Characterization of nano-crystalline Co-La mixed oxide thin films prepared by the spray pyrolysis technique

Abstract

Abstract Nano-crystalline thin films of pure and La-Co mixed oxides were deposited using the spray pyrolysis technique. All deposition parameters were kept constant and the deposition took place at a substrate temperature of 723 K. The structures of all films were evaluated by X-ray diffraction. Films were found to be phase pure Co3O4 with a single diffraction peak for the (3 1 1) plane. By increasing the La/Co ratio the structure was significantly affected and a new phase of cobalt mono-oxide, CoO, was found at La/Co = 0.4. The grain size of all films was found to range from 6.63 to 11.68 nm. Energy dispersive X-ray spectroscopy (EDAX) was used to measure the composition of all films. A perfect ratio transfer from the solution to the solid film was found. The optical transmission and reflection was recorded in the optical spectral range 200–2500 nm. Also the extinction coefficient and absorption coefficients were estimated to determine the transition type. The band gap was found to be constant belonging to the recorded values of Co3O4. Finally the conductivity of the films was recorded using a direct measure of the electrical resistivity with temperature. The activation energy was found to be approximately constant with significant drop at La/Co ratio 0.4.