Superconductor technology: apparatus – material – process – High temperature – per se – Copper containing
Patent
1992-02-06
1994-05-03
Lieberman, Paul
Superconductor technology: apparatus, material, process
High temperature , per se
Copper containing
252521, 427 62, 505778, 505779, 505780, 505785, 505452, 505570, C01F 1102, C01F 1700, C01G 302, H01L 3912
Patent
active
053087992
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an oxide superconductor and a process for the preparation thereof.
BACKGROUND ART
A YBa.sub.2 Cu.sub.3 O.sub.7-x type (123 phase type) superconductor prepared by a QMG (quench and melt growth) method, that is, a kind of a melt method, apparently has a critical current density (Jc) of 10.sup.4 A/cm.sup.2 or more under conditions of 77K and 1T which suffices for practical use (see "New Superconducting Materials Forum News", No. 10 (1988), p. 15). Studies have been made also on an increase in the size of the QMG material and a combination of RE elements (see "Physica C", 162-164 (1989), pp. 1217-1218 or Preprints of the 50th Symposium of the Japan Society of Applied Physics, Autumn, 1989, 29a-P-10). In these methods, an oxide superconductor material containing Y element alone or various RE elements is unidirectionally grown in a temperature gradient to increase the size of a crystal.
In a polycrystalline structure, a grain boundary acts as a weak link to decrease superconducting properties. The above-mentioned study on the increase in the size of the crystal has been made for the purpose of solving this problem.
The above-mentioned prior art technique, however, can provide only a single crystal material having a size of 0.3 cm.sup.3 at the largest, and it was very difficult to unidirectionally grow the 123 phase structure to form a large single crystal.
That is, the prior art could not solve problems regarding the means for forming a nucleus of a crystal, a method of regulating the growth of a crystal, etc.
An object of the present invention is to provide a material comprising a REBa.sub.2 Cu.sub.3 O.sub.7-x phase in a large-size single crystal form (hereinafter referred to as "123 phase") in an oxide superconductor comprising a composite oxide of at least two elements selected from the group consisting of Y, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu (hereinafter referred to as "RE elements"), Ba and Cu.
Another object of the present invention is to provide a material having a structure such that a RE.sub.2 BaCuO.sub.5 phase (hereinafter referred to as "211 phase") having a very small grain diameter is dispersed in a large size 123 phase.
CONSTITUTION OF THE INVENTION
In order to attain the above-mentioned objects, the present invention provides a technique for controlling the growth of a crystal by varying the kinds of the RE elements or the kinds of the RE elements and the mixing ratio of the RE elements (hereinafter referred to as "composition of RE") through the utilization of the difference in the crystal forming temperature inherent in individual components of RE, and a process for the preparation of a large size crystal through inoculation of a seed crystal.
Specifically, the present invention-provides a superconductor comprising a composite oxide of a RE element(s), Ba and Cu, wherein said superconductor is an oxide high temperature superconductor having a micro structure comprising a monocrystalline 123 phase and a 211 phase finely dispersed therein; said 123 phase being formed in a plurality of domains respectively for individual RE compositions and in the order of the 123 phase forming temperatures in respective domains. The invention also provides a process for the preparation of the oxide high temperature superconductor, characterized by mixing oxides (including composite oxides) of RE, Ba and Cu so that the molar ratio of metal elements (RE, Ba, Cu) falls within a region defined by connecting points (10, 60, 30), (10, 20, 70) and (50, 20, 30) to each other, forming another mixed powder having a RE composition different from said mixed powder in the temperature of formation of the 123 phase of the RE composition in said mixed powder so as to have a composition falling within said region, putting said plurality of mixed powders in the order of the 123 phase forming temperature in the RE composition to form a multi-layer structure, subjecting the assembly to press molding to form a precursor, heating said precursor to a temperature region wherein
REFERENCES:
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patent: 4857504 (1989-08-01), Hermann
patent: 4990493 (1991-02-01), Lay
patent: 5084436 (1992-01-01), Morimoto
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Physica C 162-164 (1989), pp. 1217-1218 (No month available).
Preprints of the 50th Symposium of the Japan Society of Applied Physics, Autumn, 1989, 29a-P-10 (No month available).
Sawano et al., J. Ceramic Society of Japan, International Edition, vol. 97, No. 10, Oct. 1989, Tokyo, Japan, pp. 1014-1018.
Hirota et al., Patent Abstracts of Japan, vol. 13, No. 290, (C-614)(3638), Jul. 5, 1989, and (JP-A-1 083 589), (Matsushita Electric Indco Ltd), Mar. 29, 1989 *abstract*.
Kimura Keiichi
Miyamoto Katsuyoshi
Morita Mitsuru
Sawano Kiyoshi
Takebayashi Seiki
Boyd John
Lieberman Paul
Nippon Steel Corporation
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