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

The changes induced by the 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 are investigated. A small difference in the (Ba,Sr)/Ti ratio causes a shift of the Curie and Curie–Weiss temperatures of 16 and 19 °C, respectively, but does not change the diffuse character of the phase transitions. The FORC method is used for describing the local switching properties and the ac tunability characteristics. Irrespective of the stoichiometry, no clear separation between the reversible and irreversible contributions to the polarization are visible on the FORC diagrams. The maximum of the FORC distribution is 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 the solid solutions with (Ba,Sr)/Ti = 1 shrinks towards smaller coercivities in comparison with the Ba-rich samples, due to the smaller Curie temperature, making it closer to the ferro–para phase transition. The tunability determined in the FORC experiment depends not only on the actual field, but also on the reversal field. A dependence of the FORC susceptibility on the two maxima corresponding to the reversal field was found for the stoichiometric samples, while one single maximum at low reversal fields is characteristic of the 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.