ac-field-dependent structure-property relationships in La-modified lead zirconate titanate: Induced relaxor behavior and domain breakdown in soft ferroelectrics

The complex dielectric response was studied for various compositions in the (Pb1-3/2yLay)(Zr0.65Ti0.35)O-3 (PLZT y/65/35) crystalline solution as a function of ac drive amplitude, frequency, and temperature. These studies reveal the presence of nonlinearities with respect to the amplitude of the ac drive. For 0.02<y<0.04, the magnitude of the dielectric constant was observed to increase dramatically (similar to 500-1000%) and the temperature of the dielectric maximum (T-max) was observed to be shifted down significantly with increasing drive amplitude between 20 and 500 V/cm. in addition, strong frequency dispersion was observed in the nonlinear dielectric response, whereas the linear response was found to be frequency independent. For 0.06<y<0.10, the magnitude of the nonlinearities were significantly decreased with increasing La content and the value of T-max was nearly independent of drive. Frequency dispersion was observed in the linear dielectric response; however, the nonlinear response was noticeably frequency independent. Sawyer-Tower polarization studies then revealed that the polarization behavior was linear in the range of electrical-field strengths used to measure the dielectric responses. These results indicate that the observed dielectric nonlinearities are not due to polarization nonlinearities, but rather related to the dynamics of various stable domainlike structures. On the basis of the results, an attempt is made to distinguish the similarities and differences between soft and relaxer ferroelectric behaviors.