JP3851948B2 - Superconductor manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a YbBa on a substrate.₂Cu_ThreeO_{7- y}The present invention relates to a method of manufacturing a superconductor provided with a rare earth 123 structure type oxide superconductor film made of barium (Ba), ytterbium (Yb) and copper (Cu), which is represented by (hereinafter referred to as Yb123).
[0002]
[Prior art]
Various methods have been developed for forming superconducting films. One of these methods is a coating pyrolysis in which a superconducting film is formed by applying a solution containing an organic compound containing an atomic species that forms a superconducting film on a substrate and then thermally treating the film to thermally decompose. There is a law. In this method, an organic compound containing an atomic species is dissolved in a solvent solution to prepare a uniform mixed solution, the solution is uniformly coated on a support, and a high-temperature heat treatment is performed to form an organic substance material. It is required to form a superconducting film uniformly through a solid-phase reaction or a liquid-phase reaction by removing only organic components by thermally decomposing these components.
[0003]
The inventors of the present invention perform a process of generating a rare earth 123 structure type oxide superconducting phase in air or oxygen at a temperature of 800 to 970 ° C. (hereinafter referred to as a one-step heat treatment method). (Patent No. 1778693. Patent No. 1778694). According to this method, a rare earth 123 structure type oxide superconducting film having a zero resistance of about 90K can be obtained. This coating pyrolysis method is characterized in that it is a low-cost film-forming method because it does not require a vacuum device that is required for other methods, for example, vacuum deposition, etc. It has the characteristic that film formation is easy also to the base material of this. Moreover, the characteristics of the superconducting film produced by the coating pyrolysis method are highly evaluated as being favorable compared to other production methods.
[0004]
Subsequently, a two-stage heat treatment method was developed in which the oxygen partial pressure was controlled in two stages (Japanese Patent No. 1991979, Japanese Patent No. 2091583). In this method, in the final heat treatment step of crystallizing the rare earth 123 structure type superconducting phase from the precursor film formed by the coating pyrolysis method, the oxygen partial pressure at the initial stage of heat treatment is set low (oxygen partial pressure: 1 × 10^-Four~ 1x10^-3atm), and performing the heat treatment in two stages in which the atmosphere is switched to a high oxygen partial pressure (for example, pure oxygen) during the heat treatment, the heat treatment temperature can be lowered to 750 to 800 ° C. This makes it possible to form in-plane oriented (epitaxially oriented) films on various single crystal substrates such as strontium titanate, lanthanum aluminate, and sapphire substrates via a ceria intermediate layer. A / cm²High critical current density exceeding can be achieved.
[0005]
Among various substrate materials, a sapphire substrate through a ceria intermediate layer is extremely important in application from the viewpoint of price and dielectric properties. An epitaxial rare earth 123 structure type oxide superconductor (referred to as Y123) film made of barium (Ba), yttrium (Y) and copper (Cu) is also formed on the sapphire substrate by using the above two-step heat treatment method. Is possible (2001 Spring Applied Physics-related Joint Lecture 30p-ZK9), but Y123 and CeO₂Is a reaction product BaCeO by heat treatment at 750 ° C. or higher._ThreeTherefore, in order to produce the epitaxial Y123 film while preventing this production reaction, it was necessary to execute the heat treatment temperature while precisely controlling the temperature within a very narrow temperature range (740 to 750 ° C.). Therefore, further lowering the temperature for forming the superconducting film has been an important issue in improving yield and mass production.
[0006]
Further, since the difference in coefficient of thermal expansion between Y123 and sapphire is large, there is a problem in that if Y123 having a film thickness of a certain thickness or more is formed on sapphire, cracks occur during cooling from the heat treatment temperature to room temperature. The maximum film thickness without cracks is called the critical film thickness, and it is known that the critical film thickness depends on the heat treatment temperature (Appl. Phys. Lett. 58, (1991) 1682). For example, if the heat treatment temperature can be lowered by 50 ° C. from 750 ° C. to 700 ° C., the critical film thickness is predicted to increase from 350 nm to 500 nm. Therefore, in the formation of a superconducting film on a sapphire substrate, heat treatment is performed. There has been a strong demand to lower the temperature from the conventional temperature.
