Raw material solution for producing oxide superconducting material and method for producing oxide superconducting material

Abstract

A raw material solution according to the present invention comprises, as solutes, a C1-4 rare earth element carboxylate, a C1-4 barium carboxylate, and a C1-4 copper carboxylate, and comprises, as solvents, water, two or more types of C1-4 alcohols, a C1-4 carboxylic acid, and a basic organic solvent. A method for manufacturing an oxide superconducting material according to the present invention comprises: a step for preparing the raw material solution; a step for forming a coating film from the raw material solution; a step for heating the coating film to form a temporary calcined film; and a step for heating the temporary calcined film to form an oxide superconducting material.

Description

[Technical field]

[0001] The present disclosure relates to a raw material solution for producing an oxide superconducting material and a method for producing an oxide superconducting material. This application claims priority based on Japanese Patent Application No. 2021-144693, filed on September 6, 2021. All contents of the Japanese patent application are incorporated herein by reference. [Background technology]

[0002] Manufacturing method of oxide superconducting material Law One of them is a method called the coating pyrolysis method (abbreviated as MOD method). In this method, a raw material solution (hereinafter also referred to as "MOD solution") produced by dissolving an organic metal compound in a solvent is coated on a substrate, and then heat-treated (hereinafter also referred to as calcination) at around 500°C to cause pyrolysis, and the resulting pyrolyzed material (hereinafter also referred to as "calcined film") is further heat-treated (hereinafter also referred to as firing) at a higher temperature (for example, around 800°C) to crystallize it, thereby producing a superconducting material. Compared to gas-phase methods (such as evaporation, sputtering, and pulsed laser deposition) that are mainly used for production in a vacuum, the MOD method has the advantage that the production equipment is simple and it is easy to handle large areas and complex shapes.

[0003] Regarding the above-mentioned MOD method, Non-Patent Document 1 (Mizuta et al., "Synthesis of Superconducting Film by Coating Pyrolysis Method", Journal of the Chemical Society of Japan, 1997, No. 1, pp. 11-23) discloses that a raw material solution is used in which organometallic compounds of rare earth elements, barium, and copper are dissolved in a mixed solvent of pyridine and propionic acid in a ratio of 5:3, evaporated to dryness, and then further dissolved in methanol.

[0004] Patent Document 1 (JP 2012-12247 A) discloses the use of a raw material solution in which the evaporated dry matter obtained as in Non-Patent Document 1 is dissolved in a mixed solvent of methanol, 1-butanol, and water instead of methanol. Patent Document 2 (JP 2011-253764 A) discloses the use of a raw material solution to which hydrochloric acid is added as a chlorine source, and Patent Document 3 (JP 2013-122847 A) and Patent Document 4 (JP 2015-165502 A) disclose the use of a raw material solution to which ammonium chloride is added as a chlorine source. Patent Document 5 (WO 2018 / 163501 A) discloses the structure and characteristics of an oxide superconducting material manufactured by a coating pyrolysis method using the above raw material solution. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-12247 A [Patent Document 2] JP 2011-253764 A [Patent Document 3] JP 2013-122847 A [Patent Document 4] JP 2015-165502 A [Patent Document 5] International Publication No. 2018 / 163501 [Non-patent literature]

[0006] [Non-Patent Document 1] Mizuta et al., "Synthesis of Superconducting Films by Coating Pyrolysis Method," Journal of the Chemical Society of Japan, 1997, No. 1, pp. 11-23 Summary of the Invention

[0007] A raw material solution according to one embodiment of the present disclosure is a raw material solution used in the production of an oxide superconducting material using a coating pyrolysis method. The raw material solution contains, as solutes, a rare earth element carboxylate having 1 to 4 carbon atoms, a barium carboxylate having 1 to 4 carbon atoms, and a copper carboxylate having 1 to 4 carbon atoms, and contains, as solvents, water, two or more types of alcohol having 1 to 4 carbon atoms, a carboxylic acid having 1 to 4 carbon atoms, and a basic organic solvent.

[0008] A method for producing an oxide superconducting material according to one embodiment of the present disclosure includes the steps of preparing a raw material solution of the above embodiment, applying the raw material solution onto a substrate and drying the raw material solution to form a coating film, heating the coating film to thermally decompose the rare earth element carboxylate, the barium carboxylate, and the copper carboxylate in the coating film and remove organic components to form a calcined film, and heating the calcined film to crystallize it, thereby forming an oxide superconducting material. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart showing an example of a method for producing an oxide superconducting material according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Problem that this disclosure aims to solve] However, the conventional raw material solutions used in the coating pyrolysis methods disclosed in Non-Patent Document 1 and Patent Documents 1 to 5 require multiple steps, including a first dissolution step in which each organometallic compound of rare earth elements, barium, and copper is dissolved in a pyridine-propionic acid mixed solvent (hereinafter also referred to as the first solvent), an evaporation-to-dryness step of the first solution obtained in the first dissolution step, and a second dissolution step in which the evaporated and dried product is dissolved in a solvent containing methanol (hereinafter also referred to as the second solvent), as described above. In addition, if the first solvent is completely evaporated in the evaporation-to-dryness step, crystals are likely to precipitate after the second dissolution step, so the amount of the first solvent to be evaporated must be precisely controlled.

[0011] Therefore, an object of the present disclosure is to provide a raw material solution that can be efficiently produced without requiring multiple steps and precise control during preparation of the raw material solution, and a method for producing an oxide superconducting material that can efficiently produce a high-quality oxide superconducting material using the raw material solution.

