Recent progress on compositional nanostripes of REBa₂Cu ₃O_7-δ (RE ≤ Sm,Eu,Gd) superconductors

We characterized ordered compositional fluctuation in high-quality SmBa₂Cu₃O_7-δ, (Sm_0.5Eu _0.5)Ba₂Cu₃O_7-δ, and (Sm _0.33Eu_0.33Gd_0.33)Ba₂Cu ₃O_7-δ superconductors by atomic force microscopy, scanning tunnelling microscopy, and transmission electron microscopy. The presence of nanostripes along the crystalline c direction was confirmed in SmBa₂Cu₃O_7-δ single crystals and in melt-processed (Sm_0.5Eu_0.5)Ba₂Cu ₃O_7-δ, (Sm_0.33Eu_0.33Gd _0.33)Ba₂Cu₃O_7-δ materials. Meanwhile, thickness fringes originating from the twin boundaries were also identified in some samples; these could be clearly separated from real nanostripes with sample tilting. Compositional nanostripes displayed spatial variation in both shape and wavelength over a large area of RE-Ba-Cu-O single domains. The origin of the nanostripe is discussed in the context of the competitive growth mechanism of RE_1+xBa_2-xCu ₃O_7-δ solid solution.