A RAMAN AND DIELECTRIC SUSCEPTIBILITY STUDY OF SUPERPARAELECTRIC PLZT CERAMICS

Raman and dielectric susceptibility experiments have been performed on 9/65/35 PLZT ceramics. Pseudo-first-order Raman scattering is interpreted as resulting from the coupling of hard modes with the quasi-static polarization and/or distortion. An increase of the spatial correlation function of the polarization as the temperature decreases is thus inferred from the behaviour of the intensity of polar modes. Built-in stresses are also suspected to contribute to the intensity of all modes, even at high temperatures. The relaxation of the polarization has been studied between 360 and 480 K using dielectric susceptibility measurements. The corresponding relaxation times are large and most likely related to the motion of ferroelectric nanodomains. When the PLZT ceramics are cooled from high temperature to room temperature, the correlation length of the polarization extends but the simultaneous drastic increased of the relaxation times of the polarization prevents any onset of a ferroelectric long-range order.