Flux-Pinning and Irreversibility Line in Melt-Textured YBa2Cu3Oy Crystals of Different Sizes of Pinning Centers

Flux pinning force and irreversibility lines have been investigated for melt-textured YBa 2 Cu 3 O y crystals containing Y 2 BaCuO 5 (211) particles with an average size ranging from 20 to 0.02 microns. We found that the irreversibility lines are increasingly improved and that the pinning force as well as the J c is greatly enhanced as the average size of the 211 particles decreases. The F p -H curve exhibits two peaks in the samples containing very fine 211 particles (nanometer size particles), which suggests that an addition pinning mechanism is involved in this type of samples. The experimental results can be well explained with combining the interface-pinning mechanism and the match effect.