Contribution of converse flexoelectric effect in PZT ceramics in presence of Strong Electrical Fields

The flexoelectric effect of solids is an electromechanical conversion mechanism that occurs in all dielectric materials, often together with other effects such as the piezoelectric. Currently, piezoelectric, electrodynamic and electrostatic conversion mechanisms are mostly used in actuators, some of them use dielectrics. The converse flexoelectric effect, has not yet been widely explored as an additional effect in these dielectric materials. A broad understanding of this effect could lead to new applications with a wider range of materials. In this paper, we attempt to determine the contribution of the converse flexoelectric effect in a lead zirconate titanate (PZT) piezoelectric soft ceramic. For this purpose, strongly varying electric fields were applied to capacitive electrode arrangements. The electrodes were deposited on one side of PZT-wafers (PIC151). Sinusoidal as well as pulsed voltage signals were applied to the electrodes. Doing so, the samples showed displacements in all three spatial directions. To separate the converse flexoelectric effect from the piezoelectric, displacements were measured at different temperatures between 20°C and 350°C i.e. even above the Curie temperature (Tc). The resulting deflection follows the electrical input signal at all temperatures. Because piezoelectric effects can be excluded above the Tc, another effect must be responsible for the displacement. The significant displacement of 30 to 40% in comparison to room temperature is attributed to the flexoelectric effect.