Superimposition of different pinning mechanisms by combined additives in Sm-Ba-Cu-O superconductors

The critical current density (J_c) of melt-textured growth (MTG) RE-Ba-Cu-O (RE: rare earth elements) materials is strongly affected by the pinning mechanisms of various defects associated with microstructual variations. In this study, different additives were used, such as (a) 0.5 wt % Pt/1.0 wt % CeO₂ (A1), (b) nano sized Sm₂BaCuO₅ particles (N1 ), and (c) co doping of A1 and N1 (C1). The influence of individual addition of A1 and N1 species was studied. Enhancement in the J_c-H curves was shown for both types of additives, however, at different magnetic fields. Microstructural studies showed that the size of 211-particle decreased and the number of particles increased significantly in the Al samples, which resulted in increasing dislocations and stacking fault density (known as δ1 pinning) associated with the 211/123 interfaces. On the other hand, in the N1 sample, nano scale compositional fluctuation of Sm_1+xBa_2-xCu ₃O_y (where x as well as T_c varied on the nanometer scale) was proposed to result in δT_c pinning. The study shows that two types of pinning centers (δl of the Al sample and δT_c of the N1 sample) can be superimposed by the combined addition of both additives. Thus, a high J_c at different fields can be achieved due to the activation of different pinning centers.