Oxide superconducting laminate and method for manufacturing the same

Abstract

To provide an oxide superconducting laminated body which enables efficient annealing treatment, and a method for manufacturing the same.SOLUTION: An oxide superconducting laminated body 5 includes a substrate 1, an oxide superconducting layer 3 formed of an oxide superconducting body, and a protective layer 4 provided so as to come in contact with the oxide superconducting layer 3. In the protective layer 4, a gap coming in contact with an interface with the oxide superconductive layer 3 is formed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an oxide superconducting laminate and a method for manufacturing the same.

Background Art

[0002] Patent Document 1 discloses an oxide superconducting wire having a structure in which an intermediate layer, a superconducting layer, and a protective layer are sequentially laminated on a substrate. In the manufacture of an oxide superconducting wire, an oxygen annealing treatment is performed on a laminate in which a substrate, an intermediate layer, a superconducting layer, and a protective layer are laminated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the oxide superconducting wire requires a long time for the oxygen annealing treatment, it takes a long time to manufacture.

[0005] <从 One aspect of the present invention aims to provide an oxide superconducting laminate and a method for manufacturing the same that can efficiently perform an oxygen annealing treatment.

Means for Solving the Problems

[0006] One aspect of the present invention includes a substrate, an oxide superconducting layer provided on the substrate and formed of an oxide superconductor, and a protective layer provided on the oxide superconducting layer and in contact with the oxide superconducting layer, wherein a void is formed in the protective layer in contact with the interface with the oxide superconducting layer. An oxide superconducting laminate is provided. [[ID=,47]]

[0007] According to the above embodiment, in the oxygen annealing process, a portion of the oxygen-containing gas passes through the interior of the protective layer, reaches the void in contact with the interface, and comes into contact with the oxide superconducting layer. As a result, the contact area between the oxygen-containing gas and the oxide superconducting layer is increased compared to when there is no void. This makes it possible to increase the diffusion rate of oxygen in the superconducting layer. Therefore, the oxygen annealing process can be performed efficiently.

[0008] The number of voids in contact with the interface is preferably 3 to 12 per 1 μm of the interface length in a cross-section along the thickness direction of the protective layer.

[0009] The size of the void in contact with the interface in the longitudinal direction of the interface is preferably 11.3 nm to 87.2 nm in a cross-section along the thickness direction of the protective layer.

[0010] Another aspect of the present invention provides a method for manufacturing an oxide superconducting laminate, comprising the steps of: forming an oxide superconducting layer containing an oxide superconductor on a substrate; storing the oxide superconducting layer in the atmosphere; forming a protective layer on the oxide superconducting layer, including a void in contact with the interface with the oxide superconducting layer; and heating a laminate comprising the substrate, the oxide superconducting layer, and the protective layer in the presence of an oxygen-containing gas, wherein in the step of heating the laminate, the oxygen-containing gas is supplied to the oxide superconducting layer through the void.

[0011] According to the above embodiment, in the step of heating the laminate, oxygen-containing gas is supplied to the superconducting layer through the voids, thereby increasing the diffusion rate of oxygen in the oxide superconducting layer. Therefore, the oxygen annealing treatment can be performed efficiently.

[0012] The process of storing the oxide superconducting layer in the atmosphere is preferably 24 to 48 hours. [Effects of the Invention]

[0013] According to one aspect of the present invention, it is possible to provide an oxide superconducting laminate that can be efficiently annealed and a method for manufacturing the same. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view of an oxide superconducting wire according to an embodiment. [Figure 2] This is a schematic diagram showing a portion of the cross-section of the oxide superconducting layer and the protective layer. [Figure 3] This image shows a portion of the cross-section of the oxide superconducting layer and the protective layer. [Modes for carrying out the invention]

[0015] Hereinafter, an oxide superconducting laminate according to an embodiment of the present invention will be described in detail with reference to the drawings. For convenience in order to make the features of the present invention easier to understand, the drawings used in this description may show enlarged versions of key parts, and the dimensional ratios of each component may not be the same as in reality.

