JPH05229822A - Production of oxide superconducting film - Google Patents

Abstract

PURPOSE:To prevent the generation of foam in a superconducting film by forming a raw material solution layer for a superconducting film on a substrate, drying to obtain a gel layer and irradiating with infrared pulses, thereby effecting stepwise thermal degradation from the surface of the gel layer toward the inner layers. CONSTITUTION:Organometallic compounds to be used as raw materials such as yttrium acetate, barium acetate and copper acetate, etc., are dissolved in an organic solvent (e.g. hot propionic acid) at molar ratios corresponding to the composition of an oxide superconductor such as Re-Ba-Cu-0 superconductor (Re is rare earth element). A substrate such as a polycrystalline MgO is immersed in the solvent solution and pulled out of the solution to form a solution layer on the substrate. The layer is dried in vacuum and the obtained gel layer is irradiated with a prescribed number of infrared pulses to effect the stepwise thermal degradation of the gel layer from the surface toward the inner layer at 200-900 deg.C. The generation of gas in the layer is suppressed by this process. The decomposed product is sintered at 800-960 deg.C in O2 atmosphere and annealed at 300-600 deg.C to obtain an oxide superconducting film having excellent superconducting characteristics.

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 an oxide superconducting film, and more particularly to a method for producing an oxide superconducting film by a sol-gel method. There is a so-called sol-gel method as one of the manufacturing methods of the oxide superconductor. The basis of this method is to gel the sol of a raw material, an organometallic compound, which is to form an oxide superconductor, and heat the resulting gel to thermally decompose the organometallic compound to obtain a predetermined superconductor composition. .. The method for producing an oxide superconducting film by the sol-gel method is generally simpler than the PVD method or the CVD method, and the film composition is likely to be uniform at the molecular level, or a uniform film thickness and a large area are formed. There are advantages such as possible film formation.

The following methods are conventionally known as methods for producing an oxide superconducting film by the sol-gel method. (1) A method of using a carboxylic acid solution of an organic carboxylic acid salt of an element forming an oxide superconducting film (excluding oxygen. Such an element except oxygen is simply referred to as a constituent element below), (2) Structure A method of using an organic solvent solution of an alkoxide of an element, and (3) a method of using a water-soluble chelate solution of constituent elements. In any of the methods, each of the above-mentioned solutions is applied to a substrate, dried and heated to cause thermal decomposition, and then sintered.

However, in these methods, when the solution is applied to the substrate and dried and then heated, foaming often occurs, and particularly when the solution is applied as a thick film, the foaming tends to occur, which not only adversely affects the superconducting properties. However, it is difficult to obtain a homogeneous sintered body. This foaming tends to occur more markedly when the heating is rapidly performed, and there is a problem in controlling the heating operation.

[0004]

The problem to be solved by the present invention is to solve the above-mentioned conventional problems in the method for producing an oxide superconducting film by the sol-gel method, in other words, to form a gel layer. To reduce or substantially eliminate foaming during subsequent heating.

[0005]

This object is to heat by irradiating infrared rays as a means for heating in the above-mentioned methods (1) and (3), more preferably by pulsing the infrared rays. It is solved by irradiating the particles in a uniform manner and gradually causing thermal decomposition toward the inside from the surface layer of the gel layer applied on the substrate.

[0006]

In the present invention, a means of infrared irradiation is particularly adopted as the heating means, and the irradiation is carried out in order from the surface layer of the gel layer formed by arranging the irradiation at a constant pulse interval. Since thermal decomposition can be performed toward the inner layer, foaming can be prevented in advance.

According to the research by the present inventor, in the method for producing an oxide superconducting film by this kind of sol-gel method, the gel layer formed by applying it to the substrate is dried and heated to be thermally decomposed. When sintered, a gas due to thermal decomposition, such as CO ₂ or hydrocarbon, is generated from the inside of the gel layer, while the surface portion is heated to form a film, and it is difficult for the gas to volatilize to the outside, which causes foaming. Was found. It was also found that the thicker the gel layer, the more likely it is that foaming will occur as the gel layer is heated more rapidly.

