JP2014162973A - Target for forming oxide superconductive thin film, production method thereof, and production method of oxide superconductive wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a target for forming an oxide superconductive thin film comprising a sintered body, which is a target hardly generating a fracture or a crack, and to provide a production method thereof, and a production method of an oxide superconductive wire rod.SOLUTION: A target is used for generating an oxide superconductive thin film represented by a composition formula REBaCuO(RE is one or two or more kinds of rare earth elements), on a substrate by a deposition method, and comprises a sintered body containing a REBaCuOcomposition and an organic binder. The carbon content in the sintered body is 350 ppm or less.

Description

  The present invention relates to a target for forming an oxide superconducting thin film, a method for producing the same, and a method for producing an oxide superconducting wire.

It is desired to provide a superconducting conductor or a superconducting coil for power supply by processing an RE-123 series oxide superconductor (REBa ₂ Cu ₃ O _X : RE is a rare earth element) into a wire. As an example of the structure of an oxide superconducting conductor, an intermediate layer having a good crystal orientation is formed on the surface of a metal tape substrate by an ion beam assisted deposition method (IBAD method), and the oxide is formed on the intermediate layer by a film forming method. An oxide superconducting conductor having a structure in which a superconducting thin film is formed and an Ag protective layer and a Cu stabilizing layer are laminated on the surface has been developed.

As an example of the manufacturing method of the RE123-based oxide superconductor, a target made of a sintered body having the same composition as that of the RE123-based oxide superconductor is used, and this target is irradiated with pulsed laser light on the substrate. There has been a laser vapor deposition method for producing an oxide superconducting wire by forming a thin film of an oxide superconductor.
A target used in this laser vapor deposition method is generally produced by compacting a raw material powder having a composition of REBa ₂ Cu ₃ O _x and then sintering at a high temperature. For example, it is produced by obtaining a mixed powder having a target composition ratio by a chemical reaction, pulverizing, classifying, compressing and processing it into a target shape, and then sintering. However, a target made of a compacted body has a problem that defects such as cracks and cracks are likely to occur in the compacted body in the compacting process. For example, in general, when a molded body after compacting this type of powder is taken out of the mold, a force is applied to the molded body due to friction with the inner wall of the mold, and when it is peeled off from the mold, it is separated into a plate shape There is a problem that a defect called capping or lamination that causes scratches is generated.
For this reason, in general, an organic substance called a binder that serves as a binder at the time of forming a target is mixed with the raw material powder to increase the strength of the molded body so that defects such as cracks do not occur during molding.

  As an example of a technique in which this type of organic binder is used in the production of an oxide superconductor, an oxide superconductor powder and an anhydrous organic solvent solution of an organic binder having a polar group are prepared, and the oxide superconductor has a weight of 100 wt. The composition mixed so as to be 0.1 to 15 parts by weight per part is molded into a predetermined shape, and then the molded body is degreased and fired, and then heat treated at a temperature of 600 ° C. or lower in an oxygen-containing atmosphere. The technique to do is disclosed (refer patent document 1).

JP-A-1-270562

As described above, mixing an organic substance with the target may cause unnecessary element contamination in the oxide superconducting thin film. Therefore, the organic binder added at the time of molding needs to be heated and degreased after a sufficient time. .
However, when the size of the molded body is increased in order to produce a long oxide superconducting wire, the amount of the organic binder contained is also increased, and it is difficult to completely remove the organic binder from the interior of the molded body. There's a problem. As a result, carbon derived from the organic binder remains inside the obtained target, and carbon is also taken into the produced oxide superconducting thin film, which may deteriorate the characteristics of the oxide superconducting thin film. .

  The present invention has been made in view of such a conventional situation, and is a target for forming an oxide superconducting thin film made of a sintered body, and provides a target in which cracks and cracks are unlikely to occur, and a method for manufacturing the target. Objective. Moreover, this invention aims at provision of the manufacturing method of the oxide superconducting wire which used the said target.

In order to solve the above problems, the present invention generates an oxide superconducting thin film represented by a composition formula of REBa ₂ Cu ₃ O _x (RE is one or more rare earth elements) on a substrate by a film forming method. used in the case _of, a sintered body containing REBa 2 _Cu 3 _{O x} composition and an organic binder, the carbon content of the sintered body is equal to or less than 350 ppm.
If the target is a carbon content of 350 ppm or less, the amount of carbon incorporated into the oxide superconducting thin film can be sufficiently reduced when an oxide superconducting thin film is formed by a film forming method using the target. An excellent oxide superconducting thin film can be formed.

In the target of the present invention, a core part composed of a REBa ₂ Cu ₃ O _x composition to which no organic binder is added, and a REBa ₂ Cu ₃ O _x composition that surrounds the core part and to which an organic binder is added. It can be set as the structure which consists of an outer part.
In the case of a sintered body composed of a REBa ₂ Cu ₃ O _x composition containing an organic binder only in the outer part, the outer part has high strength, so when it is taken out from the mold after being compacted during production, cracks, cracks, etc. It is possible to make the structure difficult to generate. Further, if a REBa ₂ Cu ₃ O _x composition that contains an organic binder only in the outer portion, it is possible to easily remove the organics organics were vaporized decomposed by heat treatment. Therefore, when an oxide superconducting thin film is formed with a target with a low content of organic binder, the oxide superconducting thin film is excellent in superconducting properties and has few foreign substances such as carbon derived from organic substances in the formed oxide superconducting thin film. Can be formed.

