JP4200843B2 - Thin film superconducting wire and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film superconducting wire used for a superconducting device that requires generation of a high magnetic field and a method for manufacturing the same.
[0002]
[Prior art]
Conventional thin film superconducting wires have been obtained by mounting an intermediate layer on one side of a tape-like substrate and disposing the superconducting layer thereon. Since these thin film superconducting wires exhibit superconductivity at a relatively high temperature and can be cooled with nitrogen gas, they are promising materials for generators, linear motor cars, and the like. However, since the superconducting layer is a thin film, even if it has a large critical superconducting density (Jc) from the cross-sectional ratio with the tape-like base material, the superconducting layer has a tape-like base material of about 0.1 to 5 μm at most. Since the cross-sectional thickness is about 10 to 100 μm, the total current density could not be obtained.
[0003]
As a countermeasure, means for providing superconducting layers on both sides of the tape was introduced (see Patent Document 1). According to this means, an oxide superconductor layer is provided on both sides or both sides and both sides of a metal or ceramic substrate via a silver or silver alloy layer, and this is fired. However, the manufacturing method is such that a superconducting layer is provided on one side of a silver or silver alloy tape, and this is applied with a silver paste on both sides of a tape of a metal or ceramic base material, or a width double the tape width of the base material. A silver tape is used, a superconducting layer is provided on one side, and the base tape is wrapped with this. Certainly, since the superconducting layer is provided on both sides of the tape, the current density in the cross section of the tape can be increased.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 08-212846 (0015, 0022-0026)
[0005]
[Problems to be solved by the invention]
In the invention described in Patent Document 1, the current density can surely be increased. However, operations such as tape bonding are complicated in the production. Moreover, it is a combination of materials that must have such a configuration. Along with a simpler manufacturing method, a combination of materials to achieve the manufacturing method is an issue.
[0006]
[Means for Solving the Problems]
The present invention is a thin film superconducting wire characterized in that an oxide superconducting layer is formed on both sides of a tape-like metal via an intermediate layer of a metal oxide film. With such a configuration, a current density approximately twice that of a thin film superconducting wire having a superconducting layer on one side can be obtained.
Here, it is preferable to have a metal layer outside the oxide superconducting layer because the superconducting thin film is protected. Further, it is more preferable that the metal layer is provided on both surfaces, and the metal layers are electrically connected to each other, whereby the uniformity of both the front and back surfaces can be measured.
The intermediate layer is a metal oxide containing one or more metal elements having a pyrochromic, fluorite, rock salt, or perovskite crystal structure in which a superconducting thin film can be stably stacked and the crystal orientation is stable Can be used in a single layer or multiple layers, but preferably cerium oxide (CeO ₂ ), yttria stabilized zirconia (YSZ), stabilized zirconia, barium zirconate (BaZrO ₃ ), lanthanum aluminate (LaAlO ₃₎ ), Gd ₂ Zr ₂ O ₇ , SmGdO ₃ , RE ₂ O ₃ (RE; Y, lanthanoid), or one or more monolayers or multilayers. Further, it is preferable that the intermediate layer is in-plane oriented because the crystal orientation of the superconducting thin film is stabilized.
It is particularly preferable to use an intermediate layer composed of a YSZ layer and a CeO ₂ layer thereon.
The tape-shaped metal to be used may be any of a simple metal, an alloy or a composite selected from Ni, Cr, Mn, Co, Fe, Pd, Au, Cu, and Ag. In-plane orientation is preferred. When the tape-shaped metal serving as the base material is oriented, the orientation of the intermediate layer formed on the surface is improved.
[0007]
The method for producing a thin film superconducting wire of the present invention described above has a feature that a metal tape as a base material is prepared and formed using the following steps.
a) A step of precisely polishing both surfaces of the metal tape.
b) A step of forming an intermediate layer on the surface using a vapor phase method.
c) A step of forming a superconducting layer on the surface.
d) A step of introducing oxygen into the formed superconducting layer.
That is, the method for producing a thin film superconducting wire according to the present invention has a feature that an intermediate layer and a superconducting layer are formed without taking a step of bonding two tapes or a step of wrapping.
In particular, it is preferable that the step of forming the intermediate layer is a step of forming both surfaces simultaneously, since problems such as oxidation of the other surface during single-side processing can be eliminated.
