JP5556410B2 - Method for manufacturing oxide superconducting thin film - Google Patents

Description

  The present invention relates to a method for producing an oxide superconducting thin film, and more particularly to a method for producing an oxide superconducting thin film capable of producing an oxide superconducting thin film having excellent superconducting properties by a coating pyrolysis method.

  In order to further spread superconducting wires using oxide superconducting thin films, research on the production of oxide superconducting thin films with excellent superconducting properties has been conducted.

  One method for manufacturing an oxide superconductor is a method called a coating organic decomposition method (abbreviation: MOD method) (Patent Document 1). In this method, for example, a solution in which each metal organic compound of rare earth elements (Re), barium (Ba) and copper (Cu) is dissolved is applied to a substrate, and then pre-baked at around 500 ° C. The organic component is thermally decomposed, and the resulting pyrolyzed product (MOD calcined film) is crystallized by heat treatment (main firing) at a higher temperature (for example, around 800 ° C.) to obtain a superconductor. Compared with vapor phase methods (evaporation method, sputtering method, pulsed laser deposition method, etc.) that are mainly manufactured in vacuum, manufacturing facilities are simple, and it is easy to handle large areas and complex shapes. It has the characteristics.

  As the coating pyrolysis method, a TFA-MOD method (Metal Organic Deposition using TriFluoroacetates) using an organic acid salt containing fluorine as a raw material, and a fluorine-free MOD method (FF-MOD method) using a metal organic compound not containing fluorine, (Non-Patent Document 1).

When the TFA-MOD method is used, an oxide superconducting thin film excellent in in-plane orientation can be obtained (Patent Document 1). However, in this TFA-MOD method, BaF ₂ (barium fluoride), which is a fluoride, is generated at the time of temporary baking, and this BaF ₂ is thermally decomposed at the time of main baking to generate dangerous hydrogen fluoride gas. Therefore, an apparatus and equipment for processing hydrogen fluoride gas are required.

  In contrast, the FF-MOD method does not generate a dangerous gas such as hydrogen fluoride gas, so no special processing equipment is required, and the manufacturing equipment can be used with general-purpose products. And, it has an advantage that the cost of the wire can be reduced.

However, in the conventional FF-MOD method, BaCO ₃ (barium carbonate), which is an alkaline earth metal carbonate, is generated at the time of temporary firing, and this BaCO ₃ is not thermally decomposed sufficiently until the main firing process. The problem is that the CO ₂ gas generated by the decomposition of BaCO ₃ forms voids in the superconducting layer film, hinders crystal orientation growth from the substrate to the film surface, and cannot obtain high Ic. there were.

Therefore, an intermediate heat treatment step of decomposing BaCO ₃ and removing the generated CO ₂ gas from the film by holding it at a decomposition temperature of BaCO ₃ for a certain time between the calcining heat treatment step and the main heat treatment step. Has been proposed (Patent Document 2).

JP 2007-165153 A JP 2010-49891 A

Toshiya Kumagai and two other authors, “Preparation of Superconducting Films by Coating Pyrolysis”, Surface Technology, Japan Surface Technology Association, 1991, Vol. 42, no. 5, P500-507

However, although such an intermediate heat treatment step is provided to sufficiently decompose BaCO ₃ and suppress the generation of voids due to the CO ₂ gas generated along with the decomposition, the substrate faces the film surface. In some cases, the crystals could not be grown sufficiently and high Ic could not be obtained.

Therefore, the present invention sufficiently decomposes BaCO ₃ , suppresses the generation of voids due to CO ₂ gas, and further allows crystals to be sufficiently oriented and grown from the substrate to the film surface. It is an object of the present invention to provide a method for producing an oxide superconducting thin film capable of obtaining an oxide superconducting thin film.

The present inventor has conducted extensive studies, by the technique shown in below, it found that the above problems can be solved, and have completed the present invention. Hereinafter, each technology will be described.

The first technology is
An oxide superconducting thin film used for the production of a superconducting wire is a method for producing an oxide superconducting thin film produced from a metal organic compound containing no fluorine by a coating pyrolysis method using an atmosphere furnace,
A coating film preparation step of preparing a coating film by applying a solution of the metal organic compound on a substrate;
A calcining heat treatment step for producing a calcined film by thermally decomposing and removing an organic component contained in the metal organic compound of the coating film;
A calcination heat treatment step of crystallizing the calcined film to produce an oxide superconducting thin film,
An intermediate heat treatment step for decomposing carbonate contained in the calcined film is provided between the calcining heat treatment step and the main heat treatment step,
The intermediate heat treatment step is an intermediate heat treatment step in which the calcined film is heated to decompose the carbonate contained in the calcined film in an oxygen atmosphere that does not generate a crystalline phase of the oxide superconducting thin film. This is a manufacturing method of a superconducting thin film.

