Electrical conductivity of NbN–SiO2 films obtained by ammonolysis of Nb2O5–SiO2 sol–gel derived coatings

The studies of electrical conductivity of NbN–SiO2 films are reported. To obtain these films, sol–gel derived xNb2O5–(100 − x)SiO2 (where x = 100, 90, 80, 70, 60, 50 mol%) coatings were nitrided at 1200 °C. The nitridation process leads to the formation of some disordered structures, with NbN metallic grains dispersed in insulating SiO2 matrix. The structure of the samples was studied using X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical conductivity was measured with the conventional four-terminal method in the temperature range from 5 to 280 K. The superconducting transition was not observed even for the sample that does not contain silica. All the samples exhibit negative temperature coefficient of resistivity. The results of conductivity versus temperature may be described on the grounds of a model proposed for a weakly disordered system.