Relaxor based ferroelectric single crystals for electro-mechanical actuators

Abstract

 The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn_1/3Nb_2/3)O3−PbTiO₃ (PZN-PT) and Pb(Mg_1/3Nb_2/3)O₃−PbTiO₃ (PMN-PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O₃ (PZTs), morphotropic phase boundary (MPB) compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d₃₃’s ) >2200 pC/N and subsequent strain levels up to >0.5% 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, possibly being related to an E-field induced phase transformation. High electromechanical coupling (k₃₃) >90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.