New Superhard Phases for Three-Dimensional $C_{60}$-based Fullerites

We have explored new possible phases of 3D ${\mathrm{C}}_{60}$-based fullerites using semiempirical potentials and ab initio density functional methods. We have found three closely related structures—two body-centered orthorhombic and one body-centered cubic—having 52, 56, and 60 tetracoordinated atoms per molecule. These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and shear moduli around 240 GPa, which make them good candidates for new low density superhard materials.