BEHAVIOR OF SOFT PIEZOELECTRIC CERAMICS UNDER HIGH SINUSOIDAL ELECTRIC-FIELDS

The behavior of piezoelectric, dielectric, and elastic characteristics of soft piezoelectric lead zirconate titanate (PZT) ceramics was inve stigated under sinusoidal electric field E applied along the poling di rection and under mechanical stress-free conditions for a frequency ra nge 10 Hz-10 kHz. Electrical displacement D-3 along the poling directi on, mechanical strain S-1 in the direction perpendicular to the poling direction, and the resonant frequency nu(r) of electromechanically un coupled bending vibrations of polarized plates were measured. Commerci al ceramics PZT5H, 3203HD, and PKI550 with chemical composition near t he morphotropic phase boundary were used in the study. It was found th at the amplitude and phase of the first harmonic of the relative strai n S-1((1))/E-m and of the relative electrical displacement D-3((1)) / E-m increase similarly with increasing amplitude E-m of the electric f ield if the amplitude is less than coercive field. The corresponding i ncrease in the square of the resonant frequency is more moderate. The dependencies are described well by linear functions except for low ele ctric fields. The functions S-1m((1))/E-m and D-3m((1))/E-m demonstrat e frequency dispersion as well. Relative amplitude of the second harmo nic of the electrical displacement, D-3m((2))/D-3m((1)), which is pola r, also increases almost linearly with increasing E-m. The relative th ird harmonic D-3m((3))/D-3m((1)) demonstrates saturationlike behavior. By means of the electric pulse technique, it was found that irreversi ble changes in the remnant polarization take place even at electric fi elds much smaller that the coercive field. A mathematical model of a h ysteretic transducer, describing the electric field dependence of elec tromechanical properties of soft piezoelectric PZT ceramics, was sugge sted. According to this approach, the response depends not only on the instantaneous magnitude of the input signal (e.g., electric field) bu t also on its past extreme values. It was shown that the experimental Rayleigh law is a particular case of the suggested approach. The model relates directly electric field dependencies of complex piezoelectric coefficient d(31)(E-m) and S-1((1))/E-m, of complex dielectric permit tivity epsilon(33)(T)(E-m) and D-3((1))/E-m, and of elastic compliance s(11)(E)(E-m) and v(r)(2). Application of the model to experimental d ata showed that the model describes well the first three complex harmo nics of D3 and the irreversible change in the remnant polarization. Ph ysical causes of the observed behavior were analyzed. As an alternativ e to the model based on the 90 degrees polarization reorientation and tetragonl/rhombohedral phase boundary motion, a new approach was sugge sted. In this model, the observed hysteretic changes in the electromec hanical properties are assumed to be caused by the electric field depe ndency of the mechanical stress acting at interdomain boundaries in th e partly constrained crystallites of these ceramics. (C) 1998 American Institute of Physics. [S0021-8979(98)08217-6]