Phenomenological description of dielectric permittivity peak in relaxor ferroelectrics

We found that, at the so-called diffuse phase transition in relaxer ferroelectrics, the dielectric permittivity epsilon obeys the relation epsilon(A)/epsilon = 1 + 0.5(T - T-A)(2)/delta(A)(2) in a wide temperature range above the temperature of permittivity maximum T-m (T-m > T-A). The parameter delta(A) remains invariant with the variation of measurement frequency and characterizes the diffuseness of the transition. (C) 2000 Elsevier Science Ltd. All rights reserved.