JPH0393110A - superconducting wire - Google Patents

Abstract

PURPOSE:To improve the critical current density of a superconducting wire-rod as well as providing a metal base-body functioning as a stabilizing material by having at least the oxide superconducting layer formation plane of the metallic base-body to be formed of a plane prepared by the process of orienting the 100 crystal plane and/or 110 crystal plane of silver in parallel to the oxide superconducting layer formation plane. CONSTITUTION:The oxide superconducting layer formation plane of a metallic base-body is made up of a plane prepared by the process of orienting the 100 crystal plane and/or 110 crystal plane of silver. Since the lattice constant (a-axis = 4.09Angstrom ) of silver crystal approximates to the lattice constant (3.8Angstrom to 3.9Angstrom ) of each of a-axis of and b-axis of an oxide superconducting crystal, an oxide superconducting layer having the c-axial plane of the oxide superconducting crystal oriented directly on the surface of the metal base-body can be obtained by forming the oxide superconducting layer on the crystal plane of silver through a thin-film formation process. This provides improvement in the critical current density as well as providing metal base-body functioning as a stabilizing material to the superconducting layer.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a superconducting wire using an oxide superconductor.

(Prior art) Since it was announced in 1988 that Ba-La-Cu-0-based layered perovskite oxides have a high critical temperature of 40K or more, oxide-based superconductors have attracted attention. Research is being actively conducted to collect and search for new materials.

Among them, there are defective Peropsite type oxide superconductors represented by the Y-Ba-Cu-0 system which has a high critical temperature higher than the liquid nitrogen temperature, the at-sr-ca"cu-o system and the TI- Ba-Ca-Cu-0-based oxide superconductors have important industrial value because they can use inexpensive liquid nitrogen as a coolant instead of expensive liquid helium.

When considering the application of such oxide superconductors to the energy field, it is first necessary to make them into wires. Therefore, attempts have been made to produce wires from oxide superconductors using various methods.

Methods for producing a superconducting wire using an oxide superconductor include (a) a method of enclosing an oxide superconductor in a metal tube and drawing it into a wire; (b) a method of forming an oxide superconductor powder into a wire; (e) A method of forming an oxide superconductor layer on a metal tape by thermal spraying or various film forming methods and forming a wire into a wire. .

The critical current density of superconducting wires using these oxide superconductors tends to gradually improve, and among the above methods, especially (
Method C) is attracting particular attention because it is easy to obtain an oxide superconductor layer with excellent coordination properties and is expected to improve superconducting properties.

However, if method (e) above is applied and an oxide superconductor layer is directly formed on a metal substrate by a sputtering method or a vapor deposition method, it is very difficult to obtain an oxide superconductor layer with a κ orientation. It is. For example, attempts have been made to use sputtering to form an oxide superconductor layer on a substrate made of Hastelloy alloy, which is a heat-resistant material, but the substrate and oxide superconductor react and produce reactants at the interface. Inconveniences may occur, such as the formation of an oriented film or the inability to obtain an alignment film.

Therefore, as a practical method for obtaining an oriented layer, a layer such as MgO having a lattice constant similar to that of the oxide superconductor is formed as a buffer layer on a metal substrate, and an oxide superconductor layer is formed on the buffer layer. A method of forming a thin film has been adopted.

According to such a method of forming an oxide superconductor layer via a buffer layer, reactions at the interface can be prevented, an oriented oxide superconductor layer can be obtained, and the critical current density can be improved. On the other hand, since an insulating layer such as MgO is present at the interface between the oxide superconductor layer and the metal substrate,
There is a drawback that electrical continuity cannot be established between the oxide superconductor layer and the metal substrate. Therefore, if part of the oxide superconductor layer transitions to a normal conductive state during use, the metal substrate cannot function as a so-called stabilizing material that bypasses the current to the metal substrate and protects the superconductor. .

(Problems to be Solved by the Invention) As mentioned above, in superconducting wires to which the conventional thin film method is applied, a buffer layer such as MgO is interposed in order to obtain an oriented layer of oxide superconductors. There was a drawback in that the substrate could not function as a stabilizing material.

The present invention was made to address the problems of the prior art, and aims to improve critical current density by forming an oxide superconductor layer with excellent orientation on a metal substrate.
The object of the present invention is to provide a superconducting wire that allows a metal base to function as a stabilizing material.

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention is based on a composite of a long metal substrate and an oxide superconductor layer formed continuously in the longitudinal direction on the metal substrate. In the superconducting wire, at least the oxide superconductor layer forming surface of the metal substrate has a (100) crystal plane and/or a (lie) crystal plane of silver oriented parallel to the oxide superconductor layer forming surface. It is characterized by being made up of two sides.

