High-Resolution and Energy-Filtered Transmission Electron Microscopy of YBa2Cu3O7-x/PrBa2Cu3O7 Superlattices

Structural disorder induced by epitaxial strain relaxation in c -axis oriented [YBa 2 Cu 3 O 7-x n u.c /PrBa 2 Cu 3 O 7 5 u.c. ] superlattices on (100) SrTiO 3 substrates has been analyzed by high-resolution and energy-filtered transmission electron microscopy. Epitaxial strain shows up in ultrathin YBCO layers with thickness below 4 unit cells. Strain relaxation takes place when layer thickness increases above this value. Microscopy observations for epitaxially strained superlattices show a good morphology of the layers, with sharp and flat interfaces. However, in relaxed samples rougher interfaces are observed, together with microdomains showing the c -axis parallel to the substrate plane which preserve the superlattice compositional profile. Such microdomains of c -parallel growth provide a path for reduced lattice mismatch, conforming a very efficient mechanism for strain relaxation.