Characteristics of the electromechanical response and polarization of electric field biased ferroelectrics

The electromechanical and dielectric responses of ferroelectric materials near paraelectric-ferroelectric (PF) phase transitions are examined both experimentally and theoretically. It is shown that the type of PF transition, i.e., first order and continuous transitions, and diffused phase transition found in relaxor ferroelectrics, has marked effect on the electromechanical and dielectric response behavior for materials under electric field bias. It is demonstrated that an exceptionally large piezoelectric and electromechanical response can be achieved in materials with a first order PF transition. For example, in Ba_1-xSr_xTiO₃ (x∼0.35) ceramics at room temperature, a piezoelectric d₃₃ larger than 1500 pm/V with very little frequency dispersion can be obtained.