FRACTON EXCITATION AND LEVY FLIGHT DYNAMICS IN ALKALI SILICATE-GLASSES

We have examined the relaxation behavior of alkali metal ions in lithi um metasilicate glasses by means of molecular dynamics simulation. We have observed a change of slope of the mean squared displacement at si milar to 300 ps. In shorter time regions, localized motion of lithium ions within neighboring sites is observed, which is caused by the smal l fracton dimension (fracton excitation). On the other hand, an accele rated motion of particles due to cooperative jumps is found, which cha racterizes the diffusion and conduction mechanisms of the alkali metal ions in longer time regions. The dynamics of accelerated motion is di scussed in relation to Levy flight dynamics.