Tunability properties of the Pb(Mg1/3Nb2/3O3) relaxors and theoretical description

In the present paper, the dc-tunability properties of two types of Pb(Mg1/3Nb2/3O3) relaxor ceramics in their paraelectric state are investigated. By using two different precursors: MgO and (MgCO3)(4) Mg(OH)(2) 4H(2)O in preparing the ceramics. a difference of the temperature corresponding to the relaxor-paraelectric transition of similar to 35 K was obtained. Their permittivity-field dependences at a few temperatures in their paraelectric state were accurately determined The tunability, data were discussed in terms of the Johnson model completed with a Langevin term to describe the reorientation of the polar nanoregions existing in relaxors above their transition temperature. The experimental and computed epsilon(E) dependences at a few temperatures above T-m were compared Two types of temperature dependences of epsilon(E) were found, as predicted also by the theoretical approach: a faster epsilon(E) decrease closer to the transition temperature. where the mobility of the nanodomains is higher and a non-intersecting small epsilon(E) variation far away from the transition temperature. Another approach for experimental data is a simple model considering random non-interacting dipolar units in a double-well potential was considered. This model allowed to determine the average size of the nanopolar domains around 7.6-8.2 nm. which are values in agreement with experimental values reported for PMN in the literature. (C) 2009 Elsevier B.V. All rights reserved.