Nanoscopic netted structure of compositional modulation in (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors

We report a nanoscaled crisscross network in high-quality melt-processed (Sm0.33Eu0.33Gd0.33)Ba2Cu3O7−δ superconductors investigated with atomic force microscopy (AFM) and transmission electron microscopy. In the ten-micrometer scale, such a net was unveiled as a consequence of crossing annular stripes originating from ordering compositional modulation. The AFM topographic images further displayed that this compositional stripe result in a surface modulation with a few-nanometer wavelength and roughness. The forming mechanism of this compositional stripe and its role as strong δTc-type pinning defects were discussed in the context of rare earth∕Ba oscillation around the stoichiometric ratio and the spatial fluctuation of local Tc values.