Effect of Nb and K doping on the crack propagation behaviour of lead zirconate titanate ceramics

In the present study, we investigated the effect of doping on the crack propagation behaviour of lead zirconate titanate ceramics (PZT), particularly crack growth resistance and slow crack growth. Three PZT grades were processed: an undoped PZT, a soft PZT doped with niobium, PNZT, and a hard PZT doped with potassium, PKZT. The composition was chosen close to that of the morphotropic phase boundary (MPB), known to give excellent electromechanical properties. The soft material showed an important crack growth resistance and its slow crack growth curve V– K I (crack velocity versus stress intensity factor, K I) is shifted toward higher values of K I. The results are discussed in terms of toughening due to ferroelastic domain switching under mechanical loading.