Interrelationship between phase transition characteristics and piezoelectric response in lead lanthanum zirconate titanate relaxor ceramics

Dielectric and piezoelectric responses are investigated in relaxor-like lanthanum-modified lead zirconate titanate (PLZT) ceramics, for a La/Zr/Ti ratio of /60/40 ( = 8 and 10 at.%), obtained by the conventional ceramic method. No significant differences were observed from the room temperature ferroelectric properties, for both PLZT compositions. On the other hand, from evaluation of the nonlinear dielectric response in terms of the Rayleigh's model, a typical 'soft' behaviour is achieved in both materials, although the increments of the dielectric losses are slightly higher than the predicted by this model. The piezoelectric coefficient shows a remarkable increment with the applied dynamics stress, nevertheless without noticeable differences as a function of the lanthanum concentration. However, a significant difference is displayed in the weak-field direct longitudinal piezoelectric response. The dielectric properties revealed a higher diffuseness degree of the phase transition for the highest lanthanum content composition (PLZT 10/60/40). Thus, the observed difference in the piezoelectric response is discussed based on the nature of the phase transition in the studied relaxor materials.