In the conventional intermediate heat treatment process, the present inventor has sufficiently decomposed BaCO ₃ and suppressed the generation of voids due to CO ₂ gas, but sufficiently oriented growth of crystals from the substrate to the film surface. Various experiments were conducted to investigate the cause of the failure. As a result, it was found that the conventional intermediate heat treatment process was performed in a low oxygen atmosphere having an oxygen concentration of 1 vol% or less.

  This will be described with reference to FIG. FIG. 4 is a diagram schematically showing the state of the film in the conventional FF-MOD method, in which (a) is a film after calcining heat treatment, (b) is a film after intermediate heat treatment, and (c) is main firing. It is a film after heat treatment.

As shown in FIG. 4A, a calcination heat treatment is performed at a temperature of about 500 ° C., whereby a calcination film 2 (precursor film) containing BaCO ₃ (carbonate) is formed on the substrate 1. Yes.

In the conventional FF-MOD method, this calcined film is subjected to intermediate heat treatment at a temperature of about 650 ° C. in a low oxygen atmosphere of 100 ppm, for example. By this intermediate heat treatment, BaCO ₃ is thermally decomposed, and the generated CO ₂ gas escapes from the film surface, so that the generation of voids due to the CO ₂ gas is suppressed.

However, since this intermediate heat treatment is performed in a low-oxygen atmosphere, the RE123 phase 4 with c-axis orientation is formed in the vicinity of the substrate 1, although part of the RE123 is crystallized simultaneously with the thermal decomposition of BaCO _3. In a portion other than the vicinity of the substrate 1, a minute non-oriented RE123 crystal phase 5 is formed. This is shown in FIG.

  When such a film after the intermediate heat treatment is subjected to a heat treatment in the same low oxygen atmosphere at a temperature of about 800 ° C., the non-oriented RE123 crystal phase 5 grows together with the c-axis oriented RE123 crystal phase 4, and the c-axis The fired film 3 in which the growth of oriented crystals is inhibited is formed. As a result, it becomes difficult to obtain a high Ic oxide superconducting thin film.

In contrast, in the present technology , the intermediate heat treatment is performed in an oxygen atmosphere that does not generate the crystal phase of RE123. This will be described with reference to FIG. FIG. 1 is a diagram schematically showing the state of a film in the present technology . As in the case of FIG. 4 described above, (a) is a film after a calcination heat treatment, (b) is a film after an intermediate heat treatment, (C) is the film after the main annealing heat treatment.

In FIG. 1A, a calcined film 2 (precursor film) containing BaCO ₃ (carbonate) is formed on the substrate 1 as in FIG.

When this calcined film is subjected to an intermediate heat treatment in an oxygen atmosphere that does not generate the RE123 crystal phase, BaCO ₃ is sufficiently decomposed, the generation of voids due to CO ₂ gas is suppressed, and FIG. As shown, the RE123 crystal phase is not generated, and the calcined film 2 in which the oxide phase 6 of Cu or Ba is scattered in the oxide phase of RE is formed.

  When the calcined film 2 subjected to such an intermediate heat treatment is subjected to the main heat treatment, as shown in FIG. 1C, the non-oriented RE123 crystal phase 5 is formed in the vicinity of the surface layer. Then, the burned film 3 on which the c-axis oriented RE123 crystal phase 4 is grown is formed.

As described above, according to the present technology , BaCO ₃ is sufficiently decomposed to suppress generation of voids due to CO ₂ gas, and a c-axis oriented crystal is grown to a sufficient thickness from the substrate toward the film surface. Therefore, a high Ic oxide superconducting thin film can be obtained.

The “oxygen atmosphere in which the crystal phase of the oxide superconducting thin film is not generated” referred to in the present technology includes not only an oxygen atmosphere in which the crystal phase of the oxide superconducting thin film is not generated at all, but also a c-axis oriented crystal having a sufficient thickness. As long as it can be grown, an oxygen atmosphere in which some crystal phase is generated is also included.

The second technology is
The method for producing an oxide superconducting thin film according to the first technique , wherein the intermediate heat treatment step is an intermediate heat treatment step performed in an oxygen atmosphere exceeding an oxygen concentration of 1 vol%.

  By performing the intermediate heat treatment step in an oxygen atmosphere exceeding the oxygen concentration of 1 vol%, it is possible to reliably produce a calcined film in which the crystal phase of the oxide superconducting thin film is not generated prior to the main heat treatment. More preferably, it is 10 vol% or more.

