Glass Transition by Gelation in a Phase Separating Binary Alloy

We use molecular dynamics simulations to show that glass transition in a model phase separating amorphous alloy, ${\mathrm{Cu}}_{50}{\mathrm{Nb}}_{50}$, occurs by gelation. At the glass transition, a mechanically stiff, percolating network of atoms with icosahedral local packing forms at the interfaces between compositionally enriched regions. This low-energy network halts coarsening of the phase-separated structure and imparts shear resistance. These features of glass transition are remarkably similar to gelation processes in polymeric and colloidal gels.