Relaxor-based ferroelectric single crystals for electromechanical actuators

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Abstract
The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3 - PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3 - PbTiO3 (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZT's), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33's) > 2500 pC/N and subsequent strain levels up to > 0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for oriented rhombohedral crystals, though 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 (k33) > 90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

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