Publications
Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 : depoling currents
Shock wave compression of poled Pb{sub 0.99}(Zr{sub 0.95}Ti{sub 0.05}){sub 0.98}Nb{sub 0.02}O{sub 3} (PZT 95/5-2Nb) results in rapid depoling and release of bound charge. In the current study, planar-impact experiments with this material were conducted on a gas-gun facility to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-induced depoling characteristics. A previous article summarized results from the first two of these areas, and this article summarizes the depoling studies. A baseline material, similar to materials used in previous studies, was examined in detail. More limited experiments were conducted with other materials to investigate the effects of different porous microstructures. Experiments were conducted over a wide range of conditions in order to examine the effects of varying shock strength, poling orientation, input wave shape, electric field strength, porous microstructure at a fixed density, and initial density. Depoling currents were recorded in an external circuit under either short-circuit or high-field conditions, and provide a convenient means of examining the kinetics associated with the ferroelectric-to-antiferroelectric phase transition. For sufficiently strong shock waves, the measured short-circuit currents indicate that the phase transition is very rapid and essentially complete. As shock strengths are reduced, short-circuit currents show increasing rise times and decreasing final levels at the end of shock transit. These features indicate that the transition kinetics can be characterized in terms of both a transition rate and a limiting degree of transition achieved in a given shock experiment. The presence of a strong electric field does not appear to have a significant effect on transition kinetics at high shock stresses, but has a strong effect at low stresses. As was found for constitutive mechanical properties, only small effects on measured currents resulted from differences in the porous microstructure of common-density materials, but large effects were observed when initial density was varied. To examine transition kinetics in more detail, short-circuit currents obtained with the baseline material and several approximate methods were used to estimate values for the rate and degree of transition as functions of shock properties. Differences between these currents and currents measured in high-field experiments using the same impact conditions were used to examine field effects on transition kinetics and corresponding dielectric properties.