Stable and metastable structures of the multiphase tantalum nitride system

Despite its growing technological importance and potential, the tantalum nitride system is suprisingly still relatively unexplored. Using density functional theory and the all-electron total energy full-potential linearized augmented plane-wave method, we investigate the relative stability of a host of structural phases and their associated electronic properties. Through consideration of the effect of the environment via the individual atom chemical potentials, a phase diagram is obtained. Our calculations indicate that there are three stable phases Ta₅N₆, Ta₂N, and Ta₃N₅---the rest being metastable. The close energies of many structures explains the complexity of this nitride materials system and why the observed structural phases depend very sensitively upon experimental synthesis and growth conditions.