A Ruddlesden-Popper-type planar fault was introduced at the SrRuO3/BaTiO3 interface of a SrRuO3/BaTiO3/ SrRuO3 heterofilm system using different processing conditions for the individual film layer. This fault occurs continuously and homogeneously along the interface, forming an extra Sr-rich sub-nanometer layer. The structure of the fault and the lattice behavior in the interface area were characterized on an atomic scale by properly imaging all types of atomic columns, especially the pure oxygen columns, by means of spherical-aberration-corrected high-resolution transmission electron microscopy. Information on local interdiffusion and lattice strain at the interface was obtained by quantitative evaluation of the atomic resolution images.' (C) 2002 Elsevier Science B.V. All rights reserved.