Further, it is preferable that the step of forming the superconducting layer is a step of forming both surfaces at the same time because the step can be simplified.
Furthermore, when the next step is added, the superconducting thin film is protected and stabilized.
e) forming a metal layer;
[0008]
Here, the vapor phase method for producing the intermediate layer is preferably any one of a sputtering method, an electron beam method and a pulsed laser deposition method (PLD method) or a combination of two or more thereof. When the intermediate layer is used, it is preferable that the second intermediate layer is laminated in tandem following the first intermediate layer. Of course, the vapor phase method can also form both sides of the intermediate layer simultaneously.
The superconducting layer is preferably formed by a vapor phase method. In this case, it is preferable to use a pulsed laser deposition method (PLD method). This method can also be formed on both sides simultaneously. When the intermediate layer is formed on both sides in the previous step, the superconducting layer may be formed on each side.
Alternatively, the superconducting layer may be produced by a liquid phase method. In this case, the metal organic vapor deposition method (MOD method) is preferable, and there is an advantage that the superconducting layer can be uniformly formed on both surfaces.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a thin film superconducting wire 4 having a superconducting film 3 on both surfaces of a tape-like metal 1 as shown in the longitudinal sectional view of FIG. By adopting such a shape, the current density (Je) per cross section can be dramatically increased as compared with the case of only one side. However, if the superconducting film 3 is formed directly on the tape-like metal 1, the critical superconducting density (Jc) cannot be increased, and the intermediate layer 2 is required.
This is because the tape-like metal 1 is composed of a metal polycrystal, and when the superconducting film 3 is formed thereon, a polycrystal film is similarly formed. This polycrystalline film has a crystal axis in the direction perpendicular to the surface of the tape, but cannot be aligned in the horizontal direction. Therefore, aligning this horizontal crystal axis showing the superconducting performance increases Jc.
For this purpose, an intermediate layer 2 made of a metal oxide is provided, and the intermediate layer 2 has a function of adjusting the crystal orientation of the superconducting film 3 formed thereon. That is, when the intermediate layer 2 is disposed on the surface of the tape-shaped metal 1, the intermediate layer 2 is provided at high speed by a pulse laser deposition method (PLD method) or the like. At this time, the substrate inclined film forming method (ISD method) is used. Can be used to adjust the orientation of the intermediate layer 2.
[0010]
In the present invention, since the metal oxide intermediate layer 2 is provided on both surfaces of the tape-like metal 1 and the superconducting film 3 is formed on the surface, the current density (Je) per cross section can be increased. Incidentally, since the thickness of the metal tape 1 is several tens μm to several hundreds μm, the intermediate layer 2 is about several μm and the superconducting film 3 is about several μm thick. Although it should not be, it is almost the same value.
[0011]
The tape-shaped metal 1 used here can increase Je by reducing the thickness as much as possible. If it is too thin, the strength is insufficient, which affects the processability of the superconducting film 3 and the processing characteristics of the superconducting wire 4. As a material, a metal containing Ni is preferable, and Ni, a Ni—Fe alloy, and a Ni composite material are particularly preferable.
Moreover, since it is necessary to form a thin film layer uniformly on the surface of the tape-like metal 1, one having a large surface smoothness value is not preferable, and both surfaces are polished and adjusted so that the surface smoothness is 50 nm or less. It is good.
[0012]
In the intermediate layer 2, since it is necessary to align the crystal axis of the superconducting film 3 as described above, cerium oxide (CeO ₂ ), yttria-stabilized zirconia (YSZ), stabilized zirconia, barium zirconate (BaZrO ₃ ), aluminum It is preferable to use lanthanum acid (LaAlO ₃ ), Gd ₂ Zr ₂ O ₇ , SmGdO ₃ , RE ₂ O ₃ (RE; Y, lanthanoid).
The intermediate layer 2 may be a single layer, but a multilayer structure is also a preferable means for adjusting the crystal axis of the superconducting film 3. Particularly preferably, the first layer is a YSZ film and the second layer is a CeO ₂ film.
It is preferable to use REBCO (REBa ₂ Cu ₂ O _7-x : RE = Y, lanthanoid) for the superconducting film 3, particularly preferably HoBCO, SmBCO, EuBCO, NdBCO, or the like.
