“…Oxynitrides, such as δ-Nb(O,N) and ε-Nb(O,N), have been also reported and their structures are similar to the corresponding nitrides [13,14]. All of the known niobium nitride/oxynitride superconductors are most likely of Bardeen-Cooper-Schrieffer (BCS) type, as already established for the δ-NbN phase [15,16].…”