JPH052935A - Manufacture of bi series oxide superconductor fabricated by fusion method - Google Patents

Abstract

PURPOSE:To enhance the crystal orientation and heighten the critical temperature and critical current density by forming over a metal base an oxide film and a buffer layer for accomplishing a composite base, and thereover forming an oxide type superconductive layer. CONSTITUTION:An oxide film 7 is formed on the over-surface of a metal base 6, and thereover a buffer layer 8 is formed, and further thereover a crude material powder layer is formed which contains elements constituting a Bi type oxide superconductor. The resultant is heated in a furnace to turn the crude material powder layer into a fusion/solidification layer. Part of this layer is irradiated with a laser beam so as to generate a locally molten band, which is moved in the longitudinal direction of the base, and the whole fusion/solidification layer is left to unidirectional solidification bit by bit so as to produce an oxide superconductive layer. This suppresses diffusion of composite base 9 constituent elements to the oxide superconductive layer side, and also lessens dispersion of the thickness compared with the case where the crude material powder is directly subjected to unidirectional solidification. This allows enhancing the workmanship of the crystal orientation of the oxide superconductive layer and also heightening the critical temp. and critical current density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a Bi-based oxide superconducting conductor using a melting method, which improves the orientation and the generation ratio of a superconducting phase after melting and solidification, and the thickness of the superconducting layer. The present invention relates to a method capable of improving the uniformity of roughness.

[0002]

2. Description of the Related Art Conventionally, as an example of a method for producing a superconducting conductor having a Bi-based oxide superconducting layer on the upper surface of a tape-shaped substrate, a method described below with reference to FIG. 8 is known. .. In this method, first, a metal tape 1 of Ni or the like is prepared, and a raw material powder layer 2 of an element forming a Bi-based oxide superconductor is formed on the upper surface of the metal tape 1. Next, a laser beam is irradiated from above the metal tape 1 to heat and melt only a small portion of the mixed powder layer 2 to form a melting zone 3. Then, in this state, the base material 1 is moved in the longitudinal direction at a constant speed, and the minute melting zone 3 is gradually moved, so that the entire mixed powder layer 2 in the longitudinal direction of the base material 1 can be unidirectionally solidified. After that, the whole is heat-treated in a heating furnace to manufacture the oxide superconducting conductor 5 having the oxide superconducting layer 4.

[0003]

When the oxide superconducting conductor 5 is manufactured by the above-mentioned method, since the base material 1 is moving, in the minute melting zone 3, the mixed powder layer 2 is supplied and this layer is supplied. It means that the three phenomena of the melting and solidification of the melted part are proceeding at the same time. In a state where three phenomena are progressing in such a minute region, there is a high possibility that the balance of the three phenomena will be lost even if a slight fluctuation occurs in the power of the laser beam. Then, even if a constant substrate moving speed is maintained, there is a problem that the amount of the melted portion changes, the thickness of the solidified portion becomes nonuniform, and the crystal orientation deteriorates. In the above case, in addition to the oxide superconductor having the desired composition, for example, Bi ₂ Sr ₂ Cu
There is a problem in that a non-superconducting phase represented by Oy or the like is deposited and the superconducting characteristics are deteriorated.

Further, the base material used in the above-mentioned manufacturing method is made of a heat-resistant material such as Ni that can withstand the heat treatment temperature. However, the constituent elements of the base material such as Ni during partial melting or heat treatment are on the oxide superconducting layer side. There was a problem of spreading to. When the element constituting the base material diffuses toward the oxide superconducting layer side in this manner, the crystal structure of the oxide superconducting layer is disturbed, which causes a problem that the critical temperature and the critical current density are lowered.

The present invention has been made in view of the above background, and a Bi-based oxide superconductor having a desired composition and a uniform thickness and a high critical temperature is formed on a substrate by applying a melting method. The purpose is to provide a possible method.

