Effects of Mg2+ doped TiO2 defect structures on TiO2 anatase-to-rutile phase transition

Rutile TiO2 is a competitive white pigment due to its high refractive index and inertness. Uncolored Mg2+ is a promising dopant for the production of TiO2 pigment because it promotes the anatase-to-rutile phase transition of TiO2 at lower temperatures (vs. Al3+). However, research on the impact of Mg2+ concentration on TiO2 phase transition is scarce, and the defect structures are still unknown. In this study, the effect of Mg2+ doping concentration on TiO2 phase transition was investigated, and the defect structures of Mg2+ doped TiO2 were proposed. Over 96% conversion of anatase to rutile was achieved with 1.48% Mg doping at 875 °C (vs. Al3+, 1050 °C) for 1 h. By using the Rietveld method, two defect structures—interstitial Mg2+ (Mgint) and substitute Mg2+ (Mgsub)—were quantified. A correlation between the defect structures and the effect on phase transition was established. At low Mg doping level (<1%), the Mgint dominates and weakly promotes the phase transition; At high Mg doping level (>1%), the Mgsub dominates and strongly promotes the phase transition. Additionally, a possible mechanism for the formation of defect structures and how that affects phase transition was proposed. The present results may provide insights into TiO2 pigment production and modulation of TiO2 defects for phase transition control and other applications.