Chemical Synthesis and High-Pressure Reaction of Nb⁵⁺Monodoped Rutile TiO₂Nanocrystals

Identifying the doping effects of extrinsic ions both during chemical reactions and in resultant products is important to deeply understand the associated material properties and to develop novel materials for practical applications. Here, we experimentally demonstrate the significant inhibitor effect of Nb5+ dopants on the formation of rutile TiO2 nanocrystals through dopant concentration-modified solvothermal reaction processes. A lower Nb5+ doping level (≤9.09 atom %) is found to be more beneficial for the nucleation and growth of rutile Ti1-2x4+Tix3+Nbx5+O2 nanocrystals while a higher one (>9.09 at.%) leads to the preferable formation of the anatase phase. At a pressure range of up to 30 GPa, the synthesized Nb5+ monodoped rutile TiO2 nanocrystals almost possess an equal slope in their respective plot of the pressure-dependent Raman frequency shifts and a similar structural transformation from rutile to baddeleyite-like (pressurization) and then to an α-PbO2-like phase (depressurization). They thus present a dopant concentration-independent high-pressure reaction behavior due to a small change in their average and local defect structures evidenced by the bond valence sum analysis and density functional theory calculations. This work not only emphasizes the key roles of dopants in material synthesis but also broadens insights into the intrinsic correlations between material properties and their specific local defects.