single crystal substrate) or the like can be used as the single crystal substrate, while an oriented Ni substrate or an IBAD method (IonBeam Assisted Deposition) is used as the polycrystalline substrate. A method of depositing particles generated from a target on a substrate while irradiating the substrate with ions from an oblique direction) and the like can be used. The oriented Ni substrate is a cold-worked Ni substrate that is heat-treated in vacuum to be highly oriented. It was developed at Oak Ridge National Laboratory in the United States and RABiTS (trademark: rol
ling-assisted biaxially textured-substrates). On this oriented Ni substrate, a thin film of a CeO ₂ epitaxial layer was provided by electron beam evaporation in a high-temperature reducing gas atmosphere, and then a YSZ (yttrium-stabilized zirconia) film was formed on it by sputtering at high temperature and reduced pressure. A thick film can be used as the substrate. The CeO ₂ layer and the YSZ layer have a function as a buffer layer, and are arranged to suppress the reaction with the superconducting layer to prevent the deterioration of the superconducting property, and to maintain the consistency with the superconducting layer. In addition, Y Ba ₂ C on top of the YSZ layer above
A substrate provided with a CeO ₂ thin film, which is excellent in crystallographic matching of u ₃ O _Y superconductor (YBCO), can also be used as the substrate.

Further, the composite substrate using the IBAD method is a non-magnetic, high-strength tape-shaped Ni-based substrate (Hastelloy etc.)
An intermediate layer (Ce) that has high orientation and is formed by depositing particles by the IBAD method and that suppresses reaction with the elements that make up the superconductor
O ₂ , Y ₂ O ₃ , YSZ, etc.) (hereinafter referred to as IBAD composite substrate), which has a two-layer structure of the above intermediate layer (YSZ or Zr ₂ Rx ₂ O ₇ / CeO ₂ or Y ₂ O ₃ etc .: Rx is Y, Nd, Sm,
Gd, Ei, Yb, Ho, Tm, Dy, Ce, La or Er is shown. ) Is also suitable (JP-A-4-329867, JP-A-4-29867).
4-331795, Japanese Patent Application No. 2000-333843). The present invention, on the above substrate, after applying a mixed solution of a metal organic acid salt containing each metal element constituting the oxide superconductor in a predetermined molar ratio, to the oxide superconducting precursor subjected to calcination heat treatment In the oxide superconductor that has been subjected to the crystallization heat treatment, the heating rate during the calcination heat treatment,
It is characterized in that the partial pressure of water vapor during calcination heat treatment and / or crystallization heat treatment is regulated.

In the above invention, the calcination heat treatment is 200
The rate of temperature increase in the temperature range of to 250 ° C is preferably 0.1 to 0.6 ° C / min.

The calcination heat treatment and / or the crystallization heat treatment are preferably performed in an atmosphere having a water vapor partial pressure of 4.0 vol% or less. The water vapor partial pressure can be increased under a constant gradient or stepwise if the above conditions are satisfied.

In the above invention, a thick film can be easily achieved by forming a plurality of oxide superconducting precursors.

In this case, the calcination heat treatment of the oxide superconducting precursor excluding the oxide superconducting precursor of the outermost layer is preferably performed at less than 400 ° C., and particularly, the oxide excluding the oxide superconducting precursor of the outermost layer is Calcination heat treatment of superconducting precursor 250 ~ 350 ℃
It is preferable to apply in the temperature range of. Further, it is preferable that the oxide superconducting precursor excluding the oxide superconducting precursor of the outermost layer is subjected to calcination heat treatment in an atmosphere having a water vapor partial pressure of 1.0 to 3.2 vol%.

Further, the crystallization heat treatment is carried out by steam partial pressure of 1.0 to 3.2.
It is preferable that the heat treatment is performed in a vol% atmosphere, and the heat treatment atmosphere of the crystallization heat treatment is preferably constituted by water vapor, a gas that does not react with the oxide superconductor, and oxygen.

In the above invention, any one or more of trifluoroacetate, octylate, naphthenate and acetate is used as the metal organic acid salt, and in particular, the metal organic acid salt is at least trifluoroacetic acid. It is preferable to include a salt (TFA salt), and RE _{1 + x} Ba _{2- x} Cu ₃ O _Y (where RE is Y,
At least one element selected from Nd, Sm, Gd, Eu, Yb, Pr or Ho is shown. Hereinafter the same) is suitable for the oxide superconductor.

