Asymmetric 90° domain switching in rainbow actuators

Asymmetry in the domain switching properties of Rainbow actuators with respect to positive and negative electric field was investigated and compared with the more symmetric properties of bulk ceramic materials. The electromechanical displacement and polarization hysteresis loops were found to be asymmetric in Rainbows. Peak-to-peak displacements in Rainbows poled at +25 kV/cm increased steadily from 88 to 450 mu m with increasing fields of +/-5 to +/-24 kV/cm. Rainbows poled at -25 kV/cm possessed a local minimum in displacement of 95 mu m at 13 kV/cm (near the coercive field) indicating a change in effective slope of the displacement versus field loop. Additionally, Rainbows possessed lower +E-C (coercive field) and higher +P-R (remanent polarization). It was found through X-ray diffraction of the tetragonal peak splitting in these materials that Rainbows exhibited enhanced 90 degrees reorientation of a-domains to c-domain alignment with positive applied electric field than with negative field. Bulk ceramic properties were consistent for both positive and negative applied fields. A mechanism for 90 degrees domain switching is discussed.