Relaxor Behaviour in Ferroelectric Ceramics

Abstract

Ferroelectric materials are commonly characterized by high dielectric permittivity values [1]. Usually, for the well-known ‘normal’ ferroelectrics the temperature of the maximum real di‐ electric permittivity (Tm) corresponds to the ferroelectric-paraelectric (FE-PE) phase transi‐ tion temperature (TC) [2]. On the other hand, there are some kinds of ferroelectrics, so-called relaxor ferroelectrics, which have received special attention in the last years because of the observed intriguing and extraordinary dielectric properties [3-25], which remain not clearly understood nowadays. For instance, some remarkable characteristics of the dielectric re‐ sponse of relaxor materials can be summarized as follows: ithey are characterized by wide peaks in the temperature dependence of the dielectric permittivity, iithe temperature of the corresponding maximum for the real (e') and imaginary (e'') component of the dielectric per‐ mittivity (Tm and Te''max, respectively) appears at different values, showing a frequency de‐ pendent behaviour, and iiithe Curie-Weiss law is not fulfilled for temperatures around Tm. So that, the temperature of the maximum real dielectric permittivity, which depends on the measurement frequency, cannot be associated with a FE-PE phase transition.