High-resolution and energy-filtered transmission electron microscopy of YBa2Cu3O7-x/PrBa2Cu3O7 superlattices

Structural disorder induced by epitaxial strain relaxation in c-axis orient ed [YBa2Cu3O7-x n u,c/PrBa2Cu3O7 5 u,c] superlattices on (100) SrTiO3 subst rates has been analyzed by high-resolution and energy-filtered transmission electron microscopy. Epitaxial strain shows up in ultrathin YBCO layers wi th thickness below 4 unit cells. Strain relaxation takes place when layer t hickness increases above this value. Microscopy observations for epitaxiall y strained superlattices show a good morphology of the layers, with sharp a nd flat interfaces. However, in relaxed samples rougher interfaces are obse rved, together with microdomains showing the c-axis parallel to the substra te plane which preserve the superlattice compositional profile. Such microd omains of c-parallel growth provide a path for reduced lattice mismatch, co nforming a very efficient mechanism for strain relaxation. (C) 2001 Elsevie r Science B.V. All rights reserved.