In the method for producing a target of the present invention, an oxide superconducting thin film represented by a composition formula of REBa ₂ Cu ₃ O _x (RE is one or more rare earth elements) is formed on a substrate by a film forming method. used _consists REBa 2 _Cu 3 _{O x} composition and the REBa ₂ Cu ₃ O _x sintered body obtained by heating the green compact with added organic binder in the composition, the organic binder is added a core portion made of a green compact of REBa ₂ Cu ₃ O _x composition not, outer portion made of a green compact of REBa ₂ Cu ₃ O _x composition organic binder is added surrounds the periphery of the core portion charged made upon the green compact to produce an oxide superconducting thin film forming target obtained by the heat treatment, the the molding cavity of the mold REBa ₂ Cu ₃ O _x composition from the The organic binder was charged with REBa ₂ Cu ₃ O _x composition comprising, by charging the REBa ₂ Cu ₃ O _x composition without the organic binder inside side of the molding cavity in the outer side of the molding cavity An inner and outer two-layer laminate is formed, the laminate is compacted with a mold, and then heat-treated to produce a target.
By this manufacturing method, a target free from defects such as cracks and cracks can be manufactured. In addition, when the organic matter contained in the outer portion of the target is removed by vaporization by heating, the vaporized components can be easily discharged to the outside. It is possible to provide a target capable of forming an oxide superconducting thin film having excellent superconducting properties with little risk of containing organic binder-derived carbon in the thin film.

In the production method of the present invention, the green compact obtained by compacting the laminate with the mold can be sintered after heat treatment and degreasing.
If degreasing is performed by heat treatment before sintering, organic substances constituting the organic binder can be vaporized and removed, and an oxide superconducting thin film with a reduced amount of carbon derived from the organic binder can be formed.

The method for producing an oxide superconducting wire according to the present invention is a case where an oxide superconducting wire is produced by forming an intermediate layer on a tape-shaped metal substrate and forming an oxide superconducting thin film thereon by a film forming method. An oxide superconducting thin film is formed using any of the targets described above.
By forming an oxide superconducting thin film using any of the targets described above, an oxide superconducting wire having an oxide superconducting thin film with a low carbon content and excellent superconducting properties can be produced.

  ADVANTAGE OF THE INVENTION According to this invention, the target which can form the oxide superconducting thin film which reduced the carbon content derived from an organic binder by the film-forming method can be provided.

FIG. 1A is a cross-sectional view of a first embodiment of a target for producing a superconducting thin film according to the present invention, and FIG. 1B is a configuration diagram for explaining an example of a method for manufacturing the target. FIG. 2 is a side view showing a schematic configuration of a film forming apparatus used when an oxide superconducting thin film is formed using the target. The perspective view of the superconducting wire manufactured using the target for superconducting thin film preparation concerning the present invention.

  Hereinafter, a target for manufacturing an oxide superconducting thin film and a method for manufacturing the same according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below. In addition, the drawings used in the following description may show the main parts in an enlarged manner for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of the respective components are the same as the actual ones. Not always.

The target for preparing an oxide superconducting thin film according to the present invention is used as a target when an oxide superconducting thin film is formed using, for example, a pulse laser deposition method (PLD method) described later.
This target includes a rare earth oxide superconducting sintered body, and calcinates a raw material powder containing a rare earth element compound (compound of element RE), a Ba compound, and a Cu compound to obtain a calcined body one or more times. A calcining step, a crushing step for crushing the calcined body to obtain a pulverized powder, a molding step for mixing the pulverized powder with an organic binder as necessary, and molding to obtain a molded product, and heating the molded product And a degreasing step for degreasing and a firing step for firing a molded body to obtain a sintered body.
As the rare earth element RE compound, Ba compound, and Cu compound, powders of oxides or carbonates of these elements can be used.

These powders are weighed and mixed so that the composition ratio of the target oxide superconductor is obtained, and calcined as necessary. The calcination is performed by heating the mixture to about 800 to 1000 ° C. and then baking after preparing a mixed powder. After firing, the calcined product is pulverized, sieved as a pulverized powder, and used as a pulverized product having a uniform particle size for a molding process described later.
In addition, in the molding process, a mold is used, but an organic binder is mixed with the pulverized powder that forms the outer portion of the molded body that touches the mold, and the inner portion of the outer portion does not contain an organic binder. It is preferable to fill only and compact. The above process will be described in detail later.