[0006]

In order to solve the above-mentioned problems, the invention described in claim 1 forms an oxide film on the surface of a metal substrate, forms a buffer layer on the oxide film, and forms a buffer layer on the buffer layer. While forming a raw material powder layer containing an element constituting a Bi-based oxide superconductor, and heating the raw material powder layer to 870 to 1000 ° C. in a heating furnace to make the raw material powder layer a melt-solidified layer, After this, a laser beam is irradiated to a part of the melt-solidified layer to form a partial melted zone on the irradiated portion, and then this partial melted zone is moved in the longitudinal direction of the substrate to sequentially move the entire melt-solidified layer in one direction. It solidifies to form an oxide superconducting layer.

[0007]

[Function] Since the oxide superconducting layer is formed after the oxide film is formed on the metal substrate and the buffer layer is formed, the oxide superconducting layer side of the constituent elements of the metal substrate during partial melting and heat treatment Is suppressed. Therefore, the disorder of the crystal of the oxide superconducting layer is reduced, and the critical temperature and the critical current density are improved.

Furthermore, since the raw material powder layer on the upper surface of the metal substrate is melted and solidified in the heating furnace, the raw material amount powder layer becomes a dense and solidified melt-solidified layer at this stage. If this melt-solidified layer is unidirectionally solidified by a laser beam, remelting and solidification of the melt-solidified layer will proceed in the minute region where unidirectional solidification occurs, and the supply of the raw material powder layer and The number of phenomena occurring is smaller than that in the case where the three phenomena of layer melting and solidification proceed. Therefore, even if the laser beam power slightly fluctuates, an oxide superconducting layer having a uniform thickness is generated. Since an oxide superconducting layer with a uniform thickness is generated, the direction of crystal grains during unidirectional melting and solidification is easily aligned, leading to improvement of the crystal orientation of the oxide superconducting layer, and high critical temperature and critical current density. Things are generated.

The present invention will be described in more detail below. In order to carry out the present invention to manufacture a Bi-Sr-Ca-Cu-O-based oxide superconductor, first, a starting material is prepared. Bi compounds, Sr compounds, Ca compounds and Cu compounds are used as the starting materials. As the compound, any of oxides, chlorides, carbonates, sulfides, fluorides and the like of each element may be used. Specifically used in this example are Bi ₂ O ₃ powder, SrCO ₃ powder, CaCO ₃ powder, and CuO powder. The compound used may be in the form of particles or powder, but it is preferable that the compound has a particle size as small as possible. In addition, when manufacturing a Bi-based superconductor containing Pb, a Pb compound may be mixed in addition to the above compounds.

If the above powders are prepared, Bi: Sr: Ca:
Weigh so as to have a ratio of Cu = 2: 2: 1: 2, and uniformly mix in an automatic mortar or the like for a required time to prepare a mixed powder. Here, in the case where the ratio of each element is 2: 2: 2: 3, powder is mixed in that ratio, and in the case where Pb is added in addition to each element, a part of Bi (for example, Bi It may be possible to substitute Pb for (a few percent of) and mix it. Next, this mixed powder is exposed to the air at 800 to 850 ° C. for 24 to 100.
Unnecessary components are removed by heating for about an hour and calcining. After the calcination, the calcination product is pulverized to powder the calcination product.

On the other hand, a metal tape-shaped metal substrate 6 as shown in FIG. 1 is prepared. The metal base material 6 is highly flexible and may be made of any metal as long as it can withstand the heat treatment described later. Specifically, a material such as Ni or Ni alloy is used. The metal base material 6 is heated by a heating device such as an electric furnace to oxidize the surface thereof to form an oxide film 7 as shown in FIG. The heating condition at this time is 1 at 950 ° C. when the metal base material 6 is made of Ni.
It shall be heated for 0 hours or more. By this treatment, an oxide film of NiO having a thickness of about 10 to 20 μm is formed on the surface of the metal substrate 6.

