JP2011204410A - Manufacturing method of oxide superconducting thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an oxide superconducting thin film capable of obtaining a temporarily baked film with generation of remains of foaming restrained in a temporarily baking treatment process, and capable of obtaining an oxide superconducting thin film having excellent superconductivity in a baking treatment process after the temporarily baking treatment process.SOLUTION: The manufacturing method of the oxide superconducting thin film, which is used for manufacturing superconducting wire rods, with a metal organic compound used as a raw material, and manufactured by the coating pyrolysis method, includes a coating film manufacturing process for manufacturing a coating film by applying solution of a metal organic compound on a substrate, a temporarily baking treatment process for manufacturing a temporarily baked film by pyrolizing and removing organic components contained in the metal organic compound of the coating film, and a baking treatment process for manufacturing the oxide superconducting thin film by crystallizing the temporarily baked film. The temporarily baked treatment process is carried out under an oxygen-free atmosphere or atmosphere with low oxygen concentration.

Description

  The present invention relates to a method for manufacturing an oxide superconducting thin film, and more particularly, to a method for manufacturing an oxide superconducting thin film having excellent superconducting characteristics used for manufacturing a superconducting wire.

  In order to further spread superconducting wires using oxide superconducting thin films, studies on the production of oxide superconducting thin films with higher superconducting properties such as critical current density Jc and critical current value Ic have been conducted.

  One method of manufacturing such an oxide superconducting thin film is a method called a coating organic decomposition method (abbreviation: MOD method) (Patent Document 1).

  In this method, a raw material solution (hereinafter, also referred to as “MOD solution”) produced by dissolving each metal organic compound of Re (rare earth element), Ba (barium), and Cu (copper) in a solvent is applied to a substrate. Thereafter, the metal organic compound was heat-treated (calcined) at, for example, around 500 ° C., and the organic components contained were thermally decomposed and removed to form a calcined film that is a precursor of the oxide superconducting thin film. A vapor phase method in which an oxide superconducting thin film is manufactured by crystallizing a calcined film by further heat treatment (main baking) at a higher temperature (for example, 750 to 800 ° C.), and mainly manufactured in a vacuum. Compared to (sputtering method, pulsed laser deposition method, etc.), manufacturing equipment is simple, and it is widely used because it has features such as easy handling of large areas and complex shapes. .

  Then, as a method of manufacturing an oxide superconducting thin film having a thick film and excellent superconducting characteristics by using the MOD method, the MOD solution is repeatedly applied and calcined, and the calcined films are laminated, that is, multilayered to obtain a thick film. In general, a method of firing after the pre-fired film is employed.

JP 2007-165153 A

  However, in the oxide superconducting thin film manufactured using the conventional MOD method, foam marks (portions appearing in a round shape) such as bubbles ruptured on the surface of the calcined film as shown in FIG. There was. This phenomenon was particularly noticeable in the calcined film having a large film thickness. And the film | membrane peeling has arisen in the location where such foaming produced.

  Even if the calcined film in which the film is peeled off is subjected to the main baking, the crystal growth is hindered at this peeled portion, so that sufficient crystal growth from the substrate surface to the film surface cannot be desired, which is favorable. An oxide superconducting thin film having superconducting properties cannot be obtained.

  Therefore, the present invention can provide a calcined film in which the formation of foam marks is suppressed in the calcining heat treatment step, and can obtain an oxide superconducting thin film having excellent superconducting characteristics in the subsequent calcining heat treatment step. It is an object to provide a method for manufacturing an oxide superconducting thin film.

  As a result of earnest research, the present inventor has found that the above problems can be solved by the inventions shown in the following claims, and has completed the present invention.

The invention described in claim 1
An oxide superconducting thin film used for the production of a superconducting wire is a method for producing an oxide superconducting thin film produced from a metal organic compound as a raw material by a coating pyrolysis method,
A coating film production step of producing a coating film by applying a solution of the metal organic compound on the substrate;
A calcining heat treatment step for producing a calcined film by thermally decomposing and removing an organic component contained in the metal organic compound of the coating film;
A calcination heat treatment step of crystallizing the calcined film to produce an oxide superconducting thin film,
The method of manufacturing an oxide superconducting thin film, wherein the calcining heat treatment step is a heat treatment step performed in an oxygen-free atmosphere or an atmosphere having a low oxygen concentration.

  In order to ascertain the cause of the occurrence of foaming marks as described above in the conventional calcination heat treatment step, the present inventor has variously investigated the relationship between the thermal decomposition behavior of the metal organic compound and the state of the coating film surface during the calcination heat treatment. Experiments and studies were conducted.

