Phase diagram including size, pressure, and surface functionalization as control parameters. In the absence of functionalization, the anatase structure in nanoparticles will transform to the baddeleyite phase (at least for d > 6 nm). In the case of surface functionalization, the defects’ density will orientate the transformation to an amorphous state for d < 10 nm. Reprinted with permission from Ref. [36], Copyright (2011) by the American Chemical Society.