Raman scattering and x-ray diffraction studies of rare earth-doped Pb0.90La0.15TiO3 thin films prepared by the sol–gel method

Abstract

The structural modification and phase transition in rare earth (Gd3+ and Ce3+)-doped Pb0.90La0.15TiO3 films, prepared by the sol–gel technique on Pt substrates, were studied utilizing x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice tetragonality with increasing content of Gd and Ce in these films. Raman spectra exhibited features characteristic of bulk PbTiO3, including the observation of the soft mode. Variations in the phonon mode wavenumber, especially that of the lowest soft mode, for Pb0.90La0.15−xCexTiO3 (x = 0.00–0.07) and Pb0.90La0.15−xGdxTiO3 (x = 0.00–0.15) as a function of the composition x and temperature corroborate the increase in tetragonality caused by rare earth doping. As a result, the ferroelectric transition temperature was found to increase almost linearly from 480 to 630 K with increasing Gd content from x = 0.00 to 0.15. In Ce-doped films, the solubility limit was found at about x = 0.05; the transition temperature increases up to 5 doping then it decreases above that composition, probably owing to Ce precipitation.