Dielectric and Piezoelectric Properties of PLZT x/40/60 (x = 5; 12) Ceramics

The results of studies of the structure, as well as piezoelectric, and dielectric properties, of lead zirconate-titanate ceramics modified with various concentrations of lanthanum (PLZT) are presented. It is found that with an increase in the La content, the grain size and the average size of the domains increase. The PLZT 12/40/60 samples contain both labyrinthine-like and periodic domains and different lateral sizes ranging from several hundred nanometers to 3 μm in diameter. It is found that with an increase in the size of domains in samples with a high content of lanthanum the signal of the piezoelectric response is enhanced. The fact of the existence of areas on the surface of PLZT x/40/60 ceramics, having an internal bias field, as indicated by the asymmetry along the voltage axis of the residual piezoelectric hysteresis loops, is established. In the PLZT 5/40/60 and PLZT 12/40/60 samples, a significant dispersion of the dielectric constant ε(f) and the maximum tangent of the dielectric loss angle in the frequency range from 105 to 106 Hz are observed. This is due to the presence of ionic relaxation polarization. It is found that the value of the dielectric constant increases markedly with an increase in La, which confirms the appearance of a rigid unipolar state in the grains of the PLZT 12/40/60 ceramics. In the samples under study, at low frequencies of the measuring field, an increase in the dielectric loss tangent is observed, which is related to the contribution of the conductivity to tan δ. The dependences of the dielectric loss factor ε'' on the dielectric constant ε' are plotted. They have the form of Cole–Cole diagrams, which indicates the presence of a spectrum of relaxation times, and it is found that the spectral width in the PLZT 5/40/60 samples is approximately half that in the PLZT 12/40/60 samples.