AC-poling of functionally graded piezoelectric bending devices

Monolithic ceramics with an uniaxial gradient of piezoelectric and/or dielectric coefficients (functionally graded materials-FGM) are suitable for bending actuators with strongly reduced internal mechanical stresses. We prepared BaTi1-xSnxO3 ceramics with a Sn-content of 7.5 mol% (BTS7.5) at the upper side and 15 mol% (BTS15) at the lower side. Two sheets of powder with different stoichiometry were pressed and sintered. The gradient of stoichiometry was modified by additional layers of powder with 10 and 12.5 mol% Sn, respectively. The Sn content after sintering across the thickness was investigated by Electron Probe Micro-Analysis (EPMA). The gradient of the chemical composition was transformed into a functionally gradient of the electromechanical properties by a poling process. An increasing of the bending deflection was obtained by cycling with an unipolar AC-voltage. In this work we studied two effects which can explain this behavior.