Orientation dependence of twinning characteristics in Y-Ba-Cu-O superconducting thin films

Abstract

The twinning characteristics of epitaxial and textured superconducting thin films grown on (100) SrTiO3 and (100) MgO substrates have been found to be dependent on the film orientation. Microstructural details of thin films deposited by the pulsed-laser evaporation technique followed by annealing in oxygen and helium atmospheres at 900 °C for short time intervals were examined using cross-section and planar transmission electron microscopy. The number density of twins in textured thin films having their c axis normal to the substrate were found to be significantly higher than those in textured films having their c axis parallel to the substrate. Calculations of stresses induced in thin films as a result of the tetragonal to orthorhombic phase transition indicated that large shear stresses and strain energies were introduced in films with their c axis perpendicular to the substrate, thereby resulting in a high number density of twins in this orientation.