First‐Principles Electronic Structure, Chemical Bonding, and High‐Pressure Phase Prediction of the Oxynitrides of Vanadium, Niobium, and Tantalum

The oxynitrides of vanadium, niobium and tantalum were investigated by density‐functional theory (LDA & GGA; plane waves & muffin – tin orbitals; pseudopotentials & all‐electron approaches). We propose a high‐pressure synthesis of stoichiometric VON beyond 12 GPa, and the unknown phase is predicted to be a small band‐gap semiconductor. Its structure is of the baddeleyite type which is also adapted by the higher homologues, TaON and NbON, at ambient pressure. Further, the high‐pressure phases of NbON and TaON were studied and phase transitions into the cotunnite type are predicted to occur at approximately 27 and 31 GPa, respectively. Electronic‐structure calculations on these high‐pressure phases show that TaON is a small band‐gap semiconductor whereas NbON appears to be a metallic conductor.