JPH0710732B2 - Superconductor manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superconductor composed of a noble metal and a superconducting composite metal oxide composed of barium, a rare earth metal and copper.

[0002]

2. Description of the Related Art In order to obtain a superconducting composite metal oxide film (hereinafter also referred to as a superconducting film), a solution containing organic acid salts of barium, a rare earth element and copper, an alkoxide or a chelate compound is prepared. , This solution is applied to the surface of a support and calcined in air at about 500 ° C. to preliminarily form an inorganic film composed of barium carbonate, a rare earth element oxide and a copper oxide on the surface of a substrate, and then air or A method of performing main firing at a temperature higher than 900 ° C. in oxygen is known. In addition, after forming a noble metal film in advance on the surface of the base material in order to stabilize the superconductivity of the composite metal oxide and / or suppress the reaction between the superconducting composite metal oxide and the base material, the superconductivity is increased by the above method. A method of manufacturing a composite metal oxide film is also known. The composite metal oxide film thus formed on the surface of the substrate exhibits superconductivity at a relatively high critical temperature, but since the temperature higher than 900 ° C. is used for the main firing, the composite metal oxide film and the substrate and / or Alternatively, the reaction with the noble metal film causes deterioration of the superconductor film, and the net amount of the composite metal oxide film that gives superconductivity decreases, and the current density (J
There is a problem that c) is lowered. On the other hand, if the main firing temperature is lowered to prevent the reaction between the superconductor film and the base material and / or the noble metal, in this case, the thermal decomposition of barium carbonate is difficult to proceed, and the composite metal formed on the base material This causes a problem that the superconducting property of the oxide is significantly impaired.

Further, the high Jc of superconductors, improvement of mechanical properties (tensile stress, bending stress) and environmental resistance (H ₂ O
In order to improve (durability against CO ₂ and CO ₂ ), a noble metal is compounded with a superconductor. The complexing of the noble metal can be performed by mixing the noble metal powder with the superconductor powder, applying the mixture to the base material, and heating the mixture to 900 ° C. or more to sinter the powder. It is difficult to mix and uniformly perform the heating, and since the heating temperature is 900 ° C. or higher, the superconductor is deteriorated due to the reaction of the superconductor with the base material, which causes a problem that the superconducting property is deteriorated.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above problems found in the prior art and provides a method for producing a noble metal composite superconductor having a high critical temperature indicating superconductivity and a high current density in the superconducting state. is there.

[0005]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, according to the present invention,
An inorganic film composed of (1) barium carbonate, (2) rare earth metal oxide, (3) copper oxide, and (4) noble metal and / or its oxide in an inert gas atmosphere with an oxygen concentration of 1 vol% or less, or Carbon dioxide gas is removed from barium carbonate contained in the film by baking at a temperature at which the partial pressure of oxygen is 0.01 atm (absolute pressure) or less and the reaction between the film and the base material is not substantially caused. While reacting barium carbonate, a rare earth metal oxide and a copper oxide, barium, a rare earth metal and a metal oxide are further oxidized by molecular oxygen at a temperature that does not substantially cause a reaction between the film and the substrate. There is provided a method for producing a superconductor, which comprises forming a superconductor film composed of a superconducting composite metal oxide made of copper and a noble metal.

In carrying out the method of the present invention, first, a coating liquid containing a noble metal and a metal for forming a superconducting complex metal oxide composed of barium, a rare earth metal and copper (hereinafter, also simply referred to as SEC metal) is prepared. To do. Examples of the noble metal include silver, gold, platinum, palladium and alloys thereof. Since the SEC metal is preferably present in a state of being dissolved in the coating liquid, it is usually used as a soluble organic compound containing the SEC metal. On the other hand, the noble metal is preferably a soluble organic compound containing a noble metal so as to be dissolved in the coating liquid, but it does not necessarily have to exist in a dissolved state in the coating liquid, and it exists as an insoluble compound or metal fine particles. You can also Examples of the insoluble compound of a noble metal include oxides, and metal fine particles include colloidal particles of gold, silver, platinum, and palladium.

