A layered melt-textured YBa2Cu3O7−x superconductor has been prepared consisting of alternate fully oxygenated and oxygen deficient bands stacked parallel to a-b planes. An anomalous decrease of Jcc(H∥ab) with field is observed at high temperatures. We show that this behavior is a signature of a field induced decoupling of the strong superconducting bands, and provides evidence of a decrease of vortex pinning energy in oxygen deficient regions of melt-textured YBa2Cu3O7−x. A large downwards shift of the irreversibility line results as a consequence of the substantially smaller area where a critical state sets in. When vortices are parallel to the c-axis Jcab(H∥c) decreases due to the smaller condensation energy of the oxygen deficient bands.
Abstnct--Melt textured superconductors have been prepared with a microstructure characterized by large domains having misaligned growth fronts. An rf mutual inductance miaoprobe has been developed which allows to identify and characterise the weak link behaviour of the high angle grain boundaries separating the domains. The mechanisms of flux penetration and trapping i n a single domain sample has been analysed in the H//c configuration at low temperature ( 25 K) where Jc is essentially field independent. A consistent description of flux penetration, isothhnal remanence and magnetic hysteresis is reached in the framework of the Bean model. The small value of the lower Critical fiyld Hcl deduced from this analysis suggest that the pn-Livingston surfacebarriers are strongly reduced in melt textured ceramics as compared to single aystals.
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