Pre-existing cracks, introduced by a Vickers diamond hardness indenter in BM500 (Navy Type II) PZT, exhibit visible
growth and thickening when subjected to low frequency electric fields with amplitudes above a threshold on the order of
1.66 Ec. Thickening, but no growth, of cracks is also observed after cycles of a field of 1.64 Ec. The threshold field is
related to the ferroelectric, piezoelectric and elastic properties of the ceramic. At fields above the threshold, cracks grow
to a limiting size after a relatively low number of cycles, and then increase in width, as opposed to length, when further
electric cycles are applied. The maximum size to which field-induced cracks grow is of the order of the separation of the
electrodes. Changes observed in the resonance peaks of impedance spectra may be used as a basis for non-destructive
identification of defects in piezoelectrics.