Rare earth oxide superconducting sintered body contained in the _target bake REBa ₂ Cu ₃ O x (RE is at least one element selected from among rare earth elements) REBa ₂ Cu ₃ O _x composition represented by Examples of constituent elements RE include Y, La, Nd, Sm, Eu, Er, and Gd. Preferably, RE123-based compositions include Y123 (YBa ₂ Cu ₃ O _x ) or Gd123 (GdBa ₂ Cu ₃ O _x ).
In addition to the REBa ₂ Cu ₃ O _x composition, the target may contain a rare-earth element compound, a Ba compound, or a heterogeneous phase derived from a Cu compound as a raw material used in manufacturing the target. . In addition, when an artificial pin is introduced into the oxide superconductor thin film, an artificial pin material may be added to the target.

As shown in FIG. 1A, the target 11 of the present embodiment has a disk shape as a whole, but a core portion 11A made of a disk-shaped sintered body that occupies the inside of the target 11, and the core portion 11A. The outer shell 11B is made of a sintered body formed so as to surround the outer side of the outer shell. The outer diameter of the target 11 used in the present embodiment is about 100 to several hundred mm, the overall thickness is about 10 to several tens mm, and the thickness of the outer portion 11B covering the core portion 11A is about 1 to 4 mm and uniform. The thickness is preferably about 2 to 3 mm.
In the target 11, the core part 11A does not contain carbon derived from an organic binder, and the outer part 11B contains some carbon derived from an organic binder.
In the target 11, the REBa ₂ Cu ₃ O _x composition in which the compound powder of the element RE constituting the target RE-123-based oxide, the Ba compound powder, and the Cu compound powder are blended so as to have a target composition ratio, or the REBa ₂ Cu ₃ O _x composition REBa ₂ Cu ₃ O _x core portion 11A of the composition of a sintered body obtained by sintering after powder after calcination was calcined is formed 0.5 to 5 on the raw material mixture The outer portion 11B is composed of a sintered body obtained by compacting and sintering a REBa ₂ Cu ₃ O _x composition to which an organic binder of about mass% is added.

In order to produce the target 11 having a two-layer structure, as an example, the use of the mold P with the inside of the punch P ₁ and the lower punch P ₂ of the cylindrical die body P ₃ on shown in FIG. 1 (b) Can do. The upper punch P ₁ and the advance of the lower punch P ₂ is separated vertically between them the mold cavity C is formed.
A required amount of REBa ₂ Cu ₃ O _x composition B1 containing the organic binder and REBa ₂ Cu ₃ O _x composition B2 containing no organic binder are charged into the molding cavity C, and the upper punch P ₁ and the lower punch P ₂ are loaded. By applying pressure in a uniaxial direction and compacting (consolidating), a disk-shaped compact can be obtained.
When charging the REBa ₂ Cu ₃ O _x composition into the mold, the upper punch P ₁ is removed, and the molding cavity C on the lower punch P ₂ is thinly about ₁ to 4 mm, more preferably about 2 to 3 mm. After filling and spreading the raw material mixture containing an organic binder, a cylindrical frame having a slightly smaller outer diameter than the molding cavity is inserted, and the REBa ₂ Cu ₃ O _x composition does not contain an organic binder inside the frame. And the REBa ₂ Cu ₃ O _x composition containing the organic binder is charged to the outside of the frame up to the upper end of the frame.
Thereafter, the frame is pulled out and removed, and the REBa ₂ Cu ₃ O _x composition further containing an organic binder is added to the lower side of the molding cavity as described above on the remaining REBa ₂ Cu ₃ O _x composition. By inserting the same amount as the thickness, a two-layer structure of a core portion and an outer portion surrounding the core portion can be obtained. In addition, a frame slightly lower than the target thickness can be used for the height of the frame, and a frame whose outer diameter is about several mm smaller than the inner diameter of the molding cavity can be used.

After charging the REBa ₂ Cu ₃ O _x composition, when the upper punch P ₁ is lowered as shown by the arrow in FIG. 1B, a necessary uniaxial press pressure such as about 0.5 t / cm ² is applied. A disk-shaped green compact having a two-layer structure consisting of a core portion and an outer portion surrounding the core portion can be obtained.
In this green compact, an organic binder is included in the portion constituting the outer portion to improve the strength. Therefore, when the green compact is removed from the mold P, the green compact is placed in either the upper punch P ₁ or the lower punch P _2. , can be removed slightly even if the adhesion state, or even powder compact in a state of being slightly close contact with the inner surface of the die body P _3, without causing such cracking and cracks.

A two-layer disk-shaped green compact is taken out from the mold P and degreased. Since the degreasing treatment is performed for the purpose of removing the organic binder, the degreasing treatment is performed by heating at a temperature at which the organic matter can be volatilized, for example, a temperature of about 300 to 500 ° C. for several hours to several tens of hours. By this degreasing treatment, the organic binder present in the outer portion of the green compact can be volatilized and removed, and the amount of the organic binder present in the outer portion of the green compact can be reduced as much as possible. When the organic binder is volatilized, there is a high possibility that the organic binder cannot be completely removed if the organic binder is present up to the deep part inside the green compact. Since the binder is present, it is possible to efficiently remove the organic binder by efficiently letting off the volatilized gas of the organic substance to the outside of the green compact by utilizing the vaporization phenomenon accompanying the heat treatment.
The green compact after the degreasing treatment is heated to about 900 to 1000 ° C. and baked for several tens of hours, so that the green compact can be made into a sintered body. A disk-shaped target 11 whose cross-sectional structure is shown in FIG. 1A of the structure can be obtained.

