MICROSTRUCTURE OF BARIUM-DEFICIENT SUPERCONDUCTING Y-BA-CU-O THIN-FILMS - OBSERVATIONS USING TRANSMISSION ELECTRON-MICROSCOPY

The structure of barium-deficient YBa2-yCu3O7-x (y almost-equal-to 0.3 ) thin films was investigated using analytical electron microscopy. Th e films were grown in situ on SrTiO3 by laser deposition and exhibited quite perfect superconducting properties (T(c) up to 91 K, J(c) > 10( 6) A cm-2 at 77 K). The excess yttrium and copper combined with a rela tively low growth temperature, produces several microstructural featur es, e.g. cation disorder, planar faults and precipitation yttrium-and/ or copper-rich secondary phases. In spite their rather defective struc ture, the superconducting parameters of the films are good. These resu lts confirm the proposal that certain defects enhance the high tempera ture superconducting properties. Barium-deficient and perfectly stoich iometric films were compared. Stoichiometric films with minimum conten ts of structural defects still display the highest parameters.