JP2012113864A - Superconducting rebco oxide thin film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a superconducting oxide thin film offering sufficiently high Ic with stability by thickening the film by a fluorine-free metal organic deposition (FF-MOD) method.SOLUTION: The method for manufacturing a superconducting REBCO oxide thin film comprises the steps of making a superconducting oxide layer by calcining a coating film of a fluorine-free metal organic compound solution and applying firing treatment to the calcined film by a MOD method; forming a non-superconducting material layer on the superconducting oxide layer; and making a dispersion layer by making a superconducting oxide layer on the non-superconducting material layer by the MOD method and dispersing the product of a chemical reaction between the non-superconducting material and the superconducting oxide layer caused by heat applied at the manufacture of the superconducting oxide layer to work as pins. The superconducting REBCO oxide thin film comprises the plurality of superconducting oxide layers made by the MOD method, and contains a dispersion layer made by dispersing the non-superconducting material to work as pins, between the superconducting oxide layers.

Description

  The present invention relates to a REBCO-based oxide superconducting thin film and a method for producing the same, and more particularly, to a REBCO-based oxide superconducting thin film excellent in superconducting properties produced using a coating pyrolysis method and a method for producing the same.

  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 these, an oxide superconducting thin film wire in which an oxide superconducting thin film is formed on a substrate has attracted attention.

  One method for producing the oxide superconducting thin film is a coating pyrolysis method (Metal Organic Deposition, abbreviated as MOD method) (Patent Document 1).

In this method, a raw material solution (MOD solution) produced by dissolving each organic metal compound of RE (rare earth element) such as Y (yttrium), Ba (barium), and Cu (copper) in a solvent is applied to a substrate. After the coating film is formed, for example, a calcined film that is a precursor of the oxide superconducting thin film is subjected to a calcining heat treatment at around 500 ° C. to thermally decompose the organometallic compound and remove the pyrolyzed organic component. Then, the prepared calcined film is crystallized by subjecting it to a heat treatment at a higher temperature (for example, around 750 to 800 ° C.) to produce a REBCO superconducting thin film represented by REBa ₂ Cu ₃ O _7-X. Compared with vapor phase methods (evaporation, sputtering, pulsed laser deposition, etc.) that are mainly manufactured in a vacuum, the manufacturing equipment is simple, and it can handle large areas and complex shapes. Special features such as Because it has been widely used.

  Examples of the MOD method include a TFA-MOD method (Metal Organic Deposition using TriFluoroAcetates) using an organometallic compound containing fluorine in a raw material solution and a fluorine-free MOD method (FF-MOD method) using an organometallic compound containing no fluorine. is there.

When the TFA-MOD method is used, an oxide superconducting thin film excellent in in-plane orientation can be obtained. However, in this method, BaF ₂ (barium fluoride), which is a fluoride, is generated during calcination, and this BaF ₂ is decomposed during the main firing to generate dangerous hydrogen fluoride gas. For this reason, the apparatus and installation which process hydrogen fluoride gas are needed.

  On the other hand, the FF-MOD method has an advantage that it does not generate a dangerous gas such as hydrogen fluoride gas, and therefore is environmentally friendly and does not require processing equipment.

  In such an FF-MOD method, in order to obtain an oxide superconducting thin film having a higher critical current value Ic, the oxide superconducting thin film is laminated by repeating the application of the raw material solution, the calcination heat treatment, and the main calcination heat treatment. Thus, it is attempted to increase the film thickness.

  However, for example, when a YBCO superconducting thin film is manufactured using the conventional FF-MOD method, there is a problem that Ic does not increase sufficiently even if the film thickness is increased.

Therefore, instead of simply laminating the YBCO superconducting thin film as an attempt to improve the film thickness by adopting a laminated structure, the YBCO superconducting thin film and a non-superconducting thin film such as CeO ₂ have a sandwich structure, and each YBCO superconducting A technique for achieving high Ic by connecting thin films has been proposed (Non-patent Document 1).

JP 2007-165153 A

Q. X. Jia, et al ,: “High-temperature superconducting thick film with enhanced supercapacity carrying capability”, Appl. Phys. Lett. 80, 1601-1603 (2002).

  However, even if oxide superconducting thin films are stacked by the technique shown in Non-Patent Document 1, it cannot be said that a sufficiently high Ic oxide superconducting thin film has been obtained.

