Universal temperature corrections to the conductivity of niobium-carbon nanocomposites

The evolution of wide-temperature range (4.2–300 K) electron transport in niobium-carbon nanocomposites was studied at niobium concentration range 0.15–0.35. It was found that electron transport in the nanocomposites has the features of universality, being expressed in the existence of two characteristic temperature intervals on the temperature dependences of conductivity. The crossover temperature between the intervals is in the range 20–30 K. Within each temperature interval, corrections to the conductivity are found to be as power-like ones. Power exponent p is characterized by the non-monotonic dependences on niobium concentration and varies in the ranges 0.5–1.4 and 0.2–1.4 in the low- and high-temperature intervals with a minimum at 0.30 and 0.27 of Nb content, respectively. The satisfactory description of electron transport in niobium-carbon nanocomposites was achieved within the model of the inelastic tunneling of the electrons between the metal grains in the framework of the effective medium approximation.