||Temperature dependence of the bending strength, together with the elastic compliance, mechanical loss, and spontaneous strain of ferroelectric PZT-841 and PZT-4 ceramics was studied in the temperature range from room temperature to the Curie point (272 °C). The experimental results showed that the elastic compliance exhibits a peak at about 225 °C , while bending strength as a function of temperature exhibits a minimum at similar temperature. A model of 90°-domain wall motion has been herein proposed to interpret the observed behaviors. Effects of an applied electric field on the bending strength and fracture toughness of PZT-841 and PZT-4 ceramics were investigated. reduced by the application of an electric field. The results showed that both properties are Electric field is able to fracture a sample sustained with a constant load. A post-effect of the electric field was observed in electrically preloaded PZT-841, which was found to disappear under an annealing at above Curie temperature. The model of 90°-domain wall motion was extended to understand the observed fracture behaviors under combined electrical and mechanical load. Dielectric breakdown was studied in PZT-4 samples containing an embedding electrode by applying fracture mechanics concepts. The results verified that the critical energy release rate at dielectric breakdown is a material property and is termed as breakdown toughness. This breakdown toughness can serve as a criterion for dielectric breakdown. Effect of residual stress in thin films deposited on brittle substrate on indentation crack growth was studied. Theoretical analysis showed that the mean stress intensity factor, induced by the combination of the indentation load and the residual stress in the film and averaged over the entire crack front, is proportional to the reverse square root of the crack length, the magnitude of the residual stress, and the film thickness. To take account of the mechanical correlation between neighboring points of the crack front, we proposed that the mean stress intensity factor determine the indentation crack length at equilibrium. Indentation fracture tests on BaTiO3/Si system confirmed the theoretical prediction.