Dynamical heterogeneity and diffusion in high-density Al2O3·2SiO2 melts

Dynamical heterogeneity (DH) in high-density Al2O3·2SiO2 melts has been studied in a model containing 3025 atoms via molecular dynamics (MD) simulation and at the fixed density of 4.0 g/cm3. Non-Gaussian parameter of atomic species in the system has been found and discussed. We found a clear evidence of the existence of DH in high-density Al2O3·2SiO2, which has specific features differed from those observed in the lower-density one. The most mobile and immobile atoms in the system have a tendency to form clusters and temperature dependence of their mean cluster size was found. On the other hand, diffusion constant of atomic species in the system has been calculated at temperatures ranged from 3150 to 7000 K. Calculations show that at relatively not high temperatures, temperature dependence of diffusion constant shows an Arrhenius law and at higher temperatures it shows a power law: D∝(T−TC)γ. Diffusion data of high-density melts have been compared with those for the low-density ones. Diffusion mechanism in the system has been discussed via the temperature dependence of diffusion constant ratio and activation energy. And we found the existence of cooperative diffusion mechanism in the system.