Schottky defects induced effects on the behaviors of high velocity shock compression of MgO

Abstract

Molecular dynamics (MD) simulation was performed on high velocity plane shock compression of sodium chloride MgO along [100] lattice direction using a long-range coulombic potential. It was found that the shock compressions of MgO revealed three distinct regions depending on piston velocities, i.e., single elastic shock wave, two-wave structure consisting of an elastic wave followed by a plastic deformation wave, and single plastic deformation shock wave. The critical pressure of 120 GPa was obtained for the transition from elastic to plastic deformation under the high strain rate of 10¹⁰ s⁻¹. For getting a better understanding the experimental results, we also investigated the effects of Schottky defects in MgO single crystal on the Hugoniot Elastic Limit (HEL), the velocity of shock wave and the critical piston velocity (CPV) resulting in plastic deformation. Our results demonstrated that the HEL decreases from 120 GPa to 100 GPa, and the CPV decreases a little from 2.8 km s⁻¹ to 2.2 km s⁻¹. Significantly, a double yielding phenomenon occurs for shock wave propagating in MgO sample with Schottky defects, i.e., homogeneous nucleation of dislocations accompanied by vacancy emission of dislocations, which has never been reported before. This work helps to clarify the contradictory results of HEL of MgO in the literature and to understand the plastic deformation mechanism of MgO.