Cyclic damage in lead zirconate titanate

The effect of mechanical cycling (four-point bending),and electrical cycling (ac excitation at the longitudinal resonance frequency) on the degradation of the mechanical properties of PZT-8 bars was examined, Transmission electron microscopy (TEM) revealed microcracks which originated from second-phase material located at triple junctions, Energy-dispersive spectroscopy (EDS) showed that this second-phase material contained Pb, Ti, and Fe, but no detectable Zr. High intergranular microcrack densities were observed for mechanically cycled samples and samples electrically cycled at temperatures less than or equal to 80 degrees C. Electrically cycled samples allowed to heat to a steady-state temperature of 180 degrees C showed much lower crack densities. Piezoelectric coefficient (d(33)) measurements revealed that depolarization occurs in the 180 degrees C electrically cycled samples, but not in mechanically cycled materials nor in the 80 degrees C electrically cycled material, Also, samples heated in a furnace to 180 degrees C in the absence of external stress showed no evidence of depolarization. It appears that elevated temperatures (approximate to 180 degrees C) are necessary to cause depolarization in PZT-8 at the resonance-induced stresses used in this work.