[0012] [Effects of this disclosure] According to the present disclosure, it is possible to provide a raw material solution that can be efficiently produced without requiring multiple steps and precise control during preparation of the raw material solution, and a method for producing an oxide superconducting material that can efficiently produce a high-quality oxide superconducting material using the raw material solution.

[0013] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0014] [1] A raw material solution according to an embodiment of the present disclosure is a raw material solution used in the production of oxide superconducting material using a coating pyrolysis method. The raw material solution contains, as solutes, a rare earth element carboxylate having a carbon number of 1 to 4, a barium carboxylate having a carbon number of 1 to 4, and a copper carboxylate having a carbon number of 1 to 4, and contains, as solvents, water, two or more types of alcohol having a carbon number of 1 to 4, a carboxylic acid having a carbon number of 1 to 4, and a basic organic solvent. The raw material solution of this embodiment does not require evaporation to dryness during its preparation, and has high solubility, dissolution stability, and wettability to the substrate. Therefore, the raw material solution can be efficiently produced without requiring multi-stage processes and precise control during preparation, and can efficiently produce high-quality oxide superconducting material.

[0015] [2] In the raw material solution, at least one of the rare earth element carboxylate, the barium carboxylate, and the copper carboxylate may be a monocarboxylate having 2 to 3 carbon atoms. Such a raw material solution does not require evaporation to dryness during its preparation, and has high solubility of the solute, high dissolution stability, and high wettability to the substrate. Therefore, the raw material solution can be efficiently prepared without requiring multiple steps and precise control, and a high-quality oxide superconducting material can be efficiently produced.

[0016] [3] In the raw material solution, at least one of the rare earth element carboxylate, the barium carboxylate, and the copper carboxylate may be a dicarboxylate having 2 to 4 carbon atoms. Such a raw material solution does not require evaporation to dryness during its preparation, and has high solubility of the solute, high dissolution stability, and high wettability to the substrate. Therefore, the raw material solution can be efficiently prepared without requiring multiple steps and precise control, and a high-quality oxide superconducting material can be efficiently produced.

[0017] [4] In the raw material solution, the alcohol may include an alcohol having a carbon number of 1 to 2 and an alcohol having a carbon number of 3 to 4. Such a raw material solution does not require evaporation to dryness during its preparation, and has high solubility of solutes, high dissolution stability, and high wettability to substrates. Therefore, such a raw material solution can be efficiently prepared without requiring multiple steps and precise control, and can efficiently produce high-quality oxide superconducting materials.

[0018] [5] In the above-mentioned raw material solution, the volume ratio of the alcohol having 1 to 2 carbon atoms and the alcohol having 3 to 4 carbon atoms can be within a range of 5:1 to 1:5. Such a raw material solution does not require evaporation to dryness during its preparation, and has a well-balanced high level of solute solubility, dissolution stability, and wettability to the substrate. Therefore, such a raw material solution does not require multi-stage processes and precise control during preparation, and can be produced more efficiently, and high-quality oxide superconducting material can be produced more efficiently.

[0019] [6] In the raw material solution, the carboxylic acid may be a monocarboxylic acid having 2 to 3 carbon atoms. Such a raw material solution does not require evaporation to dryness during its preparation, and has high solubility of solutes, high dissolution stability, and high wettability to substrates. Therefore, the raw material solution does not require multi-stage processes and precise control during its preparation, and can be efficiently produced, and a high-quality oxide superconducting material can be efficiently produced.

[0020] [7] In the raw material solution, the basic organic solvent may be an organic compound containing a nitrogen atom. Such a raw material solution does not require evaporation to dryness during its preparation, and has high solubility of the solute, high dissolution stability, and high wettability to the substrate. Therefore, the raw material solution can be efficiently prepared without requiring multiple steps and precise control, and can efficiently produce high-quality oxide superconducting materials.

[0021] [8] In the raw material solution, the solvent may contain 10% by volume or more and 30% by volume or less of the water, 20% by volume or more and 80% by volume or less of the alcohol, and 10% by volume or more and 50% by volume or less of the total content of the carboxylic acid and the basic organic solvent. Such a raw material solution does not require evaporation to dryness during its preparation, and has a well-balanced high solubility of the solute, dissolution stability, and wettability to the substrate. Therefore, the raw material solution can be efficiently prepared without requiring multiple steps and precise control, and a high-quality oxide superconducting material can be efficiently produced.

[0022] [9] A method for producing an oxide superconducting material according to an embodiment of the present disclosure includes the steps of preparing the raw material solution, applying the raw material solution onto a substrate and drying to form a coating film, heating the coating film to thermally decompose the rare earth carboxylate, the barium carboxylate, and the copper carboxylate in the coating film and remove organic components to form a calcined film, and heating the calcined film to crystallize the film to form an oxide superconducting material. The method for producing an oxide superconducting material according to this embodiment uses the raw material solution, and therefore can efficiently produce a high-quality oxide superconducting material.

[0023]

[10] The method for producing an oxide superconducting material may further include a step of filtering the raw material solution after the step of preparing the raw material solution and before the step of forming the coating film. By removing insoluble impurities in the raw material solution, the method for producing an oxide superconducting material can efficiently produce a higher quality oxide superconducting material.

