JPH04315705A - Superconducting tape wire material - Google Patents

Abstract

PURPOSE:To provide a practical superconduct tape wire material excellent in a superconductive characteristic by application of film forming technology. CONSTITUTION:After a laminated body of an amorphous thin film 12 and a stabilizing material thin film 3 both to be a base of a superconducting thin film 2 is laminated for forming a tape wire material source 11 on an organic substance tape 5 having relatively small surface roughness and thermally decomposed under a temperature (about 800 deg.C or higher) within a crystallizing temperature to a superconductor, the organic substance tape 5 and a laminated body thereon are heated under a temperature of 800 deg.C or higher to decompose and burn the organic substance tape 5, thus producing a superconducting tape wire material. Consequently, the amorphous thin film 12 is crystallized to a superconducting thin film 2 of a relatively excellent quality. In addition, adjustment of thickness of the stabilizing material thin film 3 can make a ratio of thickness of the superconducting film 2 to the total thickness a practical value of 0.2 or more.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to power transmission cables, for example.
The present invention relates to a superconducting tape wire that can be suitably used for power leads for superconducting magnets, small superconducting magnets, etc., and particularly relates to a superconducting tape wire provided with an oxide superconductor film formed by a film-forming method.

0002

2. Description of the Related Art As the above-mentioned superconducting tape wire, there is conventionally a ribbon sheath wire using a Y-based or Bi-based oxide superconductor. The above-mentioned ribbon sheath wire is usually produced by filling a metal pipe made of silver, copper, etc. with oxide powder of a desired composition, and rolling the pipe in the radial direction to orient the oxide crystals inside. It is finally produced by applying heat treatment. According to the above-mentioned ribbon sheath wire, although it has to be kept at a relatively low temperature (4.2 K), it currently has good superconducting properties (critical current density (Jc), which is an indicator of the quality of superconducting material) ≧104 A
/cm2 at 1T) was obtained.

0003

[Problem to be solved by the invention] In the above-mentioned ribbon sheath wire, calcined powder is used as the raw material powder for the superconductor, and bonding (superconducting bonding) between these crystal grains is achieved through final heat treatment. There is. However, depending on the bonding method described above, the superconducting bond is not necessarily sufficient, and as a result, the critical current density Jc
Alternatively, it is not possible to obtain a high critical magnetic field Hc. This is due to insufficient bonding between the bonded grains of the ribbon sheath wire, and this is also reflected in the temperature dependence of AC magnetic susceptibility shown in FIG. As described above, oxide superconductors have complex crystal structures, and it is extremely difficult to eliminate non-superconducting phases at grain boundaries from the above-mentioned calcined powder by heat treatment. Therefore, it has been difficult to produce a ribbon sheath wire having a critical current density Jc exceeding 105 A/cm2 even at a considerably low temperature. By the way, as a method for producing a material with excellent superconducting properties at a relatively high temperature, there is a film forming process in which a thin film is formed using vacuum film forming technology. In this film formation process, for example, a Y-based oxide superconductor is used to deposit a film on a single-crystal substrate such as MgO or SrTiO3 (a substrate polished to a surface roughness of Rmax≦10 nm) that is far superior to a ribbon sheath wire. Superconducting properties (Jc≧105 A for epitaxial films crystallized during film formation)
/cm2 at 1T, 77K, highly oriented polycrystalline film formed on amorphous (non-crystalline) and crystallized by heat treatment, Jc≧104 ~ 105A/cm2
At 1T, 77K) thin films were obtained. In the film formation process described above, the physical properties and surface shape of the substrate greatly affect the superconducting properties. For example, (1) the surface is less likely to be oxidized than copper, (2) the surface roughness is Rmax 10
nm or less, preferably 5 nm or less, (3) the components of the substrate and the oxide superconductor are difficult to diffuse into each other during film formation or heat treatment, (4) the thermal expansion coefficients of both are similar, etc. is required. In the case of a substrate that does not meet these conditions (for example, a Si single crystal substrate), the above (3) and (4)
If the above conditions are not met), the superconducting properties of the superconducting thin film will deteriorate significantly and the superconducting thin film may not become superconducting.