  Specifically, the TG-DTA measurement (differential thermal-thermogravimetric measurement) is performed by heating the coating film in the same atmosphere as that in the calcination heat treatment process of the ReBCO thin film manufactured using the conventional manufacturing method. The thermal decomposition behavior of the metal organic compound during the calcining heat treatment was analyzed. On the other hand, the condition of the coating film surface during the calcination heat treatment was observed, and the temperature at which foaming occurred was confirmed.

  An example of the result of the TG-DTA measurement is shown in FIG. In FIG. 3, the horizontal axis indicates temperature. The right vertical axis is DTA (Differential Thermal Analysis), and the data is shown by a solid line. Further, the left vertical axis is TG (Thermogravimetry), and the data is indicated by a broken line.

  FIG. 3 shows that heat is greatly generated at a temperature at which the Cu organic compound at about 250 ° C. is decomposed and at a temperature at which the Re organic compound or Ba organic compound is decomposed at about 430 ° C.

  On the other hand, according to the observation of the state of the coating film surface during the calcining heat treatment, the organic component decomposed from the metal organic compound causes a combustion reaction at about 250 ° C. and about 430 ° C. It was found that foam marks were generated on the surface.

  Thus, the temperature at which a large exotherm was confirmed in the TG-DTA measurement and the temperature at which the occurrence of foaming marks was confirmed in the observation of the coating surface condition were the same, and the calcining heat treatment step of the conventional manufacturing method , It was found that organic components decomposed from metal organic compounds cause a rapid exothermic reaction (combustion reaction) with oxygen in the atmosphere to generate a large amount of decomposition gas and produce foaming marks on the film surface. It was.

  Therefore, the present inventor changed the atmosphere in the calcination heat treatment process of the ReBCO thin film from a conventional air atmosphere to a helium atmosphere for the purpose of controlling the occurrence of such a rapid exothermic reaction. The experiment was conducted.

  The result of TG-DTA measurement obtained by the above experiment is shown in FIG. As shown in FIG. 1, in the absence of oxygen, it was found from the DTA curve that no rapid exothermic reaction occurred as the temperature increased due to heating. On the other hand, it was found from the TG curve that the weight decreased as the temperature increased due to heating, and it was confirmed that the organic components necessary for forming the calcined film were sufficiently decomposed.

  Then, according to the observation of the state of the coating film surface during the calcining heat treatment, it was found that there was no sudden gas generation during heating and no foaming marks were formed on the film surface.

  As described above, by setting the atmosphere to have a low oxygen concentration, the organic component is sufficiently decomposed from the metal organic compound, but a rapid exothermic reaction does not occur as in the conventional case, and the film surface is exposed. It was found that no foam marks were generated.

  The invention of this claim is an invention based on these findings, and since the calcining heat treatment step is performed in an oxygen-free atmosphere or an atmosphere having a low oxygen concentration and the combustion of decomposed organic components is suppressed, rapid heat generation The thermal decomposition of the metal organic compound proceeds without accompanying. As a result, the generation of foam marks can be suppressed, and peeling does not occur even with a thick calcined film.

  And even if the calcined film in which the generation of foaming marks is suppressed is a thick film, there is no risk of peeling off, so that in the main annealing process, crystals are sufficiently formed from the substrate interface to the film surface. Epitaxial growth can be achieved, and an oxide superconducting thin film having excellent superconducting properties can be provided.

  The term “atmosphere having a low oxygen concentration” in the present claims refers to the above-mentioned meaning, that is, an atmosphere having a low oxygen concentration to the extent that an exothermic reaction of an organic component can be suppressed so as not to cause foaming marks. Specifically, for example, an inert gas atmosphere such as helium, neon, argon or nitrogen can be used.

  The “oxygen-free atmosphere” and the “atmosphere with low oxygen concentration” do not need to be a pressurized atmosphere, but may be a pressurized atmosphere, and the pressure is not particularly limited.

The invention described in claim 2
The method for producing an oxide superconducting thin film according to claim 1, wherein the calcining heat treatment step is a heat treatment step performed in an atmosphere having an oxygen concentration of 10 vol% or less.

  By performing the calcination heat treatment step in an atmosphere having an oxygen concentration of 10 vol% or less, combustion of the organic component of the metal organic compound can be more reliably suppressed.

  According to the present invention, it is possible to obtain a calcined film in which the formation of foam marks is suppressed in the calcining heat treatment step, and it is possible to obtain an oxide superconducting thin film having excellent superconducting characteristics in the subsequent calcining heat treatment step. A method for manufacturing an oxide superconducting thin film can be provided.