[0024] [Details of the embodiment of the present disclosure] <Embodiment 1: Raw material solution> The raw material solution of this embodiment is a raw material solution used in the production of oxide superconducting material using the coating pyrolysis method, and contains rare earth element carboxylates (hereinafter also referred to as RE carboxylates) having a carbon number of 1 to 4, barium carboxylates (hereinafter also referred to as Ba carboxylates) having a carbon number of 1 to 4, and copper carboxylates (hereinafter also referred to as Cu carboxylates) having a carbon number of 1 to 4 as solutes, and contains water, two or more types of alcohols having a carbon number of 1 to 4, carboxylic acids having a carbon number of 1 to 4, and a basic organic solvent as solvents. The raw material solution of this embodiment does not require evaporation to dryness during its preparation, and has high solubility, dissolution stability, and wettability to the substrate. Therefore, the raw material solution of this embodiment can be efficiently produced without requiring multi-stage processes and precise control during preparation, and can efficiently produce high-quality oxide superconducting material.

[0025] As described above, the conventional raw material solutions used in Non-Patent Document 1 and Patent Documents 1 to 5 require multiple steps including the first dissolving step, the evaporation to dryness step, and the second dissolving step. In addition, if the first solvent is completely evaporated in the evaporation to dryness step, crystals are likely to precipitate after the second dissolving step, so the amount of the first solvent to be evaporated needs to be precisely controlled.

[0026] Here, when the solvent removed by distillation (hereinafter also referred to as distilled off) during evaporation to dryness in the production of the conventional raw solution used in Patent Documents 1 to 5 was analyzed, it was found to contain acetylacetone in addition to pyridine and propionic acid contained in the first solvent. This is because, during the first dissolving step and the evaporation to dryness step in the production process of the conventional raw solution, the acetylacetonate (hereinafter also referred to as acetylacetonate) coordinated to the rare earth element (hereinafter also referred to as RE), barium (hereinafter also referred to as Ba), and copper (hereinafter also referred to as Cu) in the organometallic compounds rare earth acetylacetonate (hereinafter also referred to as RE acetylacetonate, where acetylacetonate is also referred to as acetylacetonate), barium acetylacetonate (hereinafter also referred to as Ba acetylacetonate, where acetylacetonate is also referred to as acetylacetonate), and copper acetylacetonate (hereinafter also referred to as Cu acetylacetonate, where acetylacetonate is also referred to as acetylacetonate) was removed. say ; The conjugate base of acetylacetone) is propionate (also known as propionate) derived from propionic acid. say This shows that acetylacetonate is replaced by propionate (the conjugate base of propionic acid) and released as acetylacetone. Because of this ligand replacement reaction from acetylacetonate to propionate, the amount of the ligand replacement varies depending on the amount of solvent distilled off in the evaporation and drying process, which causes variation in the quality of the raw solution.

[0027] In order to prevent the occurrence of the above-mentioned variation in the amount of ligand substitution, we have considered performing the second dissolution step in the process of producing the raw material solution without performing the first dissolution step and the evaporation to dryness step, that is, limiting the process of producing the raw material solution to the solute dissolution step alone. Here, in the conventional raw material solution, the ligands of RE, Ba, and Cu in the organometallic compound of the solute are derived from carboxylic acids in the solvent. Carboxylate Since the metal carboxylate is replaced by propionate (the conjugate base of a carboxylic acid), the inventors have attempted to solve the above problem by dissolving a solute containing a metal carboxylate as an organometallic compound in a solvent containing a carboxylic acid.

[0028] [Solute] The raw material solution of this embodiment contains, as solutes, RE carboxylates having a carbon number of 1 to 4, Ba carboxylates having a carbon number of 1 to 4, and Cu carboxylates having a carbon number of 1 to 4. The RE carboxylates, Ba carboxylates, and Cu carboxylates as solutes all have a ligand of RE, Ba, and Cu that is not acetylacetonate, Carboxylate Therefore, multi-step processes and precise control are not required when preparing the raw material solution.

[0029] The RE carboxylate, Ba carboxylate, and Cu carboxylate as solutes all have carbon numbers of 1 or more. top 4 The following carboxylates are used. Such carboxylates have high solubility and dissolution stability in a solvent. From the viewpoint of high solubility and dissolution stability in a solvent, the RE carboxylate, Ba carboxylate, and Cu carboxylate are preferably carboxylates having a carbon number of 2 or more and 3 or less.

[0030] In addition, examples of the RE carboxylate, Ba carboxylate, and Cu carboxylate as the solute include monocarboxylates and dicarboxylates, but from the viewpoint of high solubility in a solvent and high dissolution stability, at least one of the RE carboxylate, Ba carboxylate, and Cu carboxylate is preferably a monocarboxylate. Here, examples of the monocarboxylate having 1 to 4 carbon atoms include formates, acetates, propionates, and butyrates. Examples of the dicarboxylate having 2 to 4 carbon atoms include oxalates, malonates, and succinates.

[0031] Furthermore, from the viewpoint of high solubility and dissolution stability in a solvent, it is more preferable that at least one of the RE carboxylate, Ba carboxylate, and Cu carboxylate is a monocarboxylate having a carbon number of 2 or more and 3 or less. Here, examples of the monocarboxylate having a carbon number of 2 or more and 3 or less include acetate and propionate.

[0032] In addition, from the viewpoint of high solution stability, it is preferable that at least one of the RE carboxylate, Ba carboxylate, and Cu carboxylate as the solute is a dicarboxylate having 2 to 4 carbon atoms (i.e., oxalate, malonate, and / or succinate).

