Superconductor technology: apparatus – material – process – High temperature – per se – Having tc greater than or equal to 150 k
Patent
1989-11-22
1991-11-12
Lieberman, Paul
Superconductor technology: apparatus, material, process
High temperature , per se
Having tc greater than or equal to 150 k
423 211, 423 23, 423155, 423604, 501123, 501126, 505725, 505737, C01B 1314, C01F 1104, C01G 302
Patent
active
050648080
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to oxide superconductors containing a rare-earth metal and metals of the first and second groups of the periodic system, and to manufacturing methods therefor.
The quality of superconductors is essentially characterized by: initial (T.sub.initial), mean (T.sub.m) and final (T.sub.final) temperatures in transition to a superconducting state; a temperature transition range (.DELTA.T); a critical current density; and time stabilizes of said characteristics.
The known LnBa.sub.2 CuO.sub.6,5-7 oxide superconductors, in which Ln is Sc, Y or a metal of the lanthanide series, have T.sub.initial from 40 to 95K, T.sub.final from 26 to 75K and a fairly wide transition range (up to 50K). As a rule, such superconductors are characterized by low quality, inclusion of source constituents in addition to a superconducting phase with resultant spread in T.sub.initial, T.sub.final and .DELTA.T, and time instability (impaired superconducting characteristics due to the effect of air in storage). Moreover, this withstand only small critical currents.
They are pressed black materials having a particle size of 1 to 30.mu.. Density of the final product varies.
They are produced by heat treatment of the La, Ba and Cu source oxides. The powdered La.sub.2 O.sub.3 :BaO and CuO oxides are normally compacted after vigorous agitation, placed in an electric furnace and heat-treated at 900.degree. to 1100.degree. C. for a fairly long time period.
The prior-art methods of obtaining superconductors have been generally unsatisfactory due to great power consumption, a long and multistage production process, low efficiency and small output of a superconducting phase.
For example, another known superconductor includes a rare-earth metal (yttrium), a first-group metal (copper) and a second-group metal (barium), its composition being (Y.sub.0.9 Ba.sub.0.1) CuO.sub.y at T.sub.initial =95K, T.sub.final =75K and .DELTA.T=20K. To obtain the aforesaid superconductor, source powders of Y.sub.2 O.sub.3 :BaCO.sub.3 and CuO taken in a proper weight proportion are heat-treated at 1000.degree. C. at the initial stage and then at 1100.degree. C. for several hours (cf. Hidenori Takagi, Shin-Ichi Uchida, Kohji Kishio, Koichi Kitazawa, Kazuo Fueki and Shoji Tanaka: "High-Tc Superconductivity and Diamagnetism of Y--Ba--Cu Oxides", Japanese Journal of Appl. Phys., Vol. 26, No. 4, April, 1987, pp L-320-L-321).
The superconductor obtained in compliance with the above method is a multiphase material with nonuniform distribution of phases in the bulk of the specimen. It is characterized by inclusion of source constituents such as Y.sub.2 O.sub.3, CuO and Cu.sub.2 O, in addition to the main superconducting phase. The known superconductor manufacturing method involves a long and multistage production process, another disadvantage thereof being great power consumption.
Another known Y--Ba--Cu--O superconductor has T.sub.initial =90K and T.sub.final =77K. The method of manufacturing said superconductor comprises preparation of a mixture of Y.sub.2 O.sub.3, BaCO.sub.3 and CuO taken in appropriate weight proportions, compaction of said mixture to form a blank, its heat treatment at 900.degree. C. for 6 hours in a rarefied oxygen medium (at P=2.times.10.sup.-5 bar), grinding of the blank, its repeated moulding to obtain a pellet and subsequent heat treatment at 925.degree. C. for 24 hours.
The obtained superconductor is a low-quality material characterized by a heterogeneous phase composition with inclusion of carbon up to 0.1% by mass. Moreover, the afore-mentioned superconductor manufacturing method involves a long (up to 10 h) and multistage production process consuming much power (cf. M. K. Wu, J. R. Ashburn and C. J. Torng: "Superconductivity at 93K in a New Mixed-Phase Y--Ba--Cu--O Compound System at Ambient Pressure", Phys. Rev. Letters, Vol. 58, No. 9, March, 1987, p 908).
Another known superconductor includes barium, copper and such a rare-earth metal as holmium (Ho). Its manufacturing method comprises prepa
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Borovinskaya Inna P.
Merzhanov Alexandr G.
Nersesian Mikael D.
Peresada Andrei G.
Boyd John
Institut Strukturnoi Makrokinetiki an SSSR
Lieberman Paul
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