Low-compressibility and hard material carbon nitride imide C2N2(NH): First principles calculations

First principles calculations are performed to investigate the structural, mechanical, and electronic properties of C2N2(NH). Our calculated lattice parameters are in good agreement with the experimental data and previous theoretical values. Orthorhombic C2N2(NH) phase is found to be mechanically stable at an ambient pressure. Based on the calculated bulk modulus and shear modulus of polycrystalline aggregate, C2N2(NH) can be regarded as a potential candidate of ultra-incompressible and hard material. Furthermore, the elastic anisotropy and Debye temperatures are also discussed by investigating the elastic constants and moduli. Density of states and electronic localization function analysis show that the strong C–N covalent bond in CN4 tetrahedron is the main driving force for the high bulk and shear moduli as well as small Poisson's ratio of C2N2(NH).

Graphical abstractContours of electronic localization function (ELF) of C2N2(NH) on the: (0 0 1) plane (a), (1 0 0) plane (b), an ELF of Si2N2(NH) on the: (0 0 1) plane (c) and (1 0 0) plane (d).Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► The structural, mechanical, and electronic properties of C2N2(NH) have been studied. ► C2N2(NH) is a potential low compressible and hard material. ► Both C2N2(NH) and Si2N2(NH) are found to have insulating feature with large band gaps. ► The strong covalent C–N bonding in CN4 tetrahedrons play a key role in the incompressibility and hardness of C2N2(NH). ► The chemical bonding in these two solids is a complex mixture of covalent and ionic characters.