Microstructural influence on critical currents and irreversibility line in melt-textured YBa2Cu3O7-x reannealed at high oxygen pressure

We present a study of flux pinning by in-plane partial dislocations in melt-textured grown YBa2Cu3O7/Y2BaCuO5 (123/211). The in-plane dislocations are generated by high oxygen pressure (HOP) postprocessing treatment as confirmed by transmission electron microscopy (TEM). In order to characterize the dislocation density and the perimeter to surface ratio (PSR) of the associated stacking faults a large number of TEM micrographs have been analyzed. We demonstrate that the evolution of the microstructure correlates with the oxygen absorbed by the samples during different HOP treatments. Two regimes of oxygenation activity are identified: first, the low oxygenation regime where the PSR of the stacking faults stays almost constant but the in-plane dislocation density is increased near the 123/211 interfaces and second, the high oxygenation regime where the stacking faults extend over the entire 123 matrix inducing a drastic enhancement of the dislocation density and a strong decrease in the PSR. Two contributions to the critical current density have been identified and quantified: the weak pinning and the correlated disorder pinning. We demonstrate that the correlated disorder comes from 123/211 interfaces and that this remains invariant with the HOP process. On the other hand, the weak pinning contribution is associated to the in-plane dislocations and this contribution strongly correlates with the HOP treatments. The temperature and field dependencies of the in-plane dislocations' contribution to the critical currents are in agreement with a pointlike single vortex pinning mechanism. Finally, we demonstrate that the dislocation pinning can be counterbalanced by wide stacking faults inducing a downward shift of the irreversibility line.