Dependence of crystalline orientation on film thickness in laser-ablated YBa2Cu3O7−δ on LaAlO3

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Abstract
The microstructure of YBa2Cu3O7−δ 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 μm, the occurrence of 90° 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.