Metal–insulator phase transition in thin films of a nickel-doped vanadium dioxide

The electrical conductivity of thin polycrystalline VNi$_{x}$O$_{2}$ films has been studied in a wide range of temperatures, which covers the regions of both metallic and insulator phase. It is shown that the metal–insulator phase transition temperature decreases as the nickel concentration increases, and the temperature range of coexistence of the phases increases monotonically. The temperature dependence of the conductivity of the insulating VNi$_{x}$O$_{2}$ phase is explained using the hopping conduction model that takes into account the influence of thermal atomic vibrations on the resonance integral. Parameter $\epsilon$ has been calculated as a function of the doping level of VO$_2$.