Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – Superconducting wire – tape – cable – or fiber – per se
Reexamination Certificate
1999-07-08
2001-06-26
Kopec, Mark (Department: 1751)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
Superconducting wire, tape, cable, or fiber, per se
C505S234000, C505S236000, C505S238000, C174S125100
Reexamination Certificate
active
06253096
ABSTRACT:
TECHNICAL FIELD
This invention relates to composite superconductors and more particularly to Bi-2223 superconductors surrounded by other superconducting materials.
BACKGROUND OF THE INVENTION
The powder-in-tube (PIT) process, which yields a highly textured (Bi, Pb)
2
Sr
2
Ca
2
Cu
3
O
y
(Bi-2223) superconductor with its c-axis aligned parallel to the tape surface, is an industrially scalable technique for fabricating long-length superconductors. In zero applied magnetic field, the critical current density (J
c
) of superconducting tape is controlled by its microstructure. Grain boundaries act as barriers to the transfer of transport current between grains. The crystallographic anisotropy of Bi-2223, which exhibits a micaceous or platelike morphology, allows large contact areas alignment of grains with their c-axis perpendicular to the rolling direction of the tape, easy transfer of current across its grain boundaries, and high J
c
values. The fabrication of YBa
2
Cu
3
O
7-&dgr;
(Y-123) wires by the PIT technique has not been successful because of YBCO's granularity. Y-123 exhibits greater isotropy than Bi-2223 and its intergranular transport current is poor because of weak links. In an applied magnetic field, Y-123 shows much better J
c
response than Bi-2223 and the irreversibility line (IRL) of high-T
c
materials can provide insight into materials limitations for various applications.
Recent progress in growing single crystals of Bi-2223 provided an opportunity to study its IRL line. A sharp irreversibility field (H*) drop was observed between 20 and 40 K. At 75 K, H* was only ≈0.3 T. This observation clearly shows very weak intrinsic pinning in Bi-2223 single crystals. Intrinsic pinning in Y-123 single crystal is sufficiently strong to keep H* at 77 K to ≈8 T. Using ion-beam-assisted deposition (IBAD), c-axis-oriented Y-123 thin films have been deposited on polycrystalline metallic tapes buffered with yttria stabilized zirconia (YSZ). A significant improvement of the in-plane texture led to a high J
c
above 10
6
(A/cm
2
).
Another method of depositing thin films is called rolling-assisted biaxial textured substrates (RABiT). A biaxially textured nickel substrate was aligned to within a few degrees.
Epitaxial growth of oxide buffer layers on the substrate made possible the growth of Y-123 films that were 1.5 &mgr;m thick and exhibited superconducting properties comparable to those observed for epitaxial films on single-crystal substrates. The transport current density as a function of temperature and applied magnetic field of Bi-2223/Ag wires and tapes, show that practical applications are limited to either low temperature and high magnetic field ≈20 K and ≈10 T or high temperature and low magnetic field ≈77K and less than 0.5 T.
BRIEF SUMMARY OF THE INVENTION
It is a general object of the invention to combine the good alignment of Bi-2223 grains in Ag-sheathed superconducting tapes to obtain high J
c
values at high temperature and low field, and the good intrinsic pinning of Y-123 thin film in order to maintain high J
c
values in high fields.
Another object of the present invention is to provide a new composite tape in which the primary function of a central Ag-sheathed (Bi,Pb)
2
Sr
2
Ca
2
Cu
3
O
y
(Bi-2223) filaments was to conduct transport current, with a YBa
2
Cu
3
O
7-&dgr;
(Y-123) thin films deposited on the Ag-sheathed Bi2223 tape to shield the applied magnetic field and protect the central Bi-2223 filaments.
Yet another object of the invention was to obtain critical current densities of the Y-123-coated, Ag sheathed Bi-2223 tapes which were better than those of an uncoated tape.
Still other aspects of the invention was that the Y-123 thin film exhibited a T
c
≈72 K and a broad transition region that shifted the effect to lower temperatures. Pole figure measurements showed widely spread a,b planes along the rolling direction, indicating high-angle grain boundaries that diminished the magnitude of the effect. Microstructural observations showed platelike grains of Y-123 with fine growth ledges in the thin film that was heat treated, in contrast with the microstructure of an as-coated thin film that showed large twinned grains. The experimental results showed that heat treating Y-123 thin film according to the previously known Bi-2223 tape schedule was compatible with an beneficial for Y-123.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
FIG. 1
is a graphical representation of the orientation distribution function (ODF) of Ag in as-rolled state in Ag-sheathed Bi-2223, showing cube-on-edge texture on corners and Goss texture in middle of Phi line for first quadrant at Phi2=0;
FIG. 2
is a schematic representation of Y-123 shielded Bi-2223 multifilament tape;
FIG. 3A
is a SEM photomicrograph of the top surface of Y-123 thin film in an as-coated tape 250× drawing grain size of 10-20 microns;
FIG. 3B
are SEM photomicrographs of top surface of Y-123 thin film in as-coated tape 1575×, showing grain size of ≈10-20 &mgr;m;
FIG. 3C
shows an overall EDX scan with peaks for all three cations;
FIG. 4
is a graphical representation showing magnetic measurements of Y-123 thin film in as-coated tape, showing transition temperature T
c
=72 K and broad transition region for H
app
=100 Oe;
FIG. 5A
is a SEM photomicrograph of the top surface of Y-123 thin film after heat treatment at 2625×, showing phase separation and much finer grain size.
FIG. 5B
is a SEM photomicrograph of the top surface of Y-123 thin film after heat treatment at 21000×, showing phase separation and much finer grain size.
FIG. 5C
is a SEM photomicrograph showing the EDX analysis from platelike grain showing peaks for Y, Ba and Cu;
FIG. 5D
is a SEM photomicrograph showing the EDX analysis from platelike grain showing peaks for Y, Ba and Cu wherein the analysis from white region shows absence of Cu peak;
FIG. 6
is a graphical representation of XRD scans taken from top surfaces of as-coated and heat-treated tapes, showing presence of another peak in heat-treated tape, characteristic of BaY
2
O
4
phase;
FIG. 7A
is a graphical representation of pole figures of Y-123 thin films in as-coated tapes indicating that films grown on Ag-sheathed Bi-2223 tapes are not well treated;
FIG. 7B
is a graphical representation of pole figures of Y-123 thin films in heat-treated tapes indicating that films grown on Ag-sheathed Bi-2223 tapes are not well treated; and
FIG. 8
is a graphical representation of the J
c
at 20, 40, and 60 K as a function of magnetic field applied parallel to c-axis: solid triangles represent Bi-2223 tape coated with Y-123 thin films and heat treated; open squares represent uncoated, and heat-treated reference tape.
REFERENCES:
patent: 5151406 (1992-09-01), Sawada et al.
patent: 5504058 (1996-04-01), Tanaka et al.
patent: 5874384 (1999-02-01), Balachandran et al.
patent: 5908812 (1999-06-01), Cotton et al.
patent: 5952614 (1999-09-01), Ries
Balachandran Uthamalingam
Eror Nicholas G.
Lelovic Milan
Emrich & -Dithmar
Kopec Mark
The University of Chicago
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