Oxide superconducting conductor and its production method

Details Oxide superconducting conductor and its production method Oxide superconducting conductor and its production method

2002-06-19

2004-06-01

Silverman, Stanley S. (Department: 1754)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S702000, C428S930000, C505S237000, C505S434000, C505S447000, C427S062000, C427S327000

Reexamination Certificate

active

06743531

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an oxide superconducting conductor, and its production method, that can be used in fields such as superconducting power cables, superconducting magnets, superconductive energy storage, superconducting power generation systems, medical MRI systems and superconducting current leads.
2. Background Art
Known methods of producing oxide superconducting conductors of the prior art include solid phase methods such as the powder-in-tube (PIT) method in which a powder of an oxide superconductor, or a mixed powder of a composition that is able to become an oxide superconductor by heat treatment, is pressed into the shape of a cylindrical column, inserted into a silver tube and then drawn or rolled followed by a heat treatment step to form a wire material, as well as film deposition methods in which an oxide superconductor layer is continuously formed on a long base material such as metal tape by a vapor phase method such as laser deposition or sputtering.
As shown in
FIG. 11
, the structure of oxide superconducting conductors produced by a vapor phase method such as laser deposition or CVD is widely known to consist of the formation of a YBaCuO-based oxide superconductor layer
193
formed on the upper surface of a base material
191
composed of a metal such as Ag, and the formation of a surface protective layer
195
composed of Ag on this oxide superconductor layer
193
.
In order to obtain superior superconductor characteristics in such oxide superconducting conductors produced by a vapor phase method such as laser deposition of CVD, it is important to realize biaxial orientation (in-plane orientation) of oxide superconductor layer
193
produced on base material
191
. In order to accomplish this, it is preferable that the lattice constant of base material
191
approach the lattice constant of oxide superconductor layer
193
, and that the crystal grains that compose the surface of base material
191
be uniformly arranged in the manner of pseudo single crystals.
Therefore, in order to solve this problem, as shown in
FIG. 12
, various attempts have been made to produce an oxide superconducting conductor having superior superconductivity by forming a polycrystalline intermediate layer
192
such as YSZ (yttrium-stabilized zirconium) using a sputtering device on the upper surface of a metal base material
191
such as hastelloy tape, forming an oxide superconductor layer
193
such as YBaCuO on this polycrystalline intermediate layer
192
, and then additionally forming a stabilizing layer
194
of Ag on the oxide superconductor layer
193
. Alternatively, studies have also been conducted on Ag base materials in which a texture is formed by rolling and heat treatment, and Ni base materials in which a texture is formed by rolling and heat treatment followed additionally by the formation of an oxide intermediate layer.
Among these, since Ag is the only metal material that has little reactivity with oxide superconductor layer
193
and allows oxide superconductor layer
193
to be formed directly on base material
191
, while also having the characteristics of being non-magnetic and having low resistance, a wire material structure can be realized in which base material
191
itself also functions as the stabilizing layer.
Examples of materials that have been developed as Ag base materials in the form of tape that form a texture by rolling and heat treatment include Ag {100}<001> having surface {100} for the surface of the base material and a cube texture in which <001> is preferentially oriented in the lengthwise direction, or Ag {110}<110> having surface (110) for the surface of the base material and a cube texture in which <110> is preferentially oriented in the lengthwise direction, and in consideration of lattice matching with a YBaCuO-based oxide superconductor layer, the Ag {110}<110> oriented Ag base material is the more promising.
In an oxide superconducting conductor in which oxide superconductor layer
193
is formed on a polycrystalline intermediate layer
192
as shown in
FIG. 12
, the surface formed by oxide superconductor layer
193
has superior smoothness and in-plane orientation due to the action of this polycrystalline intermediate layer
192
, thereby allowing the obtaining of an oxide superconductor layer
193
having a satisfactory in-plane orientation, and has recently been confirmed to enable a high Jc value of 1,000,000 A/cm
2
or higher. In addition, since hastelloy is used as the metal tape, wire materials can be produced having adequate strength. However, since base materials equipped with this polycrystalline intermediate layer
192
require the use of sophisticated and expensive technology in the form of ion beam sputtering for their film deposition, at present, these base materials are only able to be produced at the rate of about 1 meter per hour, while also having the disadvantage of extremely high production costs.
On the other hand, in an oriented Ag base material using a rolling texture of Ag, although the productivity of the base material can be increased and production costs are comparatively low making this promising, there are hardly any reports of obtaining a high Jc value of 100,000 A/cm2 or more using this oriented Ag base material, thereby resulting in the problem of insufficient superconductor characteristics. This is thought to be due to impaired continuity of the oxide superconductor layer caused by irregularities in the crystal grain boundary of the Ag base material. In addition, in the case of using an Ag base material, since Ag itself is an extremely soft metal and is softened even more as a result of being heated to a high temperature during deposition of the oxide superconductor layer, in order to apply oxide superconductors using an Ag base material to wire materials and so forth, it is necessary to solve the problem of strength.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an oxide superconducting conductor having superior strength and superconductor characteristics by using a base material consisting mainly of Ag, its production method, and an oxide superconducting conductor base material.
The inventors of the present invention conducted the following test in order to investigate the cause of being unable to obtain a high Jc value with a superconducting conductor using an oriented Ag base material during completion of the oxide superconducting conductor and its production method of the present invention. Although the oriented Ag base material is promising with respect to allowing the production of an oxide superconducting conductor at low costs, it had the disadvantage of not allowing the obtaining of adequate current density (Jc).
(1) After producing an oxide superconducting conductor by forming a YBaCuO-based superconducting layer having a thickness of 1.0 &mgr;m on a pure Ag base material measuring 10 mm (W)×10 mm (L)×0.5 mm (t) by CVD, and the removing only the oxide superconductor layer of the sample by etching, the amounts of the elements Y, Ba and Cu contained in the pure Ag base material were analyzed, and a comparison was made with the contents of each element in the pure Ag base material prior to deposition. Those results are shown in Table 1. As shown in Table 1, the Cu content of the pure Ag base material after formation of the oxide superconductor layer had clearly increased significantly. This is thought to be due to the Cu contained in the YBaCuO that composes the oxide superconductor layer having reacted by diffusing in the pure Ag base material.
TABLE 1
Y (&mgr;g)
Ba (&mgr;g)
Cu (&mgr;g)
Sample
analyzed
analyzed
analyzed
10 mm ×
Ag weight
value/
value/
value/
10 mm × 0.5 mm
(g)
difference
difference
difference
Ag base material
0.525
0.0/—
1.6/—
11/—
Ag base material
No.1
0.56
0.1/0.1
1.8/0.2
49/38
after forming
No. 2
0.584
0.1/0.1
1.5/0.0
41/30
oxide
superconductor
layer
(2) Next, a detailed analysis was conducte

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