Understanding Medium-Range Order of Fused Silica under High Pressure through Simulations

Keywords:
fused silica, high pressure, medium-range order, simulations

Abstract:
Silica glass (SiO2) is a technologically important material used in applications including gas transport, laser optics, fiber optics, vacuum systems (He-sensitive windows), silicates and zeolites. Often this glass undergoes extreme conditions of high pressures and temperatures during service. For instance, fused silica lens undergoes drastic structural changes upon large pressure variations in laser optics components. Predictive models can play a key role in the selection and development of materials for such extreme conditions. Our theoretical work here focuses in the study of the structural changes that occur in this well-known candidate material for optics at high pressures using MD simulations. In particular, we are interested in the changes occurring in the medium-range order (MRO) below 10 nm. MD simulations were performed to study the nature of the densification of fused silica under shock pressures. Our simulations using two different methods reproduce the equation of state (EOS) obtained from flyer plate experiments. The elastic-to-plastic transition in the EOS curve is directly related to structural variations exhibited in the ring size distribution of this glass. The ring distribution stays practically unchanged during the elastic compression. However, at the elastic-plastic transition in the EOS curve this distribution begins to change continuously. Those structural changes observed in these simulations could also result in changes in the optical properties of this material. We have performed ab-initio studies of the absorption of the pristine and the modified material.

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Nanotech 2005 Conference Program Abstract