Experimental Study On Shock Compressive Damage And Electric Breakdown Of Ferroelectic Ceramics

Ferroelectric ceramics is utilized for the use in shock-driven pulsed power supplies for many years. Not only the electric field, but also the shock stress is applied to the ferroelectric ceramics as shock-driven pulsed power supplies. The failure, induced by electric field or stress, is a key problem to the application of ferroelectric ceramics under shock compression.This paper is primarily devoted to study the failure behaviors of PZT95/5ferroelectric ceramics under shock compression through experimental study aided with theoretical analyses. Electric and mechanical failure behaviors of PZT95/5were systematically investigated. The results confirm that the failure mechanism of high density PZT95/5ceramics is different from that of porous PZT95/5ceramics, and the threshold of failure stress and the evolution rules of failure wave have been getted. This kind of failure behaviors are important to the application of PZT95/5or other dielectric materials under shock compression and the optimization of shock-driven pulsed power supplies.Following is the main content and conclusion of this study:To the unpoled PZT95/5, no obvious recompression signal is observed when the shock pressure is2.0GPa, whereas at2.5GPa, not only the free-surface particle velocity increases, but also a reload signal similar to the recompression signal appears. At a shock stress of4.0GPa or much higher, the reload signals disappear and the free-surface velocity increases slowly to the final state signifying a ramp-wave behavior.An innovative experimental method that using a high impendance window (sapphire) adheared to the back of the PZT95/5sample has been established to confirm the existence of failure wave in PZT95/5. The PZT/sapphire interface particle velocity profile indicates that a low impendence zone truelly exists in PZT95/5when the shock stress is2.4GPa and the reload signal is caused by the failure wave but not by pore collapse or pahse transition. In addition, the occurrence of a multi-reload signal in the rear free surface velocity also confirms the failure wave in PZT95/5.The delay time and velocity of the failure layer has been determined by measuring samples of varying thicknesses at fixed pressure. Results show that the velocity of failure wave is the same as the shock wave speed, and the delay time decreases with increasing shock stress. When the shock stress increases to4.0GPa, the delay time falls to zero, which means the failure layer and the shock wave will disperse synchronously, and the recompression signal disappears and a ramp wave appears. The disappearance of the recompression signal and the observation of the ramp wave mean the increasing of shock damaged in failure layer. Comparing with the failure signal of glass by Gadry, it finds the same points that when the stress is lower than the threshold of failure stress, the velocity profiles suggest nominal elastic response. The successively high stress will induce the behavior of failure wave. If further increasing the stress, a ramp wave will be formed.On the poled samples, the reload signal resulted by the the FEâ†'AFE phase transition is observed at first. In addition to this reload signal, when the pressure increases to2.4GPa or much more, it still has the failure wave. Comparing the failure behaviors of the poled PZT95/5with that of unpoled PZT95/5, results show that the delay time in poled PZT95/5is greated than that of unpoled PZT95/5. This difference is resulted by phase transition (FEâ†'AFE) reinforcement effect.Base on the theoretical calculation, the direct current or pulse electric field induced failure of PZT95/5is discussed in this paper, and the current waveforms of PZT95/5under different shock stress have been investigated. The results show that the electric failure dominates the failure behaviors of PZT95/5when the shock pressure is2.0GPa. As the shock stress reaches3.0GPa, which pressure means that the failure wave exists in PZT95/5, and its dielectric strength slightly decreases and equivalent internal resistant decreases to the order of kΩ due to the existence of failure wave in PZT95/5. When the pressure further increased to4.3GPa, not only the internal resistant but also the dielectric strength dramatically decreases. The evolution of the failure wave, such as expansion of microcracks, induces that the dielectric strength and internal resistant of PZT95/5decreases with increasing the shock stress. This point is important to understand the failure behaviors of PZT95/5ceramics under shock compression.