JPH0453817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing oxide superconductors with excellent properties, which have a wide variety of applications in the fields of electronic technology and power technology.

[Prior Art] Niobium-Nb alloys such as Nb ₃ Sn and Nb ₃ Ge are most commonly used as superconducting materials whose electrical resistance becomes zero at extremely low temperatures. However, these Nb
The critical temperature of the alloy is around 20K, and it cannot be used unless it is cooled with liquid helium. Therefore, Nb
Alloys are used in cryoelectronic devices, electromagnets,
When applied to superconducting wires, rotating machines such as generators, transformers, etc., they were used while being cooled with liquid helium.

[Problems to be solved by the invention] However, in conventional superconducting application technology, it is not easy to use elements and magnets because they are cooled with liquid helium, which limits their application and widespread use. There was a problem with this. Another problem was that helium, which is a scarce resource and is expensive, must be used for cooling.

Recently, a number of materials have been discovered that become superconducting at temperatures higher than Nb alloys. For example, in a superconducting material represented by the composition formula (La _1-x Sr _x ) ₂ CuO _4-y ,
The superconducting critical temperature is 50K. Also,
(YBa ₂ ) ₂ Cu ₆ O ₁₄ becomes superconductive at a liquid nitrogen temperature of 90K. However, it is difficult to obtain high-quality oxide superconducting materials such as (YBa ₂ ) ₂ Cu ₆ O ₁₄ because the manufacturing process involves volatilization of metal components. For example, an oxide superconductor is formed by heating in air using an oxalate powder obtained by a coprecipitation method in which an oxalic acid solution is added to a nitrate solution of yttrium, barium, and copper as a starting material. analysis·
FIG. 3 shows the results of simultaneous differential thermal analysis and thermogravimetric analysis using a thermogravimetric analyzer. Curve A in the figure
is the result of differential thermal analysis, and curve B is the result of thermogravimetric analysis.

When oxalate powder is heated, an endothermic reaction occurs up to about 70°C. This is due to the evaporation of the remaining solvent, and the 2% weight loss determined by thermogravimetric analysis is also due to the evaporation of the solvent. The exotherms at about 260°C, about 280°C and about 390°C are exothermic reactions due to decomposition and oxidation of oxalate. However, it has not been determined which of the three peaks corresponds to the formation of yttrium oxide, barium oxide, and copper oxide. 21.4% and 15.6%
The two-stage weight loss corresponds to the change from oxalate to oxide, and the total weight loss of 37% is
This value is quite close to the calculated value assuming that (YB ₂ ) ₂ Cu _{6 O 14 is} formed from YC _{2 O 4 , BaC 2 O 4} and CuC ₂ O ₄ .

Oxides containing yttrium, barium, and copper can be obtained by heating up to around 500°C, but further heating to 750°C to 950°C is required to obtain perovskite-structured oxides that exhibit superconductivity. . In FIG. 3, this process is observed as an endothermic process in curve A, but is accompanied by a weight loss as seen in curve B. This weight loss of up to 9% of the raw material is due to the volatilization of copper and barium oxides.
When an organic acid salt or an oxide carbonate is used as a starting material, an oxide with a perovskite structure can be obtained through a similar process.

For this reason, when a manufactured oxide superconductor is analyzed using, for example, an energy dispersive X-ray analyzer, the composition of the surface layer is different from that of the center layer due to volatilization.
It does not exhibit superconductivity and therefore cannot be a high-quality superconductor. This is particularly important in thin film manufacturing.

A similar problem occurs when an oxide magnetic material is produced by mixing and sintering powders of yttrium oxide, barium carbonate, copper oxide, and the like.

An object of the present invention is to solve the above-mentioned problems and provide a method for obtaining a uniform oxide superconductor with a small composition distribution.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for producing an oxide superconductor, in which an oxide superconductor or an oxide having a composition to become a superconductor, The method is characterized by including a step of heating in an atmosphere containing a metal component constituting the oxide.

[Function] According to the present invention, an oxide superconductor can be manufactured while preventing volatilization of metal components, and therefore a uniform and high-quality oxide superconductor can be obtained.