[0033] The RE in the RE carboxylate is not particularly limited as long as it is an RE that can be used to produce a high-quality oxide superconducting material, and suitable examples of the RE include Y (yttrium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

[0034] The molar ratios of RE, Ba, and Cu in the RE carboxylate, Ba carboxylate, and Cu carboxylate contained in the solute are preferably the stoichiometric ratio of the oxide superconducting material to be manufactured or close to it. 7-δ The RE carboxylate, Ba carboxylate, and Cu carboxylate in the raw material solution for producing a superconducting material (hereinafter also referred to as RE123 superconducting material) preferably have a molar ratio of RE:Ba:Cu of 1±0.1:2±0.2:3±0.3, more preferably 1±0.05:2±0.10:3±0.15, and particularly preferably 1:2:3.

[0035] Also, from the viewpoint of producing a high-quality oxide superconducting material, it is preferable to add Cl (chlorine) to the raw material solution. For this purpose, examples of the Cl source to be added include organic compounds such as trichloroacetic acid, hydrochloric acid, and ammonium chloride. The raw material solution to which Cl is added forms chlorides such as CuCl (melting point 430°C) and CuCl2 (melting point 498°C) that have a melting point lower than the firing temperature by calcination, and becomes a molten liquid during crystallization of the oxide superconductor in the firing (for example, 800°C). Since the c-axis orientation of the oxide superconductor crystal is not hindered, the quality is improved, for example, by increasing the critical current Ic of the oxide superconducting material. As the Cl source to be added, ammonium chloride is preferable from the viewpoint of leaving Cl in the calcined film during firing.

[0036] [solvent] The raw material solution of the present embodiment contains, as a solvent, water, two or more types of alcohols having a carbon number of 1 to 4, a carboxylic acid having a carbon number of 1 to 4, and a basic organic solvent. Such a solvent has high solubility and dissolution stability of the solute, and also has high wettability of the raw material solution to the substrate.

[0037] (water) Water enhances the solubility and dissolution stability of the solute, particularly the dissolution stability. For this reason, water prevents the precipitation of the solute from the raw material solution. There are no particular limitations on the water, so long as it is possible to produce an oxide superconducting material. The water is preferably one having a resistivity of 1 MΩ·cm or more, such as ion-exchanged water, distilled water, or RO (reverse osmosis) water.

[0038] (2 or more types of alcohol with carbon numbers between 1 and 4) Two or more types of alcohols having a carbon number of 1 to 4 increase the solubility of the solute and also increase the wettability of the raw material solution to the substrate. Here, the smaller the carbon number of the alcohol, the higher the solubility of the solute, and the larger the carbon number of the alcohol, the higher the wettability of the raw material solution to the substrate.

[0039] The two or more types of alcohols having a carbon number of 1 to 4 preferably include an alcohol having a carbon number of 1 to 2 and an alcohol having a carbon number of 3 to 4. The alcohol having a carbon number of 1 to 2 increases the solubility of the solute, and the alcohol having a carbon number of 3 to 4 increases the wettability of the raw material solution to the substrate. For this reason, the solvent includes an alcohol having a carbon number of 1 to 4, and an alcohol having a carbon number of 3 to 4, as the two or more types of alcohol having a carbon number of 1 to 4, so that the solubility of the solute and the wettability of the raw material solution to the substrate can be increased and adjusted. Here, examples of the alcohol having a carbon number of 1 to 2 include methanol and ethanol. Examples of the alcohol having a carbon number of 3 to 4 include 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol (also called 2-methylpropan-1-ol or 2-methylpropyl alcohol), and tert-butyl alcohol (also called 2-methyl-2-propanol).

[0040] From the viewpoints of increasing the solubility of the solute and the wettability of the raw material solution to the substrate as well as increasing their adjustability, it is more preferable that the two or more types of alcohols having 1 to 4 carbon atoms include an alcohol having 1 carbon atom and an alcohol having 4 carbon atoms, and it is more preferable that the two or more types of alcohols have, for example, methanol and 1-butanol or 2-butanol.

[0041] The volume ratio of the alcohol having a carbon number of 1 to 2 and the alcohol having a carbon number of 3 to 4 contained in the two or more kinds of alcohols having a carbon number of 1 to 4 is preferably within a range of 5:1 to 1:5. By setting the volume ratio of the alcohol having a carbon number of 1 to 2 and the alcohol having a carbon number of 3 to 4 within a range of 5:1 to 1:5, the solubility of the solute and the wettability of the raw material solution to the substrate can be improved in a well-balanced manner. From this viewpoint, the volume ratio of the alcohol having a carbon number of 1 to 2 and the alcohol having a carbon number of 3 to 4 is more preferably within a range of 4:1 to 1:4.

[0042] (Carboxylic acid with 1 to 4 carbon atoms) Carboxylic acids with carbon numbers of 1 to 4 increase the solubility of the solute. In addition, the solutes RE carboxylate, Ba carboxylate, and Cu carboxylate are all carboxylates with carbon numbers of 1 to 4, so the ligands of RE, Ba, and Cu in the dissolved solutes are all the same before and after the substitution. Carbon Number is between 1 and 4 Carboxylate Therefore, the change in the coordination species is small or does not occur. That is, the above RE carboxylate, Ba carboxylate, and Cu carboxylate are the same. Carboxylate There is no difference in the number of carbon atoms, or at most it is within a range of 1 to 3. Therefore, carboxylic acids having a carbon number of 1 or more and 4 or less also enhance the dissolution stability of the solute.

