JP7844183B2 - Oxide superconducting laminate and method for manufacturing the same - Google Patents

Description

This invention relates to an oxide superconducting laminate and a method for producing the same.

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 manufacturing of the oxide superconducting wire, the laminate, consisting of the substrate, intermediate layer, superconducting layer, and protective layer, is subjected to oxygen annealing.

Japanese Patent Publication No. 2014-89954

Oxide superconducting wires require a long time to manufacture because the oxygen annealing process is time-consuming.

One aspect of the present invention aims to provide an oxide superconducting laminate capable of efficiently undergoing oxygen annealing treatment, and a method for manufacturing the same.

One aspect of the present invention provides an oxide superconducting laminate comprising 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 in contact with the oxide superconducting layer, wherein a void is formed in the protective layer that is in contact with the interface with the oxide superconducting layer.

According to the above embodiment, during the oxygen annealing process, a portion of the oxygen-containing gas passes through the interior of the protective layer, reaches the voids in contact with the interface, and comes into contact with the oxide superconducting layer. Therefore, the contact area between the oxygen-containing gas and the oxide superconducting layer is increased compared to the case without voids. This increases the diffusion rate of oxygen in the superconducting layer. Thus, the oxygen annealing process can be performed efficiently.

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.

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.

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.

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 process can be performed efficiently.

The process of storing the oxide superconducting layer in the atmosphere is preferably 24 to 48 hours.

According to one aspect of the present invention, an oxide superconducting laminate capable of efficiently undergoing annealing treatment and a method for manufacturing the same can be provided.

This is a cross-sectional view of an oxide superconducting wire according to an embodiment. This is a schematic diagram showing a portion of the cross-section of the oxide superconducting layer and the protective layer. This image shows a portion of the cross-section of the oxide superconducting layer and the protective layer.

The oxide superconducting laminate according to an embodiment of the present invention will be described in detail below with reference to the drawings. For convenience, the drawings used in this description may show enlarged versions of key parts to clearly illustrate the features of the present invention; therefore, the dimensional ratios of each component may not be the same as those of the actual components.

[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.

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".

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, intermediate layer 2, oxide superconducting layer 3, and 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 perpendicular to the length and thickness directions of the oxide superconducting laminate 5 and the oxide superconducting wire 10.

The metal substrate 1 is made of metal. Specific examples of metals constituting the metal substrate 1 include nickel alloys such as Hastelloy (registered trademark); stainless steel; and oriented Ni-W alloys with a textured surface introduced into the nickel alloy. The thickness of the metal substrate 1 can be adjusted as appropriate depending on the purpose, for example, in the range of 10 to 500 μm. One side of the metal substrate 1 (the side on which the intermediate layer 2 is formed) is called the first main surface 1a, and the side opposite to the first main surface 1a is called the second main surface 1b. The metal substrate 1 is an example of a "substrate." The first main surface 1a is an example of a "main surface."

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, and may include, for example, a diffusion prevention layer, a bed layer, an orientation layer, a capping layer, etc., in the order from the metal substrate 1 side to the oxide superconducting layer 3 side. These layers are not necessarily provided one by one; some layers may be omitted, or two or more layers of the same type may be repeatedly laminated. Note that the intermediate layer 2 is not an essential component of the oxide superconducting laminate 5; if the metal substrate 1 itself has orientation properties, the intermediate layer 2 may not be formed.

The diffusion prevention layer has the function of suppressing the diffusion of some components of the metal substrate 1 and their incorporation into the oxide superconducting layer ₃ as impurities. The diffusion prevention layer is composed of, for example, _Si₃N₄ , _Al₂O₃ , GZO ( _{Gd₂Zr₂O ₷} ), _etc. The thickness of the diffusion prevention layer is, for example _, 10 to 400 nm.

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 , _La₂O₃ , etc. The thickness of _the bed layer is, for example, 10 _{to 100 nm} .

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 Gd₂Zr₂O₃} , _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.