The multi-layered tape-shaped oxide superconductor described above has four-fold symmetry obtained by rotating the (103) plane in the in-plane direction from polar figure measurement of X-ray analysis of the crystallized superconducting film. The half-value width of the peak having the average value has an orientation of 12 ° or less.

[0024]

EXAMPLES Example 1 As a substrate, a LAO single crystal substrate having a length of 10 mm, a width of 10 mm and a thickness of 0.5 mm was used.

The raw material solution was prepared by mixing each TFA salt of Y, Ba and Cu in a methanol solution at a metal molar ratio of Y: Ba: Cu = 1: 2: 3, and the solution concentration was 0.25 mol / Y in terms of Y. It was prepared by adjusting to L. This raw material solution was applied onto the LAO single crystal substrate by spin coating, placed in an electric furnace, and a gas adjusted to a water vapor partial pressure of 2.1 vol% and an oxygen partial pressure of 97.9 vol% was charged to the electric furnace for 1 L. It was introduced at a flow rate of / min and was subjected to calcination heat treatment according to the heat treatment pattern of FIG. 1 (single application). Then, coating and calcination heat treatment are repeated (3
Multiple coatings) to obtain a Y-Ba-Cu precursor thick film. At this time, for the final calcination heat treatment, the heat treatment pattern shown in FIG. 2 was adopted.
Then, steam partial pressure 2.1vol%, oxygen partial pressure 0.1vo in the electric furnace.
In an atmosphere in which a gas adjusted to l% is introduced at a flow rate of 1 L / min
The crystallization heat treatment was performed at a substrate temperature of 775 ° C for 1 to 3 hours by heating at a heating rate of 25 ° C / min. After that, the atmosphere in the furnace was switched to a dry gas, and the atmosphere was maintained for 10 minutes, and then the furnace was cooled.

The film thickness of the superconductor obtained by one coating is 0.3
was μm.

The superconducting film (YBCO
On the film, silver was vapor-deposited to form an electrode, and heat treatment was performed at 450 ° C. for 1 hour in an oxygen atmosphere to prepare a superconductor.

A width of about 100 μm and a length of 500 are applied to these superconducting films.
After performing a patterning process of μm, the Jc value (voltage reference: 1 μV / cm) was measured by a DC four-terminal method in liquid nitrogen. In addition, the crystal phase was identified by X-ray diffraction and the orientation of the superconducting film was evaluated. The results are shown in Table 1.

[0029]

[Table 1]

Comparative Example 1 A raw material solution was applied, calcining heat treatment and crystallization heat treatment were performed under the same conditions as in Example 1 except that the heat treatment pattern shown in FIG. It was made.

Further, in the same manner as in Example 1, the Jc value was measured, the crystal phase was identified by X-ray diffraction, and the orientation of the superconducting film was evaluated. The results are shown in Table 1.

In Example 1 of the present invention, θ-2 by X-ray diffraction was used.
As a result of θ measurement, no impurity phase other than YBCO was observed. In addition, the YBCO film obtained by polarographic measurement on the (102) plane of YBCO exhibited 4-fold symmetry, and the half-width (Δφ) of the peak was 1.5 ° on average. In addition, the ratio of the crystal c-axis oriented in the direction perpendicular to the substrate is 95%, which indicates that uniform epitaxial growth is performed from the substrate to the film surface.

Therefore, in the examples of the present invention, the decrease of Jc with the increase of the film thickness was hardly recognized, and the YBCO film coated three times had a high characteristic of 3.5 MA / cm ² .

On the other hand, the coating according to Comparative Example 1 was performed three times.
The YBCO film showed 8-fold symmetry, and the full width at half maximum of its peak was 13 ° on average. It was also found that the ratio of the c-axis oriented in the direction perpendicular to the substrate was 85%.

As a result, the Jc value sharply decreased with an increase in film thickness, and was 0.5 MA in the YBCO film coated three times.
It was / cm ² .

Example 2 By the same method as in Example 1 except that an IBAD composite substrate was used as a substrate, coating of a raw material solution, calcination heat treatment and crystallization heat treatment were performed to form a superconductor.

This IBAD composite substrate was obtained by forming a YSZ film on a Hastelloy tape by the IBAD method, cutting it into a length of 10 mm and a width of 10 mm, and forming a CeO ₂ intermediate layer having a thickness of 0.5 μm thereon by the sputtering method. It is a thing.

