Superimposition of Different Pinning Mechanisms by Combined Additives in Sm–Ba–Cu–O Superconductors

概要

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The critical current density ($J_{\text{c}}$) 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 $J_{\text{c}}--H$ 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 A1 samples, which resulted in increasing dislocations and stacking fault density (known as $\delta l$ pinning) associated with the 211/123 interfaces. On the other hand, in the N1 sample, nano scale compositional fluctuation of Sm1+xBa2-xCu3Oy (where $x$ as well as $T_{\text{c}}$ varied on the nanometer scale) was proposed to result in $\delta T_{\text{c}}$ pinning. The study shows that two types of pinning centers ($\delta l$ of the A1 sample and $\delta T_{\text{c}}$ of the N1 sample) can be superimposed by the combined addition of both additives. Thus, a high $J_{\text{c}}$ at different fields can be achieved due to the activation of different pinning centers.
2005-08-15