Résumé
In order to explore the structural mechanisms responsible for the plastic behavior andpolyamorphism in silica glasses v-SiO2, we have performed Molecular Dynamics (MD)simulations using different approaches. Recently, a Density Functional Tight-Binding(DFTB) (1) study has shown that the structural changes from low- to high-densityamorphous structures in v-SiO2 occur through a sequence of percolation transitions (2).These transitions also explain some of the mechanical properties of v-SiO2.To gain a deeper insight into the properties of the clusters and percolations networks, wehave performed classical MD simulations using a reliable pair potential (3). Due to its lowcomputational load, this method has allowed us to significantly increase the size of thesimulated system and have access to large length scales, from 2.5 to 12.0 nm. Similarpercolation transitions have been identified also for these new models. Generating severalorders of magnitude of cluster sizes allows the extraction of scaling laws associated witheach property of the clusters such as mass, correlation length, order parameter etc... Thescaling of such properties is correlated to the critical exponents or the fractal dimensionalityof the clusters. The collection of these quantities related to the transitions for the differentconnectivities SiO4-SiO4, SiO5-SiO5, SiO6-SiO6 and SiO6-stishovite, leads to thecharacterization of the percolation model, providing compelling evidence for amorphous-amorphous “phase” transitions in compressed silica glasses.