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 i n the (Pb1-3/2yLay)(Zr0.65Ti0.35)O-3 (PLZT y/65/35) crystalline soluti on as a function of ac drive amplitude, frequency, and temperature. Th ese 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 diele ctric constant was observed to increase dramatically (similar to 500-1 000%) and the temperature of the dielectric maximum (T-max) was observ ed to be shifted down significantly with increasing drive amplitude be tween 20 and 500 V/cm. in addition, strong frequency dispersion was ob served in the nonlinear dielectric response, whereas the linear respon se was found to be frequency independent. For 0.06<y<0.10, the magnitu de of the nonlinearities were significantly decreased with increasing La content and the value of T-max was nearly independent of drive. Fre quency dispersion was observed in the linear dielectric response; howe ver, the nonlinear response was noticeably frequency independent. Sawy er-Tower polarization studies then revealed that the polarization beha vior was linear in the range of electrical-field strengths used to mea sure the dielectric responses. These results indicate that the observe d dielectric nonlinearities are not due to polarization nonlinearities , but rather related to the dynamics of various stable domainlike stru ctures. On the basis of the results, an attempt is made to distinguish the similarities and differences between soft and relaxer ferroelectr ic behaviors.