JP2012129084A - Oxide superconductive thin film wire rod manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an oxide superconductive thin film wire rod which, in manufacturing an oxide superconductive thin film wire rod by an MOD process, restrains a heterogeneous phase from being formed on an orientated metal substrate to ensure that an oxide superconductive thin film wire rod having desired superconducting characteristics will be manufactured.SOLUTION: A manufacturing method of an oxide superconductive thin film wire rod involves forming an oxide superconductive thin film from a metal organic compound by an application thermal decomposition process using an atmosphere furnace to manufacture an oxide superconductive thin film wire rod. The manufacturing method comprises a coated film making step in which a solution of a metal organic compound is applied to an orientated metal substrate having an intermediate layer formed therein to make a coated film, a temporary calcining step in which organic components contained in the metal organic compound of the coated film are removed by thermal decomposition to make a temporarily calcined film, and a formal calcining step in which the temporarily calcined film is crystallized to make an oxide superconductive thin film. The formal calcining step is a heat treatment step in which formal calcining is carried out under a low oxygen partial pressure and high temperature atmosphere, after which, in a region other than an oxide superconductor decomposition region, operation is performed to reduce oxygen partial pressure while the temperature is lowered to cool.

Description

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

  Since the discovery of high-temperature superconductors that have superconductivity at the temperature of liquid nitrogen, development of high-temperature superconducting wires aimed at application to power devices such as cables, current limiters, and magnets has been actively conducted. Among them, an oxide superconducting thin film wire obtained by thinning an oxide superconductor has attracted attention.

One method for producing an oxide superconducting thin film wire is a coating pyrolysis method (Metal Organic Deposition, abbreviated as MOD method) (Patent Document 1). In this method, a metal organic compound solution is applied to a substrate to prepare a coating film (coating film manufacturing process), and then the metal organic compound is heat-treated (calcined) at, for example, around 500 ° C. to remove the organic component of the metal organic compound. Crystallization is achieved by thermally decomposing (calcination heat treatment step) and heat-treating (main firing) the obtained pyrolyzate (MOD calcined film) at a higher temperature (for example, around 800 ° C.) (main heat treatment step). To produce an oxide superconducting thin film made of an oxide superconductor represented by, for example, REBa ₂ Cu ₃ O _7-X (RE: rare earth element), and is a vapor phase method mainly produced in vacuum Compared with (evaporation method, sputtering method, pulsed laser deposition method, etc.), the manufacturing facility is simple, and it is easy to cope with a large area and a complicated shape.

JP 2007-165153 A

However, in the production of the oxide superconducting thin film wire by the conventional MOD method, RE ₂ Ba which is a non-superconductor other than a crystal of RE ₁ Ba ₂ Cu ₃ O _7-x which is a superconductor on an oriented metal substrate. _In some cases, a different phase such as ₁ Cu ₁ O ₅ is formed, and the desired superconducting characteristics may not be exhibited.

  Thus, the present invention provides an oxide superconducting thin film wire having a desired superconducting characteristic by suppressing the formation of a heterogeneous phase on an oriented metal substrate in the production of an oxide superconducting thin film wire by the MOD method. It aims at providing the manufacturing method of a thin film wire.

  As a result of intensive studies, the present inventor has found that the above-mentioned problems can be solved by the inventions of the following claims, and has completed the present invention. Hereinafter, the invention of each claim will be described.

The invention described in claim 1
Using a metal organic compound as a raw material, an oxide superconducting thin film wire is produced by forming an oxide superconducting thin film by a coating pyrolysis method using an atmospheric furnace, and a method for producing an oxide superconducting thin film wire,
A coating film preparation step of applying a solution of the metal organic compound on the oriented metal substrate on which the intermediate layer is formed to prepare a coating film;
A calcining heat treatment step for producing a calcined film by thermally decomposing and removing organic components 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,
The main heat treatment step is a heat treatment step in which the main firing is performed in a low oxygen partial pressure and high temperature atmosphere, and then the temperature is lowered and cooled outside the decomposition region of the oxide superconductor while performing an operation to lower the oxygen partial pressure. This is a method for producing an oxide superconducting thin film wire.

  The present inventor first analyzed and examined each step in the conventional MOD method in detail, and as a result, the formation of the above-mentioned heterogeneous phase occurred in the main annealing process, and the treatment atmosphere at this time was heterogeneous. It was found that it greatly influenced the formation.

  That is, in the conventional heat treatment process of the main furnace, after the heat treatment of the main heat treatment is performed under a low oxygen partial pressure and high temperature atmosphere, the furnace cooling is performed under the same oxygen partial pressure. I found out that Due to the formation of this heterogeneous phase, the superconducting properties were degraded.

  Furthermore, when furnace cooling is performed under the same oxygen partial pressure, the alignment metal substrate is oxidized, and when this oxidation proceeds, the intermediate layer provided on the alignment metal substrate as a buffer layer is destroyed, and the alignment metal substrate and the superconductor are Direct contact with the layer. As a result, it was found that migration of metal atoms to the superconducting layer occurred, resulting in further deterioration of superconducting properties.

