Theoretical exploration of novel boron-carbon clathrate in Sr(B,C)10 at high pressure

The discovery of clathrate SrB3C3 under high pressure has inspired the exploration of new B–C clathrates. Here, we studied the structural evolution of a B–C framework over B and C contents in Sr(B,C)10 at a pressure of 0–20 GPa using an unbiased structure search method in combination with first principles calculations. Analysis of the formation enthalpies and lattice dynamics suggest that a clathrate SrB8C2 and two ‘tubular-like’ SrB7C3 and SrB9C may be synthesized at 20 GPa and quenched to ambient pressure. All compounds have excellent mechanical properties with Vickers hardness reaching 23.6–32.1 GPa. The ‘tubular-like’ SrB7C3 and SrB9C are metals with their Fermi level crossing the bonding and antibonding states of B-p orbitals, respectively. However, unexpectedly, the clathrate SrB8C2 is a semiconductor with a direct bandgap of 0.3 eV and is fundamentally different from metallic SrB3C3. The calculated thermoelectric figure of merit ZT of SrB8C2 is 0.47, indicating that it is a potential thermoelectric material. The findings highlight the diversity of structures and physical properties of this new family of ternary B–C compounds.