As the soluble organic compound of SEC metal,
Examples thereof include organic acid salts, alkoxides and organic chelate compounds. Examples of soluble organic compounds of noble metals include organic acid salts and organic chelate compounds. Examples of the organic acid salt include naphthenic acid, 2-ethylhexanoic acid, caprylic acid, stearic acid, lauric acid, butyric acid, propionic acid, neodecanoic acid, cyclohexylbutyric acid, acetic acid, trifluoroacetic acid, trichloroacetic acid, oxalic acid, Examples thereof include salts of citric acid, tartaric acid, lactic acid, phenol, catechol, benzoic acid, salicylic acid and the like. Examples of the alkoxide include alcohol alkoxides such as ethanol, propanol, butanol, ethylene glycol and glycerin. Examples of the organic chelate compound include acetylacetonate and EDTA.
When a noble metal is dispersed in the coating solution as an insoluble compound or fine metal particles, the particle size is 5 μm or less, preferably 1 μm.
It is better to be m or less.

The coating solution is produced by dissolving the SEC metal in an organic solvent and dissolving or dispersing the noble metal compound or the noble metal. The SEC metal concentration in the coating solution is not particularly limited, and its upper limit is determined by the solubility of the SEC metal-containing compound, etc.
It is 3 to 40% by weight in terms of C metal-containing compound. Further, a suitable amount of a polymeric substance or the like can be added to this solution as an auxiliary component.

Any solvent can be used as long as it can dissolve the above-mentioned SEC metal-containing compound, and various solvents can be used alone or in the form of a mixture. Examples of such a solvent include hydrocarbons such as hexane, octane, benzene, toluene and tetralin, alcohols such as methanol, ethanol, propanol, butanol, amyl alcohol, ethylene glycol and glycerin, acetone, methyl ethyl ketone and acetylacetone. Ketones, ethers such as dibutyl ether, aldehydes such as acetaldehyde and benzaldehyde, formic acid, acetic acid, propionic acid, butyric acid, caprylic acid, lauric acid, stearic acid, naphthenic acid, linoleic acid, oleic acid, oxalic acid, citric acid Acids, lactic acid, organic acids such as phenol and p-toluic acid, esters such as butyl butyrate, amines such as dimethylamine and aniline, formami such as N-methylacetamide, formamide and dimethylformamide. Examples include amides such as amide derivatives, sulfur-containing compounds such as dimethyl sulfoxide, chlorine-containing compounds such as chloroform and carbon tetrachloride, pyridine derivatives such as pyridine, methylpyridine, vinylpyridine, and heterocyclic substances such as furfural. it can. These solvents are appropriately selected as one kind or a combination of two or more kinds according to the kind of the SEC metal-containing compound used specifically. These solvents can be used at high temperature or after solvent substitution, if necessary.

The preferred coating liquid according to the present invention is exemplified below in connection with the SEC metal-containing compound. (1) SEC Metal Alkoxide-Containing Solution In the case of this solution, it is preferable to use a solvent containing an organic acid, pyridine or a derivative thereof, or a mixture thereof so that the SEC metal alkoxide can be stably dissolved. The solvent may be formed only from those compounds, or the compounds and other solvents such as ethanol,
It can be formed from a mixture with alcohols and ketones such as butanol, acetone and the like. In this case, examples of the organic acid include formic acid, acetic acid, propionic acid, butyric acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, and the like, and examples of the pyridine derivative include methylpyridine, vinylpyridine, and the like.

(2) Solution containing SEC metal acetylacetonate or its derivative In the case of this solution, the SEC metal salt of SEC metal acetylacetonate or acetylacetone derivative [CH ₃ COCH ₂ COR (R: organic group)] is stable. As in the case of the SEC metal alkoxide-containing solution, it is preferable to use a solvent containing an organic acid or pyridine or a derivative thereof or a mixture thereof so as to be dissolved. These solvents may be mixed solvents with other solvents, for example, alcohols and ketones such as methanol, ethanol, butanol, and acetone, if necessary, and solvents formed by solvent substitution using these solvents. Can be In this case, examples of the organic acid and the pyridine derivative include those shown for the SEC metal alkoxide solution. (3) SEC metal organic acid salt In the case of this solution, various solvents are used, for example,
Organic acids, alcohols, ketones, hydrocarbons and the like are used.

