Influence of mobile 90° domains on the complex elastic modulus of PZT ceramics

Measurements of the complex elastic Young's modulus of PZT ceramics as a function of the frequency of a triangular switching electric field and of an ac dynamic mechanical stress were performed. The results show that the electrostrictive character of the ceramics provides a complex elastic Young's modulus, which depends on the 90 degrees domains reorientation velocity which, in turn, is driven by the low-frequency switching electric field. This dependence has a relaxational character with a tau = 30 s relaxation time. For a given frequency of the switching electric field, the behaviour of Young's modulus as a function of the frequency of the mechanical stress is quite similar to that corresponding to point defects that are pinning the ferroelectric 90 degrees immobile domain walls: it is relaxational with a relaxation time tau = 0.04 s.