R-curve and subcritical crack growth in lead zirconate titanate ceramics

R-curves and subcritical crack growth curves (V–KI) were determined for undoped, K doped (PKZT) and Nb doped (PNZT) lead zirconate titanate (PZT) ceramics and the results are discussed including the effect of doping, grain size and the polarisation state. A pronounced crack growth resistance was observed in the soft PNZT ceramic, which is attributed to ferroelastic domain switching. Subcritical crack growth in the studied PZT materials is governed by both environmentally stress-induced corrosion at the crack tip and the crack shielding due to domain switching. Increasing domain switching capacity by structural modification of the material (i.e. by donor doping or by increasing the grain size) or by poling sifts the V–KI curve to higher values of the stress intensity factor.