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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Critical current densities Jc of silver sheathed Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 composite tapes fabricated by a partial melt and a powder-in-tube process, respectively, were measured at 4.2, 27, and 64 K as a function of applied magnetic field and the angle between the tape face and the direction of applied magnetic field. These measurements indicate that (1) the fraction of the grain boundaries, which are strongly coupled, are greater in the Bi(2:2:1:2)/Ag tapes than in the Bi(2:2:2:3)/Ag tapes; (2) the alignment of the Bi cuprate platelets with the c-axis perpendicular to the tape face is significantly greater for the Bi(2:2:1:2) than for the Bi(2:2:2:3)/Ag tapes; and (3) the E-J curves for both kinds of the tapes are described well by an expression, E∼exp[−(J0/J)μ], where μ and J0 are constants below their transition magnetic fields H*g.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4584-4590 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alternating current (ac) losses in silver sheathed mono- and multicored (Bi,Pb)2Sr2Ca2Cu3O10 superconducting tapes were investigated at liquid neon temperature (27 K) under various direct current (dc) background magnetic fields. The loss behavior was well accounted for by the Bean critical state model with the inclusion of eddy current loss in the silver sheath. The interfilamentary coupling loss was found to be negligibly small for the present orientation of the tape. In addition, a severe distortion of the loss signal and the B-H hysteresis curve was observed at 27 K when a high dc magnetic field was applied simultaneously with ac fields. The losses of the tapes were also measured at 77 K and compared with the 27 K values. © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3122-3132 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structural properties of superconducting (Bi,Pb)2Sr2Ca2Cu3O10–Ag (2223) tapes have been measured using synchrotron x-ray scattering techniques. The x-ray photon energy was tuned just below the silver K absorption edge so the penetration depth was large, which allowed the measurements to be performed in a transmission geometry without removing the silver cladding. Analysis of the peaks in 2θ scans indicates that residual (Bi,Pb)2Sr2CaCu2O8 (2212) superconductor starting material is present in all samples studied. The amount of 2212 varied widely among the tapes, and was not homogeneous along the length of each individual tape. Residual 2212 content increased near the ends of most samples, suggesting that 2223 phase development is sensitive to whether the superconducting material is encased in silver or not. The bulk c-axis alignment was measured in ∼100 mono- and multifilament samples, and correlations between c-axis alignment and current carrying capacity at 77 K were found. Multifilament samples generally had better alignment than monofilament samples. The c-axis alignment along the length of the tapes was uniform, and the superconducting material within ∼1 μm of the Ag was better textured than the bulk of the sample. Intermediate pressings were directly shown to have an adverse affect on c-axis alignment. Finally, the evolution of texture and phase development was examined in a series of samples annealed for varying times. The 2212 starting material acquired the final c-axis alignment state after brief heating times, and only after much longer heating times did the 2212 transform into the 2223 phase. These results and their implications for improving processing procedures are discussed. © 1996 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 3574-3578 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured intragrain critical currents in field-oriented samples of a rare-earth-free high-Tc superconductor (Tl0.75Bi0.25)1.33Sr1.33Ca1.33Cu2 O6.67+δ, the "1212'' phase. The critical current Jc is anisotropic. For fields oriented along the conducting planes, a simple scaling of Jc with field is found. The critical current scales to zero at a field HBc2 (T) which is in good agreement with the form predicted by the flux creep theory.