  Accordingly, an object of the present invention is to provide an oxide superconducting thin film produced by using the FF-MOD method, which has a sufficiently high Ic oxide superconducting thin film and a method for producing the same. .

  The present inventor has investigated the cause that Ic does not become sufficiently high in the conventional manufacturing method even when the oxide superconducting thin film is stacked and the film thickness is increased by using the FF-MOD method. Obtained knowledge.

  That is, in the conventional manufacturing method, as described above, the oxide superconducting thin film is laminated and thickened by repeating the application of the MOD solution, the calcination heat treatment, and the main heat treatment on the substrate. Yes. However, since this stacked oxide superconducting thin film has high crystallinity, defects and heterogeneous phases that function as pinning points related to the improvement of Ic were formed in the first oxide superconducting thin film layer and the substrate. It is formed only between the intermediate layer and hardly formed when the oxide superconducting thin film layer after the second layer is formed.

  As described above, the oxide superconducting thin film thickened by using the conventional manufacturing method does not work on the entire oxide superconducting thin film due to insufficient pinning points, so that the pinning effect can be sufficiently exerted. Thus, it was found that Ic could not be sufficiently improved.

  Accordingly, the present inventor can sufficiently improve Ic by sufficiently providing a pinning effect by appropriately providing a sufficient amount of pinning points on the thick oxide superconducting thin film. The means were intensively studied.

  First, when an organometallic compound is dissolved in a solvent, a MOD solution in which fine particles of a non-superconducting substance that can be expected to function as a pinning point is dispersed in a solvent is prepared. Using this MOD solution, non-superconductivity is prepared. We thought about forming an oxide superconducting thin film in which fine particles of the material are dispersed in the film. However, as a result of the experiment, the fine particles of the non-superconducting material are appropriately arranged and controlled to function sufficiently as a pinning point. This is not easy, and it has been found that it is difficult to stably obtain a high Ic oxide superconducting thin film.

  Therefore, the present inventor further studied a method for appropriately providing pinning points, and as a result, appropriately controlled the thickness of each oxide superconducting thin film layer to be laminated, and pinned between each oxide superconducting thin film layer. By providing a layer in which fine particles of non-superconducting material are dispersed, which functions as a stopping point, that is, by alternately laminating oxide superconducting thin film layers and layers in which fine particles of non-superconducting material are dispersed, pinning points are appropriately arranged. Thus, the inventors have found that the pinning effect can be sufficiently exerted over the entire oxide superconducting thin film, and that a high Ic oxide superconducting thin film can be obtained.

  Further, as a specific method for forming a layer in which fine particles of a non-superconducting material are dispersed, a non-superconducting material that functions as a pinning point by reacting with the oxide superconducting thin film layer by heating on the oxide superconducting thin film layer By forming a thin film of a substance that generates fine particles, it is possible to easily form a layer in which fine particles of a non-superconducting substance that functions as a pinning point are dispersed when an oxide superconducting thin film layer to be subsequently laminated is formed. I found.

The invention according to claim 1 is based on the above knowledge,
Using the MOD method, a step of preparing an oxide superconducting layer by a calcining heat treatment of a coating film of an organometallic compound solution containing no fluorine and a calcining heat treatment of the calcined film;
Forming a layer made of a non-superconducting material on the oxide superconducting layer;
On the layer made of the non-superconducting material, an oxide superconducting layer is further produced by using the MOD method, and the non-superconducting material and the oxide sandwiching the non-superconducting material by heating at the time of producing the oxide superconducting layer. Chemically reacting with the superconducting layer to produce a dispersed layer in which the reaction product of the non-superconducting substance functioning as a pinning point is dispersed;
It is a manufacturing method of the REBCO type oxide superconducting thin film characterized by comprising.

  The oxide superconducting layer and the layer made of the non-superconducting material chemically react to generate fine particles of a reaction product that functions as a pinning point, thereby forming a dispersion layer. The pinning effect can be sufficiently exhibited over the entire oxide superconducting thin film by being appropriately disposed between the oxide superconducting layers.

  In addition, the dispersion layer is not a dense layer made of a non-superconducting material, but a layer in which fine particles of the non-superconducting material are dispersed. Therefore, in the vicinity of the fine particles forming the dispersion layer, between the upper and lower oxide superconducting layers. Since a continuous crystal phase is formed, an oxide superconducting layer having the same orientation can be formed, and a thick oxide superconducting thin film having a uniform orientation in the film thickness direction can be obtained.

