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Modeling Amorphization of Tetrahedral Structures Using Local Approaches
Published online by Cambridge University Press: 15 February 2011
Abstract
Many crystalline ceramics can be topologically disordered (amorphized) by disordering radiation events involving high-energy collision cascades or (in some cases) successive single-atom displacements. We are interested in both the potential for disorder and the possible aperiodic structures adopted following the disordering event. The potential for disordering is related to connectivity, and among those structures of interest are tetrahedral networks (such as SiO2, SiC and Si3N4) comprising corner-shared tetrahedral units whose connectivities are easily evaluated. In order to study the response of these networks to radiation, we have chosen to model their assembly according to the (simple) local rules that each corner obeys in connecting to another tetrahedron; in this way we easily erect large computer models of any crystalline polymorphic form. Amorphous structures can be similarly grown by application of altered rules. We have adopted a simple model of irradiation in which all bonds in the neighborhood of a designated tetrahedron are destroyed, and we reform the bonds in this region according to a set of (possibly different) local rules appropriate to the environmental conditions. When a tetrahedron approaches the boundary of this neighborhood, it undergoes an optimization step in which a spring is inserted between two corners of compatible tetrahedra when they are within a certain distance of one another; component forces are then applied that act to minimize the distance between these corners and minimize the deviation from the rules. The resulting structure is then analyzed for the complete adjacency matrix, irreducible ring statistics, and bond angle distributions.
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- Copyright © Materials Research Society 1997
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