Non-stoichiometric 10mol% excess-BaO thin films, grown onto a (100) SrTiO3 substrate, consisted of heteroepitaxial c-axis oriented BaTiO3 perovskite crystals which contained Ruddlesden-Popper planar faults and nm-scale multiple (111) twin lamellae. High-resolution electron microscopy and electron energy-loss spectroscopy revealed that nano-twins with coherent (111) Σ = 3 coincident site lattice boundaries terminated in the BaTiO3 matrix to form incoherent (211) Σ = 3 boundaries that accommodated excess Ba ions. Both the Ruddlesden-Popper planar fault, and incoherent (211) boundary formation, were proposed as being possible mechanisms for accommodating excess Ba ions in the perovskite film.

Ruddlesden-Popper Planar Faults and Nano-Twins in Heteroepitaxial Non-Stoichiometric Barium Titanate Thin Films. T.Suzuki, Y.Nishi, M.Fujimoto: Journal of the American Ceramic Society, 2000, 83[12], 3185-95