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Abstract
Piezoelectric ceramics, especially lead zirconate titanate (PZT) ceramics, have been widely used and studied for their extraordinary and adjustable electro-mechanical properties. However, defects such as cavities and micro-cracks are unavoidable during manufacturing and operation. These defects can degrade the piezoelectric properties and undermine their performance in service. Conventional methods of determining structural reliability, such as measuring the mechanical strength of piezoelectric ceramics are destructive and inevitably cause the ceramic sample to fail after testing. Therefore, a practical non-destructive method for evaluating mechanical reliability is required.
This study investigates the applicability of using partial discharge (PD) test to evaluate the reliability of piezoelectric ceramics PZT. Preliminary PD and four-point flexure tests were conducted on a soft PZT ceramic and the influence of PD test on PZT samples is discussed. Weibull analysis of the results reveal an analogy between PD inception field and mechanical strength distribution, which suggests that the PD and fracture may originate from the same group of defects in PZT.
The results also show that PD occurs at low electric field in piezoelectric ceramics. In order to further understand the factors influence PD, PD behaviours are examined in different types (i.e. hard and soft) of PZT ceramics. The PD results are also compared to traditional alumina and mullite ceramic and epoxy polymer dielectric materials. In general, materials with higher permittivity or/and larger defects demonstrate a lower PD inception electric field. More PDs occur when the applied electric field is increased, especially in soft PZT. This indicates that the change in polarization during domain switching in soft PZT can facilitate PD occurrences in piezoelectric ceramics. A further study of PD under unipolar and bipolar electric field confirms this assumption. PD starts at a higher electric field under a unipolar electric field than it does under a bipolar electric field.
The results of this project suggest that the PD test is a promising method for estimating the structural reliability of piezoelectric ceramics in an essentially non-destructive manner. The study has also investigated the contribution of relative permittivity, defect size, and polarization reversal to PD, improving the understanding of PD characteristics in piezoelectric ceramics.