Niobium K-Edge X-ray Absorption Spectroscopy of Doped TiO₂ Produced from Ilmenite Digested in Hydrochloric Acid

Niobium doping of TiO₂ creates a conductive material with many new energy applications. When TiO₂ is precipitated from HCl solutions containing minor Nb, the Nb in solution is quantitatively deposited with the TiO₂. Here, we investigate the structure of Nb doped in anatase and rutile produced from ilmenite digested in hydrochloric acid. Nb K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) are used to characterize the environment of 0.08 atom % Nb doped in TiO₂. XANES shows clear structural differences between Nb-doped anatase and rutile. EXAFS for Nb demonstrates that Nb occupies a Ti site in TiO₂ with no near neighbors of Nb. Hydrolysis of Ti and Nb from acid solution, followed by calcination, leads to a well dispersed doped material, with no segregation of Nb. Production of Nb-doped TiO₂ by this method may be able to supply future demand for large quantities of the material and in energy applications where a low cost of production, from readily available natural resources, would be highly desirable.