Next, the metal substrate 6 is set in a film forming apparatus such as a high frequency sputtering apparatus and subjected to a film forming process, and a buffer layer 8 having a thickness of about 1 to 10 μm is formed on one oxide film 7 in FIG. The composite base material 9 is obtained by forming as shown. The buffer layer 8 has a thermal expansion coefficient close to that of an oxide superconductor, such as MgO and SrTiO _3, and has a crystal structure of B.
A material close to an i-based oxide superconductor is preferable.

Further, the powder obtained in the above process is put into a container 11 filled with an organic solvent 10 as shown in FIG. 4 to form a dispersion medium. Next, the composite substrate 9 is added to this dispersion medium.
Is immersed and pulled up, and the composite substrate 9 has a thickness 10 shown in FIG.
The raw material powder layer 13 having a thickness of about 100 μm is formed.

Next, the composite base material 9 to which the raw material powder layer 13 is fixed is heated in a heating furnace such as an infrared image furnace to 870-870.
It is heated and melted at a temperature of 1000 ° C. for about 1 minute to 1 hour. When the raw material powder layer 13 is melted at this temperature, the whole or a part of the raw material powder layer 13 is melted, so that the raw material powder layer 13 becomes a melt-solidified layer 14 having a uniform thickness shown in FIG. 6 after solidification. Adhere to 8. This melting and solidifying layer 14
Since the raw material powder layer 13 is melted and solidified, pores and the like existing inside the raw material powder layer 13 are closed, and unnecessary components contained in the raw material powder layer 13 are discharged. Since it is a material, the density and purity are high, it is slightly thinner than the raw material powder layer 13, and its thickness is also uniform.

Then, the melting and solidifying layer 14 is irradiated with a laser beam from above as shown in FIG. 7, and is also irradiated with a laser beam from the back surface side of the composite base material 9 corresponding to the irradiated portion of the laser beam. A minute partial melting zone 15 shown in FIG. 7 is formed in a part of the solidified layer 14. Since the partial melting zone 15 is formed in a portion corresponding to the focus of the laser beam, it is a narrow region having a width of about 2 mm. Irradiation of the laser beam from the back surface side of the composite base material 9 is achieved by irradiating the laser beam only from above the melting and solidifying layer 14 so that the portion on the surface side of the melting and solidifying layer 14 is easily heated to the heating temperature by the laser beam. Although it is heated, the bottom portion of the melt-solidified layer 14 is less likely to be heated. Therefore, if the acid composite substrate 9 is also heated by the laser beam from the back surface side of the composite substrate 9, the partial melting zone 15 The temperature of can be made uniform on the surface side and the bottom side.

After the partial melting zone 15 is formed, the composite substrate 9 is moved in the direction of arrow B in FIG. 7 at a constant speed. By this treatment, the partial melting zone 15 gradually moves along the melting and solidifying layer 14, and the portion after the partial melting zone 15 has moved solidifies to form the oxide superconducting base layer 16. Since the oxide superconducting base layer 16 thus generated is generated by unidirectionally solidifying the melt-solidified layer 14 once melt-solidified in the heating furnace, unlike the case where the raw material powder layer 13 is directly melt-solidified, No thickness variation occurs.

After the unidirectional solidification treatment, 800
By heat treating at 870 ° C. for several hours to several hundred hours, the entire oxide superconducting base layer 16 can be converted into the oxide superconducting layer 17, and the oxide superconducting conductor 18 shown in FIG. 8 can be obtained.

In the unidirectionally solidified minute region, the re-melting and solidification of the melt-solidified layer 14 progresses, and three kinds of feeding of the raw material powder layer and melting and solidification of the layer are performed as in the conventional case. The number of phenomena occurring is smaller than that in the case where the phenomenon progresses, and even if a slight fluctuation occurs in the power of the laser beam, the superconducting base layer 16 having a uniform thickness is generated. Since the superconducting base layer 16 having a uniform thickness is generated in this way, the directions of the crystal grains during melt solidification are easily aligned, which leads to improvement of the crystal orientation of the oxide superconducting layer 17, and the critical temperature and the critical current density. High ones produce.

The oxide superconducting layer 17 obtained as described above has a uniform thickness and a high density, and the voids existing in the raw material powder layer 13 are almost eliminated inside. Further, when the unidirectional solidification is performed, the originally melted and solidified layer 14 having a high density is remelted, so that the crystal orientation is smoothly performed. Therefore, the oxide superconducting layer 17 is excellent in crystal orientation, has a high density, and has a high critical temperature and a high critical current density.
It is possible to obtain the oxide superconducting conductor 18 provided with.

The Bi-based oxide superconducting conductor 18 manufactured by the above method has a critical temperature higher than the liquid nitrogen temperature (77 K), so that a temperature margin can be secured when it is cooled with liquid nitrogen and used. Since it has a denser crystal structure than an oxide superconductor produced simply by sintering powder, it exhibits a high critical current density.

[0021]

EXAMPLES Bi ₂ O ₃ powder, SrCO ₃ powder, CaCO ₃ powder and CuO powder were mixed with Bi: Sr: Ca: Cu = 2: 2:
Mix so that the molar ratio is 1: 2, and mix in an automatic mortar for 1 hour. This mixed powder is 800-85 in the air.
It is calcined at 0 ° C. for 24 to 100 hours to pulverize the calcined product.

Next, a Ni tape having a width of 2 mm and a thickness of 0.5 mm was prepared, and the Ni tape was heated at 950 ° C. for 1 hour in an electric furnace.
By heating for 0 hour, an oxide film having a thickness of 15 μm was formed on the surface of the Ni tape. Subsequently, a MgO film having a thickness of 5 μm was formed on the upper surface of this tape by a high frequency sputtering device to obtain a composite base material. When the crystal structure of this MgO film was measured by an X-ray diffractometer, a diffraction peak on the (100) plane of MgO appeared strongly and it was found that the MgO film was crystallized.

On the other hand, 400 g of the crushed product was added to 1 liter of ethanol in a container filled with the crushed product.
To prepare a dispersion medium, and the composite substrate was immersed in the dispersion medium and pulled up to form a mixed powder layer having a thickness of 100 μm on the composite substrate. Next, the Ni tape on which the mixed powder layer was formed was heated to 900 ° C. in an electric furnace to melt the mixed powder layer and then solidified to form a melt-solidified layer having a thickness of 50 μm. In this state, the entire raw material powder layer was uniformly heated and melted in the heating furnace, so that the raw material powder layer was a melt-solidified layer having a uniform thickness and no unevenness.

Next, a CO ₂ gas laser was radiated from the front side of the melt-solidified layer and the back side of the metal base material to form a melt zone having a width of 2 mm in a part of the melt-solidified layer. At the same time as N
The i-tape was moved at a speed of 5 mm / hour, and the melting zone was also moved to unidirectionally solidify the entire melt-solidified layer. After solidification,
An oxide superconducting conductor could be obtained by heat treatment at 800 to 870 ° C. for 100 hours.

The obtained oxide superconducting conductor was cooled with liquid nitrogen and the critical temperature (Tc) and critical current density (Jc) were measured. As a result, Tc = 82K, Jc = 1000A / cm ²
showed that.

[0026]

Comparative Example A raw material powder layer equivalent to the above is formed on a base material equivalent to the metal base material used in the above example, and the process of melting and solidifying the raw material powder layer once in a heating furnace is omitted. The same treatment as in the above example was performed to obtain an oxide superconducting conductor. When the critical temperature and the critical current density of the obtained oxide superconducting conductor were measured, Tc = 78K, Jc = 50A / c
m ² was shown. In the oxide superconducting layer thus obtained, it was confirmed that fine irregularities were partially formed.