[0016] [Oxide superconducting laminate] An oxide superconducting laminate according to this embodiment will be described with reference to Figure 1. Figure 1 is a cross-sectional view showing an oxide superconducting wire 10 in which a stabilizing layer 6 is formed on an oxide superconducting laminate 5 according to an embodiment. Figure 1 is a diagram showing a cross-section of the oxide superconducting wire 10 perpendicular to the longitudinal direction.

[0017] The oxide superconducting wire 10 comprises an oxide superconducting laminate 5 and a stabilizing layer 6. The oxide superconducting laminate 5 comprises a metal substrate 1, an intermediate layer 2, an oxide superconducting layer 3, and a protective layer 4. The oxide superconducting laminate 5 has a structure in which the oxide superconducting layer 3 and the protective layer 4 are formed on the metal substrate 1 via the intermediate layer 2. That is, the oxide superconducting laminate 5 has a configuration in which the intermediate layer 2, the oxide superconducting layer 3, and the protective layer 4 are laminated in this order on one side of the metal substrate 1. The oxide superconducting laminate 5 is an example of a "laminated structure".

[0018] The oxide superconducting laminate 5 and the oxide superconducting wire 10 are formed in a tape shape. The Y direction is the thickness direction of the oxide superconducting laminate 5 and the oxide superconducting wire 10, and is the direction in which the metal substrate 1, the intermediate layer 2, the oxide superconducting layer 3, and the protective layer 4 are laminated. The X direction is the width direction of the oxide superconducting laminate 5 and the oxide superconducting wire 10, and is a direction orthogonal to the length direction and the thickness direction of the oxide superconducting laminate 5 and the oxide superconducting wire 10.

[0019] The metal substrate 1 is made of metal. Specific examples of the metal constituting the metal substrate 1 include nickel alloys such as Hastelloy (registered trademark); stainless steel; and oriented Ni-W alloys in which a structure is introduced into a nickel alloy. The thickness of the metal substrate 1 may be appropriately adjusted according to the purpose, and is, for example, in the range of 10 to 500 μm. One surface of the metal substrate 1 (the surface on which the intermediate layer 2 is formed) is referred to as the first main surface 1a, and the surface opposite to the first main surface 1a is referred to as the second main surface 1b. The metal substrate 1 is an example of the "substrate". The first main surface 1a is an example of the "main surface".

[0020] The intermediate layer 2 is provided between the metal substrate 1 and the oxide superconducting layer 3. The intermediate layer 2 is formed on the first main surface 1a of the metal substrate 1. The intermediate layer 2 may have a multilayer structure. For example, in the order from the metal substrate 1 side to the oxide superconducting layer 3 side, it may have a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, etc. These layers are not necessarily provided one by one, and there may be cases where some layers are omitted or two or more layers of the same type are repeatedly laminated. Note that the intermediate layer 2 is not an essential component in the oxide superconducting laminate 5, and the intermediate layer 2 may not be formed when the metal substrate 1 itself has orientation.

[0021] The diffusion prevention layer has a function of suppressing a part of the components of the metal substrate 1 from diffusing and mixing into the oxide superconducting layer 3 side as impurities. The diffusion prevention layer is composed of, for example, Si3N4, Al2O3, GZO (Gd2Zr2O7), etc. The thickness of the diffusion prevention layer is, for example, 10 to 400 nm.

[0022] A bed layer may be formed on the diffusion prevention layer to reduce the reaction at the interface between the metal substrate 1 and the oxide superconducting layer 3 and to improve the orientation of the layer formed thereon. Examples of materials for the bed layer include Y2O3, Er2O3, CeO2, Dy2O3, Eu2O3, Ho2O3, and La2O3. The thickness of the bed layer is, for example, 10 to 100 nm.

[0023] The orientation layer is formed from a biaxially oriented material to control the crystal orientation of the cap layer above it. Examples of materials for the orientation layer include metal oxides such as Gd2Zr2O7, MgO, ZrO2-Y2O3(YSZ), SrTiO3, CeO2, Y2O3, Al2O3, Gd2O3, Zr2O3, Ho2O3, and Nd2O3. The orientation layer is preferably formed by the IBAD (Ion-Beam-Assisted Deposition) method.

