Nickel oxide and cobalt oxide may crystallize in a rock salt structure or a spinel structure depending upon the heating temperatures. A rock-salt solid solution is usually observed at temperature higher than 500°C. On the other hand, the spinel structure is preferred at lower temperature. The Ni/Co oxide spinel tends to adopt the inverse-spinel arrangement with the tetrahedral sites completely occupied by Co⁺³ since the ionic radius of Ni⁺² is much larger than that of Co⁺³. In this study, Ni/Co oxide spinel nanopowder was obtained by wet-chemical method. The crystal structure and morphology of Ni/Co oxide powders were examined using XRD and TEM.

NiCo₂O₄ spinel may be used as a bifunctional catalyst for oxygen evolution and reduction reaction as electrode in both inorganic and organic electrosyntheses. Recently, NiCo₂O₄ spinel was found to be an infrared transparent conducting material with potential for solar or photoelectrochemical cell applications. For these applications, NiCo₂O₄obtained in thin film form is preferred.

By using rf magnetron sputtering technique, a NiCo₂O₄ solid film was deposited on a glass substrate from a sintered oxide target with the same composition. With annealing at adequate temperature, a thin film of nickel-cobalt oxides showing spinel structure was obtained. The electrical property of spinel film was measured using 4-probe technique. A resistivity as low as 10^-2~10^-1ohm/cm was obtained. The optical property of this spinel was also measured as a function of thickness/deposition time in the wavelength range of infrared radiation. The morphology and nano/microstructure of deposited and annealed films were examined using high resolution SEM.