Influence of stoichiometry on the dielectric and ferroelectric properties of the tunable (Ba,Sr)TiO3 ceramics investigated by First Order Reversal Curves method

Changes induced by different stoichiometries in Ba0.9Sr0.1TiO3 solid solutions, with (Ba, Sr)/Ti = 1 and (Ba, Sr)/Ti > 1, on the dielectric, ferroelectric and ac tunability characteristics were investigated. A small difference in the (Ba, Sr)/Ti ratio caused a shift of the Curie and Curie-Weiss temperatures of 16 and 19 C, respectively, but did not change the diffuse character of the phase transitions. The First Order Reversal Curves (FORC) method was used to describe the local switching properties and the ac tunability characteristics. Irrespective of the stoichiometry, no clear separation between the reversible and irreversible contributions to the polarisation were visible on the FORC diagrams. The maximum of the FORC distribution was located in almost the same position, at low fields, meaning that small fields are necessary to switch the majority of the dipolar units of these systems. The diagram obtained for (Ba, Sr)/Ti = 1 shrank towards smaller coercivities compared with Ba-rich samples, due to the smaller Curie temperature, making it closer to the ferro-para phase transition. The tunability depended on the actual field, and on the reversal field. A dependence of the FORC susceptibility on two maxima corresponding to the reversal field was found for stoichiometric samples, while one single maximum at low reversal fields was characteristic of Ba-rich samples. These results are interpreted in relationship to domain wall mobility, which is higher for the ferroelectric sample, close to its ferro-para phase transition. 22 refs.