JPH02263709A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having a desired critical temp. with high work efficiency by dissolving org. monocarboxylates or hydroxides of the constituent elements of the oxide superconductor with the exception of oxygen in org. monocarboxylic acid, applying the resulting soln. to a base material and carrying out sintering. CONSTITUTION:Org. monocarboxylates or hydroxides of the constituent elements of an oxide superconductor such as a Y-Ba-Cu-O type oxide superconductor with the exception of oxygen are dissolved in org. monocarboxylic acid such as acetic acid or propionic acid. The mono-carboxylates may be yttrium acetate, barium acetate and copper acetate. The hydroxides may be yttrium hydroxide, barium hydroxide and copper hydroxide. The resulting soln. is applied to a base material and sintering is carried out to obtain the oxide superconductor. Since the soln. does not deteriorate with the lapse of time, is easy to handle, has satisfactory film forming property and can be applied to the base material by brush coating, the oxide superconductor can easily be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing an oxide superconductor, and more particularly to a novel method for producing an oxide superconductor thin film by a sol-gel method.

[Conventional technology]

The method for manufacturing oxide superconductor thin films using the sol-gel method is generally simpler than the PVD or CVD methods, and it is easier to produce films with uniform composition at the molecular level, or it is possible to form films with uniform thickness over a large area. There are advantages such as:

The following methods are conventionally known as methods for producing oxide superconductors using the sol-gel method.

(1,) A method using a carboxylic acid aqueous solution of an organic carboxylate of an element constituting an oxide superconductor (excluding oxygen; such elements excluding oxygen are hereinafter simply referred to as constituent elements); (2) Configuration (3) A method using an aqueous inorganic acid solution of an inorganic acid salt of a constituent element.

However, method (1) requires very strict control of the pH of the solution, and if this control is insufficient, some organic carboxylates of the constituent elements may precipitate during the solution application process. There are problems in that it is difficult to obtain a superconductor exhibiting the desired Tc, and in method (2), the alkoxide used as a raw material is expensive, and method (3) is more expensive than method (1) above. Abnormal precipitation of the constituent elemental inorganic acid salts tends to occur, which makes it difficult to obtain a superconductor exhibiting a desired Tc due to microscopic compositional variations in the superconductor.

[Problem to be solved by the invention]

The problem to be solved by the present invention is to overcome the difficulties encountered in conventional methods for obtaining oxide superconductors.

[Means to solve the problem]

This problem is solved by using an organic monocarboxylic acid instead of the aqueous carboxylic acid solution used in the method fl) above.

That is, in the present invention, an organic monocarboxylic acid salt or hydroxide of a constituent element is used as a solute, an organic monocarboxylic acid is used as a solvent, an organic monocarboxylic acid solution of the solute is applied to a substrate, and then sintering is performed. This is a method for producing an oxide superconductor, characterized in that the oxide superconductor is bonded.

[Function and structure of the invention]

In the present invention, the organic monocarboxylic acid itself is used as a solvent in place of the conventionally used aqueous carboxylic acid solution. As a result, the problem of adjusting the pH of the solution that occurred in method <1) and the problem of precipitation of some of the organic carboxylates of the constituent elements during the coating process of the solution are resolved, and the desired result is solved. A superconductor exhibiting Tc can be easily obtained.

In the present invention, an oxide superconductor that can have a perovskite three-dimensional crystal structure and exhibits superconducting properties, such as Re-Ba-Cu-0 (where Re represents a rare earth element, Among the rare earth elements, yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium are particularly preferred.
-Ca-Cu-0, Tl-Ba-CaCu-0, etc. are to be manufactured. The constituent elements of these superconductors are used as monocarboxylic acid salts or hydroxides. Examples of the organic monocarboxylic acid in this case include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, and those having more carbon atoms.

Organic monocarboxylic acids as solvents include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid,
Alternatively, those having more carbon atoms can be exemplified.

In the present invention, as described later, an organic monocarboxylic acid solution of an organic monocarboxylate or hydroxide of a constituent element is applied to a base material, and in a preferred embodiment, it is then dried and heated at about 200 to 900 °C. Heat treatment is carried out at high temperature and finally sintering. In this drying and heat treatment process, it is preferable that the solvent evaporates and scatters rather than thermally decomposes. This is because the solvent used has a high boiling point. This is because carbon is more likely to scatter due to thermal decomposition rather than evaporation, and carbon tends to remain during thermal decomposition, which tends to have an adverse effect on superconducting properties. On the other hand, when an organic monocarboxylic acid salt of a constituent element is used as a solute, it is conceivable that the organic monocarboxylic acid group of the salt and the organic monocarboxylic acid of the solvent are partially or completely substituted.

