Topological modeling of cascade amorphization in network structures using local rules

A local rules-based assembly procedure was used to erect large periodic and aperiodic models of the tetrahedral network compounds SiO2, Si3N4 and SiC, whose topological properties were assessed in a prior investigation. Several hundred tetrahedra in central regions of the models were disconnected and randomly rotated, then allowed to reconnect according to an imposed set of the same or different rules, in order to simulate radiation disordering within a dense collision cascade. Alterations in the rebonded cascade region were characterized by assessment of density, underconnection, tetrahedral distortion, inter-tetrahedral bond angle, radial correlations and local topology. While SiO2 networks amorphize easily and acceptably in this way, Si3N4 and SiC networks do not. It is concluded that the experimental difficulty in amorphizing Si3N4 is due to the topological difficulty in tetrahedral reconnection from random orientations according to the applicable local rules for Si3N4, while the observed ease of amorphizing SiC must arise from the potential for chemical disorder in that compound.