Unravelling the Impact of Ta Doping on the Electronic and Structural Properties of Titania: A Combined Theoretical and Experimental Approach

Abstract

The introduction of new energy levels in the forbidden band through the doping of metal ions is an effective strategy to improve the thermal stability of TiO 2 . In the present study, the impact of Ta doping on the anatase to rutile transition, structural characteristics, and anion and cation vacancy formation were investigated in detail using density functional theory and experimental characterization, including X-ray diffraction, Raman, Brunauer−Emmett−Teller surface area, UV−vis diffuse reflectance spectroscopy, high-resolution transmission electron spectroscopy, and X-ray photoelectron spectroscopy. The average crystallite size of TiO 2 decreases with an increase in the Ta concentration. At high temperatures, more oxygen atoms enter the crystal lattice and occupy the vacancies, leading to lattice expansion. Importantly, we find that Ta doping preserved the anatase content of TiO 2 up to annealing temperatures of 850 °C which allows anatase stability to be maintained at typical ceramic processing temperatures. The substitution of Ti 4+ by the Ta 5+ ions increased the electron concentration in the crystal lattice through formation of Ti 3+ defect states. Raman studies revealed the formation of new Ta bonds via disturbing the Ti−O−Ti bonds in the crystal lattice. It is concluded that under the oxidizing conditions the Ta 5+ ions could be enhanced on the Ta−TiO 2 surface due to slow diffusion kinetics.

First principles study of the electronic and optical properties of high‐valence transition metal‐doped anatase titanium dioxide

“…Density functional theory calculation is a powerful and fundamental tool to reveal the internal mechanism of photoelectric behavior of semiconductor materials. Over the years, a good deal of work has been done to study the effect of transition metals on anatase titanium dioxide by first-principles density functional theory [25][26][27][28][29][30][31][32]. However, no systematic research and explanation on electron transport mechanism of niobium, tantalum, tungsten, and molybdenum-doped anatase titanium dioxide have been presented.…”