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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 6 (1993), S. 247-254 
    ISSN: 1572-9605
    Keywords: Melt-texture growth ; YBa2Cu3O7−δ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The melt-texture growth (MTG) method has been shown to be effective in fabricating high-T csuperconducting bulk samples with highly oriented layers of single crystals. The critical current densityJ cof the typical samples are enhanced significantly. Furthermore, making use of the nonzero spatial temperature gradient at certain locations of a common tube furnace, we fabricated Y-123 bulk samples with various dopants allowingJ cup to ≈3.0×104 A cm−2 in our recent investigations. We followed up our project by analyzing the relations among the crucial parameters involved in the modified version of the MTG process. These parameters include the temperature gradient, the time rate of change of temperature, the “growth front” of the crystal, etc. Our study indicates that some of the empty space regions that appear between layers are only shallow “gap lines.” True layers of single crystals do exist, and we present an explanation for the growth of crystal layers along special directions as observed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 6 (1993), S. 327-334 
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7−δ ; transmission electron microscope ; grain alignment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Previously, we have observed that parallel lattice fringes show up regularly in MTG samples, indicative of good alignment of unit cells in strips of size ∼ 100 nm × a few times 100 nm. We have prepared films (∼ 80 nm) for TEM observation using YBCO material fabricated by the conventional solid-state reaction method in order to study the crystal texture in a length scale from a few 100 nm down to ∼3 Å. Parallel lattice fringes are observed to stretch across a cross-section ∼0.3×0.5 μm2. Cross lattice fringes intersecting at 90° and 45° are observed as rare events. This result suggests that the degree of alignment in the crystal texture is higher than expected inside a grain of size ∼ a few μm.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 3 (1990), S. 395-403 
    ISSN: 1572-9605
    Keywords: High-T c superconductivity ; oxygen deiects ; electron-phonon interaction ; YBa2Cu3O7−δ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In this investigation we consider the formation of Cooper pairs near the oxygen-deficient sites in Y-Ba-Cu-O ceramic superconductors which would give rise to an energy-dependent potential as seen by conduction charge carriers. It is shown that Cooper pairs could be formed under such conditions, resulting in a supercurrent. We use the Bogoliubov transformation technique to calculate the energy gap, the energy difference, and the transition temperature of the model superconductor using certain data obtained from previous experiments. Numerical analysis shows that the superconducting current can be explained by the presence of such oscillating Cooper pairs.
    Type of Medium: Electronic Resource
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