Phenomenological description of dielectric permittivity peak in relaxor ferroelectrics

We found that, at the so-called diffuse phase transition in relaxor ferroelectrics, the dielectric permittivity ε obeys the relation εA/ε=1+0.5(T−TA)2/δA2 in a wide temperature range above the temperature of permittivity maximum Tm (Tm>TA). The parameter δA remains invariant with the variation of measurement frequency and characterizes the diffuseness of the transition.