Therefore, in the present invention, the organic monocarboxylic acid used to produce the salt of the constituent elements and the organic monocarboxylic acid used as the solvent may be the same or different, but both may be applied to the base material. Low-molecular compounds that evaporate and scatter during the drying process and heat treatment process of the resulting solution layer, especially those with carbon numbers of 10 or less, particularly 7 or less, that are liquid at room temperature are preferred.However, the salts of each constituent element may contain two or more organic mixed salts of carboxylic acids,
Furthermore, it may be a mixed salt with a hydroxide, and the organic monocarboxylic acid as a solvent may also be a mixture of two or more types.As mentioned above, the organic monocarboxylic acid is not used as an aqueous solution, but as a solvent. It can be used as such, but it can also contain a small amount of water as an impurity, on the order of less than 5% by weight. In addition, organic monocarboxylic acid salts of constituent elements,
The hydroxide may contain water of crystallization.

Regarding the amount ratio of the salts of each constituent element dissolved in the organic monocarboxylic acid solvent, it is preferable that the molar ratio between the constituent elements matches the molar ratio in the desired superconductor.For example, Re+-Ha, -Cus. -0, the salt is added so that the ratio of Re (if it consists of two or more rare earth elements, the total amount):Ba:Cu dissolved in the organic monocarboxylic acid solvent is 11:3. Measure and dissolve the amount ratio. As long as the salts of each constituent element dissolve well in the organic monocarboxylic acid,
There is no particular limit to its concentration, but the monocarboxylic acid 10
0mj! from 10-' to 10'' mole, especially from 10-3 to
About 5 x 10-' moles are preferred.

In the present invention, the base material to which the organic monocarboxylic acid solution is applied is made of a heat-resistant material that can withstand the sintering temperature of the superconductor and has various shapes. For example, MgO1
Ceramics such as SrTiOz, stainless steel, platinum, gold,
These are plates, wires, tapes, etc. made of high melting point metals such as copper and tungsten. The organic monocarboxylic acid solution can be applied to the surface of the substrate by various methods such as dip coating, spin cording, brush coating, and applicator coating.

The monocarboxylic acid solution applied to the substrate may be immediately subjected to a sintering process, but it may also be subjected to a drying process at room temperature to mild heating, followed by a drying process at 200 to 900°C, especially 350 to 80°C.
Sintering is preferably carried out after a heat treatment step at 0° C. for about 10 minutes to 10 hours, preferably about 20 to 5 hours.

Further, the drying step is preferably accompanied by vacuum drying, the heat treatment step is preferably performed in an atmosphere of air, nitrogen, argon, helium, etc., and the sintering step is performed in an oxygen atmosphere.
It is preferable to carry out at 90 to 960°C. Further, after the sintering step, it is preferable to anneal at 300 to 500° C. for about 30 minutes to 10 hours.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.

Example 1 0.0 to 100 ml of pure propionic acid heated to 80°C
0.07 mol of yttrium acetate, 0.014 mol of barium acetate, and 0.021 mol of copper acetate were each dissolved to obtain a homogeneous solution of pure propionic acid. 2 in this solution
An MgO polycrystalline substrate of 0 mm square and 0.5 mm thick was dipped and pulled up at a speed of 0.2 m/sec to apply a propionic acid solution onto the substrate. Let the paint film dry naturally for 1 hour, and
．． Vacuum heat drying at 1 Torr and 150°C for 1 hour, then heat treatment at 450°C for 1 hour to form a coating (gel)
was thermally decomposed.

After repeating the above dip coating, drying, and heat treatment 5 times, heating at 950°C for 30 minutes in an oxygen atmosphere, then 4
Heating was performed at 00°C for 5 hours to form yl-Bat-Cus-O.
A superconducting film with a thickness of 1.5 μm consisting of a single phase of MgO
It was formed on the surface of a polycrystalline substrate.

As a result of measuring the electrical resistance of the film using the four-terminal method in the temperature range from room temperature to 60K, T c (onset)
was 91 K and T c (end) was 84.

Comparative Example 1 Y
-Baz-Cu3-0, thickness 1.5 consisting of a single phase
A superconducting film of μ steel was formed on the surface of an MgO polycrystalline substrate.

Its T c (on 5et) is 70, Tc (end
) was below 60.

