JPH01100818A - High temperature superconducting material - Google Patents

Abstract

PURPOSE:To obtain an excellent high temperature superconducting material by forming the layer of the A-B-C-D system via a molecularbeam epitaxial method and another layer thereon 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 in group Ib and Nb, and D for O and the like in group VIb. 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 Se in group IIIa of the periodic table, B for one or more elements such as Sr and Ba in group IIa, C for two or more elements containing Ib group elements such as Cu and Ag and Nb, or Cu, and D for two or more elements containing O among group VI elements such as O and S, or O. And the high temperature superconducting material of an oxide system having a two-layer structure is formed on a substrate 1, and the superconducting material 2 comprises a superconducting material 2a formed via a molecular-beam epitaxial method and a superconducting material 2b formed via a laser deposition method. According to the aforesaid process, it is possible to display high critical current density and critial temperature, and to form a thick superconducting layer efficiently.

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. Various research and developments are being conducted on superconducting materials as extremely promising superconducting materials.

Incidentally, it is known that the critical temperature and critical current density (Jc) of such an oxide-based superconductor vary considerably depending on various factors such as the manufacturing method and manufacturing conditions. At present, it is known that superconductors formed by thin film forming methods such as molecular beam epitaxy (hereinafter referred to as MBE) and laser vapor deposition exhibit relatively good superconducting properties. .

[Problems to be Solved by the Invention] However, by using the MBE method, 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. Since the film speed is slow, it takes a long time to obtain a thick oxide superconductor, resulting in poor manufacturing efficiency. On the other hand, laser vapor deposition has the advantage that it is possible to increase the film formation rate and that even a thick superconducting layer can be formed in a relatively short time.

This invention was 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, large current capacity, and
The aim is to provide high-temperature superconducting materials with high manufacturing efficiency.

[Means for solving the problem] This invention is based on the A-B-C-D system (where A is Y, Sc
, La, Yb, Er, Ho, Dy etc. Periodic Table I [la
B represents one or more of the Group Ila elements of the periodic table such as Sr, Ba, Ca, etc., and C represents C.
Group 1b elements of the periodic table such as u, A g, A u and N
b represents Cu or two or more types containing Cu; D is 0, S, Se, etc., elements of the VRB group of the periodic table, as well as F, CI
.

Indicates two or more elements containing 0 or O among Group VIIb elements of the periodic table, such as Br. ) is a high-temperature superconducting material comprising an A-B-C-D system first superconducting layer formed by molecular beam epitaxy and an A-B-C-D system formed on this first superconducting layer by laser evaporation. The solution was to consist of a B-CD-based second superconducting layer.

[A first superconducting layer with a structure with good crystal orientation and a large critical current density is formed by the action MBE method, and a laser evaporation method that allows the formation of a large film thickness in a short time on this layer] A second superconducting layer is formed. By performing the MBE method and the laser evaporation method in this way, a sufficient thickness can be ensured as a whole, and the critical current density can also be increased.

Further, the second superconducting layer formed by the above laser vapor deposition method is MBE
Since the second superconducting layer is formed on the first superconducting layer by the method, the crystal orientation of the second superconducting layer follows the good orientation of the first superconducting layer, and becomes a superconducting layer with good crystal orientation. Therefore, it exhibits even better superconducting properties.

The present invention will be explained in more detail below.

FIG. 1 shows an example of the oxide-based high-temperature superconducting material of the present invention, and the reference numeral l in the figure represents a substrate.

A two-layered oxide-based high-temperature superconducting material 2 is formed on the surface of this base 1. This high temperature superconducting material 2 is MB
It is composed of a first superconducting layer 2a formed by the E method and a second superconducting layer 2b formed by the laser evaporation method.

Next, an example of a method for forming such a high temperature superconducting material 2 will be described.

The substrate 1 for forming the high-temperature superconducting material 2 may be of various shapes, such as a plate, a wire, a tape, a cylinder, a column, or the like. As the constituent material of such a substrate l, a material is selected that can withstand the high temperature during the heat treatment applied during the production of the oxide-based high-temperature superconducting material, and specifically, silver,
Metal materials such as gold, platinum, aluminum, copper, alloy materials thereof, nitrides, carbides of these metals, or stainless steel, and furthermore, strontium titanate (S rT +03), alumina (AIzOs), etc. ), Silico 7 (Si), Silica (Sift
), lithium niobate (L 1Nbot), sapphire, ruby, and other crystalline materials are preferably used.

