Carbon-based clathrates

Clathrate structures are found throughout nature in tetrahedral systems including water, silicates, silicon, germanium, tin and even colloids. Given similarities in bonding, it is natural to presume the existence of clathrate frameworks based on carbon, but attempts to prepare these materials have been unsuccessful thus far. If synthesized, these materials are expected to exhibit diamond-like mechanical properties due to the nature of covalent bonding, as well as strong electron-phonon coupling that could lead to high superconducting transition temperatures. We develop a stabilization principle based on the substitution of boron within the polyhedral carbon cages. Using this approach, we predict and synthesize the first carbon-based clathrate comprised of truncated octahedral C₁₂B₁₂ cages that trap Sr atoms in the “type-VII” structure. The mechanical properties, electronic structure and superconducting properties of this material will be discussed, as well as the potential for different structures and compositions within this new family of carbon-based materials.