Role of atomic charge transfer on sintering of TiO2 nanoparticles: Variable-charge molecular dynamics

The stability of surface structure and space-charge distribution in free Ti O2 nanoparticles are investigated for both rutile and anatase phases using a variable-charge interaction potential in which atomic charges vary dynami cally depending on their environment. We find the dynamic charge transfer: (i) enhances atomic diffusion at surfaces of the spherical nanoparticles at high temperatures; and (ii) creates additional repulsive force between the two nanospheres through formation of a double-charge surface layer in each nanosphere. The surface diffusion due to the charge transfer clearly disti nguishes the two nanospheres with different underlying crystalline structur es; the surface diffusion constant of the anatase sphere is almost three ti mes as great as that of the rutile sphere. Variable-charge molecular dynami cs simulations are then applied to sintering of two TiO2 nanospheres. It tu rns out that the enhanced surface diffusion in the anatase nanosphere at hi gh temperatures significantly promotes neck formation between the two spher es. (C) 2000 American Institute of Physics. [S0021-8979(00)08323-7].