Many oxide superconductors are known, but in the present invention, rare earth element-containing perovskite oxide superconductors, old -Sr-Ca-Cu-0 based oxide superconductors, TI -Ba-Ca-Cu-0 based oxide superconductor etc. are applied.

The oxide superconductor containing a rare earth element and having a berovskite structure may be one that can realize a superconducting state, for example, REMCuO 2 3 7-δ (RE is Y SLas Ses Nd, 81% E
LISGdSDF% HO, Ers Ttss YbS
At least one element selected from rare earth elements such as Lu, H is at least one element selected from Bas, Sr, Ca, δ represents an oxygen defect, usually a number of 1 or less, and a part of Cu is T1% V s Cr, Mn, Fe,
Can be replaced with CO% Niq Zn, etc. ) are exemplified. In addition, rare earth elements are defined in a broad sense, and S
It shall include e% Y and La systems.

In addition, the Bl-Sr-Ca-Cu-0-based oxide superconductor has the chemical formula: Bl2 Srz Ca2Cu30x
--=(I):Biz(Sr.Ca)xcu
;+Ox --(n) (in the formula, a part of Bl can be replaced with pb etc.), and TI-B
The a-Ca-Cu-0 based oxide superconductor has the chemical formula: Tl2 Ba2Ca2Cux Ox
= (III):TI2(Ba.Ca)3Cu20x
-(IV) etc.

The metal substrate used in the present invention is one in which at least the surface on which the oxide superconductor layer is formed is made of silver,
The entire metal substrate may be made of silver, or it is also possible to use one in which a silver layer is formed on a core made of iron, carbon dioxide, chromium, or alloys thereof, which are difficult to form a solid solution with silver. Moreover, various shapes such as a tape shape and a wire shape can be used as the shape of the metal base.

In any of these cases, the formation surface of the oxide superconductor layer is the (100) crystal plane of silver or the (11G)
It is constituted by a plane in which the crystal plane is oriented parallel to the formation plane, or a mixed oriented plane.

In this way, the shape and appearance of the oxide superconductor layer can be changed to silver (100
) crystal plane or (11G) crystal plane, it is possible to obtain an oxide superconductor layer that is C-plane oriented with respect to this formation plane. Suitable for orientation.

Note that the thickness of the silver layer when forming the metal substrate from a composite of silver and other metals is not particularly limited;
Considering the orientation of silver, it is practically preferable to set it to 1μ or more. In addition, as a composite method, methods such as forming a silver layer on the surface of the metal member serving as the core material by plating or various film formation methods, or mechanically integrating the core material and silver may be adopted. I can do it.

The degree of orientation of these silver crystal planes must be 60% or more parallel to the formation plane of the oxide superconductor layer, with the (100) crystal plane, (110) crystal plane, or a mixture thereof. Yes, especially the (100) crystal plane of silver is 8
The orientation is preferably 0% or more.

Such a (100) crystal plane or (1.10) crystal plane of silver can be obtained by rolling silver in the direction of the oriented plane and aligning the crystal orientation by a slip plane. Since the crystal planes obtained by rolling are likely to have (11G) crystal planes aligned, it is preferable to recrystallize the material by subsequently performing heat treatment. This recrystallization coarsens the silver crystal grains and improves the degree of orientation of the (100) crystal plane, making it easier to orient the crystal orientation of the oxide superconductor.

The method for forming the oxide superconductor layer on the metal substrate having at least the surface made of silver is a physical vapor deposition method such as a sputtering method, a reactive vapor deposition method, a laser vapor deposition method, or a chemical vapor deposition method. Various thin film forming methods such as CVD method and MOCVD method can be used.

(Function) In the superconducting wire of the present invention, the oxide superconductor forming surface of the metal base is a silver (100) crystal plane or a (11G) crystal plane.
It is composed of oriented planes based on crystal planes. The lattice constants of these silver crystal planes (a-axis - 4.09A) are the lattice constants of the a- and b-axes of the oxide superconductor crystal (3.8λ~3,
9), by forming an oxide superconductor layer on the silver crystal plane using a thin film formation method,
It becomes possible to obtain an oxide superconductor layer in which the C-plane of the oxide superconductor crystal is oriented directly on the surface of the metal substrate. Therefore, the critical current density can be improved, and the metal substrate can function as a stabilizing material for the superconductor.

(Example) Next, examples of the present invention will be described.

Example 1 First, a silver material was rolled and drawn in a certain direction to produce a long tape-like substrate with a width of 10 ms and a thickness of 1 ms. When the crystal orientation of the main surface (pressure application surface) of the silver tape-shaped substrate thus obtained was analyzed by X-ray diffraction, the (11G) plane was oriented almost parallel to the longitudinal direction of the main surface. was.

