Optical and structural properties of CdO + CdTiO 3 thin films prepared by sol–gel

Abstract

Undoped thin films of the (CdO) 1− X + (TiO 3) 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 TiO 2 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 CdTiO 3 predominates for X > 0.30. The oxide formed is a mixture of CdO and CdTiO 3. The energy band gap ( E g), measured from PA data, changes abruptly from 2.5 eV to 3.5 eV when X ≅ 0.40, and the maximum E g = 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.