First-principles prediction of metastable niobium and tantalium nitrides M4N5 and M5N6 stoichiometry

A first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the structural, elastic and electronic properties of M4N5 and M5N6 (M = a transition metal (TM) Nb, Ta). C33 elastic constant for all compounds is found to be much larger than C11, indicating that a-axis is more compressible than c-axis. Interestingly, we find that C33 and C11 are significantly larger than other elastic constants, resulting in a pronounced elastic anisotropy.

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