  As a result, an oxide superconducting thin film having a high Ic can be provided stably.

  In addition, in the lamination of the non-superconducting thin film layer and the oxide superconducting thin film layer as shown in Non-Patent Document 1, the oxide superconducting material reacts with the non-superconducting material in the MOD method, and the orientation in the film thickness direction is increased. An ordered thick oxide superconducting thin film was not easily obtained.

Examples of the non-superconducting material include CeO ₂ (cerium oxide), SrTiO ₃ (strontium titanate), ZrO ₂ (zirconium dioxide), and the like, and BaCeO ₃ (barium cerate) and BaTiO ₃ ( Reaction products such as barium titanate) and BaZrO ₃ (barium zirconate) are produced.

  In addition, as a method for forming a layer made of a non-superconducting material, the same sputtering method as the conventional intermediate layer forming method can be employed, so that it is not necessary to introduce new equipment.

The invention described in claim 2
Forming a layer made of the non-superconducting material on the oxide superconducting layer;
And by repeating the step of forming the oxide superconducting layer using the MOD method on the layer made of the non-superconducting material,
The REBCO-based oxide superconducting thin film according to claim 1, wherein the REBCO-based oxide superconducting thin film in which the oxide superconducting layer and the dispersion layer are alternately provided is manufactured.

  By repeating the preparation of the oxide superconducting layer and the dispersion layer, the pinning point can be easily arranged appropriately and the pinning effect can be achieved throughout the oxide superconducting thin film, even though it is a multilayered oxide superconducting thin film. Can be sufficiently exhibited, and a high Ic oxide superconducting thin film can be obtained.

The invention according to claim 3
3. The method for producing a REBCO-based oxide superconducting thin film according to claim 1, wherein the layer made of the non-superconducting material has a thickness of 1 to 10 nm.

  If the thickness of the layer made of the non-superconducting material is too thick, the size of the reaction product increases, and there is a possibility that it does not function sufficiently as a pinning point. On the other hand, if it is too thin, a sufficient amount of reaction product is not produced, and the pinning point may be insufficient.

The invention according to claim 4
Wherein the non-superconductive _material, CeO _2, SrTiO _3, REBCO based oxide superconducting thin film according to any one of claims 1 to 3, characterized in that a ZrO 2, any one of the BaZrO ₃ It is a manufacturing method.

BaCeO ₃ (barium cerate), BaTiO ₃ (barium titanate), etc. produced by the chemical reaction of CeO ₂ , SrTiO ₃ , ZrO ₂ , BaZrO ₃ with the oxide superconducting layer have sufficient functions as pinning points. This is preferable.

  In addition, these materials are materials that have been generally used in the past in the formation of oxide superconducting thin films, are easily available, and can suppress an increase in cost.

The invention described in claim 5
A plurality of oxide superconducting layers prepared by a calcining heat treatment of a coating film of an organometallic compound that does not contain fluorine and a calcining heat treatment of a calcined film,
A REBCO-based oxide superconducting thin film is characterized in that a dispersion layer in which a non-superconducting material functioning as a pinning point is dispersed is formed between each oxide superconducting layer.

  As described above, in the oxide superconducting thin film in which the non-superconducting material functioning as the pinning point is dispersed, the oxide superconducting thin film is formed between the oxide superconducting layers. Since it functions effectively as a pinning point, a stable high Ic oxide superconducting thin film can be provided.

  The dispersion layer is not only a dispersion layer formed by a chemical reaction between the oxide superconducting layer and the layer made of a non-superconducting material as described above, but also fine particles of a substance that functions as a pinning point are dispersed in advance. It may be a dispersion layer.

The invention described in claim 6
The REBCO-based oxide superconducting thin film according to claim 5, wherein the thickness of the dispersion layer is 2 to 30 nm.

  The above-described layer made of a non-superconducting material having a thickness of 1 to 10 nm chemically reacts with the oxide superconducting layer, thereby generating a dispersion layer having a thickness of 2 to 30 nm.

The invention described in claim 7
The REBCO-based oxide superconducting thin film according to claim 5 or 6, wherein the oxide superconducting layer has a thickness of 50 to 500 nm.

