Direct observation of plastic deformation in diamond under extreme loading

High-power pulsed laser-driven shock compression was conducted on [001]-oriented single-crystalline diamond specimens encapsulated in impedance-matched metal capsules, generating shock pressures of 69, 93, and 115 GPa at a pulse duration of approximately 1 ns. At a pressure of 69 GPa, the defect-free lattice is retained, and diamond exhibits only elastic deformation. At a pressure of 115 GPa, defects are generated in the structure by the high shear stresses, which are relaxed by stacking faults, dislocations, and twins. These shear-induced lattice defects on crystallographic slip planes are crucial to the onset of amorphization. The amorphous bands are extremely localized and as narrow as a few nanometers. This amorphization is consistent with other covalently bonded materials with negative Clapeyron behavior subjected to extreme loading. Consequently, shock-induced amorphization is proposed as a new deformation mechanism of diamond under extremely-high-strain-rate deformation.