Next, a two-layered oxide-based high-temperature superconducting material 2 is formed on the surface of such a substrate 1. The process of forming the high temperature superconducting material 2 in this example consists of two steps.

In the first step, molecular beam epitaxy (MBE)
In a second step, a second superconducting layer 2b is formed using a laser evaporation method.

The MBE apparatus used in the MBE method in the first step reacts molecules and atoms scattered from an evaporation source (molecular beam source) in a vacuum state to epitaxially grow a superconducting layer on a substrate mounted on a holder. Therefore, when a film is formed by this MBE method, the critical current density can be improved compared to when a film is formed by laser evaporation. In addition,
The temperature of the substrate 1 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 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.

Since this first superconducting layer 2a is formed by the MBE method, it has a relatively small thickness, but it has a structure with uniform crystal orientation, and therefore has a particularly high criticality. It indicates the current density.

Next, on this first superconducting layer 2a, a second superconducting layer 2b which is thicker than the first superconducting layer 2a is formed using a laser vapor deposition method.
form.

As a laser evaporation device used in the second step, for example, a second
Use the apparatus shown in the figure. The apparatus shown in FIG. 2 includes a container 10 that can maintain a vacuum atmosphere or an oxygen gas atmosphere inside, and a laser beam emitting device 9 attached to the side of this container 10.
It is configured with the following.

Inside the container 10, 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 IO and on the side of the substrate holder 11, a concave mirror 15 is installed so that its mirror surface faces the rotating base material 12 and the transparent window 14. The rotating base material 12 can be irradiated with a laser beam that enters the interior of the room through the transparent window 14 . On the other hand, the rotating base material 12 is attached to the substrate holder 11.
The board 1 is mounted facing the board holder 1.
1 is attached with a heater 16 that can heat the substrate l. Note that the rotating base material 12 is rotatably supported around the circumference by a rotating device shown in the illustrated path provided inside the container IO.

The rotating base material 12 is made of an oxide superconductor, specifically an A-B-C-D system (where A is Y, Sc,
La, Ce, Pr, Nd, Pa, 5III, Eu, Gd
,Tb.

B represents one or more elements of the NLA group of the periodic table, such as Dy, Ho, Er, T's, Yb, and Lu, and B is Sr.

Represents one or more elements of Group IIa of the periodic table such as Ba, Ca, Be, Mg, and Ra; C is Cu;
A Group 1b elements of the periodic table such as gsAu and C of Nb
Indicates two or more types containing u or Cu, and D is O, Se,
Te.

Of the group VIb elements of the periodic table, such as Po, O or two or more elements containing O) are used. In addition, Y-
In the case of Ba-Cu-0 based oxide high temperature superconductor, Y:
Ba:Cu:0=1:(1~3)2(2~4
): (7-X), where X is in the range O≦X≦5.

In order to form the second superconducting layer 2b using the laser evaporation apparatus having the structure shown in FIG. The interior of the rotating base member 12 is made to have an oxygen atmosphere, and is heated to a predetermined temperature, and the rotating base member 12 is rotated. Next, the laser beam emitted from the laser beam emitting device 9 is transmitted to the concave mirror 1.
5 to the rotating base material 12 to evaporate the outer circumference of the rotating base material 12, and the evaporated atoms are deposited on the first superconducting layer 2a formed on the substrate l. By such treatment, the second superconducting layer 2b can be formed on the surface of the first superconducting layer 2a on the upper surface of the substrate l.

Since a thick superconducting layer can be formed in a short time by such a laser vapor deposition method, a second superconducting layer 2b having a sufficient thickness can be obtained. Further, the first superconducting layer 2a serving as the base is formed by the MBE method and has a crystal structure with good orientation, and the second superconducting layer 2a
Since b grows epitaxially using the crystals of the first superconducting layer 2a as nuclei, it similarly has a crystal structure with good orientation.

