Electrical measurements on fused quartz under shock compression

Abstract

The resistivities of specimens of SiO_2 (fused quartz) singly and doubly shocked in the 10–45 and 27–90 GPa ranges, respectively, demonstrate a marked decrease from values of ∼10–0.1 Ω⋅m at a single‐shock pressure of ∼40 and a double‐shock pressure of ∼74 GPa. These states correspond to calculated shock temperatures of ∼3300 and ∼3600 K, respectively. At shock pressures below 36 GPa the measured resistivity versus calculated shock temperature agrees closely with ambient‐pressure and high‐temperature resistivity data. This suggests that the ionic conduction mechanisms inferred to control electrical properties at ambient pressure also act under shock‐induced high temperatures in quartz and the presumed high‐pressure phase, stishovite into which fused quartz appears to transform above 20 GPa. At 36–40 GPa the rapid decrease in resistivity by a factor of 10^2 suggests a further transformation to an unknown phase which may correspond to the onset of melting. The existing pressure‐density Hugoniot data do not demonstrate any anomalous density change associated with this phase change.