Study of the formation of Co3O4 thin films using sol-gel method

Sol-gel derived coatings containing cobalt have been analyzed using impedance and reflection measurements. It is found that during the thermal treatments in air at temperatures in the range of 35-400degreesC, cobalt migrates to the front surface of the coating where it is oxidized by the atmospheric oxygen and forms a top layer rich in nanocrystalline Co3O4. In samples heated above 260degreesC, the current flows entirely through this top layer because it has higher conductivity than the rest of the coating. For these samples, the impedance spectra show two semicircles, related with the electrical properties of grain and grain boundaries of the cobalt oxide layer. Using the brick model, the grain boundary volume fraction was calculated as a function of the heating temperature. (C) 2003 Elsevier Science Ltd. All rights reserved.