Seminar Series - 1999-2000

Microscopic Damages in PZT Ceramics

Zuoyi Wang
Department of Engineering Mechanics
University of Nebraska, Lincoln, NE 68588-0526
Advisor:  Dr. Qing Jiang

Date:  Monday, January 24, 2000
Time:  1:30 p.m.
Place:  W213.3 Nebraska Hall


Lead Zirconate Titanate (PZT) ceramics have been used in designing actuators and transducers, owing to their strong electro-mechanical coupling effect and prompt response to applied electric fields.  A major obstacle in the application of PZT actuators and transducers is electric fatigue, which refers to deterioration of macroscopic properties under cyclic electric loading. Several experimental investigations show that such fatigue specimens often contain a large number of microcracks.  Some theoretical studies suggest that the interaction of domain walls with processing flaws, such as pores and second-phase materials, causes stress concentrations and it contributes to microcracking.

The present study has investigated the processing flaws in a commercial PZT transducer ring.  Our scanning electron microscopy (SEM) examination of fracture surfaces of the PZT transducer ring fractured during poling shows the presence of pores and microcracks as well as high correlation of microcracks with pores of size significantly larger than the average grain size.  Evaluation of the semi-finished and finished rings obtained from product runs of the manufacturer indicates that the pores formed during pressing and that the microcracks were initiated during poling stage in which the domain wall motion is the principal activity.  The strong correlation of microcracks with sharp wedges at the edges of the pores suggests that these microcracks originated from the sharp wedges. Significant inhomogeneities in composition of the as-sintered rings were detected by energy dispersive spectroscopy and our SEM has revealed second phase particles at some triple grain junctions.

In order to investigate the interaction of domain walls with the processing flaws, we have explored an experimental technique, atomic force microscopy, for observing domains in fine grain PZT ceramics.  We have also shown that carefully conducted light polishing can result in no significant disturbance to domain patterns.

To study rotation sensitivity of the admittance of PZT ceramics, we have designed an apparatus to measure the admittance of PZT bars in rotation, and have observed their sensitivity to rotation at the rate of several thousand revolutions per minute.


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