JPH01100820A - High temperature superconducting material - Google Patents

Abstract

PURPOSE:To obtain an excellent high temperature superconductor by sandwiching a layer formed via an MBE method between two layers of an A-B-C-D system formed via a laser deposition method, where A stands for Y and the like in group IIIa of the periodic table, B for Sr and the like in group IIa, C for Cu and the like in Ib group and Nb, and D for O and the like in group VI. CONSTITUTION:The A-B-C-D system comprises a high temperature superconducting material, where A stands for one or more elements such as Y and Sc in IIIa group of the periodic table, C for two or more elements containing Cu among Ib group elements such as Cu and Ag, and Nb, or Cu and D for elements containing O among element VIb such as O and S and group VIIb elements such as F and Cl. And the high temperature superconductor of an oxide system having a three-layer structure is formed on a substrate 2. A superconducting layer 1a is formed on the substrate 2 via a laser deposition method, another superconducting layer 1b formed thereon via a molecular-beam epitaxial(MBE) method and another superconducting layer 1c further thereon via a laser deposition method. According to the aforesaid process, it is possible to obtain high critical current density and make film thickness larger.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a high-temperature superconducting material that can be used as a superconducting device such as a Josephson element or a superconducting memory element, or a coil for a superconducting magnet.

"Prior Art" Recently, various oxide-based superconductors have been discovered that exhibit a critical temperature (T c ) for transitioning from a normal conducting state to a superconducting state that is higher than the temperature of liquid nitrogen. These oxide-based superconductors can be used under much more advantageous cooling conditions than conventional alloy-based or intermetallic compound-based superconductors, which require cooling with liquid helium. It is considered to be an extremely promising superconducting material.

By the way, the superconducting properties such as critical temperature (Tc) and critical current density (Jc) in such an oxide superconductor are as follows.
It is known that it varies depending on various factors such as the manufacturing method and manufacturing conditions. And at present,
Molecular beam epitaxy (hereinafter referred to as MBE) method,
Superconductors formed by thin film forming means such as laser evaporation are considered promising as they may exhibit relatively good superconducting properties.

"Problem to be Solved by the Invention J" However, if the MBE method is used, it is possible to epitaxially grow an oxide superconductor on a substrate, and it is possible to obtain an oxide superconductor that exhibits a high critical current density. Because the film speed is slow, it takes a long time to obtain a thick oxide superconductor, which poses the problem of poor manufacturing efficiency.On the other hand, laser evaporation can increase the film formation speed, making it possible to obtain a thick superconductor. It has the advantage that even layers can be produced in a relatively short time.

The present invention has been made in view of the above problems, and takes advantage of the respective advantages of the laser evaporation method, which has a high film formation rate, and the previously mentioned MBE method, and has a sufficient film thickness, a large current capacity, and a manufacturing efficiency. The purpose is to provide high-temperature superconducting materials with high performance.

"Means for Solving the Problems" In order to solve the above problems, the present invention provides
-D system (A is Y, Sc, La, Yb, Er, Ho
.

Indicates one or more elements of the ms group of the periodic table such as Dy, B
represents one or more elements of group Ib of the periodic table, such as Sr, Ba, Ca, etc., and C represents elements of group Ib of the periodic table, such as Cu, Ag, and Au.
Denotes Cu or two or more of the group elements and Nb, including Cu, and D is 0 of the group VIb elements of the periodic table such as O, S, and Se, and the group VIIb elements of the periodic table such as F, Cl, and Br.
Indicates one or more types including. ) high-temperature superconducting materials, including an A-B-C-D system laser-deposited superconducting layer formed by a laser evaporation method and an A-B-C-D system formed by a molecular beam epitaxy (MBE) method. MBE superconducting layers are alternately laminated, and two or more superconducting layers of at least one of the laser-deposited superconducting layer and the MBE superconducting layer are laminated.

"Function" A laser-deposited superconducting layer formed by a laser vapor deposition method that can form a thick film in a short time, and an MBE superconducting layer formed by a molecular beam epitaxy (MBE) method that can obtain a high critical current density. Since two or more superconducting layers of at least one of the laser-deposited superconducting layer and the MBE superconducting layer are laminated alternately, at least one laser-deposited superconducting layer is formed on the MBE superconducting layer. As a result, this laser-deposited superconducting layer grows with the crystal orientation aligned using the MBE superconducting layer immediately below as a growth nucleus.

Hereinafter, this invention will be explained in detail by giving two examples.