[0043] The carboxylic acid having 1 to 4 carbon atoms is preferably a carboxylic acid having 2 to 3 carbon atoms in terms of increasing the solubility and dissolution stability of the solute. Examples of the carboxylic acid having 1 to 4 carbon atoms include monocarboxylic acids and dicarboxylic acids, and from the viewpoint of increasing the solubility and dissolution stability of the solute, the monocarboxylic acid is preferable. Examples of the monocarboxylic acid having 1 to 4 carbon atoms include formic acid, acetic acid, propionic acid, and butyric acid. Examples of the dicarboxylic acid having 1 to 4 carbon atoms include oxalic acid, malonic acid, and succinic acid.

[0044] Furthermore, from the viewpoint of enhancing the solubility and dissolution stability of the solute, the carboxylic acid having 1 to 4 carbon atoms is more preferably a monocarboxylic acid having 2 to 3 carbon atoms. By dissolving the RE carboxylate, Ba carboxylate, and Cu carboxylate, which are monocarboxylic acid salts having 2 to 3 carbon atoms as the solute, in a solvent containing a monocarboxylic acid having 2 to 3 carbon atoms, the ligands of RE, Ba, and Cu in the dissolved solute all have 2 to 3 carbon atoms both before and after the substitution. Carboxylate Therefore, the change in the coordination species is small or does not occur. In other words, the combination of a solute that is a monocarboxylate having 2 to 3 carbon atoms and a solvent that contains a monocarboxylic acid having 2 to 3 carbon atoms results in the same monocarboxylate. Carboxylate and the difference in the number of carbon atoms is equal to or at most 1, which is more preferred.

[0045] (Basic organic solvent) The basic organic solvent increases the solubility of the solute. The basic organic solvent also neutralizes carboxylic acids having 1 to 4 carbon atoms. There are no particular limitations on the basic organic solvent as long as it is compatible with other solvents and neutralizes carboxylic acids having 1 to 4 carbon atoms. However, from the viewpoint of efficiently neutralizing carboxylic acids having 1 to 4 carbon atoms (for example, the pKa of formic acid is 3.75, the pKa of acetic acid is 4.76, the pKa of propionic acid is 4.87, and the pKa of butyric acid is 4.82), it is preferable that the pKa of the conjugate acid of the basic organic solvent is 5 to 14.

[0046] The basic organic solvent is preferably an organic compound containing a nitrogen atom from the viewpoint of neutralizing a carboxylic acid having a carbon number of 1 to 4. Examples of such a basic organic solvent include pyridine, whose conjugate acid has a pKa of 5.25, and ethylenediamine, whose conjugate acid has a pKa of 10.7.

[0047] (Proportion of each component in the solvent) From the viewpoint of improving the solubility and dissolution stability of the solute and the wettability of the raw material solution to the substrate in a well-balanced manner, the proportion of each component in the solvent is preferably 10% by volume or more and 30% by volume or less for water, 20% by volume or more and 80% by volume or less for two or more types of alcohol having a carbon number of 1 to 4, and 10% by volume or more and 50% by volume or less for the total content of the carboxylic acid having a carbon number of 1 to 4 and the basic organic solvent. More preferably, the total content of the carboxylic acid having a carbon number of 1 to 4 and the basic organic solvent is 20% by volume or more and 40% by volume or less.

[0048] [Solute concentration in raw solution] The concentration of the solute in the raw material solution is not particularly limited, but is preferably 1.0 mol / l or more from the viewpoint of efficiently producing a high-quality oxide superconducting material, and is preferably 1.5 mol / l or less from the viewpoint of the solubility of the solute in the raw material solution. In addition, the raw material solution may be appropriately diluted with a solvent to adjust the concentration of the solute in the solution to 0.1 mol / l or more and 1.0 mol / l or less according to the coating process.

[0049] [Method of manufacturing raw solution] The method for producing the raw material solution of this embodiment is not particularly limited, but from the viewpoint of eliminating the need for multi-stage processes and precise control during preparation, it is preferable to dissolve a solute containing an RE carboxylate having a carbon number of 1 to 4, a Ba carboxylate having a carbon number of 1 to 4, and a Cu carboxylate having a carbon number of 1 to 4 in a solvent containing water, two or more types of alcohol having a carbon number of 1 to 4, a carboxylic acid having a carbon number of 1 to 4, and a basic organic solvent. Here, the RE carboxylate having a carbon number of 1 to 4, the Ba carboxylate having a carbon number of 1 to 4, the Cu carboxylate having a carbon number of 1 to 4, the water, the two or more types of alcohol having a carbon number of 1 to 4, the carboxylic acid having a carbon number of 1 to 4, and the basic organic solvent are as described above, so the description thereof will not be repeated.

[0050] In addition, high-quality oxide superconductors GuidanceFrom the viewpoint of producing a material, Cl (chlorine) may be added to the raw material solution. For this purpose, examples of Cl sources include organic compounds such as trichloroacetic acid, hydrochloric acid, and ammonium chloride. Any of the above Cl sources can be added as a solute.

[0051] <Embodiment 2: Method for producing oxide superconducting material> 1, the method for producing an oxide superconducting material of this embodiment is a method for producing an oxide superconducting material by a coating pyrolysis method using the raw material solution of embodiment 1, and includes the steps of preparing a raw material solution S10, coating the raw material solution on a substrate and drying it to form a coating film S20, heating the coating film to pyrolyze the RE carboxylate, Ba carboxylate, and Cu carboxylate in the coating film and removing organic components to form a calcined film S30, and heating the calcined film to crystallize it to form an oxide superconducting material S40. The method for producing an oxide superconducting material of this embodiment uses the raw material solution of embodiment 1, and therefore can efficiently produce a high-quality oxide superconducting material.