[0004] In order to make the superconducting wire produced using the above film forming process practical, that is, in order to maintain an effectively large critical current that is necessary when it is made into a coil, it is necessary to The ratio of the thickness of the superconducting film to the thickness of the entire superconducting wire, including the stabilizing and insulating materials that serve as a current bypass when the superconducting film transitions to normal conductivity, is 20%.
It is necessary to do more than that. On the other hand, in order to create a tape wire, a small flexible superconductor film alone is not enough; a flexible tape-shaped substrate material is required. In the case of oxide superconductor films, good superconducting properties are obtained on the oxide substrate as described above, but the surface roughness is Rm
Oxide tapes (substrates) with ax≦100 nm and a thickness of 50 μm or less are not available at present. In addition, when using metal foil as the base material, metal foil with a thickness of around 10 μm is easily available;
The surface roughness is Rmax≧0.1 μm. Therefore, it is difficult to form a high quality oxide superconductor film on the metal foil. Therefore, at present, a superconducting tape wire to which the above film formation method is applied has not been realized. In addition,
It is conceivable to increase the thickness of the superconductor film, but according to the vacuum film-forming technology described above, the film-forming speed is at most 10
μm/h or less, and if a high-quality epitaxial superconductor film is required, the film formation rate needs to be 0.5 μm/h. Also, by forming an amorphous superconductor oxide film on the above substrate and crystallizing it as the superconductor film through heat treatment in a post-process, it is necessary to form the film at a film formation rate of 2 μm/h or less. There is. Furthermore, even if the base material is an oxide single crystal, the film quality of the superconductor film laminated thereon, such as orientation and homogeneity, deteriorates as the distance from the base material increases; As shown,
It is not a good idea to try to obtain a large critical current by increasing the thickness of the superconductor film. That is, a superconducting tape wire in which the superconductor film is made as thin as possible and the film thickness ratio is large is desired. Therefore, an object of the present invention is to provide a practical superconducting tape wire with excellent superconducting properties by applying film forming technology. Specifically, under a magnetic field strength of 1 T, the critical current density Jc of the superconductor alone is 104 A/cm2 or more, and the current density Joc of the overall is 103 A/cm2.
The above object is to provide a superconducting tape wire having a critical current of 5A or more.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the main means adopted by the present invention is to provide at least an oxide superconductor film and an oxide superconductor film adjacent to the oxide superconductor film. A superconducting tape wire formed by laminating a stabilizing material film provided therein, wherein the ratio of the thickness of the oxide superconductor film to the thickness of the laminate is 0.2 or more. ing. As a means for manufacturing the superconducting tape wire, the above-described lamination is performed at a temperature below the crystallization temperature on an organic tape that thermally decomposes at a temperature within the crystallization temperature range to crystallize into the oxide superconductor film. A method for manufacturing a superconducting tape wire, which comprises laminating the organic tape and the laminate laminated thereon to a temperature within the crystallization temperature range to decompose and remove the organic tape. It is configured as.

[0006]

