First-principles calculations on the mechanical properties of niobium nitrides

We have calculated the mechanical properties of cubic delta-NbN and hexagonal delta'-NbN with density functional theory (DFT). It is found that the calculated ideal strength of delta'-NbN is higher than that of delta-NbN, which is consistent with the experimental findings. The tensile strength perpendicular to the polar plane in delta'-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. (C) 2009 Elsevier Ltd. All rights reserved.