THIN-FILMS OF LITHIUM COBALT OXIDE

Thin films of lithium cobalt oxide have been prepared by rf sputtering from crystalline LiCoO2. Chemical analysis shows that the films as deposited are deficient in lithium. X-ray diffraction suggests that the films retain the basic rhombohedral structure of LiCoO2. A plausible structure defect model for these lithium deficient films is that of a disordered alpha-NaFeO2 structure. Little absorption and moderate reflectivity are found in the transmission and reflectance spectra in the infrared range- The visible absorption corresponds to a direct allowed optical transition with an energy gap of 2.2 eV. Electrical conductivity measurements of the films show that at 300 K the films behave as semiconductors, with an activation energy of 0. 12 eV. Ionic conductivity does not contribute significantly to the measured conductivity. Thermopower measurements indicate that the films are p-type conductors and suggest a narrow conduction band.