Example 2 0.007 mol of yttrium hydroxide, 0.014 mol of barium hydroxide, and 0.007 mol of yttrium hydroxide were added to 100 mj+ of a pure acetic acid-pure brobionic acid mixture (concentration of pure acetic acid: 10% by weight) heated to 90°C. 0.21 moles of copper hydroxide were dissolved in each to obtain a homogeneous solution. This solution was spin-coated onto a 20 mm square, 0.5 mm thick MgO polycrystalline substrate rotating at 2000 rpm. The W1 membrane was naturally dried for 1 hour, and
Vacuum heat drying at 1 Torr and 150°C for 1 hour, followed by heat treatment at 450°C for 1 hour to form a coating (gel).
was thermally decomposed.

After repeating the above spin cord, drying, and heat treatment 7 times, it was heated at 950°C for 30 minutes in an oxygen atmosphere, and then heated at 950°C for 40 minutes.
Heating was performed at 0° C. for 5 hours to form a superconducting film with a thickness of 1.7 μI consisting of a single phase of Y-Bat-Cu3-Oy on the surface of the MgO polycrystalline substrate.

As a result of measuring the electrical resistance of the film using the four-terminal method in the temperature range from room temperature to 60K, T c (onset)
was 93 K and T c (end) was 84.

Comparative Example 2 100ml of 10% by weight gluconic acid aqueous solution heated to 50°C
l, 0.01 mol of yttrium propionate, 0.01 mol of yttrium propionate,
0.02 mol of barium propionate and 0.03 mol of copper propionate were each melted to obtain a homogeneous solution. Using this solution, spin code, drying, and heat treatment were repeated 12 times in the same manner as in Example 2, followed by heating at 950°C for 30 minutes in an oxygen atmosphere, and then heating at 400°C for 5 minutes.
A superconducting film having a thickness of 1.7 μm consisting of a single phase of 'l-Ba-Cu2-0y was formed on the surface of the MgO polycrystalline substrate by heating for a certain period of time. 'l' c (on
5et) was 73 K, and T c (end) was less than 60.

Example 3 Instead of 0.007 mol of yttrium acetate, 0.00
A 1.8μ thick superconducting film consisting of a single phase of Ho1-Bag-Cu2-Oy was formed on the surface of an MgO polycrystalline substrate in the same manner as in Example 1 except that 7 mol of holmium acetate was used. .

As a result of measuring the electrical resistance of the film using the four-terminal method in the temperature range from room temperature to 60K, T c (onset)
was 91 K and T c (end) was 87.

Example 4 0.007 mole of yttrium hydroxide was replaced with 0.00 mole of yttrium hydroxide.
A superconducting film with a thickness of 1.9 μm and width consisting of a single phase of Ho+-Bat-Cuz-Oy was formed on the surface of an MgO polycrystalline substrate in the same manner as in Example 2 except that 7 mol of holmium hydroxide was used. did.

As a result of measuring the electrical resistance of the film using the four-terminal method in the temperature range from room temperature to 60K, T c (onset)
was 91 K and T c (end) was 86.

Examples 5 to 21, Comparative Examples 3 to 7 Conducted by changing the type, temperature, amount of solvent, type and amount of solute, method of coating on MgO polycrystalline substrate, number of times of coating, etc. as shown in Table 1. The superconducting film was formed using MgO in the same manner as in Examples 1 to 4.
It was formed on the surface of a polycrystalline substrate. The same table includes the ultra@, the film thickness of the conductive film, and the 'l' c (on
5et) and 'l' c (end) values are also shown. Note that DC and SC in the coating method in the same table represent dip coat and spin code, respectively.

Margin below C] 〔Effect of the invention〕 The present invention has the following excellent effects.

(1) The organic monocarboxylic acid solution used in the present invention has less deterioration over time than conventional solutions and is easy to handle.

(2) The organic monocarboxylic acid solution also has good film-forming properties and can be applied to the substrate by various methods such as dip coating, spin cording, brush coating, and applicator coating. Furthermore, coating can be performed over a wide temperature range and concentration range, and therefore gelation of the coating film can proceed over a wide temperature range and concentration range.

(3) Furthermore, when an aqueous solution of an organic monocarboxylic acid is used as a solvent, there is no need to adjust the pH, which is particularly required when an acetic acid aqueous solution is used.

that's all

Claims (2)

[Claims] (1) An organic monocarboxylic acid solution of an organic monocarboxylate or hydroxide of an element constituting the oxide superconductor (excluding oxygen) is applied to a base material, and then sintered. Method for manufacturing oxide superconductor. (2) The oxide superconductor is Re_1_-Ba_2_-Cu
_3_-O_y (here, Re is at least one or two or more selected from the group consisting of yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium). A method for producing an oxide superconductor according to claim 1.