Spherical model of relaxor polymers

Abstract

Recent dielectric experiments have revealed a striking analogy between inorganic relaxor ferroelectrics and disordered organic ferroelectric polymers. We propose a model description of these relaxorlike polymers by considering a statistical ensemble of randomly oriented polar nanoregions, embedded in an amorphous matrix. In analogy to the spherical random bond-random field (SRBRF) model of inorganic relaxor ferroelectrics, we assume that the polar nanoregions are coupled through infinitely ranged random interactions of a spin-glass type and are subject to random local fields. The second moment of the probability distribution of dipole moments is required to have a fixed value, which is equivalent to a global spherical condition. A general solution of the SRBRF model is presented, and the linear and nonlinear static dielectric susceptibilities are calculated and compared with the experimental data. The phenomenon of giant electrostriction in relaxor polymers is also discussed.