An example of the oxide-based high temperature superconducting material of the present invention is shown in FIG.

The superconducting material 1 of this example is formed on the surface of a base body 2, and includes a first superconducting layer 1a (laser-deposited superconducting layer) formed on this base body 2 by a laser vapor deposition method, A second superconducting layer 1b (MBE superconducting layer) formed on the superconducting layer La by the MBE method, and a second superconducting layer 1b formed by the laser vapor deposition method on the second superconducting layer 1b. It consists of three layers, including the third superconducting layer 1c (laser-deposited superconducting layer).

A method for forming such a superconducting material 1 will be explained.

First, the base body 2 is prepared. The base body 2 may be of various shapes, such as a plate material, a wire material, a tape material, a cylindrical body, a columnar body, etc., for example. Further, as the constituent material of such a base 2, a material that can withstand high heat during heat treatment applied during the generation of the oxide-based high-temperature superconducting material is selected, and specifically,
Metal materials such as silver, gold, platinum, aluminum, copper, alloy materials thereof, nitrides, carbides of these metals or alloys, stainless steel, etc.
Furthermore, strontium titanate lh (S rT io
s>, alumina (AI!03), silicon (S i),
Silica (SiO2), lithium niobate (LiNbOs)
), sapphire, ruby, and other crystalline materials are preferably used.

Next, a three-layered oxide-based high-temperature superconducting material 1 is formed on the surface of such a base 2. The process of forming high temperature superconducting Ht in this example consists of three consecutive steps. That is, in the first step, the first superconducting layer 1a is formed using a laser vapor deposition method, and in the second step, the first superconducting layer L is formed using the first superconducting layer 1a as a growth nucleus using the MBE method.
A second superconducting layer tb is formed on the second superconducting layer lb, and in a third step, a third superconducting layer 1c is formed on the second superconducting layer lb using a laser evaporation method.

The laser evaporation method in the first step is performed using, for example, a laser evaporation apparatus shown in FIG. The apparatus shown in FIG. 2 includes a container IO that can maintain a vacuum atmosphere or an oxygen gas atmosphere inside, and a laser beam emitting device 9 attached to the side of the container IO.

Inside the container IO, a substrate holder 11 and a cylindrical rotating base 12 are provided facing each other, and an introduction hole is formed in the outer wall of the container IO on the side of the rotating base 12. A transparent window 14 made of Zn5e or the like is attached.

Further, inside the container 10 and on the side of the substrate holder 11, a concave mirror 15 is installed so that its mirror surface is directed toward the H rotary base material 12 and the transparent window 14. The rotating base material 12 can be irradiated with a laser beam that enters the container through the transparent window 14. On the other hand, the substrate 2 is mounted on the substrate holder 11 so as to face the rotating base material 12, and the substrate holder 11 is also provided with a heater I6 capable of heating the substrate 2. Note that the rotating base material I2 is rotatably supported around the circumference by a rotating device (not shown) provided inside the container IO.

The rotating base material 12 is made of an oxide superconductor, and specifically is an A-B-CD system (where A is Y).

Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, G
d, Tb, Dy.

Periodic table of Ho, Er, T'ffi, Yb, Lu, etc.■
Indicates one or more types of group a elements, B is S
r, B a.

Represents one or more than 2N of Group IIa elements of the periodic table such as Ca, Be, Mg, and Ra, and C represents Cu, Ag, and A.
Among the group 1b elements of the periodic table of u and Nb, Cu or Cu
D is O, S, Se, Te, P.

and two or more elements of group VIIb of the periodic table such as F, Cl, and Br containing 0 or O) are used. The composition of each constituent element of this oxide superconductor is, for example, Y-Ba-
In the case of Cu-0 based oxide high temperature superconductor, Y:Ba:
Cv:O=l:C1-3):(2-4):(7-δ
), and δ is in the range O≦δ≦5.

To form the first superconducting JiI2a using the laser evaporation apparatus having the structure shown in FIG. 2, the substrate 2 is mounted on the substrate holder 11, and the container is opened! 0 is made into an oxygen atmosphere, the temperature is set to a predetermined value, and the rotating base material 12 is rotated. Next, the rotating base material 12 is irradiated with a laser beam emitted from the laser beam emitting device 9 via the concave mirror I5.
The outer peripheral portion of the substrate 2 is evaporated, and the evaporated atoms are deposited on the substrate 2. The first superconducting layer 1a can be formed on the upper surface of the substrate 2 through such processing.

