The glass transition and thermodynamics of liquid and amorphous TiO(2) nanoparticles

The glass transition and thermodynamics of spherical liquid TiO(2) nanoparticles, with different sizes ranging from 2 to 5 nm, have been studied in a model under non-periodic boundary conditions. We use the pairwise interatomic potentials proposed by Matsui and Akaogi. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. The structural properties of liquid nanoparticles at 3500 K have been analyzed in detail through the partial radial distribution functions (PRDFs), coordination number distributions, bond-angle distributions and interatomic distances. Moreover, we also show the radial density profile in nanoparticles. Calculations show that size effects on the structure of a model are significant and that liquid TiO(2) nanoparticles have a distorted pentahedral network structure with the mean coordination numbers Z(Ti-O)≈5.0 and Z(O-Ti)≈2.5, while amorphous TiO(2) nanoparticles have an octahedral network structure. The temperature dependence of the surface structure and surface energy of the nanoparticles has been obtained and is presented. In addition, the size dependence of the glass transition temperature and the temperature dependence of the diffusion constant of atomic species have been found and are discussed.