Superconducting properties and electrical resistivities of NbN thin films have been studied as a function of sputtering parameters, film structure, and composition. A good correlation exists between superconducting Tc's and film structure and composition regardless of the sputtering conditions used to achieve this structure. The most important parameters affecting Tc are lattice parameter, crystal structure, island structure, and impurity content. Substrate temperature, Ar/N2 ratio, and impurity content are the principal sputtering parameters affecting film structure, and thus Tc.

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Superconducting critical fields, current densities and temperatures have been measured as a function of composition in the Nb–Ti–N, Nb–Hf–N and Nb–V–N ternary systems. In the Nb–Ti–N system the upper critical fields increase sharply and monotonically with increasing NbN concentration to over 130 kOe at about 90 mole % NbN. In the Nb–Hf–N system the highest upper critical-field value observed was 130 kOe for the composition Nb0.92Hf0.08N. In the Nb–Hf–N system the Tc increases monotonically with NbN concentration, in the Nb–Ti–N system a maximum in Tc exists at about 65 mole % NbN and in the Nb–V–N system a broad minimum exists between 30 and 50 mole % VN.

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