Epitaxial lead titanate (PbTiO) thin films were grown on MgO(100) single-crystal substrate by metal-organic chemical-vapor deposition at a growth temperature of 650 °C. The films were dense, stoichiometric, and epitaxial. The domain structure was studied via x-ray-diffraction ω scans and in-plane Φ scans. Existence of c and a domains in the PbTiO films was evident. Consistent with literature reports, the a domains were found to have four variants 90° apart from each other, tilting about 2.2° away from the surface normal. The population ratio between c and a domain of the PbTiO films was determined to be approximately 2.3 to 1. The domain structure was found to be stable and reproducible during repeated thermal cycling above and below T. Furthermore, lattice parameters and Curie temperatures of PbTiO thin films were measured during the thermal cycles. The lattice parameters were found to be smaller and the Curie temperatures were shifted lower than the corresponding bulk values. This is attributed to the film stress effect. A theory based on the Landau-Ginzburg-Devonshire function has been developed to explain the shift of the Curie temperatures. © 1996 American Institute of Physics.