Dynamic slowing-down and crystal nucleation in a supercooled metallic glass former induced by local icosahedral order

A long-standing question in condensed matter and material science is understanding how local structural order determines the fate of a liquid on cooling, i.e., whether it crystallizes or experiences dynamic slowing down leading to glass formation. Here we address this issue by focusing on a metallic glass former with concurring crystal and amorphous local order based on icosahedral symmetry. Using atomistic simulations, we study its deep supercooled regime in which we clearly identify spontaneous crystal nucleation close to the glass transition. We find that regions of slow dynamics characterized by a high degree of icosahedral orientational order play a central role in the nucleation process. Our study brings a new perspective into the microscopic mechanism of crystallization from the supercooled phase, which could be of significance for the in silico design of materials with selected glass-forming ability.