WO2009084763A1

WO2009084763A1 - Superconducting tapes and method of manufacturing the same

Info

Publication number: WO2009084763A1
Application number: PCT/KR2008/000371
Authority: WO
Inventors: Jai-Moo Yoo; Young-Kuk Kim; Kook-Chae Chung
Original assignee: Korea Institute Of Machinery & Materials
Priority date: 2008-01-03
Filing date: 2008-01-21
Publication date: 2009-07-09
Also published as: KR100922371B1; KR20090074910A

Abstract

A superconducting thin film exhibiting a high critical current density in a magnetic field and a manufacturing method thereof are provided. The method comprises the steps of: synthesizing a solution containing nanodots dispersed therein using a chemical method; mixing the synthesized solution with a superconducting metal-organic deposition precursor solution to prepare a metal- organic deposition precursor solution containing the nanodots dispersed therein; and coating the metal-organic deposition precursor solution on a substrate and heat-treating the coated solution, thus forming a superconducting thin film.

Description

SUPERCONDUCTING TAPES AND METHOD OF MANUFACTURING THE SAME

Technical Field

The present invention relates to a superconducting thin film exhibiting a high critical current density in a magnetic field and a manufacturing method thereof, and more particularly to a superconducting thin film in which the occurrence of an agglomeration of fine flux pinning centers can be minimized and a manufacturing method thereof.

Background Art

Oxide superconducting tapes based on REBa2Cu3O7-x (RE=Y,Sm,Er,Yb,...) have excellent current transport properties and exhibit excellent critical current properties in a high magnetic field. Thus, it is expected that, when such superconducting tapes are applied to power cables, industrial motors, power generators, etc., the miniaturization, high efficiency and large capacity of large-capacity power devices can be achieved. In order to apply the oxide superconducting tapes to such a variety of applications, superconducting tapes exhibiting high critical current values in a magnetic field must be able to be manufactured economically.

Currently, studies on the manufacture of oxide superconducting films using various processes, including laser evaporation, metal-organic chemical vapor deposition (MO-CVD), thermal evaporation and e-beam evaporation, are being actively conducted. However, such processes are high-vacuum deposition processes which are economically disadvantageous in that expensive high-vacuum apparatuses are required and much maintenance cost is incurred. Meanwhile, processes enabling superconducting tapes having excellent critical current properties to be manufactured at low costs include metal organic deposition (MOD). Metal organic deposition is a process comprising applying a precursor solution including salts of rare earth metals, alkaline earth metals or transition metals to a substrate, and subjecting the applied solution to, for example, heat treatment, thus forming a superconducting layer. Metal organic deposition is a non- vacuum process, has high economic efficiency compared to other processes due to low raw material costs, and can manufacture superconducting tapes having high critical current values.

In order to manufacture superconducting tapes exhibiting excellent critical current properties in a magnetic field, efforts to introduce various flux pinning centers into superconducting materials have been actively made. As described above, the superconducting tapes developed to date have a problem in that the decrease in critical current density in a magnetic field is severe. In order to solve such a problem, it is required to introduce high-density defects capable of serving as flux pinning centers. Naturally occurring crystal defects cannot satisfy conductor conditions required for the application of superconducting tapes to devices, because the density or flux pinning properties thereof are not sufficient. In the case of flux pinning centers which are formed in superconducting tapes, it is theoretically expected that, when they have a size of about 1-3 nm and are uniformly distributed at a density of more than 1011/αif, the flux pinning properties thereof can be maximized, thus achieving a critical current density of a maximum of 28 MA/cuf. Accordingly, broad research and development activities have been conducted in order to form fine flux pinning centers using artificial methods, but most of these methods have the problems of not being practical and it being difficult to manufacture long tapes for industrial applications.

