piezoelectric materials, which are a class of ferroelerctric materials first discovered by Pierre Curie in 1883. By far, the
ABO3 perovskite type crystal structures have dominated the field due to their relatively large electromechanical coupling:
As illustrated in the preceding sections, when a voltage is applied to these materials, they undergo a physical
distortion (actuation mode), and conversely, when a mechanical stress is applied to these materials a voltage is produced (sensor mode).