Structural, electronic and optical properties of nano-structural BNC₃ alloys

Fundamental properties of a hypothetical BNC₃ nano-alloy comprised of covalently linked tetrahedral “B–N–C₃″ units are studied using density functional theory. In analogy with the recently synthesized “silicon-like” AlPSi₃ the BNC₃ alloy adopts a near-cubic symmetry with lattice parameter slightly larger (∼1%) than that of diamond, and bulk modulus slightly larger than that of c-BN but smaller than that of diamond. The compound is predicted to be stable relative to its elemental constituents, but metastable relative to disproportionation into cubic BN and carbon (diamond). Orientationally disordering the “B–N–C₃″ slightly increases the energy while the corresponding random alloy is found to be significantly less stable. The direct/indirect band gaps of ordered BNC₃ are found to be 6.38 and 4.72 eV–5% and 8% smaller in diamond, respectively, leading to a moderate increase in the absorption coefficient over the 6–10 eV range, and a ∼0.4 eV red shift in the absorption edge compared with diamond. Infrared and Raman spectra calculated using density functional perturbation theory exhibit rich vibrational structure compared to diamond.