Iron behavior during the continuous phase transition of iron-doped titanium dioxide determined via high-temperature in-situ X-ray diffraction, rietveld refinement, and density functional theory studies

Abstract

Titanium dioxide (TiO2) is widely used in various fields, and doped TiO2 exhibits different characteristics in different fields. Although numerous studies of Fe-doped TiO2 have been reported, they mainly analyze the influence of Fe on TiO2. The behavior of Fe during the phase transition of TiO2 has been rarely studied. To explore the continuous behavior of Fe during the phase transition of Fe-doped TiO2, the real-time phase transitions of Fe-doped and pure TiO2 at 300–1000 °C were characterized using high-temperature in-situ X-ray diffraction (XRD). Based on the experimental results, models of Fe-doped TiO2 were established using density functional theory (DFT). By comparing the calculated and refined values of the in-situ XRD data of Fe-doped TiO2 and an analysis of the defect formation energies, the evolution of Fe was as follows: Fe is located at a lattice interstice of anatase with an oxygen vacancy → Fe at a Ti site in anatase with an oxygen vacancy → Fe at a Ti site in rutile with an oxygen vacancy → Fe at a Ti site in rutile without an oxygen vacancy. This study reveals the deep connection between the microscopic properties of Fe and the phase transition of Fe-doped TiO2 and clarifies the states of Fe. It provides a theoretical basis for determining the states of doped atoms during the phase transition of TiO2 and theoretical guidance for research regarding the phase transitions of doped TiO2 systems.