In order to manufacture superconducting tapes having high critical current values by introducing flux pinning centers into superconducting materials, fine structures having nanosized particles uniformly dispersed therein must be able to be formed. A method which has been mainly used to obtain such fine structures is the highly economically efficient metal-organic deposition (MOD), which is a method comprising adding rare-earth metal elements to a MOD precursor solution to prepare a uniform solution, and coating and heat-treating the solution. In this case, rare-earth oxide particles having a size of 10-100 nm are formed in the manufactured superconducting material. However, the size of the formed rare- earth oxide particles is as large as a few tens of nanometers (nm) or more, and it is almost impossible to control the size, thus making it difficult to control fine textures for maximizing critical current properties in a magnetic field.

Meanwhile, in order to prepare a solution containing nanosized particles dispersed therein, a method of adding nanosized powders directly to a precursor solution is generally being used. Currently available generic nanosized powders contain a large amount of agglomerates, and for uniform dispersion of nanosized powders in a solution, various additives including a dispersing agent must be added to the solution. Even when the additives are used, nanosized powders are dispersed in an agglomerated form in many cases. Thus, when nanosized powders are added directly to a superconducting MOD precursor solution to introduce flux pinning centers, there are problems in that a large amount of agglomerates are formed and uniform dispersion of the nanosized particles is almost impossible.

In prior methods which are used to form flux pinning centers, it is impossible to control the size of nanodots and it is difficult to uniformly disperse them. Thus, agglomerates having a size of a few hundreds of nanometers (run), which are unsuitable for serving as flux pinning centers, frequently form, and such problems need to be urgently solved. Accordingly, if a MOD precursor solution can be prepared using a method which can control the size of nanodots and uniformly disperse flux pinning centers without causing agglomeration, the critical current density of superconducting tapes in a magnetic field can be maximized by controlling the size and distribution of flux pinning centers, and a cost-effective process for manufacturing superconducting tapes will have become possible. Thus, significant spillover effects on the development and application of superconducting tapes will be created.

Disclosure Technical Problem

It is an object of the present invention to provide a superconducting thin film in which flux pinning centers are uniformly dispersed without agglomeration and a manufacturing method thereof.

Technical Solution

To achieve the above object, the present invention provides a method for manufacturing a superconducting thin film, which comprises the steps of: synthesizing a solution containing nanodots dispersed therein using a chemical method; mixing the synthesized solution with a superconducting metal-organic deposition precursor solution to prepare a metal-organic deposition precursor solution containing the nanodots dispersed therein; and, coating the metal-organic deposition precursor solution on a substrate and heat-treating the coated solution, thus forming a superconducting thin film.

The step of synthesizing the solution containing the nanodots dispersed therein comprises the steps of dissolving a metal precursor in a solvent, adding an additive to the solution to control the reactivity of the metal precursor, and adding water thereto to induce hydrolysis and condensation.

The metal precursor may be any one selected from the group consisting of metal alkoxides, metal hydroxides, metal nitrates and metal organic acid salts. The solvent may be any one selected from the group consisting of alcohols, ester liquids, ketones, and mixtures thereof.

The additive may be any one selected from the group consisting of diketones, dialcohols, carboxylic acids and amines.

The superconducting metal-organic deposition precursor solution can be prepared using as a precursor any one metal salt selected from the group consisting of metal trifluoroacetate, metal carboxylate and metal beta-diketonate.

The metal constituting the metal salt may be any one selected from the group consisting of rare-earth elements, alkaline earth metal elements, and transition metal elements.

Advantageous Effects

According to an embodiment of the present invention, an MOD precursor solution containing nanodots uniformly dispersed therein without agglomeration can be prepared using a chemical method, and a superconducting thin film containing nanodots uniformly dispersed therein can be manufactured using the prepared MOD precursor solution. The present invention is advantageous in that a superconducting thin film in which nanodots having a size of a few nanometers (nm) are uniformly distributed can be manufactured by mixing the nanodot- dispersed solution synthesized using the chemical method with the MOD precursor solution to prepare an MOD precursor solution containing nanodots uniformly dispersed therein without agglomeration, and subjecting the MOD precursor solution to a metal-organic deposition process. Thus, the present invention is very advantageous for improving the critical current properties (in a magnetic flux) of superconducting tapes which are manufactured by the metal- organic deposition process. Particularly, the present invention suggests a method of forming effective flux pinning centers in superconducting tape using an inexpensive chemical process, such that superconducting tapes having excellent current properties in a magnetic field compared to those manufactured according to prior methods can be manufactured. Thus, the present invention is significantly superior to the prior methods in terms of economic efficiency and industrial application. Accordingly, it is considered that the present invention will greatly contribute to the practical application of oxide superconducting tapes in the future. In addition, it is expected that the present invention for manufacturing a functional thin film by directly and chemically synthesizing a solution having nanodots uniformly dispersed therein and mixing the synthesized solution with another precursor solution will find applications in various fields, including quantum dot solar cells and thermoelectric modules, and will cause significant spillover effects in the energy conversion technology field.

