The mechanical response of glassy carbon recovered from high pressure

Glassy carbon (GC) is a predominately sp² bonded disordered material. It is considered to have prototypical super-elastic mechanical properties and has been used as a precursor in many high-pressure studies. We have shown that by compressing GC in a diamond anvil cell (DAC) at room temperature, a permanent structural change occurs at pressures above 35-45 GPa. In this current study, GC is compressed to a range of different pressures up to 54 GPa. We show a much lower starting point for the loss of GC’s super-elasticity of ~6 GPa and the material becomes mechanically anisotropic beyond ~30 GPa, measured by nanoindentation probing along both the DAC compression axis and a direction perpendicular to DAC compression axis. Our results show a minimum elasticity of GC at around 30 GPa, with a recovery after compression at higher pressures only along the DAC compression direction. Calculation of the Young’s modulus by molecular dynamics simulations both before and after compression within the same pressure range supported the experimental findings.