Piezoelectric functionally gradient material for bending devices based on Ba(Ti,Sn)O3 ceramics

Functionally gradient materials (FGM) with one dimensional gradient of the piezoelectric activity can be used for bending actuators. For this, monolithic ceramics consisting of N layers with different chemical properties are prepared. The gradient of the chemical properties has to be transformed into a gradient of the piezoelectric properties by a poling process. In this work the poling and bending behavior of such FGM devices was investigated and described by analytical approximations. Monolithic samples with 2, 3 or 4 layers of BaTi_1-xSn_xO₃ (BTS) ceramics with different amount of tin (0.075 ≤ x ≤ 0.15) were prepared. The poling behavior was characterized by measurements of the dielectric virgin loops P(E). The bending deflection of poled devices depends on the amount of tin in the layers and slightly increases with increasing number of layers. Additionally, conventional glued bending devices with the same number of layers and a corresponding chemical composition were investigated. The experimental data were compared with the results of analytical approximations. Here, measured properties of single BTS ceramics with the appropriate amount of tin were used for the calculation of hysteresis loops and bending deflection of the layered systems. A good correspondence between the model structures and the theory was found. However, slight differences for the monolithic ceramics were obtained. We suppose that this is due to the existence of interface layers with indefinite material properties between neighboring layers.