On the other hand, in the present invention, the surface of the gel layer is irradiated with infrared rays, and only the surface portion is first heated to complete the thermal decomposition of this portion, and then only the next layer is similarly heated, Since this is sequentially irradiated with infrared rays in a pulsed manner toward the inner layer, the gas generated by thermal decomposition is only the part irradiated with the infrared rays, and it is possible to prevent the generation of gas from the inside, and finally The entire layer will be pyrolyzed without successful foaming.

In the present invention, the interval of infrared pulse irradiation is adjusted, for example, as shown in FIG. 1, so that the undecomposed layer l ₃ is not heated during heating of the layer l ₂ during thermal decomposition. Note that FIG. 1 exemplifies a case where the gel layer is divided into three layers of l ₁ , l ₂ , and l ₃ for the sake of convenience and infrared rays are sequentially irradiated in a pulsed manner to perform thermal decomposition. Then l ₁
Indicates a layer whose thermal decomposition has already been completed. Therefore, the pulse interval varies depending on the thickness of the gel layer and how many layers the layer is divided into, and the interval may be appropriately selected so that the undecomposed layer is not substantially heated. However, in FIG. 1, (a) is before pyrolysis, (b) is after the _first pulse (only l ₁ is pyrolyzed),
(C) shows after the second pulse (only ₁ and l ₂ are thermally decomposed), (1) shows the gel film, and (2) shows the substrate.

The infrared ray may be one having a wavelength in the range usually called infrared ray, and the irradiation means may be any means capable of irradiating the infrared light in a pulsed manner. The output of infrared rays is not particularly limited as long as the gel layer can be thermally decomposed at a predetermined portion.

In the present invention, an oxide superconductor having a perovskite type crystal structure and exhibiting superconducting properties, for example, Re-Ba-Cu-O (wherein Re represents a rare earth element, one or two thereof). Among the rare earth elements, yttrium, lanthanum, neodymium, samarium, europium, gadolinium, dysprosium, holmium, erpium, thulium, ytterpium, and lutecium are preferable.), Bi-Pb-Sr-C.
A-Cu-O, Tl-Ba-Ca-Cu-O, etc. are targeted for production. The constituent elements of those superconductors are used as a carboxylic acid solution of an organic carboxylic acid salt, an organic solvent solution of an alkoxide of the element, or a chelate aqueous solution of the element, that is, according to any one of the above methods (1) to (3). .. In any of these cases, those conventionally known can be widely used in the present invention. Particularly in the present invention, the case where the constituent element is an organic metal compound, that is, an organic carboxylate is preferable.

In the present invention, a solution of the constituent elements is applied to the base material as described below, and in a preferred embodiment, it is dried, pyrolyzed at a temperature of about 200 to 600 ° C., and finally sintered. More specifically, the gel layer applied to the substrate is subjected to a drying step under normal temperature to mild heating, then 200 to 900 ° C., particularly
It is preferable to perform a thermal decomposition step at 350 to 800 ° C. for about 10 minutes to 2 hours, preferably about 20 minutes to 1 hour before sintering. Further, the drying step is preferably accompanied by vacuum drying, and the sintering step is preferably performed in an oxygen atmosphere at 800 to 960 ° C. Further, it is preferable to anneal at 300 to 600 ° C. for about 30 minutes to 10 hours after the sintering step.

The amount ratio of the salt of each constituent element to be dissolved in a predetermined solvent may be the same as the molar ratio between constituent elements. For example, when producing Y ₁ Ba ₂ Cu ₃ O _Y ,
The molar ratio of Y: Ba: Cu dissolved in the solvent is 1: 2: 3.
The amount ratio of salt is measured and dissolved so that The concentration of each of the constituent elements is not particularly limited as long as it dissolves well in the solvent, but 10 ^-3 to 10 ^-1 mol, especially 10 ^-2 mol, per 100 ml of the solvent.
It is preferably about 10 ^-1 mol.

As the base material to which the solution is applied in the present invention, various shapes made of a heat-resistant material capable of withstanding the sintering temperature of the superconducting film are used. For example, MgO, SrTiO
Ceramics such as ₃ and silver and silver alloy plates, wires, tapes, etc. The organic monocarboxylic acid solution can be applied to the surface of such a substrate by various methods such as dip coating, spin coating, brush coating, and applicator coating.

