Direct piezoelectric effect in relaxor-ferroelectric single crystals

Direct measurements of longitudinal (d₃₃) and transverse (d₃₁) piezoelectric coefficients have been made on cuboid samples of [001]_C-poled 0.955Pb[Zn_1/3Nb_2/3]O₃-0.045PbTiO₃ (PZN-4.5PT) and 0.68Pb[Mg_1/3Nb_2/3]O₃-0.32PbTiO₃ (PMN-32PT) single crystals. The measurements were made in a Berlincourt-type press over a wide range of dynamic and static bias stresses. In the transverse mode, the response was found to be essentially anhysteretic and d₃₁ was independent of the dynamic stress amplitude. In contrast, for the longitudinal mode, the piezoelectric charge-stress behavior is hysteretic. Moreover, the relative hysteresis size and the d₃₃ coefficient are both strong functions of bias stress, dynamic stress amplitude, and frequency; coupling of the dynamic stress dependency of d₃₃ to the charge-stress hysteresis is demonstrated by a quasi-Rayleigh-type relationship. The observed hysteretic response could be due to domain switching in the crystals although this would be unexpected for a [001]_C-poled rhombohedral crystal. Instead, following the observed difference between transverse and longitudinal behaviors, it is suggested that polarization rotation away from the poling direction leads to a hysteretic response. © 2004 American Institute of Physics.