[0052] (Step S10 of preparing raw material solution) In the step of preparing a raw material solution, the raw material solution is prepared by preparing the raw material solution by the manufacturing method of the raw material solution of embodiment 1, or by obtaining a raw material solution prepared in such a manner. Here, in the step of preparing the raw material solution, the raw material solution of embodiment 1 can be prepared only by dissolving a predetermined solute in a predetermined solvent, so that multi-stage steps and precise control are not required when preparing the raw material solution.

[0053] (Step S11 of filtering the raw material solution) From the viewpoint of removing insoluble impurities in the raw material solution and improving the quality of the oxide superconducting material, the method for producing an oxide superconducting material of this embodiment may include a step S11 of filtering the raw material solution after the step S10 of preparing the raw material solution and before a step S20 of applying the raw material solution to a substrate and drying the solution to form a coating film, which will be described later. There are no particular limitations on the filter used for filtration as long as it has chemical and mechanical durability when filtering the raw material solution, and a suitable example is a PTFE (polytetrafluoroethylene) filter with a pore size of 0.2 μm.

[0054] (Step S20: applying the raw material solution onto a substrate and drying to form a coating film) In the process of applying the raw material solution onto a substrate and drying it to form a coating film, the raw material solution prepared as described above, or the raw material solution prepared and filtered as described above, is applied onto a substrate and dried to form a coating film.

[0055] The substrate is not particularly limited as long as it has heat resistance and mechanical strength in the heat treatment described below, but is preferably a textured metal substrate, an IBAD (Ion Beam Assisted Deposition) substrate, etc. The textured metal substrate may be, for example, a clad substrate in which a copper layer, a nickel layer, etc. are laminated on a base metal substrate of SUS or Hastelloy (registered trademark).

[0056] The coating method is not particularly limited as long as the raw material solution can be uniformly coated, and examples of the coating method include die coating, spin coating, spray coating, and inkjet coating. The thickness of the coating film is not particularly limited, but from the viewpoint of forming an oxide superconducting material with a suitable thickness, it is preferable that the thickness is 1 μm or more and 20 μm or less per coating. The drying method is not particularly limited as long as the raw material solution can be uniformly dried, and examples of the drying method include heat drying, hot air drying, and infrared drying. The drying temperature is not particularly limited, but from the viewpoint of sufficiently drying the solvent, it is preferably 100° C. or more and 250° C. or less, and more preferably 150° C. or more and 230° C. or less. When the next step of calcination is performed continuously after coating, if drying occurs naturally during the temperature increase process of the calcination step, it is not necessary to provide a separate drying step.

[0057] (Step S30 of heating the coating film to thermally decompose the RE carboxylate, Ba carboxylate, and Cu carboxylate in the coating film and remove the organic components to form a calcined film) From the viewpoint of forming a uniform calcined film, the heating atmosphere for the coating film in the step of forming the calcined film preferably contains oxygen at 0.1 atmospheres or more, and if necessary, preferably further contains water vapor having a dew point of 10° C. or more. The heating temperature is preferably 450° C. or more and 600° C. or less, and more preferably 480° C. or more and 550° C. or less.

[0058] The above steps from step S20 of forming the coating film to step S30 of forming the calcined film can be repeated multiple times as necessary until the calcined film has a desired thickness, thereby forming a multi-layer structure.

[0059] (Step S40 of forming an oxide superconducting material by heating and crystallizing the calcined film) The oxide superconducting material forming step produces a film-like oxide superconducting material (hereinafter also referred to as oxide superconducting film). The thickness of the oxide superconducting film is not particularly limited, but is preferably 10 nm to 500 nm per coating from the viewpoint of shortening the process time and preventing cracks in the calcined film. From the viewpoint of forming a high-quality oxide superconducting film, the oxide superconducting material forming step preferably includes a firing step of crystallizing the calcined film to form a fired film. The heating atmosphere in the firing step is preferably a low oxygen partial pressure (1 Pa to 500 Pa). The heating temperature in the firing step is preferably 700°C to 900°C, more preferably 750°C to 850°C.

[0060] The above-mentioned steps from the step S20 of forming the coating film through the step S30 of forming the calcined film to the firing step of forming the fired film can be repeated several times as necessary until the oxide superconducting film has a desired thickness, forming a multi-layer structure. The final oxide superconducting film preferably has a thickness of 10 μm or less, but can be made thicker as necessary.

[0061] From the viewpoint of forming a high-quality oxide superconducting film, the step of forming the oxide superconducting material preferably further includes an annealing step of forming an oxide superconducting thin film by controlling the oxygen in the fired film. The heating atmosphere in the annealing step is a high oxygen partial pressure (1×10 4 The heating temperature in the annealing step is preferably 150° C. or higher and 600° C. or lower, and more preferably 200° C. or higher and 550° C. or lower. EXAMPLES

[0062] (solute) Referring to Tables 1 to 4, in Comparative Examples 1 to 3 and Examples 1 to 34, solutes used were prepared by mixing RE carboxylates Gd propionate, Gd acetate, Gd oxalate, Y propionate, Y acetate, or Y oxalate, Ba carboxylates Ba propionate, Ba acetate, or Ba oxalate, and Cu carboxylates Cu propionate, Cu acetate, or Cu oxalate in a molar ratio of 1:2:3.