From the results described above, it was found that by carrying out the method of the present invention, it is possible to produce a Bi-based oxide superconducting conductor having excellent characteristics of uniform thickness and high critical temperature and critical current density. ..

By the way, in the case of unidirectional solidification by the laser beam, if the moving speed of the substrate 12 is set to 20 mm / hour or more, the moving speed is too fast to obtain satisfactory superconducting characteristics. By the way, in the oxide superconducting conductor manufactured by setting the moving speed to 20 mm / hour, Tc
= 72K was shown. (# Changing the moving speed of the base material may affect future patent requirements if it affects the critical temperature and critical current density of the resulting oxide superconductor. Please enter the value of.)

[0029]

As described above, according to the present invention, the oxide superconducting layer is formed on the composite substrate formed by forming the oxide film on the metal substrate and further forming the buffer layer. Diffusion of constituent elements of the composite base material to the oxide superconducting layer side during the partial melting and the heat treatment performed after the layer formation is suppressed. Therefore, the disorder of the crystal of the oxide superconducting layer is reduced, and an excellent oxide superconducting conductor having a good orientation and a high critical temperature and a high critical current density can be obtained.

Further, since the raw material powder layer formed on the composite base material is once melted and then unidirectionally solidified, the variation in thickness is small and the material powder is dense as compared with the case where the raw material powder is directly unidirectionally solidified. Thus, an oxide superconducting conductor having a Bi-based oxide superconducting layer having excellent crystal orientation can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a metal base material.

FIG. 2 is a cross-sectional view showing a state in which an oxide film is formed on a metal base material.

FIG. 3 is a cross-sectional view of a composite substrate.

FIG. 4 is an explanatory view showing a state in which a raw material powder layer is formed on a composite base material.

FIG. 5 is a cross-sectional view showing a state in which a raw material powder layer is formed on a composite base material.

FIG. 6 is a sectional view showing a state in which a raw material powder layer is melted and solidified.

FIG. 7 is a cross-sectional view showing a state in which the melt-solidified layer is unidirectionally solidified.

FIG. 8 is a cross-sectional view of an oxide superconducting conductor.

FIG. 9 is a cross-sectional view for explaining the unidirectional solidification method in the conventional method.

[Explanation of symbols]

6 ... Metal base material, 7 ... Oxide film, 8 ...
Buffer layer, 9 ... Composite base material, 13 ... Raw material powder layer, 14 ... Melt solidification layer, 15 ... Melt zone, 16
... Oxide superconducting base layer, 17 ... Oxide superconducting layer,
18 ... Oxide superconducting conductor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuyuki Tadakata Inventor Nobuyuki Kiba 1-5-1, Kiba, Koto-ku, Tokyo Within Fujikura Electric Line Co., Ltd. (72) Hideo Ishii 2-4-1 Nishiazajigaoka, Chofu-shi, Tokyo TEPCO Technical Research Institute (72) Inventor Tsukushi Hara 2-4-1 Nishitsujigaoka, Chofu-shi, Tokyo Tokyo Electric Power Co. Technical Research Institute (72) Inventor Takahiko Yamamoto 2-4-1 Nishiazajigaoka, Chofu-shi, Tokyo No. TEPCO Technical Research Institute

Claims (1)

Claim: What is claimed is: 1. An oxide film is formed on the surface of a metal base material, a buffer layer is formed on the oxide film, and the buffer layer contains an element constituting a Bi-based oxide superconductor. Forming a raw material powder layer, and 870 this raw material powder layer in a heating furnace.
While heating the raw material powder layer to a melting and solidifying layer by heating to ˜1000 ° C., a part of the melting and solidifying layer is thereafter irradiated with a laser beam to form a partial melting zone at the irradiated portion, and then this partial melting zone is formed. A method for producing a Bi-based oxide superconducting conductor by a melting method, which comprises moving the base material in the longitudinal direction to sequentially unidirectionally solidify the entire melt-solidified layer to form an oxide superconducting layer.