Preparation and characterization of the semiconductor CuMnO2 by sol-gel route

Nano crystallites of the crednerite CuMnO2 are prepared by sol-gel method with two-step annealing process. The powder heated at 450 °C under air flow shows a mixture of CuO, Mn2O3 and CuxMn3−xO4. However, when calcined at 900 °C under N2 atmosphere, the crednerite CuMnO2 with a monoclinic structure (space group: C2/m) is obtained. The Raman spectrum shows a single peak at 679 cm−1 assigned to A1g mode whereas the infrared analysis confirms the linearity of CuO23− units. The optical transition at 1.70 eV, determined from the diffuse reflectance is attributed to the inter-band d-d transition of Cu+ ion. The oxide exhibits semiconducting properties with an activation energy of 0.21 eV. The photo-electrochemical measurement shows p-type conduction due to O2− insertion in the two dimensional lattice. The flat band potential (+0.12 VSCE), indicates a cationic character of both valence and conduction bands deriving from Cu+: 3d orbital.