Investigation of microstructure of textured YBCO with addition of nanopowder SnO2

By using top seeding melt-textured growth (TSMTG) process, large single domain YBa2Cu3O7-delta/Y2BaCuO5 (YBCO) samples were prepared with addition of nanometric SnO2 and normal CeO2. Polarized light microscope studies at each step of the TSMTG process showed that before YBa2Cu3O7-delta (123) melting, the Sn-based reacted products were uniformly distributed in micrometer scale; after solidification, the trapped Y2BaCuO5 (211) and Sn-based inclusions were more homogeneously distributed and with mean sizes of about one micrometer. Composition images of scanning electronic microscope for the textured samples showed that, on the whole, the Sn-based inclusions were smaller than the 211. They must be on average below one micrometer in size. Although evidence was found that very fine Sn-based inclusions were uniformly trapped in 123 matrix, the fraction of them was small in comparison to that of 211. No significant enhancement of superconducting critical current density (J(c)) was evidenced for the nanometric SnO2-doped samples at a low magnetic field (B < I T). However, values of J(c) were decreased at intermediate magnetic field (I < B < 3 T). (C) 2001 Elsevier Science B.V. All rights reserved.