Method for synthesis of high-temperature Hg-Ba-Ca-Cu-O (HBCCO) superconductors
AssigneeUniversity of Houston
InventorsChing-Wu Chu, Ruling Meng, Y. Q. Wang
Life of this patent
Estimating the term…
Abstract
The present invention is a controlled vapor/solid reaction process for the synthesis of samples of bulk compositions with a structure defined by the homologous series HgBa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2+.delta. [Hg-12(n-1)n] with n=2, 3, . . . with up to 75 to 90% Hg-1212 and 65 to 75% Hg-1223 by volume, which display sharp superconducting transitions up to 135 K.
Claims33
A method of synthesizing a high temperature superconductor composition, comprising the steps of:
- (a) preparing a precursor consisting essentially of Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x, where n=2 or 3, and x=2n+1, by mixing starting materials having cation-proportions of Ba:CaO:Cu equal to about 2:(n-1):n;
- compressing said mixture;
- and then heating said compressed mixture in an oxygen atmosphere to about 840.degree.-900.degree. C.;
- (b) sealing precursor pellets together with pellets of a composite Hg-source reactant having a mass ratio between about 0 and 0.4 in an evacuated container having a fixed volume;
- (c) heating said precursor and composite Hg-source pellets to about 750.degree. to 860.degree. C. for about five hours and controlling vapor pressure in said container by slowly releasing Hg such that a reaction of said precursor with HgO takes place and CaHgO.sub.2 formation is substantially limited so as to form HgBa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2+.delta. (Hg-12(n-1)n), where n=2 or 3 and .delta. is the oxygen surplus;
- and
- (d) oxygenating said formed Hg-12(n-1)n in flowing oxygen at about 100.degree. to 330.degree. C. for about 1 to 90 hours.
A method of synthesizing a high temperature superconductor composition, comprising the steps of:
- (a) preparing a Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x precursor, where n=2 to 3 and x.congruent.2n+1, by the following steps:
- (i) dissolving starting materials which consist essentially of Ba(NO.sub.3).sub.2, Ca(NO.sub.3).sub.2.4H.sub.2 O and Cu(NO.sub.3).sub.2.3H.sub.2 O in a solvent;
- (ii) heating said solution to about 300.degree. C.;
- (iii) agitating said solution;
- (iv) drying said solution at about 600.degree.-650.degree. C. so essentially all nitrate gas is driven off and a black mixture of Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x is formed;
- (v) compacting said black mixture;
- and
- (vi) sintering said compacted mixture at about 840.degree.-900.degree. C.;
- (b) reacting said precursor with a composite Hg-source reactant, wherein vapor pressure is regulated in said container by slowly releasing Hg such that a reaction of said precursor with HgO takes place and CaHgO.sub.2 formation is substantially limited so as to form HgBa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.3n+2+.delta. (Hg-12(n-1)n), where N=2 or 3 and .delta. is the oxygen surplus;
- and
- (c) oxygenating said formed Hg-12(n-1)n in flowing oxygen at about 100.degree. to 300.degree. C.
A method of synthesizing a high temperature superconductor composition, comprising the steps of:
- (a) preparing a precursor consisting essentially of Ba.sub.2 C.sub.n-1 Cu.sub.n O.sub.x.delta., where n=2 or 3 and x.congruent.2n+1, with Ba:CaO:Cu equal to about 2:(n-1):n;
- and
- (b) sealing said Ba.sub.2 C.sub.n-1 Cu.sub.n O.sub.x precursor and a composite Hg-source reactant in a container whereby the mass of said precursor and said reactant used is varied and a volume of the container is fixed and wherein vapor pressure in said container is controlled by slowly releasing Hg such that a reaction of said precursor with HgO takes place and formation of CaHgO.sub.2 is substantially limited when said precursor and reactant are heated to more than about 500.degree. C.;
- and
- (c) forming HgBa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+2+.delta. (Hg-12(n-1)n, where n=2 or 3 and .delta. is the oxygen surplus.
Dependencies are inferred from the claim text.