[Function] The superconducting tape wire of the present invention is coated on an organic tape that thermally decomposes at a temperature within the crystallization temperature range that crystallizes into an oxide superconductor film at a temperature below the crystallization temperature. After laminating a laminate consisting of a film and a stabilizing material film provided adjacent to the oxide superconductor film,
It is manufactured by a manufacturing method in which the organic tape and the laminate laminated thereon are heated to a temperature within the crystallization temperature range to decompose and remove the organic tape. Therefore, it is possible to realize a practical superconducting tape wire having good superconducting properties and having a ratio of the thickness of the oxide superconductor film to the thickness of the laminate of 0.2 or more.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples embodying the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. It should be noted that the following examples are examples of embodying the present invention, and are not intended to limit the technical scope of the present invention. Here, FIG. 1 is a schematic perspective view showing a film forming apparatus for producing a tape wire rod according to an embodiment of the present invention, FIG. 2 is a schematic plan view of the film forming apparatus, and FIG. 3(a) is a tape wire rod. FIG. 3(b) is an external view showing a tape wire manufactured from the tape wire source shown in FIG. 3(a).
FIG. 4(a) shows a second example of the tape wire source, and FIG. 4(b) is an external view showing the tape wire manufactured from the tape wire source shown in FIG. 4(a). (a) shows a third example of the tape wire source, and FIG. 5(b) shows a third example of the tape wire source.
6(a) is an external view showing the tape wire manufactured from the tape wire source shown in FIG. 6(a), and FIG. 6(b) is a fourth example of the tape wire source. FIG. 7 is an external view showing tape wire rods produced from the tape wire source shown in FIG. 7A, and FIG. 7 is a graph showing changes in critical current density or critical current with respect to magnetic field strength. As shown in FIGS. 1 and 2, the film forming apparatus 20 for manufacturing the tape wire of this embodiment includes a set of tape reels 22 and 23 that are rotated in both directions to wind up or feed out the organic tape 5. and a tape cooling drum 21 disposed between the pair of tape reels 22 and 23 to cool the organic tape 5 to a predetermined temperature or lower, and a tape cooling drum 21 that cools the organic tape 5 to a predetermined temperature or lower, and a Y-based oxide, magnesium oxide, and silver alloy respectively onto the organic tape 5. sputter guns 24, 25, 26 for forming a layered film on the
This magnetron sputtering apparatus is equipped with a partition plate 30 that is arranged around sputtering guns 4, 25, and 26 to prevent the film-forming operations of other sputtering guns from being affected. Each of the above sputter guns 2
The compositions of targets 27, 28, and 29 of No. 4, 25, and 26 are Y1 Ba2 Cu3 Ox, MgO, respectively.
, Ag-15%Pd. In addition, when performing oxide sputtering, in order to avoid re-sputtering due to oxygen (atoms, molecules, negative ions), these oxide targets 27,
The surface 28 is arranged perpendicular to the surface of the tape 5 on the tape cooling drum 21. Further, a silver-palladium alloy target 29 serving as a stabilizing material is arranged so that its surface is parallel to the surface of the organic tape 5 on the tape cooling drum 21.

[0008] The organic tape 5 is used as a first substrate material of a tape wire source to be described later, and in this embodiment, a polyester film subjected to a reinforcement stretching process is used. The organic tape 5 may be made of polyacetate, polypropylene, polyimide, polyamideimide, polyethylene, polyethylene terephthalate, polycarbonate,
The decomposition temperature of polyvinyl chloride, polychlorinated biphenyl, polypropylene, polystyrene, polyfluoroethylene, etc. is 5.
An organic polymer material having a temperature of 00° C. or lower can also be used. For example, reinforced and stretched polyester films and polyethylene terephthalate films are used as base materials for commercially available digital cassette tapes and video tapes, and these have excellent mechanical strength, are flammable, and have a low surface roughness Rmax. Those with a diameter of 5 nm or less are easily available and are suitable as a material for manufacturing the superconducting tape wire of the present invention. In addition, the above-mentioned stabilizing material is used as the second substrate material of the tape wire source, and is less likely to be oxidized than copper, which is one of the constituent elements of oxide superconductors, in an oxidizing atmosphere, has high electrical conductivity, and is a mechanical material. A material with sufficient physical strength and flexibility is required, and noble metals such as silver, platinum, palladium, and silver-palladium alloys or alloys thereof are suitable. The raw materials for the oxide superconductor film include Y-based 123 phase, Y-based 124 phase, Y-based Ca-doped 124 phase, Bi-based 2212 phase, Bi-based 2223 phase, and all oxide superconductors such as Tl-based. can be used. Each target 27 of the film forming apparatus 20,
The film forming conditions according to Nos. 28 and 29 are shown in Table 1 below.

[Table 1] The tape temperature during film formation is the same as that of the tape cooling drum 21 mentioned above.
Both are maintained below 100°C.