The high-temperature superconducting material 2 formed as described above is preferably heat-treated in an atmosphere containing oxygen gas, if necessary. This heat treatment is performed by heating at a temperature of about 400 to 1000° C. for about t-too hours. By such heat treatment, the constituent elements within the high temperature superconductor 2 react more sufficiently with each other, so that the superconducting properties of the high temperature superconductor material 2 can be improved. Furthermore, the first superconducting layer 2a
has a crystal structure with good orientation, and the second superconducting layer 2b is in close contact with this layer, so by heat-treating both, the crystal structure of the second superconducting layer 2b changes to that of the first superconducting layer. 2a, and the superconducting properties are further improved.

Therefore, the high temperature superconducting material 2 exhibits a high critical temperature and critical current density. Further, according to the laser vapor deposition method described above, even a second superconducting layer 2b having a sufficient thickness can be produced in a short time, so that even a high temperature superconducting material 2 having a sufficient thickness can be efficiently manufactured.

Note that the atmosphere during the heat treatment includes S in addition to oxygen gas.
, gas of Group VIb elements of the periodic table such as Se, or F, C
Gases from group VIIb of the periodic table, such as 118r, 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 the substrate l on which the high-temperature superconducting material 2 is formed is made of silver or a silver alloy, oxygen in the heat treatment atmosphere will permeate through the inside of the substrate l, so that the first superconducting layer 2a will have enough oxygen. Oxygen can be supplied, and the superconducting properties can also be improved in this way.

[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 in the figure.

First, a substrate made of S rT io 3 was set in an MBE apparatus, and evaporation sources of y, o, BaCO3, and CuO were used on the surface of the substrate, and the composition of Y IB atc uso 7-X and the thickness were A first superconducting layer of 0.1 μm was formed.

Next, the substrate on which the first superconducting layer was formed was mounted on a substrate holder of a laser evaporation apparatus, and used as a rotating base material.
Cylindrical Y + B at, ac ua, sO? A base material made of an oxide superconductor having a composition of -X was used, and the inside of the container was made into an atmosphere with an internal pressure of 10-' Torr. Next, a carbon dioxide gas laser beam was emitted to irradiate the rotating base material, and the rotating base material was rotated 2 times/second. Through the above operations, the atoms of the rotating base material were melted and scattered by a laser to form a second superconducting layer with a thickness of 0.6 μm on the substrate surface.

In the above steps, it takes 2 hours to form a film using an MBE device.
It took 0.5 hours to form the film using a laser evaporation device. Thereafter, heat treatment was performed at 900° C. for 3 hours in an oxidizing atmosphere to obtain a final product of high-temperature superconducting material.

This superconducting material has a critical temperature (Tc) of 92.8 and a critical current density (J c) I
11” (77K)).

As a comparative example, a superconducting layer with a thickness of 0.3 μm was
A high-temperature superconducting material was obtained by manufacturing only by method E and heat-treating it under the same conditions as above.

This superconducting material has a critical current density (J c) of 5 X I O'A/cm
” (77K)).

From the above results, it has been found that by employing the structure of the present invention, a superconducting material having a high critical current density and a sufficient thickness can be manufactured.

[Effects of the Invention] As explained above, the high temperature superconducting material of the present invention has a first superconducting layer formed by the MBE method and having a crystal structure with high critical current density and good orientation, and Since it consists of a thick second superconducting layer formed by a laser vapor deposition method that can obtain a structure, it is possible to obtain a high-temperature superconducting material that has a high critical current density as a whole and has a sufficient film thickness. can. In addition, since the second superconducting layer is grown using the first superconducting layer as a nucleus, the second superconducting layer also has a structure with good crystal orientation, which further improves the conductivity properties of the layer material. be. Further, according to the present invention, since the structure is such that even a thick superconducting layer can be formed efficiently in a short time, there is an effect that a superconducting material with a large current capacity can be obtained in a short time.

[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 carrying out the invention. ! ...Substrate, 2.. High temperature superconducting material, 2a.. First superconducting layer, 2b.. Second superconducting layer.

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. Alternatively, it represents two or more types containing O. ) is a high-temperature superconducting material formed by molecular beam epitaxy.
A high-temperature superconducting material comprising a first superconducting layer of an A-B-C-D system and a second superconducting layer of an A-B-C-D system formed on the first superconducting layer by a laser evaporation method.