Stacking-fault structure explains unusual elasticity of nanocrystalline diamonds

This letter reveals that unusual elasticity of nanocrystalline diamond is consistently explained by stacking fault inside the diamond grains instead of the graphitic plate inclusion, which was only possible mechanism. Ab initio calculation shows that stacking fault introduced in the diamond structure behaves as graphitic sp2 bonds, and the elastic constants calculated from the strain-energy relationship agree with the acoustic measurements.