JPH0645046A - Method for forming electrode in oxide superconductor - Google Patents

Abstract

PURPOSE:To form a compound phase on the critical surface between an electrode and a superconductor and improve adhesive strength by forming the electrode by use of a silver base alloy containing an element forming the superconductor. CONSTITUTION:When spperconductive bulk frame spraying of 20 atomic %R copper-silver allay is conducted, the cluster of a flame sprayed metal covers the surface of a superconductor 1, and the superconductor and the flame sprayed metal are divided into two phases. When this superconductive bulk is thermally treated at 800-900 deg.C, a solid soluble element 5 is deposited on the surface of a silver base metal 4 or therein, a compound phase 3 containing much copper is partially formed on the critical surface between the silver base alloy 4 and the superconductor 1. The formed compound phase 3 has an effect of wedge to the critical surface to enhance the adhesive strength between the superconductor and an electrode, the adhesion is also enhanced, and the deterioration of the electrode by peeling can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrode having low contact resistance and good adhesive strength on an oxide superconductor.

[0002]

2. Description of the Related Art When an oxide superconductor is used as a conductor, it is essential to form an electrode for connecting to the outside. The contact resistance is extremely low in order to stably utilize the characteristic that the superconductor can be operated with almost zero resistance.
Improvements in methods for forming electrodes with suppressed Joule heat are being made.

Conventionally, electrodes have been formed by using a metal material such as gold or silver which has a small resistance at an extremely low temperature and which does not deteriorate the oxide superconductor even by heating. A method of winding such a metal foil around an oxide superconductor and press-bonding it by cold isostatic pressing (CIP) and heat treatment, and a method of forming a metal film by plasma spraying or sputtering and heat-treating are devised. Has been done. With these methods, a low contact resistance of about 10 ⁻⁸ Ωcm ² is realized.

[0004]

As described above, in the current lead using the oxide superconductor, the electrode is formed of a metal having low resistance and chemically stable with respect to the oxide superconductor. It is also important that the electrodes do not impair the characteristics of the superconductor, but on the other hand, no reaction phase is formed at the interface between the oxide superconductor and the metal forming the electrode, and the adhesive strength between the metal and the superconductor is Extremely weak. Since the adhesion of the electrodes is weak, the electrodes may deteriorate due to peeling of the metal film.

Further, the superconductor is repeatedly cooled and heated between extremely low temperature and room temperature, and expansion and contraction occur at the interface between the superconductor and the electrode due to temperature, and thermal stress acts. The difference in the linear expansion coefficient between the superconductor and the electrode metal promotes the peeling of the electrode film.

It is an object of the present invention to obtain an electrode forming method having a good adhesive strength, and to provide an oxide superconductor which is resistant to peeling of the electrode and can be stably used.

[0007]

In order to solve the above problems, in the present invention, a silver-based alloy is used as an electrode material of an oxide superconductor to perform thermal spraying, foil winding, and the like. After that, a heat treatment is performed to form a reaction phase between the superconductor and the metal at the interface between them, thereby enhancing the adhesive strength of the electrode.

An example of the method of forming the electrode of the oxide superconductor of the present invention will be described below with reference to the drawings. A 20 atomic percent copper-silver alloy is sprayed onto the superconducting bulk. Figure 1
Figure 3 shows a schematic diagram of the interface between the superconductor and the alloy immediately after alloy spraying. As shown in the figure, the cluster of the sprayed metal 2 covers the surface of the superconductor 1, and the superconductor and the sprayed metal are divided into two phases.

Next, this superconducting bulk is heated to 800 to 900 ° C.
Heat treatment is performed at the heat treatment temperature of. FIG. 2 shows a schematic view of the interface between the superconductor and the alloy after the heat treatment. Silver-based alloy 4 as shown
Solid solution element 5 is deposited on the surface and inside. At the interface between the silver-based alloy 4 and the superconductor 1, a copper-rich compound phase 3, for example, CuO, (Sr _x Ca _1-x ) ₂ CuO ₃ is partly produced.

The formed compound phase has a wedge effect on the interface and contributes to increase the adhesive strength between the superconductor and the electrode. Since the adhesion between the superconductor and the electrode is also improved, the electrode is less likely to deteriorate due to peeling or the like.

Further, the coefficient of thermal expansion of the electrode material can be adjusted by selecting the material to be solid-soluted in the silver-based alloy used for the electrode and changing the composition of the alloy. By forming the electrode using an alloy having a thermal expansion coefficient similar to that of the oxide superconductor, thermal stress generated at the interface between the electrode and the superconductor can be relieved and peeling of the electrode can be suppressed.

[0012]

As described above, according to the method for forming an electrode of an oxide superconductor of the present invention, the electrode is formed by using a silver-based alloy containing an element constituting the superconductor such as copper. , A compound phase is formed at the interface between the electrode and the superconductor,
The adhesion strength between the electrode and the superconductor is improved.

Since the adhesion between the electrode and the superconductor is also improved, deterioration due to peeling of the electrode can be suppressed.
Further, by selecting a solid solution element for the silver-based alloy and adjusting the difference in thermal expansion coefficient between the superconductor and the electrode material, peeling of the electrode can be suppressed, and repeated use of cooling and heating can be endured.

[Brief description of drawings]

FIG. 1 is a schematic view of an interface between a superconductor and an alloy in an example of a method for forming an electrode of an oxide superconductor according to the present invention.

FIG. 2 is a schematic view of an interface between a superconductor and an alloy in an example of a method for forming an electrode of an oxide superconductor according to the present invention.

[Explanation of symbols]

 1 Superconductor 2 Thermal spraying alloy 3 Compound phase 4 Silver-based alloy 5 Solid solution element

Claims (2)

[Claims] 1. A silver-based alloy containing 20 atomic% or less of a solid solution element is used as an electrode material of an oxide superconductor,
A method for forming an electrode of an oxide superconductor, which comprises forming an electrode film and then heat treating it to form an electrode. 2. The solid solution element of the silver-based alloy is selected from an element forming an oxide superconductor, Au, and Ti.
Alternatively, the method for forming an electrode of an oxide superconductor according to claim 1, wherein the electrode is composed of two or more elements.