Brillouin scattering study of La-modified lead zirconate titanate relaxor

Elastic properties of La-modified (Pb1-xLax)(Zr0.65Ti0.35)O-3 (lead zirconate titanate) with x = 10 (PLZT 10/65/35) relaxor ferroelectric ceramic were studied by high-resolution Brillouin scattering technique in a wide temperature range from 90 to 1033 K. The Brillouin frequency shift (v) and sound velocity of the acoustic phonon modes, showed deviation from the high-temperature linear behaviour and a broad softening on cooling towards the dielectric maximum temperature T-m. The temperature dependence of the maximum relaxation time was obtained from the Vogel-Fulcher relationship by combining the Brillouin scattering and dielectric data. The onset of the acoustic mode frequency dispersion from paraelectric to the relaxor ferroelectric state can be explained by the concept of freezing of the relaxation time spectrum of PLZT at a finite temperature.