The film forming apparatus 20 of this embodiment is constructed as described above. Therefore, the operation of manufacturing a tape wire on which a superconductor thin film is formed using the film forming apparatus 20 will be described below with reference to FIGS. 1 to 3(b). First, the tape is fed out from the tape reel 22 and reeled to the tape reel 23.
When the organic tape 5 having a thickness of 20 μm is passed over the tape cooling drum 21, the sputter gun 24 acts to form the amorphous thin film 12 of the Y-based oxide on the organic tape 5. The next sputter gun 25 is not in operation, and when the organic tape 5 passes through the subsequent sputter gun 26, the stabilizing material thin film 3 is laminated by the sputter gun 26 on the previously laminated amorphous thin film 12. . As a result, the organic tape 5
A laminate consisting of an amorphous thin film 12 and a stabilizing material thin film 3 as shown in FIG. This tape wire source 11 is the tape reel 23
It is wound up. The thickness of the stabilizing material thin film 3 at this time is 5
.mu.m, and the thickness of the amorphous thin film 12 of Y-based oxide is 2 .mu.m. Subsequently, the tape wire source 11 is transferred to an electric furnace separate from the film forming apparatus 20, and is heated to a pressure of 105 N/
The sample was heat treated by being held at 880°C for 30 minutes and then at 500°C for 2 hours in an oxygen atmosphere. The temperature at which the Y-based oxide crystallizes into a superconductor is approximately 800° C. or higher. In addition, the organic tape 5 is 5
Thermal decomposition occurs below 00°C. Therefore, the tape wire source 1
1 is subjected to the above heat treatment, the amorphous thin film 12 is crystallized into a polycrystalline superconductor thin film 2, and the organic tape 5 is decomposed and incinerated, as shown in FIG. 3(b).
A tape wire 1 having a superconductor thin film shown in ) is manufactured. In the tape wire 1 manufactured at this time, the thickness of the superconductor thin film 2 is 2 μm, and the thickness of the stabilizing material thin film 3 provided adjacent to the superconductor thin film 2 is 5 μm. The ratio of the thickness of the body thin film 2 to the thickness of the superconductor thin film 2 and the stabilizing material thin film 3 (laminate) is approximately 0.29 (
2/(2+5)), which is 20% or more. Therefore, the tape wire 1 is practical. Furthermore, as described above, the amorphous thin film 12 and the stabilizing material thin film 3 laminated on the relatively flat organic tape 5 maintain flatness before and after the heat treatment, and after crystallization from the amorphous thin film 12, The superconductor thin film 2 exhibits high orientation,
Critical temperature Tc = 85K, critical current density Jc (77K, 1T)≧104 ~ 105 A for this superconductor thin film 2 alone
/cm2, and the overall critical current density of the tape wire 1 as a whole Joc (77K, 1T)≧103
~104 A/cm2 could be achieved.

[0010] When producing the tape wire source, the running direction of the organic tape 5 is specified and the sputtering guns 24, 25, 2
By setting the operation order of 6 in advance, Fig. 4(a),
Tape wire sources 11a, 11b, 11c having four or more layers as shown in FIGS. 5(a) and 6(a), respectively, can be manufactured. Note that the amorphous thin film 14 is made of Mg
The insulating thin film 4 is made of O amorphous and crystallized by the heat treatment described above. Even in these cases, as long as the amorphous thin film 12 serving as the base of the superconductor thin film 2 and at least one layer of the stabilizing material thin film 3 are laminated adjacent to each other, other layer combinations are free. Subsequently, the tape wire sources 11a, 11b, and 11c are subjected to the same heat treatment as described above, thereby producing the results shown in FIGS. 4(b) and 5(
b), tape wire rod 1a as shown in FIG. 6(b), respectively.
, 1b, 1c are manufactured. Note that when the organic tape 5 is incinerated, reducing gases such as CO are generated.
This gas may cause insufficient oxidation and reduce a portion of the superconductor thin film 2, resulting in deterioration of superconducting properties. Therefore, by sandwiching the amorphous thin film 12 between the stabilizing material thin film 3 and the amorphous thin film 14 as shown in the tape wire source 11a (FIG. 4(a)), the amorphous thin film 12 is removed when the organic tape 5 is incinerated. This can prevent contact between the reducing gas and the reducing gas. Also,
Tape wire material 1 manufactured from this tape wire material source 11a
a can omit the insulating layer between the tape wires when wound as a coil in a later process, thereby making it possible to maintain a high overall critical current density Joc. For example, the amorphous thin film 14 may have a thickness of 0.
When 5 μm of MgO is used, the critical temperature Tc = 88K, Jc (77K, 1T) for the superconductor thin film 2 alone.
≧2×104 ~3×105 A/cm2, Joc(
77K, 1T) ≧2×103 ~3×104 A/cm
I was able to achieve 2. Also in the tape wire 1a, the film thickness ratio exceeds 20%.