[0007]
Further, among various base materials, a metal tape base material coated with a ceria intermediate layer or a YSZ intermediate layer is extremely important for aiming at superconductor power cable and wire application. Again, CeO₂Product BaCeO with Y123_ThreeOr the reaction product BaZrO of YSZ and Y123_ThreeIn order to produce the epitaxial Y123 film while preventing the production reaction, lowering the heat treatment temperature has been an important issue in improving yield and mass production. Further, since the metal tape base material is easily oxidized and deteriorated by high-temperature heat treatment, it has been an important issue to reduce the heat treatment temperature from this aspect.
[0008]
[Problems to be solved by the invention]
It is an object of the present invention to provide a method of manufacturing a superconductor capable of overcoming the problems in the conventional coating pyrolysis method and heat-treating an epitaxially oriented rare earth 123 type superconductor film at a reduced temperature. To do.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the following problems can be solved by adopting the following requirements.
All or part of the rare earth element of the rare earth 123 type superconductor film is Yb.
In the final heat treatment step, heat treatment is performed in a temperature range of 675 to 800 ° C. and a high oxygen partial pressure atmosphere (oxygen partial pressure of 0.25 atm to 1 atm) as a first step, and 675 to 850 ° C. and a low oxygen content as a second step. Pressure (1 × 10 as oxygen partial pressure)^-Five~ 1x10^-3atm) at the initial stage as a third stage, using an oxygen or high oxygen pressure atmosphere, and then switching the atmosphere to a low oxygen pressure, with a temperature range of 200-500 ° C. and a high oxygen partial pressure (oxygen content). Use a three-stage heat treatment in which heat treatment is performed at a pressure of 0.2 atm to 1 atm).
[0010]
By satisfying the above two requirements, YbBa₂Cu_FourO₈Through a chemical reaction path using an oxide mixture containing (hereinafter referred to as Yb124) as a reaction intermediate, the temperature is lower than that of the conventional one-step coating pyrolysis method or two-step coating pyrolysis method, for example, around 700 ° C. A Yb123 superconductor film epitaxially oriented at the heat treatment temperature can be formed.
[0011]
That is, according to the present invention, the following method is provided.
1st invention is YbBa on a base material.₂Cu_ThreeO_{7- y}A precursor film made of barium carbonate or a mixture of barium fluoride, ytterbium oxide, and copper oxide is formed on a base material in a method of manufacturing a superconductor provided with a rare earth 123 structure type oxide superconductor film represented by Then, the precursor film is heat-treated in a high oxygen partial pressure atmosphere with an oxygen partial pressure of 0.25 atm to 1 atm in a temperature range of 675 to 800 ° C., and YbBa₂Cu_FourO₈One stage to form oxygen, oxygen partial pressure 1 × 10^-Five~ 1x10^-3Heat treatment is performed at a temperature range of 675 to 850 ° C. under a low oxygen partial pressure of atm, and tetragonal YbBa₂Cu_ThreeO₆The orthorhombic YbBa is heat-treated at a temperature in the range of 200 to 500 ° C. under the second stage of forming the oxygen and a high oxygen partial pressure of oxygen partial pressure of 0.2 atm to 1 atm.₂Cu_ThreeO_{7- y}By sequentially performing the third stage heat treatment to form YbBa epitaxially oriented₂Cu_ThreeO_{7- y}A method of manufacturing a superconductor characterized by forming a film.
[0012]
A second invention is a method of manufacturing a superconductor according to the first invention, wherein the precursor film is formed by a solution coating pyrolysis method.
[0013]
A third invention is a method of manufacturing a superconductor according to the first invention, wherein the precursor film is formed by a vacuum deposition method.
