Critical current enhancement in YBCO-Ag melt-textured composites: influence of microcrack density

摘要

A strong increase of the critical current density of YBa2Cu3O7 (YBCO) melt-textured composites has been observed by adding Ag2O particles in the precursor mixture while the concentration of Y2BaCuO5 (Y211) precipitates remains constant. Critical current density enhancement factors as high as 200% at 5 K (J(c)(ab)(5 K, 0 T) similar to 2.5 x 10(6) A/cm(2)) and 1000% at 77 K and 2 T (J(c)(ab)(77 K, 2 T) similar to 2.2 x 10(4) A/cm(2)) have been reached in samples with 20 wt.% of Ag2O. Critical current measurements at 77 K for H parallel to ab also confirm the increase of the J(c) enhancement factor with the magnetic field (similar to 100% at 0 T and 140% at 2 T). The improvement of the critical currents in the YBCO-Ag melt-textured composites is correlated with the reduction of the density of microcracks parallel to the ab plane, as observed by scanning electron microscopy (SEM). Results are interpreted in terms of a release of the current limiting factors and an improvement of flux pinning properties by preexisting defects. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 30]