The dual nature of orthorhombic B2CN: theoretical study of hardness and superconductivity

In this detailed investigation, we utilize density functional theory and evolutionary algorithms to explore the electronic structure properties of orthorhombic B2CN. Our extensive analysis establishes both the mechanical and dynamical stability of the Pmm2-B2CN phase, as evidenced by detailed calculations of elastic constants and phonon dispersion spectra. B2CN exhibits outstanding mechanical properties, featuring notably elevated elastic constants, a substantial bulk modulus, and significant shear rigidity, highlighted by a Vickers hardness of 58 GPa. In addition, we uncover considerable electron–phonon coupling, with a λ value of 0.628. By applying the modified McMillan equation proposed by Allen-Dynes, we predict that orthorhombic B2CN exhibits superconducting properties, with a critical temperature estimated at 26 K. This superconductivity is intimately associated with low- to mid-frequency phonons derived from boron, which exhibit strong coupling to the carbon-2p electronic states near the Fermi level, thus facilitating effective electron pairing.