Variable range hopping conduction and microstructure properties of semiconducting Co-doped TiO2

The surface morphology, phases existing in the microstructure and conductivity behavior of Co-doped TiO2 have been investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), electrical conductivity measurements and X-ray diffraction technique. The semiconducting phase is found to obey Mott's variable range hopping mechanism of the conduction. The conduction mechanism of the ceramic shows a crossover from the, exp[-(T0/T)1/4] law to a simply activated law, exp(-ΔE/kT). This behavior is attributed to temperature-induced transition from 3D to thermally activated behavior. The hopping conduction parameters such as the characteristic temperature (T0), localization length (α), hopping distance (R), activation energy (ΔE) and density of states at Fermi level (N(EF) have been calculated. Surface morphology shows that the ceramic has a regular surface. The SEM study indicates that there are grains which have a certain type in the microstructure. Rutile phases with different plane in microstructure were found.