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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.

By using atomic force microscopy (AFM) and scanning tunnelling microscopy (STM) at ambient conditions, we have investigated the topographies of various surfaces of bulk samples of YBa2Cu3Ox (YBCO), SmBa2Cu3Ox (SmBCO), and (Sm,Eu,Gd)Ba2Cu3Ox (SEG) oxidic high-Tc superconductors. We find that the last two systems exhibit microstructures on the nanometer scale which are remarkably different from those obtained in the YBCO system. The stripe-like growth structures observed in our topography measurements may be the key for the considerable improvements concerning the critical current densities especially at high magnetic fields and elevated operating temperature (77 K). The properties of the microstructures are discussed in detail.

Nanostripes are observed in melt-textured, Gd-enriched light-rare-earth (LRE)-based ternary (Nd0.33Eu0.28Gd0.38)Ba2Cu3Ox (NEG-38) superconductors. Employing atomic force microscopy/scanning tunneling microscopy topographic scans together with electron backscatter diffraction (EBSD) analysis, the authors determine the direction of the nanostripes with respect to the twin structure. Details of the topography measurements and of the EBSD maps reveal that the nanostripes are composed of nanoclusters of the LRE-rich phase. The nanostripes in the NEG-38 samples have a periodicity of about 40–60nm, and in lateral direction between 300 and 500nm. The role of these nanostripes for flux pinning in these compounds is discussed.