Role of aluminum doping on phase transformations in nanoporous titania anodic oxides

The role of aluminium doping on anatase to rutile phase transformation of nanoporous titanium oxide films were investigated. For this purpose pure and aluminum doped metal films were deposited on alumina substrates by cathodic arc physical deposition. The nanoporous anodic oxides were prepared by porous anodizing of pure and aluminum doped titanium metallic films in an ethylene glycol + NH₄F based electrolyte. Nanoporous amorphous structures with 60–80 nm diameter and 2–4 μm length were formed on the surfaces of alumina substrates. The amorphous undoped and Al-doped TiO₂ anodic oxides were heat-treated at different temperatures in the range of 280–720 °C for the investigation of their crystallization behavior. The combined effects of nanoporous structure and Al doping on crystallization behavior of titania were investigated using X-ray diffraction (XRD) and micro Raman analysis. The results indicated that both Al ions incorporated into the TiO₂ structure and the nanoporous structure retarded the rutile formation. It was also revealed that presence or absence of metallic film underneath the nanopores has a major contribution to anatase-rutile transformation. - Highlights: • Al-doped TiO₂ nanopores were grown on alumina substrates using anodization method. • The crystallization behavior of nanoporous Al-doped TiO₂ were investigated. • Al doping into nanoporous TiO₂ retarded the anatase-rutile transformation. • Nanostructuring has significant role in controlling rutile formation temperature. • The absence of the metallic film under the nanopores delayed the rutile formation