Kinetic Study on the Crystal Transformation of Fe-Doped TiO₂ via In Situ High-Temperature X-ray Diffraction and Transmission Electron Microscopy

Abstract

Titanium dioxide (TiO2) is widely used in various major industries owing to its different crystal forms and functions. Therefore, fabricating suitable crystalline TiO2 through reasonable processes is necessary. In this study, Fe-doped TiO2 precursors were prepared via hydrolysis. Further, in situ high-temperature X-ray diffraction and transmission electron microscopy were used to transform the synthesized precursor in its crystal form. The Rietveld full-spectrum fitting method could accurately yield two different crystal forms at instant temperatures. Additionally, the rate relation between the crystal form transformation and reaction conditions was obtained. Results showed that the addition of Fe increased the temperature of phase transition of TiO2 anatase to rutile and accelerated the anatase → rutile transformation process. Further, crystal phase transition kinetic analysis showed that the phase transition kinetic model of Fe-doped TiO2 matched the Johnson–Mehl–Avrami–Kohnogorov (JMAK) model and that its phase transition was affected by crystal defects. Finally, Fe3+ in Fe-doped TiO2 was reduced to Fe2+ to generate oxygen vacancies, thus promoting the rate of transformation from titanium ore to rutile.

Phase transition of individual anatase TiO2 microcrystals with large percentage of (001) facets: a Raman mapping and SEM study

“…72 Zhang et al recently reported that pure TiO 2 powder matches the first-order model. 72 Other models have been adopted to describe the ART process for the anatase powders. 39,44,73,74 A model based on a uniform spherical inward growth of spherical particles follows .…”

New Insights into Crystal Defects, Oxygen Vacancies, and Phase Transition of Ir-TiO2

“…The rutile phase is augmented by the Ir dopant, which favors the formation of oxygen vacancies in the crystal lattice. Moreover, the XRD results clearly demonstrated that the Ir doping promotes the rutile formation at low calcination temperatures, through decreasing the activation energy for the ART …”

“…The broadening of Raman modes for the samples with high Ir % demonstrates the increase in anharmonicity with the cell volume . The low-temperature rutile formation indicates that the activation energy of Ir-TiO 2 samples for phase transition is lower than that of pure TiO 2 . The substitution of the Ir dopant in the TiO 2 crystal lattice or TiO 6 2– octahedra could lead to the d–d electronic transition .…”

“…The grain size of TiO 2 is less than 10 nm at 400 °C. Then, the crystalline phases started to grow through the reduction of Ti–OH groups at high temperatures . Theoretically, an average crystallite size of 14 nm is required for the ART .…”

Combined Experimental and Simulation Studies of Lithium and Cobalt‐Modified TiO2 and Their Impacts on the Performance and Stability of Perovskite Solar Cells

“…This could be explained by the fact that if (any) dopant substitutes TiO 2 in a bulk, it affects the presence of oxygen vacancies, lowering the temperature needed for the transformation from the anatase to rutile phase. [23][24][25] The (101) diffraction peak position was slightly shifted (≈0.04°) toward a lower angle, which might imply substitution of the larger ionic cations of both Li and Co at the Ti site and/or lattice distortion (see the inset plot of Figure 1d). Photographs of the TiO 2 powder with and without Li/Co treatment after annealing at 500 and 1000 °C are depicted in Figure S1 of the Supporting Information.…”