Crystal structure and superconductive characteristics of Nb sub(0.89)Al sub(0.11) oxynitrides

The crystal structure and superconductive characteristics of the niobium-aluminum oxynitrides were investigated. Single-phase products were successfully obtained starting from a cation ratio of Nb sub(0.89)Al sub(0.11). The as-nitrided product crystallized in a cation-deficient rock-salt type structure with a chemical formula of (Nb sub(0.60)Al sub(0.08) sub(0) sub(.32))(O sub(0.21)N sub(0.79)), while annealing at 1773 K under a nitrogen pressure of 0.5 MPa led to a highly crystallized product with a simple rock-salt type structure represented as (Nb sub(0.89)Al sub(0.11))(O sub(0.17)N sub(0.85)). Upon post-annealing, both the critical temperature (T sub(c)) and the superconductive volume fraction (V sub(SC)) of the oxynitride were significantly enhanced from T sub(c)[asymptotic to]7 K and V sub(SC)=23% for the as-nitrided product to T sub(c)=17.3 K and V sub(SC)=91% for the post-annealed product.