Time-Resolved Analysis of the Rate-Dependent Behavior of PZT Ceramics
Ferroelectric ceramics have a wide variety of applications, ranging from ultrasonic devices to pressure sensors. In many of these applications, the ferroelectric material is subjected to transient mechanical loading and its electro-mechanical response is of critical importance. There is a lack of characterization for the responses of Lead Zirconate Titanate (PZT) ceramics to stress pulses with magnitudes below 1 GPa. A split Hopkinson pressure bar (SHPB) apparatus is used to subject PZT specimens to transient stress pulses of 50 to 500 MPa in magnitude. The duration of the stress pulse is approximately 150 microseconds, corresponding to load frequency of 6.7 kHz if repeated. A time-resolved analysis of the electro-mechanical response is carried out using high-speed digital oscilloscopes with a resolution of 500 nanoseconds. For comparison purposes, quasistatic experiments are also conducted. The materials tested are four different hard and soft PZT ceramics. These materials allow the effects of composition and grain size on behavior to be characterized.
Experiments conducted show that the PZTs analyzed have significant rate-sensitive electric responses to mechanical loads. The stress required to yield a certain amount of electric displacement is higher under dynamic loading that what is observed in quasistatic experiments. For the hard PZT (TRS300FG), little or no residual depolarization is observed under both quasistatic and dynamic conditions. For the soft PZTs (TRS600FG, TRS200, TRS200FG), the residual depolarization of the permanent electric displacement retained by the materials after stress is removed decreases with increasing loading rate. However, this difference becomes smaller and tends to disappear as full depolarization is obtained at high loading amplitude. The experiments use a soft recovery configuration that subjects the specimens to a single specified stress pulse, therefore eliminating any unintended mechanical loading and allowing the specimens to be recovered for postmortem analysis. Scanning electron microscopy indicates that the materials remain mechanically intact until macroscopic failure is observed. The initiation of failure occurs at stress levels between 200 and 500 MPa, depending on the material composition and grain size. For the hard PZT under transient loading conditions, onset of mechanical failure is found to occur without residual depolarization. For the soft PZTs under transient loading conditions, the initiation of mechanical failure occurs at loading amplitudes higher than what is required to initiate residual depolarization.