JPS63299010A - Ceramic superconductive material - Google Patents

Abstract

PURPOSE:To increase critical current density by forming a thin, normally conductive metallic film on the surface of ceramic seperconductive particles and providing an equivalent superconductive band gap in the normally conductive metallic film. CONSTITUTION:Forming a normally conductive metallic film 3 of an appropriate thickness on the particle surface of a ceramic superconductive body 2, an equivalent superconductive band gap is provided, at the same time intensifying electrical bond between the particles. Here, oxide of perovskite type having rare-earth elements is preferable as the ceramic superconductive body 2. As the normally conductive metal on the other hand, Au, Ag, Cu, etc., having a work function approximately equal to that of the oxide superconductive material are preferable. This makes it possible to increase the critical current density.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to ceramic superconductor materials that are high temperature superconductors.

(Prior Art) Oxide ceramic superconductors have recently attracted attention as high-temperature superconductors. Most of these are oxides containing rare earth elements and having a perovskite structure. It has been confirmed that such oxide superconductors can exhibit superconductivity at temperatures higher than the liquid nitrogen temperature depending on the composition, and it is possible that materials with even higher critical temperatures will be obtained with advances in material production technology. There is. Oxide superconductors also have superior stability in the atmosphere compared to conventional metal or intermetallic superconductors.

In producing such an oxide superconductor material, one major problem is how to increase the current density Jc of the critical current. Even if the critical temperature is high, if the current density of the critical current is low, it is difficult to apply it to a wide range of applications. In order to increase the current density, it is fundamentally important to make the formed acid-arsenide superconductor dense. However, there is a limit to the improvement of superconducting current density by controlling processes such as sintering, sputtering, and vapor deposition alone.

(Problems to be solved by the invention) As mentioned above, oxide superconductors with high critical temperatures are attracting attention and are expected to be applied to various uses. It is desired to increase the current density.

The present invention was made in view of these points, and an object of the present invention is to provide a ceramic superconducting material with improved critical current density based on a new principle.

[Structure of the Invention] (Means for Solving the Problems) The ceramic superconducting material according to the present invention has a thin normal metal film formed on the surface of ceramic superconductor particles, and an equivalent superconductor in the normal metal. having a conduction bandgap;
and the superconductor particles are strongly electrically coupled by a normal conducting metal.

(Function) The junction between a ceramic superconductor with a low carrier concentration and a normal metal is shown in Figure 1. That is, due to the proximity effect between the two, the normal-conducting metal portion in contact with the superconductor has a large superconducting bandgap, and the normal-conducting metal becomes superconducting within a predetermined distance from the junction with the superconductor. The theory itself of such a junction between a superconductor and a normal conducting metal is, for example, P,
G.

It is known for the papers of da G ncncs (R
cvicvsof' Modern Physi
cs, Jan, 1904゜pp225-21
(see 7). Here, Δ. is the superconducting bandgap of the ceramic superconductor, ξ0 is the coherence length of the ceramic superconductor, ノ is the mean free path, N is the electronic state density of the normal metal, and n is the electron of the ceramic superconductor. The density of states, Tj, is the transmittance of electrons through the junction interface.

Coherence length ξ of the region that becomes a superconductor on the normal metal side
N becomes h V F / k T in ξ. h is Blank's constant, Vp is the Fermi velocity of the metal, k is Boltzmann's constant, and T is the absolute temperature. When the electronic state density n of an oxide superconductor is about two orders of magnitude lower than that of a normal conducting metal and the transmittance TJ is approximately 1, the superconducting bandgap in the normal conducting metal as shown in the figure is larger than that of Ceramic and Mick superconductors within the approximation range of the above theory, and it behaves as a superconductor.

The present invention applies the theory of superconductor-normal metal bonding to form a normal metal film of an appropriate thickness on the surface of ceramic superconductor particles, thereby achieving an equivalent superconducting band gap. The object of the present invention is to obtain a ceramic superconductor material which has a high critical current density by strengthening the electrical coupling between the particles and increasing the critical current density.

The serpentine superconductor used in the present invention is preferably a perovskite-type oxide containing a rare earth element. for example,
ABa 2 Cu 307-v system with oxygen defects (A is Y, Yb, Ho
.

These are defective perovskite type oxides such as rare earth elements such as Dy, Eu, Er, T@, and Lu, and layered perovskites such as Sr-La-Cu-〇-based oxides. Further, the normal conductive metal used in the present invention includes Au.

