From quartz (qtz) to diamond (dia) carbon topologies: Stepwise rationale from crystal chemistry and DFT investigations

Abstract

From crystal chemistry and density functional theory DFT calculations, a stepwise rationale is proposed for the transformation from standalone distorted tetrahedron α-C5favored over standalone regular tetrahedron β-C5to high density – ultra hard orthorhombic α-C6and β-C6withqtz(quartz-based) topology characterized by 3D arrangements of distorted tetrahedra to lower densitydia-C topology (diamond-like, with regular C4 tetrahedra). Progressive C insertions into orthorhombic α-C5, α-C6, and lastly into C7were operated leading to ultimate C8stoichiometry identified as diamond-like. C7was also used as template to devise C3N4carbonitride with exceptional mechanical properties. The induced structural and physical changes are supported with elastic properties pointing to ultra-hardness, larger forqtzα,β-C6thandiaC8and inferred dynamic stability for all stoichiometries from the phonons band structures. The thermodynamic quantities as the specific heat were compared with diamond experimental CV. The electronic band structures reveal semi-conducting C6, metallic C7characterized by diamond-defect structure, and insulating C8. The results are meant to help further systemic understanding of tetrahedral carbon allotropes.