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The microstructural features over a wide range of cation nonstoichiometry in barium titanate thin films grown on (100) SrTiO3substrates by pulsed laser deposition were investigated by X-ray diffraction and transmission electron microscopy. Well-crystallized perovskite barium titanate was heteroepitaxially grown even with 20% excess titanium, but the film contained column-like amorphous secondary phases and some planar defects. In the case of 50% excess titanium, the film consisted of columnar nanocrystallites epitaxially grown on the substrate and a surrounding titanium-rich amorphous matrix. The incorporation of 50% excess barium, on the other hand, significantly degraded film crystallinity due to the formation of nanometer-scale amorphous phases.

Microstructures of (Sr1-xMgx)TiO3thin films epitaxially grown on (001) SrTiO3substrates were investigated by X-ray diffraction and high-resolution transmission electron microscopy to discuss the solid-solution of the SrTiO3-MgTiO3system under pulsed laser deposition processes. In cases of x=0.15 and x=0.3, magnesium ions were mostly accommodated at A-sites of the perovskite structure of general formula ABO3, to form single-phase perovskite thin films without ilmenite secondary phases, and the possibility of partial B-site occupation of magnesium ions was inferred to interpret the formation of (100) and (010) planar defects with a crystallographic shear structure. The (Sr0.5Mg0.5)TiO3thin film exhibits a phase-separated microstructure consisting of an epitaxial crystalline perovskite phase and an amorphous phase, which could be derived from the limitation of the magnesium solubility in the SrTiO3perovskite lattice.

The interface and domain structures in epitaxial (116)-oriented SrBi2Ta2O9films on (110) SrTiO3substrates were investigated by high-resolution transmission electron microscopy. The film contains domain boundaries due to the formation of two types of (116)-oriented crystallites with symmetrical tilted c-axis directions and numerous wavy c/6 translational boundaries originating from the domain boundaries. Each epitaxial crystallite forms a semicoherent interface accompanying periodic lattice strain, where the alternate continuity of perovskite layers in the film to the perovskite structure of SrTiO3is found. Such a quasi-stable interface structure may be the primary cause of difficulty in the preparation of epitaxial SrBi2Ta2O9films with the tilted c-axis.

Interface and defect structures of epitaxial c-axis oriented SrBi2Ta2O9thin films on well lattice-matched (001) SrTiO3substrates were crystallographically characterized by transmission electron microscopy. The film was coherently grown on the SrTiO3substrate without interfacial layers and misfit dislocations, preserving the crystallographic relation of (001)[110] SrBi2Ta2O9//(001)[100] SrTiO3. The plausible atomic stacking sequence at the interface was found to be (SrTiO3bulk)-SrO-TiO2-SrO-TaO2-Bi2O2-TaO2-SrO-(film bulk), where an electrically neutral SrO layer could be preferentially formed on the TiO2-terminated SrTiO3substrate. High-resolution lattice images of the film showed that distinctive wedge-shaped contrasts could be attributed to the formation of c/6 translational boundaries originating from single unit cell steps on the SrTiO3substrate.