Raman spectroscopy and X-ray diffraction study of sol–gel derived (Pb 1− xLa x)Ti 1− x/4 O 3 thin films on Si substrates

Abstract

A series of sol–gel derived lead lanthanum titanate (PLT) thin films with composition of (Pb 1− x La x )Ti 1− x/4 O 3, where x=0.00 (pure PbTiO 3), 0.05, 0.10, 0.15, 0.20, 0.25 and 0.28, on Si substrates are studied using X-ray diffraction (XRD) and Raman spectroscopy. XRD patterns show that the films are polycrystalline. The tetragonality of the films is found to decrease with the increase of La concentration in the films. This indicates a gradual change from tetragonal to cubic structure as La concentration increases. Raman spectroscopy shows extreme sensitivity to La dopant in the films. The frequencies of Raman modes for the films are found to shift clearly to low wavenumbers with increasing La concentration. This phenomenon is similar to the shift of Raman mode frequencies in PbTiO 3 thin films when sample temperature increases, approaching the Curie temperature. Raman spectroscopy measurements are also carried out on PLT thin films with the same La concentration but annealed at different temperatures. Results are compared with earlier reports on PLT or pure PbTiO 3 thin films.