[0014]
According to a fourth aspect of the present invention, a part of Yb of the precursor film is at least one other rare earth element selected from Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, and Er. Substituted and epitaxially oriented YbBa₂Cu_ThreeO_{7- y}The method for producing a superconductor according to any one of the first to third inventions, wherein a part of Yb of the film is substituted with the other rare earth element.
[0015]
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[0016]
DETAILED DESCRIPTION OF THE INVENTION
The superconductor produced by the method of the present invention has a structure in which an oxide superconductor film having the following composition is provided on a substrate:
YbBa₂Cu_ThreeO_{7- y}
Or (RE_{1- x}Yb_x) Ba₂Cu_ThreeO_{7- y}
(Wherein, RE represents a rare earth atom selected from Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, x is a number of 1> x> 0, and y is 0. 5> y> 0). The production method of the present invention will be described below in the case where the rare earth element is Yb alone, but the following description is similarly applied to the case where a combination of Yb and RE is used.
[0017]
In the method of the present invention, first, a precursor film made of a mixture of barium carbonate or barium fluoride, ytterbium oxide and copper oxide is formed on a substrate.
As the base material, single crystals of various ceramics capable of epitaxial growth of Yb123 can be used. Specific examples of the substrate include strontium titanate, lanthanum aluminate, LSAT (LaAlO_Three-SrTaO_ThreeSolid solution), NdGaO_ThreePerovskite related compounds such as MgO, MgAl₂O_FourRock salt related compounds such as Al₂O_ThreeCorundum type compounds such as YSZ (yttria stabilized zirconia), CeO₂And fluorite-type compounds. Also, ceramic substrates coated with these various ceramic alignment films, such as CeO₂Coat Al₂O_ThreeOr a metal coated with an orientation film of these various ceramics, such as YSZ-coated silver, YSZ-coated nickel, YSZ-coated Hastelloy, and the like.
[0018]
In one embodiment of the present invention, the precursor film is formed on the substrate by a solution coating pyrolysis method. In the solution coating pyrolysis method, a metal-containing compound mixed solution having a metal element composition almost stoichiometrically corresponding to the composition of the metal element constituting the oxide superconductor film, which is the final product, is prepared. Is coated on a substrate, dried, and thermally decomposed to form a precursor thin film. Specifically, a coating solution is prepared by dissolving a metal-containing compound of barium, ytterbium (or a combination of ytterbium and another rare earth element), which is a metal serving as a component of a superconductor, and a copper metal-containing compound.
[0019]
Examples of the metal-containing compound dissolved in the solvent include metal alkoxides, organic acid salts, inorganic acid salts, chelate compounds, and various compounds such as halides, hydroxides and oxides.
[0020]
Preferred examples of the metal-containing compound include naphthenic acid, 2-ethylhexanoic acid, caprylic acid, stearic acid, lauric acid, butyric acid, propionic acid, succinic acid, citric acid, lactic acid, phenol, catechol, benzoic acid, salicylic acid, EDTA. , Metal salts of organic or inorganic acids such as trifluoroacetic acid, nitric acid, carbonic acid and hydrochloric acid, alcohol metal alkoxides such as ethanol, propanol, butanol, ethylene glycol, glycerin and 2-penten-4-one-2-ol, metals Examples include chelate compounds such as acetylacetonate.
[0021]
The metal-containing compound solution can be prepared by dissolving a mixture of metal-containing compounds previously formulated in a predetermined component composition in a solvent, and preparing each metal compound solution in advance, and then mixing these solutions. Can also be done. The metal concentration in the solution is not particularly limited, and the upper limit is usually 3 to 40% by weight, preferably 5 to 30% by weight, in terms of a metal-containing compound. Furthermore, an appropriate amount of a polymer substance can be added to this solution as a viscosity modifier, if necessary.
