The order parameter in relaxors

Abstract

A lamellar structure consisted of dielectric and ferroelectric slabs is considered within the continuous media theory. It is shown that, at the ferroelectric phase transition, in the ferroelectric slabs, there appears an alternating domain structure which resembles the structure studied earlier in a ferroelectric thin film with dead layers and in a ferroellastic thin films on a substrate. It is shown that the dielectric properties of this structure depend on the relative width of the dielectric and ferroelectric layers. We suggest that this microscopic model can be generating for heterogeneous ferroelectrics and, in particular, for relaxors. We show that, by using this model, it is possible to introduce an order parameter of the relaxor state in heterogeneous ferroelectrics which corresponds to a nanodomain structure. We computed strains generating by the polarization alternation, calculated neutron scattering intensities and compared them with experiment.