Intragranular critical current density in Ag-sheathed(Bi, Pb)_2Sr_2Ca_2Cu_3O_x tapes

摘要

Transport critical current density J~j_c as a functionof external magnetic field perpendicular to a tape is investigatedfor Ag-sheathed (Bi, Pb)_2Sr_2Ca_2Cu_3O_x monofilamentarytapes at 77K. the history effect of J~j_c on the magnetic fieldbetween increasing and decreasing fields is observed in a zero-field-cooled sample and is interpreted by the influence of trappedmagnetic fields in grains on the intergranular (transport) current.The experimental results reveal the full flux penetration field B_pfor the grains. Using a critical state model and the value of B_p,the intragranular critical current density J~g-c is estimated to be~5000 A mm~-2, which is nearly the same value among allsamples and much larger than the value of J~j_c. The present studyshows that the current carrying capacity for the tape is limited bythe weak links at grain boundaries, and strong pinning in grainsdoes not lead to a high transport critical current density unlessfurther improvements in grain connectivity are made.