Optical and structural properties of CdO + CdTiO3 thin films prepared by sol–gel

Undoped thin films of the (CdO)1−X + (TiO3)X system were prepared on glass substrates using the sol–gel technique. The precursor solution was obtained starting from the mixture of two precursor solutions for CdO and TiO2 prepared separately. The Ti and Cd atomic concentrations in the precursor solution, X and (1 − X), respectively, were varied in the range 0.20 ≤ X ≤ 0.65. The films were sinterized at 450 °C in open atmosphere. X-ray diffraction, photoacoustic (PA) and Raman spectroscopies, atomic force microscopy, optical absorption and reflectivity, both in the intermediate infrared region, and dark resistivity (ρ) measurements were carried out for characterization. The films present predominantly the monteponite cubic phase of CdO for X ≤ 0.30. The ilmenite rhombohedrical crystalline phase of CdTiO3 predominates for X > 0.30. The oxide formed is a mixture of CdO and CdTiO3. The energy band gap (Eg), measured from PA data, changes abruptly from 2.5 eV to 3.5 eV when X ≅ 0.40, and the maximum Eg = 3.70 eV was observed when X = 0.55. ρ also experiences a steep variation of eight orders of magnitude when X ∼ 0.40. The photocatalytic activity was found to be maximum for X = 0.40. The resultant oxide displays some physical properties different of a simple mixture of materials.