[0013]
In addition, the manufacturing method of this invention has the characteristics in a process. In particular, the double-side polishing process for metal tape is characterized in that a plurality of stages of polishing machines are installed alternately and passed between them to sequentially finish both sides to a highly polished surface. The schematic diagram is shown in FIG. The metal tape 5 supplied from the supply 9 is polished on both sides by a plurality of polishing machines 6, the surface is cleaned by the cleaning unit 7, the cleaning liquid and the like are dried by the drying unit 8, and stored in the take-up 10. Here, the surface smoothness is adjusted to 50 nm or less.
[0014]
Next, in the step of forming the intermediate layer using a vapor phase method, after removing the oxide film and the like generated on the surface of the metal tape after the step, the film is formed by a sputtering method, an electron beam method, a pulse laser deposition method, or the like. Form. As an example, FIG. 3 shows a schematic diagram of forming a multilayer intermediate layer on both sides simultaneously. In FIG. 3, the outside air is blocked from the supply 11 to the take-up 16. After the surface of the metal tape 12 with adjusted surface smoothness sent from the supply 11 is cleaned with an oxide film removing device 13 such as a vacuum reduction furnace, a film is simultaneously formed from both sides by a first intermediate layer forming device 14. As a result, the film is simultaneously formed on both sides of the tape. Further, as shown in FIG. 3, when the intermediate layer is formed into a plurality of layers, the film forming apparatuses are arranged in tandem, and immediately after the first layer is formed, the second intermediate layer forming apparatus 15 continues to form a film. Thus, the film can be efficiently formed. The metal tape 12 on which the multilayer intermediate layer is formed is wound up by a winding 16. In FIG. 3, a sputtering apparatus is exemplified for forming the intermediate layer. Of course, as long as it is a vapor phase method, other methods than the sputtering method, the electron beam method, and the pulse laser deposition method may be used. The example of FIG. 3 is a method for forming a plurality of intermediate layers at the same time on both sides, but it may be formed on each side, or a plurality of intermediate layers may be formed separately.
[0015]
However, when forming this intermediate layer one side at a time, there is a high possibility that the metal on the surface where the intermediate layer is not formed is oxidized in the step of forming the intermediate layer on one surface. Therefore, it is preferable to form the intermediate layer simultaneously on both sides. When a plurality of intermediate layers are formed, it is preferable that at least the first intermediate layer is formed on both sides simultaneously, and the second intermediate layer may be formed separately.
[0016]
Thereafter, in the step of forming the superconducting layer on the surface of the intermediate layer, a vapor phase method and a liquid phase method can be used. When using the vapor phase method, the above-described PLD method is preferably used. In this case, the superconducting layer can be formed on each side. When both surfaces are formed simultaneously, as shown in the schematic diagram of FIG. 4, the both surfaces are not exposed to the plasma 23, 23 'from the target surfaces 22, 22' by the excimer lasers 21, 21 'at the same position. The position is slightly moved back and forth like the lasers 21 and 21 '. Also, if the plasma 23, 23 'is applied obliquely as in the ISD method rather than the plasma 23, 23' being applied perpendicularly to the tape surfaces 24, 24 ', the superconducting layer is formed with the crystal axis direction aligned. Therefore, it is particularly preferable.
[0017]
Further, in the formation of the superconducting layer, it is preferable to form both surfaces simultaneously as described above, but in some cases, one surface may be formed. This is because the intermediate layer is already formed on the surface of the metal tape, so that even if the superconducting layer is formed on only one side, the opposite side not formed is not affected by oxidation. In addition, the superconducting layer formed on one side has a function of continuing the characteristics of the first superconducting layer when the superconducting layer is formed on the back side.
[0018]
When such a superconducting layer is formed on each side, there is a preferred method, unlike the method of FIG. 5 and 6 are explanatory diagrams. In FIG. 5, the metal tape 30 formed on the intermediate layer or both surfaces supplied from the supply 31 forms a superconducting layer on the surface by the plasma 35 from the target surface 34 by the excimer laser 33, and guide reels 36, 37, 38. Go back through. The returned metal tape 30 has a surface on which the superconducting layer is not formed, and a superconducting layer is formed on the surface by plasma 35 from the target surface 34 by the excimer laser 33 in the same manner as described above. The take-up 32 accommodates a thin film superconducting wire having a superconducting layer formed on both sides. Although FIG. 5 shows a method of forming a superconducting layer on each side, it is completed in one process.
