Stress Effects in Ferroelectric Ceramics

Abstract

Electromechanical transducers made of ferroelectric ceramic materials such as those based on barium titanate (BT) or on various lead zirconate titanate (PZT) compositions have become widely used for a variety of applications over the past 25 years [1]. Most of these applications utilize the linear piezoelectric effect for the conversion between electrical and mechanical energy, and one of the prime advantages of the BT or PZT materials is that their piezoelectric coupling coefficients are large. Another kind of application of ferroelectric ceramics — one that is perhaps not as generally familiar — is based on non-linear and non-reversible processes that can take place in these materials. One example of this kind of application is the single-shot, shock-activated power supply [2,3]. In this device, electrical energy is stored in a ferroelectric element by the initial poling process, and the passage of a shock wave through the material releases part or all of this stored energy (into an external electrical load) by actually destroying (non-reversibly) the State of initial polarization. There are two important mechanisms by which the destruction of polarization may occur. The first is by domain reorientation processes [4] whereby the directions of the polarization vectors in the individual ferroelectric domains change from one preferred crystallographic axis to another in response to the external stress. This process tends to randomize the domains and dramatically reduce the net polarization of the ceramic. The second possible mechanism for shock-induced depoling is a structural phase transition [3,5] induced by the stress behind the shock front, which transforms the material into a non-ferroelectric State. When such a transformation occurs, the polarizations of the individual crystallites of the ceramic become zero, so that all of the initial poling energy is released.