Impurity Conduction in Ti-Doped VO2 Studied by Microwave Frequency Conductivity

The d c and 24 GHz conductivities of VO 2 containing various amounts of Ti have been measured below the semiconductor-to-metal transition point. Above 290 K the activation energy for d c conductivity is not affected by the small amounts of Ti impurity and the 24 GHz conductivity coincides with the d c conductivity. The pronounced frequency dispersion of conductivity is observed at low temperature, where the impurity conduction arises from hopping motion of electrons between impurity sites. The 24 GHz conductivity can be explained as a function of temperature by the formula expressing the dielectric loss due to the hopping diffusion of electrons between pair centers given by Pollak.