[0019]
FIG. 6 shows an application example thereof, which is a method of forming a superconducting layer by passing a metal tape having an intermediate layer formed on both sides through one plasma a plurality of times. Superconducting layers are formed on a plurality of metal tapes 30 on which the plasma 35 from the target surface 34 reciprocates by the excimer laser 33. The metal tape 30 can be used in various ways, for example, when the same metal tape is used repeatedly on both sides and when a plurality of metal tapes are used in parallel.
[0020]
When using the liquid phase method, it is preferable to use the organometallic folding method (MOD method), and an organic compound of a metal component that becomes a superconducting composition, for example, metal acetate is made into an aqueous solution, and this is coated on a tape and dried. Get. If the coating is further heated, organic matter can be removed.
In particular, in the case of the MOD method, there is an advantage that simultaneous film formation on both sides is facilitated with simple equipment.
[0021]
Although a superconducting film layer can be formed as described above, it is necessary to use an oxide film in order to exhibit superconductivity. After the above steps, an oriented crystal layer of the superconducting film can be obtained by adding an oxygen introduction step such as a heat treatment step or a baking step.
[0022]
【Example】
Examples are given below, but the present invention is not limited to the contents of the examples.
(Example 1)
A Ni—Fe alloy tape having an in-plane orientation of 11 ° with a width of 1 cm and a thickness of 0.1 mm was prepared, polished on both sides, and the surface smoothness was measured with an atomic force microscope (AFM). It was. A YSZ film was formed on both surfaces of this using a high frequency sputtering method, and then a CeO ₂ film was formed to a thickness of 2 μm. On both surfaces of this intermediate layer, a CeO ₂ film was used as a cap layer to form a 0.05 μm film by the PLD method. On top of this, a HoBCO film was formed on both sides by using a high-frequency sputtering method. After the heat treatment, the critical current was measured by an energization method using four terminals. As a result, Ic = 440A (77K, 0T) and Jc = 1.1 MA / cm ² (77K, 0T) were obtained. As a result, the current density (Je) per total cross-sectional area was Je = about 44 kA / cm ² (77K, 0T).
[0023]
(Example 2) A Ni / stainless / Ni composite tape having a width of 1 cm and a thickness of 0.05 mm with an in-plane orientation of 10 ° was prepared, and both surfaces were polished and the surface smoothness was measured by AFM. It was. A YSZ film was formed on both sides of this using an electron beam evaporation method, and then a CeO ₂ film was formed to a thickness of 2 μm. On both surfaces of this intermediate layer, a CeO ₂ film was used as a cap layer to form a 0.05 μm film by the PLD method. A HoBCO film was formed on both sides by 1.5 μm using a high frequency sputtering method. After the heat treatment, the conductivity was measured by an energization method using four terminals. As a result, Ic = 350A (77K, 0T) and Jc = 1.25 MA / cm ² (77K, 0T) were obtained. As a result, a current density of Je = about 70 kA / cm ² (77K, 0T) was obtained.
[0024]
(Example 3) A Ni-Fe alloy tape having a width of 1 cm and a thickness of 0.1 mm with an in-plane orientation of 12 ° was prepared, and both surfaces were polished and the surface smoothness was measured by AFM. A YSZ film was formed on both surfaces of this using a high frequency sputtering method, and then a CeO ₂ film was formed to a thickness of 2 μm. On both surfaces of this intermediate layer, a CeO ₂ film was used as a cap layer to form a 0.05 μm film by electron beam evaporation. A SmBCO film was formed on each side using the PLD method, and 3 μm was formed on both sides as a result. After the heat treatment, the conductivity was measured by an energization method using four terminals. As a result, Ic = 480A (77K, 0T) and Jc = 0.8 MA / cm ² (77K, 0T). As a result, a current density of Je = about 48 kA / cm ² (77K, 0T) was obtained.
[0025]
(Comparative Example 1) A Ni-Fe alloy tape having an in-plane orientation of 11 ° and a width of 1 cm and a thickness of 0.1 mm was prepared, polished on one side, and the surface smoothness measured by AFM was 20 nm. A YSZ film was formed on this surface by using a high frequency sputtering method, and then a CeO ₂ film was formed to a thickness of 2 μm. A 0.05 μm film was formed on the surface of the intermediate layer by a PLD method using a CeO ₂ film as a cap layer. A 2 μm thick HoBCO film was formed thereon using the PLD method. After the heat treatment, the conductivity was measured by an energization method using four terminals. As a result, Ic = 240A (77K, 0T) and Jc = 1.2 MA / cm ² (77K, 0T). As a result, a current density of Je = about 24 kA / cm ² (77K, 0T) was obtained.
