Phase Transformations during Sintering of Titania Nanoparticles

The size below which anatase nanoparticles become more stable than rutile nanoparticles (crossover diameter) is dependent on the environment of the nanoparticles. It is smaller for nanoparticles in vacuum than those in water and continues to decrease with increase in temperature. Phase transformation between anatase and rutile phases is facilitated by enhanced ionic mobility at temperatures near the melting point of the nanoparticles. Multiparticle multiphase molecular dynamics simulations of TiO₂ nanoparticles undergoing sintering-induced phase transformations are reported here. Over the time scales accessible to molecular dynamics simulations, we found that the final sintering agglomerate transformed to the rutile phase, provided one of the sintering nanoparticles was rutile, while sintering of anatase and amorphous nanoparticles resulted in a brookite agglomerate. No such phase transformations were observed at temperatures away from nanoparticle's melting temperatures.