Ph.D. Dissertation Defense by Tieqi Liu
Friday, October 15, 2004

(Dr. Christopher S. Lynch, Chair)

"Electromechanical Behavior of Relaxor Ferroelectric Crystals"

Abstract

Relaxor ferroelectric PZN-xPT and PMN-xPT single crystals exhibit extraordinary electromechanical properties. They are under development for sensors, actuators and transducers. The polarization switching and phase transition behavior of these crystals under external loading have been investigated.

Experimental study elucidates the polarization switching and phase transition behavior of relaxor ferroelectric PZN-4.5%PT and PMN-32%PT crystals at <001>, <110> and other orientation cuts under different temperature, electric field and stress loading. External fields including temperature, stress and electric field all strongly affect the poling and phase states of the crystals. Fracture behavior of relaxor single crystals under non-uniform electric fields at the edge of partial electrodes has also been measured and analyzed.

Based on experimental investigation, crystal variant based modeling is developed to compute the physical properties of multi-domain rhombohedral crystals at different orientation cuts from a set of properties for the single domain. Experimental measurements also provide data for thermodynamics analysis of the polarization switching and phase transitions of relaxor ferroelectric single crystals. Work-energy analysis of field induced phase transitions sheds light on the mechanism of structural phase transitions of these crystals.