[0022]
Solvents used for preparing the coating solution in the present invention include, for example, formic acid, acetic acid, trifluoroacetic acid, propionic acid, butyric acid, caprylic acid, lauric acid, stearic acid, naphthenic acid, linoleic acid, oleic acid, succinic acid, citric acid, Organic acids such as lactic acid, phenol and p-toluic acid, halogenated organic acids, ketones such as acetylacetone, amides such as N-methylacetamide, formamideform, dimethylformamide, sulfur-containing solvents such as dimethylsulfoxide, Examples thereof include pyridine derivatives such as pyridine, methylpyridine, and vinylpyridine. These solvents can be used alone or in combination of two or more as required.
[0023]
Examples of preferred coating solutions used in the present invention are as follows in relation to metal-containing compounds.
(1) Metal acetylacetonate or its derivative-containing solution
In the case of this solution, an organic acid, pyridine, a pyridine derivative, or a mixture thereof is used so that metal acetylacetonate or a metal salt of an acetylacetone derivative is stably dissolved. Examples of the organic acid include formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, lauric acid, stearic acid, naphthenic acid, linoleic acid, oleic acid, succinic acid, citric acid, lactic acid, phenol, and p-toluic acid. Examples of pyridine derivatives include methyl pyridine and vinyl pyridine. These solvents can be used in combination with other solvents, for example, alcohols and ketones such as methanol, ethanol, propanol, butanol, and acetone as necessary.
[0024]
(2) Metal alkoxide-containing solution
In the case of this solution, it is preferable to use an organic acid, pyridine, a pyridine derivative, or a mixture thereof so that each metal alkoxide can be stably dissolved. The above solvent can be used as a mixed solvent with other solvents, for example, alcohols such as methanol, ethanol, propanol, butanol, and acetone, and ketones as necessary. The metal alkoxide can also be a solution of aliphatic and aromatic hydrocarbons or alcohols.
[0025]
(3) Metal nitrate containing solution
In the case of this solution, depending on the metal species, it can be used as an aqueous solution. In view of the ability to stably dissolve a material such as Ba nitrate that is difficult to dissolve in water, it is preferable to use acetylacetone, dimethylsulfoxide, formamide, methylacetamide, propionic acid, pyridine or a derivative thereof. Said solvent can be made into a mixed solvent with methanol, ethanol, acetone, etc. as needed.
[0026]
(4) Metal organic acid salt
In the case of this solution, as a solvent, an organic acid, pyridine, a pyridine derivative, or a mixture of these solvents with alcohols, ketones, and hydrocarbons is used. The metal organic acid salt can also be a solution of aliphatic or aromatic hydrocarbon or alcohol.
[0027]
A coating solution in which the metal-containing compound is dissolved is applied onto a substrate to form a solution thin film of the metal-containing compound. For the application, various known methods such as a dipping method, a spray method, a brush coating method, and a spin coating method are employed.
[0028]
The thin film formed as described above is dried. Drying can be performed at normal temperature, reduced pressure, or vacuum conditions at room temperature or in a heated state. By repeatedly applying and drying, the film thickness can be increased. The repeated operation is performed several times as appropriate, but is usually performed 2 to 10 times. This drying step can be performed by performing drying at an initial stage in the next baking treatment after the drying, so that the drying step is not performed, and as a result, included in the baking step.
The obtained dried coating film is then thermally decomposed to form a precursor film. Pyrolysis is usually performed under conditions of a maximum temperature of 450 ° C. and an atmosphere containing air or oxygen. When the starting metal-containing compound is trifluoroacetate, a precursor containing barium fluoride is generated by thermal decomposition. In the case of other metal-containing compounds (compounds not containing fluorine), a precursor containing barium carbonate is generated by thermal decomposition.
[0029]
The precursor film can be formed by a known method other than the solution coating pyrolysis method as described above. Examples of such a method include a vacuum vapor deposition method and a chemical vapor deposition method (CVD method). Practically, chemical vapor deposition is not an advantageous method in terms of cost.
