BaTiO(3)/SrTiO(3)(001) epitaxial thin films were prepared at various growth rates by pulsed laser deposition, and their heterostructures were evaluated by synchrotron x-ray diffraction measurements and cross-sectional scanning transmission electron microscopy observations. In a film grown at a low deposition rate (0.01 nm/s), misfit dislocations are found near the interface and a fully relaxed BaTiO(3) thin film grows epitaxially on the substrate. On the other hand, a film grown at a high deposition rate (0.04 nm/s) consists of strained and relaxed BaTiO(3) lattices. Our results showed that the critical thickness of BaTiO(3)/SrTiO(3)(001) epitaxial thin films can be controlled by the deposition rate and that the critical thickness increases with increasing deposition rate, and by adjusting the deposition rate, we were able to prepare epitaxial thin films consisting of fully strained BaTiO(3), partially strained BaTiO(3), or fully relaxed BaTiO(3). (c) 2007 American Institute of Physics.