Short- and medium-range orders in as-quenched and deformed SiO2 glasses: An atomistic study

Using a truncated BKS interatomic potential, we compare the coordination number, ring size distribution and distributions of activation energies in silica glasses of different densities processed with two different routes: either directly quenched from the high temperature melt at different densities, or deformed from an ambient temperature, low density glass through cycles of quasistatic compression-decompression. We find that the coordination number and ring size distribution vary simultaneously in both quenched and deformed glasses and are irreversible in compressed glasses unloaded to zero pressure, but are surprisingly close to reversible (with a hysteresis) when the decompressions are continued back to the initial density. At a given density, the pressure is significantly lower in quenched glasses than in compressed glasses but the coordination number and ring size distribution are unexpectedly similar, showing that their evolution during compression is mostly a steric effect. Also, distributions of activation energies in quenched and deformed glasses are significantly different, with the deformed glasses showing the classical overabundance of low activation energies characteristic of far-from-equilibrium systems. (C) 2015 Elsevier B.V. All rights reserved.