  Based on the above knowledge, the present inventor has intensively studied the countermeasure. As a result, the furnace cooling process after performing the main annealing heat treatment under a low oxygen partial pressure and high temperature atmosphere is not performed under the same oxygen partial pressure as in the prior art, but the furnace cooling is performed while lowering the oxygen partial pressure. As a result, it has been found that the formation of heterogeneous phases can be suppressed, the oxidation of the oriented metal substrate can also be suppressed, and an oxide superconducting thin film wire having desired superconducting characteristics can be obtained, leading to the present invention. It was.

This will be described in detail with reference to FIG. FIG. 3 is a diagram showing the relationship between YBCO crystal formation, temperature, and oxygen partial pressure, using YBCO (Y ₁ Ba ₂ Cu ₃ O _7-x ) as an example of the superconducting layer. In FIG. 3, a line aa ′ is a line indicating the boundary between formation and decomposition of YBCO, and indicates that YBCO is decomposed in a region on the left side of aa ′. The line bb ′ is a line indicating the boundary between the formation of CuO and Cu ₂ O. In the region on the right side of bb ′, CuO is stable and close to the Y124 generation region where the superconducting transition temperature is low. Thus, different phases such as Y124, Y211 and CuO are formed as the different phases. That is, it can be said that the region between the line aa ′ and the line bb ′ is a region where YBCO crystallizes.

The main heat treatment process in the conventional MOD method can be indicated by a dotted arrow, and the heat treatment is performed along the path of P → Q → P. In this case, the temperature rise and fall are performed under a constant oxygen partial pressure (10 Pa), but intersect the line bb ′ at a considerably high temperature stage. However, when the temperature crosses the line bb ′, that is, the temperature at which Cu ₂ O changes to CuO is high and the oxygen partial pressure is somewhat high, a heterogeneous phase is likely to be formed.

  On the other hand, the main heat treatment step in the present invention can be indicated by a solid line arrow, and the heat treatment is performed along the path of P → Q → R → S. At this time, while Q → R is controlled so as not to intersect the line aa ′ (so as not to enter the YBCO decomposition region), the oxygen partial pressure lowering operation and the temperature lowering are performed. The temperature falls under pressure. For this reason, the intersection with the line b-b 'is performed at a considerably low temperature, and the formation of a different phase is suppressed. Moreover, since the oxygen partial pressure is lowered, oxidation of the oriented metal substrate is suppressed. As a result, an oxide superconducting thin film wire having desired superconducting characteristics can be obtained.

The invention described in claim 2
The oxygen partial pressure PO ₂ in the temperature lowering process of the main annealing process is 1 Pa ≦ PO ₂ ≦ 3 Pa, 680 ° C. ≦ T ≦ 700 ° C. in the range of 700 ° C. ≦ T ≦ 720 ° C. The manufacturing method of an oxide superconducting thin film wire according to claim 1, wherein 0.2 Pa ≦ PO ₂ ≦ 1 Pa.

  In the temperature lowering process of the main heat treatment step, for example, the temperature range of 700 to 720 ° C. so that the oxygen partial pressure is reduced from 10 Pa to 1 Pa at 720 ° C. and the oxygen partial pressure is reduced from 1 Pa to 0.3 Pa at 700 ° C. Then, the oxygen partial pressure is controlled to 1 to 3 Pa, and the oxygen partial pressure is controlled to 0.2 to 1 Pa in the temperature range of 680 to 700 ° C., whereby the line aa ′ and the line bb ′ shown in FIG. Thus, the oxide superconducting thin film wire having the desired superconducting characteristics can be obtained.

The invention according to claim 3
_{3. The} method for producing an oxide superconducting thin film wire according to claim 1, wherein the oxide superconducting thin film wire is a YBa ₂ Cu ₃ O _7-X oxide superconducting thin film wire. 4.

In the production of a YBa ₂ Cu ₃ O _7-X oxide superconducting thin film wire, the above-described effects are remarkably exhibited.

  According to the present invention, in the production of an oxide superconducting thin film wire by the MOD method, an oxide superconducting material for producing an oxide superconducting thin film wire having desired superconducting characteristics by suppressing the formation of a heterogeneous phase on an oriented metal substrate. A method for producing a thin film wire can be provided.

It is a figure which shows the relationship between oxygen partial pressure and temperature in an Example, and elapsed time. It is a figure which shows the relationship between oxygen partial pressure and temperature, and elapsed time in a comparative example. It is a figure which shows the relationship between the crystal production | generation of YBCO, temperature, and oxygen partial pressure.

  Hereinafter, the present invention will be specifically described based on examples.

1. Example (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 the 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) Preparation of coating film and calcination heat treatment A substrate provided with an Y ₂ O ₃ , YSZ, CeO ₂ intermediate layer (total thickness: 1 to 2 μm) on an oriented metal substrate was prepared.

  On the oriented metal substrate with an intermediate layer, the MOD solution was applied by a spin coating method and then dried to prepare a coating film having a thickness of 0.65 μm.

  Then, it heated at 500 degreeC under atmospheric pressure atmosphere for 120 minutes, and produced the calcined film.