Further, in the same manner as in Example 1, the Jc value was measured, the crystal phase was identified by X-ray diffraction, and the orientation of the superconducting film was evaluated. The results are shown in Table 2.

[0039]

[Table 2]

Comparative Example 2 By the same method as in Comparative Example 1 except that the same IBAD composite substrate as in Example 2 was used as the substrate, coating of the raw material solution, calcination heat treatment and crystallization heat treatment were performed to obtain a superconductor. Created.

Further, in the same manner as in Example 1, the Jc value was measured, the crystal phase was identified by X-ray diffraction, and the orientation of the superconducting film was evaluated. The results are shown in Table 2.

In Example 2 of the present invention, θ-2 by X-ray diffraction was used.
As a result of θ measurement, no impurity phase other than YBCO was observed. The YBCO film obtained by polarographic measurement on the (102) plane of YBCO exhibited 4-fold symmetry, and the half-value width (Δφ) of its peak was 5 ° on average. The ratio of the crystal c-axis oriented in the direction perpendicular to the substrate is 95 to 98%, which indicates that uniform epitaxial growth is performed from the substrate to the film surface.

Therefore, in Example 2 of the present invention, almost no decrease in Jc with the increase in film thickness was observed, and a high characteristic of ² MA / cm ² was obtained in the YBCO film coated three times.

On the other hand, the coating of Comparative Example 2 was performed three times.
The YBCO film showed 8-fold symmetry, and the full width at half maximum of its peak was 13 ° on average. It was also found that the ratio of the c-axis oriented in the direction perpendicular to the substrate was 80%.

As a result, the Jc value sharply decreased with the increase of the film thickness, and was 0.3 MA / c in the YBCO film coated three times.
It was m ² .

As a result, even when the IBAD substrate is used,
According to the present invention, it was found that the thick film tape-shaped oxide superconductor exhibits remarkably high characteristics.

[0047]

According to the present invention, by using the MOD method which is a non-vacuum film forming process, a long oxide superconducting thick film having a significantly higher critical current characteristic than that of the prior art can be continuously and rapidly formed on a metal substrate. It becomes possible to form a film, and it is possible to significantly reduce the cost of manufacturing a tape-shaped oxide superconducting wire suitable for application to a superconducting macnet or a superconducting cable.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a calcination heat treatment pattern of layers excluding the outermost layer of the tape-shaped oxide superconductor in the present invention.

FIG. 2 is a diagram showing an example of a pattern of calcination heat treatment of the outermost layer in the present invention.

FIG. 3 is a diagram showing a pattern of calcination heat treatment of a comparative example.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 39/24 H01L 39/24 B (71) Applicant 000173784 Ichimitsu, Kokubunji, Tokyo Metropolitan Railway Research Institute 2-chome, 38 38 (72) Inventor Tetsuro Honjo 1-10-13 Shinonome, Koto-ku, Tokyo International Superconductivity Technology Center, Superconductivity Research Institute (72) Inventor Fuji Hiro Shinonome, Koto-ku, Tokyo 1-10-13 International Superconductivity Industrial Technology Research Center Superconductivity Research Institute (72) Inventor Yuichi Nakamura 1-10-13 Shinonome, Koto-ku, Tokyo International Superconductivity Industrial Research Center Superconductivity Research Institute (72) Inventor Teruo Izumi 1-10-13 Shinonome, Koto-ku, Tokyo International Superconductivity Technology Center, Superconductivity Foundation Within the Institute of Engineering (72) Inventor Yuru Shiobara 1-10-13 Shinonome, Koto-ku, Tokyo International Superconducting Industrial Technology Research Center Superconducting Research Institute F-term (reference) 4G047 JA03 JA04 JA05 JC02 KA04 KC01 KD02 KD04 LA01 LA06 LB01 4M113 AD35 AD36 AD68 BA04 BA23 BA29 CA34 4M114 AA10 AA29 DB62 5G321 AA01 AA04 BA01 BA03 CA18 CA22 CA24 CA27 DB25 DB46 DB47

Claims (14)

