High-resolution identification of ½⟨110⟩ stacking faults in epitaxial Ba_0.3Sr_0.7TiO₃ thin films

The near-interface region of an epitaxial Ba_0.3Sr_0.7TiO₃ thin film grown on LaAlO₃ (001) was found to consist of a high density of ½⟨110⟩ stacking faults bounded by partial dislocations. The stacking faults can extend over large distances (greater than 50 nm). Various possible atomic configurations of the faults were considered. The atomic structures of the faults were identified using high-resolution electron microscopy and simulation as well as energy-filtered imaging. The ½[101] and faults (where [001] is normal to the film plane) were found to lie predominately on the {100} and {110} planes. The ½lsqb;101] faults on (010), (110) or (1&1tilde;0) have never been observed before in perovskites. The stacking faults on [100] have a structure consisting of a double layer of edge-sharing TiO₆ octahedra. The excess of Ti was detected by energy-filtered imaging. The formation of the extended stacking faults is probably related to a small amount of excess Ti during the film deposition, which may originate from the non-stoichiometry of the ceramic targets BaTiO₃ and SrTiO₃. It is also enhanced by the misfit-induced compressive strain in the early stages of the film growth.