Theoretical study on stability, mechanical properties and thermodynamic parameters of the orthorhombic-A2N2O (A=C, Si and Ge)

The structural stability, mechanical properties and thermodynamic parameters such as Debye temperature, minimum thermal conductivities of orthorhombic-A2N2O (A=C, Si and Ge) are calculated by first principles calculations based on density functional theory. The calculated lattice parameters, elastic constants of Si2N2O and Ge2N2O using PBEsol function are consisted with the experimental data and other calculated values. The full set elastic constants of the orthorhombic-A2N2O (A=C, Si and Ge) are calculated by stress-strain method. The mechanical moduli (bulk modulus, shear modulus and Young's modulus) are evaluated by the Voigt-Reuss-Hill approach. The orthorhombic-C2N2O exhibits larger mechanical moduli than the other two structures. The hardness of orthorhombic-A2N2O (A=C, Si and Ge) is evaluated according to the intrinsic hardness calculation theory of covalent crystal relying on Mulliken overlap population. The results indicate that the orthorhombic-C2N2O is a super hard material. Furthermore, the mechanical anisotropy, Debye temperature and minimum thermal conductivity of the orthorhombic-A2N2O (A=C, Si and Ge) have been estimated by empirical methods. The orthorhombic-Ge2N2O shows the lowest thermal conductivity, which may have useful applications as gas turbine engines and diesel engines.