Theoretical investigation of size and shape effects on the melting temperature and energy bandgap of TiO2 nanostructures

In this letter, we report a theoretical investigation concerning the size effect on the melting temperature and energy bandgap of TiO2 nanostructures. Within the thermodynamical approach, we predict a structural phase transition from rutile to anatase for the sizes around 40, 29, and 48 nm, respectively, in the cases of spherical nanoparticles, cylindrical nanowires, and nanotubes. For spherical nanoparticles, this means that the more stable phase is anatase for sizes smaller than ~40 nm and rutile for sizes larger than ~40 nm. The energy bandgap of these structures is also estimated.