MODELING THE CASCADE AMORPHIZATION OF SILICAS WITH LOCAL-RULES RECONSTRUCTION

Displacement-cascade disorder was modeled topologically in two crystal line SiO2 polymorphs (quartz, cristobalite) and one amorphous silica i n an attempt to understand the origins of the experimentally observed common terminal density after prolonged irradiation, Cascades were sim ulated by imposing random rotations of constituent [SiO4] tetrahedra f ollowed by reconnection according to several sets of local assembly ru les derived previously for crystalline or non-crystalline assemblages. The resulting arrangements were characterized by their bond-angle dis tributions, ring topology of their local clusters, and pair correlatio ns. It is concluded from their similarity that fundamental topological constraints underlie the commonalities of the endpoint configurations . (C) 1998 Elsevier Science B.V. All rights reserved.