The first superconducting layer 1a formed as described above is formed by laser evaporation, and therefore has a dense -like crystal structure. In addition, according to such a laser vapor deposition method, by adjusting the output of the laser, adjusting the rotation speed of the rotating base material 12, and controlling the temperature of the rotating base material 12, the deposition rate can be reduced by 0.5 to 1.
A superconducting layer with a thickness of about 1 μm can be formed in 0 hours.

Next, a second step of forming a second superconducting layer 1b on the first superconducting FJ 1 a using the MBE method is performed. The MBE device used in this second step epitaxially grows a superconducting layer on a substrate 2 mounted on a holder by reacting molecules and atoms scattered from an evaporation source (molecular beam source) in a vacuum state. When a film is formed by the MBE method, the critical field current density can be improved compared to when a film is formed by laser evaporation. Note that the temperature of the substrate 2 during the reaction is preferably about 600 to 1000°C. Further, in this step, it is necessary to prepare a plurality of evaporation sources in advance depending on the N type, composition, etc. of the oxide superconductor. This evaporation source can be obtained by calcining or sintering a material containing the elements constituting the oxide superconductor, or a mixture of this material and the oxide superconductor.

The second superconducting layer 1b formed by such a second step is thin, but the crystal orientation is controlled by epitaxial growth of the oxide superconductor. , especially the critical current density (Jc
), the superconducting properties will be good.

Next, in this way, the first superconducting layer is formed on the substrate 2! After forming superconducting layer a and second superconducting layer 1b, a third superconducting layer Ic is formed on second superconducting layer Ib by the same method as that of forming first superconducting layer 1a.

The third superconducting layer 1c formed in such a third step
The crystal orientation follows the good crystal orientation of the second superconducting layer 1b, and exhibits good superconductivity.

For the high temperature superconducting material 1 formed in this way,
Heat treatment can be performed in an atmosphere containing oxygen gas if necessary. This heat treatment is performed at a treatment temperature of 1, for example, 400 to 1
The treatment is carried out at a temperature of 000°C and a treatment time of 1 to 100 hours. Through such heat treatment, each constituent element in the high temperature superconducting material 1 reacts with each other more fully, so the high temperature superconducting material 1
It is possible to improve the superconducting properties of.

In addition to oxygen gas, the atmosphere during heat treatment contains S, S
Gases of group VIb elements of the periodic table such as e or F.

Gases of Group VIIb elements of the periodic table, such as C1 and Br, can also be included. These elemental gases penetrate into the crystal as part of the constituent elements of the obtained high-temperature superconductor and contribute to improving the superconducting properties.

Furthermore, if a substrate 2 made of silver or a silver alloy is used as the substrate 2 on which the high-temperature superconducting material 1 is formed, oxygen in the heat treatment atmosphere permeates through the inside of the substrate 1, so that the first superconducting layer 1a has sufficient oxygen. Oxygen can be supplied, and the superconducting properties can also be improved in this way.

In such a high-temperature superconducting material 1, two of the three superconducting layers are formed by laser vapor deposition, so that a desired film thickness can be obtained in a short time. Furthermore, since the third superconducting layer 1c was formed by the laser evaporation method on the second superconducting layer lb formed by the MBE method, this third superconducting layer IC grows using the second superconducting layer 1b as a growth nucleus. However, as a result, the crystal orientation of the third superconducting layer IC becomes uniform and a high critical current density is exhibited. Furthermore, if this high temperature superconducting material 1 is heat treated in an oxygen atmosphere, oxygen can be sufficiently supplied into the high temperature superconducting material 1, and the superconducting properties of the high temperature superconducting material 1 can be improved.

FIG. 3 is a diagram showing another example of the high temperature superconducting material of the present invention.

The high temperature superconducting material 3 of this example is formed on the surface of the base 2, and includes a first superconducting layer 3a formed on the second base 2 by the MBE method, and a first superconducting layer 3a formed on the second base 2 by the MBE method. It consists of three layers: a second superconducting layer 3b formed by laser vapor deposition, and a third superconducting layer 3C formed on this second superconducting layer 3b by MBE.

According to such a high temperature superconducting material 3, the second superconducting layer 3b is formed by laser vapor deposition on the first superconducting layer 3a formed by the MBE method, and the third superconducting layer 3b is formed by the MBE method on top of the second superconducting layer 3b. Since the layer 3C is formed, the first superconductor 13
Following the good crystal orientation of a, the second superconducting layer 3b
And since the crystal orientation of the third superconducting layer 3c is aligned,
The crystal orientation of the entire high temperature superconducting material 3 made up of these layers is well controlled and exhibits a high critical current density.

