Exploration of superconductivity in light element compounds has drawn considerable attention because those materials can easily realize the high $T_{c}$ superconductivity, such as ${mathrm{LnNi}}_{2}{mathrm{B}_{2}}{mathrm{C}}$ ($T_{c}$ =17 K), ${mathrm{Mg}}{mathrm{B}}_{2}$ ($T_{c}$ =39 K), and very recently super-hydrides under pressure ($T_{c}$ =250 K). Here we report the discovery of bulk superconductivity at 7.8 K in scandium borocarbide ${mathrm{Sc}}_{20}{mathrm{B}}{mathrm{C}}_{27}$ with a tetragonal lattice which structure changes based on the compound of ${mathrm{Sc}}_{3}{mathrm{C}}_{4}$ with very little B doping. Magnetization and specific heat measurements show bulk superconductivity. An upper critical field of Hc2(0) ~ 8 T is determined. Low temperature specific-heat shows that this system is a BCS fully gapped s-wave superconductor. Electronic structure calculations demonstrate that compared with ${mathrm{Sc}}_{3}{mathrm{C}}_{4}$ there are more orbital overlap and hybridization between Sc 3d electrons and 2p electrons of C-C(B)-C fragment in ${mathrm{Sc}}_{20}{mathrm{B}}{mathrm{C}}_{27}$, which form a new electric conduction path of Sc-C(B)-Sc. Those changes influence the band structure at the Fermi level and may be the reason of superconductivity in ${mathrm{Sc}}_{20}{mathrm{B}}{mathrm{C}}_{27}$.
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