[0024] The cap layer is formed on the surface of the orientation layer described above, and consists of a material that allows the crystal grains to self-orient in the in-plane direction. Examples of materials for the cap layer include CeO2, Y2O3, Al2O3, Gd2O3, ZrO2, YSZ, Ho2O3, Nd2O3, and LaMnO3. The thickness of the cap layer can range from 50 to 5000 nm.

[0025] The oxide superconducting layer 3 is composed of an oxide superconductor. The oxide superconductor is not particularly limited, but for example, one with the general formula REBa2Cu3O X An example is the RE-Ba-Cu-O oxide superconductor (REBCO oxide superconductor) represented by (RE123). The rare earth element RE can be one or more of the following: Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. Among these, one of Y, Gd, Eu, or Sm, or a combination of two or more of these elements, is preferred. Generally, X is 7-x (oxygen deficiency x: about 0 to 1). The thickness of the oxide superconducting layer 3 is, for example, about 0.5 to 5 μm. This thickness is preferably uniform in the longitudinal direction. The oxide superconducting layer 3 is formed on the main surface 2a of the intermediate layer 2 (the surface opposite to the metal substrate 1 side). The oxide superconducting layer 3 is an example of a "superconducting layer." The oxide superconducting layer 3 is provided on the first main surface 1a of the metal substrate 1 via the intermediate layer 2.

[0026] The protective layer 4 has functions such as bypassing overcurrents generated during an accident and suppressing chemical reactions between the oxide superconducting layer 3 and the layer provided on top of the protective layer 4. Examples of materials for the protective layer 4 include silver (Ag), copper (Cu), gold (Au), gold-silver alloys, other silver alloys, copper alloys, and gold alloys. The protective layer 4 covers at least the main surface 3a of the oxide superconducting layer 3 (the surface opposite to the intermediate layer 2). The protective layer 4 is in contact with the main surface 3a of the oxide superconducting layer 3. The thickness of the protective layer 4 is not particularly limited, but examples include about 1 to 100 μm.

[0027] 5a is the first main surface of the oxide superconducting laminate 5 (main surface 4a of the protective layer 4). The first main surface 5a is the side of the oxide superconducting laminate 5 on which the oxide superconducting layer 3 is formed. 5b is the side surface of the oxide superconducting laminate 5 (side surface of the metal substrate 1, side surface of the intermediate layer 2, side surface of the oxide superconducting layer 3, and side surface of the protective layer 4). 5c is the surface opposite to the first main surface 5a and is the second main surface of the oxide superconducting laminate 5 (second main surface 1b of the metal substrate 1). The second main surface 5c is the side of the oxide superconducting laminate 5 on which the metal substrate 1 is formed.

[0028] The stabilization layer 6 covers the first main surface 5a, the side surfaces 5b, 5b and the second main surface 5c of the oxide superconducting laminate 5. The stabilization layer 6 is formed surrounding the oxide superconducting laminate 5. The stabilization layer 6 functions as a bypass that commutates the overcurrent generated when the oxide superconducting layer 3 transitions to a normal conducting state.

[0029] The constituent materials of the stabilization layer 6 include metals such as copper, copper alloys (e.g., Cu-Zn alloy, Cu-Ni alloy, etc.), aluminum, aluminum alloys, and silver. The thickness of the stabilization layer 6 is, for example, about 3 to 300 μm. The stabilization layer 6 can be formed by a plating method (e.g., electroplating).

[0030] Figure 2 is a schematic diagram showing a portion of the cross-section of the oxide superconducting layer 3 and protective layer 4 of the oxide superconducting laminate 5. Figure 2 shows a cross-section along the thickness direction of the protective layer 4. As shown in Figure 2, "7" is the interface between the oxide superconducting layer 3 and the protective layer 4. As shown in the schematic diagram of Figure 2, the interface between the oxide superconducting layer 3 and the protective layer 4 can be observed using a transmission electron microscope (TEM). When observing the cross-sections of the oxide superconducting layer 3 and the protective layer 4 with a TEM, it is possible to observe them at any magnification. For example, in the cross-sectional view of the oxide superconducting layer 3 and the protective layer 4 shown in Figure 2, the width of the drawing area is 1 μm, and the total length of the linear interface 7 is also 1 μm. The total length of the interface 7 in Figure 2 is 1 μm.