[0011] Then, the tape wire rod 1b (Fig. 5(b)
)) is an example in which insulator thin films 4 are laminated on both sides of a superconductor thin film 2 and a stabilizing material thin film 3, and the thickness of each insulator thin film 4 is 0.5 μm. Thickness is 2μ
m, and the thickness of the stabilizing material thin film 3 is 6 μm, and the above thickness ratio exceeds 20%. Also in this tape wire 1b, Tc of the superconductor thin film 2 alone is 83K.
, Jc (77K, 1T)≧104 ~105 A/cm
2, Joc (77K, 1T) ≧103 ~ 104 A
/cm2. Since both sides of the tape wire 1b are insulating layers, the insulation between the tape wires becomes better when the wire tape is wound into a coil in a subsequent process. Also, Figure 6(b)
For the tape wire 1c, Tc of the superconductor thin film 2 alone =
84~88K, Jc (77K, 1T)≧2×104~
2×105 A/cm2, Joc (77K,
1T)≧2×103 to 2×104 A/cm2 could be achieved. In this case as well, the above thickness ratio is 20
% or more. Furthermore, the critical current Ic was 15 A or more, making it possible to realize a practical tape wire. For each of the tape wire rods 1 to 1c described above, the thickness ratio of the above thickness can be reduced to 20% by adjusting the thickness of the stabilizing material thin film 3.
It is possible to do more than that and adjust it. Each tape wire rod 1 to 1 of the above-described two-layer structure (FIG. 3(b)), three-layer structure (FIG. 4(b)), and four- to five-layer structure (FIGS. 5(b) to 6(b))
The critical current density Jc with respect to the magnetic field strength B(T) in each of the superconducting thin films 2 of c is as shown in FIG. 7, and it was possible to realize a practical tape wire in each case. Although magnetron sputtering, which is one of the vacuum film forming methods, was used to form a film on the organic tape 5, other vacuum film forming methods may be used instead. Thin films may be laminated by a coating method.

0012

[Effects of the Invention] Since the present invention is constructed as described above, film forming technology can be applied to the production of superconducting tape wires. This makes it possible to provide an extremely practical superconducting tape wire with excellent superconducting properties.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing a film forming apparatus for manufacturing a tape wire according to an embodiment of the present invention.

FIG. 2 is a schematic plan view of the film forming apparatus.

FIG. 3(a) shows a first example of the tape wire source, and FIG. 3(b) is an external view of each tape wire manufactured from the tape wire source in FIG. 3(a).

FIG. 4(a) shows a second example of the tape wire source, and FIG. 4(b) is an external view of the tape wire manufactured from the tape wire source of FIG. 4(a).

FIG. 5(a) shows a third example of the tape wire source, and FIG. 5(b) is an external view of each tape wire manufactured from the tape wire source of FIG. 5(a).

FIG. 6(a) shows a fourth example of the tape wire source, and FIG. 6(b) is an external view of the tape wire manufactured from the tape wire source of FIG. 6(a).

FIG. 7 is a graph showing changes in critical current density or critical current with respect to magnetic field strength.

FIG. 8 is a graph diagram showing the relationship between temperature and AC magnetic susceptibility in a ribbon sheath wire.

FIG. 9 is a graph diagram showing the relationship between film thickness and critical current density in a superconducting film on a single crystal substrate.

[Explanation of symbols]

1, 1a, 1b, 1c...Tape wire 2...Superconductor thin film 3...Stabilizing material thin film 4...Insulator thin film 5...Organic tape 11, 11a, 11b, 11c...Tape wire source 1
2, 14... Amorphous thin film 20... Film forming device 21... Tape cooling drum 22, 23... Tape reel 24, 25, 26... Sputter gun 27, 28, 29... Target 30... Partition plate

Claims (3)

[Claims] Claim 1: A superconducting tape wire formed by laminating at least an oxide superconductor film and a stabilizing material film provided adjacent to the oxide superconductor film, wherein the thickness of the oxide superconductor film and the A superconducting tape wire characterized in that the thickness ratio of the laminate is 0.2 or more. Claim 2: The laminate includes an oxide superconductor film and/or an oxide superconductor film.
The superconducting tape wire according to claim 1, further comprising an insulating film adjacent to the stabilizing material film. 3. After laminating the laminate at a temperature below the crystallization temperature on an organic tape that thermally decomposes at a temperature within the crystallization temperature range that crystallizes into the oxide superconductor film, the organic material is The superconducting tape wire according to claim 1 or 2, wherein the organic tape is decomposed and removed by heating the tape and the laminate laminated thereon to a temperature within the crystallization temperature range. manufacturing method.