Superconductor technology: apparatus – material – process – High temperature – per se – Free metal containing
Patent
1996-07-23
1999-09-14
Kopec, Mark
Superconductor technology: apparatus, material, process
High temperature , per se
Free metal containing
505125, 505482, 505500, 505779, 505785, C04B 35057, C04B 3545, C04B 35645
Patent
active
059522682
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to superconductors of the high critical temperature ceramic type.
Superconductors are known of the Ba--Ca--Cu--O system such as the ABa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x families where n is an integer greater than 1, x is greater than 2n+2, and A is mercury or thallium. Those materials have high critical temperatures, exceeding 100 K for certain phases, i.e. for certain values of n. The critical temperature increases when the material is used at high pressure. For mercury and thallium, it has been observed that the critical temperature increases within a given family with increasing value of n up to n=3, and decreases thereafter.
Those materials are manufactured in the form of ceramics by taking a mixture of precursors in substantially stoichiometric proportion with excess oxygen and subjecting it to high temperatures and pressures.
In spite of the highly advantageous properties represented by compounds of the Hg--Ba--Ca--Cu--O and Tl--Ba--Ca--Cu--O type, research is continuing to find other high critical temperature superconductor ceramics, firstly in the hope of reaching even higher critical temperatures, and secondly for the purpose of avoiding the use of highly toxic substances such as thallium, and to a lesser but non-negligible degree, mercury.
OBJECTS AND SUMMARY OF THE INVENTION
Thus, the present invention provides a superconductor material of the A--Ba--Ca--Cu--O family in which A is copper. The present invention also proposes a method of manufacturing superconductor ceramics starting from a precursor of the Ba--Ca--Cu--O type in substantially stoichiometric proportion for forming CuBa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x and silver oxide. A superconductor ceramic is thus obtained comprising grains having the above-specified formula plus grains of silver metal. Nevertheless, in the present state of research, it is not impossible that silver atoms are present in the superconductor grains and contribute to obtaining the superconductive qualities of the compound as explained below.
These objects, characteristics, and advantages, together with others of the present invention are described in detail in the following description of particular embodiments given with reference to accompanying FIGS. 1 to 4 which are graphs showing magnetic susceptibility as a function of temperature for the substances obtained by the method of the present invention.
The inventors have prepared ceramic samples at high pressure (greater than 4 GPa) and at high temperature (850.degree. C. to 1000.degree. C., and preferably 900.degree. C. to 950.degree. C.) using a belt type pressurizing appliance. A precursor of the nominal composition Ba.sub.2 Ca.sub.n-1 Cu.sub.n+1 O.sub.x or Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x was prepared in the manner indicated in the article by Antipov et al., Physica C, 215, 1 (1993). More generally, the precursor could be obtained by mixing oxidized compounds in powder form such as oxides, nitrates, or carbonates of barium, calcium, and copper in the specified proportions, said operation being implemented under an atmosphere of oxygen at atmospheric pressure and at a temperature lying in the range 850.degree. C. to 950.degree. C. for a period of several hours. The resulting precursor is hygroscopic and must be conserved under an atmosphere of oxygen or under an inert atmosphere.
In parallel, silver oxide, AgO or Ag.sub.2 O or a mixture thereof, was synthesized.
The silver oxide and the precursor (optionally together with excess copper oxide) were finely ground and mixed prior to being placed in the above-mentioned synthesizer system.
In conventional manner, the pressure was initially increased to a value of about 5 GPa, and then the temperature was increased up to the desired value substantially in one hour. Thereafter, temperature and pressure were maintained for more than one hour.
After returning to normal temperature and pressure, a ceramic block was obtained comprising grains having a size of about 100 micrometers and they were identified
REFERENCES:
Ihara et al "New High-Tc Superconductor Family of Cu-based . . ." JJAP, vol. 33 (Part 2) No. 4A, Apr. 1994 pp. 503-506 (Abstract).
Ihara et al "More Than Half Way to Room Temperature Superconductors . . . " Electrotech, Lab. Tsukuba, 305, Jun. 1994, 58(6) pp. 448-452 (Abstract).
H. Ihara et al, "New High-T.sub.c Superconductor Ag.sub.1-x Cu.sub.x Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+3.delta. Family with T.sub.c >117 K", Japanese Journal of Applied Physics, vol. 33, No. 3A, Mar. 1, 1994, pp. L300-303.
Wu et al, "Novel Homologous Series of Superconduction Copper Oxides, Cu-129n-1)n", Physica C, vol. 223, 1994, pp. 243-248 (No Month).
Wu et al, "Ag distribution in superconducting Ag-Ba-Ca-Cu-O sample", Physica C, vol. 224, 1994, pp. 175-178 (No Month).
Alario-Franco Miguel Angel
Capponi Jean-Jacques
Chaillout Catherine
Souletie Benedicte
Tholence Jean-Louis
Alcatel
Kopec Mark
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