Dense as diamond: Pn-C_(10), a superhard sp~3 carbon allotrope

摘要

We introduce a carbon allotrope with rhombic symmetry and a high crystal density reached 3.56 g/cm~3, named Pn-C_(10), which was found using an unbiased particle-swarm structural-searching technique. This fully sp~3-bonded carbon phase is dynamically and mechanically stable in its ground state. Results from our calculations reveal the excellent mechanical nature of Pn-C_(10) with a claimed shear modulus and Vickers hardness of 484 GPa and 88.45 GPa, respectively, which also suggested its slight anisotropy in elasticity. The predicted electronic band structure indicates that Pn-C_(10) is an indirect-bandgap material with a bandgap of 5.05 eV. Natural tiling analysis and simulations of x-ray diffraction and Raman spectra were performed to provide insights for further studies into Pn-C_(10) and other carbon phases.