The reported concentration corresponds to 0.08 atom % Nb of the Ti + Nb. The TiO 2 hydrates that were the basis for the anatase and rutile materials used in this work both contained Nb at the level of 0.13% “Nb 2O 5” (see Table 1, taken from ref (3)) this oxide represents the conventional method to convey elemental concentrations and does not mean the oxide must be in this form. The beam size at the sample was about 1.5 × 0.4 mm ( H × V). Reference standards were Nb foil as well as 0.02% NbO 2 (Aldrich) and Nb 2O 5 (Aldrich) both diluted to 0.02% in boric acid and loaded into 1 mm thick sample holders. No signs of radiation damage were detected from repeat scans, permitting multiple scans to be summed in order to improve signal-to-noise. The photon flux at the sample was around 10 10 photons s –1. The energy scale was calibrated by simultaneously measuring a Nb foil placed between the two downstream ion chambers. In the EXAFS range, k-steps of 0.035 Å –1 (up to 5 s/step) were used. Energy steps of 10 eV pre-edge and 0.35 eV across the edge (1 s/step) were used. The samples were held in a He-cooled cryostat ( T < 20 K). Spectra across the Nb K-edge ( E 0 = 18,985.6 eV (25)) were recorded in the fluorescence mode with a 100-element detector (Canberra). Samples were finely ground with a mortar and pestle and pressed into pellets. X-ray absorption spectroscopy (XAS) was performed at the wiggler XAS beamline at the Australian Synchrotron. Production of Nb-doped TiO 2 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. Hydrolysis of Ti and Nb from acid solution, followed by calcination, leads to a well dispersed doped material, with no segregation of Nb. EXAFS for Nb demonstrates that Nb occupies a Ti site in TiO 2 with no near neighbors of Nb. XANES shows clear structural differences between Nb-doped anatase and rutile. 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 TiO 2. Here, we investigate the structure of Nb doped in anatase and rutile produced from ilmenite digested in hydrochloric acid. When TiO 2 is precipitated from HCl solutions containing minor Nb, the Nb in solution is quantitatively deposited with the TiO 2. Niobium doping of TiO 2 creates a conductive material with many new energy applications.
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