If this target 11 is taken out from the mold in the form of a green compact, it is difficult to generate defects such as cracks and cracks, so a high-quality target free from defects such as cracks and cracks even after sintering. Can be obtained. In addition, since the organic binder added to the outer portion when molding the green compact is almost removed by the degreasing treatment and the heating during sintering, the extremely small amount of carbon is removed only from the outer portion 11B. Can be obtained.
For this reason, when the oxide superconducting wire is manufactured by forming an oxide superconducting thin film by laser vapor deposition using the target 11 as will be described later, carbon is not taken into the oxide superconducting thin film, and there is little foreign matter. High quality oxide superconducting thin film can be formed.

Hereinafter, an example of a laser vapor deposition apparatus used when an oxide superconducting wire is manufactured using the target 11 manufactured as described above will be described.
A laser deposition apparatus (film forming apparatus) A to which a target 11 according to the present invention is applied includes a traveling apparatus 10 for traveling a tape-shaped substrate 2 in its longitudinal direction as shown in FIG. A target 11 installed on the lower side and a laser light source 12 provided outside the processing vessel (vacuum chamber) 18 as shown in FIG. 2 are provided to irradiate the target 11 with laser light.
The traveling device 10 includes, for example, turning member groups 16 and 17 which are a collection of turning reels for guiding the tape-like substrate 2 that travels along the film formation region 15. , 17 is configured as an apparatus capable of guiding the base material 2 so as to form a plurality of lanes of the base material 2 in the film forming region 15 around the base material 2.

The traveling device 10 and the target 11 are accommodated in a processing container 18, and the processing container 18 is a container that partitions the outside and the film formation space, has airtightness, and has a pressure resistance because the inside is in a high vacuum state. It is set as the structure which has. An exhaust means (vacuum pump) 19 for exhausting the gas in the processing container is connected to the processing container 18, and in addition, a gas supply means for introducing a carrier gas and a reactive gas is formed in the processing container. In FIG. 2, the gas supply means is omitted, and only the outline of each device is shown.
The base material 2 is wound around a supply reel 20 provided inside the processing container 18 so that the necessary length can be fed out. The base material 2 fed out from the supply reel 20 is alternately wound around a turning member group 16 in which a plurality of turning reels 16a are coaxially arranged adjacently and a turning member group 17 in which a plurality of turning reels 17a are arranged coaxially adjacently. It is hung. These turning member groups 16 and 17 are arranged apart from each other inside the processing vessel 18, and the base material 2 is arranged so as to form a plurality of parallel lanes 2A therebetween. The base material 2 is the turning member group. It is configured to be pulled out from 17 and taken up on a take-up reel 21.

Further, turning member groups 16 and 17 and a rectangular box-shaped heater box 23 surrounding the periphery thereof are provided inside the processing container 18, and the base material 2 fed out from the supply reel 20 is an inlet on one side of the heater box 23. The base member 2 is configured to pass through the portion 23 a and reach the turning member group 16, and the base material 2 drawn out from the turning member group 17 is taken up on the take-up reel 21 side through the outlet portion 23 b on the other side of the heater box 23. It is like that. In the apparatus shown in FIG. 2, the heater box 23 is provided to control the temperature of the film formation region 15, but the heater box 23 may be omitted.
A disk-shaped target 11 according to the present invention is provided below an intermediate position between the turning member groups 16 and 17. The target 11 is mounted on and supported by a disk-shaped target holder 25. The target holder 25 is rotatably supported (rotatable) by a support rod 26 attached to the center of the lower surface thereof, and further, not shown. The reciprocating mechanism is supported so as to be able to reciprocate horizontally in the Y ₁ and Y ₂ directions (the front-rear direction along the lane 2A of the base member 2 formed between the turning member groups 16 and 17) shown in FIG. The irradiation position of the laser beam with respect to the surface of the target 11 can be appropriately changed by the rotational movement of the target holder 25 and the reciprocating back-and-forth movement by these mechanisms.

  An opening 23 c is formed on the lower surface of the heater box 23 above the target 11 so as to correspond to the entire width of the plurality of lanes 2 </ b> A where the base material 2 travels between the turning member groups 16 and 17. Further, in the heater box 23, a heating device 27 such as a hot plate is disposed inside the opening 23c, and the base material 2 that travels in a plurality of lanes between the turning member groups 16 and 17 is disposed on the back side thereof. To be heated to a desired temperature. The heating device 27 may be any device as long as it can heat the base material 2 from the back side thereof, but a general heater composed of a metal disk incorporating a current-carrying electric heater can be used.

