MICROSTRUCTURE OF AS-GROWN FULLY OXYGENATED EPITAXIAL YBA2CU3O7-DELTATHIN-FILMS - A TRANSMISSION ELECTRON-MICROSCOPY STUDY

Epitaxial YBa2Cu3O7-delta (YBCO) thin films grown by magnetron sputter ing on MgO(001) substrate have been studied by transmission electron m icroscopy (TEM). The films are fully oxygenated during their growth. S lowly and rapidly cooled samples, both showing good superconducting pr operties, have been prepared. The high-resolution and moirC fringe TEM methods have been used to analyse the microstructure and to estimate the orthorhombicity of the samples. The rapidly cooled samples show th e presence of a superconducting O-7 (delta=0) tetragonal phase, which is not ordered and where unrelaxed lattice strains are revealed by the curvature of the lattice planes. In both samples the twin boundaries are broaden and the high-resolution TEM contrast reveals a dense super position of the twin domains in the thickness of the c-perpendicular Y BCO grains.