As described above, the composition of the SEC metal species in the coating solution used in the present invention may be selected so as to correspond to the SEC metal composite oxide exhibiting superconductivity. For example, it can be selected so as to correspond to the superconducting composite metal oxide represented by the following composition formula (I). ABa ₂ Cu ₃ Oy (I) (In the formula, A is a rare earth metal, for example, Y, La, Nd, Sm, E
u, Gd, Dy, Ho, Er, Yb, Lu or a mixture of two or more thereof is used. (y is 7-x, and x is a number in the range -1 <x <1)

Further, in the case where the SEC source metal-containing compound causes a composition change due to sublimation or evaporation, the composition of the SEC metal species corrected so that a superconducting composite metal oxide is formed can be selected. The amount of precious metal in the coating liquid is
Atomic ratio M / A to rare earth metal contained in coating liquid
(M: number of noble metal atoms, A: number of rare earth metal atoms)
It is 0.05 to 1, preferably 0.1 to 0.5.

In order to obtain a superconductor film according to the present invention, a coating solution is applied on a substrate to form a coating film, which is then dried, calcined, calcined and then oxidized. Next, each of these steps will be described in detail.

[Coating Process of Coating Liquid] This process is a process of coating the coating liquid on a substrate to form a coating film containing a SEC metal and a noble metal. In this case, as the coating method, conventionally known methods, for example, various methods such as a dipping method, a spin coating method, a spraying method and a brush coating method can be used. As the base material, various materials and shapes can be used. In this case, examples of the material include metals such as copper, titanium, nickel, gold, and silver, silica, alumina, and yttria-stabilized zirconia (YS).
Z), titania, LaAlO ₃ , SrTiO ₃ , metal oxides / complex metal oxides such as sapphire, ceramics such as silicon carbide and graphite, and their shapes are
It can be used regardless of whether it is a curved surface or a flat surface.
Any shape such as a coil shape, a fibrous shape, a knitted or woven cloth shape, or a tubular shape is adopted. The support may be porous. When the base material is ceramics, a metal film, particularly a noble metal film, can be previously formed on the surface thereof.

[Drying Step] The coating film formed on the substrate as described above is dried at room temperature or under heating under atmospheric pressure or reduced pressure. Since the drying can be completed in the initial stage of the calcination step that follows this drying step, it is not necessary to completely dry the coating film in this drying step. Further, since the subsequent calcination step can also be used as a drying step, this drying step can be omitted.

[Calcination step] In this step, the coating film formed on the substrate as described above is heated and baked, and the coating film is
(1) barium carbonate, (2) rare earth metal oxide, (3)
It is a step of converting into a film made of copper oxide and (4) noble metal and / or its oxide. The firing temperature is 400
Temperatures of ~ 700 ° C, preferably 500-600 ° C are employed.
As the firing atmosphere, an atmosphere of air, oxygen, nitrogen, argon or the like is adopted. In addition, this firing step can also be performed in vacuum or reduced pressure. Furthermore, this baking step can also be performed by spraying the coating liquid on a substrate that has been heated in advance. In this case, the coating process of the coating liquid described above is omitted.

[Main firing step] In this step, the inorganic film formed in the calcination step is fired to remove carbon dioxide gas from barium carbonate, and at the same time, the barium carbonate is allowed to react with the rare earth metal oxide and the copper oxide. It is a process. In the present invention, this firing step is performed under the condition that the oxygen concentration in the atmosphere is 1% (Vol%) or less, preferably 0.005-1%. The oxygen concentration of 1% or less can be formed by using an inert gas. The firing step can also be performed under a reduced pressure (under vacuum) of oxygen partial pressure of 0.01 atm (absolute pressure) or less, preferably 0.00005-0.01 atm. By adopting such firing conditions, decomposition of barium carbonate in the film formed in the calcination step is promoted and a composite metal oxide is formed. Further, in this firing step, since the conditions of low oxygen concentration or low oxygen partial pressure are adopted as described above,
Since the decomposition of barium carbonate can be carried out smoothly at a lowered temperature, the reaction between the base material and the composite metal oxide can be substantially avoided. A general firing temperature in this step is 700 to 900 ° C. The above-mentioned firing conditions in the present invention can substantially prevent the reaction between the base material and the composite metal oxide, which has been conventionally observed.