  If the thickness of one oxide superconducting layer is too thin, the formation of the oxide superconducting layer may become unstable. On the other hand, if it is too thin, composition deviation may occur in the formation of the oxide superconducting layer in the chemical reaction for producing the dispersion layer, which may cause heterogeneous phases and defects.

  On the other hand, if each oxide superconducting layer is too thick, deposition on the entire oxide superconducting thin film of the dispersion layer is reduced, which may reduce the pinning effect.

  According to the present invention, a sufficiently high Ic oxide superconducting thin film can be stably provided by increasing the film thickness using the FF-MOD method.

(A)-(e) is sectional drawing which shows typically the manufacturing process of the YBCO superconducting thin film of an Example. (A) (b) is sectional drawing which shows typically a mode that the dispersion layer which functions as a pinning point is formed.

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

  Hereinafter, the present invention will be described in more detail with reference to examples in which a YBCO superconducting thin film is formed using the FF-MOD method.

1. Configuration of YBCO Superconducting Thin Film FIGS. 1A to 1E are cross-sectional views schematically showing a production process of a YBCO superconducting thin film of an example. FIGS. 2A and 2B are cross-sectional views schematically showing how a dispersion layer that functions as a pinning point is formed.

2. Formation of YBCO superconducting thin film (1) Example 1

(1-1) Preparation of first YBCO superconducting layer (a) Preparation of MOD solution First, Y: Ba: Cu = 1: 2: 3 starting from acetylacetonate salts of Y, Ba and Cu. Thus, a MOD solution using alcohol as a solvent was prepared. The total cation concentration of Y ³⁺ , Ba ²⁺ and Cu ²⁺ in the MOD solution was 1 mol / L.

(B) Coating film production process Next, as a substrate, a substrate in which an intermediate layer composed of three layers of CeO ₂ , YSZ, and CeO ₂ is provided on a clad substrate in which a Cu layer and a Ni layer are sequentially formed on SUS. 1 was prepared, and the MOD solution was applied onto the substrate 1 to prepare a coating film.

(C) Calcination Heat Treatment Step The substrate 1 on which the coating film is formed is heated to 500 ° C. at a temperature increase rate of 5 ° C./min in an air atmosphere at atmospheric pressure, and then held for 2 hours as it is. A calcined film was formed thereon.

(D) Main firing heat treatment step The calcined film obtained in the example was heated up to 780 ° C. at a heating rate of 50 ° C./min in an argon / oxygen mixed gas atmosphere having an oxygen concentration of 100 ppm, and then kept for 20 minutes. Then, a heat treatment for main firing was performed. When the temperature was lowered to 500 ° C. in about 3 hours after the main heat treatment, the gas atmosphere was switched to an oxygen concentration of 100 vol% gas, and the furnace was cooled to room temperature over about 5 hours to prepare a YBCO superconducting layer. As a result, the first YBCO superconducting layer 2 having a thickness of 100 nm shown in FIG.

(1-2) Production of first-layer CeO ₂ layer On the first YBCO superconducting layer 2, a 5 nm thick CeO ₂ film was formed by sputtering, as shown in FIG. Thus, a CeO ₂ layer 3a was produced.

(1-3) Production of second YBCO superconducting layer As shown in FIG. 1C on the first CeO ₂ layer 3a under the same conditions as the first YBCO superconducting layer 2. Then, a second YBCO superconducting layer 2 having a thickness of 100 nm was prepared. At this time, CeO ₂ reacted with YBCO and changed to BaCeO ₃ , thereby producing a dispersion layer 4 in which BaCeO ₃ grains 3 were dispersed as shown in FIG.

(1-4) on the prepared second layer YBCO superconducting layer 2 of the second layer of CeO ₂ layer, in the same conditions as the first layer of the CeO ₂ layer 3a, as shown in FIG. 1 (d) Then, a second CeO ₂ layer 3a having a thickness of 5 nm was produced.

(1-5) On the second CeO ₂ layer 3a, under the same conditions as the first YBCO superconducting layer 2, the third YBCO superconducting layer 2 as shown in FIG. Was made. At this time, as in the case of (1-3) above, CeO ₂ reacted with YBCO and changed to BaCeO ₃ , thereby forming dispersion layer 4.

  As described above, a YBCO superconducting thin film was produced.

In FIG. 1, the CeO ₂ layer 3a becomes the dispersion layer 4 (BaCeO ₃ ) in the process of forming the superconducting thin film. However, for the convenience of explanation, the CeO ₂ layer 3a is displayed with the reference numeral.

