The influence of the mixed phase (Ti-TiO<SUB>2</SUB>(A): TiO<SUB>2</SUB>(R)) on the optical band gap of TiO<SUB>2</SUB> nanotubes heat treated at different temperatures

International audienceHighly ordered TiO2 nanotubes (NTs) were synthesized by electrochemical anodization than annealed at different temperatures between 300 and 900 °C for 3 h. The elaborated NTs adhere well to the Ti substrate over the annealing temperature range of 300-600 °C. The TiO2 NTs morphology begins to gradually evolve for temperatures up to 700 °C and approaches that of nanoparticles until the latter become predominant at T above 800 °C. Reflection measurements show that the NTs present reflection of 7% at 600 °C, corresponding to the lowest band gap 2.59 eV. This can be related to the presence of the mixed phase (Ti-TiO2(A)-TiO2(R)).The charge carrier density decreases from 2.34 × 10+21 to 3.61 × 10+13 cm−3when the annealing temperature increases, that accompanied by a reduction in the resistivity from 142.23 to 29.56Ω.cm which is adequate to photo anode application