[0030]
In order to make the precursor film made of barium carbonate or a mixture of barium fluoride, ytterbium oxide and copper oxide obtained as described above as a metal oxide superconducting film, in the method of the present invention, A three-stage heat treatment is performed: a first heat treatment stage under a high oxygen partial pressure, a second heat treatment stage under a low oxygen partial pressure, and a third heat treatment stage under a high oxygen partial pressure. All of these three stages can be performed by changing the partial pressure of oxygen present in the base gas. As the base gas, an inert gas such as nitrogen, argon, or helium is used. The three-stage heat treatment can be performed as follows.
[0031]
(1) First heat treatment stage
First, the temperature of the precursor film is raised to a predetermined temperature within a temperature range of 700 to 800 ° C., preferably 700 to 750 ° C. in a high oxygen partial pressure atmosphere (oxygen partial pressure of 0.5 atm to 1 atm). Under these conditions, barium carbonate or barium fluoride is decomposed by holding for a certain period of time (about 2 minutes to 1 hour). At this stage, an oxide mixed phase containing oriented Yb 124 is formed in the film as a reaction intermediate. Water vapor may be present in the atmosphere of the first heat treatment stage.
[0032]
(2) Second heat treatment stage
The film obtained in the first heat treatment stage is then treated with a low oxygen pressure atmosphere (oxygen partial pressure of 1 × 10 10^-Four~ 1x10^-3atm) at a predetermined temperature within a temperature range of 700 to 850 ° C., preferably 700 to 750 ° C., for a predetermined time (usually about 30 minutes to 2 hours). At this stage, the oriented reaction intermediate Yb 124 is decomposed, and epitaxially oriented tetragonal Yb 123 is formed in the film.
[0033]
(3) Third heat treatment stage
Subsequently, the film obtained in the second heat treatment stage is subjected to a heat treatment at a predetermined temperature of 200 to 500 ° C. by switching the atmosphere to a high oxygen pressure atmosphere (0.2 atm to 1 atm as an oxygen partial pressure). The third heat treatment step can be usually performed by slowly cooling from 500 ° C. to room temperature over 30 minutes in the high oxygen pressure atmosphere. It is also possible to hold at the predetermined temperature (between 200 and 500 ° C.) for a certain time (usually about 30 minutes to several hours) and then rapidly cool to room temperature. In this third heat treatment stage, tetragonal Yb123 absorbs oxygen and converts to orthorhombic Yb123, and finally a superconducting Yb123 film epitaxially oriented is formed. Note that air can be used as it is as the gas having an oxygen partial pressure of 0.21 atm.
[0034]
The above three-stage heat treatment can be performed continuously in the same heating furnace, or after each step, once cooled to near room temperature and moved to another heating furnace, the next step can be performed. is there. By performing the above-described three-step heat treatment of (1) to (3), a superconducting film having a film thickness of 100 to 20 μm made of the target epitaxially oriented Yb123 phase (or (Yb, RE) 123 phase) is obtained. be able to.
[0035]
【Example】
Next, the present invention will be described in more detail with reference to examples. The present invention is not limited to this.
[0036]
Example 1
A coating solution in which Ba-acetylacetonate, Yb-acetylacetonate and Cu-acetylacetonate were dissolved was applied on a lanthanum aluminate substrate by a spin coating method to form a coating film. Next, the coating film was heated from room temperature to 500 ° C. in air at a temperature rising rate of 2 ° C./min, kept at this temperature for 30 minutes, and then cooled. Application of this solution and heating and heating were repeated three times to form a precursor film (thickness: 300 nm) made of barium carbonate, ytterbium oxide and copper oxide on the substrate.
Next, the precursor film thus obtained was heated to 720 ° C. in a pure oxygen stream and held for 3 minutes after reaching 720 ° C. (first heat treatment stage). After that, the oxygen concentration of the gas is 1 × 10^-FourIt switched to the argon gas flow adjusted to atm, and hold | maintained at this temperature for 1 hour (2nd heat treatment stage). Further, after being cooled to room temperature in that atmosphere, an oxygen treatment (third heat treatment stage) was performed in which it was kept in a pure oxygen stream at 300 ° C. for 2 hours and then gradually cooled to room temperature to produce a Yb123 film.