The third technology is
The method for producing an oxide superconducting thin film according to the first technique or the second technique , wherein the intermediate heat treatment process is an intermediate heat treatment process performed by heat transmitted from the heated substrate. .

When the intermediate heat treatment step is performed by heating from the substrate side (bottom surface heating), the CO ₂ gas generated by the thermal decomposition of BaCO ₃ can be smoothly escaped from the film surface.

The present invention is based on the above technique, and the invention according to claim 1
  An oxide superconducting thin film used for the production of a superconducting wire is a method for producing an oxide superconducting thin film produced from a metal organic compound containing no fluorine by a coating pyrolysis method using an atmosphere furnace,
  A coating film preparation step of preparing a coating film by applying a solution of the metal organic compound on a substrate;
  A calcining heat treatment step for producing a calcined film by thermally decomposing and removing an organic component contained in the metal organic compound of the coating film under an air atmosphere;
  A main heat treatment step of crystallizing the calcined film to produce an oxide superconducting thin film;
With
  An intermediate heat treatment step for decomposing carbonate contained in the calcined film is provided between the calcining heat treatment step and the main heat treatment step,
  The intermediate heat treatment step is an intermediate heat treatment step of heating the calcined film and decomposing carbonate contained in the calcined film in an oxygen atmosphere exceeding an oxygen concentration of 1 vol% that does not generate a crystal phase of the oxide superconducting thin film.
This is a method for producing an oxide superconducting thin film.

And the invention of Claim 2 is
  2. The method of manufacturing an oxide superconducting thin film according to claim 1, wherein the intermediate heat treatment step is an intermediate heat treatment step that is performed by heat transmitted from the heated substrate.

According to the present invention, BaCO ₃ can be sufficiently decomposed to suppress the generation of voids due to CO ₂ gas, and the crystal can be sufficiently oriented and grown from the substrate to the film surface. The manufacturing method of the oxide superconducting thin film which can obtain a thin film can be provided.

It is a figure which shows typically the mode of crystallization in the heat processing of this invention. It is sectional drawing which shows typically the structure of the bottom furnace heating atmosphere furnace used for the intermediate heat treatment of this invention. It is an expanded sectional view showing typically the method of intermediate heat treatment of the present invention. It is a figure which shows typically the mode of crystallization in the conventional heat processing.

  Hereinafter, the present invention will be described based on embodiments.

1. Atmosphere furnace First, the atmosphere furnace used in the intermediate heat treatment step in the method for producing an oxide superconducting thin film of the present invention will be described.

  FIG. 2 is a cross-sectional view schematically showing a configuration of a bottom surface heating type atmospheric furnace used in the intermediate heat treatment of the present invention. As shown in FIG. 2, the atmospheric furnace A includes a tubular furnace body A1, and a ceramic heater 7 for heating the bottom surface of the sample B1 on which the calcined film is formed in the furnace body A1 at a predetermined temperature. Is arranged.

2. Intermediate heat treatment method Next, an intermediate heat treatment method according to the present invention will be described. FIG. 3 is an enlarged sectional view schematically showing the intermediate heat treatment method of the present invention. In FIG. 3, 1 is a substrate and 2 is a calcined film. As shown in FIG. 3, the sample B <b> 1 is configured by forming a calcined film 2 on the substrate 1.

  The intermediate heat treatment is performed under an oxygen concentration exceeding 1 vol%. For this reason, RE123 is not generated.

Further, as shown in FIG. 3, the ceramic heater 7 heats the substrate 1 of the sample B1 as indicated by the white arrow 8, whereby heat is transmitted from the substrate 1 side toward the calcined film 2. For this reason, the decomposition of BaCO _{3 in} the calcined film proceeds from the substrate side of the calcined film 2 to the surface layer portion.

3. EXAMPLES Next, the present invention will be described specifically by way of examples.

(1) Preparation of MOD Solution First, starting from each acetylacetonate salt of Y, Ba, and Cu, synthesis was performed at a ratio (molar ratio) of Y: Ba: Cu = 1: 2: 3, and alcohol was used as a solvent. A MOD solution was prepared. The total cation concentration of Y ³⁺ , Ba ²⁺ and Cu ²⁺ in the MOD solution was 1 mol / L.

(2) Coating and calcination heat treatment Next, the MOD solution is applied by spin coating on the CeO ₂ intermediate layer 2 epitaxially grown on a 2 cm square YSZ single crystal substrate 1 to a thickness of 1 μm. After the coating film was formed, the prepared coating film was heated at 500 ° C. for 120 minutes under an atmospheric pressure atmosphere to prepare a calcined film. This application and calcination heat treatment were repeated twice to produce a calcination film having a thickness of 400 nm.

