A RAMAN AND DIELECTRIC SUSCEPTIBILITY STUDY OF SUPERPARAELECTRIC PLZTCERAMICS

Raman and dielectric susceptibility experiments have been performed on 9/65/35 PLZT ceramics. Pseudo-first-order Raman scattering is interpr eted as resulting from the coupling of hard modes with the quasi-stati c polarization and/or distortion. An increase of the spatial correlati on function of the polarization as the temperature decreases is thus i nferred from the behaviour of the intensity of polar modes. Built-in s tresses are also suspected to contribute to the intensity of all modes , even at high temperatures. The relaxation of the polarization has be en studied between 360 and 480 K using dielectric susceptibility measu rements. The corresponding relaxation times are large and most likely related to the motion of ferroelectric nanodomains. When the PLZT cera mics are cooled from high temperature to room temperature, the correla tion length of the polarization extends but the simultaneous drastic i ncreased of the relaxation times of the polarization prevents any onse t of a ferroelectric long-range order.