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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of local current flow in polycrystalline, anisotropic superconductors using finite element simulation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5283-5288 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A finite element program was used to calculate current distributions in superconductors, assuming a nonlinear (power-law or percolation-type) local dependence of the electrical field on current density. A bicrystal geometry, which forms the basic building block of (Bi,Pb)2Sr2Ca2Cu3Ox powder-in-tube tapes and other polycrystalline conductors, was studied. Current–voltage curves and critical currents were calculated for different geometrical and electromagnetic parameters. Bicrystals of "brick-wall" and "railway-switch" geometry were compared, and it was found that in both cases anisotropy is the dominating factor determining the overall critical current. Strong anisotropy leads to current concentration around grain boundaries, thereby reducing the critical current. Addition of a grain boundary with finite resistance does not significantly change the current distribution within the grains. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1314332
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  • 2
    Electronic Resource
    Electronic Resource
    Large low-field magnetoresistance over a wide temperature range induced by weak-link grain boundaries in La0.7Ca0.3MnO3 (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 396-398 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polycrystalline bulk porous samples with a large number of weak-link grain boundaries and high density polycrystalline bulk samples with strong-link boundaries were synthesized by conventional solid-state reaction and a partial melting technique. The weak-link samples showed large magnetoresistance (MR,Δρ/ρH=[ρ0−ρH]/ρ0), 20–30%, at a low magnetic field of 300 mT and over a wide temperature range from the magnetic transition at 235 to 77 K. The partially melted samples exhibited the same magnetoresistance behavior as that of single crystals with a maximum peak MR of 15% at a narrow temperature range around the ferromagnetic transition. It is suggested that grain boundaries are necessary but not sufficient to account for the MR at low field over a large temperature range. Weak-link grain boundaries rather than strong-link boundaries are responsible for the MR at low field over a large temperature range. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121846
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  • 3
    Electronic Resource
    Electronic Resource
    Application of percolation theory to current transfer in granular superconductors (2002)
    Springer
    The European physical journal 29 (2002), S. 359-367 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 64.60.Ak Renormalization-group, fractal, and percolation studies of phase transitions – 74.25.Fy Transport properties (electric and thermal conductivity, thermoelectric effects, etc.) – 4.80.Bj Granular, melt-textured, and amorphous superconductors; powders
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We investigate the description of current transfer in polycrystalline superconductors by percolation theory and its limitations. Various computer models that have been proposed are reviewed and related to the experimental and theoretical framework. While some conductor properties can be well described by percolation theory and models, we argue that a conceptual gap exists between experiment and theory. This gap has to be bridged by finding relations between electromagnetic and statistical parameters. We derive various such relations and compare them with recent simulation data. In particular, we suggest a new scaling law between the two fundamental variables “current” and “probability”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2002-00275-9
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