Description of Drawings

FIG. 1 is a process flowchart showing a method of manufacturing a superconducting tape according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a method of manufacturing a superconducting tape according to an embodiment of the present invention.

FIG. 3 shows the results of particle size analysis of a chemically synthesized solution containing nanodots dispersed therein.

FIG. 4 is a transmission electron microscope photograph showing the fine structure of a superconducting thin film having nanodots dispersed therein.

FIG. 5 shows that the critical current density in a magnetic field was increased due to the dispersion of nanodots.

Best Mode

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so as to enable those skilled in the art to carry out the present invention. However, the present invention is not limited to the embodiments set forth herein and can be embodied in other forms. Rather, the embodiments set forth herein are provided so that the disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

FIG. 1 is a process flowchart showing a method of manufacturing a superconducting tape according to an embodiment of the present invention, and FIG. 2 is a schematic diagram showing a method of manufacturing a superconducting tape according to an embodiment of the present invention.

Referring to FIGS. 1 and 2, an additive is added to a metal precursor solution to control the reactivity of the metal precursor, and water is added thereto to induce hydrolysis and condensation, thus synthesizing a solution containing nanodots dispersed therein. Then, a superconducting MOD precursor solution is mixed with the nanodot-dispersed solution to prepare a MOD precursor solution having nanodots dispersed therein. Then, the prepared MOD precursor solution is coated on a substrate and subjected to calcination and heat treatment processes, thus manufacturing a superconducting thin film. Namely, the MOD precursor solution containing nanodots dispersed therein is coated on a substrate, followed by heat treatment, thus forming a superconducting thin film. To synthesize the solution containing nanodots dispersed therein, a metal precursor, such as metal alkoxide, metal hydroxide, metal nitrate or a metal organic acid salt, which can be hydrolyzed according to the following reaction equations by the addition of water, is dissolved in a suitable solvent:

M2+ + H2O => M(OH2)2+ —(equation 1-1)

M2+ + H2O => M(0H)(z-l)+ + H+ —(equation 1-2)

M2+ + H2O => M0(z-2)+ + 2H+ —(equation 1-3) wherein M2+ indicates a metal ion.

As the solvent for synthesizing the solution, an alcohol such as methanol or ethanol, an ester-based liquid such as ethyl acetate or ethyl butyrate, a ketone such as acetone or protan, or a mixture of two or more thereof may be mainly used, and one having the lowest possible water content is preferably used. Also, to control the reactivity of the metal precursor, a suitable additive is added. As the additive, a diketone such as 2,4-pentanedione, a dialcohol such as ethylene glycol, or a carboxylic acid such as acetic acid or propionic acid, or an amine such as triethanolamine may be used.

To the stabilized solution obtained by dissolving the metal precursor in a suitable solvent and adding the additive to the solution, a suitable amount of water is added to induce the hydrolysis reaction shown in the above equations 1-1 to 1-3 and a condensation reaction. A condensation reaction which can occur is shown in, for example, the following equation:

M-OR + M-OR --> M-O-M + ROR (equation 2) wherein M indicates a metal ion, and R indicates an alkyl group.

The amount of water added is 1 -20 times the molar ratio of the metal ion, and more preferably 4-15 times by molar ratio.

The solution formed in the above process is kept at room temperature or a temperature of less than 100 "C for 2-24 hours, whereby a nanodot-dispersed solution having a size distribution ranging from a few nanometers to a few tens of nanometers can be finally synthesized.

