High- Tc superconductivity in doped boron-carbon clathrates

We report a high-throughput ab initio study of the thermodynamic and superconducting properties of the recently synthesized XB3C3 clathrates. These compounds, in which boron and carbon form a spongelike network of interconnected cages each enclosing a central X atom, are attractive candidates to achieve high-Tc conventional superconductivity at ambient pressure, due to the simultaneous presence of a stiff B-C covalent network and a tunable Fermi energy due to the X atom acting as a charge reservoir. Ternary compounds like CaB3C3, SrB3C3, and BaB3C3 are predicted to exhibit Tc ≲ 50 K at moderate or ambient pressures, which may further increase up to 77 K if the original compounds are hole doped, by replacing the divalent alkaline earth with a monovalent alkali metal to form an ordered XYB6C6 alloy.