Low-Field and High-Field Fatigue in PZT-Based Rainbow Actuators

Abstract

The fatigue characteristics of the electromechanical and ferroelectric properties of high-displacement RAINBOW (Reduced And INternally Biased Oxide Wafer) actuators were investigated. Rainbows were fabricated from three types of lead-zirconate-titanate-based ferroelectric materials: soft ferroelectrics (PZT-SA and PZT-5H), hard ferroelectrics (PZT-4) and slim-loop ferroelectrics (PLZT 9/65/35). The PZT-4,-5A and-SH compositions were piezoelectric, and PLZT 9/65/35 was electrostrictive. Before fatigue testing, the flexural strength and electromechanical displacement versus load properties were measured for these compositions. Fatigue in the electromechanical displacement properties of Rainbows with increasing number of electric field cycles was observed at low field levels (below the coercive field) under various static loading conditions. For all of the compositions evaluated, actuator free displacement (no load) decreased <10% over 107 electric field cycles. Under 300 g of static load, displacements decreased 20-50% over 107 cycles with PZT-5A and PLZT 9/65/35 exhibiting the least fatigue. The decrease in displacement at high electric field levels (above the coercive field) was measured simultaneously with the degradation of ferroelectric polarization with increasing number of cycles for all compositions except PZT-4. High-field displacements decreased only 7% over 108 cycles for electrostrictive PLZT 9/65/35 Rainbows, whereas the displacements of the piezoelectric PZT-5A and PZT-5H compositions decreased 66% and 43%, respectively. The ferroelectric polarization in PZT-5A and PZT-5H Rainbows fatigued more rapidly than in bulk ceramics of these compositions. PLZT 9/65/35 Rainbows and bulk ceramics exhibited similar fatigue behavior and were more fatigue resistant than PZT-5A and PZT-5H at high fields. The effects of post-fatigue heat-treatment and electrical repoling were also observed.