High transport J c and magnetization in textured Bi-Pb-Sr-Ca-Cu-O superconductors

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Abstract
High transport Jc is essential for major bulk applications of the high‐Tc superconductors. In this paper, we report transport critical current and magnetization behavior in c‐axis textured Bi‐Pb‐Sr‐Ca‐Cu‐O superconductor ribbons. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport Jc values as high as 2.3 × 105 A/cm2 at 4.2 K, H=8 T (H⊥ab) have been obtained, which is one of the highest reported so far. The high Jc at H≥ (R18)5 T is maintained to temperatures near 20 K. A comparison of Jc (transport) and Jc (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders‐of‐magnitude‐smaller grain size, thus demonstrating that the a‐b grain boundaries in the melt‐processed ribbons are not weak links. A similar bulk processing technique with more extensive deformation can also be used to produce weak‐link‐free thin films, as demonstrated by preparation of ∼3000‐Å‐thick films. Since epitaxial growth from single crystal substrates is not required, the technique may be suitable for high‐speed, low‐cost production of large area thin films.