[0026]
(Comparative Example 2) A Ni / stainless steel composite tape having an in-plane orientation of 10 ° in width 1 cm and thickness 0.05 mm was prepared, and this Ni surface side was polished on one side and the surface smoothness was measured by AFM. It was 10 nm. A YSZ film was formed on this surface by using a high-frequency sputtering method, and then a CeO ₂ film was combined to form 2 μm. A 0.05 μm film was formed on the surface of the intermediate layer by an electron beam evaporation method using a CeO ₂ film as a cap layer. A HoBCO film having a thickness of 1.5 μm was formed thereon using the PLD method. After the heat treatment, the conductivity was measured by an energization method using four terminals. As a result, Ic = 150A (77K, 0T) and Jc = 1.0 MA / cm ² (77K, 0T) were obtained. As a result, a current density of Je = about 30 kA / cm ² (77K, 0T) was obtained.
[0027]
By comparing the above examples and comparative examples, the current density (Je) of the cross section of the tape is greatly increased, and a value nearly doubled is obtained. That is, by forming superconducting layers on both sides of the tape, the current density in the tape cross section can be increased almost twice. Moreover, according to the manufacturing method of the present invention, it can be manufactured without greatly increasing the number of steps compared to the conventional case of forming a superconducting film on one side.
[0028]
【The invention's effect】
According to the present invention, the current density per cross section in the thin film superconducting wire can be dramatically increased, and the manufacturing method is a means that can be manufactured without significantly increasing the workability of the single-sided superconducting wire.
[Brief description of the drawings]
FIG. 1 is a schematic view of a longitudinal section of the present invention.
FIG. 2 is a schematic view of a step of precisely polishing both surfaces in the production method of the present invention.
FIG. 3 is an example of a step of forming an intermediate layer in the manufacturing method of the present invention.
FIG. 4 is an example of a process for forming a superconducting layer in the manufacturing method of the present invention.
FIG. 5 is another example of a process of forming a superconducting layer in the manufacturing method of the present invention.
FIG. 6 is still another example of the step of forming a superconducting layer in the manufacturing method of the present invention.
[Explanation of symbols]
1. Tape-like metal Intermediate layer 3. 3. Superconducting film 4. Thin film superconducting wire Metal tape6. Polishing machine 7. 7. Cleaning unit Drying section 9. Supply 10. Winding 11. Supply 12. Metal tape 13. Oxide film removing device 14. First intermediate layer forming device 15. Second intermediate layer forming device 16. Winding 21, 21 '. Excimer lasers 22, 22 '. Target surfaces 23, 23 '. Plasma 24, 24 '. Tape surface 30. Metal tape 31. Supply 32. Winding 33. Excimer laser 34. Target surface 35. Plasma 36, 37, 38. Guide reel

Claims (5)

An oxide superconducting layer is formed on both sides of the tape-shaped metal via an intermediate layer of a metal oxide film, and has metal layers on both outer sides of the oxide superconducting layer, and the metal layers on both sides are mutually connected. A thin film superconducting wire characterized by being electrically connected . The intermediate layer is cerium oxide (CeO ₂ ), yttria stabilized zirconia (YSZ), stabilized zirconia, barium zirconate (BaZrO ₃ ), lanthanum aluminate (LaAlO ₃ ), Gd ₂ Zr ₂ O ₇ , SmGdO ₃ , RE The thin film superconducting wire according to claim 1, comprising one or more single layers or multiple layers selected from the group of ₂ O ₃ (RE; Y, lanthanoid). The thin film superconducting wire according to claim 1, wherein the intermediate layer is in-plane oriented. It said tape-like metal is Ni, Cr, Mn, Co, Fe, Pd, Au, Cu, and metal plain selected from Ag, according to any one of claims 1 to 3 is either alloys and composites Thin film superconducting wire. The thin film superconducting wire according to claim 4 , wherein the tape-shaped metal is in-plane oriented.

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