[0063] (solvent) Referring to Table 1, in Comparative Example 1, a solvent in which water and methanol were mixed at a volume ratio of 1:5 was used. In Comparative Example 2, a solvent in which water, methanol, and 1-butanol were mixed at a volume ratio of 1:4:1 was used. In Comparative Example 3, a solvent in which water, methanol, and 1-butanol were mixed at a volume ratio of 1:4:1 was used. - A solvent was used in which butanol and propionic acid were mixed at a volume ratio of 1:4:1:1. In Examples 1 to 34, a solvent was used in which the solvents shown in Tables 1 to 4 were mixed at the volume ratios shown in Tables 1 to 4. The numbers in parentheses to the right of the volume ratios in the solvent columns of Tables 1 to 4 indicate the volume % of each solvent when the total volume of the solvent is 100%.

[0064] [1] Evaluation test of the solubility of solutes in the raw solution A total of 0.01 mol of the solute was added to the solvent, and the solvent was shaken at 25° C. for 5 hours, after which the presence or absence of dissolution of the solute was evaluated. In the evaluation of solubility, a solubility of 1.0 mol / L or more (good) is preferable, and a solubility of 1.5 mol / L or more (excellent) is more preferable. The results are summarized in Tables 1 to 4.

[0065] The solute solubility was poor, less than 1.0 mol / l, in Comparative Examples 1 and 2, but was good or excellent in Comparative Example 3 and Examples 1 to 34. This shows that in order to increase the solubility of the solute in the raw material solution, propionic acid (a carboxylic acid having 1 to 4 carbon atoms) is necessary as a solvent in addition to water, methanol, and 1-butanol (two types of alcohol having 1 to 4 carbon atoms).

[0066] [2] Evaluation test of the coating property of the raw solution on the substrate The state of the coating film was evaluated when the raw material solutions of Comparative Examples 1 to 3 and Examples 1 to 34 were die-coated to a thickness of 5 μm on a clad substrate of length 220 mm × width 30 mm × thickness 120 μm. The raw material solutions were repelled by the substrate and no uniform coating film was obtained, and the coating film was evaluated as N (poor), and the coating film was evaluated as G (good). The results are summarized in Tables 1 to 4.

[0067] The coating property of the raw material solution on the substrate was poor only in Comparative Example 1. From this, it was found that in order to improve the coating property of the raw material solution on the substrate, 1-butanol (alcohol having 3 to 4 carbon atoms) is necessary as a solvent in addition to water and methanol (alcohol having 1 to 2 carbon atoms).

[0068] [3] Evaluation test of the dissolution resistance of calcined membrane The raw material solutions of Comparative Examples 1 to 3 and Examples 1 to 34 were die-coated to a thickness of 5 μm on a clad substrate having a length of 220 mm, a width of 30 mm, and a thickness of 120 μm, and then heat-treated (calcined) at 500° C. in an oxygen atmosphere humidified to a dew point of 20° C. In Comparative Examples 2 and 3 and Examples 1 to 34, a calcined film having a thickness of 150 nm was obtained. In Comparative Example 1, the coating property of the raw material solution on the substrate was poor, so that the film could not be formed and no calcined film was obtained. The calcined films were each immersed in the raw material solution at room temperature for 10 minutes to evaluate their dissolution resistance. Calcined films whose mass reduction after the above immersion was less than 10% were evaluated as A, and calcined films whose mass reduction after the above immersion was 10% or more were evaluated as B.

[0069] The calcined film of Comparative Example 3 had poor solubility in the raw material solution, being little soluble, whereas the calcined films of Comparative Example 2 and Examples 1 to 34 had good solubility in the raw material solution. Here, it was considered that the reason why the solubility resistance of the calcined film of Comparative Example 3 was poorer than that of Comparative Example 2 was due to the raw material solution of Comparative Example 3 being acidic since it contained propionic acid, i.e., a carboxylic acid having 1 to 4 carbon atoms. From this, it was found that in order to improve the solubility resistance of the calcined film, in addition to water, two types of alcohols having 1 to 4 carbon atoms, methanol and 1-butanol, and propionic acid, a basic organic solvent such as pyridine to neutralize propionic acid is necessary as a solvent.

[0070] [4] Manufacturing of oxide superconducting materials (1) Preparation of raw material solution With reference to Tables 1 and 2, solutes prepared so that the molar ratio of Gd carboxylate, Gd propionate or Gd acetate, Ba carboxylate, Ba propionate or Ba acetate, and Cu carboxylate, Cu propionate or Cu acetate, was 1:2:3 were dissolved in a solvent in which the components shown in Tables 1 and 2 were mixed in their volume ratios to prepare raw material solutions with a solute concentration of 0.2 mol / l in Comparative Examples 1 and 2, and raw material solutions with a solute concentration of 1.0 mol / l in Comparative Example 3 and Examples 1 to 34.

[0071] (2) Filtration of raw solution All the raw material solutions prepared in the Examples and Comparative Examples were filtered. A PTFE (polytetrafluoroethylene) filter (50J, manufactured by Advantec Co., Ltd.) with a pore size of 0.2 μm was used as the filtration filter. P 020AN or its equivalent) was used.

[0072] (3) Formation of calcined membrane The raw material solutions of Comparative Examples 1 to 3 and Examples 1 to 34 were die-coated to a thickness of 5 μm on a clad substrate having a length of 5000 mm, a width of 30 mm, and a thickness of 120 μm, and then heat-treated (calcined) at 500° C. in an atmosphere with an oxygen partial pressure of 1 atm and a dew point of 19° C. This coating and heat-treatment operation was repeated multiple times. Note that in Comparative Example 1, the raw material solution was poorly applied to the substrate, so film formation was not possible and a calcined film was not obtained.

