Microstructure and properties of oxygen controlled melt textured NdBaCuO superconductive ceramics

Nd1+xBa2-xCu3O7-delta (123) bulk superconductors have been synthesised by t he oxygen controlled melt growth method. Unlike the YBaCuO system, platinum doping or Nd4Ba2Cu2O10 (422) rich compositions do not refine the peritecti c '422' secondary phase, but the latter improves the microstructural qualit y. Low oxygen partial pressure and high purity precursors are necessary to achieve in a reproducible manner high T-c and J(c) (up to 56 000 A/cm(2) in 0T and 30 000 A/cm(2) under 1.5T). The fishtail effect observed at 77 K is compared with the one observed in the YBCO system, and is discussed in ter ms of oxygen deficiency, Nd-Ba substitution, defects and vortex lattice. Ou r TEM observations did not evidence any Nd-Ba substituted clusters in the N d123 matrix; however, some diffuse streaks, observed in the [100] zone ED p attern, support the fact that the source of the peak effect in this system is mainly due to oxygen disorder and low stability of the orthorhombic phas e. (C) 1999 Elsevier Science S.A. All rights reserved.