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 TiO2 nanoparticles are investigated for both rutile and anatase phases using a variable-charge interaction potential in which atomic charges vary dynamically 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 distinguishes the two nanospheres with different underlying crystalline structures; the surface diffusion constant of the anatase sphere is almost three times as great as that of the rutile sphere. Variable-charge molecular dynamics simulations are then applied to sintering of two TiO2 nanospheres. It turns out that the enhanced surface diffusion in the anatase nanosphere at high temperatures significantly promotes neck formation between the two spheres. (C) 2000 American Institute of Physics. [S0021-8979(00)08323-7].