Cracking behavior in lead zirconate titanate films with different Zr/Ti ratios

Abstract

Crack initiation stresses for different lead zirconate titanate (PZT) film compositions were investigated. PZT/Pt/TiO2/SiO2/Si stacks with 2.0 μm thick {100} oriented PZT films at the morphotropic phase boundary (MPB) showed a characteristic strength of 1137 MPa, and the film thickness served as the limiting flaw size for failure of the film/substrate stack. In contrast, for Zr/Ti ratios of 40/60 and 30/70, the characteristic stack strength increased while the Weibull modulus decreased to values typical for that of Si. This difference is believed to be due to toughening from ferroelasticity or phase switching. X-ray diffraction showed that the volume fraction of c-domains increased in Ti-rich compositions. This would allow for more switching from c to a-domains under biaxial tensile stress. Zr/Ti concentration gradients were present for all compositions, which contributed to the observation of a rhombohedral phase off the MPB. Due to the reduced tendency toward cracking, off-MPB compositions are potentially of interest in actuators, albeit with the trade-off of needing a high actuation voltage.