Transmission Electron Microscopy and Atomic Force Microscopy Observation of Air-Processed GdBa 2 Cu 3 O 7-δ Superconductors Doped with Metal Oxide Nanoparticles (Metal = Zr, Zn, and Sn)

Single-domain, c -axis-oriented 30-mm-diameter GdBa 2 Cu 3 O 7-δ (Gd123) melt-textured bulk superconductors have been successfully grown by the top-seeded melt growth method from precursors of Gd123, Gd 2 BaCuO 5 , and Ag 2 O in air with doping of nanosized ZrO 2 , ZnO, or SnO 2 . Transmission electron microscopy (TEM) unveils a large amount of BaZrO 3 or BaSnO 3 particles with an average diameter of approximately 50 nm respectively embedded in ZrO 2 or SnO 2 doped samples, while no Zn-rich nanoparticles are observed in the ZnO-doped samples. The critical temperature T c is almost unchanged up to a doping amount of 10 mol % for ZrO 2 - or SnO 2 -doped Gd123 melt-textured bulks, while ZnO-doped Gd123 becomes non-superconductive at this doping level. By atomic force microscopy (AFM), nanostripes with a wavelength of 15 nm are observed in the ZnO-doped Gd123 sample. Nanoscale particles in the grown Gd123 single domain, together with the micro-defects induced by nanoparticle doping, can account for the enhanced superconducting properties.