In the processing container 18, an irradiation window is formed on a side wall located on one side of the target 11 with the target 11 as a center so as to face the target 11. A condensing lens 32 and a reflection mirror 33 are provided outside the irradiation window. A laser light source 12 for ablation is disposed.
As the laser light source 12 for ablation, a laser light source showing a good energy output as a pulse laser such as an excimer laser or a YAG laser can be used. As an output of the laser light source 12, for example, a laser light source having an energy density of about 1 to 5 J / cm ² and a pulse frequency of 200 to 600 Hz can be used.
In the laser vapor deposition apparatus A, an infrared radiation thermometer for measuring the temperature of the laser light irradiation region on the target surface is installed inside the processing vessel 18 and obliquely above the target 11.

  By the way, the oxide superconducting wire 1 has an intermediate layer 5, an oxide superconducting thin film 6, and a first metal stabilizing layer 7 on one surface (surface) of a tape-like substrate 2 as shown in FIG. 3 as an example. The laminated body 9 is formed by laminating the second metal stabilizing layer 8, and almost all the circumference of the laminated body 9 is covered with a coating layer 10 made of an insulating material or the like. The covering layer 10 is in close contact with the bonding body 10a so as to cover almost the entire circumference of the laminate 9, but the covering layer 10 may be omitted if no insulation treatment is required as a superconducting wire.

In the oxide superconducting wire 1 shown in FIG. 3, the base material 2 may be any material that can be used as a substrate for a normal oxide superconducting conductor, and is preferably in the form of a flexible tape, and has heat resistance. Those made of these metals are preferred. Among heat-resistant metals, nickel (Ni) alloys are preferable. Among them, if it is a commercial product, Hastelloy (trade name, manufactured by Haynes) is suitable, and the amount of components such as molybdenum (Mo), chromium (Cr), iron (Fe), cobalt (Co) is different, Hastelloy B, Any kind of C, G, N, W, etc. can be used. Alternatively, an oriented Ni—W alloy tape base material in which a texture is introduced into a nickel alloy or the like may be used as the base material 2, and the intermediate layer 5 and the oxide superconducting layer 6 may be formed thereon.
What is necessary is just to adjust the thickness of the base material 2 suitably according to the objective, Usually, it is preferable that it is 10-500 micrometers, and it is more preferable that it is 20-200 micrometers.

The intermediate layer 5 functions as a buffer layer that relieves differences in physical properties (thermal expansion coefficient, lattice constant, etc.) from the oxide superconducting thin film 6 formed thereon, and the physical properties are the same as those of the base material 2 and oxidized. A metal oxide showing an intermediate value with the superconducting thin film 6 is preferable. Specifically as the intermediate layer _{5, Gd 2 Zr 2 O 7} , MgO, ZrO 2 -Y 2 O 3 (YSZ), SrTiO 3, CeO 2, Y 2 O 3, Al 2 O 3, Gd 2 O 3, Examples thereof include metal oxides such as Zr ₂ O ₃ , Ho ₂ O ₃ , and Nd ₂ O ₃ , and those formed by IBAD method (ion beam assisted deposition method) to adjust the crystal orientation are preferable.

The intermediate layer 5 may be a single layer or a plurality of layers. In the case of a plurality of layers, the outermost layer (the layer closest to the oxide superconducting thin film 6) has at least good crystal orientation. preferable. For this reason, after forming a first alignment layer with good crystal orientation by the IBAD method, a second alignment layer capable of epitaxial growth is laminated on the first alignment layer by a film forming method such as sputtering. It can also be a layered structure. In the case of a multilayer structure, the first alignment layer and the second alignment layer may be layers made of the same material or layers made of different materials.
The intermediate layer 5 may have a multi-layer structure in which a bed layer is interposed on the substrate 2 side. The bed layer is arranged as necessary, and is made of yttria (Y ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ , also referred to as “alumina”), or the like. The thickness of the bed layer is, for example, 10 to 200 nm.

Further, in the present invention, the intermediate layer 5 may have a multi-layer structure in which a base layer 5A composed of a diffusion prevention layer and a bed layer is laminated on the substrate 2 side. In this case, a diffusion preventing layer is interposed between the base material 2 and the bed layer. The diffusion prevention layer has a single-layer or multi-layer structure made of silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ ), or rare earth metal oxide, and has a thickness of, for example, 10 to 400 nm. .
The intermediate layer 5 may have a multilayer structure in which a cap layer 5C is further laminated on the metal oxide alignment layer 5B by the IBAD method. The cap layer 5 </ b> C has a function of controlling the orientation of the oxide superconducting layer 6 and achieving a good crystal orientation like a single crystal. Capping layer 5C is not particularly limited, specifically as _{preferred, CeO 2, Y 2 O 3} , Al 2 O 3, Gd 2 O 3, ZrO 2, Ho 2 O 3, Nd 2 O 3, YSZ And LaMnO _{3 and the} like. Among these, CeO ₂ and LaMnO ₃ are preferable from the viewpoint of matching with the oxide superconducting thin film 6. When the material of the cap layer 5C is CeO ₂ , the cap layer 5C may include a Ce—M—O-based oxide in which a part of Ce is substituted with another metal atom or metal ion.

