Topological Defects in Size-Dispersed Solids

We study the behavior of the topological defects in the inherent structures of a two-dimensional binary Lennard-Jones system as the size dispersity varies. We find that topological defects arising from the particle size dispersity are responsible for destabilizing the solid as follows: (i) for particle density $\rho \le 0.9$, the solid melts through intermediate states of decreasing hexatic order arising from the proliferation of unbounded dislocations, (ii) for $\rho >0.9$, the dislocations form grain boundaries, dividing the system into micro-crystallites and destroying the translational and orientational order.