Beyond VN: Multifunctional Tetragonal VN₂ as a Promising Ultrahard Coating and Ultraviolet-Visible Photonic Material

We conducted a comprehensive first-principles investigation of the electronic structure, photoresponse, mechanical, and thermodynamic characteristics of the newly synthesized compound tetragonal-VN₂ using density functional theory. The calculated lattice parameters closely align with both experimental and theoretical data. Electronic structure analysis reveals that VN₂ exhibits metallic conductivity, with significant hybridization between V-3d and N-2p states, indicating strong covalent bonding. VN₂ demonstrates isotropic optical properties, with a high static dielectric constant (56.9), notable reflectivity (59% at 0 eV), and significant absorption in the ultraviolet-visible range. It is mechanically stable, exhibits a degree of elastic anisotropy, and possesses a brittle nature. VN₂ has a Vickers hardness of 26.2 GPa, approximately three times greater than that of VN, suggesting that it is suitable for use in wear-resistant coatings and cutting tools. From a thermodynamic perspective, VN₂ is characterized by a high Debye temperature (1023.5 K) and significant lattice thermal conductivity (59.8 W·m^{- 1}·K^{- 1}). Its melting temperature, which exceeds 3177 K, distinguishes it as a promising candidate for applications that require extreme temperatures. These findings establish a strong foundation for the future applications of VN₂ in advanced materials science, particularly in high-performance coatings and photonic devices.