[Claims] 1. An oxide superconducting precursor obtained by applying a mixed solution of a metal organic acid salt containing a metal element constituting an oxide superconductor in a predetermined molar ratio onto a substrate and then subjecting it to a calcination heat treatment. A tape-shaped oxide superconductor characterized by comprising a step of increasing the heating rate during the calcining heat treatment in the range of 0.1 to 0.6 ° C./min in the oxide superconductor subjected to the chemical heat treatment. 2. An oxide superconducting precursor obtained by applying a mixed solution of a metal organic acid salt containing each metal element constituting an oxide superconductor in a predetermined molar ratio onto a substrate and then subjecting it to calcination heat treatment to crystallize. In the oxide superconductor which has been subjected to the heat treatment for crystallization, including the step of the temperature rising rate during the calcination heat treatment of 0.1 to 0.6 ° C / min, the thickness of the superconducting film after crystallization is [t] μm, the critical value at 77K. A tape-shaped oxide superconductor having a characteristic of [t] × [Jc] ≧ 0.8 when the current density is [Jc] MA / cm ² . 3. The rate of temperature rise during calcination heat treatment at 200 to 250 ° C. is 0.
The tape-shaped oxide superconductor according to claim 1 or 2, which has a temperature of 1 to 0.6 ° C / min. 4. The tape-shaped oxidation according to any one of claims 1 to 3, wherein the calcination heat treatment and / or the crystallization heat treatment are performed in an atmosphere having a water vapor partial pressure of 4.0 vol% or less. Thing superconductor. 5. The tape-shaped oxide superconductor according to claim 1, wherein a plurality of oxide superconducting precursors are formed. 6. The tape-shaped oxide superconductor according to claim 5, wherein the calcination heat treatment of the oxide superconducting precursor excluding the oxide superconducting precursor of the outermost layer is less than 400 ° C. 7. The tape-shaped oxide superconductor according to claim 6, wherein the calcination heat treatment of the oxide superconducting precursor excluding the oxide superconducting precursor of the outermost layer is in the temperature range of 250 to 350 ° C. body. 8. The calcination heat treatment of the oxide superconducting precursor excluding the oxide superconducting precursor of the outermost layer has a water vapor partial pressure of 1.0 to 3.2 vo.
The tape-shaped oxide superconductor according to any one of claims 5 to 7, which is applied in an atmosphere of 1%. 9. The crystallization heat treatment is carried out at a steam partial pressure of 1.0 to 3.2 vol%.
9. The method according to claim 1, wherein the treatment is performed in an atmosphere of
The tape-shaped oxide superconductor according to any one of claims 1. 10. The metal organic acid salt is trifluoroacetate,
3. The tape-shaped oxide superconductor according to claim 1, comprising at least one kind of octylate, naphthenate and acetate. 11. The tape-shaped oxide superconductor according to claim 10, wherein the metal organic acid salt contains at least trifluoroacetic acid salt (TFA salt). 12. The oxide superconductor is RE _{1 + x} Ba _2-x Cu ₃ O.
_{12. Y} (wherein RE represents at least one or more elements selected from Y, Nd, Sm, Gd, Eu, Yb, Pr or Ho. The same applies hereinafter) 1 to 11. Either 1
The tape-shaped oxide superconductor according to the item. 13. A mixed solution of a metal organic acid salt containing each metal element constituting an oxide superconductor in a predetermined molar ratio is coated on a substrate, and then a temperature range of 200 to 250 ° C. is set to 0.1 to 0.6 ° C. / The oxide superconducting precursor is formed by performing calcination heat treatment at a temperature rising rate of min, and then the oxide superconducting precursor is subjected to crystallization heat treatment to reduce the thickness of the superconducting film after crystallization to [t]. μ
A tape-shaped oxide superconducting film having a characteristic of [t] × [Jc] ≧ 0.8 when the critical current density at m and 77K is [Jc] MA / cm ² Manufacturing method of oxide superconductor. 14. A substrate is coated with a mixed solution of a metal organic acid salt containing each metal element constituting an oxide superconductor in a predetermined molar ratio, and then 200 to 200% in an atmosphere having a water vapor partial pressure of 4.0 vol%. twenty five
A calcination heat treatment is performed in a temperature range of 0 ° C. at a temperature rising rate of 0.1 to 0.6 ° C./min to form an oxide superconducting precursor, and then the oxide superconducting precursor is provided with an atmosphere of water vapor partial pressure of 1.0 to 3.2 vol%. A method for producing a tape-shaped oxide superconductor, characterized in that crystallization heat treatment is performed in the film.