LOW-FIELD AND HIGH-FIELD FATIGUE IN PZT-BASED RAINBOW ACTUATORS

The fatigue characteristics of the electromechanical and ferroelectric properties of high-displacement RAINBOW (Reduced And INternally Biase d Oxide Wafer) actuators were investigated. Rainbows were fabricated f rom three types of lead-zirconate-titanate-based ferroelectric materia ls: soft ferroelectrics (PZT-5A and PZT-5H), hard ferroelectrics (PZT- 4) and slim-loop ferroelectrics (PLZT 9/65/35). The PZT-4, -5A and -5H compositions were piezoelectric, and PLZT 9/65/35 was electrostrictiv e. Before fatigue testing, the flexural strength and electromechanical displacement versus load properties were measured for these compositi ons. Fatigue in the electromechanical displacement properties of Rainb ows with increasing number of electric field cycles was observed at lo w field levels (below the coercive field) under various static loading conditions. For all of the compositions evaluated, actuator free disp lacement (no load) decreased <10% over 10(7) electric field cycles. Un der 300 g of static load, displacements decreased 20-50% over 10(7) cy cles with PZT-5A and PLZT 9/65/35 exhibiting the least fatigue. The de crease in displacement at high electric field levels (above the coerci ve field) was measured simultaneously with the degradation of ferroele ctric polarization with increasing number of cycles for all compositio ns except PZT-4. High-field displacements decreased only 7% over 10(8) cycles for electrostrictive PLZT 9/65/35 Rainbows, whereas the displa cements of the piezoelectric PZT-5A and PZT-5H compositions decreased 66% and 43%, respectively. The ferroelectric polarization in PZT-5A an d PZT-5H Rainbows fatigued more rapidly than in bulk ceramics of these compositions. PLZT 9/65/35 Rainbows and bulk ceramics exhibited simil ar fatigue behavior and were more fatigue resistant than PZT-5A and PZ T-5H at high fields. The effects of post-fatigue heat-treatment and el ectrical repoling were also observed.