A combination of large unipolar electrostrain and d(33) in a non-ergodic relaxor ferroelectric

One of the important requirements for piezoelectric materials for use as high strain actuators is that they exhibit large unipolar electrostrain with minimum hysteresis. While large unipolar electrostrain >1% is generally achievable in good quality single crystals, most polycrystalline piezoelectric show low values < 0.4%. Unipolar electrostrain 0.5%-0.7% in polycrystalline piezoelectrics has often been reported in Na(0.5)Bi(0.5)TiO(3-)based compositions at the non-ergodic ergodic boundary. Not amenable to poling, such materials exhibit almost nearly zero direct piezoelectric coefficient (d(33) similar to 0 pC/N) and cannot be simultaneously used as a sensor. In this paper, we report a combination of large unipolar electrostrain of similar to 0.6% with small strain hysteresis of 25% in a Sn-modified relaxor ferroelectric system PbTiO3-Bi(Ni1/2Zr1/2)O-3. It exhibits d(33) similar to 340 pC/N, which is stable up to 130 degrees C, and large signal converse piezoelectric coefficient d(33)* similar to 1200 pm/V. A combination of large d(33) and d(33)* in the same material makes it an important candidate for simultaneous use as a sensor and high strain actuators. X-ray diffraction study in situ with the electric field suggests that large electrostrain with low strain hysteresis in this system is because of the increased reversible switching of the field stabilized tetragonal ferroelastic domains.