Theoretical study on stability, mechanical properties and thermodynamic parameters of the orthorhombic-A _2N _2O (A=C, Si and Ge)

摘要

The structural stability, mechanical properties and thermodynamic parameters such as Debye temperature, minimum thermal conductivities of orthorhombic-A _2N _2O (A=C, Si and Ge) are calculated by first principles calculations based on density functional theory. The calculated lattice parameters, elastic constants of Si _2N _2O and Ge _2N _2O using PBEsol function are consisted with the experimental data and other calculated values. The full set elastic constants of the orthorhombic-A _2N _2O (A=C, Si and Ge) are calculated by stress-strain method. The mechanical moduli (bulk modulus, shear modulus and Youngs modulus) are evaluated by the Voigt-Reuss-Hill approach. The orthorhombic-C _2N _2O exhibits larger mechanical moduli than the other two structures. The hardness of orthorhombic-A _2N _2O (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-C _2N _2O is a super hard material. Furthermore, the mechanical anisotropy, Debye temperature and minimum thermal conductivity of the orthorhombic-A _2N _2O (A=C, Si and Ge) have been estimated by empirical methods. The orthorhombic-Ge _2N _2O shows the lowest thermal conductivity, which may have useful applications as gas turbine engines and diesel engines.