Development, Characterization, and Piezoelectric Fatigue Behavior of Lead- Free Perovskite Piezoelectric Ceramics

The development of lead-free perovskite piezoelectrics as environmentally compatible alternatives to lead zirconate titanate (PZT) has received significant attention recently. Two main categories of lead free perovskite piezoelectric ceramic systems were investigated as potential replacements to lead zirconate titantate (PZT) for actuator devices. First, solid solutions based on Li, Ta, and Sb modified (K0.5Na0.5)NbO3 (KNN) lead-free perovskite systems were created using standard solid state methods. Secondly, Bi-based materials a variety of compositions were explored. In one of these systems, it was shown that when (Bi0.5K0.5)TiO3– (Bi0.5Na0.5)TiO3 (BKT-BNT) is combined with increasing concentrations of Bi(Zn1/2Ti1/2)O3 (BZT), a transition from normal ferroelectric behavior to a material with large electric field induced strains was observed. The higher BZT containing compositions are characterized by large hysteretic strains (> 0.3%) with no negative strain. In piezoelectric materials, fatigue is observed as degradation in the electromechanical properties under the application of a bipolar or unipolar cyclic electrical load. In Pb-based materials such as lead zirconate titanate (PZT), fatigue has been studied in great depth for both bulk and thin film applications. Ultimately, it is electronic and ionic point defects that are the most influential mechanism. This work analyzes the fatigue characteristics of bulk polycrystalline ceramics of the compositions developed. It is shown that while some Pb-free materials show severe property degradation under cyclic loading, other materials, such as BNT-BKT-BZT, essentially exhibit fatigue-free piezoelectric properties with chemical doping or other modifications. Based on these results, these new Pb-free materials have great potential for use in piezoelectric applications requiring a large number of drive cycles such as MEMS devices or high frequency actuators.