Electronic Densification and Stiffening of Diamond

Abstract

Diamond, with a bulk modulus of 435 GPa, is the most incompressible natural material. Searching for ultra-incompressible materials with a bulk modulus significantly higher than diamond has attracted much attention. However, this search has been long questioned since it has not found incompressible materials significantly superior to diamond to date. From first-principles calculations, we here demonstrate that the density (4.34 g/cm3) and the bulk modulus (645 GPa) of the electronically modified diamond can exceed 23% and 48% of the pristine diamond. Meanwhile, the tensile strength and strain-to-failure increase from 86 GPa and 13% for the pristine diamond to 242 GPa and 30% for the electronically modified diamond. These results indicate simultaneous stiffening, strengthening, and toughening of the diamond upon electronic modifications. Electronic structure analyses show that the ultrahigh density and mechanical performance of the electronically modified diamond are attributed to the shortening and stiffening of covalent bonds from the increase of bonding electron density.