Raman scattering in sol–gel derived PbTiO3 films modified with Ca

X-ray diffraction (XRD) and Raman scattering in sol–gel derived Pb1−xCaxTiO3 (PCT) thin films are studied as a function of Ca content x. It is found that Ca2+ addition to PbTiO3 films results in a gradual decrease of tetragonality of the perovskite lattice accompanied with a considerable modification of the Raman spectra. A significant difference in Raman spectra of PCT films and available reference data for single crystals (x=0) is explained in terms of the large internal stress, small grain size, and structural disorder produced by Ca2+ substitution. It is found that the shift of the frequency of ferroelectric soft mode correlates well with the variation of tetragonality for x≤xc=0.4. The concentration dependence of the shift is strongly non-linear being qualitatively different from that observed earlier in other A-site doped lead titanate-based systems. According to XRD data, the averaged crystal structure for xc≈0.4 appears as pseudo-cubic, while Raman scattering revealed short-range order tetragonal distortion. The structural characteristics of PCT films are linked to their electromechanical properties measured earlier by interferometric technique.