Hardness of new boron-rich chalcogenides B12S and B12Se

Hardness of bulk polycrystalline boron-rich chalcogenides, rhombohedral B12S and B12Se, has been predicted using contemporary theoretical models and experimentally studied by microindentation. Both chalcogenides exhibit Vickers hardness of about 33 GPa exceeding that of boron carbide and hence belong to a family of (super)hard phases.