Random field based theory of the relaxor ferroelectrics

Abstract

We present the random field based theory of relaxor ferroelectrics such as PMN, PSN and PLZT. We consider relaxors as systems of defects of different type (e.g. random site and orientation electric dipoles, lattice vacancies etc) embedded into Burns reference phase with long-range ferroelectric order; this order is being destroyed by the aforementioned defects. The equations for description of relaxors phase diagram as well as other observable properties like static or dynamic linear and nonlinear dielectric susceptibility has been derived. These equations also permit to obtain the relaxation times distribution function in relaxors. The latter function has been calculated for different parameters of relaxor ferroelectrics, corresponding to several well-known empirical relaxation laws like Cole-Cole (CC), Davidson-Cole (DC) and Kohlrausch-Williams-Watts (KWW). Fairly good agreement between theory and experiment has been achieved.

Key Words:

• relaxor ferroelectric
• distribution function
• disordered system
• random field
• dipole