Photoelectrochemical Study of Oxides Thermally Grown on Titanium in Oxygen or Water Vapor Atmospheres

Abstract

Titanium oxide thin scales isothermally grown at on titanium metal in pure oxygen, pure water vapor, or water vapor/oxygen mixtures were submitted to room temperature photoelectrochemical characterization (PEC) to assess the nature of oxides in function of the composition of the oxidizing atmosphere. The results indicated that minor lower valency oxides were present in addition to rutile, of which the bandgap energy was experimentally determined to be . As bandgap energies of and have not been reported in the literature, an empirical model relating bandgap energy and reticular enthalpy was revisited and adapted to the case of oxides. From photoelectrochemical measurements on thermal oxides, new bandgap values of for and for were obtained, correctly matching the empirical model. High sensitivity of the technique was demonstrated as these phases could be identified by PEC on samples grown in oxygen, where classical techniques of characterization like X-ray diffraction could not detect them. They were observed in larger amounts on samples grown in the presence of water vapor, showing closer metal-oxide equilibrium during thermal oxidation.