Role of cobalt doping on the electrical conductivity of ZnO nanoparticles

Cobalt doped zinc oxide (Zn1-xCoxO; x = 0, 0.05, 0.10, 0.15) samples were synthesized using co-precipitation method. The Co doped ZnO nanoparticles showed the maximum solubility limit. The XRD patterns confirm the hexagonal type wurtzite structure without secondary phase in Co substituted ZnO samples. The particle size was studied using transmission electron microscope (TEM) and grain size estimated using scanning electron microscope (SEM). We report the study of temperature dependence of conductivity on ZnO and Co doped ZnO nanoparticles. It is found that at a higher temperature range (above 470 K) thermally activated type of conduction is in dominance with the lower temperature range of conduction in which donor carrier hopping mechanism is dominated. DC conductivity result shows the reduction nature for cobalt doped ZnO. The obtained results are discussed on basis of potential barrier, donor concentration, point defects and adsorption-desorption of oxygen. Cobalt substitution increases resistivity, reduces grain growth, lower particle size and increase in activation energy. Detailed mapping of two regions of electrical conductivity is done to understand the activation energy mechanisms prevailing in cobalt doped ZnO.