[0031] One or more voids are formed inside the protective layer 4. At least one void is in contact with the interface 7. Preferably, the number of voids in contact with the interface 7 is 3 to 12 per 1 μm of interface 7 length. The presence of voids in contact with the interface 7 allows oxygen gas to accumulate in the voids of the interface 7 during the oxygen annealing treatment described later, enabling efficient oxygen supply from the voids to the oxide superconducting layer 3. The number of voids in contact with the interface 7 may be, for example, 100 or less per 1 μm of interface 7 length. This ensures a contact area between the oxide superconducting layer 3 and the protective layer 4, and suppresses interfacial resistance between the oxide superconducting layer 3 and the protective layer 4. Voids that are not in contact with the interface 7 may be formed inside the protective layer 4. Gases such as air, oxygen, and organic compound gases may be present in the voids.

[0032] The number of voids in contact with interface 7 may be the average value of the number of voids in multiple observation images (e.g., TEM images) of the cross-section of the protective layer 4. The number of voids in contact with interface 7 may be, for example, the average value of the number of voids in three or more observation images. The number of voids in contact with interface 7 may also be, for example, the average number per 1 μm of interface 7 length for interfaces 7 with a length of 3 μm or more.

[0033] In the example shown in Figure 2, the voids V1 to V8 formed inside the protective layer 4 are in contact with interface 7. Therefore, the number of voids in contact with interface 7 is 8 per 1 μm of interface 7 length. Note that voids V9 to V16 are not in contact with interface 7 and are therefore not included in the "number of voids in contact with interface 7".

[0034] The size of the void in contact with interface 7 (the lengthwise dimension of interface 7) is not particularly limited. The size of the void that can affect the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4 is, for example, 0.1 nm or larger. The size of the void is, for example, 100 nm or less. Examples of void sizes include the range of 11.3 nm to 87.2 nm. The lengthwise direction of interface 7 is perpendicular to the thickness direction of the protective layer 4 (left-right direction in Figure 2).

[0035] In Figure 2, the shapes of the voids V1 to V8 are semicircular, but the shape of the voids in contact with the interface 7 is not particularly limited. The shape of the voids in the cross-section of the protective layer 4 may be arched, circular, elliptical, etc. The three-dimensional shape of the voids is, for example, hemispherical.

[0036] Figure 3 is a TEM image showing a portion of the cross-section of the oxide superconducting layer 3 and protective layer 4 of the oxide superconducting wire 10. As shown in Figure 3, a void V is formed within the protective layer 4 that is in contact with the interface 7.

[0037] [Method for manufacturing oxide superconducting laminates] Next, an example of a manufacturing method for the oxide superconducting laminate 5 will be described. Note that the manufacturing method described below is just one example, and other manufacturing methods may be used.

[0038] As shown in Figure 1, an intermediate layer 2 is formed on the metal substrate 1. The intermediate layer 2 can be formed using the IBAD method.

[0039] Next, an oxide superconducting layer 3 is formed on the intermediate layer 2. The oxide superconducting layer 3 can be formed using a vapor deposition method such as PLD or MOCVD. For example, the oxide superconducting layer 3 is deposited using the PLD method with a target made of REBCO-based material. The deposition of the oxide superconducting layer 3 is carried out in the vacuum chamber of the PLD apparatus. Once deposition is complete, the partially fabricated oxide superconducting laminate 5 is removed from the vacuum chamber and stored in a clean, temperature- and humidity-controlled environment until the formation of the next protective layer 4 begins. The storage time can range from a few hours to several tens of hours.