As a result of X-ray diffraction of the film formed on the substrate in this manner, it was confirmed that Yb123 was epitaxially grown. Next, when the superconducting critical temperature of the film was measured by an induction method, Tc = 87K was obtained. Further, when the critical current density of the film was measured by an induction method in liquid nitrogen, 3 × 10^FiveA / cm²was gotten. Furthermore, when the microwave surface resistance of the film was measured by the dielectric resonator method, 3.5 mΩ was obtained at 12 GHz and 70K.
[0037]
Example 2
In Example 1, a film sample in which the film was rapidly cooled to room temperature when the first heat treatment stage was completed, and a film sample in which the film was rapidly cooled to room temperature when the second heat treatment stage was completed were prepared. As a result of analyzing these produced phases by X-ray diffraction, oriented Yb124 and tetragonal Yb123 are observed, respectively. In the production process of Example 1, a Yb123 superconducting film is produced via Yb124 as a reaction intermediate. It could be confirmed.
[0038]
Example 3
CeO₂A coating solution in which Ba-acetylacetonate, Yb-acetylacetonate and Cu-acetylacetonate were dissolved was applied on a sapphire R-plane base material using a spin coat method to form a coating film. . In the air, this was heated from room temperature to 500 ° C. at a temperature rising rate of 2 ° C./min, kept at this temperature for 30 minutes, and then cooled. Application of this solution and heating and heating were repeated three times to obtain a precursor film (film thickness: 300 nm) composed of barium carbonate, ytterbium oxide and copper oxide.
Next, the precursor film thus formed was heated to 700 ° C. in a pure oxygen stream and held for 1 minute after reaching 700 ° C. (first heat treatment stage). The oxygen concentration continues to be 1 × 10^-FourIt switched to the argon + oxygen mixed gas stream adjusted to atm, and hold | maintained for 1 hour (2nd heat treatment stage). Thereafter, the atmosphere was switched to a pure oxygen stream, and oxygen treatment (third heat treatment stage) of gradually cooling to room temperature was performed to produce a Yb123 film. As a result of X-ray diffraction, it was confirmed that Yb123 was epitaxially grown on the film formed on the substrate in this way. As a result of surface observation with an electron microscope, the presence of cracks was not observed. When the superconducting critical temperature of the film was measured by the induction method, Tc = 87K was obtained.
[0039]
Example 4
In Example 3, a precursor film having a thickness of 500 nm was produced by increasing only the number of repetitions of application of the solution and heating and heating. This was subjected to the same three-stage heat treatment process as in Example 2 to produce a Yb123 film. As a result of X-ray diffraction, it was confirmed that Yb123 was epitaxially grown. As a result of surface observation with an electron microscope, the presence of cracks was not observed. When the superconducting critical temperature of the film was measured by the induction method, Tc = 87K was obtained.
[0040]
Comparative Example 1
CeO₂A coating solution in which Ba-acetylacetonate, Y-acetylacetonato and Cu-acetylacetonato were dissolved was applied on a sapphire R-plane base material using a spin coat method to form a coating film. . The coating film was heated from room temperature to 500 ° C. in air at a temperature rising rate of 2 ° C./min, held at this temperature for 30 minutes, and then cooled. By repeatedly applying this solution and heating and raising the temperature and changing the number of repetitions, precursor films made of barium carbonate, ytterbium oxide and copper oxide having various thicknesses (film thickness: 100 to 500 nm) were formed.
