Oxygen vacancy-induced phase transformations of iron-doped titanium oxide nanostructures

Oxygen vacancies play a pivotal role in tailoring electronic, optical, and catalytic properties of reducible metal oxides. Here, we provide a complete overview of oxygen vacancy-induced structural evolution of iron-doped titanium oxide nanomaterials with insights into their synthesis, formation, and crystallization processes. Structural analysis combining multiple techniques reveals the formation of anatase nanoparticles at low Fe loadings (i.e., ≤ 10 at. % Fe). At intermediate Fe concentrations (i.e., 15-20 at. % Fe), a mixture of anatase and rutile forms with the presence of extended disordered defects similar to crystallographic shear planes. These become more notable at high Fe loadings (i.e., ≥ 30 at. % Fe) with the complete transition to the rutile phase with a high density of defects. Moreover, we provide important information on the nucleation, growth, and crystallization processes during synthesis, highlighting the impact of Fe atoms incorporation on the TiO2 lattice, the formation of reaction intermediates, and the structural evolution at the nano regime. The ability to control oxygen vacancies and engineer defects in Fe-doped TiO2 opens new possibilities for optimizing charge transport, enhancing catalytic activity, and tuning optical properties for applications in environmental remediation, sensing, and next-generation semiconductor technologies.