  The subcarbides B12C3 and B13C2 known for their abrasive properties, can be
structurally considered as carbon inserted rhombohedral alpha-B12 and expressed
as B12{C-C-C} and B12(C-B-C). Using density functional theory DFT computations,
the substitution of the central atom in the linear triatomic interstitials by N
leads to an original new boron subcarbonitride B12C2N or B12(C-N-C) identified
as slightly more cohesive than the two subcarbides. While B12C3 is insulating
with a E(Gap) close to 0.2 eV, and B13C2 a weak metal with small density of
state DOS at the Fermi level, B12C2N ground state is a half-metallic
ferromagnet with M= 1 BM. From the equation of state, the magnetization is
found unchanged over a broad volume range around equilibrium. Total and
magnetic charge density projections, in accordance with charge transfer
calculations, show the charge envelopes to be concentrated on (C:N:C) and the
magnetic charge having the shape of a torus centered on N. The triatomic
interstitials interact through terminal carbons specifically with one of the
two boron substructures of alpha-B12 forming 3B1-C-N-C-3B1-like complex.
Further syntheses and experimental characterizations are expected to extend the
field of investigation of such an original class of materials.
