The defect structures in non-stoichiometric thin films which were grown epitaxially onto (100) SrTiO3 substrates, by pulsed-laser deposition, were studied by using transmission electron microscopy and X-ray diffraction techniques. The A-site excess thin films adopted a completely unrelaxed pseudomorphic perovskite structure, with an enlarged lattice parameter normal to the surface. Excess SrO was accommodated as Ruddlesden-Popper planar faults which exhibited a peculiar 3-dimensional mosaic structure, without forming secondary phases or dislocations due to non-stoichiometry. The biaxial compressive stress which was induced by the lattice mismatch between the film and the substrate was estimated to be 9.7GPa. Such a highly strained film was attributed to a planar fault formation which increased the cell volume and suppressed misfit dislocations. The B-site excess thin-film microstructure consisted of crystalline SrTiO3 and amorphous TiO2-rich phases. A slight increase in the lattice parameter normal to the surface, and a crystallographic shear structure with a TiO2 double layer, suggested that there was a low solubility of excess TiO2.

Defect Structure in Homoepitaxial Non-Stoichiometric Strontium Titanate Thin Films. T.Suzuki, Y.Nishi, M.Fujimoto: Philosophical Magazine A, 2000, 80[3], 621-37