Pinning performance of (Nd,Eu,Gd)-123 superconductors: Comparison of melt-textured pellet and single crystal

We studied pinning homogeneity and the content fluctuation of light rare earth ions in a (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy melt-textured (MT) pellet 16 mm in diameter, doped by 0.035 mol% ZnO. The pinning performance was compared to that of the recently grown (Nd0.33Eu0.2Gd0.47)Ba2Cu3Oy single crystal. While magnetic properties of most test samples cut from the MT pellet were surprisingly uniform, two samples from the pellet center behaved significantly different. This anomaly was found to correlate with the significant departure of the Eu:Nd ratio from the average. Nearly all MT samples showed a high-field shoulder on Jc(B) curve that was attributed to the pinning effect of a nanoscopic correlated lamellar substructure filling channels between regular twin boundaries. As a result, the irreversibility field at 77 K reached in all 20 measured MT samples 9 T. In the single crystal no high-field Jc(B) shoulder was observed, and the irreversibility field at 77 K was about 6 T. The strip-like structure observed on the crystal surface was evidently of another origin than the lamellar substructure in the MT samples and did not significantly contribute to vortex pinning. The secondary peak in Jc(B) of the single crystal was quite strong, showing a well set point-like disorder. All magnetic characteristics of the single crystal were strongly affected by twin-plane channeling effect.