Determination of the quasistatic linear and non-linear dielectric response in relaxor materials

Temperature dependence of the first epsilon(1) and third harmonic dielectric response epsilon(3) in relaxor systems was studied both as a function of the dc electric field by utilising the charge accumulation technique and as a function of the ac electric field. Additional non-linear contribution was found in the ac field dependence of epsilon(1) in lead magnesium niobate single crystals and in lanthanum-modified lead zirconate titanate ceramics. This dominating contribution in the field dependence of epsilon(1) (omega) has an origin in the fact that the increasing field shifts the relaxor state from the glassy to a particular crossover state in the glassy-to-ferroelectric crossover region. This was confirmed by quasistatic measurements of the total third-order non-linear dielectric response as a function of the dc electric field throughout the glassy-to-ferro-electric crossover region. It is shown that the total third-order non-linear dielectric response can be understood within the extended spherical random bond-random field model of relaxor ferroelectrics. (C) 2002 Elsevier Science B.V. All rights reserved.