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 .

The oxide superconducting layer 3 is composed of an oxide superconductor. The oxide superconductor is not particularly limited, but examples include the RE-Ba-Cu-O oxide superconductor (REBCO oxide superconductor) represented by the general formula REBa ₂ Cu ₃ O _X (RE123). As the rare earth element RE, one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu can be used. Among these, one of Y, Gd, Eu, and 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.

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 approximately 1 to 100 μm.

5a is the first main surface of the oxide superconducting laminate 5 (the 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 a side surface of the oxide superconducting laminate 5 (the side surface of the metal substrate 1, the side surface of the intermediate layer 2, the side surface of the oxide superconducting layer 3, and the 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 (the 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.

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 section that commutates the overcurrent generated when the oxide superconducting layer 3 transitions to a normal conducting state.

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).

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, observation can be performed at any magnification. For example, in the cross-sectional view of the oxide superconducting layer 3 and 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.

The protective layer 4 contains one or more voids. At least one void is in contact with the interface 7. Preferably, the number of voids in contact with the interface 7 is between 3 and 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 during the oxygen annealing process described later, efficiently supplying oxygen to the oxide superconducting layer 3 from the voids. 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 sufficient contact area between the oxide superconducting layer 3 and the protective layer 4, suppressing interfacial resistance between the oxide superconducting layer 3 and the protective layer 4. Voids not in contact with the interface 7 may be formed within the protective layer 4. Gases such as air, oxygen, or organic compound gases may be present in these voids.

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 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 the average number per 1 μm of interface 7 length for interfaces 7 with a length of 3 μm or more.

In the example shown in Figure 2, the voids V1 to V8 formed inside the protective layer 4 are in contact with the 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".

The size of the void in contact with interface 7 (the lengthwise dimension of interface 7) is not particularly limited. For example, the size of the void that can affect the interfacial resistance between the oxide superconducting layer 3 and the protective layer 4 is 0.1 nm or larger. For example, the void size is 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 (the left-right direction in Figure 2).

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.

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.

[Method for manufacturing oxide superconducting laminates]
Next, an example of a method for manufacturing 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.

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.

Next, an oxide superconducting layer 3 is formed on the intermediate layer 2. The oxide superconducting layer 3 can be formed using vapor deposition methods such as PLD or MOCVD. For example, the oxide superconducting layer 3 is deposited using a PLD method with a target made of REBCO-based material. The deposition of the oxide superconducting layer 3 is carried out in a 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. Storage time can range from a few hours to several tens of hours.

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.

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.

[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, a portion 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 increased compared to 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.

[Effects of the manufacturing method of the oxide superconducting laminate according to the embodiment]
In the above 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.

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.

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.

An oxide superconducting layer 3 was deposited on the intermediate layer 2 by a PLD method using a target made of _REBCO - _based material ( _EuBa2Cu3Oy ).

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.

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) was found ( _Ic / _Ic0 in the range of 0.95 to 1.05), and this was designated as Example 1. The ratio of the oxygen annealing time _T1 of Example 1 sample to the annealing time _T0 of a conventional oxide superconducting laminate ( _T1 / _T0 ) was determined.
Furthermore, TEM observation was performed on a cross-section along the thickness direction of the protective layer 4, 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.

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.

(Example 2)
The oxide superconducting laminate 5 was fabricated in the same manner as in Example 1, except that the interval from the completion of the formation of the oxide superconducting layer 3 to the start of the formation of the protective layer 4 was set to 36 hours.
The ratio of the oxygen annealing time _T2 of the Example 2 sample to the annealing time _T0 of the conventional oxide superconducting laminate ( _T2 / _T0 ) 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.

(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 of the oxygen annealing time _T3 of the sample in Example 3 to the annealing time _T0 of the conventional oxide superconducting laminate ( _T3 / _T0 ) 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.

(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.

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. The shorter the waiting time, the shorter the 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.

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 (4)

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. 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 . 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. 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 .