Characterization and first-principles calculations of WO3/TiO2 composite films on titanium prepared by microarc oxidation

The potous WO3/TiO2 composite films were in-situ prepared by microarc oxidation (MAO) process on pure titanium in sodium tungstate electrolyte at different applied voltages. Morphology, phase structure, chemical composition and optical property of films were characterized and the first-principles calculation for analyzing the band structure of films was performed. The results showed that the WO3/TiO2 composite films as n-type material consisted of anatase TiO2, rutile TiO2 and WO3 phases. The composite film at positive voltage of 400 V has lowest electron hole recombination rate. Their flat band potential was in the range of 038 V to 0.86 V, and the doping density value varied between 1.70 x 10(17) cm(-3) and 6.84 x 10(22) cm(-3). The band gap energy of WO3/TiO2 composite films prepared at different applied voltages was 2.49 eV-2.61 eV. The WO3 and defects (the W doping, oxygen vacancy, titanium vacancy) could reduce the gap width between conduction band (CB) and valence band (VB) of anatase or rutile phase in WO3/TiO2 films. That resulted in a red-shift of optical absorption. Furthermore, the WO3/TiO2 composite films could extend the optical absorption threshold and enhance the utilization of solar light. (C) 2017 Elsevier B.V. All rights reserved.