[Oxidation Step] This step is a step of oxidizing the composite metal oxide formed in the main firing step using molecular oxygen to obtain a superconducting composite metal oxide. In the main firing step, since the oxygen concentration in the atmosphere was kept at 1% or less or the oxygen partial pressure was kept at 0.01 atm or less, the superconducting characteristics of the obtained composite metal oxide are unsatisfactory, but the superconducting characteristics due to this oxidation step It can be converted into excellent mixed metal oxides. Pure oxygen or air is used as the molecular oxygen. When air is used as the oxidizer, carbon dioxide contained therein adversely affects the superconducting properties of the film, so the concentration of carbon dioxide in the air is
It is preferable to adjust to 10 ppm or less, preferably 5 ppm or less by decarboxylation. This oxidation step can be carried out at moderately high temperatures to substantially avoid the reaction between the substrate and the composite metal oxide. The temperature of this oxidation step is generally 400
~ 900 ° C. When carrying out the method of the present invention, the calcination step, the main firing step and the oxidation step can be continuously performed in the same apparatus. According to the method of the present invention, the film thickness is about 100Å to 20 μm, especially 1000Å to 10 μm on the surface of the substrate.
It is possible to form a superconductor film composed of a superconducting composite metal oxide of m and a noble metal. In this case, the film thickness can be controlled by adjusting the metal concentration in the coating liquid, or can be controlled by repeating the above-mentioned coating / calcining process. The noble metal used in the present invention is present as a metal and / or oxide thereof in a dispersed state between the composite metal oxide fine particles forming the superconductor film.

[0021]

In the present invention, the calcination step, the main calcination step and the oxidation step are all carried out while substantially avoiding the reaction between the base material and the composite metal oxide. The composite metal oxide formed above has excellent superconducting properties, and has a high critical temperature (Tc) indicating superconductivity and a large current density (Jc) in the superconducting state.

Further, in the present invention, since the superconducting film contains the evenly dispersed noble metal, there is an advantage that when the superconductor becomes a normal conductor due to magnetic flux escape, current bypass occurs through the noble metal. . Moreover, by using this noble metal, the stress generated when the volumetric shrinkage of the inorganic film occurs due to the thermal decomposition of barium carbonate and the stress caused by the difference in the coefficient of thermal expansion between the superconducting composite metal oxide and the substrate. Is buffered, and a high-quality superconductor can be obtained.

[0023]

EXAMPLES Next, the present invention will be described in more detail by way of examples. Example 1 Barium naphthenate, yttrium naphthenate, copper naphthenate and silver naphthenate were used in a metal atomic ratio of Ba: Y: Cu: Ag.
To 2.0: 1.0: 3.0: X (X = 0.05 to 1.0) to obtain a coating solution (concentration of SEC metal-containing compound: 8% by weight). Next, this coating solution was applied to a plate-like body made of yttria-stabilized zirconia as a base material by spin coating, and then heated in air at a heating rate of 20 ° C. /
The temperature was raised from room temperature to 500 ° C. in minutes, and the temperature was maintained for 30 minutes and then cooled. Applying this coating solution and heating up to 1
Repeated 5 times, an inorganic film (film thickness: 2 μm) made of barium carbonate, yttrium oxide, copper oxide and silver was formed on the substrate. Next, the inorganic film (calcined film) thus formed on the substrate was heated to a baking temperature (main baking temperature) of 750 ° C. in an argon gas atmosphere in which the oxygen concentration was adjusted to 0.01%. After heating up and holding at this temperature for 2 hours,
The atmosphere gas was changed to argon gas in which the oxygen concentration was adjusted to 1%, kept at the same temperature for 0.5 hours, then gradually cooled to 450 ° C. in this atmosphere, the atmosphere gas was changed to oxygen gas again, and at this temperature 2 After holding for a period of time, the product was obtained by gradually cooling to room temperature in an oxygen gas atmosphere. The film formed on the base material in this manner showed that YBa ₂ C
It was confirmed that u ₃ Oy was the main component and Ag was mixed when the added amount X of Ag was 0.5 or more. Next, on the film, silver was vapor-deposited at four places at intervals of about 2 mm to form electrodes,
The electrical resistance was measured by the four probe method from room temperature to 77K. The electrical resistance of the film gradually decreases from room temperature, and
At the critical temperature (Tc) shown in, the electric resistance became zero, and the state of complete superconductivity was observed. The critical current density (Jc) of the film at 77K was determined, and the results are shown in Table 1.

