Raman Scattering Study of Cubic to Tetragonal Phase Transitions of Ti-rich Pb(ZrxTi 1-x)O 3

The temperature dependences of Raman scattering spectra were investigated through the ferroelectric phase transition in Ti-rich Pb(Zr x Ti1-x )O3 (x=0.25–0.40). Low frequency spectra show marked dependences on both composition and temperature. Another lower frequency mode appears below the E symmetry soft mode of PbTiO3 as the x increases. The frequencies of the lowest two modes soften slightly, whereas the damping factor of the two modes increases markedly near T c. These phenomena suggest that the displacive type at x=0 gradually changes to the order-disorder type as x increases. The internal bands higher than 100 cm-1 are insensitive to both composition and temperature. The intensity of these modes gradually decreases with increasing temperature. Although all optical modes should be Raman inactive above T c, a quasielastic scattering and a few internal modes are still observed in the spectra. Since the intensities of these modes decrease on further heating, the origin of this intensity cannot be the second order Raman scattering but must be the first order one due to local breakdown of cubic symmetry by some kind of disorder.