Comparison of Flux Pinning in Single Crystals and Melt-Textured YBa2Cu3O7-x

Flux pinning properties of single crystals and melt-textured samples of YBa2 Cu3 O 7-x were studied for external magnetic field oriented parallel and perpendicular to the CuO 2 planes (ab-planes).For H ab vortex behaviour is mainly determined by a very effective intrinsic pinning mechanism.The irreversibility line is located in the region of higher fields and temperatures in comparison with the irreversibility line for H 1 ab.In a single crystal for H 1 ab, we observed an increase in the critical current density j c with magnetic field -the so-called "fishtail effect" -in a very broad temperature range.For H ab, this effect is observed only at temperatures close to 71, when the intrinsic pinning is much weaker.