Effects of uniaxial and isostatic compacting pressures on the Jc(Ba) behavior in Bi1.65Pb0.35Sr2Ca2Cu3Oy compounds

The effects of uniaxial and isostatic compacting pressures on the superconducting critical current density J(c)(B-a) dependence under low applied magnetic fields (B-a < 6 mT) have been investigated in ceramic samples of Bi1.65Pb0.35Sr2Ca2Cu3Oy. Two batches of this material were made and pelletized by using different procedures. One of them was pressed uniaxially and the other one isostatically under pressures ranging from 100 to 300 MPa before the last heat treatment. X-ray diffraction patterns revealed that increasing compacting pressure results in an improvement of the grain alignment which is more pronounced in samples subjected to uniaxial pressure. The superconducting critical current density in zero applied magnetic field J(c)(0) in both batches was found to increase with increasing compacting pressure. However, samples subjected to uniaxial pressure show J(c)(0) values over four times higher than those pressed isostatically. In addition, the J(c)(B-a)/J(c)(0) ratio for these batches was found to be very similar: it exhibits a clear Josephson-like behavior at low compacting pressure, which changes to a more magnetic field independent behavior at higher compacting pressures. The experimental results are interpreted in terms of changes in the pinning energy and grain alignment with increasing compacting pressure. (C) 2004 Elsevier B.V. All rights reserved.