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Processing of oxide superconductors

Inactive Publication Date: 2002-09-12
AMERICAN SUPERCONDUCTOR
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0025] An advantage of the invention is the production of highly defect-free oxide superconductor and superconducting composites which exhibit superior critical current densities. A further advantage of the invention is a marked improvement in critical transition temperature and critical current density as compared to oxide superconductors and superconducting composites which are not subjected to the method of the invention.

Problems solved by technology

Processing long lengths of oxide superconductor is particularly difficult because deformation leads to microcracking and other defects which may not be healed in the subsequent heat treatment.
Cracks that occur perpendicular to the direction of current flow limit the performance of the superconductor.
The issue of healing defects, such as microcracks, which develop during processing of the oxide superconductor, has not been addressed.
Further, the prior art has not addressed the possibility of using a two-step process where the oxide superconductor is stable in both steps for the healing of cracks and defects.
While reports of high transition temperatures by magnetization studies are of interest, they can sometimes be misleading.
Because the samples do not reach equilibrium during the observation period, it is difficult to determine the exact processing conditions experienced by the samples.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0108] The following example compares the transport critical current characteristics of a samples treated with the two-step heat treatment of the present invention to those of conventionally processed samples.

[0109] Precursor powders were prepared from the solid state reaction of freeze-dried precursor of the appropriate metal nitrates having the nominal composition of 1.7:0.3:1.9:2.0:3.1 (Bi:Pb:Sr:Ca:Cu). Bi.sub.2O.sub.3, CaCO.sub.3, SrCO.sub.3, Pb.sub.3O.sub.4 and CuO powders could be equally used. After thoroughly mixing the powders in the appropriate ratio, a multistep treatment (typically, 3-4 steps) of calcination (800.degree. C..+-.10.degree. C., for a total of 15 h) and intermediate grinding was performed in order to remove residual carbon, homogenize the material and to generate the low T.sub.c BSCCO-2212 oxide superconductor phase. The powders were packed into silver sheaths having an inner diameter of 0.625" (1.5875 cm) and a length of 5.5" (13.97 cm) and a wall thickness...

example 2

[0114] This example demonstrates that silver alloys can be used in place of silver for the silver billet without detrimental effect on the electrical properties of the composite. A composite tape is prepared as described in Example 1; however, a silver alloy containing low levels of Mg and Ni was used to sheathe the oxide superconductor. The tape was processed as in Example 1 according to the method of the invention. The average I.sub.c (77K, 10 cm) was 7.68 A as compared to ca, 4.08 A for a conventional process.

example 3

[0115] This example compares samples which have been pressed or rolled as the intermediate deformation.

[0116] Composite tapes were prepared as described in Example 1. A statistically designed experiment was performed using the following process parameters for the first anneal and final heat treatments.

2 two-step heat treatment first heat treatment high temperature low temperature T(.degree.C.) t(h) T(.degree.C.) t(h) T(.degree.C.) t(h) - 820 12 - 820 12 - 810 36 0 827 24 0 827 24 0 815 54 + 835 48 + 835 48 + 815 72

[0117] Up to sixty four statistically selected combinations of reaction conditions were run both with and without the two-step heat treatment of the invention. The intermediate deformation step between the first heat treatment and two-step heat treatment consisted of a pressing with 12% strain reduction.

[0118] Comparable statistically designed experiments were carried out for rolled samples with and without the two-step heat treatment of the invention. The intermediate def...

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Abstract

A method for preparing a BSCCO-2223 oxide superconducting article includes annealing an oxide superconductor article comprised of BSCCO-2223 oxide superconductor at a temperature selected from the range of about 500.degree. C..ltoreq.T.ltoreq.787.degree. C. and an annealing atmosphere having an oxygen pressure selected from within the region having a lower bound defied by the equation, P.sub.O2(lower).gtoreq.3.5.times.10.sup.10e- xp(-32,000 / T+273) and an upper bound defined by the equation, P.sub.O2(upper).ltoreq.1.1.times.10.sup.12exp(-32,000 / T+273). The article is annealed for a time sufficient to provide at least a 10% increase in critical current density as compared to the critical current density of the pre-anneal oxide superconductor article. An oxide superconductor having the formula Bi.sub.2-yPb.sub.ySr.sub.2Ca.sub.2Cu.sub.3O.sub.10+x, where 0.ltoreq.x.ltoreq.1.5 and where 0.ltoreq.y.ltoreq.0.6 is obtained, the oxide superconductor characterized by a critical transition temperature of greater than 111.0 K, as determined by four point probe method.

Description

[0001] The application is a continuation-in-part application of co-pending application U.S. Ser. No. 08 / 041,822 filed Apr. 1, 1993, also entitled "Improved Processing for Oxide Superconductors".FIELD OF THE INVENTION[0002] The present invention relates to high-performance oxide superconductors and oxide superconductor composites. The present invention further relates to a method for healing defects introduced into the oxide superconductor phase during processing thereby improving superconducting properties. The present invention also relates to the processing of high performance bismuth-strontium-calcium-copper oxide superconductors and oxide superconductor composites and a method for improving the critical transition temperature (T.sub.c) and critical current density (J.sub.c) of these oxide superconductors.BACKGROUND OF THE INVENTION[0003] Oxide superconductors of the rare earth-barium-copper-oxide family (YBCO), bismuth(lead)-strontium-calcium-copper-oxide family ((Bi,Pb)SCCO) an...

Claims

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Application Information

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IPC IPC(8): C01G1/00C04B35/45C01G3/00C01G29/00H01B12/02H01B13/00H01L39/24
CPCH01L39/2464Y10S505/742Y10S505/785Y10S505/782H10N60/0661
Inventor OTTO, ALEXANDERRILEY, GILBERT N. JR.CARTER, WILLIAM L.
Owner AMERICAN SUPERCONDUCTOR
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