There are many simple metals such as Ag, Cu, Al, In, and Nb, but among them, Au, Ag, Cu, and the like, whose work functions are close to those of oxide superconductors, are preferable.

Further, the present invention can be applied to both a thin film material produced by a sputtering method or a steaming method, and a powder aggregate material produced by a sintering method.

(Example) Y-Ba-Cu-0 will be taken as an example of an oxide superconductor. Its general manufacturing method begins with the raw material Y
20s, BaCO3 and CuO are mixed, calcined, ground and mixed. By pressing, sintering, and annealing this, an oxide superconductor is obtained. Alternatively, the pulverized mixed powder after calcination is packed into a metal tube, sintered, and annealed to obtain an oxide superconductor. The oxide superconducting thin film can be formed by a sputtering method using a target made by solidifying powder as a starting material or a target made by solidifying the above-mentioned calcined, pulverized and mixed powder. Alternatively, an oxide superconductor thin film can also be formed by a printing method using a printing paste that is a combination of the above-mentioned powder and a suitable solvent.

Among the oxide superconducting materials of the present invention, the thin film material can be easily obtained by sequentially stacking an oxide superconducting material film and a normal conducting metal film. FIG. 2 shows an example of this.

A predetermined substrate 1 is coated with Y-Ba- as an oxide superconductor film.
A Cu-0 film 2 is deposited to a thickness of about 3,000 layers by sputtering, and an Au film 3 is deposited thereon by, for example, 500 layers. As a result, the surface molecules of the Y-Ba-Cu-0 film 2 become Au.
Covered with the Au film 3, a superconducting band gap is generated equivalently within the Au film, and the electrical coupling is improved, so that the in-plane critical current is nearly one order of magnitude larger than when the Au film 3 is not formed.
00A/cII2 is obtained.

When a Y-Ba-Cu-0 film with a thickness of 1 μm was formed by screen printing and a 1,000-layer Au film was deposited thereon, the critical current density was similarly improved. However, the value of the superconducting current density is smaller than that of the sputtering method. this is,
This is because the density of the film obtained by the printing method is inferior to that obtained by the sputtering method.

In the case of oxide superconducting ceramic materials produced by the sintering method,
In order to form a thin normal metal layer along the grain boundaries, a method for manufacturing cermet (ceramic sintered body in which a metal layer is formed at the grain boundaries of ceramic powder) may be applied. Specifically, ■ melting a metal with a lower melting point than ceramics, adding ceramic powder to it and cooling it, ■ mixing ceramic powder and metal powder and baking, ■ forming a metal film on the surface of ceramic powder. Methods such as baking things are used. To obtain the metal-coated ceramic powder, a method is used in which metal is vapor-deposited or sputtered while stirring the ceramic powder, or a metal is vapor-deposited or sputtered on the ceramic powder while being dropped little by little. By such a method, it is possible to obtain an oxide superconducting ceramic in which a metal layer is interposed at the powder grain boundaries to increase the critical current.

[Effects of the Invention] As described above, according to the present invention, by forming a thin normal metal film on the surface of the constituent particles, a superconducting band gap is equivalently generated in the normal metal and electrical By improving the bonding, it is possible to provide a ceramic superconducting material with an increased critical current density.

[Brief explanation of drawings]

FIG. 1 is a potential diagram for explaining the increase in critical current of the oxide superconducting material according to the present invention, and FIG. 2 is a film of the oxide superconducting material according to an embodiment of the present invention. 1...Substrate, 2-Y-Ba-Cu-0 film, 3...
・Au film. Applicant's agent Patent attorney Takehiko Suzue SN i Figure 1 Figure 2

Claims (3)

[Claims] (1) A ceramic superconducting material characterized by having a thin normal-conducting metal film formed on the surface of ceramic superconductor particles and having an equivalent superconducting band gap in the normal-conducting metal. (2) The ceramic superconductor according to claim 1, wherein the ceramic superconductor material is a thin film formed on a predetermined substrate by sputtering or vapor deposition, and this thin film is coated with a normal metal film. material. (3) The ceramic superconductor material is a powder aggregate formed by a sintering method, and the ceramic superconductor according to claim 1 has a normal-conducting metal film at the grain boundaries of the powder constituting the aggregate. material.