The oxide superconducting thin film 6 can be widely applied to an oxide superconductor having a generally known composition, such as REBa ₂ Cu ₃ O _y (RE is Y, La, Nd, Sm, Er, Gd, etc. And a material such as Y123 (YBa ₂ Cu ₃ O _y ) or Gd123 (GdBa ₂ Cu ₃ O _y ). Further, other oxide superconductors, for _{example, Bi 2 Sr 2 Ca n-} 1 Cu n for _{O 4 + 2n + δ} becomes may be used in compositions such as those made of other oxide superconductors having high critical temperatures representative Of course. The thickness of the oxide superconductor thin film 6 is preferably about 0.5 to 5 μm and is preferably uniform.

The first metal stabilizing layer 7 is made of a metal material such as Ag or an Ag alloy, which has a good conductivity and a low contact resistance with the oxide superconducting thin film 6 and is compatible.
The reason why the first metal stabilizing layer 7 is made of Ag is that it has the property of making it difficult to escape the doped oxygen from the oxide superconducting thin film 6 in the annealing step of doping the oxide superconducting thin film 6 with oxygen. Can be mentioned. In order to form the first metal stabilizing layer 7 made of Ag, a film forming method such as a sputtering method is adopted, and the thickness thereof is set to about 1 to 30 μm.

The second metal stabilizing layer 8 is made of a highly conductive metal material as an example, and when the oxide superconducting thin film 6 is about to transition from the superconducting state to the normal conducting state, the first stabilizing layer 7 It functions as a bypass through which the current of the oxide superconducting thin film 6 is commutated.
The metal material constituting the second metal stabilizing layer 8 is not particularly limited as long as it has good conductivity, and copper alloys such as copper, brass (Cu—Zn alloy), Cu—Ni alloy, etc. It is preferable to use a material made of a relatively inexpensive material such as stainless steel. Among them, copper is preferable because it has high conductivity and is inexpensive. When the oxide superconducting conductor 1 is used for a superconducting fault current limiter, the second metal stabilizing layer 8 is made of a resistance metal material, and a Ni-based alloy such as Ni—Cr can be used.

  In order to manufacture the oxide superconducting wire 1 having the structure shown in FIG. 3, a diffusion prevention layer and a bed layer are formed on the base material 2 by the above-described various film forming methods as required, and then the IBAD method is used. Then, after forming the intermediate layer 5 and forming the oxide superconducting thin film 6 by the laser vapor deposition method described below, a tape-like laminate in which the first metal stabilizing layer 7 and the second metal stabilizing layer 8 are laminated. The body 9 is produced, and the oxide superconducting wire 1 can be formed by forming a coating layer 10 as necessary. When the coating layer 10 is unnecessary, the oxide superconducting wire as the final product is formed by forming the second metal stabilizing layer 8.

Below, the method to form the oxide superconducting thin film 6 using the laser vapor deposition apparatus A shown in FIG. 2 is demonstrated.
In order to form the oxide superconducting thin film 6, as an example, a tape-like substrate formed by the various film forming methods described above on the base layer 2 and the intermediate layer 5 including the alignment layer 5B and the cap layer 5C. Use materials.
The tape-like base material is wound around the take-up reel 21 from the supply reel 20 via the turning member groups 16 and 17 as shown in FIG. 2, and the target 11 is mounted on the target holder 25. The pressure is reduced.
After reducing the pressure to the target pressure, the laser light source 12 collects and irradiates the surface of the target 11 with pulsed laser light.

In this case, the target holder 25 provided with the target 11 is rotated about the support rod 26 and further reciprocated horizontally in the directions Y ₁ and Y ₂ shown in FIG. The laser beam is scanned so as to irradiate the laser beam to almost the entire region except the peripheral portion of the laser beam. In addition, since it may cause a crack and a chip | tip in the outer periphery part of the target 11 when a laser beam is irradiated to the outer periphery part of the target 11, a laser beam is irradiated to the area | region except the outer periphery part of the target 11. preferable.

  When the surface of the target 11 is irradiated with laser light, a vapor jet (plume) composed of atoms, molecules or evaporated particles of the target constituent material is generated from the surface of the target 11, and this plume is formed on the intermediate layer 5 of the substrate 2. The oxide superconducting thin film 6 can be formed on the intermediate layer 5. Specifically, while winding the long base material 2 from the supply reel 20 to the take-up reel 21 via the turning member groups 16 and 17, the travel lane between the turning member groups 16 and 17 moves from the plume while moving. Thus, the oxide superconducting thin film 6 can be formed on the intermediate layer 5.