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 637-639 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on our detailed measurements of current–voltage characteristics for a Bi2Sr2Ca2Cu3O10/Ag tape (Jc(approximately-equal-to)2×104 A/cm2 at 77 K and zero field) immersed in liquid neon (27 K) and in liquid oxygen (54–90 K) as a function of applied magnetic field up to 17 T, we extended the vortex phase diagram of superconducting Bi2Sr2Ca2Cu3O10 in the mixed state and show that Jc for this tape at T≥27 K in magnetic field (except at very low field) is fundamentally limited by the transition of the vortex-solid-to-liquid within grains rather than the dissipation from grain boundaries. © 1995 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1827-1829 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed measurements of voltage–current (E–J) characteristics have revealed a distinct low level resistive tail for silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10 superconducting tapes. The residual tail is observed at very low voltage (E≤10−8–10−7 V/cm) of the E–J curves and can be described by E∝(J−Jc')n, where Jc' is a field and temperature dependent critical current and n=1.0–1.2. The dynamic resistivity is, typically, in the range of 10−13 Ω cm, but could be as high as 10−11 Ω cm in some specimens. This residual resistance can be induced by a severe thermal cycling treatment, although it may also be intrinsic, i.e., as-grown, to some of the specimens. © 1995 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 604-606 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using improved processing conditions, we have succeeded in increasing the transport critical current density (Jc) of powder-in-tube fabricated silver sheathed Bi-Pb-Sr-Ca-Cu-O superconducting tapes. Jc values at zero field now exceed 1.6×105 A/cm2 (Ic∼164 A) at 4.2 K and 1.3×105 A/cm2 (Ic∼133 A) at 20.2 K for short tape samples. At 77 K the same samples exhibit values greater than 3.0×104 A/cm2 (Ic∼32 A). They continue to carry 6.5×104 A/cm2 at 4.2 K and 4.8×104 A/cm2 at 20.2 K with applied magnetic fields as high as 20 T. Long lengths of tape were also fabricated and measured by winding the composites into small spiral or pancake coils. The small pancake coils carried 4.8×104 A/cm2 at 4.2 K and 5.2×103 A/cm2 at 77 K, zero field. More recently, 1 m lengths have been measured with Jc's as high as 1.0×104 A/cm2 at 77 K, zero field. Detailed transport measurements at liquid helium and hydrogen temperatures with applied magnetic fields up to 20 T are reported for short and long lengths of monocore tapes.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3025-3027 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improved strain sensitivity of critical currents Ic of the multicored over the monocored (Bi,Pb)2Sr2Ca2Cu3O10–Ag tapes is shown for bending strains, but not for axial tensile strains. The improved mechanical tolerance is due, in part, to a better alignment of the Bi-cuprate platelets achieved in the multicored tapes. Furthermore, the difference in the response to these tapes to axial tensile and bending strains is due to the difference in the precise manner in which the strains are applied to the tapes. © 1995 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 495-497 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Critical current densities up to 24 000 A/cm2 (Ic∼23.6 A) at 77 K, zero field, have been measured in short tape samples of silver-sheathed Bi-Pb-Sr-Ca-Cu-O superconductors made by the powder-in-tube technique. These samples carried 3000 A/cm2 at 1 T and 1000 A/cm2 at 2 T, also at liquid-nitrogen temperature. A repeated cold work (rolling and pressing) together with an intermediate heat treatment were required to achieve these properties. Without the pressing, tapes were made with Jc's as high as 15 000 A/cm2 at 77 K, zero field. The role of uniaxial pressing as compared to rolling is discussed and its implications to long length conductor fabrication described.
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 59 (1991), S. 736-738 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a "powder-in-tube'' process long lengths of high Tc prototype tape have been fabricated with high critical currents at liquid-nitrogen temperature and excellent high field properties at liquid-helium temperature. A Pb-doped bismuth-based 2223 powder was initially prepared then packed into silver tubes. Using a combination of cold work and heat treatment, a high degree of texture and good compaction with uniform properties was achieved. Current densities exceeding 10 000 A/cm2 at 77 K and 50 000 A/cm2 at 4.2 K in zero field were measured. At the 4.2 K temperature, the material still carried approximately 14 000 A/cm2 at 8 T. Tests on spirally wound and reacted coils, 52 cm long, have also demonstrated high current carrying capability. Effects of process variations and observed microstructure on superconducting properties are described.
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