A calcium-modified lead titanate (Pb0.76Ca0.24TiO3) thin film has been prepared by spin-on sol–gel on an Si(100) substrate. The film deposited from a stoichiometric solution was subjected to thermal treatment at 650 °C for 720 s with a heating rate of 8 °C s−1. The film presents a perovskite-type structure, as indicated from x-ray diffraction powder pattern data, giving it ferroelectrical properties. The chemical composition at the film surface and at increasing depth into the substrate was studied by XPS combined with 4 keV Ar+ depth profiling. Ion bombardment gives rise to compositional and chemical changes in the sample surface, in which case lead and oxygen are sputtered preferentially. After 50 min of 4 keV Ar+ bombardment, a steady-state composition is reached. At further depth (>200 min) an increase of the Pb 4f signal indicates a non-homogeneous Pb distribution in the film. At the interface between the ferroelectric film and the Si(100) substrate, silicon is found as Si(IV), as well as chemical shifts of the O 1s and Ca 2p3/2 peaks to higher binding energies are observed. Both facts support the formation of calcium silicate. At the same time, titanium is reduced from Ti(IV), Ti(III) and Ti(II) to Ti(0). Copyright © 2000 John Wiley & Sons, Ltd.