The target 11 according to the present embodiment includes a core portion 11A and an outer portion 11B. The outer portion 11B includes an organic binder at the green compact stage as described above, and cracks and cracks occur when releasing from the mold P. Therefore, it is of high quality, and therefore, it is difficult to generate cracks and chips during laser vapor deposition, and the plume can be stably generated. Therefore, this is a case where a long oxide superconducting wire 1 is manufactured. However, the oxide superconducting thin film 6 with stable quality can be produced.
The laser vapor deposition method forms a film while irradiating the target 11 with a high energy laser beam. Therefore, the target 11 is easy to apply a load. When the target 11 has small cracks or defects, the entire target 11 is formed. There is a risk of cracking. In this respect, the ability to manufacture the target 11 having no defects as described above is particularly preferable as a laser deposition target capable of performing stable film formation continuously for a long time.

"Example 1"
Y ₂ O ₃ powder, BaCO ₃ powder and CuO powder as raw material powder are weighed so that the ratio of Y: Ba: Cu is 1: 2: 3, wet-mixed using a ball mill, and uniformly mixed slurry is obtained. The mixed powder was obtained by drying. The mixed powder was put into an alumina crucible and subjected to a calcining process of firing for 24 hours in an electric furnace heated to 900 ° C. Thereby, YBa ₂ Cu ₃ O _x (YBCO) powder was obtained.
The YBCO powder was coarsely pulverized with a disk mill and further pulverized with a ball mill to produce a fine powder. The fine powder was screened into fine powder having a particle size of less than 53 μm by sieving to obtain a raw material mixture.
To the YBCO fine powder after selection, 1.0% by weight of an acrylic binder was added, and a slurry was prepared by ball mill mixing using isopropyl alcohol as a solvent. This was dried by a spray drying method to obtain a REBa ₂ Cu ₃ O _x composition comprising a binder-added fine powder having a particle size of about 100 to 150 μm.

A disc having a two-layer structure using the REBa ₂ Cu ₃ O _x composition comprising the binder-added fine powder produced as described above and the REBa ₂ Cu ₃ O _x composition comprising the fine powder not containing the organic binder. A molded body made of a green compact was produced as follows.
First, an organic binder-added fine powder was filled at the bottom of a mold cavity (inner diameter 200 mm) of a circular mold until the thickness became 2 to 3 mm, and the filled fine powder was adjusted to be flat. Next, a thin resin cylindrical frame was placed on a fine powder. The inside of the frame is filled with fine powder not containing an organic binder so as to have a height of about 12 to 13 mm, and the fine powder containing an organic binder on the outside of the frame is about 12 to 13 mm in height. After filling, the frame was drawn right above so that the inner and outer fine powders were not mixed.

After pulling out the frame, the fine powder filled inside and outside the frame flowed slightly to fill the part where the frame was pulled out, but basically an organic binder was added inside the position where the frame was inserted. The fine powder to which the organic binder was added was maintained on the outside of the position where the frame was inserted. Subsequently, the fine powder to which the organic binder was added was filled on the filled fine powder so as to have a height of 2 to 3 mm, and the filling was completed.
Thereafter, the upper punch and the lower punch of the mold were brought close to each other, and a uniaxial press was applied to the fine powder with a pressure of about 0.5 t / cm ² to form a disk-shaped green compact.
The weight ratio between the binder-added fine powder and the binder-free fine powder used in this molding step is shown in Table 1 below.

After compacting, the disk-shaped compact is removed from the mold and inspected for the presence of defects such as cracks and cracks. Degreasing is performed by heating the compact without defects for 24 hours at 350 ° C. gave.
Then, it sintered in air | atmosphere for 48 hours at 950 degreeC, and obtained the target which consists of a sintered compact.
The carbon content of each target obtained was measured using a high frequency combustion / infrared absorption method. The results are shown in Table 1.

Using the samples Nos. 2 to 8 shown in Table 1, an oxide superconducting wire was prepared by forming an oxide superconducting layer on a tape-like substrate through an intermediate layer based on the following steps.
First, Al ₂ O ₃ (diffusion prevention layer; film thickness 150 nm) is formed on a tape-shaped base material made of Hastelloy C276 (trade name, manufactured by Haynes, USA) having a width of 10 mm, a thickness of 100 μm, and a length of 10 m by sputtering. After film formation, Y ₂ O ₃ (bed layer; film thickness 20 nm) was formed by ion beam sputtering. Next, MgO (intermediate layer; film thickness: 10 nm) was formed on the bed layer by ion beam assisted sputtering (IBAD), and then 300 nm thick CeO ₂ (cap layer) by pulsed laser deposition (PLD). ) Was formed.

Next, each of the above-described targets was set in a laser vapor deposition apparatus having the configuration shown in FIG. 2, and an oxide superconducting layer was formed on the cap layer. A 1 μm-thick YBa ₂ Cu ₃ O ₇ layer (oxide superconducting thin film) is formed by a laser deposition apparatus, and an 8 μm-thick Ag first metal stabilizing layer is formed on the oxide superconducting thin film by sputtering, Further, a second metal stabilizing layer made of Cu tape and having a thickness of 300 μm was bonded with solder to produce a tape-shaped oxide superconducting wire.

