Relaxor based ferroelectric single crystals for electromechanical actuators

The piezoelectric properties of relaxer based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O-3 - PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O-3 - PbTiO3 (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O-3 (PZT's), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d(33)'s) > 2500 pC/N and subsequent strain levels up to >0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for < 001 > oriented rhombohedral crystals, though < 111 > is the polar direction Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, being related to an E-field induced phase transformation. Strain vs. E-field behavior under external stress was also much superior to that of conventional piezoelectric ceramics. High electromechanical coupling (k(33)) > 90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.