Superconductivity of Carbon Compounds with Sodalite Structure

We investigate the superconductivity of carbon compounds with a sodalite structure, which are similar to hydrogen compounds showing the high-temperature superconductivity. A systematic analysis by first-principles calculations is carried out, including examination of mechanical and dynamic instabilities under external pressure P. These instabilities are classified on the phase diagram for the effective doping charge versus the lattice constant of the system. We also present the superconducting transition temperature Tc as a function of P for many carbon compounds and a pure carbon system with the sodalite structure. Some of them have Tc of up to about 100 K at P≳30 GPa, and the results suggest that the sodalite structure of carbon may be a key to producing phonon-mediated high-Tc superconductivity.