Bending Actuators Based on Monolithic Barium Titanate-Stannate Ceramics as Functional Gradient Materials

Abstract

In the field of applications of piezoelectric materials properties, functional gradient materials (FGM) are suitable for bending devices due to reduced internal mechanical stresses and lower production costs as well as for ultrasonic transducers because of their increased band width. This paper reports both on preparation, poling, characterization of FGM actuators, and on the description of suitable models of the poling and the bending processes. The calculations of the bending behavior show that the deflection at the end of the cantilever with a continuous gradient still reaches 2/3 of the deflection of a bimorph, whereas the maximum stress goes to zero, which is the main advantage of FGM compared to the commonly used bimorph devices. As a model system with well-defined electromechanical and dielectric properties of the homogeneous components the solid solution of BaTi1-xSnxO3 (BTS) with 0.075 £ x £ 0.15 was chosen. The FGMs approximated by a layered system with a one-dimensional gradient of the Sn-content were prepared both by successive uniaxial powder pressing and by tape casting with the doctor blade method. The chemical gradient was transformed into a gradient of the piezoelectric properties by a poling process. Several models were developed for the description of the non-trivial problem of the poling process in layered systems. The calculated data were compared with experimental results. It was shown that the very small electrical conductivity of the single layers generally cannot be neglected during the poling process and must be incorporated into more sophisticated models. The bending properties of several poled BTS structures with up to 4 layers were measured and discussed.