DEPENDENCE OF CRYSTALLINE ORIENTATION ON FILM THICKNESS IN LASER-ABLATED YBA2CU3O7-DELTA ON LAALO3

The microstructure of YBa2Cu3O7-delta thin films deposited on (001)LaAlO3 substrates by a laser ablation process has been investigated by scanning electron microscopy, x-ray diffraction, and cross-sectional transmission electron microscopy. Adjacent to the substrate, the film is entirely oriented with the c-axis perpendicular to the surface. At a thickness of about 0.4-mu-m, the occurrence of 90-degrees boundaries brings about a transition to grains with their c-axes parallel to the surface (aligned along the [100] and [010] directions of the pseudocubic LaAlO3 substrate). This transition is discussed in terms of the crystal growth anisotropy and the retained strain that may precipitate the transition.