[0015]

The present invention will be described in more detail with reference to the following examples. Example 1 0.05 mol of yttrium acetate, 0.1 mol of barium acetate, and 0.15 mol of copper acetate were dissolved in 100 ml of propionic acid heated to 80 ° C., and cooled to room temperature to obtain a uniform solution of propionate. It was This solution is 20mm square, thickness 0.5
A MgO polycrystalline substrate of mm was dipped, and the solution was applied onto the substrate by pulling it up at a speed of 0.2 m / sec. The coating film was naturally dried for 1 hour, and vacuum-dried for 1 hour at 0.1 Torr and 150 ° C. The dry film thickness was 10 μm. This coating film was divided into 10 times, and infrared rays (wavelength: l ₁ to l ₁₀ , l ₃ layers)
0.7 to 4 μm) was irradiated for 10 seconds in a pulsed manner with an output of 100 W. The interval between irradiations was 60 seconds. During this time, while irradiating l ₁ , l ₂ to l ₁₀ could be similarly performed, and thermal decomposition could be performed as a whole without foaming. After completion of the above dip coating, drying and thermal decomposition treatment, heating at 950 ° C. for 120 minutes in an oxygen atmosphere and then at 400 ° C. for 5 hours is performed to form a single phase of Y ₁ Ba ₂ Cu ₃ O _Y. It
A 3.1 μm superconducting film was formed on the surface of the MgO polycrystalline substrate. As a result of measuring the electric resistance of the film by the 4-terminal method in the temperature range from room temperature to 60 K, Tc (on set) was 91.
The K and Tc (end) were 82K.

Example 2 H 2 was prepared in the same manner as in Example 1 except that 0.05 mol of holmium acetate was used instead of 0.05 mol of yttrium acetate.
A 3.5 μm-thick superconducting film composed of a single phase of o ₁ Ba ₂ Cu ₃ O _Y was formed on the surface of the MgO polycrystalline substrate. From room temperature to 6
As a result of measuring the electric resistance of the film by the 4-terminal method in the temperature range up to 0 K, Tc (on set) was 91 K and Tc (end) was 83 K.

Example 3 A single-phase thickness of Ho ₁ Ba ₂ Cu ₃ O _Y was prepared in the same manner as in Example 2 except that 0.05 mol of holmium hydroxide was used instead of 0.05 mol of yttrium hydroxide. A 3.7 μm superconducting film was formed on the surface of the MgO polycrystalline substrate. As a result of measuring the electric resistance of the film by the four-terminal method in the temperature range from room temperature to 60K, Tc (on set) was 91K, Tc (end)
Was 83K.

Comparative Examples 1 to 3 In each of the above Examples 1 to 3, the thermal decomposition step was carried out at 500 ° C.
It heated on the condition of 30 minutes, and everything else was processed like Example 1-3. Foaming was recognized in the obtained superconducting film, and the respective characteristics were as follows.

[0019]

[Table 1]

Example 4 Instead of the carboxylate in Example 1, Y, Ba,
A nitrate of Cu was used, and this was dissolved in an aqueous solution of triethanol to form a chelate solution, and otherwise the same as in Example 1. A good superconducting film could be obtained without foaming. Tc
(on set) was 90K and Tc (end) was 82K.

Example 5 The same procedure as in Example 1 was carried out except that the irradiation of infrared rays was carried out under the following conditions in Example 1. A good superconducting film could be obtained without foaming. (Infrared irradiation condition) Interval: 10 seconds Film thickness: 20 μm Number of pulse intervals: 20 seconds

[0022]

According to the method of the present invention, a superconducting film based on the sol-gel method can be easily produced by a simple operation without any foaming, and a superconducting film having excellent superconducting properties can be industrially advantageously produced. It is possible, and the industrial effect is extremely large.

[0023]

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram when the method of the present invention is applied.

Claims (1)

[Claims] 1. A method for producing a superconducting film by a sol-gel method, wherein a solvent solution of a raw material organic or inorganic metal compound for forming a superconducting film is applied to a substrate to form a solvent solution layer on the substrate. When the above-mentioned compound is pyrolyzed by heating it after forming a gel layer by drying, the pyrolysis is radiated with infrared rays in a pulsed manner and the pyrolysis step by step from the surface of the gel layer toward the inner layer. A method for producing an oxide superconducting film, which comprises: