JPH01151110A - Manufacture of oxide system superconductive film - Google Patents

Abstract

PURPOSE:To manufacture an oxide system superconductive film having nonorientation, a thick film thickness, and a high critical temperature by laminating film bodies with a series of processes composed of a film forming process and a heat treatment process repeated two times or more, and also changing an application direction in the film forming process at every film body. CONSTITUTION:A film body B1, composed of an oxide superconductor or its precursor body, of the first layer is formed with a given film thickness on a base substrate A. Then a heat treatment is applied to the body B1. After that a film body B2 of the second layer, a film body B3 of the third layer... a film body Bn, are laminated in order on the body B1 with the series of processes, composed of a film forming process and a heat treatment process forming such body B1, repeated required times. In this case, an application direction is made to a cross direction to the application direction of the body B, of the first layer when the body B2 of the second layer is formed by an application method. Similarly, the application direction in the body B3 of the third layer is made to cross the application direction of the body B2 of the second layer. An oxide system superconductive film B composed of film bodies B1, B2... Bn is manufactured on the base substrate A with the application direction changed at every film body in the same manner.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides an oxide-based superconducting film that can be used for superconducting devices such as Josephson elements and superconducting memory elements, coils for superconducting magnets, superconducting magnetic shielding materials, etc. Relating to a manufacturing method.

[Conventional technology]

Recently, the critical temperature at which the normal conducting state transitions to the superconducting state (
Various oxide-based superconductors are being discovered that exhibit a high value of T c) higher than the liquid nitrogen temperature.

Such oxide-based superconductors are, for example, A-B-Cu-
0 series (However, A is Y, Sc, La, Yb, Er, Eu.

Represents one or more elements of group 111a of the periodic table such as Ho and Dy, and B represents Be, Mg, Ca, Sr, and Ba.
(expressing one or more elements of Group 1Ia of the periodic table), compared to conventional alloy-based or intermetallic compound-based superconductors that required cooling with liquid helium. Because it can be used under extremely advantageous cooling conditions, it is considered to be an extremely promising superconducting wire material in practical use.

In order to manufacture this kind of oxide-based superconductor, for example, in the case of a Y-Ba-Cu-0 based superconductor, Y,03 powder and B a CO! A mixed powder is obtained by mixing L powder and Cu2O powder at a predetermined ratio, and then this mixed powder is used as it is or this mixed powder is made into a slurry or paste, and then applied along a specific direction onto a substrate made of strondium titanate, etc. A method is known in which an oxide-based superconducting film is formed on a substrate by coating to form a film body and then subjecting the film body to heat treatment in an oxygen atmosphere.

According to this method, it is possible to manufacture an oxide-based superconducting film exhibiting a high critical temperature, critical current density, etc. on the substrate.

[Problem that the invention seeks to solve]

However, in such a manufacturing method, the thickness of the obtained oxide-based superconducting film is very thin, on the order of several μR, and therefore, for example, the critical current (Ic ) has an extremely small capacity, which makes it difficult to produce an oxide-based superconducting film that has a Tc value that can be put to practical use. In addition, in this manufacturing method, since the film body is formed by specifying the direction in which the mixed powder, slurry, or paste is applied, the resulting thin superconducting film is oriented in a specific direction.

For this reason, when the above superconducting film is used, for example, as a magnetic shield, there is a problem that a sufficient magnetic shielding effect cannot be obtained because the superconducting film has insufficient perfect diamagnetic properties.

[Means for solving problems]

Therefore, the present invention provides a series of steps consisting of a film formation step of forming a film body made of an oxide superconductor or a precursor of an oxide superconductor on a substrate by a coating method, and a heat treatment step of heating the film body. By repeating this process two or more times to sequentially laminate the film bodies, and by changing the coating direction for each film body in the film forming process, it is possible to achieve an overall non-oriented and large Ic.
A thick oxide-based superconducting film capable of exhibiting a certain value can be obtained.

The present invention will be explained in detail below.

In this example, first, a substrate A is prepared as shown in FIG. The substrate A may be of various shapes, such as a plate, a wire, a tape, a cylinder, or a column. Examples of materials for forming the base A include metal materials such as silver, gold, platinum, stainless steel, aluminum, and copper;
These alloy materials, nitrides and carbides of the above-mentioned metals or alloy materials, and crystalline materials such as strontium ditanate, alumina, silicon, silica, lithium niobate, sapphire, and ruby are preferably used.

Next, a first layer film B1 made of an oxide superconductor or its precursor is formed on the substrate A to a predetermined thickness. The oxide superconductor here is ABC
-D series (A is Y, Sc.

La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, T
b, Dy, Ho.

Periodic table 11 of Er, T m, Y b, Lu
Represents one or more types of group 1a elements, B is S
r, Ba, Ca.

Represents one or more of Group Ia elements of Be, Mg, and Ra of Group Ia, and C includes Cu or Cu of Group 1B elements of the Periodic Table of Cu, Ag, and Au, and Nb elements. Represents two or more types, D is O, S, Se, Te.

Group V+B elements of the periodic table of Po and F, Ca, Br,
I.

Represents two or more elements containing O or 0 among the elements of group 1b of the periodic table of At. ) are used. The composition of each constituent element of this oxide superconductor is, for example, Y-Ba
-Cu-0 based superconductor, Y 1゜8a (2-3
), Cu (3-4), O(7-δ), where δ is 0≦
The range is δ≦5. In addition, the precursor of the oxide superconductor described above has poor superconducting properties because a part of its constituent oxygen is deficient compared to the composition of the A-B-(, -D-based superconductor). It is something.

As a film forming method for forming such a film body B, a method that can form a film body with a uniform thickness and that can orient the film body in a specific direction is used, and specifically, a method such as a doctor blade method is used. Application methods are used. During film formation, the oxide superconductor or its precursor is processed into powder, slurry, paste, etc., depending on the type of film formation method, film formation conditions, and the like. To make powder,
Usually, a powder method is used, but it is not limited to this method. For example, coprecipitation is performed by coprecipitating each element constituting the oxide superconductor as an oxalate and drying the precipitate to form a powder. Laws can also be used. In addition, constituent elements of oxide superconductors such as alkoxide compounds, oxyketone compounds, cyclopentadienyl compounds, acetylacetone compounds, etc. are mixed in a predetermined ratio to form a mixed solution, and water is added to this mixed solution for hydrolysis. A sol-gel method may be applied in which the substance is made into a sol, the sol-like substance is heated to gel, the gel is further heated to form a solid phase, and the solid phase is pulverized using a ball mill or the like to obtain a powder. Furthermore, by adding a vehicle to the powder thus obtained, the powder can be made into a slurry or paste. The vehicle may vary depending on the heat treatment conditions for the paste, etc., but for example, volatile fest prepared by dissolving synthetic resins in alcohol, turpentine oil, esters, etc., vaseline, etc. are used. In addition to the above vehicles, organic solvents such as acetone, benzene, and alcohols can also be added for viscosity adjustment.

Next, the film body Bl formed by such a film forming process is
Heat treatment is applied to. This heat treatment is performed at a temperature of 800 to 1
After heating at 000°C for 1 to several 100 hours, the process is performed under conditions of gradual cooling to a crystal transformation temperature of 400 to 600°C. The atmosphere during this heat treatment is normally an oxygen atmosphere, but if necessary, S
, Se, and other gases of Group V+B elements of the periodic table, F, and C.
(It is also possible to include gases of Group B elements of the periodic table, such as 2, Br. By heat treatment in such an atmosphere, each constituent element in the film body B is made to sufficiently react with each other, and at the same time, the elements from the surface of the film body B to the inside of the film body B are Oxygen element or oxygen element and elements of Group V+B of the periodic table such as S and Se, F, CQ, and B
Elements of group 1b of the periodic table, such as r, are efficiently diffused. Therefore, in the entire film body B or at least in the surface layer portion of the film body B, an oxide-based superconductor exhibiting good superconducting properties is generated.

Next, a series of steps consisting of a film formation step and a heat treatment step, which are the same steps as those for forming the film body B1 exhibiting such superconducting properties, is repeated a necessary number of times (for example, n times, n is a natural number) to form the film body. B, second layer film body B2. The third layer film body B3...membrane body Bn are sequentially laminated. Here, when forming the second layer film body B2 by the above-mentioned coating method, the coating direction is set to be a direction intersecting the coating direction of the first layer film body B1.

Similarly, the coating direction of the third layer film body B3 is made to intersect with the coating direction of the second layer film body B2. Thereafter, in the same way, film B is applied onto substrate A while changing the coating direction for each film.
,,B,... An oxide-based superconducting film B made of Bn is manufactured. Here, the number of repetitions in the series of steps described above is determined as appropriate depending on the intended use of the obtained oxide-based superconducting film, the necessary film thickness, and the like.

The thus obtained oxide-based superconducting film B has a multilayer structure in which film bodies B1, B2,...Bn are successively laminated, each of which exhibits good superconducting properties by heat treatment in an oxygen atmosphere. Since it is a thick oxide-based superconductor with adjacent film bodies firmly bonded to each other, in addition to superconducting properties such as high critical temperature and critical current density, for example, The capacity of the critical current (Tc) that can be passed in the orthogonal direction is large, making it sufficiently usable for practical use.

In addition, in this oxide-based superconducting film B, each of the film bodies B, B2...Bn of its constituent units has a different orientation, so the orientation as a whole is weak or Since it exhibits non-orientation, when this oxide-based superconducting film B is used, for example, as a magnetic shield, it can be used as a magnetic shielding material with a high magnetic shielding effect.

Furthermore, in this oxide-based superconducting film B, the first layer film body B is formed based on the crystal structure of the substrate A, and the second and subsequent layers film bodies B2 and B3 are formed based on the crystal structure of the substrate A. . . . Film bodies B, , B 2 and Bn exhibiting good superconducting properties, respectively.
Since it is formed based on the crystal structure of . 3...
Bn also has excellent superconducting properties. Incidentally, in general, current flowing through a conductor has a property that it tends to flow more easily to the surface layer side of the conductor than to the inside of the conductor. For this reason, in oxide superconducting film B, which exhibits slightly better superconducting properties in the film body on the surface layer side away from substrate A than in the film body on the surface layer side, the critical current is efficiently transferred to the surface layer side. It is possible to flow in large quantities.

According to such a manufacturing method, a series of steps consisting of a film formation step and a heat treatment is repeated two or more times to form film bodies B, B, B,
... Bn is sequentially laminated and the coating direction is changed for each film body, so that the film body B , , B 2 ... has a multilayer structure consisting of Bn, which exhibits good superconducting properties, and the adjacent It is possible to produce a thick oxide superconducting film B with a large Ic value in which the film bodies are firmly bonded to each other.

In addition, in this manufacturing method, the series of steps described above is repeated as many times as necessary, so the thickness of the resulting oxide-based superconducting film B can be easily controlled. The system superconducting film B can be manufactured freely. Further, in this manufacturing method, the oxide superconducting film B can be applied to various superconducting products by appropriately selecting the shape of the base A, which is the base on which the oxide superconducting film B is formed. For example, if the substrate A is plate-shaped, it can be used as a superconducting device such as a Josephson element or a superconducting memory element, or a superconducting product such as a superconducting magnetic shield material, or if the substrate A is linear. In this case, it can be used as a superconducting wire such as a coil for a superconducting magnet.

〔Example〕

A mixed powder consisting of Y2O3 powder, BaO powder, and CuO powder was prepared, and then the mixed powder was dispersed in vaseline to obtain a paste. Next, this paste is applied along a specific direction onto a substrate made of strontium titanate using a doctor blade method to form a first layer film with a thickness of about 1 μm, and then this film is coated on a substrate made of strontium titanate. After heating at 900°C for 24 hours, heat treatment was performed by slowly cooling to about 400°C. This heat treatment produced an oxide superconductor in the film body. Next, when the critical current density (Jc) of this film body was measured at liquid nitrogen temperature (77K), it was 90A/Qx'', and the critical current (Ic) was 20mA.
Met.

Next, the same operation was repeated on the first layer film thus obtained, changing the coating direction for each film, to form nine layers of film. When the Jc value at 77 was investigated for the oxide superconducting film with a thickness of 10 μM consisting of these 10 layers, it was found to be 500 A/cri2, and the Tc value of the entire oxide superconducting film was 1. It was .1A. Furthermore, when this oxide-based superconducting film was placed in a magnetic field and its shielding effect was investigated, it was confirmed that it exhibited magnetic shielding properties sufficient for practical use.

〔Effect of the invention〕

As explained above, according to the manufacturing method of the present invention, a multilayer structure consisting of a plurality of film bodies exhibiting good superconducting properties is produced, and a thick Ic film in which adjacent film bodies are firmly bonded to each other is produced. In addition to being able to produce oxide-based superconducting films with large values, since the orientation differs for each film, the overall orientation is weak or non-oriented, making it ideal for magnetic shielding, etc. can.

In addition, in this manufacturing method, the series of steps described above are repeated as many times as necessary, so the film thickness can be easily controlled, so oxide-based superconducting films that meet various required characteristics can be freely manufactured.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of an oxide-based superconducting film manufactured by the manufacturing method of the present invention. A: Substrate, BI: Bn: Film body, B: Oxide-based superconducting film.

Claims (1)

[Claims] A series of steps consisting of a film formation step of forming a film made of an oxide superconductor or a precursor of an oxide superconductor on a substrate by a coating method, and a heat treatment step of heating the film is repeated two or more times. A method for manufacturing an oxide-based superconducting film, comprising sequentially stacking film bodies and changing the coating direction in the film forming step for each film body.