Next, the oxygen concentration of the precursor film thus formed is continuously 1 × 10^-FourThe temperature was raised to 750 ° C. in an argon + oxygen mixed gas stream adjusted to atm, and held for 1 hour (conventional method first heat treatment stage). Thereafter, the atmosphere was switched to a pure oxygen stream, and oxygen treatment (conventional method second heat treatment stage) of gradually cooling to room temperature was performed to produce a Y123 film. As a result of X-ray diffraction, it was confirmed that Y123 was epitaxially grown in the entire film thickness range of 100 to 500 nm. As a result of surface observation with an electron microscope, no crack was observed for a film having a film thickness of 400 nm or less, whereas it was confirmed that a crack was present on the surface of a film having a film thickness of 500 nm.
[0041]
Example 5
A coating solution in which Ba-acetylacetonato, Yb-acetylacetonato and Cu-acetylacetonato were dissolved was applied onto a YSZ single crystal substrate by a spin coating method to form a coating film. The coating film was heated from room temperature to 500 ° C. in air at a temperature rising rate of 2 ° C./min, held at this temperature for 30 minutes, and then cooled. Application of this solution and heating and heating were repeated three times to obtain a precursor film (film thickness: 300 nm) composed of barium carbonate, ytterbium oxide and copper oxide.
Next, the precursor film thus formed was heated to 700 ° C. in a pure oxygen stream and held for 1 minute after reaching 700 ° C. (first heat treatment stage). Subsequently, the oxygen concentration was 1 × 10.^-FourIt switched to the argon + oxygen mixed gas stream adjusted to atm, and hold | maintained for 1 hour (2nd heat treatment stage). Thereafter, the atmosphere was switched to a pure oxygen stream, and oxygen treatment (third heat treatment stage) of gradually cooling to room temperature was performed to produce a Yb123 film. As a result of X-ray diffraction, it was confirmed that Yb123 was epitaxially grown on the film formed on the substrate in this way. Also, the reaction product BaZrO between the membrane and the substrate_ThreeWas not confirmed. When the superconducting critical temperature of the film was measured by the induction method, Tc = 87K was obtained.
[0042]
Example 6
CeO₂A coating solution in which Ba-acetylacetonato, Yb-acetylacetonato, Y-acetylacetonato and Cu-acetylacetonato are dissolved on a sapphire R-plane base material having a buffer layer (Ba: Y: in terms of metal elements) Yb: Cu = 4: 1: 1: 6) was applied by spin coating to form a coating film. The coating film was heated from room temperature to 500 ° C. in air at a temperature rising rate of 2 ° C./min, held at this temperature for 30 minutes, and then cooled. Application of this solution and heating and heating were repeated three times to form a precursor film (film thickness: 300 nm) made of barium carbonate, ytterbium oxide and copper oxide.
Next, the precursor film thus formed is heated to 750 ° C. in a pure oxygen stream, and after reaching 750 ° C. (first heat treatment stage), the oxygen concentration is 1 × 10 5.^-FourIt switched to the argon + oxygen mixed gas stream adjusted to atm, and was hold | maintained at this temperature for 1 hour (2nd heat treatment stage). Then, after cooling to room temperature in that atmosphere, oxygen treatment was performed at 300 ° C. in a pure oxygen stream (third heat treatment stage) to produce a film. As a result of X-ray diffraction, the film formed on the substrate in this way has observed an epitaxially-arranged rare earth 123 phase single phase, and Y has randomly substituted some of the Yb sites of the Yb123 crystal (Yb, Y) It was found to be 123 film.
Next, when the superconducting critical temperature of the film was measured by an induction method, Tc = 88K was obtained. Further, when the critical current density of the film was measured by an induction method in liquid nitrogen, Jc = 8 × 10^FiveA / cm²was gotten.
[0043]
Example 7
The precursor film formed by the same method as in Example 6 was heated to 700 ° C. in a pure oxygen stream, and after reaching 700 ° C. (first heat treatment stage), the oxygen concentration was 1 × 10.^-FourIt switched to the argon + oxygen mixed gas stream adjusted to atm, and was hold | maintained at this temperature for 2 hours (2nd heat treatment stage). Then, after cooling to room temperature in that atmosphere, oxygen treatment was performed at 300 ° C. in a pure oxygen stream (third heat treatment stage) to produce a film. As a result of X-ray diffraction, the film formed on the substrate in this way has observed an epitaxially-arranged rare earth 123 phase single phase, and Y has randomly substituted some of the Yb sites of the Yb123 crystal (Yb, Y) It was found to be 123 film.
