Effect of Co Doping on the Functional Properties of MnO2 Thin Films

Thin films of Co-doped alpha-MnO2 have been deposited on Pyrex glass substrates by the sol-gel dip-coating method with Co concentrations of 1, 3, 5 and 7 at.%. The deposited thin films were characterized for their structural, morphological, optical and electrical properties. The XRD spectra confirm that all the samples have tetragonal phase of alpha-MnO2. FTIR spectra reveal the presence of Mn-O in all of the samples. AFM measurements indicate that the surfaces of films have been affected with cobalt content incorporation. Transmittance spectra of the undoped and Co-doped MnO2 thin films were recorded by a UV-vis spectrometer. Optical gap was found to be in the 2.60-2.51-eV scale. This decrease is due to the presence of manganese vacancies and/or oxygen defects. From the complex impedance measurements that show semicircular arcs at different cobalt contents, an equivalent parallel RPCP electrical circuit has been proposed.