It is a figure which shows a measurement result when the TG-DTA measurement of a coating film is performed in the same atmosphere as the calcination heat treatment process in the manufacturing method of the oxide superconducting thin film which concerns on this invention. It is a SEM photograph which shows the surface state of the coating film in the calcination heat treatment process in the manufacturing method of the conventional oxide superconducting thin film. It is a figure which shows a measurement result when the TG-DTA measurement of a coating film is performed in the same atmosphere as the calcination heat treatment process in the manufacturing method of the conventional oxide superconducting thin film.

  Hereinafter, the present invention will be described based on embodiments.

[1] Example This example is an example in which a superconducting thin film made of YBCO (YBa ₂ Cu ₃ O _7-δ ) was produced by the MOD method.

1. Preparation of calcined film (1) Preparation of MOD solution Starting from acetylacetonate salts of Y, Ba, and Cu, synthesis was performed at a ratio of Y: Ba: Cu = 1: 2: 3, and alcohol was used as a solvent. A MOD solution was prepared. The total cation concentration of Y ³⁺ , Ba ²⁺ and Cu ²⁺ in the MOD solution was 1 mol / L.

(2) Application Next, a substrate in which CeO ₂ was epitaxially grown on a 2 cm square YSZ single crystal was prepared, and the MOD solution was applied on the substrate by a spin coating method to form a coating film having a thickness of 10 μm. Formed.

(3) Calcination Heat Treatment Next, using the atmosphere furnace, the formed coating film was subjected to calcination heat treatment according to the following procedure to prepare the calcination film of the example. The calcination heat treatment was performed in an atmosphere of 1 atm helium gas (oxygen concentration: 0.1 vol%).

I. First, the formed coating film was heated from room temperature (20 ° C.) to 550 ° C. at a heating rate of about 20 ° C./min.

B. Holding-Cooling Next, the temperature was kept at 550 ° C. for 120 minutes. Thereafter, the temperature was lowered to room temperature at a temperature lowering speed of about 2 ° C./min, and a calcined film (thickness 0.2 μm) of the example was produced. Foaming marks were not observed on the surface of the obtained calcined film.

2. Preparation of YBCO superconducting thin film (1) Main baking heat treatment The calcined film obtained in the example was heated to 770 ° C. at a heating rate of 10 ° C./min in an argon / oxygen mixed gas atmosphere having an oxygen concentration of 100 ppm, The heat treatment was performed for 60 minutes while maintaining the temperature. When the temperature was lowered to 520 ° C. in about 3 hours after completion of the main heat treatment, the gas atmosphere was switched to a 100% oxygen concentration gas, and the furnace was cooled to room temperature over about 5 hours to prepare a YBCO thin film superconducting material.

(2) the critical current density Jc as an example of the measurement fabricated superconducting properties of YBCO superconducting wires of the superconducting properties were measured 77K, under the self-magnetic field was 5.5 mA / cm ^2.

[2] Comparative Example 1. Preparation of calcination film A calcination film of a comparative example was prepared in the same manner as in the example except that the calcination heat treatment was performed in an atmosphere of an atmospheric flow (oxygen concentration 20 vol%). On the surface of the obtained calcined film, foam marks of an average of 80 pieces / 100 μm × 100 μm were confirmed.

2. The YBCO films were prepared by performing the same process firing heat treatment and measurement example of the superconducting properties, as well was measured was measured Jc, it was 0.5 MA / cm ^2.

  Thus, in this example, unlike the comparative example, a calcined film in which foaming marks are suppressed is formed, so that the YBCO crystals grow sufficiently without being hindered in the main annealing process. To do. As a result, a superconducting thin film having excellent superconducting properties can be produced.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment. Various modifications can be made to the above-described embodiment within the same and equivalent scope as the present invention.

Claims (2)

An oxide superconducting thin film used for the production of a superconducting wire is a method for producing an oxide superconducting thin film produced from a metal organic compound as a raw material by a coating pyrolysis method,
A coating film production step of producing a coating film by applying a solution of the metal organic compound on the substrate;
A calcining heat treatment step for producing a calcined film by thermally decomposing and removing an organic component contained in the metal organic compound of the coating film;
A calcination heat treatment step of crystallizing the calcined film to produce an oxide superconducting thin film,
The method for producing an oxide superconducting thin film, wherein the calcining heat treatment step is a heat treatment step performed in an oxygen-free atmosphere or an atmosphere having a low oxygen concentration. The method for producing an oxide superconducting thin film according to claim 1, wherein the calcining heat treatment step is a heat treatment step performed in an atmosphere having an oxygen concentration of 10 vol% or less.