EFFECT OF CYCLIC ELECTRIC FIELDS ON CRACK GROWTH IN A MODERATELY SOFT PIEZOELECTRIC CERAMIC

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 E c . Thickening, but no growth, of cracks is also observed after cycles of a field of 1.64 E c . 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.