High-pressure synthesis of boron-rich chalcogenides B12S and B12Se

Two boron-rich chalcogenides B12S and B12Se isostructural to {\alpha}-rhombohedral boron were synthesized by chemical reaction of the elements at high-pressure - high-temperature conditions. The crystal structures and stoichiometries of both compounds were confirmed by Rietveld refinement and elemental analysis. The experimental Raman spectra of B12S and B12Se were investigated for the first time. All observed Raman bands have been attributed to the theoretically calculated phonon modes, and the mode assignment has been performed.