(3) Intermediate heat treatment The prepared calcined film was performed in an atmosphere having a high oxygen concentration. Specifically, using the bottom surface heating atmosphere furnace shown in FIG. 3, the heating rate is 20 ° C./min in an argon / oxygen mixed gas (oxygen concentration: 10 vol%, CO ₂ concentration: 1 ppm or less) atmosphere. The temperature was raised to 680 ° C. and maintained at that temperature for 90 minutes, and then cooled to room temperature in a furnace to carry out an intermediate heat treatment.

(4) Main baking heat treatment The calcined film was subjected to a main baking heat treatment in a bottom heating atmosphere furnace shown in FIG. Specifically, in an argon / oxygen mixed gas atmosphere with an oxygen concentration of 10 ppm, the temperature was increased to 770 ° C. at a temperature increase rate of 10 ° C./min, and then held for 60 minutes to perform the main heat treatment. After performing the main heat treatment, when the temperature is lowered to 520 ° C. in about 3 hours, the gas atmosphere is switched to an oxygen concentration of 100 vol% gas, and the furnace is cooled to room temperature over another 5 hours. That is, a YBCO superconducting thin film was produced.

4). Comparative Example A fired film was produced in the same manner as in the example except that the intermediate heat treatment was performed under an oxygen concentration of 140 ppm.

5. Evaluation of YBCO superconducting thin film (1) Observation of cross section The cross section of the fired film of the example and the comparative example was observed by S-TEM. In the comparative example, the non-oriented portion was thick and the c-axis oriented layer was thin. On the other hand, in the examples, it was confirmed that the non-oriented portion was thin and the c-axis oriented layer was thick.

(2) Evaluation of superconducting properties a. Measurement of Ic The superconducting properties (Ic) of the YBCO superconducting thin films obtained in Examples and Comparative Examples were measured under a self magnetic field of 77 K, and Ic (A / cm) per unit width (1 cm) was obtained. Table 1 shows the measurement results.

B. Measurement of YBCO (005) peak intensity by X-ray diffraction (XRD) Similarly, the YBCO (005) peak intensity by X-ray diffraction (XRD) of the YBCO superconducting thin films obtained in Examples and Comparative Examples is 77 K, self-magnetic field. Measured below. Similarly, Table 1 shows the measurement results.

  From Table 1, it can be seen that in the examples, since Ic is high and the YBCO (005) peak intensity is also high, the crystal is sufficiently c-axis grown. On the other hand, in the comparative example, since Ic is low and the YBCO (005) peak intensity is low, it can be seen that the crystal is not sufficiently c-axis grown.

  From the above, it can be seen that according to this embodiment, an oxide superconducting thin film having a high Ic in which crystals are sufficiently c-axis grown can be manufactured by the FF-MOD method.

  As mentioned above, although this invention was demonstrated based on embodiment, this invention is not limited to said embodiment. Various modifications can be made to the above-described embodiment within the same and equivalent scope as the present invention.

1 substrate 2 calcined film (precursor film)
3 Burned film 4 c-axis oriented RE123 crystal phase 5 Non-oriented RE123 crystal phase 6 Cu or Ba oxide phase 7 Ceramic heater 8 Arrow indicating heating direction A Atmosphere furnace A1 Furnace B1 Sample

Claims (2)

An oxide superconducting thin film used for the production of a superconducting wire is a method for producing an oxide superconducting thin film produced from a metal organic compound containing no fluorine by a coating pyrolysis method using an atmosphere furnace,
A coating film preparation step of preparing a coating film by applying a solution of the metal organic compound on a substrate;
A calcining heat treatment step for producing a calcined film by thermally decomposing and removing an organic component contained in the metal organic compound of the coating film under an air atmosphere ;
A calcination heat treatment step of crystallizing the calcined film to produce an oxide superconducting thin film,
An intermediate heat treatment step for decomposing carbonate contained in the calcined film is provided between the calcining heat treatment step and the main heat treatment step,
The intermediate heat treatment step is an intermediate heat treatment step of heating the calcined film and decomposing carbonate contained in the calcined film in an oxygen atmosphere exceeding an oxygen concentration of 1 vol% that does not generate a crystal phase of the oxide superconducting thin film. A method for producing an oxide superconducting thin film. 2. The method of manufacturing an oxide superconducting thin film according to claim 1, wherein the intermediate heat treatment step is an intermediate heat treatment step that is performed by heat transmitted from the heated substrate.

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