Second generation, high-temperature superconducting wires are based on buffered, metallic tape substrates of near single crystal texture. Strong alignment of adjacent grains was found to be necessary from previous work that suggested large angle, YBa2Cu3O7−δ [001]-tilt boundaries reduce Jc exponentially with increasing misorientation angle (θ). We pursue the low-θ regime by evaluating single grain boundaries (GB) and biaxially aligned polycrystalline films utilizing both the rolling-assisted biaxially textured substrates and ion-beam assisted deposition coated conductor architectures. Analysis concludes that an exponential dependence on Jc is applicable for θ≳4°, where the spacing between the periodic disordered regions along the GB become smaller than a coherence length.
We report the first study of the optical conductivity of MgB2 covering the range of its lowest-energy superconducting gap. Terahertz time-domain spectroscopy is utilized to determine the complex, frequency-dependent conductivity sigma(omega) of thin films. The imaginary part reveals an inductive response due to the emergence of the superconducting condensate. The real part exhibits a strong depletion of oscillator strength near 5 meV resulting from the opening of a superconducting energy gap. The gap ratio of 2Delta0/k(B)TC approximately 1.9 is well below the weak-coupling value, pointing to complex behavior in this novel superconductor.
Figure 5. Charge-discharge curves of Li-graphite half cells (a and b) and LNMO-graphite full cells (c and d) in the electrolyte without (a and c) and with (b and d) 0.05 m LiBMFMB additive cycled under a current density of C/10.
Deformation-textured, non-silver substrates, and solution-based
deposition of buffer and superconductor layers offer routes to a low-cost YBCO
coated-conductor technology for high-temperature superconducting wire. Several
significant steps towards such a technology are reported here: a
solution-based Gd2O3 seed buffer layer was deposited by a
web-coating technique over a metre-length tape of deformation-textured nickel
with excellent texture and uniformity. Also, short full-stack samples with
YBCO performance up to 0.8 MA cm-2 at 77 K were prepared at
Oak Ridge National Laboratory (ORNL) and American Superconductor (ASC) using a
CeO2/YSZ/CeO2 buffer sequence on textured nickel and a
trifluoroacetate (TFA) precursor YBCO process; in this case the buffers are
deposited by e-beam and magnetron sputtering.
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