First-principles calculations on the mechanical properties of niobium nitrides

We have calculated the mechanical properties of cubic δ -NbN and hexagonal δ ′ -NbN with density functional theory (DFT). It is found that the calculated ideal strength of δ ′ -NbN is higher than that of δ -NbN, which is consistent with the experimental findings. The tensile strength perpendicular to the polar plane in δ ’-NbN is comparable to the weakest bonding direction in diamond, which provides huge potential technological and industrial applications. The electronic origins of mechanical properties are discussed.