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)2·4H2O in preparing the ceramics, a difference of the temperature corresponding to the relaxor-paraelectric transition of ∼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 ɛ(E) dependences at a few temperatures above Tm were compared. Two types of temperature dependences of ɛ(E) were found, as predicted also by the theoretical approach: a faster ɛ(E) decrease closer to the transition temperature, where the mobility of the nanodomains is higher and a non-intersecting small ɛ(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.