Theoretical exploration of novel compounds in Sr(B,C)x (x = 7,8) at high pressure.

• The high-pressure crystal structures of Sr(B,C) x (x = 7,8) systems are explored. • SrB 5 C 2 , SrB 6 C and SrB 5 C 3 exhibit significant mechanical strength. • SrB 5 C 2 is a superconductor with t c of 10.5 K at ambient pressure. Boron-carbon-based compounds have attracted considerable attention due to their exceptional properties and increasing applications in industry. In this study, we conducted a systematic structural prediction of the SrB x C 7- x and SrB x C 8- x systems under ambient and high pressures up to 20 GPa using an unbiased global structure search. Through the calculations of formation enthalpy and phonon dispersion curves, we identified three new compounds, namely SrB 5 C 2 , SrB 6 C and SrB 5 C 3 , as thermodynamically and dynamically stable under ambient pressure and high pressures up to 20 GPa. Calculations of mechanical properties reveal that these three compounds have significant mechanical strength, with estimated theoretical Vickers hardness values ranging from 23.2 to 39.8 GPa. Electronic structure calculations suggest that both SrB 5 C 2 and SrB 5 C 3 are hole conductors, with the bands crossing the Fermi level, and SrB 6 C is a semiconductor with an indirect bandgap of 2.4 eV. The electron-phonon coupling calculations using the Migdal-Eliashberg theory indicate that SrB 5 C 2 exhibits superconductivity at 10.5 K under ambient pressure, while SrB 5 C 3 shows superconductivity at a much lower temperature of 0.4 K. This finding adds to our knowledge of boron-carbide materials and provides valuable insights for the development of similar materials with good mechanical properties. [ABSTRACT FROM AUTHOR]