We report a high-throughput ab initio study of the thermodynamic and superconducting properties of the recently synthesized X B 3 C 3 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-T c 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 CaB 3 C 3 , SrB 3 C 3 , and BaB 3 C 3 are predicted to exhibit T c 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 XY B 6 C 6 alloy.

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