Comparison of Flux Pinning in Single Crystals and Melt-Textured YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-x}$

Flux pinning properties of single crystals and melt-textured samples of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7-x}$ were studied for external magnetic field oriented parallel and perpendicular to the CuO$\text{}_{2}$ 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 ⊥ ab. In a single crystal for H ⊥ ab, we observed an increase in the critical current density j$\text{}_{c}$ 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 T$\text{}_{c}$, when the intrinsic pinning is much weaker.