(2) Example 2
A YBCO superconducting thin film was produced under the same conditions as in Example 1 except that the dispersion layer 4 having a thickness of 30 nm was formed by changing the thickness of the CeO ₂ layer 3a to 15 nm.

(3) Example 3
A YBCO superconducting thin film was produced under the same conditions as in Example 1 except that the thickness of each YBCO superconducting layer 2 was 40 nm.

(4) Comparative Example 1
A YBCO superconducting thin film was produced under the same conditions as in Example 1 except that the CeO ₂ layer was not formed.

3. Evaluation of YBCO superconducting thin film (1) Analysis of dispersion layer The dispersion layer was analyzed by cross-sectional TEM, and it was confirmed that the dispersion layer was formed by BaCeO ₃ grains.

(2) Superconducting properties Using the YBCO superconducting thin films obtained in Examples 1 to 3 and Comparative Example 1, Jc and Ic were measured under a self magnetic field of 77K. Table 1 shows the measurement results.

(3) Discussion (a) About Examples 1 to 3 As shown in Table 1, Examples 1 to 3 show higher Jc and higher Ic than Comparative Example 1. This is because CeO ₂ reacts with YBCO to form a dispersion layer, and BaCeO ₃ grains in the dispersion layer serve as a pinning point. In Examples 2 and 3, Jc and Ic are lower than those in Example 1. This is because in Example 2, the size as the pinning point is larger than the optimum size, and in Example 3, the YBCO superconducting layer 2 is thin and a composition shift occurs in the YBCO superconducting layer. .

(B) About Comparative Example 1 As shown in Table 1, Jc and Ic of Comparative Example 1 are smaller than those of Examples 1 to 3. In Comparative Example 1, CeO _{2 in} the intermediate layer of the substrate reacts with YBCO in the first YBCO superconducting layer to play a role of pinning, but the second layer and the third layer This is because there is no layer serving as a pin for the YBCO superconducting layer.

  From the above, it can be seen that according to this example, an oxide superconducting thin film having a high Ic can be produced without increasing Jc even when the film thickness is increased 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.

1 Substrate 2 YBCO superconducting layer 3 BaCeO ₃ grains 3a CeO ₂ layer 4 Dispersed layer

Claims (7)

Using the MOD method, a step of preparing an oxide superconducting layer by a calcining heat treatment of a coating film of an organometallic compound solution containing no fluorine and a calcining heat treatment of the calcined film;
Forming a layer made of a non-superconducting material on the oxide superconducting layer;
On the layer made of the non-superconducting material, an oxide superconducting layer is further produced by using the MOD method, and the non-superconducting material and the oxide sandwiching the non-superconducting material by heating at the time of producing the oxide superconducting layer. Chemically reacting with the superconducting layer to produce a dispersed layer in which the reaction product of the non-superconducting substance functioning as a pinning point is dispersed;
A process for producing a REBCO-based oxide superconducting thin film characterized by comprising: Forming a layer made of the non-superconducting material on the oxide superconducting layer;
And by repeating the step of forming the oxide superconducting layer using the MOD method on the layer made of the non-superconducting material,
The method for producing a REBCO-based oxide superconducting thin film according to claim 1, wherein a REBCO-based oxide superconducting thin film in which the oxide superconducting layer and the dispersion layer are alternately provided is manufactured. The method for producing a REBCO-based oxide superconducting thin film according to claim 1 or 2, wherein the layer made of the non-superconducting material has a thickness of 1 to 10 nm. Wherein the non-superconductive _material, CeO _2, SrTiO _3, REBCO based oxide superconducting thin film according to any one of claims 1 to 3, characterized in that a ZrO 2, any one of the BaZrO ₃ Manufacturing method. A plurality of oxide superconducting layers prepared by a calcining heat treatment of a coating film of an organometallic compound that does not contain fluorine and a calcining heat treatment of a calcined film,
A REBCO-based oxide superconducting thin film in which a dispersion layer in which a non-superconducting material functioning as a pinning point is dispersed is formed between the oxide superconducting layers. The REBCO-based oxide superconducting thin film according to claim 5, wherein the dispersion layer has a thickness of 2 to 30 nm. The REBCO-based oxide superconducting thin film according to claim 5 or 6, wherein the oxide superconducting layer has a thickness of 50 to 500 nm.

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