[Examples] Examples of the present invention will be described below with reference to the drawings.

Example 1 Figure 1 is a flowchart for explaining the process of producing a thin film of oxide superconductor (Y _0.4 Ba _0.6 ) CuO _7-x using copper, barium, and yttrium octylate as starting materials. be.

Thinner solutions or toluene solutions of Cu, Ba and Y octolates, specifically 2-ethylhexylate salts, are prepared. The atomic ratio of the mixture is Cu:Ba:Y=1:0.6:0.4
shall be.

The solution is homogenized, the viscosity is adjusted, and the Ittria-stabilized zirconia plate is immersed in the solution. Alternatively, apply the solution evenly to the Ittria-stabilized zirconia plate with a brush.

Dry in air at room temperature to form a coating.

Heat in an electric furnace at 500℃ for about 15 minutes to oxidize and thermally decompose the coating.

Repeat ~ to produce an oxide with a thickness of 1 to 2 μm.

The yttria-stabilized zirconia plate on which an oxide of a predetermined thickness has been formed is buried in a separately prepared oxide powder containing copper, barium, and yttrium, such as (Y _0.4 Ba _0.6 )CuO ₇ powder.

An oxide thin film buried in oxide powder was heated at 800°C for 5 hours to produce an oxide superconductor thin film.

In this example, the atmosphere was adjusted by embedding a powder of an oxide superconducting material separately produced by a conventional method and embedding it therein. As a result, around the target thin film, the metal components from the powder are released and condensed in other parts, along with the volatilization and condensation from the thin film, and as a result, changes in the composition of the thin film are prevented. . As a result, we were able to obtain a superconducting thin film with a uniform composition without causing any change in the composition between the surface layer and the center.

Note that the composition of the oxide powder for embedding the oxide thin film is preferably the same as the composition of the target superconductor thin film, but it is not necessary that the composition be the same.

In this example, as a superconductor (Y _0.4
Although the description has been given using a Ba _0.6 ) CuO _7-x thin film as an example, it goes without saying that the present invention can be widely applied to the production of oxide superconductors.

In addition, although we have explained a method for producing an oxide superconductor using octylate as a starting material, we can form an oxide with the composition that should become a superconductor by other methods, and then heat it to form an oxide with a perovskite structure. It goes without saying that the present invention is widely applicable to the production of physical superconductors.

Example 2 FIG. 2 shows a process diagram of an example using the sintering method.

Copper oxide, barium carbonate, and yttrium oxide powders are mixed in the desired molar ratio and heated to 800℃~
Calcined at 900℃ for 1 to 5 hours, pressed and molded at a pressure of about 400Kg/ ^cm2 , and heated to 800℃ in an oxygen-containing atmosphere.
C. to 900.degree. C. for 1 to 5 hours and sintered to obtain an oxide superconductor with a perovskite structure. In this step, the sintering step, or the sintering step and the calcination step, are performed in an atmosphere containing copper, barium, and yttrium, for example, in (Y _0.4 Ba _0.6 )CuO ₇ powder.

This operation allows the produced oxide superconductor to have a uniform desired composition.

[Effects of the Invention] As explained above, according to the present invention, an oxide superconductor can be produced without changing its components;
Since it is possible to produce superconductors of high quality and excellent properties, especially thin films thereof, it becomes possible to utilize oxide superconductors in various fields of electronic technology and power technology to fully demonstrate their effects.

[Brief explanation of the drawing]

Figure 1 is a process diagram showing one embodiment of the present invention, Figure 2 is a process diagram showing an embodiment of the present invention.
The figure is a process diagram showing another example, and FIG. 3 is a diagram showing the results of differential thermal analysis and thermogravimetric analysis in the manufacturing process of an oxide superconductor by a conventional method.

Claims (1)

[Claims] 1. In a method for producing an oxide superconductor, an oxide superconductor or an oxide having a composition to become a superconductor is mixed into an oxide containing all of the metal components constituting the oxide. A method for producing an oxide superconductor, the method comprising embedding it in a superconductor and heating it. 2. The method for producing an oxide superconductor according to claim 1, wherein the heating is performed by embedding the oxide in oxide superconductor powder prepared in advance.