First-principle studies of the stability, electronic and elastic properties of trigonal-type M2N (M=Cr, V, Nb and Ta)

Starting from theoretical calculations based on the generalized gradient approximation (GGA), we compute the lattice parameters, cohesive energy and formation enthalpy of trigonal-type M2N (M=Cr, V, Nb and Ta) compounds by first principles. The cohesive energy and formation enthalpy of these compounds show that these compounds are thermodynamically stable. The electronic structure indicates that the bonds of M2N (M=Cr, V, Nb and Ta) have the characteristic of covalent and metallic bonds, and then Ta2N is the most stable in the projected metal nitrides in our work. The values of bulk modulus, shear modulus, Youngʹs modulus and Poissonʹs ratio indicate M2N compounds are brittle and metallic character. The figures of anisotropy in Youngʹs modulus of M2N (M=Cr, V, Nb and Ta) compounds investigate that these nitrides have the strong anisotropy character in Youngʹs modulus at the (100) plane.