Influence of grain size on ferroelastic toughening and piezoelectric behavior of lead zirconate titanate

Lead zirconate titanate specimens, at composition Zr-48.9+/-1.0/Ti-51.1+/-1.0, of grain sizes ranging from 0.5 to 15 mu m mere prepared by hot pressing. The fracture toughness showed a 40% increase in the fine-grained specimens, Poling produced anisotropy in the fracture toughness. A tensor representation for the fracture toughness, now a function of the crack plane normal and the poling direction, is developed. The maximum and minimum values in the toughness tensor are shown to be related to the unpoled toughness by a simple phenomenological relationship. We also find that the piezoelectric coefficient, d(33), shows a slight increase for the fine-grained specimens, which is in conflict with the general view that smaller-grained materials can sustain vanishingly small values of spontaneous polarization.