(Dr. Min Zhou, advisor)
"A Time-Resolved Analysis of the Rate-Dependent Behavior of PZT Ceramics "
Ferroelectric ceramics have a 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 a 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 clear rate-sensitive electric responses to mechanical loads. The stress required to yield a certain amount of electric displacement is higher under dynamic loading than what is observed in quasistatic experiments. For the hard PZT, little or no residual depolarization is observed under both quasistatic and dynamic conditions. For the soft PZTs, the residual depolarization or 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.