The synthesized solution containing nanodots dispersed therein is readily mixed with the superconducting MOD precursor solution to form a MOD precursor solution containing nanodots dispersed therein. The MOD precursor solution used herein may be selected from among various MOD precursor solutions, including a general MOD-TFA precursor solution comprising a rare- earth element (Y, Sm, Ho, Dy, etc.) and metal (barium, copper, etc.) trifluoroacetate, a MOD precursor solution comprising metal carboxylate and metal trifluoroacetate, and a metal beta-diketonate solution, which are used to manufacture superconducting thin films.

The prepared MOD precursor solution containing nanodots dispersed therein can be coated on a substrate using various methods, including dip coating, slot die coating, spin coating and gravure coating. To the surface of, for example, a metal substrate having excellent orientation properties and having a buffer layer formed thereon, the above-prepared buffer solution is applied using the above coating method, and the applied solution is calcined and heat-treated to form an acid fluoride film having no fiowability. The precursor thin film obtained after the calcination process can be heated in an Ar/02 or N2/O2 mixed gas containing water, thus obtaining a superconducting thin film. Hereinafter, an embodiment of the present invention will be described.

A solution containing nanodots dispersed therein was prepared using the following components:

Precursor: zirconium propoxide;

Additive for forming stabilized solution: 2,4-pentanedione; Solvent: methanol; Amount of water added: [H2O]/[Zr]=12; and

Superconducting MOD precursor solution: REBCO MOD precursor solution comprising metal acetate and metal trifluoroacetate.

The prepared solution containing nanodots dispersed therein was analyzed for particle size by dynamic light scattering. As a result, as shown in FIG. 3, nanosized particles having an average diameter of 16 nm were dispersed in the prepared solution, and agglomerates having an average particle size of about 400 nm were also contained in an amount of about 30%. The prepared solution was mixed with a superconducting MOD precursor solution to prepare a MOD precursor solution containing nanodots dispersed therein, and the prepared MOD precursor solution was coated on a single-crystal substrate, and then heat-treated, thus manufacturing a YBCO superconducting thin film. The manufactured

YBCO thin film was analyzed by transmission electron microscopy (TEM). As a result, as shown in FIG. 4, ZrO2 nanodots having a size of 10-20 nm were uniformly distributed in the YBCO thin film. A change in the critical current density (Jc) of the thin film was analyzed with a vibrating sample magnetometer

(VSM) on the basis of the Bean's critical state model. As a result, the critical current density in a magnetic field was increased (see FIG. 5).

Claims

Claims :

1. A method for manufacturing a superconducting thin film, which comprises the steps of: synthesizing a solution containing nanodots dispersed therein using a chemical method; mixing the synthesized solution with a superconducting metal-organic deposition precursor solution to prepare a metal-organic deposition precursor solution containing the nanodots dispersed therein; and coating the metal-organic deposition precursor solution on a substrate and heat-treating the coated solution, thus forming a superconducting thin film.

2. The method of Claim 1, wherein the step of synthesizing the solution containing the nanodots dispersed therein comprises the steps of dissolving a metal precursor in a solvent, adding an additive to the solution to control the reactivity of the metal precursor, and adding water thereto to induce a hydrolysis reaction and a condensation reaction.

3. The method of Claim 2, wherein the metal precursor is any one selected from the group consisting of metal alkoxides, metal hydroxides, metal nitrates and metal organic acid salts.

4. The method of Claim 2, wherein the solvent is any one selected from the group consisting of alcohols, ester liquids, ketones, and mixtures thereof.

5. The method of Claim 2, wherein the additive is any one selected from the group consisting of diketones, dialcohols, carboxylic acids and amines.

6. The method of Claim 1, wherein the superconducting metal-organic deposition precursor solution is prepared using as a precursor any one metal salt selected from the group consisting of metal trifluoroacetate, metal carboxylate and metal beta-diketonate.

7. The method of Claim 6, wherein the metal constituting the metal salt is any one selected from the group consisting of rare-earth elements, alkaline earth metal elements, and transition metal elements.

8. A superconducting thin film manufactured according to the method of

Claim 1.