[0024]

[Table 1]

Example 2 In Example 1, X was 0.2 and the substrate was SrTiO _3.
A film obtained in the same manner except that a plate-shaped body consisting of
It showed Tc: 89K and Jc: 800A / cm ² . Example 3 In Example 1, barium, yttrium, copper acetylacetonates, and silver acetate were used, with the metal atomic ratio B thereof.
a: Y: Cu: Ag is 2.0: 1.0: 3.0: 0.2
To obtain a coating solution (concentration of SEC metal-containing compound: 10% by weight), which is dissolved in a mixture of pyridine and propionic acid (volume ratio 5: 3), and applied to a substrate by a dropping method. A film obtained in the same manner except that the liquid coating and heating steps were repeated 8 times had Tc: 89K and Jc: 520A.
/ Cm ² was shown. Example 4 A film obtained in the same manner as in Example 3 except that each of acetylacetonates of barium, yttrium, and copper and silver cyclohexylbutyrate was used had Tc: 88K, Jc:
It showed 420 A / cm ² .

Example 5 In Example 1, fine gold particles (particle size: about 0.1 μm) as an insoluble noble metal were dispersed in a toluene solution of SEC metal naphthenate, and the metal atomic ratio Ba: Y: Cu:
A film composed of YBa ₂ Cu ₃ Ov and Au obtained in the same manner except that Au was adjusted to 2.0: 1.0: 3.0: 0.5 was Tc: 88K, Jc: 460A / It showed cm ² . Example 6 In Example 1, barium naphthenate, holmium naphthenate, copper naphthenate, and silver naphthenate were added at a metal atomic ratio of Ba: Ho: Cu: Ag of 2.0: 1.0: 3.
The coating solution (S
A film composed of HoBa ₂ Cu ₃ Ov and Ag obtained in the same manner except that the concentration of EC metal-containing compound: 8% by weight) was Tc: 89K, Jc: 530A / cm ² . Example 7 In Example 1, barium naphthenate, erbium naphthenate, copper naphthenate and silver naphthenate were added at a metal atomic ratio of Ba: Er: Cu: Ag of 2.0: 1.0: 3.
The coating solution (S
A film composed of ErBa ₂ Cu ₃ Ov and Ag obtained in the same manner except that the concentration of the EC metal-containing compound was 8% by weight, showed Tc: 88K and Jc: 460A / cm ² .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuyoshi Kondo 1-1 Higashi, Tsukuba-shi, Ibaraki Industrial Technology Institute, Institute of Chemical Technology (72) Inventor Susumu Mizuta 1-1-chome, Tsukuba, Ibaraki Industrial Technology In-house (72) Inventor Akira Hamaoka 2-20-5 Shimotani, Taito-ku, Tokyo Masahiro Hiratsuka Examiner, Nippon Kagaku Sangyo Co., Ltd.

Claims (1)

[Claims] 1. An inorganic film formed of (1) barium carbonate, (2) rare earth metal oxide, (3) copper oxide and (4) noble metal and / or its oxide formed on a substrate is treated with oxygen. In an inert gas atmosphere having a concentration of 1 vol% or less, or under a reduced pressure having an oxygen partial pressure of 0.01 atm (absolute pressure) or less, baking is performed at a temperature at which a reaction between the film and the substrate does not substantially occur, After removing carbon dioxide gas from the barium carbonate contained in the film, the barium carbonate was reacted with the rare earth oxide and the copper oxide, and then the reaction between the obtained metal oxide film and the substrate was substantially carried out. A method for producing a superconductor, which comprises forming a superconductor film composed of a noble metal and a superconducting composite metal oxide composed of barium, a rare earth metal and copper by oxidizing with molecular oxygen at a temperature at which it does not occur.