Nonequilibrium of the physical state of copper under impact compression

The question of whether the physical state of shock-compressed copper is in equilibrium is discussed. For this, experimental data on defect electrical resistivity are used to estimate the concentration of point defects. Quantitative information on the concentration of defects can be obtained if the type of arising defects is known. Assuming the predominant formation of vacancies, the dependence of the concentration of defects in copper on the pressure of the shock wave is obtained. It is shown that the number of defects monotonically increases with increasing pressure of the shock wave. The found concentration of vacancies $\approx$0.8% at a pressure of 20 GPa) exceeds the corresponding equilibrium value by ten orders of magnitude. Thus, the state of copper under shock compression is highly defective and highly nonequilibrium. Comparison of data for shock-compressed copper and silver shows the general features of the state of these metals. Comparison of the data obtained immediately after the passage of the shock wave through the sample (in situ) with the known results for the samples preserved after the experiment demonstrates that in the first case, noticeably higher (up to two orders of magnitude) defect concentrations are recorded. Thus, the technique of stored samples does not provide objective information on the state of matter directly behind the shock front. The problem of constructing the equation of state under conditions of nonequilibrium physical state is briefly discussed.