In addition, two layers of the three-layer structure, the first superconducting layer 3a and the third superconducting layer 3c, are formed by the MBE method to increase the critical current density. For example, since most of the current flows inside these two layers, it is possible to flow a large amount of superconducting current throughout the high temperature superconducting material 3. Furthermore, since the third superconducting layer 3c exposed on the surface is formed by the MBE method to provide a margin for the critical current density, even when devices, wiring materials, etc. are connected to the surface, the connection part will be Decrease in critical current density due to deterioration is not a problem.

"Example" A high-temperature superconducting material was manufactured using a laser evaporation device having the same configuration as the device shown in FIG. 2 and an MBE device along the path shown.

First, a substrate made of S rT io 3 was mounted on a substrate holder, and a cylindrical substrate was used as a rotating base material.

A base material made of Yl Bav, a Cua, a 0 (7-δ) was used, and a vacuum atmosphere of 10 −3 Torr was created inside the container. Next, a carbon dioxide gas laser beam was emitted to irradiate the rotating base material, and the rotating base material was rotated at 10 times/second.

Through the above operations, the atoms of the rotating base material were melted and scattered by a laser to form a first superconducting layer with a thickness of 0.3 μm on the substrate surface.

Subsequently, the substrate on which the first superconducting layer was formed was set in an MBE apparatus, and Y t O- and B a C were applied to the surface of the substrate.
Y, Ba, Cu using O3 and CuO evaporation source.

A second superconducting layer having a composition of 0(7-δ) and a thickness of 0.1 μm was formed.

Subsequently, the substrate on which the first and second superconducting layers were formed was set in the same laser evaporation apparatus used for forming the first superconducting layer, and a layer of 0.3 μm thick was deposited on the surface of the substrate.
A third superconducting layer was formed to obtain a high temperature superconducting material with a thickness of 0.7 μm.

Thereafter, a ripening treatment was performed in which the material was heated to 900° C. for 2 hours in an oxidizing atmosphere to obtain a high-temperature superconducting material as a final product.

This high temperature superconducting material has a critical temperature (Tc) = 92.9 and a critical current density (Jc) = 1, 2 x 106A/c.
m'' (at 77 K), indicating that excellent superconducting properties can be obtained.

"Effects of the Invention" As explained above, the high temperature superconducting material of the present invention was formed by laser vapor deposition. The above A-B-C-D system laser-deposited superconducting layer and the above A formed by MBE method
-B -C-D system MBE superconducting layers are laminated alternately, and two or more superconducting layers of at least one of the laser-deposited super-N layer and the MBE superconducting layer are laminated, so a plurality of thin film layers are laminated. This allows the critical current density to be higher than that of a single-layer high temperature superconducting material, and at least one laser-deposited superconducting layer is formed on top of the MBE superconducting layer, which allows this laser-deposited superconducting layer to be immediately Growth occurs with the crystal orientation aligned using the underlying MBE superconducting layer as a growth nucleus. Therefore, a laser-deposited superconducting layer with a fast growth rate can be formed with the crystal orientation aligned, and the film thickness can be increased and the critical current density can also be increased.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a configuration diagram showing an example of a laser evaporation apparatus used for implementing the present invention.
FIG. 3 is a sectional view showing another embodiment of the present invention. 1.3... High-temperature superconducting material, Ia, Ic, 3b... Laser-deposited superconducting layer, l b, 3 a, 3 c...
MBE superconducting layer, 2...substrate.

Claims (1)

[Claims] A-B-C-D system (where A is Y, Sc, La, Yb, Er, Ho, D
Indicates one or more elements of group IIIa of the periodic table such as y, B
represents one or more elements of group IIa of the periodic table such as Sr, Ba, and Ca, and C represents elements of group I of the periodic table such as Cu, Ag, and Au.
Denotes Cu or two or more of group b elements and Nb, including Cu, and D is an element of group VIb of the periodic table such as O, S, and Se, and O of group VIIb of the periodic table elements such as F, Cl, and Br. Indicates one or more types including. ) high-temperature superconducting material, which includes an A-B-C-D system laser-deposited superconducting layer formed by a laser evaporation method and an A-B-C-D system formed by a molecular beam epitaxy (MBE) method. The above laser-deposited superconducting layer and the MBE superconducting layer are alternately laminated with
A high-temperature superconducting material characterized in that it is formed by laminating two or more superconducting layers, at least one of which is one of the superconducting layers.