Next, when the superconducting critical temperature of the film was measured by an induction method, Tc = 85K was obtained.
[0044]
Example 8
Lanthanum aluminate substrate and CeO₂On a sapphire R-plane substrate with a buffer layer, and using a three-way evaporation source of barium fluoride, ytterbium fluoride and copper oxide (total pressure 1 × 10^-6at room temperature to form a precursor film (thickness: 300 nm) made of a mixture of these.
Next, the precursor film thus formed is heated to 720 ° C. in an oxygen stream containing water vapor at 70 ° C. dew point, and after reaching 720 ° C. (first heat treatment stage), water vapor at 70 ° C. dew point. And the oxygen concentration is 1 × 10^-FourIt switched to argon + oxygen + water vapor | steam mixed gas stream adjusted to atm, and hold | maintained at this temperature for 1 hour (2nd heat treatment stage). Then, after cooling to room temperature in that atmosphere, oxygen treatment was performed at 300 ° C. in a pure oxygen stream (third heat treatment stage) to produce a Yb123 film. As a result of X-ray diffraction, it was confirmed that Yb123 was epitaxially grown on the films formed on both substrates in this manner. When the superconducting critical temperature of the film was measured by the induction method, Tc = 88K was obtained.
[0045]
【The invention's effect】
In the present invention, it is possible to form an epitaxially oriented Yb123 film by a heat treatment at a temperature lower than that in the prior art. As a result, CeO₂For example, it is easy to form a superconducting film on a material having high chemical reactivity with the superconductor, or to form a superconducting film on a base material having a low heat resistance such as a metal tape base material. In addition, the problem of crack generation based on the difference in thermal expansion coefficient between the base material and the superconductor film is reduced, and a film having a larger film thickness is formed on the sapphire base material having a large difference in thermal expansion coefficient from the superconductor film. It can be formed free of cracks.

Claims (4)

In a superconductor manufacturing method in which a rare earth 123 structure type oxide superconductor film having a composition of YbBa ₂ Cu ₃ O _{7- y} is provided on a base material, barium carbonate or barium fluoride, ytterbium oxide, and copper oxide A precursor film made of a mixture is formed on a substrate, and then the precursor film is subjected to a heat treatment in a temperature range of 675 to 800 ° C. in a high oxygen partial pressure atmosphere with an oxygen partial pressure of 0.25 atm to 1 atm. One step of forming YbBa ₂ Cu ₄ O ₈ , heat treatment is performed at a temperature range of 675 to 850 ° C. under a low oxygen partial pressure of 1 × 10 ⁻⁵ to 1 × 10 ⁻³ atm of tetragonal YbBa ₂ Cu. Forming orthorhombic YbBa ₂ Cu ₃ O _{7- y} by heat treatment at a temperature range of 200 to 500 ° C. under the second stage of forming ₃ O ₆ and high oxygen partial pressure of 0.2 atm to ₁ atm In order of the third stage heat treatment The method for producing a superconductor, characterized in that to form YbBa ₂ Cu ₃ O _{7- y} film epitaxially oriented performed. The method for producing a superconductor according to claim 1, wherein the precursor film is formed by a solution coating pyrolysis method. The method of manufacturing a superconductor according to claim 1, wherein the precursor film is formed by a vacuum deposition method. A part of Yb of the precursor film is substituted with at least one other rare earth element selected from Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, The method for producing a superconductor according to any one of claims 1 to 3, wherein a part of Yb of the epitaxially oriented YbBa ₂ Cu ₃ O _{7- y} film is substituted with the other rare earth element.