Trans-Regime Structural Transition of (In3+ + Nb5+) Co-Doped Anatase TiO2 Nanocrystals under High Pressure

Abstract

Chemical co-doping and high pressure reactions have been broadly used to synthesize novel materials or to tune the physicochemical properties of traditional materials. Here, we take In3+ and Nb5+ ions co-doped anatase TiO2 nanocrystals as an example and report that a combination of both a chemical and a high pressure reaction route is more powerful for the preparation of metastable polymorphs. It is experimentally demonstrated that In3+ and Nb5+ co-doping significantly changes the high-pressure reaction behaviors of anatase TiO2 nanocrystals (<10 nm) and leads to their trans-regime structural transition in terms of in situ Raman analysis, from an anatase to a baddeleyite-like phase under compressive pressures and then to an α-PbO2-like structure under decompressive pressures. This abnormal phase transition is attributed to a defect-induced heterogeneous nucleation mechanism. Furthermore, the stiffness of co-doped TiO2 nanocrystals is significantly enhanced due to the synergistic effects of co-dopants. This research not only proposes a potentially effective strategy to synthesize co-doped metastable polymorphic phases but also suggests one feasible method to improve the mechanical properties of anatase TiO2 nanocrystals. Show more