Pinning forces and scaling in high-T-c superconductors.

The volume pinning forces, F-p, of several high-T-c superconductors are compared to each other using literature data and to those obtained in NdBa2Cu3O7-delta samples. It is shown that the pinning at small normal inclusions which is dominant in most high-T?c systems, leads to a peak at around 0.3 when plotting the normalized volume pinning forces, F?p/F?(p,max, versus the reduced field defined by h = H/H-irr. Furthermore, relaxation effects play a significant role in the F, diagrams, especially in the high h regions thus causing the typical rounded-off 'tail'. In contrast to this, NdBCO shows the peak at approximate to 0.5, thus indicating a strong pinning at small superconducting regions (Delta(kappa)/Delta T-c-pinning).