The oxide superconducting thin film is formed by using an excimer laser (KrF: 248 nm) as a laser light source, an energy density of 3.0 J / cm ² , a linear speed of 30 m / h when moving the tape substrate, and a pulse laser Repetition frequency 300 Hz, oxygen partial pressure PO ₂ of treatment container = 80 mTorr, heating temperature of tape-like substrate by hot plate 800 ° C., number of lanes of substrate arranged between turning members is 5 lanes, film thickness on cap layer An oxide superconducting thin film was deposited to a thickness of 1 μm. In the laser vapor deposition apparatus shown in FIG. 2, film formation was performed while scanning a laser beam over the entire target surface at a disc-shaped target rotation speed of 45 rpm and a target moving speed of 55 mm / min. The target used for the pulse laser deposition method is the target of each sample described above.

For the oxide superconducting wire, a part of the sample before forming the first stabilizing layer is cut out, the thickness of the oxide superconducting thin film is measured, the crystallinity is evaluated by X-ray diffraction, and the composition analysis is performed by ICP emission spectroscopic analysis. As a result, no significant difference was found depending on the target. In addition, it was tried whether the amount of carbon in the superconducting thin film could be detected by ICP emission spectroscopic analysis, but carbon in the thin film could not be detected.
Next, the critical current density (Jc) was measured for each oxide superconducting wire sample provided with the oxide superconducting thin film produced using each target. The results are also shown in Table 1.

As shown in Table 1, when the target was produced only with fine powder not added with an organic binder, cracking occurred during demolding from the mold. As long as the target was prepared using fine powder to which an organic binder was added, cracking did not occur during demolding at any ratio. However, it was found that a target with an increased amount of the organic binder formed had an oxide superconducting thin film and produced an oxide superconducting wire, the critical current density decreased.
From the results shown in Table 1, it was found that in order to produce an oxide superconducting wire having a good critical current density, an excellent critical current density can be obtained when the carbon content is 350 ppm or less. It has also been found that the carbon content is preferably 190 ppm or less in order to satisfy a level at which the critical current density hardly decreases.

  The present invention can be used for manufacturing oxide superconducting wires used in various superconducting devices such as superconducting cables, superconducting magnets, superconducting motors, and superconducting fault current limiters.

DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting wire, 2 ... Base material, 5 ... Intermediate layer, 6 ... Oxide superconducting thin film, 7 ... 1st metal stabilization layer, 8 ... 2nd metal stabilization layer, 9 ... Superconducting laminated body, 11 ... target, 11A ... core part, 11B ... outer portion, P ... mold, P 1 _... upper punch, P 2 _... lower punch, P 3 _... die body, A ... laser deposition apparatus (film formation apparatus) 12 ... Laser light source, 13 ... running device, 15 ... film formation region, 16, 17 ... turning member group, 18 ... processing vessel, 19 ... exhaust means.

Claims (5)

This is used when an oxide superconducting thin film represented _by a composition formula of REBa ₂ Cu ₃ O _x (RE is one or more rare earth elements) is formed on a substrate by a film forming method, and REBa ₂ Cu ₃ O _A target for forming an oxide superconducting thin film comprising a sintered body containing an _x composition and an organic binder, wherein the sintered body has a carbon content of 350 ppm or less. It consists of a core part made of a REBa ₂ Cu ₃ O _x composition to which no organic binder is added and an outer part made of a REBa ₂ Cu ₃ O _x composition to which the organic binder is added surrounding the core part. The target for forming an oxide superconducting thin film according to claim 1. This is used when an oxide superconducting thin film represented _by a composition formula of REBa ₂ Cu ₃ O _x (RE is one or more rare earth elements) is formed on a substrate by a film forming method, and REBa ₂ Cu ₃ O _a sintered body obtained by heat-treating a green compact of an _x composition and an organic binder added to the REBa ₂ Cu ₃ O _x composition,
A core portion made of a green compact of REBa ₂ Cu ₃ O _x composition organic binder is not added, powder compact of REBa ₂ Cu ₃ O _x composition organic binder surrounds the periphery of the core portion is added When manufacturing a target for forming an oxide superconducting thin film obtained by heat-treating a green compact composed of an outer portion made of
When the REBa ₂ Cu ₃ O _x composition is charged into the molding cavity of the mold, the REBa ₂ Cu ₃ O _x composition containing the organic binder is charged on the outer side of the molding cavity, and the inner side of the molding cavity A REBa ₂ Cu ₃ O _x composition not containing the organic binder is charged to form a two-layered laminate, and the laminate is compacted with a mold and then heat-treated to produce a target. The manufacturing method of the target for oxide superconducting thin film formation characterized by these.   4. The method for producing a target for forming an oxide superconducting thin film according to claim 3, wherein the green compact obtained by compacting the laminate with the mold is heat treated to degrease and then sintered. .   When producing an oxide superconducting wire by forming an intermediate layer on a tape-shaped metal substrate and forming an oxide superconducting thin film thereon by a film forming method, the target according to claim 1 or 2 is used. A method for producing an oxide superconducting wire characterized by forming an oxide superconducting thin film.

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