Next, this silver tape-shaped substrate was heated at TOO°C x 60°C.
Heat treatment for recrystallization was carried out under conditions of 10 minutes.

The crystal orientation and crystal grain size on the same plane after heat treatment are
When examined by line diffraction, it was found that the (100) plane was oriented, with a degree of orientation of 80%, and the rest were (110) planes. Moreover, the crystal grains were coarsened to 0.5 ms to 2 ms.

Note that the degree of orientation of this crystal plane is the result of measurement based on the intensity ratio of each crystal plane by X-ray diffraction.

Next, the above-mentioned silver tape-shaped substrate was installed in a film forming apparatus so that the (100) oriented plane faced the vapor deposition source, and while heating this silver tape-shaped substrate to about 700°C, Y%Ha%
Heat and evaporate Cu, and measure the film thickness by 1 on a film thickness monitor.
A superconducting wire was produced by continuously depositing the material on the (100) oriented surface of a silver tape-shaped substrate while controlling the μ to be constant.

Note that during film formation, oxygen was blown from a nozzle near the surface of the silver tabular substrate, and was further supplied while being excited by high frequency. In addition, each evaporated element is clustered and ionized,
The film is deposited at an accelerated rate, and the film composition is YBa2Cu30.
The amount of each evaporated element was adjusted to be 7-δ.

When the crystal orientation of the oxide superconductor layer of the superconducting wire obtained in this way was analyzed by X-ray diffraction, it was found that the C plane was aligned with the (100) plane of the silver tape-shaped substrate, as shown in Figure 1. It was confirmed that they were oriented in parallel.

Further, regarding the superconducting properties, the critical temperature was 85K, and the critical current density at 77K was l×10'A/cj.

Example 2 Using nickel as the core material, the surface of the nickel material was first coated with silver by plating, and then this composite material was rolled in a certain direction and wire-drawn to a width of 1 h.
A long tape-like substrate having a thickness of m×1111 was produced. The thickness of the silver layer on the surface was 5 μm. Then,
After heat-treating this composite tape-shaped substrate for recrystallization at 700°C for 30 minutes, the crystal orientation and crystal grain size of the silver surface were examined by X-ray diffraction. was coarsened to 1 to 2I hazy, and the (100) plane was oriented parallel to the longitudinal direction of the principal surface, and the degree of orientation was 70%.

Next, the composite tape-shaped substrate was placed in a film forming apparatus so that the silver layer faced the vapor deposition source, and a Y-Ba-Cu-0 based oxide with a thickness of about 1μ was deposited under the same conditions as in Example 1. A superconducting wire was fabricated by continuously forming superconducting layers.

When the crystal orientation of the oxide superconductor layer of the superconducting wire thus obtained was analyzed by X-ray diffraction, it was confirmed that the C-plane of the oxide superconductor was oriented parallel to the silver layer surface. . In addition, the superconducting property has a critical temperature of 85K,
The critical current density at 77K was 8XlO"^/c.

Comparative Example 1 First, a composite metal substrate was prepared by coating the surface of a plate-shaped stainless steel core material with silver by electroplating.

When the crystal orientation of the silver layer of the obtained composite metal substrate was analyzed by X-ray diffraction, the crystal plane of silver was oriented in the (Ill) direction.

Next, Y was applied on the silver layer of the composite substrate under the same conditions as in Example 1.
A superconducting wire was produced by forming a -Ba-Cu-0 based oxide superconductor layer.

The obtained oxide superconductor layer exhibited a superconducting state at 82K, but when its crystal orientation was analyzed by X-ray diffraction, diffraction peaks similar to the powder X-ray diffraction pattern were obtained, and in particular, the C-plane orientation was observed. was not recognized.

[Effects of the Invention] As is clear from the above examples, the superconducting wire of the present invention is such that the C-plane of the oxide superconductor through which superconducting current easily flows is oriented in the longitudinal direction of the metal base. An oxide superconductor layer having a specific coordination property is formed directly on a metal substrate. Therefore, it has excellent superconducting properties such as critical current density, and since the metal substrate functions as a stabilizing material, it is possible to stably exhibit superconducting properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the results of X-ray diffraction of a superconducting wire according to an embodiment of the present invention.

Claims (1)

[Claims] (1) In a superconducting wire consisting of a composite of a long metal substrate and an oxide superconductor layer formed continuously in the longitudinal direction on the metal substrate, at least the oxide superconductor layer is formed on the metal substrate. The surface is
A superconducting wire characterized in that a (100) crystal plane and/or a (110) crystal plane of silver is constituted by a plane oriented parallel to the oxide superconductor layer forming plane.