Shock-Induced Conduction in Elastic Dielectrics

The sample-polarity anomaly in current pulses from x-quartz shocked above the Hugoniot elastic limit gave the first indication of unusual conduc- 

88 Chapter 4. Physical Properties Under Elastic Shock Compression 

Certainly the most prominent feature of the breakdown process is its dependence on the polarity of the electric field relative to the shock-velocity vector. This effect is manifest in current pulse anomalies from minus-x orientation samples or positively oriented samples subjected to short-pulse loading (see Fig. 4.8). The individual effects of stress and electric field may be delineated with short-pulse loadings in which fields can be varied by utilizing stress pulses of various durations [72G03]. 

As shown in Fig. 4.9, these studies provide evidence that the breakdown was characterized by a fixed threshold stress of 11 GPa and a fixed threshold field of 2.8 X 10 Vm Once the threshold stress is exceeded, the conduction is controlled by the field and is independent of the stress. The threshold field is in reasonable agreement with the field of 7 x 10 V m below which a recovery from breakdown is observed when the field decreases due to the 

It appears that the observed breakdown must be explained in terms of the transient behavior of stress-induced defects even though the stresses are well within the nominal elastic range. In lithium niobate [77G06] and aluminum oxide [68G05] the extent of the breakdown appears to be strongly influenced by residual strains. In the vicinity of the threshold stress, dielectric relaxation associated with defects may have a significant effect on current observed in the short interval preceding breakdown. 

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