[0040] Next, a protective layer 4 is formed on the oxide superconducting layer 3. The protective layer 4 can be formed by sputtering or the like. This gives rise to an oxide superconducting laminate 5. When the protective layer 4 is formed, voids are formed inside the protective layer 4. In particular, voids are formed that are in contact with the interface 7 between the oxide superconducting layer 3 and the protective layer 4. Next, an oxygen annealing treatment is performed. Specifically, the oxide superconducting laminate 5 is heated to, for example, 300 to 1000°C in an oxygen atmosphere (in the presence of an oxygen-containing gas). The oxygen-containing gas is, for example, oxygen gas or air. Because voids are formed in the protective layer 4 that are in contact with the interface 7, the oxygen-containing gas comes into contact with the oxide superconducting layer 3 in the voids. This supplies the oxygen-containing gas to the oxide superconducting layer 3 through the voids. Through the above process, the oxide superconducting laminate 5 shown in Figure 1 is obtained.

[0041] Next, a stabilizing layer 6 may be formed on the outer periphery of the oxide superconducting laminate 5. The stabilizing layer 6 can be formed by plating or the like. By forming the stabilizing layer 6 on the outer periphery of the superconducting laminate 5, the oxide superconducting wire 10 shown in Figure 1 is obtained.

[0042] [Effects of the oxide superconducting laminate of the embodiment] In the oxide superconducting laminate 5, a void is formed in the protective layer 4 that is in contact with the interface 7. During the oxygen annealing process, some of the oxygen-containing gas passes through the interior of the protective layer 4, reaches the void in contact with the interface 7, and comes into contact with the oxide superconducting layer 3. Therefore, the contact area between the oxygen-containing gas and the oxide superconducting layer 3 is larger than when there is no void. This increases the diffusion rate of oxygen in the oxide superconducting layer 3. Consequently, the time required for the oxygen annealing process can be shortened while obtaining the required current characteristics (critical current value, etc.). Thus, the oxygen annealing process can be performed efficiently.

[0043] [Effects of the manufacturing method of the oxide superconducting laminate according to the embodiment] In the aforementioned manufacturing method, a void is formed in the protective layer 4 that is in contact with the interface 7. During the oxygen annealing process, oxygen-containing gas is supplied to the oxide superconducting layer 3 through the void, thereby increasing the diffusion rate of oxygen in the oxide superconducting layer 3. Therefore, the oxygen annealing process can be carried out efficiently.

[0044] Although the present invention has been described above based on preferred embodiments, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, the structure of the oxide superconducting laminate is not limited to the structure shown in Figure 1. The oxide superconducting laminate may include layers other than the metal substrate, intermediate layer, oxide superconducting layer, and protective layer. [Examples]

[0045] The present invention will be specifically described below with reference to Examples 1 to 3. (Example 1) A sample of the oxide superconducting wire 10 shown in Figure 1 was prepared as follows. An intermediate layer 2 was formed on one side (first main surface 1a) of a tape-shaped metal substrate 1 made of Hastelloy (registered trademark) using the IBAD method or the like.

[0046] On top of the intermediate layer 2, an oxide superconducting layer 3 is made of REBCO-based material (EuBa2Cu3O yThe film was deposited by PLD using a target formed with ).

[0047] After forming the oxide superconducting layer 3, a protective layer 4 composed of Ag was formed on the oxide superconducting layer 3 by sputtering. The waiting time from the formation of the oxide superconducting layer 3 to the start of the formation of the protective layer 4 was 48 hours. This resulted in obtaining an oxide superconducting laminate 5. The oxide superconducting laminate 5 was subjected to oxygen annealing by heating it to 500°C in an oxygen atmosphere. In the oxygen annealing process, multiple samples with different oxygen annealing times were prepared.

[0048] For several samples with different oxygen annealing treatment times, the critical current value Ic at 77K was measured for each sample. A sample with a critical current value equivalent to that of a conventional oxide superconducting laminate (comparative example sample described later) (Ic / Ic0 in the range of 0.95 to 1.05) was identified and designated as Example 1 sample. The ratio (T1 / T0) of the oxygen annealing time T1 of Example 1 sample to the annealing time T0 of a conventional oxide superconducting laminate was determined. Furthermore, TEM observation of the cross-section along the thickness direction of the protective layer 4 was performed, and the presence or absence of voids in contact with the interface 7 was confirmed from the TEM image of the cross-section. If voids were present, the number of voids per 1 μm of interface 7 and the size of the voids (size in the longitudinal direction of interface 7) were investigated. The results are shown in Table 1.

