Microstructure of epitaxial YBa₂Cu₃O₇ films on step-edge SrTiO₃ substrates

The microstructure of YBa₂Cu₃O₇ films epitaxially grown on step-edge (100) SrTiO₃ substrates has been characterized by means of high resolution transmission electron microscopy. The results indicate a relationship between the microstructure of the film acreoss a step and the angle step makes with the substrate plane. On a steep, high-angle step, the film grows with its c-axis perpendicular to that of the film on the substrate surface so that two grain boundaries are formed. On a low-angle step, the film grows without any change in c-axis orientation across the step and without grain boundaries. Epitaxial second phases intergrowths across the steps have been found in some cases which may act as barrier layers when they cut through th YBa₂Cu₃O₇ film.