Atomistic modelling of radiation damage in zircon

We report the results of simulation of radiation damage in zircon structure using the molecular dynamics technique. The phases of the damage production process, including the ballistic and thermal spike phases, are detected, quantified and visualized. We find that the higher ambient temperature results in substantial decrease of the damage throughout the damage production process. We simulate the overlap of the displacement cascades and find that the damaged structure is less able to resist the damage, in that more damage is produced in the structure that is already damaged and the relaxation time increases. The calculated density of the damaged structure shows the increase in the core of the damaged region. We relate this densification to the appearance of chains of connected SiOn polyhedra in the damaged structure. The number of connected polyhedra increases with the increase of the damage, consistently with recent nuclear magnetic resonance results. 'Polymers' of connected SiOn are found to be essentially stable on annealing for the timescales available in computer simulations and their alignment may possess the 'memory' of the alignment of SiO4 tetrahedra in crystalline zircon.