Cobalt doped zinc oxide (Zn 1-x Co x O; x = 0, 0.05, 0.10, 0.15) samples were synthesized using coprecipitation 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.

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Weak ferromagnetic behaviour was obtained in a systematic way at room temperature by doping of where x = 0.00, 0.05, 0.15 and 0.20). The obtained results were correlated with conductivity and impedance studies. Diamagnetic to ferromagnetic change was observed with increased concentration of nickel. X-ray diffraction analysis confirmed wurtzite ZnO structure of prepared nanopowders while microstrain was increased with nickel concentration. Incorporation of nickel in ZnO structure was confirmed using EDAX analysis, while FTIR spectroscopy provided further information on functional groups. Transmission electron microscopy images showed that the particle sizes are in the range of 12-20 nm, and scanning electron microscopy analyses that grain size decreases with increase in nickel concentration. Photo luminescence studies confirmed the presence of V O and Zn i defects in the prepared samples. It was concluded that the defect induced strain, grain boundaries and lower particle sizes are the reasons for weak ferromagnetic behaviour of the investigated samples.

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The most extensively explored gas sensors are metal oxide semiconductor materials owing to their high selectivity, stability and cost-effective, simple synthesis technique. Despite these characteristics, they can operate at low...