(3) Main baking heat treatment About the produced calcined film, a main baking heat treatment was performed according to the temperature profile and oxygen partial pressure profile shown in FIG. In FIG. 1, the solid line indicates the oxygen partial pressure profile, and the dotted line indicates the temperature profile.

  Specifically, in an argon / oxygen mixed gas atmosphere having an oxygen partial pressure of 10 Pa, the temperature was increased to 770 ° C. at a temperature increase rate of 30 ° C./min, and then held for 60 minutes to perform the main heat treatment.

  After the main heat treatment, the furnace was cooled to 720 ° C. at a temperature lowering rate of 3 ° C./min, and the oxygen partial pressure was reduced to 1 Pa at the same temperature. Furthermore, the furnace was cooled to 700 ° C., and the oxygen partial pressure was reduced to 0.3 Pa. Thereafter, while maintaining the same oxygen partial pressure, the furnace was cooled to room temperature to produce a YBCO superconducting thin film having a thickness of 0.15 μm.

2. Comparative Example A calcined film was produced under the same conditions as in the example, and then a heat treatment was performed according to the temperature profile and oxygen partial pressure profile shown in FIG.

  Specifically, in an argon / oxygen mixed gas atmosphere having an oxygen partial pressure of 10 Pa, the temperature was increased to 770 ° C. at a temperature increase rate of 30 ° C./min, and then held for 60 minutes to perform the main heat treatment.

  After the main heat treatment, while maintaining the oxygen partial pressure of 10 Pa, the furnace was cooled to room temperature at a temperature drop rate of 3 ° C./min to produce a YBCO superconducting thin film.

3. Evaluation of YBCO Superconducting Thin Film (1) Observation of Oriented Metal Substrate and Fired Film The oriented metal substrate and superconducting thin film of each YBCO superconducting thin film obtained in Examples and Comparative Examples were observed by S-TEM.

  As a result, it was confirmed that in the YBCO superconducting thin film obtained in the example, no heterogeneous phase was generated over the entire film. Moreover, since no abnormality was observed in the intermediate layer formed on the oriented metal substrate, it was confirmed that oxidation of the oriented metal substrate was suppressed. On the other hand, in the YBCO superconducting thin film obtained in the comparative example, a different phase was formed in a part of the film. Moreover, since a part of intermediate | middle layer was destroyed, it was confirmed that oxidation has generate | occur | produced in the orientation metal substrate. The results are shown in Table 1.

(2) Evaluation of superconducting characteristics Next, for each YBCO superconducting thin film obtained in Examples and Comparative Examples, the YBCO (005) peak intensity was measured by Ic and X-ray diffraction (XRD) to evaluate the superconducting characteristics. went.

(A) Measurement of Ic The superconducting property (Ic) of each YBCO superconducting thin film obtained in Examples and Comparative Examples was measured at 77K under a self-magnetic field, and Ic (A / cm) per unit width (1 cm) was measured. Asked. The measurement results are shown in Table 1.

(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 77K. , Measured under self-magnetic field. The measurement results are shown in Table 1.

  As can be seen from Table 1, in the case of the examples, the oxidation of the oriented metal substrate is suppressed, no heterogeneous phase is generated in the crystal layer, and Ic is also high. Since the YBCO (005) peak intensity is high, it can be seen that the YBCO crystal is sufficiently c-axis grown.

  On the other hand, in the case of the comparative example, oxidation occurs in the oriented metal substrate and a heterogeneous phase occurs in the crystal layer, and Ic is low. And since YBCO (005) peak intensity is low, it turns out that the YBCO crystal is not fully c-axis grown.

  From the above, it can be seen that according to this example, an oxide superconducting thin film wire having a high Ic in which a heterogeneous phase is not generated in the crystal and the YBCO crystal is sufficiently c-axis grown can be produced by the 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.

Claims (3)

Using a metal organic compound as a raw material, an oxide superconducting thin film wire is produced by forming an oxide superconducting thin film by a coating pyrolysis method using an atmospheric furnace, and a method for producing an oxide superconducting thin film wire,
A coating film preparation step of applying a solution of the metal organic compound on the oriented metal substrate on which the intermediate layer is formed to prepare a coating film;
A calcining heat treatment step for producing a calcined film by thermally decomposing and removing organic components 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,
The main heat treatment step is a heat treatment step in which the main firing is performed in a low oxygen partial pressure and high temperature atmosphere, and then the temperature is lowered and cooled outside the decomposition region of the oxide superconductor while performing an operation to lower the oxygen partial pressure. A method for producing an oxide superconducting thin film wire, characterized in that: The oxygen partial pressure PO ₂ in the temperature lowering process of the main annealing process is 1 Pa ≦ PO ₂ ≦ 3 Pa, 680 ° C. ≦ T ≦ 700 ° C. in the range of 700 ° C. ≦ T ≦ 720 ° C. The manufacturing method of the oxide superconducting thin film wire according to claim 1, wherein 0.2 Pa ≦ PO ₂ ≦ 1 Pa in the range of _{3. The} method for producing an oxide superconducting thin film wire according to claim 1, wherein the oxide superconducting thin film wire is a YBa ₂ Cu ₃ O _7-X oxide superconducting thin film wire.

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