Relaxor-based ferroelectric single crystals for electromechanical actuators

Abstract

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn<SUB>1/3</SUB>Nb<SUB>2/3</SUB>)O<SUB>3</SUB> - PbTiO<SUB>3</SUB> (PZN-PT) and Pb(Mg<SUB>1/3</SUB>Nb<SUB>2/3</SUB>)O<SUB>3</SUB> - PbTiO<SUB>3</SUB> (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O<SUB>3</SUB> (PZT's), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d<SUB>33</SUB>'s) &gt; 2500 pC/N and subsequent strain levels up to &gt; 0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for &lt;001&gt; oriented rhombohedral crystals, though &lt;111&gt; 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<SUB>33</SUB>) &gt; 90% and low dielectric loss &lt;1%, along with large strain make these crystals promising candidates for high performance solid state actuators.