[0073] (4) Formation of oxide superconducting material The calcined films of Comparative Examples 2 and 3 and Examples 1 to 34 were subjected to a heat treatment (firing) in which they were heated at 800°C in an atmosphere of argon / oxygen mixed gas (oxygen concentration 100 ppm, CO2 concentration 1 ppm or less). Thereafter, oxygen annealing was performed at 500°C in an atmosphere of 100% oxygen concentration, and an oxide superconducting film was obtained by controlling the amount of oxygen in the fired film. In Comparative Example 1, a calcined film could not be formed, and therefore an oxide superconducting material could not be formed. In Comparative Examples 2 and 3 and Examples 1 to 34, a film-like oxide superconducting material having a thickness of 3 μm was obtained.

[0074] (5) Evaluation of the critical current of oxide superconducting materials The oxide superconducting materials of Comparative Examples 2 and 3 and Examples 1 to 34 were subjected to measurement of the critical current Ic per 4 mm width at 77.3 K (Kelvin) by a four-terminal method. The results are summarized in Tables 1 and 2. The critical current Ic was classified into 200 A or less (≦200 A) and over 200 A (>200 A). Those below 200 A were poor, and those over 200 A were good.

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] [Table 4]

[0079] Referring to Tables 1 to 4, as shown in Examples 1 to 34, it was found that a raw material solution used in the production of oxide superconducting material by the coating pyrolysis method, which contains as solutes an RE carboxylate having a carbon number of 1 to 4, a Ba carboxylate having a carbon number of 1 to 4, and a Cu carboxylate having a carbon number of 1 to 4, and as a solvent water, two or more types of alcohol having a carbon number of 1 to 4, a carboxylic acid having a carbon number of 1 to 4, and a basic organic solvent, has high solubility of the solutes, dissolution stability, and wettability to the substrate, and therefore does not require multi-stage processes and precise control during preparation, allowing efficient production, and enables efficient production of high-quality oxide superconducting material.

[0080] It has also been found that a method for producing an oxide superconducting material using the coating pyrolysis method that uses the above-mentioned raw material solution, the method including the steps of preparing the raw material solution, coating the raw material solution on a substrate and drying it to form a coating film, heating the coating film to pyrolyze the RE carboxylate, the Ba carboxylate, and the Cu carboxylate in the coating film and remove organic components to form a calcined film, and heating the calcined film to crystallize it to form an oxide superconducting material, can efficiently produce high-quality oxide superconducting material because it uses the above-mentioned raw material solution.

[0081] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[0082] S10 is a step of preparing a raw material solution; S11 is a step of filtering the raw material solution; S20 is a step of applying the raw material solution onto a substrate and drying it to form a coating film; S30 is a step of heating the coating film to thermally decompose the rare earth element carboxylate, barium carboxylate, and copper carboxylate in the coating film and remove organic components to form a calcined film; S40 is a step of heating the calcined film to crystallize it, to form an oxide superconducting material.

Claims

1. A raw material solution used in the production of an oxide superconducting material by a coating pyrolysis method, The solute contains a rare earth element carboxylate having 1 to 4 carbon atoms, a barium carboxylate having 1 to 4 carbon atoms, and a copper carboxylate having 1 to 4 carbon atoms; A raw material solution containing, as a solvent, water, two or more kinds of alcohols having 1 to 4 carbon atoms, a carboxylic acid having 1 to 4 carbon atoms, and a basic organic solvent.

2. 2. The raw material solution according to claim 1, wherein at least one of the rare earth element carboxylate, the barium carboxylate, and the copper carboxylate is a monocarboxylate having a carbon number of 2 or more and 3 or less.

3. 2. The raw material solution according to claim 1, wherein at least one of the rare earth element carboxylate, the barium carboxylate, and the copper carboxylate is a dicarboxylate having a carbon number of 2 to 4.

4. The raw material solution according to claim 1 , wherein the alcohol includes an alcohol having 1 to 2 carbon atoms and an alcohol having 3 to 4 carbon atoms.

5. 5. The raw material solution according to claim 4, wherein a volume ratio of the alcohol having 1 to 2 carbon atoms to the alcohol having 3 to 4 carbon atoms is within a range of 5:1 to 1:

5.

6. The raw material solution according to claim 1 , wherein the carboxylic acid is a monocarboxylic acid having from 2 to 3 carbon atoms.

7. The raw material solution according to claim 1 , wherein the basic organic solvent is an organic compound containing a nitrogen atom.

8. 4. The raw material solution according to claim 1, wherein, in the solvent, a content ratio of the water is 10 vol% or more and 30 vol% or less, a content ratio of the alcohol is 20 vol% or more and 80 vol% or less, and a total content ratio of the carboxylic acid and the basic organic solvent is 10 vol% or more and 50 vol% or less.

9. A step of preparing a raw material solution according to any one of claims 1 to 3; applying the raw material solution onto a substrate and drying the same to form a coating film; a step of heating the coating film to thermally decompose the rare earth carboxylate, the barium carboxylate, and the copper carboxylate in the coating film and remove organic components to form a calcined film; and heating the calcined film to crystallize it, thereby forming an oxide superconducting material.

10. 10. The method for producing an oxide superconducting material according to claim 9, further comprising the step of filtering the raw material solution after the step of preparing the raw material solution and before the step of forming the coating film.

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