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Evolution of the transport critical current density and irreversibility field as a function of heat treatment and pressing pressure during processing of Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes (1997)

Edelman, H. S. ; Parrell, J. A. ; Larbalestier, D. C.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 81 (1997), S. 2296-2301

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Extended electric field-current density characteristics taken on the bare cores of monofilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes at 77 K have been used to measure the irreversibility field, H*, and the critical current density, Jc, at different stages of tape processing. The number of heat treatments and the uniaxial pressing pressure were the experimental variables. Both H* and Jc increased substantially with heat treatment and with deformation pressure. The data are consistent with an improvement in Jc from two factors, one being an increase in the 2223 phase fraction with increasing heat treatment, the second, independent cause being an increase in the flux pinning properties of the composite. The experiments show that improving Jc involves control of at least three factors: enhancing the volume fraction of 2223 phase; increasing flux pinning; and enhancement of the connectivity of the grain boundaries that lie within the current path. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.364233

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2

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Suppression of magnetic granularity by transport current in (Bi,Pb)2Sr2Ca2Cu3Ox tapes (1995)

Pashitski, A. E. ; Polyanskii, A. ; Gurevich, A. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 67 (1995), S. 2720-2722

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Using the magneto-optical technique, transport current flow in (Bi,Pb)2Sr2Ca2Cu3Ox (BSCCO) Ag-sheathed tapes has been imaged. For zero transport current, I, the magnetization currents display a pronounced macroscopic magnetic granularity (on a scale larger than the actual grain size) characterized by a percolative distribution of current loops. By applying I≈0.8Ic this granular behavior was largely replaced by a more uniform current flow. Due to the significant dependence of Ic on E in BSCCO, the extent to which the magnetic granularity is observed strongly depends on the magnetic prehistory and on the electric field E, whose characteristic values are very different for magnetization and transport measurements. © 1995 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.114304

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3

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On the role of pre-existing, unhealed cracks on the bending strain response of Ag-clad (Bi,Pb)2Sr2Ca2Cu3Ox tapes (1997)

Polak, M. ; Parrell, J. A. ; Polyanskii, A. A. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 70 (1997), S. 1034-1036

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Studies of the transport critical current (Ic), magnetization, magnetic flux penetration, and microstructure of pressed and rolled Ag-clad (Bi,Pb)2Sr2Ca2Cu3Ox tapes (2223) have been made as a function of bending strain. Pressed tapes exhibited markedly less degradation of Ic from strain than did rolled tapes, while the magnetization of pressed tapes declined much more rapidly with bending strain than did either of the transport currents. Magneto-optical imaging of nonbent pressed samples revealed a network of flux-penetrated defect channels that were primarily oriented parallel to the tape axis. Bending such samples to a small strain increased the visibility of these defects, believed to be cracks. This network correlates well to the cracks produced in intermediate thermomechanical processing deformation steps. The greater sensitivity of the transport current of rolled samples to bending is further direct proof of the fact that the tape "remembers" the cracks induced in the core during intermediate deformation and that heat treatment after the deformation does not heal all damage. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.118435

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4

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Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods (1997)

Anderson, J. W. ; Parrell, J. A. ; Polak, M. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 71 (1997), S. 3892-3894

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: The irreversibility field, H*, has been measured for a variety of mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density [Jc(0 T, 77 K)], even though this ignores the fact that significant self-fields depress Jc(0 T, 77 K) and the possibility that the in-field Jc(B) characteristics may be optimized independently of the Jc(0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H*. Having both H* and Jc(0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the Jc of a tape. We illustrate this point with results from a variety of mono- and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H* (77 K) can vary from ∼100 to ∼200 mT and not directly correlate with Jc(0 T, 77 K). The two proposed protocols for H* measurement are robust and compatible with common transport measurement procedures. © 1997 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.120546

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5

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Enhancement of the 77 K irreversibility field and critical current density of (Bi,Pb)2Sr2Ca 2Cu3Ox tapes by manipulation of the final cooling rate (1996)

Parrell, J. A. ; Larbalestier, D. C. ; Riley, G. N. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 69 (1996), S. 2915-2917

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: By manipulating the cooling rate from the final heat treatment, we have raised the 77 K, self-field critical current density (Jc) of multifilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes by a factor of 3, and the irreversibility field (H*) by more than 50%. The Jc of samples cooled in 7.5% O2 from their reaction temperature of 825 °C increased from ∼8 to ∼24 kA/cm2 and H*(77 K) increased from ∼120 to ∼200 mT as the cooling rate was decreased from 5 to 0.016 °C/min. The results unambiguously show that the flux pinning properties of 2223 tapes can be improved by simple changes in wire processing. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.117322

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