[0049] As shown in Table 1, the T1 / T0 value was 0.7. In other words, the oxygen annealing treatment time for the Example 1 sample was 70% of the conventional treatment time. The number of voids per 1 μm of interface 7 was 12, and the size of the voids was in the range of 11.3 nm to 87.2 nm.

[0050] (Example 2) The oxide superconducting laminate 5 was fabricated in the same manner as in Example 1, except that the interval between the completion of the formation of the oxide superconducting layer 3 and the start of the formation of the protective layer 4 was set to 36 hours. The ratio (T2 / T0) of the oxygen annealing time T2 of the Example 2 sample to the annealing time T0 of the conventional oxide superconducting laminate was 0.8. In other words, the processing time was 80% of that of the conventional oxygen annealing process. The number of voids per 1 μm of interface 7 was 7, and the size of the voids ranged from 13.1 nm to 72.3 nm. The results are shown in Table 1.

[0051] (Example 3) The oxide superconducting laminate 5 was fabricated in the same manner as in Example 1, except that the interval between the completion of the formation of the oxide superconducting layer 3 and the start of the formation of the protective layer 4 was set to 24 hours. The ratio (T3 / T0) of the oxygen annealing time T3 of the sample in Example 3 to the annealing time T0 of the conventional oxide superconducting laminate was 0.9. In other words, the processing time was 90% of that of the conventional oxygen annealing process. Furthermore, the number of voids per 1 μm of interface 7 was 3, and the size of the voids was in the range of 18.1 to 64.9 nm. The results are shown in Table 1.

[0052] (Comparative example) The oxide superconducting laminate 5 was fabricated in the same manner as in Example 1, except that the interval between the completion of the formation of the oxide superconducting layer 3 and the start of the formation of the protective layer 4 was set to 1 hour. The number of voids per 1 μm of interface 7 was zero. The results are shown in Table 1.

[0053] [Table 1]

[0054] As shown in Table 1, a correlation was observed between the number of voids in the samples of Examples 1 to 3 and the oxygen annealing treatment time. The more voids there were, the shorter the oxygen annealing treatment time. Furthermore, as shown in Table 1, a correlation was observed between the waiting time from the formation of the oxide superconducting layer to the formation of the protective layer and the oxygen annealing treatment time in the samples of Examples 1 to 3. A shorter waiting time resulted in a shorter oxygen annealing treatment time. This suggests that the adsorption of moisture onto the surface of the oxide superconducting layer 3 due to exposure to the atmosphere may be related to the formation of voids in contact with the interface 7. [Explanation of symbols]

[0055] 1...Metal substrate (substrate), 3...Oxide superconducting layer (superconducting layer), 4...Protective layer, 5...Superconducting laminate (laminated structure), 7...Interface, 10...Oxide superconducting wire, V,V1~V16...Voids.

Claims

1. circuit board and An oxide superconducting layer formed of an oxide superconductor is provided on the substrate, The oxide superconducting layer comprises a protective layer provided in contact with the oxide superconducting layer, A void is formed in the protective layer that is in contact with the interface with the oxide superconducting layer. The number of voids in contact with the interface is between 3 and 12 per 1 μm of the interface length in a cross-section along the thickness direction of the protective layer. Oxide superconducting laminate.

2. The size of the void in contact with the interface in the longitudinal direction of the interface is 11.3 nm to 87.2 nm in a cross-section along the thickness direction of the protective layer. The oxide superconducting laminate according to claim 1.

3. A process of forming an oxide superconducting layer containing an oxide superconductor on a substrate, The process of storing the oxide superconducting layer in the atmosphere, A step of forming a protective layer on the oxide superconducting layer, which includes voids in contact with the interface with the oxide superconducting layer, The process includes heating a laminate comprising the substrate, the oxide superconducting layer, and the protective layer in the presence of an oxygen-containing gas. In the step of heating the laminate, the oxygen-containing gas is supplied to the oxide superconducting layer through the void. A method for manufacturing oxide superconducting laminates.

4. The process of storing the oxide superconducting layer in the atmosphere lasts for 24 to 48 hours. A method for producing an oxide superconducting laminate according to claim 3.

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