High- T c superconductivity in doped boron-carbon clathrates

We report a high-throughput ab initio study of the thermodynamic and superconducting properties of the recently synthesized $X{\mathrm{B}}_{3}{\mathrm{C}}_{3}$ 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 ${\mathrm{CaB}}_{3}{\mathrm{C}}_{3}, {\mathrm{SrB}}_{3}{\mathrm{C}}_{3}$, and ${\mathrm{BaB}}_{3}{\mathrm{C}}_{3}$ are predicted to exhibit ${T}_{c} \ensuremath{\lesssim}50$ 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 $XY{\mathrm{B}}_{6}{\mathrm{C}}_{6}$ alloy.